Solar collectors are thermal devices that convert solar
energy into thermal energy by raising the temperature of a
circulating heat transfer fluid. The fluid can then be used to
heat water for domestic hot water usage or space heating.
In EnergyPlus solar collectors are components that are
connected to the plant loop. A solar heating system can be
constructed with a combination of solar collectors, pumps, and
hot water tanks.
The flat-plate solar collector model simulates glazed,
unglazed, and tubular (i.e. evacuated tube) collectors. The SolarCollector:FlatPlate:Water
object represents a single collector module connected to the
plant loop. The thermal and optical properties of the
collector module are taken from the referenced SolarCollectorPerformance:FlatPlate
object. A surface or shading object defines the collector
tilt, azimuth, and gross area. The collector surface
participates normally in all shading calculations if the
“FullExterior,” “FullInteriorAndExterior,”
FullExteriorWithReflections , or
FullInteriorAndExteriorWithReflections flags are set in the
Solar Distribution field of the Building
object. Inlet and outlet nodes are specified for plant
connections on the demand side of the plant loop.
Reference to one of the many different types of surfaces
such as the BuildingSurface:Detailed
or the Shading:Zone:Detailed
objects. The surface named here is used to define the solar
collector tilt, azimuth, and gross area.
The maximum flow rate [m\(^{3}\)/s] allowed through the
collector. This field is optional. If not specified, the
collector will allow as much flow as the rest of the plant can
deliver.
An example follows.
SolarCollector:FlatPlate:Water,
Collector 1, !- Name
ACR Solar International Fireball 2001, !- Solar Collector Performance Name
Collector Surface, !- Surface Name
Collector Inlet Node, !- Inlet Node Name
Collector Outlet Node, !- Outlet Node Name
0.00005; !- Maximum Flow Rate (m3/s)
The incident angle modifier is an important intermediate
value used in the SRCC calculation of solar collector
performance. The value reported here is the combined result
for the current time that includes incident angles of beam
solar, diffuse solar from sky, and diffuse solar from
ground.
The overall collector efficiency. This is the ratio of
collected energy and the incident solar energy. The efficiency
can be greater than 1 at times when the outdoor air
temperature is warm enough.
These are the overall rate (in W) and amount of energy ( in
J) transferred to the collector s circulating fluid. Positive
values indicate heating of the fluid while negative values
indicate cooling of the fluid.
This is the overall rate of heat addition to the collector
s circulating fluid in Watts. Values are always positive or
zero. If the fluid is actually cooled then the value is
zero.
This is the overall rate of heat loss from the collector s
circulating fluid in Watts. Values are always positive or
zero. If the fluid is actually heated then the value is
zero.
In addition, several surface variables are also relevant
for the collector s surface object (BuildingSurface:Detailed
or Shading:Zone:Detailed):
Zone,Average,Surface Outside Face Sunlit Area
[m2]
Zone,Average,Surface Outside Face Sunlit Fraction
[]
Zone,Average,Surface Outside Face Incident Solar
Radiation Rate per Area [W/m2]
Zone,Average,Surface Outside Face Incident Beam Solar
Radiation Rate per Area [W/m2]
Zone,Average,Surface Outside Face Incident Sky Diffuse
Solar Radiation Rate per Area [W/m2]
Zone,Average,Surface Outside Face Incident Ground
Diffuse Solar Radiation Rate per Area [W/m2]
Zone,Average,Surface Outside Face Beam Solar Incident
Angle Cosine Value []
The temperatures at the inlet and outlet nodes and the
collector mass flow rate can be monitored using the system
node output variables:
The SolarCollectorPerformance:FlatPlate
object contains the thermal and optical performance parameters
for a single collector module. These parameters are based on
the testing methodologies described in ASHRAE Standards 93 and
96. The Solar Rating and Certification Corporation (SRCC)
applies these standards in their rating procedures of solar
collectors. The ratings for commercially available collectors
in North America are published in the Directory of SRCC
Certified Solar Collector Ratings. The SRCC database has
also been converted into an EnergyPlus data set of SolarCollectorPerformance:FlatPlate
objects that is included with the program (see
SolarCollectors.idf in the DataSets folder).
The coefficients for the energy conversion efficiency and
incident angle modifier allow first order (linear) or second
order (quadratic) correlations. To use a first order
correlation, the second order coefficient must be left blank
or set to zero.
In order for the model to work correctly, the test
conditions for which the performance coefficients were
measured must be specified in the fields: Test Fluid,
Test Volumetric Flow Rate, and Test Correlation
Type. Currently, only water is allowed as the Test
Fluid.
For more detailed information about the performance
coefficients, see the EnergyPlus Engineering Reference
Document.
The gross area of the collector module [m\(^{2}\)]. This value is mainly for
reference. The area of the associated collector surface object
is used in all calculations.
The fluid that was used in the testing procedure that
resulted in the thermal and optical performance coefficients
below. Currently only Water is allowed. This the fluid during
the collector testing, not the fluid used during a particular
EnergyPlus run.
The volumetric flow rate during testing [m\(^{3}\)/s]. If the value is
available as flow rate per unit area, it is recommended to
multiply by the Gross Area of the collector module,
not the net aperture area.
This field specifies type of temperature used to develop
the correlation equations. The testing procedure is based on
an experimental correlation using either Inlet, Average, or
Outlet temperature. Enter one of these choices. The ASHRAE
Standards 93 and 96 always use Inlet temperature.
Third coefficient of efficiency equation for energy
conversion [W/m\(^{2}\)-K\(^{2}\)]. This field is optional.
This is the second-order term. If left blank or set to zero, a
first-order linear correlation is used.
Field:
Coefficient 2 of Incident Angle Modifier[LINK]
Second coefficient of the incident angle modifier equation.
This the first-order term. (There is no Coefficient 1 of
Incident Angle Modifier because that number is always
1.0.)
Field:
Coefficient 3 of Incident Angle Modifier[LINK]
Third coefficient of the incident angle modifier equation.
This is the second-order term. This field is optional. If left
blank or set to zero, a first order linear correlation is
used.
An example of this object follows.
SolarCollectorPerformance:FlatPlate,
Alternate Energy Technologies AE-32, !- Name
2.9646, !- Gross Area {m2}
WATER, !- Test Fluid
0.0000388, !- Test Flow Rate {m3/s}
INLET, !- Test Correlation Type
0.691, !- Coefficient 1 of Efficiency Equation {dimensionless}
-3.396, !- Coefficient 2 of Efficiency Equation {W/m2-K}
-0.00193, !- Coefficient 3 of Efficiency Equation {W/m2-K2}
-0.1939, !- Coefficient 2 of Incident Angle Modifier
-0.0055; !- Coefficient 3 of Incident Angle Modifier
The Integral-Collector-Storage (ICS) solar collector model
simulates glazed collectors with integral storage unit. The SolarCollector:IntegralCollectorStorage
object represents a single collector module connected to the
plant loop. The thermal and optical properties of the
collector module are calculated from inputs in SolarCollectorPerformance:IntegralCollectorStorage
object. A surface or shading object defines the collector
tilt, and azimuth. The collector surface participates normally
in all shading calculations if the “FullExterior,”
“FullInteriorAndExterior,” FullExteriorWithReflections , or
FullInteriorAndExteriorWithReflections flags are set in the
Solar Distribution field of the Building
object. Inlet and outlet nodes are specified for plant
connections on the demand side of the plant loop. The SurfaceProperty:ExteriorNaturalVentedCavity,
object is required to describe the surface properties, the
characteristics of the cavity and opening for natural
ventilation if OtherSideConditionsModel is specified as the
collector bottom surface outside boundary condition type.
Reference to one of the many different types of surfaces
such as the BuildingSurface:Detailed
or the Shading:Zone:Detailed
objects. The surface named here is used to define the solar
collector tilt, and azimuth. The collector shades the surface
it is mounted on and hence impacts the surface heat
balance.
This field contains the type of boundary conditions
applicable to the ICS collector bottom surface. Allowed
boundary condition types are: AmbientAir and
OtherSideConditionsModel. If the other side conditions model
is selected, specify the name of the SurfaceProperty:OtherSideConditionsModel
object in the next input field, otherwise, leave the next
input field blank. The AmbientAir boundary condition uses
outdoor air temperature as boundary condition, hence the
subsurface is assumed to be exposed to the sun and wind.
This field contains the name of a SurfaceProperty:OtherSideConditionsModel
object declared elsewhere in the input file. This will connect
the collector to the exterior boundary conditions for the
underlying heat transfer surface specified above..
The maximum flow rate [m3/s] allowed through the collector.
This field is optional. If not specified, the collector will
allow as much flow as the rest of the plant can deliver.
An example follows.
SolarCollector:IntegralCollectorStorage,
Collector 1, !- Name
ICS Solar Collector, !- Solar Collector Performance Name
ICS Collector Surface, !- Surface Name
OtherSideConditionsModel, !- Bottom Surface Boundary Conditions Type
ICS OSCM, !- Boundary Condition Model Name
Collector Inlet Node, !- Inlet Node Name
Collector Outlet Node, !- Outlet Node Name
0.00005; !- Maximum Flow Rate (m3/s)
The SolarCollectorPerformance:IntegralCollectorStorage
object contains the thermal and optical performance parameters
for a single collector module. The transmittance-absorptance
product of the absorber and cover system is determined from
optical properties specified. For more detailed information
about the calculation procedure, see the EnergyPlus
Engineering Reference Document.
This input field is the collector bottom heat loss
conductance in W/m2K. This value is calculated from thermal
conductivity and thickness of the bottom insulation.
This input field is the collector side heat loss
conductance in W/m2K. This value is calculated from thermal
conductivity and thickness of the side insulation.
This input field is the ratio of the short side (width) of
the collector to the long side (length) of the collector. This
value is used only for calculating the collector side area
along with the collector side height specified in the next
input filed. This ratio is less or equal to 1.0.
This input field is height of collector side in m. This
height is used to estimate the collector side area for heat
loss calculations along with heat loss coefficient specified
in the input field above.
This input field is thermal-mass of the absorber plate per
unit area of the collector in [J/m2×K]. This input value
multiplied by the absorber gross area determines the thermal
mass of the absorber plate. It is estimated from the specific
heat, density and average thickness of the absorber plate. If
zero is specified then the absorber plate energy balance
reduces to steady state form.
Number of transparent collector covers. Common practice is
to use two covers: glass as the outer cover and Teflon as the
inner cover. If single cover is specified leave the inner
cover optical and thermal properties input fields blank.
This input field provides the spacing between the two
transparent covers, and the spacing between the inner cover
and the absorber plate in m. Default value is 0.05m.
This is the average Refractive index for solar spectrum
range of the outer transparent cover material. Glass is used
as the outer cover. Average refractive index value for
non-absorbing glass used in solar collectors over solar
spectrum range is 1.526.
Field:
Extinction Coefficient Times Thickness of Outer Cover[LINK]
This input field is the product of the extinction
coefficient and the thickness of the out cover material. The
extinction coefficient for glass types approximately varies
from 4m\(^{-1}\) to 32 m\(^{-1}\). The extinction
coefficient for low-iron glass, which is the default outer
cover material, is 15 m\(^{-1}\). The default value for
extinction coefficient times thickness (KL) is 0.045 ( = 15.0
x0.003), which is the product of the default extinction
coefficient of 15m\(^{-1}\)
and 3.0mm thick glass.
This input field is the average Refractive index of the
inner transparent cover of the collector. Commonly Teflon
(PolytetraFluoroethylene) is used as the inner cover. The
average refractive index value over the solar spectrum range
for Teflon is 1.37.
