ERV Impact

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Hello all. After finalizing my building and obtaining what appeared to be reasonable output, I removed the ERV devices (modeled at 85% efficient cross-flow air to air heat exchangers) from the model to ascertain the energy savings attributable to those devices.

And my total energy consumption went DOWN over 6%! Inexplicably, 'space cooling' and 'pumps & aux.' energy consumption has decreased by a far larger amount than 'space heating' increased. I would have expected both of those values to increase along with the 'space heating' energy consumption (which did increase).

Anyone have any idea why that might be?

Andrew Clagett, PE, LEED AP

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Joined: 2011-09-30
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Did you use capacity control and make-up air temperature control? If not you will be over heating and over cooling in some conditions as the air will always be going through the heat recovery device.

Timothy Howe, MS, LEED? AP BD+C

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Joined: 2011-09-30
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Examine your ERV-TEMP-CTRL setpoint. If it's set to float you can end up
overshooting your mixed air temperature setpoint and having to recool the
air.

Also, ERV-RUN-CTRL should be set to WHEN-MIN-OA or one of the
OA-EXHAUST-DT/DH options for maximum energy savings.

That being said, eQUEST's ERV algoirthm has never given me good results.
I've had a lot of trouble showing savings and have experienced similar
issues as you describe.

Check your hourly reports for the system. There are a number of parameters
related to ERV's that you can monitor and check to see if its working as
intended.

[image: Inline image 2]

Robby Oylear's picture
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Joined: 2011-09-30
Reputation: 202

yep. how are you controlling the erv? interlocked with the supply air
fan so they're on all the time during occupied hours? that'll do it.
you spend more energy running the wheel and those inefficient erv supply
and erv exhaust fans than you save via the energy transfer of the wheel.

my experience has been to set the ervs to function based on a delta t
between the outdoor air and the exhaust air. the best delta t will vary
depending where your project is but in my hot/dry 2b zone i've found a
delta t of 20 was good, a delta t of 26 was peak before the energy
savings headed south again.

also, you don't need to delete/remove the ervs to see energy savings.
just set up parametric runs with the different delta t you want to test
at & you can compare the savings via the comparison reports. just don't
forget to a) set the parametric run for delta t, assign the unit(s) with
ervs, and give it a delta t. these are multiple inputs per air handler/erv.

sample:

Patrick J. O'Leary, Jr.'s picture
Joined: 2011-09-30
Reputation: 0