The object simulates the performance of a chiller-heater
which can receive pre-cooled or pre-heated water from the
source loop, and provide cooling, heating, or simultaneous
cooling-heating. The object needs to work with the Central
Heat Pump System object to be controlled properly. This model
does not simulate the thermal performance or the power
consumption of associated pumps or cooling towers. The Central
Heat Pump System object holds the input/output nodes
connection of the chiller-heater and its control scheme, once
the chiller-heater is properly referred.
Model Description[LINK]
The model uses user-input performance information at design
conditions along with three performance curves (curve objects)
for cooling capacity and efficiency to determine chiller
operation at off-design conditions. Three additional
performance curves for heating capacity and efficiency are
used when the chiller is operating in a heating-only mode or
simultaneous cooling-heating mode.
Cooling-only mode[LINK]
The following nomenclature is used in the cooling
equations:
CompMotorEffic = compressor motor efficiency
CompPowerclg = compressor power [W]
CompPower~@PLRmin~ = compressor
power at the minimum part-load ratio [W]
= chilled water specific
heat [J/kgK]
CyclingRatio~~ = compressor cycling ratio
=PLRactual /
PLRmin
EvapCapAvailclg = available full-load
cooling capacity at current conditions [W]
EvapCapFTclg = cooling capacity
function of temperature curve
EIRFTclg = electric input to cooling
output factor for temperature function curve
EIRFPLRclg = electric input to cooling
output factor for part-load function curve
= chilled water mass flow
rate [kg/s]
= chilled water maximum
available mass flow rate [kg/s]
PLRclg = cooling part-load ratio =
CoolingLoad / EvapCapAvailclg
PLRactual = actual part-load ratio at
current conditions
PLRmin = minimum part-load ratio
= total condenser heat
transfer energy [J]
= condenser heat transfer
rate [W]
= total evaporator heat
transfer energy [J]
= evaporator heat
transfer rate [W]
= false loading rate
[W]
RefCOPclg = reference coefficient of
performance [W/W]
RefEvapCapclg = reference evaporator
capacity [W]
FullLoadPwrclg = reference full load
power = EvapCapAvailclg /
RefCOPclg~~[W]
Tcond = either entering or leaving
condenser water temperature depending on user input for
condenser water independent variable.
Tcond,l, if “LeavingCondenser” is chosen,
or Tcond,e, if “EnteringCondenser” is
chosen.
Tcond,e = entering condenser water
temperature [C]
Tcond,l = leaving condenser water
temperature [C]
Tcw,e = entering chilled water
temperature [W]
Tcw,l = leaving chilled water
temperature [W]
= chilled water inlet and
outlet temperature difference [C]
= maximum chilled water
inlet and outlet temperature difference [C]
The model sequentially calls each chiller-heater module in
the order defined in the Central Heat Pump System object. It
then determines cooling load that each chiller-heater needs to
meet and water flow rates delivered to each chiller-heater.
Once each chiller-heater is assumed to operate, it determines
cooling capacity and efficiency using user-supplied
performance information.
Three performance curves are used in the calculation of
cooling capacity and efficiency as follows:
- Cooling mode cooling capacity function of temperature
curve (EvapCapFTclg)
- Cooling mode electric input to cooling output ratio
function of temperature curve
(EIRFTclg)
- Cooling mode electric input to cooling output ratio
function of part load ratio curve
(EIRFPLRclg)
The Cooling Capacity Function of Temperature Curve
(EvapCapFTclg) represents the fraction of
the cooling capacity of the chiller-heater as it varies by
temperature. The curve should have a value of 1.0 at the
reference conditions. The output of a bi-quadratic curve with
the input variables being the leaving chilled water
temperature and either the entering or leaving condenser water
temperature is given by:
.
The Cooling Mode Electric Input to Cooling
Output Ratio Function of Temperature (EIRFTclg)
curve represents the fraction of electricity to the
chiller-heater at full load as it varies by temperature. The
output of a bi-quadratic curve with the input variables being
the leaving chilled water temperature and either the entering
or leaving condenser water temperature is given by:
.