Field:
Extinction Coefficient Times Thickness of Inner Cover[LINK]
This input field is the product of the extinction
coefficient (K) and the thickness (L) of the inner cover
material. The inner cover material is more transparent than
the out cover, very thin and hence their thickness can be
assumed to be negligible. The default value for extinction
coefficient times thickness (KL) is 0.008 ( = 40.0x0.0002),
which is the product of extinction coefficient of 40m\(^{-1}\) and a thickness of
0.2mm.
This input field value is thermal emissivity of the inner
transparent collector cover. The default value assumes plastic
sheet with thermal emissivity of 0.30. This value is used in
the thermal analysis only.
Solar
Collector Storage Water Temperature [C][LINK]
This output variable is the ICS collector stored water
average temperature at a given time steps in degree Celsius.
This temperature is the same as the collector ICS collector
leaving water temperature.
Solar
Collector Absorber Plate Temperature [C][LINK]
This output variable is the ICS collector absorber plate
average temperature at a given time steps in degree
Celsius.
This output variable is the instantaneous thermal
efficiency of the ICS solar collector in per cent. This value
is determined from net useful energy collected and the total
incident solar radiation for each time step. The net useful
energy collected is the sum of the energy stored in the
collector and net useful energy delivered.
Solar
Collector Storage Heat Transfer Rate [W][LINK]
Solar
Collector Storage Heat Transfer Energy [J][LINK]
These output variables are the instantaneous rate of change
of the energy and the change in energy of the water in the ICS
solar collector in Watts, and Joules, respectively.
Solar
Collector Skin Heat Transfer Energy [J][LINK]
These output variables are the instantaneous skin heat loss
rate and the heat loss energy of the ICS solar collector for
each time steps in Watts, and Joules respectively. The skin
heat loss rate is the sum of the heat losses through the top,
bottom and sides of the collector surfaces. This value is
mostly negative, but can have a positive value (heat gain)
when the outdoor air temperature is warmer than the
collector.
This output variable is the heat rate and Energy
transferred from the ICS collector to the collector loop fluid
(water) in Watts and Joule, respectively. This value is
determined from the collector water mass flow rate, specific
heat of water and the temperature difference between the
collector water outlet and inlet nodes at each time step. The
value is positive when the fluid is heated or negative when
cooled.
Solar
Collector Transmittance Absorptance Product [][LINK]
This output variable is the transmittance-absorptance
product of the covers and absorber system of the ICS solar
collector. This value ranges from 0.0 to less than 1.0.
Solar
Collector Overall Top Heat Loss Coefficient [W/m2-C][LINK]
This output variable is the overall heat loss coefficient
from the absorber plate to the ambient air calculated for each
time step.
This object is used to model hybrid photovoltaic-thermal
(PVT) solar collectors that convert incident solar energy into
both electricity and useful thermal energy. This object
describes the PVT solar collector by referencing other objects
that provide more detail or connections to other parts of the
EnergyPlus model.
The PVT solar collectors need to be connected to either an
HVAC air system or a plant loop for collected thermal energy
to be utilized. The input field for the type of thermal
working fluid informs the program how the PVT collector is
expected to be connected. If the the working fluid is air,
then the PVT collectors are modeled as a ventilation air
pretreatment component and connected to an outdoor air system.
If the working fluid is water, then the PVT collectors are
modeled as a hot water solar collector and are connected to a
plant loop with a water thermal storage tank.
This field is the user-defined name of a surface object
(defined elsewhere) to which the PVT module is attached. These
can be any type of building surface that is exposed to the
exterior environment. The model uses the named surface s
geometry for the PVT solar collector.
Field:
Photovoltaic-Thermal Model Performance Name[LINK]
This field is the user-defined name of a Generator:Photovoltaic
object (defined elsewhere) that will be used to model the
solar electric portion of the PVT solar collector. The PVT
models make any adjustments needed to model PV performance in
the context of the PVT collector.
This field is the user s choice for the type of fluid used
to collect thermal energy. PVT solar collectors can capture
thermal energy in either air or water streams. The choices
available for this field are Water or Air. If the choice is
Air then the PVT collector needs to be connected to an HVAC
air system loop. The PVT collector should be situated as the
first component on an outdoor air inlet stream. If the choice
is Water then the PVT collector needs to be connected to a
Plant water system loop. The connections are made via node
names which are defined in the following fields, depending on
the working fluid type.
This field is the name of Plant loop node that serves as
the inlet to the PVT collector. This field is only used if the
Thermal Working Fluid Type is set to Plant/Water.
This field is the name of a plant loop node that seves as
the outlet from the PVT collector. This field is only used if
the Thermal Working Fluid Type is set to Plant/Water.
This field is the name of HVAC air loop node that serves as
the inlet to the PVT collector. This field is only used if the
Thermal Working Fluid Type is set to HVAC/Air.
This field is the name of HVAC air loop node that serves as
the outlet from the PVT collector. This field is only used if
the Thermal Working Fluid Type is set to HVAC/Air.
This field is used to describe the nominal volume flow rate
of the thermal working fluid. The units are m3/s. The volume
flow rate is autosizable.
An example of this object follows.
SolarCollector:FlatPlate:PhotovoltaicThermal,
PVT: 1_Ceiling , !- Name
1_Ceiling , !- Surface Name
30percentPVThalfArea , !- Photovoltaic-Thermal Model Performance Name
PV:ZN_1_FLR_1_SEC_1_Ceiling , !- Photovoltaic Name
Air , !- Thermal Working Fluid Type
, !- Water Inlet Node Name
, !- Water Outlet Node Name
ZN_1_FLR_1_SEC_1:Sys_OAInlet Node , !- Air Inlet Node Name
PVT:ZN_1_FLR_1_SEC_1_Ceiling Outlet , !- Air Outlet Node Name
Autosize ; !- Design Flow Rate
These outputs are the thermal energy and power produced by
the PVT collector. PVT collectors are a type of cogenerator,
producing both electrical and thermal power and these
variables report the thermal portion in the same manner as
other fuel-based cogenerators. The thermal energy is placed on
HeatProduced meter and is attributed to SolarWater or SolarAir
depending on the type of working fluid. The generator thermal
production is also reported at the load center level.
This output variable indicates the status a bypass damper.
It is only available for air-based PVT. There are no
dimensions and the range is between 0.0 and 1.0. If the value
is 0.0, then there is no bypassing and all the working fluid
goes through the collector. If the value is 1.0, then there is
complete bypassing and all the working fluid goes around the
collector. If the value is between 0.0 and 1.0, then the model
is effectively mixing bypass and collector streams to target a
temperature setpoint placed on the outlet node.
This report is the mass flow rate of the working fluid
through the PVT collector. This is the overall mass flow rate,
portions of the flow may be internally bypassed around the
collector itself for control modulation.
This object is used to provide performance details for the
simple PVT model. This is a simple user-defined efficiency
model. Thermal conversion efficiency is a constant or
scheduled value. There are no output variable for this object,
reporting is done by the parent PVT object.
Field:
Fraction of Surface Area with Active Thermal Collector[LINK]
This field is the fraction of the surface area that is
active. It should be a decimal fraction between 0.0 and 1.0.
The area of the PVT s surface will be multiplied by this
fraction to determine the active area of the PVT
collector(s).
This field is used to determine how the thermal efficiency
is input. There are two choices, Fixed or Scheduled. If this
field is set to Fixed, then a constant value for thermal
efficiency will be used (set in next field). If this field is
set to Scheduled, then the thermal efficiency values are
defined in a schedule.
Field:
Value for Thermal Conversion Efficiency if Fixed[LINK]
This field is used to provide a value for the efficiency
with which solar energy is collected in the working fluid.
This field is only used if the input mode is set to Fixed in
the previous field. Efficiency is defined as the thermal
energy collected divided by the incident solar radiation. The
value should be between 0.0 and 1.0. The user should be
careful that the thermal efficiency and the electrical
efficiency be consistent with each other because the overall
efficiency of the PVT collector is the combination of both
thermal and electrical.
Field:
Name of Schedule for Thermal Conversion Efficiency[LINK]
This field is used for the name of a schedule that provides
values for the efficiency with which solar energy is collected
in the working fluid. This field is only used if the input
mode is set to Scheduled in the field above. Efficiency is
defined as the thermal energy collected divided by the
incident solar radiation. The values in the named schedule
should be between 0.0 and 1.0. The user should be careful that
the thermal efficiency and the electrical efficiency be
consistent with each other because the overall efficiency of
the PVT collector is the combination of both thermal and
electrical.
This field is used to describe an average value for the
total hemispherical emittance of the collector s front face
exposed to the sky. This is used to model cooling applications
where the PVT collectors are operated at night to cool the
working fluid.
An example input object follows.
SolarCollectorPerformance:PhotovoltaicThermal:Simple,
20percentEffPVhalfArea , !- Name
0.5 , !- Fraction of Surface Area with Active Thermal Collector
Fixed , !- Thermal Conversion Efficiency Input Mode Type
0.2 , !- Value for Thermal Conversion Efficiency if Fixed
, !- Name of Schedule for Thermal Conversion Efficiency
0.84 ; !- Front Surface Emittance
Solar
Collector Heating System Plant Connections[LINK]
This section provides an overview of how to model solar
heating systems. A solar heating system can be constructed
using a combination of solar collectors, pumps, water tanks
and water heaters. The solar collector must be connected on
the demand side of the plant loop. Multiple collector modules
can be combined in series and parallel using the normal plant
connection rules. The supply side of the plant loop should
contain a water heater with the solar collector loop
connecting to the Source Side Inlet and Source
Side Outlet nodes. As usual, the pump must be the first
component on the supply side.
If the solar heating system is for domestic hot water (or
service water heating) usage only, the field Use Flow Rate
Fraction Schedule Name of the WaterHeater:Mixed
object can be used to avoid additional plant connections. If
the system has more complicated hot water requirements or if
the system is for space heating, the Use Side Inlet
and Use Side Outlet nodes must be connected to
another plant loop to serve zone and non-zone equipment. (See
the WaterHeater:Mixed
object documentation for more information.)
Solar Collector Plant Loop
Connection Diagram [fig:solar-collector-plant-loop-connection-diagram]
NOTE: The EnergyPlus plant simulation requires the pump to
be the first component on the supply side. This may be
different from the way the solar heating system is actually
configured. This should not affect the validity of the
simulation results.
In order to realize energy savings with a solar heating
system, it is best to use a two-tank system with a storage
tank and auxiliary water heater. The storage tank gathers heat
directly from the solar collectors and stores it for later
use. The storage tank is modeled using a WaterHeater:Mixed
object with the Heater Maximum Capacity set to zero.
The auxiliary water heater is positioned downstream of the
storage tank on the supply side of the main plant loop. The
auxiliary water heater, or booster water heater, provides
additional heat if the storage tank water is not hot enough.
The auxiliary water heater can be modeled as an
instantaneous/tankless water heater or as a standard tanked
water heater with heating source (see WaterHeater:Mixed).
Two-Tank Solar Heating System
Connection Diagram [fig:two-tank-solar-heating-system-connection]
Another strategy to consider for solar heating systems is
to allow the storage tank to reach a much higher temperature
than necessary for the end use. This allows the tank to store
more energy from the solar collectors, when it is available.
However, for applications such as domestic hot water, it is
undesirable and unsafe to supply excessive hot water
temperatures at the point of demand. To take advantage of
higher storage temperatures, yet still avoid scalding
temperatures at the faucet, the hot water leaving the storage
tank can be tempered with cold water using a three-way valve
to achieve the target temperature. See the TemperingValve
object documentation for more details.
A complete two-tank solar heating system with tempering
valve is shown below.
