Minimum cooling supply air temperature setting not honored

asked 2019-11-01 17:44:58 -0500

desie gravatar image

Dear all,

I have an EP model and I specified ideal air load in it (pictured below). In the ideal air load model, I also Minimum cooling supply air temperature such that it does not go below a certain level and becomes unreasonably uncomfortable for the occupant in real life. However, this setting is not honored and the supply air can sometimes become -8­°C for many hours in a year. Since the climate, I am simulating is a bit colder climate, so I suspect that it is because the ventilation air does not get heated up before introducing to the zone. However, I failed to find a place to make sure that the ventilation air gets heated to match the minimum temperature requirement. So if someone can please direct me with the troubleshooting step that would be great!

Thasnks all

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It seems that you are hardsizing the maximum heating capacity. Is this enough to cover your design heating load?

mdahlhausen gravatar image mdahlhausen  ( 2019-11-04 11:34:52 -0500 )edit

Dear mdahlhausen, yes, I hard sized the heating load. However, the heating load is not the problem here since I am getting very low supply air temperature when cooling is needed during the winter time. When cooling is needed, I want to make sure that the minimum air temperature is at least 15degC (cold ventilation air is heated up to at least 15 degC) to make my simulation a bit more realistic.

desie gravatar image desie  ( 2019-11-04 12:59:22 -0500 )edit

Ideal air loads is pretty straightforward, and your flow rates are autosized. To me, this means either 1) your design days don't match your location or inadequately capture the peak load, or 2) your heating is still undersized. Plot the supply air temperature versus the heating rate supplied by the ideal air loads object. My guess is that you will find your ideal air loads heating rate maxing out at 6.096 kW when the supply air temperature drops below 15C.

mdahlhausen gravatar image mdahlhausen  ( 2019-11-04 15:03:41 -0500 )edit

Dear mdahlhausen, Thank you for the comments. I did investigate what you suggested, however, when the supply air temperature drops below 15degC, the supply air heating energy is actually zero, and the zone actually needs cooling from solar heat gain or other sources. Also, the heating capacity is actually oversized. Even the zone needs cooling, however, it is still unrealistic to have supply air temp drop below 13degC. Because the outdoor air temperature is also pretty low, so I suspect the DSOA is introduced into the zone without being conditioned.

desie gravatar image desie  ( 2019-11-04 15:17:49 -0500 )edit

What are you using for design days, and is the air flow rate maxing out?

mdahlhausen gravatar image mdahlhausen  ( 2019-11-05 10:03:02 -0500 )edit