The Cooling Mode Electric Input to Cooling
Output Ratio Function of Part Load Ratio
(EIRFPLRclg) curve represents the fraction of
electricity to the chiller-heater as the load on the chiller
varies at a given set of operating temperatures. The curve is
normalized so that at full load the value of the curve should
be 1.0. Note that the bi-cubic formulation below is generally
only valid when LeavingCondenser variable is chosen for the
field of Cooling Mode Condenser Water Temperature Curve Input
Variable whereas the quadratic curve can be used for both
choices, i.e., LeavingCondenser and EnteringCondenser.
Bi-cubic may also be used when the chiller-heater uses a
variable-speed compressor motor drive. The output of this
curve can be determined by one of the following three
performance curves:
The full-load cooling capacity at specific temperature
operating conditions (i.e., at temperatures different from the
design temperatures) is then computed as follows:
.
The model then determines current chiller-heater’s
evaporator heat transfer rate based on the total cooling load
required a central heat pump system to meet and the maximum
available chiller-heater cooling capacity. The maximum
evaporator temperature difference between the entering chilled
water temperature (Tcw,e) and the leaving
chilled water temperature (Tcw,l) obtained
from the plant loop setpoint temperature can also be
determined. It then calculates mass flow rate for variable
flow control chiller-heaters and the temperature difference
for constant flow control chiller-heaters, setting the cooling
load each chiller-heater needs to meet equal to the evaporator
heat transfer rate.
As for variable flow control chiller-heaters, the chilled
water mass flow rate is computed as follows:
.
The chilled water mass flow rate calculated is then
compared to the maximum available mass flow rate for
individual chiller-heaters. If the calculated one is bigger
than the maximum, the model sets the chilled water mass flow
rate equal to the maximum. It then adjusts the temperature
difference based on the evaporator heat transfer rate and the
maximum mass flow rate. If the adjusted temperature difference
also exceeds the maximum, the model finally adjusts the
evaporator heat transfer rate at the maximum temperature
difference and mass flow rate as follows:
.
As for constant flow control chiller-heaters, the model
calculates chilled water temperature difference as
follows:
.
The temperature difference calculated is then compared to
the maximum temperature difference allowed. If the calculated
one is bigger than the maximum, the model sets the chilled
water temperature difference equal the maximum, and then
adjusts the evaporator heat transfer rate at the given
conditions as follows:
.
The model then calculates the part-load ratio as the ratio
of the evaporator heat transfer rate to the available
chiller-heater capacity as follows:
.
The part-load ratio calculated is set to be between the
maximum of 1.0 and the minimum of 0.0 when it is out of the
range. Once the part-load ratio is calculated the cycling
ratio and false loading rate can be obtained as follows:
.
The compressor power demand is then computed
by:
.
The heat transfer rate for the chiller-heater
condenser can then be computed as follows:
.
The total heat transfer energy by the evaporator and
condenser can be calculated as follows:
.
Heating-only
mode and Simultaneous cooling-heating mode[LINK]
The following nomenclature is used in the heating
equations:
CompMotorEffic = compressor motor efficiency
CompPowerhtg = compressor power demand
[W]
CompPower~@PLRmin~ = compressor
power at the minimum part-load ratio [W]
= evaporator water
specific heat [J/kgK]
= hot water specific heat
[J/kgK]
CyclingRatio~~ = compressor cycling ratio
=PLRactual /
PLRmin
EvapCapAvailhtg = available full-load
cooling capacity at current conditions [W]
EvapCapFThtg = heating mode cooling
capacity function of temperature curve
EIRFThtg = electric input to cooling
output factor for temperature function curve
EIRFPLRhtg = electric input to cooling
output factor for part-load function curve
= evaporator water
maximum available mass flow rate [kg/s]
= condenser water maximum
available mass flow rate [kg/s]
= hot water mass flow
rate [kg/s]
PLRhtg = cooling part-load ratio =
RefCap / EvapCapAvailhtg
PLRmax = maximum part-load ratio at
current conditions
PLRmin = minimum part-load ratio
= total condenser heat
transfer energy [J]
= available full-load
heating capacity at current conditions [W]
= condenser heat transfer
rate [W]
= total evaporator heat
transfer energy [J]
= evaporator heat
transfer rate [W]
= false loading rate
[W]
RefCOPhtg = reference coefficient of
performance [W/W]
RefEvapCaphtg = reference evaporator
capacity [W]
FullLoadPwrhtg = reference full load
power = EvapCapAvailhtg /
RefCOPhtg~~[W]
Tcond = either entering or leaving
condenser water temperature depending on user input for
condenser water independent variable.