Two-Tank Solar Heating System
with Tempering Valve [fig:two-tank-solar-heating-system-with-tempering]
There are several options for controlling a solar heating
system in EnergyPlus. Since the solar collectors request a
constant flow demand based on their Maximum Flow
Rate, the limiting factor is actually the flow rate
determined by the loop pump. Therefore the entire system can
be controlled using the Pump Flow Rate Schedule of
the pump. If the schedule is omitted, the pump and system will
run all the time (without any other controls specified). This
is usually not the best way to operate a solar heating
system.
To better control the collector loop, a differential
thermostat can be used to compare the temperature in the water
heater to the temperature in the collector so that the pump is
only turned on when there is a useful heat gain. The
differential thermostat is simulated using the AvailabilityManager:DifferentialThermostat
object. For a typical system, the Hot Node Name field
refers to an outlet node of one of the collector modules. The
Cold Node Name field refers to the Source Side
Outlet node, i.e. the cold storage water leaving the
water heater. The fields Temperature Difference On
Limit and Temperature Difference Off Limit are
usually 8 12 C and 1 3 C respectively. If the two temperature
differences are too close, it is possible for the system to
turn on and off rapidly without much useful heat gain. This
can also occur if the flow rate through the collector is too
high. Without flow the fluid in the collector heats up more
quickly; when high flow is turned on, all of the hot fluid is
removed and the temperature drops, forcing the system off
again.
Another control method is to use a photovoltaic panel to
power the pump. The system begins pumping when there is enough
solar radiation to operate the pump. This is not yet
implemented in EnergyPlus.
In climates with a cold season, the solar heating system
must be designed to avoid the risk of fluid freezing in the
solar collector or exposed pipes and causing damage. This is
not a problem if air is the heat transfer fluid. With water,
however, there are several strategies that can minimize the
risk.
Seasonal schedule. The simplest strategy is to not
use the system during the cold season. This is a hassle
because it requires the collector to be manually drained of
all fluid. The benefits of the solar heating system are also
lost during this time. This can be simulated in EnergyPlus
with the appropriate pump schedule for the collector
system.
Antifreeze. The freezing point of the liquid is
decreased by adding antifreeze to the water or using a
different heat transfer liquid with a lower freezing point.
This cannot yet be simulated in EnergyPlus because only pure
water is currently allowed in plant loops.
Drain-back system. This strategy automatically
empties the collector when the pump is not running. This
scenario is modeled by default in EnergyPlus, although the
extra pump energy required to start the system is not taken
into account.
Recirculation system. This strategy automatically
recirculates warm liquid from the storage tank back through
the collector to maintain the system above the freezing point.
There are system losses using this method. This can be
simulated in EnergyPlus by using AvailabilityManager:LowTemperatureTurnOn
to force the system to turn on when the outdoor air
temperature or collector outlet temperature falls below a
specified minimum.
In addition to freeze prevention, it is also necessary to
prevent the system from becoming too hot. This is usually a
safety issue for the water heater. For this case it is
important to have a high temperature cutoff to stop the pump
before damaging the water heater. This is accomplished with a
AvailabilityManager:HighTemperatureTurnOff.
To use the availability managers for the control cases
described above, a AvailabilityManagerAssignmentList
must be defined and referenced in the PlantLoop
object of the collector loop. An example of a differential
thermostat, recirculation for freeze prevention, and high
temperature cutoff is shown below:
AvailabilityManagerAssignmentList,
Collector Loop Availability Manager List, !- Name
AvailabilityManager:HighTemperatureTurnOff, !- Availability Manager 1 Object Type
High Temperature Turn Off Availability Manager, !- Availability Manager 1 Name
AvailabilityManager:HighTemperatureTurnOn, !- Availability Manager 2 Object Type
Low Temperature Turn On Availability Manager, !- Availability Manager 2 Name
AvailabilityManager:DifferentialThermostat, !- Availability Manager 3 Object Type
Differential Thermostat Availability Manager; !- Availability Manager 3 Name
AvailabilityManager:HighTemperatureTurnOff, ! For water heater safety
High Temperature Turn Off Availability Manager, !- Name
Water Heater Use Outlet Node, !- Sensor Node Name
60.0; !- Temperature (C)
AvailabilityManager:HighTemperatureTurnOn, ! For freeze prevention by recirculation
Low Temperature Turn On Availability Manager, !- Name
Collector Outlet Node, !- Sensor Node Name
0.0; !- Temperature (C)
AvailabilityManager:DifferentialThermostat, ! For useful heat gain from collector to tank
Differential Thermostat Availability Manager, !- Name
Collector Outlet Node, !- Hot Node Name
Water Heater Source Outlet Node, !- Cold Node Name
10.0, !- Temperature Difference On Limit (delta C)
2.0; !- Temperature Difference Off Limit (delta C)
This object is used to model unglazed transpired solar
collectors (UTSC) used to condition outdoor air. These
collectors are generally used to heat air drawn through
perforated absorbers that are heated by the sun and also
recover heat conducted out through the underlying wall. The SolarCollector:UnglazedTranspired
object represents a single collector attached to one or more
BuildingSurface:Detailed
objects and to one or more outdoor air systems. Therefore the
transpired collector is part of both the thermal envelope and
the HVAC system. An example file is provided called
TranspiredCollectors.idf.
The area and orientation of the collector is obtained from
BuildingSurface:Detailed
objects, which are referenced by name. Although the collector
surface itself is slightly detached from the underlying
building wall (or roof), no additional surface object is
needed to represent the collector itself. When modeling
transpired collectors, it is important to consider the size of
the collector when developing the building model s BuildingSurface:Detailed
objects because the underlying surfaces must match the
collector. For example, if the collector covers only part of
the wall, then that wall should be split into separate
surfaces where one matches the size of the collector. A single
collector can be associated with as many BuildingSurface:Detailed
objects as desired (although if you need to use more than 10
surfaces, then the IDD will need to be extended). The
collector can be arranged at any tilt angle by describing the
surfaces appropriately. The surfaces need not be contiguous
nor have the same orientation, but the program will issue
warnings if surfaces have widely ranging tilts and
azimuths.
Controls for the UTSC involve setting the rate of air flow
and the status of a bypass damper. If the bypass damper is
open, then all the ventilation air goes straight into the
outdoor air mixer; if it closed, then all the air first passes
through the UTSC. The bypass damper is modeled as completely
open or completely closed. The UTSC bypass damper control is
determined by an availability manager, the airflow set by the
outdoor air mixer controls, and thermostatic type controls
that decide if heating is useful. An availability schedule is
used to bypass the collector for certain times of the year,
eg. summer cooling season. The air flow rates are set by
controls associated with the outdoor air mixer (see SetpointManager:MixedAir,
and Controller:OutdoorAir). Thermostatic type control decides
if the collector will provide useful heating based on either
of two types of setpoints. The first type of temperature
setpoint is managed by SetpointManager:MixedAir,
where the UTSC model looks at a control node, usually the
mixed air node. The second type is an extra setpoint
especially for free heating that is managed within this object
where the UTSC model looks at the zone air node.
This field contains the name of a SurfaceProperty:OtherSideConditionsModel
object declared elsewhere in the input file. This will connect
the collector to the exterior boundary conditions for the
underlying heat transfer surface.
This field contains the name of a schedule that determines
whether or not the UTSC is available. When the schedule value
is less than or equal to zero, the UTSC is always bypassed.
When the schedule value is greater than zero, the UTSC is
available and will be used when other conditions are met, such
as outdoor air requested by mixer and preheating has been
determined to be beneficial based on thermostatic control. If
this field is blank, the schedule has values of 1 for all time
periods.
This field contains the name of an air node that provides
air into the UTSC. This node name should also be assigned to
be an outdoor air node using the OutdoorAir:NodeList
or OutdoorAir:Node
objects. This node should also be named as the actuated node
in a Controller:OutdoorAir
object. If the UTSC is connected to more than one air system,
then this field can be left blank and the SolarCollector:UnglazedTranspired:Multisystem
object should be used to define the nodes.
This field contains the name of an air node that is the
outlet of the UTSC. This node name will typically be the inlet
to the OutdoorAir:Mixer
(if there is no other equipment on the outdoor air path). If
the UTSC is connected to more than one air system, then this
field can be left blank and the SolarCollector:UnglazedTranspired:Multisystem
object should be used to define the nodes.
This field contains the name of an air node that has a
setpoint manager controlling its temperature setpoint. This
node name will typically be named as the control node in a a
Controller:OutdoorAir
object. If the UTSC is connected to more than one air system,
then this field can be left blank and the SolarCollector:UnglazedTranspired:Multisystem
object should be used to define the nodes.
This field contains the name of an air node for a thermal
zone that is ultimately connected to the air system. This node
is used with the setpoint schedule, defined in the following
field, to provide an added layer of thermostatic control for
the UTSC without affecting the control of auxiliary heating.
If there is a single air system that is connected to more than
one zone, then a single zone should be selected based on where
the thermostat might be located. If the UTSC is connected to
more than one air system, then this field can be left blank
and the SolarCollector:UnglazedTranspired:Multisystem
object should be used to define the nodes.
This field contains the name of a temperature schedule
defined elsewhere in the input file. This schedule should
define temperatures desired in the zone, but not
necessarily required. This secondary setpoint
schedule is used to allow the UTSC to operate as if it has its
own thermostat that is separate from the primary control
mechanism. When the UTSC is used with auxiliary heating, the
usual setpoint managers and temperature controllers will
determine how the auxiliary heaters are controlled. This
allows using a higher zone air temperature setpoint for
controlling UTSC bypass than for the auxiliary heating
system.
Field:
Diameter of Perforations in Collector[LINK]
This field is used to enter the effective diameter of the
perforations in the collector surface. The diameter should be
entered in meters. For perforations other than round, use an
equivalent diameter for a round hole that would have the same
area.
Field:
Distance Between Perforations in Collector[LINK]
This field is used to enter the pitch, or average, shortest
distance between perforations.
Field:
Thermal Emissivity of Collector Surface[LINK]
This field is used to enter the thermal emissivity of the
collector. This surface property is for longwave infrared
radiation. The property is used for both sides of collector.
Most painted materials have an emissivity of 0.9.
Field:
Solar Absorbtivity of Collector Surface[LINK]
This field is used to enter the solar absorbtivity of the
collector. This surface property is for shortwave, solar
radiation. The property is used for the front side of the
collector that faces the environment. Darker colors have a
higher absorbtivity. While black is the highest performance,
other colors might be used to match the color scheme of the
rest of the facade. The following table provides sample solar
absorbtivities for different colors (source: Conserval
Engineering Inc., Toronto, Ontario, Canada).
Color Name of Kynar(R)
[[1]](#_ftn1) Paint
Solar Absorptivity
Black
0.94
Classic Bronze
0.91
Chocolate Brown
0.9
Hartford Green
0.9
Med. Bronze
0.89
Boysenberry
0.86
Rocky Grey
0.85
Regal Blue
0.85
Forest Green
0.84
Hemlock Green
0.82
Slate Blue
0.8
Redwood
0.79
Teal
0.79
Slate Grey
0.79
Patina Green
0.77
Mint Green
0.71
Dove Grey
0.69
Mission Red
0.69
Sierra Tan
0.65
Brite Red
0.59
Rawhide
0.57
Sandstone
0.54
Silversmith
0.53
Coppertone
0.51
Concord Cream
0.45
Ascot White
0.4
Bone White
0.3
([1] Kynar is a registered
trademark of Elf Atochem North America, Inc.)
Field:
Effective Overall Height of Collector[LINK]
This field is used to enter a nominal height for the
collector. This value is used in the program to determine a
length scale in the vertical direction for the buoyancy-driven
portion of natural ventilation that occurs when the collector
is inactive. (Note that most of the geometry information is
obtained from the underlying surfaces.) The value entered here
is adjusted inside the program to account for tilt of the
collector. While the value here would generally correspond to
the actual distance/height, its value is not critical and it
can be used to adjust modeling the air exchange rates in
passive mode. If the collector is horizontal, then the length
scale is obtained from the following field.
