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# Revision history [back]

There are several possible reasons for this result.

1) All ZoneHVAC:TerminalUnit:VariableRefrigerantFlow units are operating and requesting more cooling capacity then the AirConditioner:VariableRefrigerantFlow can provide. At the time this happens, check the report variable:

OutputVariable,*,VRF Heat Pump Part Load Ratio,Hourly;


The VRF Heat Pump Part Load Ratio will be 1 when this happens. The limit on the total cooling capacity can be seen using these report variables. The

OutputVariable,*,VRF Heat Pump Maximum Capacity Cooling Rate,Hourly;
OutputVariable,*,VRF Heat Pump Maximum Capacity Heating Rate,Hourly;


Engineering Reference V9.2, page 1175

When multiple terminal units are operating, the terminal units near their maximum capacity
are more likely to be capacity limited than those terminal units operating well below their
available capacity. The assumption here is that terminal units that are not capacity limited
can provide more refrigerant to meet the same load. When the model finds that there is no
terminal unit capacity limit, this variable will report 1E+20 indicating that no limit exists.
The figure below demonstrates the application of the capacity limit factor for the case where
all indoor terminal units are operating at different capacities. A solution is reached when the
sum of the indoor terminal unit’s cooling capacities (accounting for piping losses) is equal to
the heat pump condenser’s available cooling capacity.


2) The outdoor conditions may limit the amount of cooling the AirConditioner:VariableRefrigerantFlow can provide and the total available cooling capacity is less than the rated cooling capacity. The VRF Heat Pump Part Load Ratio will be 1 when this happens and the VRF Heat Pump Maximum Capacity Cooling Rate and VRF Heat Pump Total Cooling Rate reports will also show the limitation.

3) There is excess cooling load in this zone that sizing did not account for. You said "there is an inline fan (air intake) to the zone", this may be causing the problem. As a test, turn the inline fan off and see if the problem is corrected. If so, this additional load may not be accounted for during sizing which would require that the "cooling factor" be increase more than 1.15.

There are several possible reasons for this result.

1) All ZoneHVAC:TerminalUnit:VariableRefrigerantFlow units are operating and requesting more cooling capacity then the AirConditioner:VariableRefrigerantFlow can provide. At the time this happens, check the report variable:

OutputVariable,*,VRF Heat Pump Part Load Ratio,Hourly;


The VRF Heat Pump Part Load Ratio will be 1 when this happens. The limit on the total cooling capacity can be seen using these report variables. The

OutputVariable,*,VRF Heat Pump Maximum Capacity Cooling Rate,Hourly;
OutputVariable,*,VRF Heat Pump Maximum Capacity Heating Rate,Hourly;


Engineering Reference V9.2, page 1175

When multiple terminal units are operating, the terminal units near their maximum capacity
are more likely to be capacity limited than those terminal units operating well below their
available capacity. The assumption here is that terminal units that are not capacity limited
can provide more refrigerant to meet the same load. When the model finds that there is no
terminal unit capacity limit, this variable will report 1E+20 indicating that no limit exists.
The figure below demonstrates the application of the capacity limit factor for the case where
all indoor terminal units are operating at different capacities. A solution is reached when the
when
the sum of the indoor terminal unit’s cooling capacities (accounting for piping losses) is equal to
equal
to the heat pump condenser’s available cooling capacity.


2) The outdoor conditions may limit the amount of cooling the AirConditioner:VariableRefrigerantFlow can provide and the total available cooling capacity is less than the rated cooling capacity. The VRF Heat Pump Part Load Ratio will be 1 when this happens and the VRF Heat Pump Maximum Capacity Cooling Rate and VRF Heat Pump Total Cooling Rate reports will also show the limitation.

3) There is excess cooling load in this zone that sizing did not account for. You said "there is an inline fan (air intake) to the zone", this may be causing the problem. As a test, turn the inline fan off and see if the problem is corrected. If so, this additional load may not be accounted for during sizing which would require that the "cooling factor" be increase more than 1.15.

There are several possible reasons for this result.

1) All ZoneHVAC:TerminalUnit:VariableRefrigerantFlow units are operating and requesting more cooling capacity then the AirConditioner:VariableRefrigerantFlow can provide. At the time this happens, check the report variable:

OutputVariable,*,VRF Heat Pump Part Load Ratio,Hourly;


The VRF Heat Pump Part Load Ratio will be 1 when this happens. The limit on the total cooling capacity can be seen using these report variables. The

OutputVariable,*,VRF Heat Pump Maximum Capacity Cooling Rate,Hourly;
OutputVariable,*,VRF Heat Pump Maximum Capacity Heating Rate,Hourly;


Engineering Reference V9.2, page 1175

When multiple terminal units are operating, the terminal units near their maximum capacity
are more likely to be capacity limited than those terminal units operating well below their
available capacity. The assumption here is that terminal units that are not capacity limited
can provide more refrigerant to meet the same load. When the model finds that there is no
terminal unit capacity limit, this variable will report 1E+20 indicating that no limit exists.
The figure below demonstrates the application of the capacity limit factor for the case where
all indoor terminal units are operating at different capacities. A solution is reached when
the sum of the indoor terminal unit’s cooling capacities (accounting for piping losses) is equal
is
equal to the heat pump condenser’s available cooling capacity.


2) The outdoor conditions may limit the amount of cooling the AirConditioner:VariableRefrigerantFlow can provide and the total available cooling capacity is less than the rated cooling capacity. The VRF Heat Pump Part Load Ratio will be 1 when this happens and the VRF Heat Pump Maximum Capacity Cooling Rate and VRF Heat Pump Total Cooling Rate reports will also show the limitation.

3) There is excess cooling load in this zone that sizing did not account for. You said "there is an inline fan (air intake) to the zone", this may be causing the problem. As a test, turn the inline fan off and see if the problem is corrected. If so, this additional load may not be accounted for during sizing which would require that the "cooling factor" be increase more than 1.15.