Tcond,l, if “LeavingCondenser” is chosen,
or Tcond,e, if “EnteringCondenser” is
chosen.
Tcond,e = entering condenser water
temperature [C]
Tcond,l = leaving condenser water
temperature [C]
Tcw,l = leaving chilled water
temperature [C]
Thw,e = entering hot water temperature
[C]
Thw,l = leaving hot water temperature
[C]
= evaporator inlet and
outlet water temperature difference [C]
= hot water inlet and
outlet temperature difference [C]
= maximum hot water inlet
and outlet temperature difference [C]
The calculations for the evaporator side are similar to the
cooling-only mode calculations. The evaporator capacity and
efficiency is determined by a different set of three
performance curves read in the cooling-only mode, and the
performance curve set is used for both heating-only mode and
simultaneous cooling-heating mode. During these modes, the
evaporator side is not connected to the chilled water loop,
but source water loop. The model thus assumes that each
chiller-heater does not meet the plant loop chilled water
setpoint temperature while the evaporator operates at the full
load capacity to produce heating at a constant water flow
rate.
The model sequentially calls each chiller-heater module in
the order of the definition in the central heat pump system.
It then determines heating load that each chiller-heater needs
to meet and water flow rates delivered to each chiller-heater.
Once each chiller-heater is assumed to operate, it determines
heating capacity and efficiency using the following
performance curves:
- Heating mode cooling capacity function of temperature
curve (EvapCapFThtg)
- Heating mode electric input to cooling output ratio
function of temperature curve
(EIRFThtg)
- Heating mode electric input to cooling output ratio
function of part load ratio curve
(EIRFPLRhtg)
The output of a Heating Mode Cooling Capacity Function of
Temperature curve with the input variables being the leaving
chilled water temperature and either the entering or leaving
condenser water temperature is given by:
The output of a Heating Mode Cooling
Output Ratio Function of Temperature curve with the input
variables being the leaving chilled water temperature and
either the entering or leaving condenser water temperature is
given by:
.
The output of Heating Mode Cooling Output
Ratio Function of Part Load Ratio curve can be determined by
one of the following three performance curves as follows:
The full-load evaporator capacity at specific temperature
operating conditions is then given by:
.
The part-load ratio is set to be between zero and the
maximum, and the evaporator heat transfer rate is computed
by:
The evaporator inlet and outlet temperature difference
is then given by:
Once the part-load ratio is calculated the cycling ratio
and false loading rate are computed by:
.
The compressor power demand is then computed by:
The heat transfer rate of the chiller-heater condenser is
then computed as follows:
Once condenser available heating capacity is determined,
the model calculates current chiller-heater’s condenser heat
transfer rate based on the total heating load required a
central heat pump system to meet as well as available heating
capacity of the chiller-heater. The maximum condenser
temperature difference between the entering hot water
temperature (Thw,e) and the leaving hot
water temperature (Thw,l) obtained from
the plant loop setpoint temperature can also be obtained. It
then calculates condenser water mass flow rate for variable
flow control chiller-heaters and the hot water temperature
difference for constant flow control chiller-heaters, setting
the cooling load that each chiller-heater needs to meet equal
the evaporator heat transfer rate.
As for variable flow control chiller-heaters, the condenser
water mass flow rate is computed as follows:
.