Field:
Effective Gap Thickness of Plenum Behind Collector[LINK]
This field is used to enter a nominal gap thickness for the
collector. This distance value is only used when the collector
is near horizontal to determine a length scale in the vertical
direction for buoyancy calculations. For example, if the
collector is mounted on a flat roof, its tilt-adjusted height
is zero and the program will use this gap thickness as a
length scale rather than the height from the previous
field.
Field:
Effective Cross Section Area of Plenum Behind Collector[LINK]
This field is used to enter the nominal cross sectional
area of the gap behind the collector. This area is used to
determine a velocity scale for surface convection heat
transfer correlations when the collector is active. This value
is generally the average gap thickness times the average width
of the collector.
This field is used to describe the pattern of perforations
in the collector surface. There are currently two choices
available: Square and Triangle. Note that the hole layout
pattern should be consistent with how the value for pitch was
determined.
This field is used to select which correlation is used to
model heat transfer from the collector surface to the incoming
air when the collector is active. There are two choices
available: Kutscher1994, and VanDeckerHollandsBrunger2001. See
the Engineering Reference for details and references.
Field:
Ratio of Actual Collector Surface Area to Projected Surface
Area[LINK]
This field is used to enter a factor that accounts for the
extra surface area resulting from corrugations in the
collector surface. Corrugations help stiffen the collector.
The projected surface area is obtained by the program from the
(flat) underlying surfaces. If the collector is flat then this
ratio is 1.0. If the collector is corrugated, then this ratio
will be greater than one. A typical value might be 1.165.
This field is used to describe the relative roughness of
the collector material. This field is similar to one in the Material
object. This parameter only influences the convection
coefficients, more specifically the outside convection
coefficient. A special keyword is expected in this field with
the options being VeryRough , Rough , MediumRough ,
MediumSmooth , Smooth , and VerySmooth in order of roughest to
smoothest options.
This field is used to enter the thickness of the collector
material. This value is only needed for the Van Decker
Hollands Brunger 2001 correlation. The material thickness
should be entered in meters.
Field:
Effectiveness for Perforations with Respect to Wind[LINK]
This field is used to enter a value for the coefficient
used to determine natural air exchanges from wind, or Cv. When
the collector is inactive, wind will cause exterior air to
move in and out of the collector. Cv is an arbitrary
coefficient used to model the effectiveness of openings and
depends on opening geometry and the orientation with respect
to the wind. Cv should probably be in the range 0.25 to 0.65.
Increasing Cv will increase the amount of natural
ventilation.
Field:
Discharge Coefficient for Openings with Respect to Buoyancy
Driven Flow[LINK]
This field is used to enter a value for the coefficient
used to determine natural air exchanges from buoyancy, or Cd.
When the collector is inactive, stack or buoyancy effects will
cause exterior air to move in and out of the collector. Cd is
an arbitrary discharge coefficient that depends on the
geometry of the opening. Cd should probably be in the range
0.4 to 1.0. Increasing Cd will increase the amount of natural
ventilation.
The remaining fields are used to name the BuildingSurface:Detailed
objects that are associated with the UTSC. These are the
underlying heat transfer surfaces and are defined elsewhere in
the input file. These other surfaces should all specify
OtherSideConditionsModel as their exterior environment. The
input object can currently accommodate up to ten surfaces, but
it is extensible.
An example of this object follows.
SolarCollector:UnglazedTranspired,
Shop OA UTSC ZN11, ! Name
UTSC OSCM ZN11, ! Boundary Conditions Model Name
HeatingAvailSched , ! Availability Schedule Name
Outside Air Inlet Node ZN11 , ! Inlet Node Name
UTSC Outlet Node ZN11 , ! Outlet Node Name
Mixed Air Node ZN11 , ! Setpoint Node Name
ZN11 Node, ! Zone Node Name
ShopFreeHeatingSetpoints, ! Free Heating Setpoint Schedule Name
0.0016, ! Diameter of Perforations in Collector
0.01689, ! Distance Between Perforations in Collector
0.9, ! Thermal Emissivity of Collector Surface
0.9, ! Solar Absorbtivity of Collector Surface
4.0, ! Effective Overall Height of Collector
0.1, ! Effective Gap Thickness of Plenum Behind Collector
2.0, ! Effective Cross Section Area of Plenum Behind Collector
Triangle, ! Hole Layout Pattern for Pitch
Kutscher1994, ! Heat Exchange Effectiveness Correlation
1.165, ! Ratio of Actual Collector Surface Area to Projected Surface Area
MediumRough , ! Roughness of Collector
0.00086, ! Collector Thickness
0.25, ! Effectiveness for Perforations with Respect to Wind
0.5, ! Discharge Coefficient for Openings with Respect to Buoyancy Driven Flow
ZN11_Shop_1:ExtWall:South; ! Surface 1 Name
The temperature of air entering the plenum after being
heated by the collector. When there is no forced air flow or
the collector is passive, then the condition of air entering
the plenum or the collector leaving air is assumed to be that
of outside air.
Solar
Collector Outside Face Suction Velocity [m/s][LINK]
The bulk velocity of air approaching the collector.
The temperature of air inside, and leaving, the plenum
behind the collector. This plenum leaving air temperature
depends on the mode of operation of the collector. When the
collector is passive (no forced flow), then the passive model
assumes the condition of air entering the plenum is that of
outside air, or else when the collector is active, then the
model sets the plenum entering air condition to transpired
collector leaving air condition determined from the collector
model.
The overall sum of energy added to the outdoor air
stream.
Solar
Collector Natural Ventilation Air Change Rate [ACH][LINK]
The rate of natural ventilation air exchange between the
plenum and ambient when the collector is inactive in Air
Changes per Hour.
Solar
Collector Natural Ventilation Mass Flow Rate [kg/s][LINK]
The mass flow rate of natural ventilation air exchange
between the plenum and ambient when the collector is
inactive.
Solar
Collector Wind Natural Ventilation Mass Flow Rate [kg/s][LINK]
The part of mass flow rate of natural ventilation air
exchange between the plenum and ambient when the collector is
inactive due to wind-driven forces.
Solar
Collector Buoyancy Natural Ventilation Mass Flow Rate
[kg/s][LINK]
The part of mass flow rate of natural ventilation air
exchange between the plenum and ambient when the collector is
inactive due to buoyancy-driven forces.
Solar
Collector Incident Solar Radiation [W/m2][LINK]
The intensity of solar radiation incident on the UTSC
collector from all sources.
This object is used to model unglazed transpired solar
collectors (UTSC) that are connected to multiple outdoor air
systems. This object supplements the SolarCollector:UnglazedTranspired
object and is only necessary if more than one air system is
connected to a single transpired collector. After the name
field, there are sets of four node names used to define the
connections of each air system. Each set contains node names
for inlet, outlet, control, and zone. If more than five air
systems are needed, this object is extensible.
This field is used to identify the name of the SolarCollector:UnglazedTranspired
object that needs to be connected to more than one air system.
This field must match the name.
Field
Set: Inlet Node, Outlet Node, Mixed Air Node, Zone Node[LINK]
The following four fields form a repeating set of four
fields. One set is used for each outdoor air system that is
connected to the collector.
Field:
Outdoor Air System <#> Collector Inlet Node[LINK]
This field contains the name of an air node that provides
air into the UTSC. This node name should also be assigned to
be an outdoor air node using the OutdoorAir:NodeList
and OutdoorAir:Node
objects. This node is also be named as the actuator node in a
Controller:OutdoorAir
object.
Field:
Outdoor Air System <#> Collector Outlet Node[LINK]
This field contains the name of an air node that is the
outlet of the UTSC. This node name will typically be the
Outdoor Air Stream Node Name in the OutdoorAir:Mixer
(if there is no other equipment on the outdoor air path).
Field:
Outdoor Air System <#> Mixed Air Node[LINK]
This field contains the name of an air node that has a
setpoint manager controlling its temperature setpoint. This
node name will typically be named as the mixed air node in a
Controller:OutdoorAir
object.
This field contains the name of an air node for a thermal
zone that is ultimately connected to the air system. This node
is used with the setpoint schedule, defined in the following
field, to provide an added layer of thermostatic control for
the UTSC without affecting the control of auxiliary heating.
If there is a single air system that is connected to more than
one zone, then a single zone should be selected based on where
the thermostat might be located.
An example of this object follows.
SolarCollector:UnglazedTranspired:Multisystem,
OFFICE MultiSystem OA UTSC , ! Solar Collector Name
Outside Air Inlet Node ZN1, ! Outdoor Air System 1 Collector Inlet Node
UTSC Outlet Node ZN1, ! Outdoor Air System 1 Collector Outlet Node
Mixed Air Node ZN1, ! Outdoor Air System 1 Mixed Air Node
ZN1 Node, ! Outdoor Air System 1 Zone Node
Outside Air Inlet Node ZN2, ! Outdoor Air System 2 Collector Inlet Node
UTSC Outlet Node ZN2, ! Outdoor Air System 2 Collector Outlet Node
Mixed Air Node ZN2, ! Outdoor Air System 2 Mixed Air Node
ZN2 Node, ! Outdoor Air System 2 Zone Node
Outside Air Inlet Node ZN3, ! Outdoor Air System 3 Collector Inlet Node
UTSC Outlet Node ZN3, ! Outdoor Air System 3 Collector Outlet Node
Mixed Air Node ZN3, ! Outdoor Air System 3 Mixed Air Node
ZN3 Node, ! Outdoor Air System 3 Zone Node
Outside Air Inlet Node ZN4, ! Outdoor Air System 4 Collector Inlet Node
UTSC Outlet Node ZN4, ! Outdoor Air System 4 Collector Outlet Node
Mixed Air Node ZN4, ! Outdoor Air System 4 Mixed Air Node
ZN4 Node, ! Outdoor Air System 4 Zone Node
Outside Air Inlet Node ZN5, ! Outdoor Air System 5 Collector Inlet Node
UTSC Outlet Node ZN5, ! Outdoor Air System 5 Collector Outlet Node
Mixed Air Node ZN5, ! Outdoor Air System 5 Mixed Air Node
ZN5 Node; ! Outdoor Air System 5 Zone Node
Group Solar Collectors[LINK]
Solar collectors are thermal devices that convert solar energy into thermal energy by raising the temperature of a circulating heat transfer fluid. The fluid can then be used to heat water for domestic hot water usage or space heating.
In EnergyPlus solar collectors are components that are connected to the plant loop. A solar heating system can be constructed with a combination of solar collectors, pumps, and hot water tanks.
Flate plate solar collectors are defined using two objects: SolarCollector:FlatPlate:Water and SolarCollectorPerformance:FlatPlate. Similarly, Integral-Collector-Storage (ICS) solar collectors are defined using two objects: SolarCollector:IntegralCollectorStorage, and SolarCollectorPerformance:IntegralCollectorStorage. The SolarCollector:FlatPlate:Water and SolarCollector:IntegralCollectorStorage objects describe the plant component connections. These object also reference SolarCollectorPerformance:FlatPlate and SolarCollectorPerformance:IntegralCollectorStorage performance objects which contains the thermal and optical performance test data for a specific make and model of collector. Parameters are defined separately so that these values can be organized into a reference data set and need only be entered once if for an array of the same type of collectors.
