RoomAirModel exhaust temperature offset does not affect exhaust heat transfer?

asked 2023-11-13 15:45:29 -0600

Jamie Sullivan's avatar

updated 2023-11-14 12:43:03 -0600

I was applying a vertical temperature gradient using the RoomAir:ConstantGradient inputs, and looking to exhaust warmer air out of the zone. According the the reference manual, having a temperature offset on the exhaust should affect the zone temperatures: "The third parameter can affect the zone air heat balance by altering the temperature of the air leaving the zone through exhaust fans".

When I tried to apply this using Fan:ZoneExhaust, there was no effect from the temperature offset. Looking at the outputs the fan is successfully removing air and heat from the zone, and if I look at the system node temperature for the exhaust node, it is indeed warmer than the zone air temperature as intended: image description

However, this does not translate into any change in the Exhaust Air Heat Transfer, or the zone air temperature. Their values stay the same regardless of what I set the exhaust temperature offset to: image description

Wondering if this might be an issue with the Fan:ZoneExhaust object, I also tried ZoneHVAC:OutdoorAirUnit, to the same result. I can change the exhaust node temperature, but this doesn't affect anything else.

I know that usually exhaust air doesn't do anything to the zone heat balance because if you're just removing air at the zone temperature then nothing about the zone temperature needs to change. But if you're removing air at a different temperature to the zone average, then this should affect matters, and the reference manual seems to say that this should be the case. So I was wondering what's going on here? Is this how the RoomAirModel is supposed to be working with the temperature offsets? Are the impacts of the room air model here purely on something like HVAC energy use, and it doesn't really affect the zone temperature or the heat transferred through the exhaust?

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