Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
I looked at your model and ran it. There are several reasons involved for your issue.
You should check where you have Zone Air System Sensible Cooling Energy in winter first. It is detected in the following 3 zones: C37073, 50E38B and 841836. They are in the same AirLoop: Auditorio Rooftop Heat Pump. This AirLoop has HEX, system(central) cooling coil, system(central) heating coil and zone(local) reheat coils.
Capacity of your Ground Source Heat Pump system (GSHP) is insufficient. You should check Output:Variable: Zone Air Temperature, Zone Heating Setpoint Not Met Time and Zone Cooling Setpoint Not Met Time. Please note that Zone Heating Setpoint Not Met While Occupied Time and Zone Cooling Setpoint Not Met While Occupied Time (so-called "Unmet Hour") is not detected because the number of people is 0 in your model.
Your setpoint setting for the system heating coil is incorrect. You use two SetpointManager:singleZone:Reheat objects for the heating coil air outlet node (Node 50-A), but you cannot use two setpoint for one node. You can see the warning message "setpoint node conflicts with another setpoint manager" in your err file. For the system heating coil, you should use SetpointManager:Scheduled for the fixed temperature setpoint or SetpointManager:MultiZone:Heating:Average.
The zone reheat coils are not autosized correctly. The heating capacity of zone reheat coils is nearly 0W. it is beacuse you set Central Heating Design Supply Air Temperature to 40 C in Sizing:System, which is very high and EnergyPlus regards that all the heating load will be handled by this system heating coil and that zone reheat coils are not necessary. I don't know your design consept. If the system heating coil is just for preheating, the temperature setpoint should be much lower, and practically, the preheat coil should be located before the system cooling coil. If you intend to handle all the heating load by the central heating coil and you don't need zone reheat coils, you can keep the current high Central Heating Design Supply Air Temperature, but I don't think this design works properly, especially for your CAV system with multiple zones.
You should know the difference of between Output:Variable Zone Air System Sensible Cooling Energy and Cooling Coil Sensible Cooling Energy. When Cooling Coil Sensible Cooling Energy is positive, the cooling coil is actually operating. GSHP in your model is cooling chilled water, and electricity is consumed for cooling. On the other hand, when Zone Air System Sensible Cooling Energy is positive, it does not necessarily mean that electricity is consumed for cooling. Zone Air System Sensible Cooling Energy becomes positive simply when the supply air temperature to the zone is lower than the zone air temperature. In your model, the outdoor air is not heated sufficiently due to insufficient GSHP capacity and insufficient reheat coil capacity, and the outdoor air with lower temerature than indoor air is fed to zones, which results in the positive Zone Air System Sensible Cooling Energy in winter. Cooling coil is not operating in winter in your model.
Lastly, I highly recommend illustrating your model when you ask something.
| | 2 | No.2 Revision |
I looked at your model and ran it. There are several reasons involved for your issue.
You should check where you have Zone Air System Sensible Cooling Energy in winter first. It is detected in the following 3 zones: C37073, 50E38B and 841836. They are in the same AirLoop: Auditorio Rooftop Heat Pump. This AirLoop has HEX, system(central) cooling coil, system(central) heating coil and zone(local) reheat coils.
Capacity of your Ground Source Heat Pump system (GSHP) is insufficient. You should check Output:Variable: Zone Air Temperature, Zone Heating Setpoint Not Met Time and Zone Cooling Setpoint Not Met Time. Please note that Zone Heating Setpoint Not Met While Occupied Time and Zone Cooling Setpoint Not Met While Occupied Time (so-called "Unmet Hour") is not detected because the number of people is 0 in your model.
Your setpoint setting for the system heating coil is incorrect. You use two SetpointManager:singleZone:Reheat objects for the heating coil air outlet node (Node 50-A), but you cannot use two setpoint for one node. You can see the warning message "setpoint node conflicts with another setpoint manager" in your err file. For the system heating coil, you should use SetpointManager:Scheduled for the fixed temperature setpoint or SetpointManager:MultiZone:Heating:Average.
The zone reheat coils are not autosized correctly. The heating capacity of zone reheat coils is nearly 0W. it is beacuse you set Central Heating Design Supply Air Temperature to 40 C in Sizing:System, which is very high and EnergyPlus regards that all the heating load will be handled by this system heating coil and that zone reheat coils are not necessary. I don't know your design consept. If the system heating coil is just for preheating, the temperature setpoint should be much lower, and practically, the preheat coil should be located before the system cooling coil. If you intend to handle all the heating load by the central heating coil and you don't need zone reheat coils, you can keep the current high Central Heating Design Supply Air Temperature, but I don't think this design works properly, especially for your CAV system with multiple zones.
You should know the difference of between Output:Variable Zone Air System Sensible Cooling Energy and Cooling Coil Sensible Cooling Energy. When Cooling Coil Sensible Cooling Energy is positive, the cooling coil is actually operating. GSHP in your model is cooling chilled water, and electricity is consumed for cooling. On the other hand, when Zone Air System Sensible Cooling Energy is positive, it does not necessarily mean that electricity is consumed for cooling. Zone Air System Sensible Cooling Energy becomes positive simply when the supply air temperature to the zone is lower than the zone air temperature. In your model, the outdoor air is not heated sufficiently due to insufficient GSHP capacity and insufficient reheat coil capacity, and the outdoor air with lower temerature than indoor air is fed to zones, which results in the positive Zone Air System Sensible Cooling Energy in winter. Cooling coil is not operating in winter in your model.
Lastly, I highly recommend illustrating your model when you ask something.