SolarCollector:FlatPlate:Water[LINK]
The flat-plate solar collector model simulates glazed, unglazed, and tubular (i.e. evacuated tube) collectors. The SolarCollector:FlatPlate:Water object represents a single collector module connected to the plant loop. The thermal and optical properties of the collector module are taken from the referenced SolarCollectorPerformance:FlatPlate object. A surface or shading object defines the collector tilt, azimuth, and gross area. The collector surface participates normally in all shading calculations if the “FullExterior,” “FullInteriorAndExterior,” FullExteriorWithReflections , or FullInteriorAndExteriorWithReflections flags are set in the Solar Distribution field of the Building object. Inlet and outlet nodes are specified for plant connections on the demand side of the plant loop.
Inputs[LINK]
Field: Name[LINK]
The unique name of the SolarCollector:FlatPlate:Water object.
Field: Solar Collector Performance Name[LINK]
Reference name of a SolarCollectorPerformance:FlatPlate object that defines the thermal and optical properties of the collector.
Field: Surface Name[LINK]
Reference to one of the many different types of surfaces such as the BuildingSurface:Detailed or the Shading:Zone:Detailed objects. The surface named here is used to define the solar collector tilt, azimuth, and gross area.
Field: Inlet Node Name[LINK]
The name of the inlet node connection to the plant loop.
Field: Outlet Node Name[LINK]
The name of the outlet node connection to the plant loop.
Field: Maximum Flow Rate[LINK]
The maximum flow rate [m\(^{3}\)/s] allowed through the collector. This field is optional. If not specified, the collector will allow as much flow as the rest of the plant can deliver.
An example follows.
Outputs[LINK]
The following output variables are reported for the SolarCollector:FlatPlate:Water object:
HVAC,Average,Solar Collector Incident Angle Modifier []
HVAC,Average,Solar Collector Efficiency []
HVAC,Average,Solar Collector Heat Transfer Rate [W]
HVAC,Average,Solar Collector Heat Gain Rate [W]
HVAC,Average,Solar Collector Heat Loss Rate [W]
HVAC,Sum,Solar Collector Heat Transfer Energy [J]
Solar Collector Incident Angle Modifier [][LINK]
The incident angle modifier is an important intermediate value used in the SRCC calculation of solar collector performance. The value reported here is the combined result for the current time that includes incident angles of beam solar, diffuse solar from sky, and diffuse solar from ground.
Solar Collector Efficiency [][LINK]
The overall collector efficiency. This is the ratio of collected energy and the incident solar energy. The efficiency can be greater than 1 at times when the outdoor air temperature is warm enough.
Solar Collector Heat Transfer Rate [W][LINK]
Solar Collector Heat Transfer Energy [J][LINK]
These are the overall rate (in W) and amount of energy ( in J) transferred to the collector s circulating fluid. Positive values indicate heating of the fluid while negative values indicate cooling of the fluid.
Solar Collector Heat Gain Rate [W][LINK]
This is the overall rate of heat addition to the collector s circulating fluid in Watts. Values are always positive or zero. If the fluid is actually cooled then the value is zero.
Solar Collector Heat Loss Rate [W][LINK]
This is the overall rate of heat loss from the collector s circulating fluid in Watts. Values are always positive or zero. If the fluid is actually heated then the value is zero.
In addition, several surface variables are also relevant for the collector s surface object (BuildingSurface:Detailed or Shading:Zone:Detailed):
Zone,Average,Surface Outside Face Sunlit Area [m2]
Zone,Average,Surface Outside Face Sunlit Fraction []
Zone,Average,Surface Outside Face Incident Solar Radiation Rate per Area [W/m2]
Zone,Average,Surface Outside Face Incident Beam Solar Radiation Rate per Area [W/m2]
Zone,Average,Surface Outside Face Incident Sky Diffuse Solar Radiation Rate per Area [W/m2]
Zone,Average,Surface Outside Face Incident Ground Diffuse Solar Radiation Rate per Area [W/m2]
Zone,Average,Surface Outside Face Beam Solar Incident Angle Cosine Value []
The temperatures at the inlet and outlet nodes and the collector mass flow rate can be monitored using the system node output variables:
HVAC,Average,System Node Temperature [C]
HVAC,Average,System Node Mass Flow Rate [kg/s]
SolarCollectorPerformance:FlatPlate[LINK]
The SolarCollectorPerformance:FlatPlate object contains the thermal and optical performance parameters for a single collector module. These parameters are based on the testing methodologies described in ASHRAE Standards 93 and 96. The Solar Rating and Certification Corporation (SRCC) applies these standards in their rating procedures of solar collectors. The ratings for commercially available collectors in North America are published in the Directory of SRCC Certified Solar Collector Ratings. The SRCC database has also been converted into an EnergyPlus data set of SolarCollectorPerformance:FlatPlate objects that is included with the program (see SolarCollectors.idf in the DataSets folder).
The coefficients for the energy conversion efficiency and incident angle modifier allow first order (linear) or second order (quadratic) correlations. To use a first order correlation, the second order coefficient must be left blank or set to zero.
In order for the model to work correctly, the test conditions for which the performance coefficients were measured must be specified in the fields: Test Fluid, Test Volumetric Flow Rate, and Test Correlation Type. Currently, only water is allowed as the Test Fluid.
For more detailed information about the performance coefficients, see the EnergyPlus Engineering Reference Document.
Inputs[LINK]
Field: Name[LINK]
The unique name of the SolarCollectorPerformance:FlatPlate object.
Field: Gross Area[LINK]
The gross area of the collector module [m\(^{2}\)]. This value is mainly for reference. The area of the associated collector surface object is used in all calculations.
Field: Test Fluid[LINK]
The fluid that was used in the testing procedure that resulted in the thermal and optical performance coefficients below. Currently only Water is allowed. This the fluid during the collector testing, not the fluid used during a particular EnergyPlus run.
Field: Test Flow Rate[LINK]
The volumetric flow rate during testing [m\(^{3}\)/s]. If the value is available as flow rate per unit area, it is recommended to multiply by the Gross Area of the collector module, not the net aperture area.
Field: Test Correlation Type[LINK]
This field specifies type of temperature used to develop the correlation equations. The testing procedure is based on an experimental correlation using either Inlet, Average, or Outlet temperature. Enter one of these choices. The ASHRAE Standards 93 and 96 always use Inlet temperature.
Field: Coefficient 1 of Efficiency Equation[LINK]
First coefficient of efficiency equation for energy conversion [dimensionless]. This is the Y-intercept term.
Field: Coefficient 2 of Efficiency Equation[LINK]
Second coefficient of efficiency equation for energy conversion [W/m\(^{2}\)-K]. This is the first-order term.
Field: Coefficient 3 of Efficiency Equation[LINK]
Third coefficient of efficiency equation for energy conversion [W/m\(^{2}\)-K\(^{2}\)]. This field is optional. This is the second-order term. If left blank or set to zero, a first-order linear correlation is used.
Field: Coefficient 2 of Incident Angle Modifier[LINK]
Second coefficient of the incident angle modifier equation. This the first-order term. (There is no Coefficient 1 of Incident Angle Modifier because that number is always 1.0.)
Field: Coefficient 3 of Incident Angle Modifier[LINK]
Third coefficient of the incident angle modifier equation. This is the second-order term. This field is optional. If left blank or set to zero, a first order linear correlation is used.
An example of this object follows.
Outputs[LINK]
This object does not generate any output; see SolarCollector:FlatPlate:Water Output
SolarCollector:IntegralCollectorStorage[LINK]
The Integral-Collector-Storage (ICS) solar collector model simulates glazed collectors with integral storage unit. The SolarCollector:IntegralCollectorStorage object represents a single collector module connected to the plant loop. The thermal and optical properties of the collector module are calculated from inputs in SolarCollectorPerformance:IntegralCollectorStorage object. A surface or shading object defines the collector tilt, and azimuth. The collector surface participates normally in all shading calculations if the “FullExterior,” “FullInteriorAndExterior,” FullExteriorWithReflections , or FullInteriorAndExteriorWithReflections flags are set in the Solar Distribution field of the Building object. Inlet and outlet nodes are specified for plant connections on the demand side of the plant loop. The SurfaceProperty:ExteriorNaturalVentedCavity, object is required to describe the surface properties, the characteristics of the cavity and opening for natural ventilation if OtherSideConditionsModel is specified as the collector bottom surface outside boundary condition type.
Inputs[LINK]
Field: Name[LINK]
The unique name of the SolarCollector:IntegralCollectorStorage object.
Field: Solar Collector Performance Name[LINK]
Reference name of a SolarCollectorPerformance:IntegralCollectorStorage object that defines the thermal and optical properties of the collector.
Field: Surface Name[LINK]
Reference to one of the many different types of surfaces such as the BuildingSurface:Detailed or the Shading:Zone:Detailed objects. The surface named here is used to define the solar collector tilt, and azimuth. The collector shades the surface it is mounted on and hence impacts the surface heat balance.
Field: Bottom surface Boundary Conditions Type[LINK]
This field contains the type of boundary conditions applicable to the ICS collector bottom surface. Allowed boundary condition types are: AmbientAir and OtherSideConditionsModel. If the other side conditions model is selected, specify the name of the SurfaceProperty:OtherSideConditionsModel object in the next input field, otherwise, leave the next input field blank. The AmbientAir boundary condition uses outdoor air temperature as boundary condition, hence the subsurface is assumed to be exposed to the sun and wind.
Field: Other Side Conditions Model Name[LINK]
This field contains the name of a SurfaceProperty:OtherSideConditionsModel object declared elsewhere in the input file. This will connect the collector to the exterior boundary conditions for the underlying heat transfer surface specified above..
Field: Inlet Node Name[LINK]
The name of the inlet node connection to the plant loop.
Field: Outlet Node Name[LINK]
The name of the outlet node connection to the plant loop.
Field: Maximum Flow Rate[LINK]
The maximum flow rate [m3/s] allowed through the collector. This field is optional. If not specified, the collector will allow as much flow as the rest of the plant can deliver.
An example follows.
SolarCollectorPerformance:IntegralCollectorStorage[LINK]
The SolarCollectorPerformance:IntegralCollectorStorage object contains the thermal and optical performance parameters for a single collector module. The transmittance-absorptance product of the absorber and cover system is determined from optical properties specified. For more detailed information about the calculation procedure, see the EnergyPlus Engineering Reference Document.
Inputs[LINK]
Field: Name[LINK]
The unique name of the SolarCollectorPerformance:IntegralCollectorStorage object.
Field: ICS Collector Type[LINK]
This input field is the ICS collector type. Currently only RectangularTank type is allowed.
Field: Gross Area[LINK]
This input field is the gross area of the collector module in m2. This gross area is used in the energy balance equations.
Field: Collector Water Volume[LINK]
This input field is the volume of water in the solar collector in m3.
Field: Bottom Heat Loss Conductance[LINK]
This input field is the collector bottom heat loss conductance in W/m2K. This value is calculated from thermal conductivity and thickness of the bottom insulation.
Field: Side Heat Loss Conductance[LINK]
This input field is the collector side heat loss conductance in W/m2K. This value is calculated from thermal conductivity and thickness of the side insulation.
Field: Collector Aspect Ratio[LINK]
This input field is the ratio of the short side (width) of the collector to the long side (length) of the collector. This value is used only for calculating the collector side area along with the collector side height specified in the next input filed. This ratio is less or equal to 1.0.
Field: Collector Side Height[LINK]
This input field is height of collector side in m. This height is used to estimate the collector side area for heat loss calculations along with heat loss coefficient specified in the input field above.
Field: Thermal Mass of Absorber Plate[LINK]
This input field is thermal-mass of the absorber plate per unit area of the collector in [J/m2×K]. This input value multiplied by the absorber gross area determines the thermal mass of the absorber plate. It is estimated from the specific heat, density and average thickness of the absorber plate. If zero is specified then the absorber plate energy balance reduces to steady state form.
