Temperature Control of Zone Level Exhaust

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Dear All,

Is it possible to model zonal exhaust schedules in eQuest to turn on/off
based on indoor temperature of the zone?

Thanks in advance for the replies,

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Omer Moltay's picture
Joined: 2011-09-30
Reputation: 0


I have not found a way to operate an EF based on OAT directly. We have modelled spaces, such as electrical rooms, that are only conditioned by an exhaust fan on a thermostat with a relief intake louver. We used a 100% OA supply fan ? usually a PSZ system with cooling set to 1 BTU/hr to prevent autosizing. The fan input power matched the exhaust fan and it is controlled either to ?intermittent? operation or it is set always to unoccupied with its night cycle control set to ?cycle on any?.

This suggestion would be less helpful if you have other systems serving the same space. In that case I guess you?d create a custom schedule for the exhaust fan. I still like RMI?s EMIT spreadsheet for creating custom eQUEST schedules.




Brian Fountain's picture
Joined: 2019-05-02
Reputation: 0

My mind immediately jumped to Brian?s second solution.

It?s helpful context while game planning your approach to consider that if you schedule a fan to operate using your own custom schedule, then you have some flexibility to specify the makeup source as either ?raw? OA (EXHAUST-SOURCE = INFILTRATION or BALANCED-INFIL), or conditioned air via the associated SYSTEM (EXHAUST SOURCE = AIR-HANDLER). With the latter option, you can achieve ?getting the load onto the system? in a sort of reverse fashion, if that is a concern.

To ?spoon feed? an operating schedule via EMIT, utilize the custom hourly reports feature to track and export the interior/exterior temperature of interest. That 8760 column can then be ?logic ?ed? in Excel to determine a binary operating schedule, which can then be pasted into EMIT to generate an INP snippet ready for import.

A shortcoming for this workaround however is that you can?t totally capture the dynamic interactions between an exhaust fan and AC system both cycling/operating based on a common space temperature and properties like space thermal mass which affect how quickly (or if at all) the space can return to an acceptable thermal state with the exhaust and/or system doing its thing. You could resolve this by doing the custom hourly thing a few times over to see if and how your exhaust operating schedule may change in reaction to the contributions of another conditioning system? until you reach a state of relative ?convergence? where the operating hours aren?t changing much between each round of edits? but then like with many things you will want to consider your time-value for model development and whether you are accomplishing improved levels of accuracy on something important or not in the scheme of things?

Kind regards,

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Nicholas Caton2's picture
Joined: 2019-03-25
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