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Zone Air system sensible Cooling Load are very high in winter

asked 2023-02-17 04:25:23 -0500

Qamar's avatar

updated 2023-02-17 08:45:57 -0500

I have been trying to fix high sensible cooling loads in winter. I have read some suggestions about setpoint manager single heating or cooling but I have some difficulties in understand this. Please any help in solving this problem will be very appreciated.

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@Qamar if you save your IDF on Dropbox, Google Drive, or something similar and then share a URL, others can access your input file and provide better solutions.

Aaron Boranian's avatar Aaron Boranian  ( 2023-02-17 08:46:43 -0500 )edit

Okay. Here is the link of the model. Many thanks, Regards,

Qamar's avatar Qamar  ( 2023-02-17 12:23:53 -0500 )edit

@Qamar Google Drive is asking me to request permission. That's fine if you want to approve each person that reviews your input file, but it may be easier to change the sharing settings to "Anyone with the link can access".

Aaron Boranian's avatar Aaron Boranian  ( 2023-02-20 10:50:46 -0500 )edit

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answered 2023-02-21 04:35:20 -0500

Keigo's avatar

updated 2023-02-21 04:39:15 -0500

I looked at your model and ran it. There are several reasons involved for your issue.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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 ...

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Dear Keigo,

Thank you very much for your answer. I surely appreciate it. Based on your comments and advices, I have corrected my model and here are my answers:

  1. List Answer comment 1: I have checked this variable. For all the zones accept the ones connected to Auditorio AirLoop, this variable is zero. When I added occupation values to people field, this variable Zone Air System Sensible Cooling Energy have considerable values which might be due to sensible energy add by occupation, right?

  2. Answer comment 2: I have checked the setpoint not met and I have few hours per month of unmet.

Qamar's avatar Qamar  ( 2023-02-22 11:43:09 -0500 )edit

I will continue here due to characteristics limitations Answer comment 3: Also i corrected this setpoint manager and substituted it with SetpointManager:MultiZone:Heating:Averagefor heating coil and SetpointManager:MultiZone:Cooling:Average for cooling coil.

Answer comment 4: I corrected this value to 29 and after that reheat coils have heating capacity around 4 and 6 kW.

Answer Comment 5: Thank you for your explanation. I had no idea about this difference.

After plotting the cooling coil sensible cooling energy, I have got this graph, which means the cooling coil is operating (link text)

Qamar's avatar Qamar  ( 2023-02-22 11:44:33 -0500 )edit

My question. Am I doing something wrong with the entering values in the sizing:zone, sizing:system and sizing:plant objects illustrated in the images in the link above?

Many many thanks for your great help, Best regards, Kamar

Qamar's avatar Qamar  ( 2023-02-22 11:56:34 -0500 )edit

I said "Cooling coil is not operating in winter in your model." I assumed winter roughly refers to November to February in your country. There is no cooling energy in that period. I'm sorry for my misunderstanding if your model is located in the southern hemisphere.

Keigo's avatar Keigo  ( 2023-02-22 19:59:00 -0500 )edit

You are hardsizing many parameters of your ground source heat pump system, e.g. Cooling Capacity in HeatPump:WaterToWater:EquationFit:Cooling, Heating Capacity in HeatPump:WaterToWater:EquationFit:Heating, Design Flow Rate and Ground Thermal Heat Capacity in GroundHeatExchanger:System, All the parameters in GroundHeatExchanger:Vertical:Properties, Number of Boreholes in GroundHeatExchanger:ResponseFactors, etc. Hardsize takes precedence over Autosize. Please double-check your hardsized parameters. Some of them may be insufficient.

Keigo's avatar Keigo  ( 2023-02-22 20:15:43 -0500 )edit

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Asked: 2023-02-17 04:25:23 -0500

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Last updated: Feb 21