Field: Number of Covers[LINK]
Number of transparent collector covers. Common practice is to use two covers: glass as the outer cover and Teflon as the inner cover. If single cover is specified leave the inner cover optical and thermal properties input fields blank.
Field: Cover Spacing[LINK]
This input field provides the spacing between the two transparent covers, and the spacing between the inner cover and the absorber plate in m. Default value is 0.05m.
Field: Refractive Index of Outer Cover[LINK]
This is the average Refractive index for solar spectrum range of the outer transparent cover material. Glass is used as the outer cover. Average refractive index value for non-absorbing glass used in solar collectors over solar spectrum range is 1.526.
Field: Extinction Coefficient Times Thickness of Outer Cover[LINK]
This input field is the product of the extinction coefficient and the thickness of the out cover material. The extinction coefficient for glass types approximately varies from 4m\(^{-1}\) to 32 m\(^{-1}\). The extinction coefficient for low-iron glass, which is the default outer cover material, is 15 m\(^{-1}\). The default value for extinction coefficient times thickness (KL) is 0.045 ( = 15.0 x0.003), which is the product of the default extinction coefficient of 15m\(^{-1}\) and 3.0mm thick glass.
Field: Emissivity of Outer Cover[LINK]
This input field value is thermal emissivity of the outer collector cover. The default value assumes low-iron glass with thermal emissivity of 0.88.
Field: Refractive Index of Inner Cover[LINK]
This input field is the average Refractive index of the inner transparent cover of the collector. Commonly Teflon (PolytetraFluoroethylene) is used as the inner cover. The average refractive index value over the solar spectrum range for Teflon is 1.37.
Field: Extinction Coefficient Times Thickness of Inner Cover[LINK]
This input field is the product of the extinction coefficient (K) and the thickness (L) of the inner cover material. The inner cover material is more transparent than the out cover, very thin and hence their thickness can be assumed to be negligible. The default value for extinction coefficient times thickness (KL) is 0.008 ( = 40.0x0.0002), which is the product of extinction coefficient of 40m\(^{-1}\) and a thickness of 0.2mm.
Field: Emissivity of Inner Cover[LINK]
This input field value is thermal emissivity of the inner transparent collector cover. The default value assumes plastic sheet with thermal emissivity of 0.30. This value is used in the thermal analysis only.
Field: Absorptance of Absorber Plate[LINK]
This input field is shortwave or solar absorptance of the absorber plate. The default value is 0.96.
Field: Emissivity of Absorber Plate[LINK]
This input field value is thermal emissivity of the absorber plate. Default value is 0.30. This input value is used in the thermal analysis only.
An example follows.
Outputs[LINK]
The following output variables are reported for the SolarCollector:IntegralCollectorStorage object:
HVAC,Average,Solar Collector Storage Water Temperature [C]
HVAC,Average,Solar Collector Absorber Plate Temperature [C]
HVAC,Average,Solar Collector Overall Top Heat Loss Coefficient [W/m2-C]
HVAC,Average,Solar Collector Thermal Efficiency []
HVAC,Average,Solar Collector Storage Heat Transfer Rate [W]
HVAC,Sum,Solar Collector Storage Heat Transfer Energy [J]
HVAC,Average,Solar Collector Heat Transfer Rate [W]
HVAC,Sum,Solar Collector Heat Transfer Energy [J]
HVAC,Average,Solar Collector Skin Heat Transfer Rate [W]
HVAC,Sum, Solar Collector Skin Heat Transfer Energy [J]
HVAC,Average,Solar Collector Transmittance Absorptance Product []
Solar Collector Storage Water Temperature [C][LINK]
This output variable is the ICS collector stored water average temperature at a given time steps in degree Celsius. This temperature is the same as the collector ICS collector leaving water temperature.
Solar Collector Absorber Plate Temperature [C][LINK]
This output variable is the ICS collector absorber plate average temperature at a given time steps in degree Celsius.
Solar Collector Thermal Efficiency [][LINK]
This output variable is the instantaneous thermal efficiency of the ICS solar collector in per cent. This value is determined from net useful energy collected and the total incident solar radiation for each time step. The net useful energy collected is the sum of the energy stored in the collector and net useful energy delivered.
Solar Collector Storage Heat Transfer Rate [W][LINK]
Solar Collector Storage Heat Transfer Energy [J][LINK]
These output variables are the instantaneous rate of change of the energy and the change in energy of the water in the ICS solar collector in Watts, and Joules, respectively.
Solar Collector Skin Heat Transfer Rate [W][LINK]
Solar Collector Skin Heat Transfer Energy [J][LINK]
These output variables are the instantaneous skin heat loss rate and the heat loss energy of the ICS solar collector for each time steps in Watts, and Joules respectively. The skin heat loss rate is the sum of the heat losses through the top, bottom and sides of the collector surfaces. This value is mostly negative, but can have a positive value (heat gain) when the outdoor air temperature is warmer than the collector.
Solar Collector Heat Transfer Rate [W][LINK]
Solar Collector Heat Transfer Energy [J][LINK]
This output variable is the heat rate and Energy transferred from the ICS collector to the collector loop fluid (water) in Watts and Joule, respectively. This value is determined from the collector water mass flow rate, specific heat of water and the temperature difference between the collector water outlet and inlet nodes at each time step. The value is positive when the fluid is heated or negative when cooled.
Solar Collector Transmittance Absorptance Product [][LINK]
This output variable is the transmittance-absorptance product of the covers and absorber system of the ICS solar collector. This value ranges from 0.0 to less than 1.0.
Solar Collector Overall Top Heat Loss Coefficient [W/m2-C][LINK]
This output variable is the overall heat loss coefficient from the absorber plate to the ambient air calculated for each time step.
SolarCollector:FlatPlate:PhotovoltaicThermal[LINK]
This object is used to model hybrid photovoltaic-thermal (PVT) solar collectors that convert incident solar energy into both electricity and useful thermal energy. This object describes the PVT solar collector by referencing other objects that provide more detail or connections to other parts of the EnergyPlus model.
The PVT solar collectors need to be connected to either an HVAC air system or a plant loop for collected thermal energy to be utilized. The input field for the type of thermal working fluid informs the program how the PVT collector is expected to be connected. If the the working fluid is air, then the PVT collectors are modeled as a ventilation air pretreatment component and connected to an outdoor air system. If the working fluid is water, then the PVT collectors are modeled as a hot water solar collector and are connected to a plant loop with a water thermal storage tank.
Inputs[LINK]
Field: Name[LINK]
This field should contain a unique name chosen by the user to identify a specific PVT collector in the building model.
Field: Surface Name[LINK]
This field is the user-defined name of a surface object (defined elsewhere) to which the PVT module is attached. These can be any type of building surface that is exposed to the exterior environment. The model uses the named surface s geometry for the PVT solar collector.
Field: Photovoltaic-Thermal Model Performance Name[LINK]
This field is the user-defined name of an object (defined elsewhere) that provides the performance details of the PVT module. This should be the name of a SolarCollectorPerformance:PhotovoltaicThermal:Simple object. Multiple different SolarCollector:FlatPlate:PhotovoltaicThermal objects can reference the same object that provides performance details.
Field: Photovoltaic Generator Name[LINK]
This field is the user-defined name of a Generator:Photovoltaic object (defined elsewhere) that will be used to model the solar electric portion of the PVT solar collector. The PVT models make any adjustments needed to model PV performance in the context of the PVT collector.
Field: Thermal Working Fluid Type[LINK]
This field is the user s choice for the type of fluid used to collect thermal energy. PVT solar collectors can capture thermal energy in either air or water streams. The choices available for this field are Water or Air. If the choice is Air then the PVT collector needs to be connected to an HVAC air system loop. The PVT collector should be situated as the first component on an outdoor air inlet stream. If the choice is Water then the PVT collector needs to be connected to a Plant water system loop. The connections are made via node names which are defined in the following fields, depending on the working fluid type.
Field: Water Inlet Node Name[LINK]
This field is the name of Plant loop node that serves as the inlet to the PVT collector. This field is only used if the Thermal Working Fluid Type is set to Plant/Water.
Field: Water Outlet Node Name[LINK]
This field is the name of a plant loop node that seves as the outlet from the PVT collector. This field is only used if the Thermal Working Fluid Type is set to Plant/Water.
Field: Air Inlet Node Name[LINK]
This field is the name of HVAC air loop node that serves as the inlet to the PVT collector. This field is only used if the Thermal Working Fluid Type is set to HVAC/Air.
Field: Air Outlet Node Name[LINK]
This field is the name of HVAC air loop node that serves as the outlet from the PVT collector. This field is only used if the Thermal Working Fluid Type is set to HVAC/Air.
Field: Design Flow Rate[LINK]
This field is used to describe the nominal volume flow rate of the thermal working fluid. The units are m3/s. The volume flow rate is autosizable.
An example of this object follows.
Outputs[LINK]
The output variables that are available for flat plate PVT include the following.
HVAC,Average,Generator Produced Thermal Rate [W]
HVAC,Sum,Generator Produced Thermal Energy [J]
HVAC,Average,Generator PVT Fluid Bypass Status []
HVAC,Average,Generator PVT Fluid Inlet Temperature [C]
HVAC,Average,Generator PVT Fluid Outlet Temperature [C]
HVAC,Average,Generator PVT Fluid Mass Flow Rate [kg/s]
Generator Produced Thermal Rate [W][LINK]
Generator Produced Thermal Energy [J][LINK]
These outputs are the thermal energy and power produced by the PVT collector. PVT collectors are a type of cogenerator, producing both electrical and thermal power and these variables report the thermal portion in the same manner as other fuel-based cogenerators. The thermal energy is placed on HeatProduced meter and is attributed to SolarWater or SolarAir depending on the type of working fluid. The generator thermal production is also reported at the load center level.
Generator PVT Fluid Bypass Status [][LINK]
This output variable indicates the status a bypass damper. It is only available for air-based PVT. There are no dimensions and the range is between 0.0 and 1.0. If the value is 0.0, then there is no bypassing and all the working fluid goes through the collector. If the value is 1.0, then there is complete bypassing and all the working fluid goes around the collector. If the value is between 0.0 and 1.0, then the model is effectively mixing bypass and collector streams to target a temperature setpoint placed on the outlet node.
Generator PVT Fluid Inlet Temperature [C][LINK]
This report is the inlet temperature of the working fluid that enters the PVT collector
Generator PVT Fluid Outlet Temperature [C][LINK]
This report is the outlet temperature of the working fluid that leaves the PVT collector
Generator PVT Fluid Mass Flow Rate [kg/s][LINK]
This report is the mass flow rate of the working fluid through the PVT collector. This is the overall mass flow rate, portions of the flow may be internally bypassed around the collector itself for control modulation.
SolarCollectorPerformance:PhotovoltaicThermal:Simple[LINK]
This object is used to provide performance details for the simple PVT model. This is a simple user-defined efficiency model. Thermal conversion efficiency is a constant or scheduled value. There are no output variable for this object, reporting is done by the parent PVT object.
Inputs[LINK]
Field: Name[LINK]
This field is the unique name for this object.
Field: Fraction of Surface Area with Active Thermal Collector[LINK]
This field is the fraction of the surface area that is active. It should be a decimal fraction between 0.0 and 1.0. The area of the PVT s surface will be multiplied by this fraction to determine the active area of the PVT collector(s).
Field: Thermal Conversion Efficiency Input Mode Type[LINK]
This field is used to determine how the thermal efficiency is input. There are two choices, Fixed or Scheduled. If this field is set to Fixed, then a constant value for thermal efficiency will be used (set in next field). If this field is set to Scheduled, then the thermal efficiency values are defined in a schedule.