The condenser water mass flow rate calculated is then
compared to the maximum available mass flow rate for
individual chiller-heaters. If the calculated one is bigger
than the maximum, the model sets the condenser water mass flow
rate equal the maximum. It then adjusts the hot water
temperature difference at the maximum mass flow rate. If the
adjusted temperature difference also exceeds the maximum, the
model finally adjusts the condenser heat transfer rate at the
maximum allowable conditions as follows:
.
As for constant flow control chiller-heaters, the model
calculates condenser temperature difference as follows:
.
The temperature difference calculated is then compared to
maximum hot water temperature difference. If the calculated
one is bigger than the maximum, the model sets the hot water
temperature difference equal the maximum, and then adjusts the
condenser heat transfer rate at the given conditions as
follows:
.
Finally, the total heat transfer energy by the evaporator
and condenser can then be calculated as follows:
.
Central Geothermal Systems, Applications Engineering
Manual, Trane Company, April 2010, SYS-APM009-EN.
ChillerHeaterPerformance:Electric:EIR[LINK]
Overview[LINK]
The object simulates the performance of a chiller-heater which can receive pre-cooled or pre-heated water from the source loop, and provide cooling, heating, or simultaneous cooling-heating. The object needs to work with the Central Heat Pump System object to be controlled properly. This model does not simulate the thermal performance or the power consumption of associated pumps or cooling towers. The Central Heat Pump System object holds the input/output nodes connection of the chiller-heater and its control scheme, once the chiller-heater is properly referred.
Model Description[LINK]
The model uses user-input performance information at design conditions along with three performance curves (curve objects) for cooling capacity and efficiency to determine chiller operation at off-design conditions. Three additional performance curves for heating capacity and efficiency are used when the chiller is operating in a heating-only mode or simultaneous cooling-heating mode.
Cooling-only mode[LINK]
The following nomenclature is used in the cooling equations:
CompMotorEffic = compressor motor efficiency
CompPowerclg = compressor power [W]
CompPower~@PLRmin~ = compressor power at the minimum part-load ratio [W]
CyclingRatio~~ = compressor cycling ratio =PLRactual / PLRmin
EvapCapAvailclg = available full-load cooling capacity at current conditions [W]
EvapCapFTclg = cooling capacity function of temperature curve
EIRFTclg = electric input to cooling output factor for temperature function curve
EIRFPLRclg = electric input to cooling output factor for part-load function curve
PLRclg = cooling part-load ratio = CoolingLoad / EvapCapAvailclg
PLRactual = actual part-load ratio at current conditions
PLRmin = minimum part-load ratio
RefCOPclg = reference coefficient of performance [W/W]
RefEvapCapclg = reference evaporator capacity [W]
FullLoadPwrclg = reference full load power = EvapCapAvailclg / RefCOPclg~~[W]
Tcond = either entering or leaving condenser water temperature depending on user input for condenser water independent variable. Tcond,l, if “LeavingCondenser” is chosen, or Tcond,e, if “EnteringCondenser” is chosen.
Tcond,e = entering condenser water temperature [C]
Tcond,l = leaving condenser water temperature [C]
Tcw,e = entering chilled water temperature [W]
Tcw,l = leaving chilled water temperature [W]
The model sequentially calls each chiller-heater module in the order defined in the Central Heat Pump System object. It then determines cooling load that each chiller-heater needs to meet and water flow rates delivered to each chiller-heater. Once each chiller-heater is assumed to operate, it determines cooling capacity and efficiency using user-supplied performance information.
