CentralHeatPumpSystem[LINK]
The CentralHeatPumpSystem
object simulates the performance of a central heat pump system
containing one or more chiller-heater objects. The main
function of the object is to call relevant calculation methods
for the chiller-heater objects depending on their operating
modes, and to calculate temperatures at the outlet nodes and
the total energy transfer. The object can be connected to
plant loops and a source loop (see Input-Output Reference
document), and the node connections are solely dependent on
individual chiller-heaters’ operating modes. The central
system receives water flows from each plant and source loop
and then distributes them to individual chiller-heaters as
requested. The conditioned water flows leaving the
chiller-heaters are then returned to the system, and in turn
flow back to the plant loops and source loop to produce
heating and cooling, or exchange heat with the source
loop.
Model Description[LINK]
The model first determines operating modes based on the
cooling and heating loads on the system, and then decides
which calculation algorithm is called. It calls the cooling
calculation subroutine when cooling load is demanded, the
heating calculation subroutine when heating load is demanded,
and both cooling and heating calculation subroutines when both
cooling and heating loads are demanded, i.e., simultaneous
cooing-heating mode. It then calculates mass-weighed
temperatures and heat transfer energy. Six different operating
modes (0 through 5) are possible:
The model reads different node information over the
operating mode so that outlet water conditions at each node of
the system can be appropriately determined.
In cooling-only mode (mode 1), the system is connected to
the chilled water loop and source loop. It thus reads the
evaporator outlet temperatures and mass flow rates of the
chiller-heaters to calculate a mass-weighed chilled water
temperature at the system outlet node, and the condenser
outlet temperatures and mass flow rates of the chiller-heaters
to calculate a mass-weighed source water temperature at the
system outlet node. In heating-only mode (mode 2), the system
is connected to the hot water loop and source loop. It thus
reads the condenser temperatures and mass flow rates of the
chiller-heaters to calculate a mass-weighed hot water
temperature at the system outlet node, and the evaporator
temperatures and mass flow rates of the chiller-heaters to
calculate a mass-weighed source temperature at the system
outlet node.
In simultaneous cooling-heating mode, three different
operating modes (mode 3 through 5) are possible. The model
checks which simultaneous cooling-heating mode (3, 4, or 5)
each chiller-heater is in, and calculates relevant
mass-weighed temperatures. The system may be connected to
three loops such as chilled water loop, hot water loop, and
source water loop in mode 4 or mode 5.
In heat recovery mode, both evaporator temperatures and
condenser temperatures are read and a mass-weighed temperature
for both chilled water and hot water is calculated. The
chiller-heaters in mode 3 do not exchange heat with source
water. At least one of the chiller-heaters within the system
is in heat recovery mode during simultaneous cooling-heating
mode. The system may be only connected to both chilled water
loop and hot water loop if all operating chiller-heaters are
in heat recovery mode.
The following nomenclature is used in the following
equations:
\({\dot
m_{cw,bypass}}\) = chilled water bypass mass flow rate
in the system [kg/s]
\({\dot
m_{hw,bypass}}\) = hot water bypass mass flow rate in
the system [kg/s]
\({\dot
m_{src,bypass}}\) = source water bypass mass flow rate
in the system [kg/s]
\({\dot m_{cw,CH}}\) =
chilled water mass flow rate of ith
chiller-heater’s evaporator [kg/s]
\({\dot m_{hw,CH}}\) =
hot water mass flow rate of ith chiller-heater’s
condenser [kg/s]
\({\dot m_{src,CH}}\)
= source water mass flow rate of ith
chiller-heater, which varies with operating modes
[kg/s]
\({\dot m_{cw,sys}}\)
= chilled water mass flow rate of the system [kg/s]