Field: Value for Thermal Conversion Efficiency if Fixed[LINK]
This field is used to provide a value for the efficiency with which solar energy is collected in the working fluid. This field is only used if the input mode is set to Fixed in the previous field. Efficiency is defined as the thermal energy collected divided by the incident solar radiation. The value should be between 0.0 and 1.0. The user should be careful that the thermal efficiency and the electrical efficiency be consistent with each other because the overall efficiency of the PVT collector is the combination of both thermal and electrical.
Field: Name of Schedule for Thermal Conversion Efficiency[LINK]
This field is used for the name of a schedule that provides values for the efficiency with which solar energy is collected in the working fluid. This field is only used if the input mode is set to Scheduled in the field above. Efficiency is defined as the thermal energy collected divided by the incident solar radiation. The values in the named schedule should be between 0.0 and 1.0. The user should be careful that the thermal efficiency and the electrical efficiency be consistent with each other because the overall efficiency of the PVT collector is the combination of both thermal and electrical.
Field: Front Surface Emittance[LINK]
This field is used to describe an average value for the total hemispherical emittance of the collector s front face exposed to the sky. This is used to model cooling applications where the PVT collectors are operated at night to cool the working fluid.
An example input object follows.
Solar Collector Heating System Plant Connections[LINK]
This section provides an overview of how to model solar heating systems. A solar heating system can be constructed using a combination of solar collectors, pumps, water tanks and water heaters. The solar collector must be connected on the demand side of the plant loop. Multiple collector modules can be combined in series and parallel using the normal plant connection rules. The supply side of the plant loop should contain a water heater with the solar collector loop connecting to the Source Side Inlet and Source Side Outlet nodes. As usual, the pump must be the first component on the supply side.
If the solar heating system is for domestic hot water (or service water heating) usage only, the field Use Flow Rate Fraction Schedule Name of the WaterHeater:Mixed object can be used to avoid additional plant connections. If the system has more complicated hot water requirements or if the system is for space heating, the Use Side Inlet and Use Side Outlet nodes must be connected to another plant loop to serve zone and non-zone equipment. (See the WaterHeater:Mixed object documentation for more information.)
NOTE: The EnergyPlus plant simulation requires the pump to be the first component on the supply side. This may be different from the way the solar heating system is actually configured. This should not affect the validity of the simulation results.
In order to realize energy savings with a solar heating system, it is best to use a two-tank system with a storage tank and auxiliary water heater. The storage tank gathers heat directly from the solar collectors and stores it for later use. The storage tank is modeled using a WaterHeater:Mixed object with the Heater Maximum Capacity set to zero. The auxiliary water heater is positioned downstream of the storage tank on the supply side of the main plant loop. The auxiliary water heater, or booster water heater, provides additional heat if the storage tank water is not hot enough. The auxiliary water heater can be modeled as an instantaneous/tankless water heater or as a standard tanked water heater with heating source (see WaterHeater:Mixed).
Another strategy to consider for solar heating systems is to allow the storage tank to reach a much higher temperature than necessary for the end use. This allows the tank to store more energy from the solar collectors, when it is available. However, for applications such as domestic hot water, it is undesirable and unsafe to supply excessive hot water temperatures at the point of demand. To take advantage of higher storage temperatures, yet still avoid scalding temperatures at the faucet, the hot water leaving the storage tank can be tempered with cold water using a three-way valve to achieve the target temperature. See the TemperingValve object documentation for more details.
A complete two-tank solar heating system with tempering valve is shown below.
Solar Heating System Control[LINK]
There are several options for controlling a solar heating system in EnergyPlus. Since the solar collectors request a constant flow demand based on their Maximum Flow Rate, the limiting factor is actually the flow rate determined by the loop pump. Therefore the entire system can be controlled using the Pump Flow Rate Schedule of the pump. If the schedule is omitted, the pump and system will run all the time (without any other controls specified). This is usually not the best way to operate a solar heating system.
To better control the collector loop, a differential thermostat can be used to compare the temperature in the water heater to the temperature in the collector so that the pump is only turned on when there is a useful heat gain. The differential thermostat is simulated using the AvailabilityManager:DifferentialThermostat object. For a typical system, the Hot Node Name field refers to an outlet node of one of the collector modules. The Cold Node Name field refers to the Source Side Outlet node, i.e. the cold storage water leaving the water heater. The fields Temperature Difference On Limit and Temperature Difference Off Limit are usually 8 12 C and 1 3 C respectively. If the two temperature differences are too close, it is possible for the system to turn on and off rapidly without much useful heat gain. This can also occur if the flow rate through the collector is too high. Without flow the fluid in the collector heats up more quickly; when high flow is turned on, all of the hot fluid is removed and the temperature drops, forcing the system off again.
Another control method is to use a photovoltaic panel to power the pump. The system begins pumping when there is enough solar radiation to operate the pump. This is not yet implemented in EnergyPlus.
Freeze Prevention[LINK]
In climates with a cold season, the solar heating system must be designed to avoid the risk of fluid freezing in the solar collector or exposed pipes and causing damage. This is not a problem if air is the heat transfer fluid. With water, however, there are several strategies that can minimize the risk.
Seasonal schedule. The simplest strategy is to not use the system during the cold season. This is a hassle because it requires the collector to be manually drained of all fluid. The benefits of the solar heating system are also lost during this time. This can be simulated in EnergyPlus with the appropriate pump schedule for the collector system.
Antifreeze. The freezing point of the liquid is decreased by adding antifreeze to the water or using a different heat transfer liquid with a lower freezing point. This cannot yet be simulated in EnergyPlus because only pure water is currently allowed in plant loops.
Drain-back system. This strategy automatically empties the collector when the pump is not running. This scenario is modeled by default in EnergyPlus, although the extra pump energy required to start the system is not taken into account.
Recirculation system. This strategy automatically recirculates warm liquid from the storage tank back through the collector to maintain the system above the freezing point. There are system losses using this method. This can be simulated in EnergyPlus by using AvailabilityManager:LowTemperatureTurnOn to force the system to turn on when the outdoor air temperature or collector outlet temperature falls below a specified minimum.
Additional Controls[LINK]
In addition to freeze prevention, it is also necessary to prevent the system from becoming too hot. This is usually a safety issue for the water heater. For this case it is important to have a high temperature cutoff to stop the pump before damaging the water heater. This is accomplished with a AvailabilityManager:HighTemperatureTurnOff.
System Availability Manager List Example[LINK]
To use the availability managers for the control cases described above, a AvailabilityManagerAssignmentList must be defined and referenced in the PlantLoop object of the collector loop. An example of a differential thermostat, recirculation for freeze prevention, and high temperature cutoff is shown below:
The AvailabilityManager:DifferentialThermostat object must always be the last manager in the availability manager list. See the AvailabilityManagerAssignmentList object documentation for more information.
SolarCollector:UnglazedTranspired[LINK]
This object is used to model unglazed transpired solar collectors (UTSC) used to condition outdoor air. These collectors are generally used to heat air drawn through perforated absorbers that are heated by the sun and also recover heat conducted out through the underlying wall. The SolarCollector:UnglazedTranspired object represents a single collector attached to one or more BuildingSurface:Detailed objects and to one or more outdoor air systems. Therefore the transpired collector is part of both the thermal envelope and the HVAC system. An example file is provided called TranspiredCollectors.idf.
The area and orientation of the collector is obtained from BuildingSurface:Detailed objects, which are referenced by name. Although the collector surface itself is slightly detached from the underlying building wall (or roof), no additional surface object is needed to represent the collector itself. When modeling transpired collectors, it is important to consider the size of the collector when developing the building model s BuildingSurface:Detailed objects because the underlying surfaces must match the collector. For example, if the collector covers only part of the wall, then that wall should be split into separate surfaces where one matches the size of the collector. A single collector can be associated with as many BuildingSurface:Detailed objects as desired (although if you need to use more than 10 surfaces, then the IDD will need to be extended). The collector can be arranged at any tilt angle by describing the surfaces appropriately. The surfaces need not be contiguous nor have the same orientation, but the program will issue warnings if surfaces have widely ranging tilts and azimuths.
The collector conditions outdoor air and is connected to the outdoor air system using the usual method of specifying node names. Using the UTSC model requires specifying a relatively complete HVAC air system that includes an outdoor air path. This will typically require using a set of objects that, at a minimum, will include: AirLoopHVAC:ControllerList, AirLoopHVAC:OutdoorAirSystem:EquipmentList, AirLoopHVAC:OutdoorAirSystem, OutdoorAir:NodeList, OutdoorAir:Mixer, SetpointManager:MixedAir, and Controller:OutdoorAir. A single UTSC can serve more than one outdoor air system but requires also using a separate object, called SolarCollector:UnglazedTranspired:Multisystem to specify node connections.
Controls for the UTSC involve setting the rate of air flow and the status of a bypass damper. If the bypass damper is open, then all the ventilation air goes straight into the outdoor air mixer; if it closed, then all the air first passes through the UTSC. The bypass damper is modeled as completely open or completely closed. The UTSC bypass damper control is determined by an availability manager, the airflow set by the outdoor air mixer controls, and thermostatic type controls that decide if heating is useful. An availability schedule is used to bypass the collector for certain times of the year, eg. summer cooling season. The air flow rates are set by controls associated with the outdoor air mixer (see SetpointManager:MixedAir, and Controller:OutdoorAir). Thermostatic type control decides if the collector will provide useful heating based on either of two types of setpoints. The first type of temperature setpoint is managed by SetpointManager:MixedAir, where the UTSC model looks at a control node, usually the mixed air node. The second type is an extra setpoint especially for free heating that is managed within this object where the UTSC model looks at the zone air node.
Inputs[LINK]
Field: Name[LINK]
This field contains a unique name for the unglazed transpired solar collector.
Field: Boundary Conditions Model Name[LINK]
This field contains the name of a SurfaceProperty:OtherSideConditionsModel object declared elsewhere in the input file. This will connect the collector to the exterior boundary conditions for the underlying heat transfer surface.
Field: Availability Schedule Name[LINK]
This field contains the name of a schedule that determines whether or not the UTSC is available. When the schedule value is less than or equal to zero, the UTSC is always bypassed. When the schedule value is greater than zero, the UTSC is available and will be used when other conditions are met, such as outdoor air requested by mixer and preheating has been determined to be beneficial based on thermostatic control. If this field is blank, the schedule has values of 1 for all time periods.
Field: Inlet Node Name[LINK]
This field contains the name of an air node that provides air into the UTSC. This node name should also be assigned to be an outdoor air node using the OutdoorAir:NodeList or OutdoorAir:Node objects. This node should also be named as the actuated node in a Controller:OutdoorAir object. If the UTSC is connected to more than one air system, then this field can be left blank and the SolarCollector:UnglazedTranspired:Multisystem object should be used to define the nodes.
Field: Outlet Node Name[LINK]
This field contains the name of an air node that is the outlet of the UTSC. This node name will typically be the inlet to the OutdoorAir:Mixer (if there is no other equipment on the outdoor air path). If the UTSC is connected to more than one air system, then this field can be left blank and the SolarCollector:UnglazedTranspired:Multisystem object should be used to define the nodes.
Field: Setpoint Node Name[LINK]
This field contains the name of an air node that has a setpoint manager controlling its temperature setpoint. This node name will typically be named as the control node in a a Controller:OutdoorAir object. If the UTSC is connected to more than one air system, then this field can be left blank and the SolarCollector:UnglazedTranspired:Multisystem object should be used to define the nodes.
Field: Zone Node Name[LINK]
This field contains the name of an air node for a thermal zone that is ultimately connected to the air system. This node is used with the setpoint schedule, defined in the following field, to provide an added layer of thermostatic control for the UTSC without affecting the control of auxiliary heating. If there is a single air system that is connected to more than one zone, then a single zone should be selected based on where the thermostat might be located. If the UTSC is connected to more than one air system, then this field can be left blank and the SolarCollector:UnglazedTranspired:Multisystem object should be used to define the nodes.
