HVAC in energyPlus is not meeting setpoints for single cooling.

asked 2018-11-05 18:36:47 -0500

Divya
177 ●5

updated 2018-11-06 08:41:16 -0500

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

I am using energyPlus to study HVAC model with Thermostat control type set to 'SingleCooling'. I am generating a random sequence of temperature setpoints but the HVAC is not meeting the requirements. Is there any other setting I need to check apart from the Schedule:Compact?

The following diagram shows the temperature setpoints of the thermostat and the zone temperature. I am creating a random sequence of 25 and 23 between business hours (8:00 am and 6:00 pm). HVAC maintains the temperature well below the setting for 30 deg C and 25 deg C. But When the setpoint is 21 C, the HVAC is unable to reach it. image description C:\fakepath\Case1.tiff

As I found that 21 C is a problem, I changed the schedule to a sequence 25 deg C and 23 deg C. Now the HVAC is able to reach the set points. image description C:\fakepath\Case2.tiff

Is there any setting in the system that is limiting this 21deg C? I am new to using energyPlus and I do not have knowledge of components in HVAC or thermodynamics. I am working on a example file provided in energyPlus 'DisplacementVent_1ZoneOffice.idf' with a few modifications.

answered 2018-11-06 07:35:56 -0500

rraustad

13599 ●72 ●12 http://www.fsec.ucf.edu/

Buildings have a large amount of thermal storage in the building materials. For this reason, changing the thermostat set point temperature will impose a large demand on the HVAC system. The HVAC system will need a very high capacity to overcome the loads (both external and internal to the building) and meet the new set point temperature. The greater the change in thermostat set point temperature the larger the capacity needed by the HVAC system. In this example file the HVAC capacity is autosized to meet the load as determined by the thermostat settings for the design days (summer and winter). You could either force the HVAC capacity by entering data for any field that is autosized or you could use the ZoneHVAC:IdealLoadsAirSystem object to provide the needed capacity at each time step. According to ExampleFiles-ObjectsLink.html, in the example files folder, the example file 5Zone_IdealLoadsAirSystems_ReturnPlenum.idf is one file that uses the ideal HVAC system. You might try using this example file for your study.

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This helped me, Thank you!

Divya ( 2018-11-06 08:45:24 -0500 )edit

Hi I have a couple of questions. 1. I am trying to see the HVAC power consumption in this example file "5Zone_IdealLoadsAirSystems_ReturnPlenum.idf" and it shows the power as 0. Can you help me identify the HVAC power. 2. I want to autosize the HVAC in another example file which has only one zone. But I get errors with node connections. Can you help me with the steps of autosizing HVAC?

Any help is greatly appreciated. Thanks in advance

Divya ( 2018-12-05 18:18:45 -0500 )edit

Look in the table output for End Uses and see District Cooling/Heating.
Autosizing simply means entering the word autosize for any field that is autosizable. Autosizable fields are air flow rate, capacity, and a few other fields. You can look up the object name in the Input Output Reference document to see which fields are autosizable. You will also need Sizing:Zone, Sizing:System and/or Sizing:plant objects depending on the HVAC system type.