\({\dot m_{hw,sys}}\)
= hot water mass flow rate of the system [kg/s]
\({\dot m_{src,sys}}\)
= source water mass flow rate of the system [kg/s]
\({T_{cw,sys}}\) =
chilled water outlet temperature of the system [C]
\({T_{hw,sys}}\) = hot
water outlet temperature of the system [C]
\({T_{src,sys}}\) =
source water outlet temperature of the system [C]
\({T_{cw,bypass}}\) =
mass-weighed bypass chilled water temperature in the system
[C]
\({T_{hw,bypass}}\) =
mass-weighed bypass hot water temperature in the system
[C]
\({T_{src,bypass}}\) =
mass-weighed bypass source water temperature in the system
[C]
\({T_{cw,CH}}\) =
mass-weighed chilled water outlet temperature from
chiller-heaters [C]
\({T_{hw,CH}}\) =
mass-weighed hot water outlet temperature from chiller-heaters
[C]
\({T_{src,CH}}\) =
mass-weighed source water outlet temperature from
chiller-heaters [C]
\({T_{cw,i}}\) =
chilled water inlet temperature of the system [C]
\({T_{hw,i}}\) = hot
water inlet temperature of the system [C]
\({T_{src,i}}\) =
source water inlet temperature of the system [C]
\({T_{cw,out}}\) =
chilled water outlet temperature of ith
chiller-heater [C]
\({T_{hw,out}}\) = hot
water outlet temperature of ith chiller-heater
[C]
\({T_{src,out}}\) =
source water outlet temperature of ith
chiller-heater [C]
The model reads node information and local variables of
individual chiller-heaters. The nodes and local variables vary
with the operating modes as described above in order to
calculate mass-weighed temperatures. In the cooling-only mode,
it calculates a mass-weighed chilled water temperature
(Tcw,CH) and a source water temperature
(Tsrc,CH) as follows:
\[{T_{cw,CH}} = \sum\limits_{CH
= 1}^n {{T_{cw,out}}} \frac{{{{\dot
m}_{cw,CH}}}}{{{m_{cw,sys}}}}\]
\[{T_{src,CH}} = \sum\limits_{CH
= 1}^n {{T_{src,out}}} \frac{{{{\dot
m}_{src,CH}}}}{{{m_{src,sys}}}}\]
In heating-only mode, it calculates a mass-weighed hot
water temperature (Thw,CH) and a source
water temperature (Tsrc,CH) as
follows:
\[{T_{hw,CH}} = \sum\limits_{CH
= 1}^n {{T_{hw,out}}} \frac{{{{\dot
m}_{hw,CH}}}}{{{m_{hw,sys}}}}\]
\[{T_{src,CH}} = \sum\limits_{CH
= 1}^n {{T_{src,out}}} \frac{{{{\dot
m}_{src,CH}}}}{{{m_{src,sys}}}}\]
When all chiller-heaters are in heat recovery mode, it
calculates a mass-weighed chilled water temperature
(Tcw,CH) and hot water temperature
(Thw,CH) as follows:
\[{T_{cw,CH}} = \sum\limits_{CH
= 1}^n {{T_{cw,out}}} \frac{{{{\dot
m}_{cw,CH}}}}{{{m_{cw,sys}}}}\]
\[{T_{hw,CH}} = \sum\limits_{CH
= 1}^n {{T_{hw,out}}} \frac{{{{\dot
m}_{hw,CH}}}}{{{m_{hw,sys}}}}\]
In cooling or heating dominant simultaneous cooling-heating
mode (mode 4 and 5), at least one chiller-heater should be in
heat recovery mode, and the other(s) are in either mode 4 or
mode 5. The system is connected to three loops such as chilled
water loop, hot water loop, and source water loop. The model
thus calculates a mass-weighed chilled water temperature
(Tcw,CH), hot water temperature
(Thw,CH), and source water temperature
(Tsrc,CH) as follows:
\[{T_{cw,CH}} = \sum\limits_{CH
= 1}^n {{T_{cw,out}}} \frac{{{{\dot
m}_{cw,CH}}}}{{{m_{cw,sys}}}}\]
\[{T_{hw,CH}} = \sum\limits_{CH
= 1}^n {{T_{hw,out}}} \frac{{{{\dot
m}_{hw,CH}}}}{{{m_{hw,sys}}}}\]
\[{T_{src,CH}} = \sum\limits_{CH
= 1}^n {{T_{src,out}}} \frac{{{{\dot
m}_{src,CH}}}}{{{m_{src,sys}}}}\]
The model then calculates a mass-weighed temperature for
the by-pass flows remained in the system as follows:
\[{T_{cw,bypass}} =
{T_{cw,i}}\frac{{{{\dot
m}_{cw,bypass}}}}{{{m_{cw,sys}}}}\]
\[{T_{hw,bypass}} =
{T_{hw,i}}\frac{{{{\dot
m}_{hw,bypass}}}}{{{m_{hw,sys}}}}\]
\[{T_{src,bypass}} =
{T_{src,i}}\frac{{{{\dot
m}_{src,bypass}}}}{{{m_{src,sys}}}}\]
The outlet temperatures at each outlet node of the system
are then determined as it sums both mass-weighed temperatures
up as follows:
\[{T_{cw,sys}} = {T_{cw,CH}} +
{T_{cw,bypass}}\]
\[{T_{hw,sys}} = {T_{hw,CH}} +
{T_{hw,bypass}}\]
\[{T_{src,sys}} = {T_{src,CH}} +
{T_{src,bypass}}\]
The total heat transfer energy of the system is also
calculated in the same manner as the temperature calculations.