Field: Free Heating Setpoint Schedule Name[LINK]
This field contains the name of a temperature schedule defined elsewhere in the input file. This schedule should define temperatures desired in the zone, but not necessarily required. This secondary setpoint schedule is used to allow the UTSC to operate as if it has its own thermostat that is separate from the primary control mechanism. When the UTSC is used with auxiliary heating, the usual setpoint managers and temperature controllers will determine how the auxiliary heaters are controlled. This allows using a higher zone air temperature setpoint for controlling UTSC bypass than for the auxiliary heating system.
Field: Diameter of Perforations in Collector[LINK]
This field is used to enter the effective diameter of the perforations in the collector surface. The diameter should be entered in meters. For perforations other than round, use an equivalent diameter for a round hole that would have the same area.
Field: Distance Between Perforations in Collector[LINK]
This field is used to enter the pitch, or average, shortest distance between perforations.
Field: Thermal Emissivity of Collector Surface[LINK]
This field is used to enter the thermal emissivity of the collector. This surface property is for longwave infrared radiation. The property is used for both sides of collector. Most painted materials have an emissivity of 0.9.
Field: Solar Absorbtivity of Collector Surface[LINK]
This field is used to enter the solar absorbtivity of the collector. This surface property is for shortwave, solar radiation. The property is used for the front side of the collector that faces the environment. Darker colors have a higher absorbtivity. While black is the highest performance, other colors might be used to match the color scheme of the rest of the facade. The following table provides sample solar absorbtivities for different colors (source: Conserval Engineering Inc., Toronto, Ontario, Canada).
([1] Kynar is a registered trademark of Elf Atochem North America, Inc.)
Field: Effective Overall Height of Collector[LINK]
This field is used to enter a nominal height for the collector. This value is used in the program to determine a length scale in the vertical direction for the buoyancy-driven portion of natural ventilation that occurs when the collector is inactive. (Note that most of the geometry information is obtained from the underlying surfaces.) The value entered here is adjusted inside the program to account for tilt of the collector. While the value here would generally correspond to the actual distance/height, its value is not critical and it can be used to adjust modeling the air exchange rates in passive mode. If the collector is horizontal, then the length scale is obtained from the following field.
Field: Effective Gap Thickness of Plenum Behind Collector[LINK]
This field is used to enter a nominal gap thickness for the collector. This distance value is only used when the collector is near horizontal to determine a length scale in the vertical direction for buoyancy calculations. For example, if the collector is mounted on a flat roof, its tilt-adjusted height is zero and the program will use this gap thickness as a length scale rather than the height from the previous field.
Field: Effective Cross Section Area of Plenum Behind Collector[LINK]
This field is used to enter the nominal cross sectional area of the gap behind the collector. This area is used to determine a velocity scale for surface convection heat transfer correlations when the collector is active. This value is generally the average gap thickness times the average width of the collector.
Field: Hole Layout Pattern for Pitch[LINK]
This field is used to describe the pattern of perforations in the collector surface. There are currently two choices available: Square and Triangle. Note that the hole layout pattern should be consistent with how the value for pitch was determined.
Field: Heat Exchange Effectiveness Correlation[LINK]
This field is used to select which correlation is used to model heat transfer from the collector surface to the incoming air when the collector is active. There are two choices available: Kutscher1994, and VanDeckerHollandsBrunger2001. See the Engineering Reference for details and references.
Field: Ratio of Actual Collector Surface Area to Projected Surface Area[LINK]
This field is used to enter a factor that accounts for the extra surface area resulting from corrugations in the collector surface. Corrugations help stiffen the collector. The projected surface area is obtained by the program from the (flat) underlying surfaces. If the collector is flat then this ratio is 1.0. If the collector is corrugated, then this ratio will be greater than one. A typical value might be 1.165.
Field: Roughness of Collector[LINK]
This field is used to describe the relative roughness of the collector material. This field is similar to one in the Material object. This parameter only influences the convection coefficients, more specifically the outside convection coefficient. A special keyword is expected in this field with the options being VeryRough , Rough , MediumRough , MediumSmooth , Smooth , and VerySmooth in order of roughest to smoothest options.
Field: Collector Thickness[LINK]
This field is used to enter the thickness of the collector material. This value is only needed for the Van Decker Hollands Brunger 2001 correlation. The material thickness should be entered in meters.
Field: Effectiveness for Perforations with Respect to Wind[LINK]
This field is used to enter a value for the coefficient used to determine natural air exchanges from wind, or Cv. When the collector is inactive, wind will cause exterior air to move in and out of the collector. Cv is an arbitrary coefficient used to model the effectiveness of openings and depends on opening geometry and the orientation with respect to the wind. Cv should probably be in the range 0.25 to 0.65. Increasing Cv will increase the amount of natural ventilation.
Field: Discharge Coefficient for Openings with Respect to Buoyancy Driven Flow[LINK]
This field is used to enter a value for the coefficient used to determine natural air exchanges from buoyancy, or Cd. When the collector is inactive, stack or buoyancy effects will cause exterior air to move in and out of the collector. Cd is an arbitrary discharge coefficient that depends on the geometry of the opening. Cd should probably be in the range 0.4 to 1.0. Increasing Cd will increase the amount of natural ventilation.
Field: Surface <#> Name[LINK]
The remaining fields are used to name the BuildingSurface:Detailed objects that are associated with the UTSC. These are the underlying heat transfer surfaces and are defined elsewhere in the input file. These other surfaces should all specify OtherSideConditionsModel as their exterior environment. The input object can currently accommodate up to ten surfaces, but it is extensible.
An example of this object follows.
Outputs[LINK]
In addition to related output that can be obtained for air nodes and surfaces, these outputs are available for UTSC systems:
HVAC,Average,Solar Collector Heat Exchanger Effectiveness []
HVAC,Average,Solar Collector Leaving Air Temperature [C]
HVAC,Average,Solar Collector Outside Face Suction Velocity [m/s]
HVAC,Average,Solar Collector Surface Temperature [C]
HVAC,Average,Solar Collector Plenum Air Temperature [C]
HVAC,Average,Solar Collector Sensible Heating Rate [W]
Zone,Meter,SolarAir:Facility [J]
Zone,Meter,SolarAir:HVAC [J]
Zone,Meter,HeatProduced:SolarAir [J]
HVAC,Sum,Solar Collector Sensible Heating Energy [J]
HVAC,Average,Solar Collector Natural Ventilation Air Change Rate [ACH]
HVAC,Average,Solar Collector Natural Ventilation Mass Flow Rate [kg/s]
HVAC,Average,Solar Collector Wind Natural Ventilation Mass Flow Rate [kg/s]
HVAC,Average,Solar Collector Buoyancy Natural Ventilation Mass Flow Rate [kg/s]
HVAC,Average,Solar Collector Incident Solar Radiation [W/m2]
HVAC,Average,Solar Collector System Efficiency []
HVAC,Average,Solar Collector Surface Efficiency []
Solar Collector Heat Exchanger Effectiveness [][LINK]
The results from UTSC correlations defined by \({\varepsilon_{HX}} = \frac{{{T_{a,HX}} - {T_{amb}}}}{{{T_{s,coll}} - {T_{amb}}}}\) .
Solar Collector Leaving Air Temperature [C][LINK]
The temperature of air entering the plenum after being heated by the collector. When there is no forced air flow or the collector is passive, then the condition of air entering the plenum or the collector leaving air is assumed to be that of outside air.
Solar Collector Outside Face Suction Velocity [m/s][LINK]
The bulk velocity of air approaching the collector.
Solar Collector Surface Temperature [C][LINK]
The surface temperature of the collector itself.
Solar Collector Plenum Air Temperature [C][LINK]
The temperature of air inside, and leaving, the plenum behind the collector. This plenum leaving air temperature depends on the mode of operation of the collector. When the collector is passive (no forced flow), then the passive model assumes the condition of air entering the plenum is that of outside air, or else when the collector is active, then the model sets the plenum entering air condition to transpired collector leaving air condition determined from the collector model.
Solar Collector Sensible Heating Rate [W][LINK]
The overall rate at which heat is being added to the outdoor air stream.
SolarAir:Facility [J][LINK]
A meter that includes the heating energy provided by the UTSC.
SolarAir:HVAC [J][LINK]
A meter that includes the heating energy provided by the UTSC.
HeatProduced:SolarAir [J][LINK]
A meter that includes the heating energy provided by the UTSC.
Solar Collector Sensible Heating Energy [J][LINK]
The overall sum of energy added to the outdoor air stream.
Solar Collector Natural Ventilation Air Change Rate [ACH][LINK]
The rate of natural ventilation air exchange between the plenum and ambient when the collector is inactive in Air Changes per Hour.
Solar Collector Natural Ventilation Mass Flow Rate [kg/s][LINK]
The mass flow rate of natural ventilation air exchange between the plenum and ambient when the collector is inactive.
Solar Collector Wind Natural Ventilation Mass Flow Rate [kg/s][LINK]
The part of mass flow rate of natural ventilation air exchange between the plenum and ambient when the collector is inactive due to wind-driven forces.
Solar Collector Buoyancy Natural Ventilation Mass Flow Rate [kg/s][LINK]
The part of mass flow rate of natural ventilation air exchange between the plenum and ambient when the collector is inactive due to buoyancy-driven forces.
Solar Collector Incident Solar Radiation [W/m2][LINK]
The intensity of solar radiation incident on the UTSC collector from all sources.
Solar Collector System Efficiency [][LINK]
The overall efficiency of the UTSC system including collected solar energy and heat recovered from the underlying surface.
Solar Collector Surface Efficiency [][LINK]
The efficiency of the UTSC solar collector.
SolarCollector:UnglazedTranspired:Multisystem[LINK]
This object is used to model unglazed transpired solar collectors (UTSC) that are connected to multiple outdoor air systems. This object supplements the SolarCollector:UnglazedTranspired object and is only necessary if more than one air system is connected to a single transpired collector. After the name field, there are sets of four node names used to define the connections of each air system. Each set contains node names for inlet, outlet, control, and zone. If more than five air systems are needed, this object is extensible.
Field: Solar Collector Name[LINK]
This field is used to identify the name of the SolarCollector:UnglazedTranspired object that needs to be connected to more than one air system. This field must match the name.
Field Set: Inlet Node, Outlet Node, Mixed Air Node, Zone Node[LINK]
The following four fields form a repeating set of four fields. One set is used for each outdoor air system that is connected to the collector.
Field: Outdoor Air System <#> Collector Inlet Node[LINK]
This field contains the name of an air node that provides air into the UTSC. This node name should also be assigned to be an outdoor air node using the OutdoorAir:NodeList and OutdoorAir:Node objects. This node is also be named as the actuator node in a Controller:OutdoorAir object.
Field: Outdoor Air System <#> Collector Outlet Node[LINK]
This field contains the name of an air node that is the outlet of the UTSC. This node name will typically be the Outdoor Air Stream Node Name in the OutdoorAir:Mixer (if there is no other equipment on the outdoor air path).
Field: Outdoor Air System <#> Mixed Air Node[LINK]
This field contains the name of an air node that has a setpoint manager controlling its temperature setpoint. This node name will typically be named as the mixed air node in a Controller:OutdoorAir object.
Field: Outdoor Air System <#> Zone Node[LINK]
This field contains the name of an air node for a thermal zone that is ultimately connected to the air system. This node is used with the setpoint schedule, defined in the following field, to provide an added layer of thermostatic control for the UTSC without affecting the control of auxiliary heating. If there is a single air system that is connected to more than one zone, then a single zone should be selected based on where the thermostat might be located.
An example of this object follows.
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