Large Unmet Cooling Hours for ~6% of 100 bldgs simulated

asked 2020-07-27 11:33:30 -0500

sashadf1 gravatar image

Hi all,

I am using ResStock v2.2.4 and OpenStudio v2.9.0.

I am trying to simulate a residential community in northern Georgia. Specifically, I noticed that regardless of the year of the simulation, or the HVAC system in place (propane furnace, ASHP, MSHP ect), for the same 6 building id #'s, I would always get huge unmet cooling hours for only 6 specific buildings out of the 100 simulated.

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Notice how the unmet hours are similar in magnitude as well. This leads me to believe that is an issue specific to these 6 particular buildings.

I know that there was a similar issue caused by unheated vs basements as separate thermal zones that was documented by a colleague of mine through this post:

However, this problem is different in that it only affects 6% of the buildings, while the above problem in the url was affecting all buildings.

Any guidance or advice would be appreciated.

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I'd suggest looking at one of these buildings in more detail. It could be that there are a lot of hours where the setpoint is not met, but the setpoint might only be off by a tiny fraction of a degree for these hours. You can check this by obtaining the timeseries outputs for the conditioned space temperature

shorowit gravatar imageshorowit ( 2020-07-27 12:41:49 -0500 )edit

There are a lot of different temperature fields in the timeseries output; which ones should I be comparing?

For example, there is: Zone Thermostat Heating Setpoint Temperature Zone Thermostat Air Temperature Zone Air Temperature Zone Operative Temperature Zone Thermostat Cooling Setpoint Temperature Zone Mean Air Temperature

I am assuming that, since I am dealing with cooling unmet hours, that I would compare the "Zone Thermostat Cooling Setpoint Temperature" with either the "Zone Air Temperature," "Zone Operative Temperature," or "Zone Mean Air Temperature."

sashadf1 gravatar imagesashadf1 ( 2020-07-27 18:33:36 -0500 )edit

When an unmet hour is computed, the difference between the a temperature field (one of the 3 zone temps listed above maybe?) and the setpoint is computed and then compared to a threshold value. If the difference exceeds the threshold, the hour is marked as an "unmet hour." Please correct me if my logic is wrong. Which temperature field used to take the difference with the setpoint?

sashadf1 gravatar imagesashadf1 ( 2020-07-27 18:35:31 -0500 )edit

I don't think that the difference between setpoint and zone temperature is only "off by a tiny fraction of a degree." I doubled my reporting control tolerance (degrees K), and the unmet hours still persisted. In other words, I doubled the temperature range from the setpoint that something will still be considered a "met hour". I will perform another simulation with the control tolerance reported even further, but at some point the tolerance needs to be capped otherwise you not seeing valid data.

sashadf1 gravatar imagesashadf1 ( 2020-07-28 19:42:44 -0500 )edit

@sashadf1 Does your analysis include multifamily buildings?

Eric Wilson gravatar imageEric Wilson ( 2020-07-30 15:34:09 -0500 )edit