The model simply sums all heat transfer energy of the
chiller-heaters depending on their operating modes.
CentralHeatPumpSystem[LINK]
Overview[LINK]
The CentralHeatPumpSystem object simulates the performance of a central heat pump system containing one or more chiller-heater objects. The main function of the object is to call relevant calculation methods for the chiller-heater objects depending on their operating modes, and to calculate temperatures at the outlet nodes and the total energy transfer. The object can be connected to plant loops and a source loop (see Input-Output Reference document), and the node connections are solely dependent on individual chiller-heaters’ operating modes. The central system receives water flows from each plant and source loop and then distributes them to individual chiller-heaters as requested. The conditioned water flows leaving the chiller-heaters are then returned to the system, and in turn flow back to the plant loops and source loop to produce heating and cooling, or exchange heat with the source loop.
Model Description[LINK]
The model first determines operating modes based on the cooling and heating loads on the system, and then decides which calculation algorithm is called. It calls the cooling calculation subroutine when cooling load is demanded, the heating calculation subroutine when heating load is demanded, and both cooling and heating calculation subroutines when both cooling and heating loads are demanded, i.e., simultaneous cooing-heating mode. It then calculates mass-weighed temperatures and heat transfer energy. Six different operating modes (0 through 5) are possible:
0: off
1: cooling-only mode
2: heating-only mode
3: heat recovery mode
4: cooling dominant simultaneous cooling-heating mode
5: heating dominant simultaneous cooling-heating mode.
The model reads different node information over the operating mode so that outlet water conditions at each node of the system can be appropriately determined.
In cooling-only mode (mode 1), the system is connected to the chilled water loop and source loop. It thus reads the evaporator outlet temperatures and mass flow rates of the chiller-heaters to calculate a mass-weighed chilled water temperature at the system outlet node, and the condenser outlet temperatures and mass flow rates of the chiller-heaters to calculate a mass-weighed source water temperature at the system outlet node. In heating-only mode (mode 2), the system is connected to the hot water loop and source loop. It thus reads the condenser temperatures and mass flow rates of the chiller-heaters to calculate a mass-weighed hot water temperature at the system outlet node, and the evaporator temperatures and mass flow rates of the chiller-heaters to calculate a mass-weighed source temperature at the system outlet node.
In simultaneous cooling-heating mode, three different operating modes (mode 3 through 5) are possible. The model checks which simultaneous cooling-heating mode (3, 4, or 5) each chiller-heater is in, and calculates relevant mass-weighed temperatures. The system may be connected to three loops such as chilled water loop, hot water loop, and source water loop in mode 4 or mode 5.
In heat recovery mode, both evaporator temperatures and condenser temperatures are read and a mass-weighed temperature for both chilled water and hot water is calculated. The chiller-heaters in mode 3 do not exchange heat with source water. At least one of the chiller-heaters within the system is in heat recovery mode during simultaneous cooling-heating mode. The system may be only connected to both chilled water loop and hot water loop if all operating chiller-heaters are in heat recovery mode.
The following nomenclature is used in the following equations:
\({\dot m_{cw,bypass}}\) = chilled water bypass mass flow rate in the system [kg/s]
\({\dot m_{hw,bypass}}\) = hot water bypass mass flow rate in the system [kg/s]
\({\dot m_{src,bypass}}\) = source water bypass mass flow rate in the system [kg/s]
\({\dot m_{cw,CH}}\) = chilled water mass flow rate of ith chiller-heater’s evaporator [kg/s]
\({\dot m_{hw,CH}}\) = hot water mass flow rate of ith chiller-heater’s condenser [kg/s]
\({\dot m_{src,CH}}\) = source water mass flow rate of ith chiller-heater, which varies with operating modes [kg/s]
