Modeling ERVs that use air from multiple zones

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Hi All,

How do you model an ERV that is using exhaust air from toilet exhaust that comes from multiple zones? The toilets are in zones that are associated with different AHUs. The ERV is providing fresh air to a corridor. There is a hot water coil in the ERV. That's the only "conditioning" the air gets.

Looking at Nicks sketch in the Energy Recovery Wheel on VAV System - zonal exhaust thread it appears that eQuest cannot use exhaust air from one zone to an ERV that is attached to another zone.

Thanks for you input.

Best regards
for KEMA Inc

Paula Saaf P.E.
Engineer, Middletown

paula.saaf at
Direct +1 860 3465001 | LinkedIn

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via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

I'd first consider grouping all restroom zones + the serving corridor zone(s) under a single "corridor" system in your model. This allows ERV inputs specified in one place only, and simplifies specifying heating-only between the system inputs and control zone(s)' thermostat schedules for the needed OA pre-conditioning.

Think about whether the restrooms actually received pre-heated corridor air vs. something "more conditioned." This might not be a perfect fit if the restrooms' conditioned makeup actually comes from cooled spaces or directly from other AHU's... but this would be a starting point in that case and the differential in terms of what's seen at the ERV might not be meaningful enough to get worked up about.

You could also go down a path of replicating/weighting ERV inputs between the affected systems instead, but I suspect that would probably end up being much more work than the above alternative for your scenario.

Getting exhaust/relief loads transposed between systems to be seen with ERV is indeed tricky, but an explored path with a destination at least. It entails quantifying the hourly sensible/latent loads you mean to transpose, and spoon-feeding those loads into a space under the receiving ERV via a "free" hourly process schedule. This is done most commonly I think in concert with the OA-FROM-SYSTEM + "dummy zone" approaches to tackle DOAS that also involves heat recovery equipment, if anyone needs some search terms to find related threads in the archives.

[cid:image001.png at 01D2A7C7.255650F0]
Nick Caton, P.E., BEMP
Senior Energy Engineer
Regional Energy Engineering Manager
Energy and Sustainability Services
Schneider Electric

D 913.564.6361
M 785.410.3317
F 913.564.6380
E nicholas.caton at

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

[cid:image002.png at 01D2A7C7.255650F0]

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400


If the transferred air is at room temperature and does not affect the loads of the room the air is going into, you could simply exhaust the air from the corridor in your model instead of exhausting it from the room. The energy use would be the same.

If the transfer air is intended to help heat or cool the rooms that the air is being transferred to, then it gets more complicated. Perhaps in the model you could supply the air (or a fraction of the air) directly to the rooms that receive transferred air instead of the corridor and put an energy recovery unit in each room. In the model you are simply dividing up the energy use of the single large unit into a number of smaller units. The total energy consumption will be the same. For energy aspects that are not on a per cfm basis, like maybe a motor to spin an energy wheel, you will need to divide the power appropriately.

Remember that an energy model doesn't need to model the building systems exactly. It just needs to estimate the energy use of the building's systems.

Hope this helps!

Keith Swartz, PE | Senior Energy Engineer

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400