Three performance curves are used in the calculation of cooling capacity and efficiency as follows:
The Cooling Capacity Function of Temperature Curve (EvapCapFTclg) represents the fraction of the cooling capacity of the chiller-heater as it varies by temperature. The curve should have a value of 1.0 at the reference conditions. The output of a bi-quadratic curve with the input variables being the leaving chilled water temperature and either the entering or leaving condenser water temperature is given by:
The Cooling Mode Electric Input to Cooling Output Ratio Function of Temperature (EIRFTclg) curve represents the fraction of electricity to the chiller-heater at full load as it varies by temperature. The output of a bi-quadratic curve with the input variables being the leaving chilled water temperature and either the entering or leaving condenser water temperature is given by:
The Cooling Mode Electric Input to Cooling Output Ratio Function of Part Load Ratio (EIRFPLRclg) curve represents the fraction of electricity to the chiller-heater as the load on the chiller varies at a given set of operating temperatures. The curve is normalized so that at full load the value of the curve should be 1.0. Note that the bi-cubic formulation below is generally only valid when LeavingCondenser variable is chosen for the field of Cooling Mode Condenser Water Temperature Curve Input Variable whereas the quadratic curve can be used for both choices, i.e., LeavingCondenser and EnteringCondenser. Bi-cubic may also be used when the chiller-heater uses a variable-speed compressor motor drive. The output of this curve can be determined by one of the following three performance curves:
The full-load cooling capacity at specific temperature operating conditions (i.e., at temperatures different from the design temperatures) is then computed as follows:
The model then determines current chiller-heater’s evaporator heat transfer rate based on the total cooling load required a central heat pump system to meet and the maximum available chiller-heater cooling capacity. The maximum evaporator temperature difference between the entering chilled water temperature (Tcw,e) and the leaving chilled water temperature (Tcw,l) obtained from the plant loop setpoint temperature can also be determined. It then calculates mass flow rate for variable flow control chiller-heaters and the temperature difference for constant flow control chiller-heaters, setting the cooling load each chiller-heater needs to meet equal to the evaporator heat transfer rate.
As for variable flow control chiller-heaters, the chilled water mass flow rate is computed as follows:
The chilled water mass flow rate calculated is then compared to the maximum available mass flow rate for individual chiller-heaters. If the calculated one is bigger than the maximum, the model sets the chilled water mass flow rate equal to the maximum. It then adjusts the temperature difference based on the evaporator heat transfer rate and the maximum mass flow rate. If the adjusted temperature difference also exceeds the maximum, the model finally adjusts the evaporator heat transfer rate at the maximum temperature difference and mass flow rate as follows:
As for constant flow control chiller-heaters, the model calculates chilled water temperature difference as follows:
The temperature difference calculated is then compared to the maximum temperature difference allowed. If the calculated one is bigger than the maximum, the model sets the chilled water temperature difference equal the maximum, and then adjusts the evaporator heat transfer rate at the given conditions as follows:
The model then calculates the part-load ratio as the ratio of the evaporator heat transfer rate to the available chiller-heater capacity as follows:
The part-load ratio calculated is set to be between the maximum of 1.0 and the minimum of 0.0 when it is out of the range. Once the part-load ratio is calculated the cycling ratio and false loading rate can be obtained as follows:
The compressor power demand is then computed by:
The heat transfer rate for the chiller-heater condenser can then be computed as follows:
The total heat transfer energy by the evaporator and condenser can be calculated as follows:
Heating-only mode and Simultaneous cooling-heating mode[LINK]
The following nomenclature is used in the heating equations:
CompMotorEffic = compressor motor efficiency
CompPowerhtg = compressor power demand [W]
CompPower~@PLRmin~ = compressor power at the minimum part-load ratio [W]
CyclingRatio~~ = compressor cycling ratio =PLRactual / PLRmin
EvapCapAvailhtg = available full-load cooling capacity at current conditions [W]
EvapCapFThtg = heating mode cooling capacity function of temperature curve
EIRFThtg = electric input to cooling output factor for temperature function curve
EIRFPLRhtg = electric input to cooling output factor for part-load function curve
PLRhtg = cooling part-load ratio = RefCap / EvapCapAvailhtg
PLRmax = maximum part-load ratio at current conditions
PLRmin = minimum part-load ratio
RefCOPhtg = reference coefficient of performance [W/W]
RefEvapCaphtg = reference evaporator capacity [W]
FullLoadPwrhtg = reference full load power = EvapCapAvailhtg / RefCOPhtg~~[W]
Tcond = either entering or leaving condenser water temperature depending on user input for condenser water independent variable. Tcond,l, if “LeavingCondenser” is chosen, or Tcond,e, if “EnteringCondenser” is chosen.