\({\dot m_{cw,sys}}\) = chilled water mass flow rate of the system [kg/s]
\({\dot m_{hw,sys}}\) = hot water mass flow rate of the system [kg/s]
\({\dot m_{src,sys}}\) = source water mass flow rate of the system [kg/s]
\({T_{cw,sys}}\) = chilled water outlet temperature of the system [C]
\({T_{hw,sys}}\) = hot water outlet temperature of the system [C]
\({T_{src,sys}}\) = source water outlet temperature of the system [C]
\({T_{cw,bypass}}\) = mass-weighed bypass chilled water temperature in the system [C]
\({T_{hw,bypass}}\) = mass-weighed bypass hot water temperature in the system [C]
\({T_{src,bypass}}\) = mass-weighed bypass source water temperature in the system [C]
\({T_{cw,CH}}\) = mass-weighed chilled water outlet temperature from chiller-heaters [C]
\({T_{hw,CH}}\) = mass-weighed hot water outlet temperature from chiller-heaters [C]
\({T_{src,CH}}\) = mass-weighed source water outlet temperature from chiller-heaters [C]
\({T_{cw,i}}\) = chilled water inlet temperature of the system [C]
\({T_{hw,i}}\) = hot water inlet temperature of the system [C]
\({T_{src,i}}\) = source water inlet temperature of the system [C]
\({T_{cw,out}}\) = chilled water outlet temperature of ith chiller-heater [C]
\({T_{hw,out}}\) = hot water outlet temperature of ith chiller-heater [C]
\({T_{src,out}}\) = source water outlet temperature of ith chiller-heater [C]
The model reads node information and local variables of individual chiller-heaters. The nodes and local variables vary with the operating modes as described above in order to calculate mass-weighed temperatures. In the cooling-only mode, it calculates a mass-weighed chilled water temperature (Tcw,CH) and a source water temperature (Tsrc,CH) as follows:
\[{T_{cw,CH}} = \sum\limits_{CH = 1}^n {{T_{cw,out}}} \frac{{{{\dot m}_{cw,CH}}}}{{{m_{cw,sys}}}}\]
\[{T_{src,CH}} = \sum\limits_{CH = 1}^n {{T_{src,out}}} \frac{{{{\dot m}_{src,CH}}}}{{{m_{src,sys}}}}\]
In heating-only mode, it calculates a mass-weighed hot water temperature (Thw,CH) and a source water temperature (Tsrc,CH) as follows:
\[{T_{hw,CH}} = \sum\limits_{CH = 1}^n {{T_{hw,out}}} \frac{{{{\dot m}_{hw,CH}}}}{{{m_{hw,sys}}}}\]
\[{T_{src,CH}} = \sum\limits_{CH = 1}^n {{T_{src,out}}} \frac{{{{\dot m}_{src,CH}}}}{{{m_{src,sys}}}}\]
When all chiller-heaters are in heat recovery mode, it calculates a mass-weighed chilled water temperature (Tcw,CH) and hot water temperature (Thw,CH) as follows:
\[{T_{cw,CH}} = \sum\limits_{CH = 1}^n {{T_{cw,out}}} \frac{{{{\dot m}_{cw,CH}}}}{{{m_{cw,sys}}}}\]
\[{T_{hw,CH}} = \sum\limits_{CH = 1}^n {{T_{hw,out}}} \frac{{{{\dot m}_{hw,CH}}}}{{{m_{hw,sys}}}}\]
In cooling or heating dominant simultaneous cooling-heating mode (mode 4 and 5), at least one chiller-heater should be in heat recovery mode, and the other(s) are in either mode 4 or mode 5. The system is connected to three loops such as chilled water loop, hot water loop, and source water loop. The model thus calculates a mass-weighed chilled water temperature (Tcw,CH), hot water temperature (Thw,CH), and source water temperature (Tsrc,CH) as follows:
\[{T_{cw,CH}} = \sum\limits_{CH = 1}^n {{T_{cw,out}}} \frac{{{{\dot m}_{cw,CH}}}}{{{m_{cw,sys}}}}\]
\[{T_{hw,CH}} = \sum\limits_{CH = 1}^n {{T_{hw,out}}} \frac{{{{\dot m}_{hw,CH}}}}{{{m_{hw,sys}}}}\]
\[{T_{src,CH}} = \sum\limits_{CH = 1}^n {{T_{src,out}}} \frac{{{{\dot m}_{src,CH}}}}{{{m_{src,sys}}}}\]
The model then calculates a mass-weighed temperature for the by-pass flows remained in the system as follows:
\[{T_{cw,bypass}} = {T_{cw,i}}\frac{{{{\dot m}_{cw,bypass}}}}{{{m_{cw,sys}}}}\]
\[{T_{hw,bypass}} = {T_{hw,i}}\frac{{{{\dot m}_{hw,bypass}}}}{{{m_{hw,sys}}}}\]
\[{T_{src,bypass}} = {T_{src,i}}\frac{{{{\dot m}_{src,bypass}}}}{{{m_{src,sys}}}}\]
The outlet temperatures at each outlet node of the system are then determined as it sums both mass-weighed temperatures up as follows:
\[{T_{cw,sys}} = {T_{cw,CH}} + {T_{cw,bypass}}\]
\[{T_{hw,sys}} = {T_{hw,CH}} + {T_{hw,bypass}}\]
\[{T_{src,sys}} = {T_{src,CH}} + {T_{src,bypass}}\]
The total heat transfer energy of the system is also calculated in the same manner as the temperature calculations. The model simply sums all heat transfer energy of the chiller-heaters depending on their operating modes.
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