Tcond,e = entering condenser water temperature [C]
Tcond,l = leaving condenser water temperature [C]
Tcw,l = leaving chilled water temperature [C]
Thw,e = entering hot water temperature [C]
Thw,l = leaving hot water temperature [C]
The calculations for the evaporator side are similar to the cooling-only mode calculations. The evaporator capacity and efficiency is determined by a different set of three performance curves read in the cooling-only mode, and the performance curve set is used for both heating-only mode and simultaneous cooling-heating mode. During these modes, the evaporator side is not connected to the chilled water loop, but source water loop. The model thus assumes that each chiller-heater does not meet the plant loop chilled water setpoint temperature while the evaporator operates at the full load capacity to produce heating at a constant water flow rate.
The model sequentially calls each chiller-heater module in the order of the definition in the central heat pump system. It then determines heating load that each chiller-heater needs to meet and water flow rates delivered to each chiller-heater. Once each chiller-heater is assumed to operate, it determines heating capacity and efficiency using the following performance curves:
The output of a Heating Mode Cooling Capacity Function of Temperature curve with the input variables being the leaving chilled water temperature and either the entering or leaving condenser water temperature is given by:
The output of a Heating Mode Cooling Output Ratio Function of Temperature curve with the input variables being the leaving chilled water temperature and either the entering or leaving condenser water temperature is given by:
The output of Heating Mode Cooling Output Ratio Function of Part Load Ratio curve can be determined by one of the following three performance curves as follows:
The full-load evaporator capacity at specific temperature operating conditions is then given by:
The part-load ratio is set to be between zero and the maximum, and the evaporator heat transfer rate is computed by:
Once the part-load ratio is calculated the cycling ratio and false loading rate are computed by:
The compressor power demand is then computed by:
The heat transfer rate of the chiller-heater condenser is then computed as follows:
Once condenser available heating capacity is determined, the model calculates current chiller-heater’s condenser heat transfer rate based on the total heating load required a central heat pump system to meet as well as available heating capacity of the chiller-heater. The maximum condenser temperature difference between the entering hot water temperature (Thw,e) and the leaving hot water temperature (Thw,l) obtained from the plant loop setpoint temperature can also be obtained. It then calculates condenser water mass flow rate for variable flow control chiller-heaters and the hot water temperature difference for constant flow control chiller-heaters, setting the cooling load that each chiller-heater needs to meet equal the evaporator heat transfer rate.
As for variable flow control chiller-heaters, the condenser water mass flow rate is computed as follows:
The condenser water mass flow rate calculated is then compared to the maximum available mass flow rate for individual chiller-heaters. If the calculated one is bigger than the maximum, the model sets the condenser water mass flow rate equal the maximum. It then adjusts the hot water temperature difference at the maximum mass flow rate. If the adjusted temperature difference also exceeds the maximum, the model finally adjusts the condenser heat transfer rate at the maximum allowable conditions as follows:
As for constant flow control chiller-heaters, the model calculates condenser temperature difference as follows:
The temperature difference calculated is then compared to maximum hot water temperature difference. If the calculated one is bigger than the maximum, the model sets the hot water temperature difference equal the maximum, and then adjusts the condenser heat transfer rate at the given conditions as follows:
Finally, the total heat transfer energy by the evaporator and condenser can then be calculated as follows:
References[LINK]
Central Geothermal Systems, Applications Engineering Manual, Trane Company, April 2010, SYS-APM009-EN.
Documentation content copyright © 1996-2026 The Board of Trustees of the University of Illinois and the Regents of the University of California through the Ernest Orlando Lawrence Berkeley National Laboratory. All rights reserved. EnergyPlus is a trademark of the US Department of Energy.
This documentation is made available under the EnergyPlus Open Source License v1.0.