My HERS rater using RemRate software says installing a HRV unit will raise (hurt) my HERS score by 3-4 points. If that's true is this a glitch in the software? This is new construction with 1.09 blower door test, using high end variable speed heat pump. Question is, have any of you had this result with HRV?

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Depends on electric usage & how you have it run - what is he comparing it to?

Beyond that you have to have ventilation - as for how you go about it can be a good or bad thing

@Gary, the HERS score is intended to reflect projected energy consumption, and since ventilation by definition adds to energy consumption (due to increased heating & cooling loads), it follows that adding ventilation should negatively impact the HERS score. An HRV should have less of a negative impact than a non-recovery system. The impact largely depends on climate zone, ventilation rate and recovery efficiency.

I say 'largely' because there's an additional factor at play in REM (and HERS in general): You don't get credit for a tight envelope unless ventilation complies with ASHRAE 62.2 (not sure which version REM checks against). So if you're trying to minimize the HERS score, you want to set the ventilation rate as low as possible while still meeting 62.2. Keep in mind that since the 2013 version, 62.2 counts part of the modeled infiltration toward meeting the ventilation rate. But given how tight your envelope is, I'm surprised that removing the ventilation system lowers (improves) the score. The only explanation I can imagine is if your ventilation settings in REM didn't meet 62.2.

Check out the context help page on the ventilation tab for more information.

Thanks, I will check it out. 

I agree with David really depends on the inputs into the model as well as the efficiency of the HRV. There's a big range of heat transfer and fan motor efficiency in the HRV/ERV world. 

If the ASHRAE 62.2-2013 ventilation rate were, for instance, 75cfm...but the Rater was inputting 200cfm, then you would likely see an increase in the HERS score. 

Thanks for the reply's. Good to have professionals here.

Gary, I think your point is a good one though.

If HERS is an asset score, taking points away for energy but having no points added back for the health/comfort benefits of fresh air seems myopic.

LOL, it is an energy asset score not a health score :) You want points for health you got to look for other certifications which most use HERS for the energy part

Holy dog chasing his tail, Batman.

I'm not sure we're thinking about the right comparison here. The comparison isn't a 1ach house with and without an HRV, since it wouldn't be responsible to build such a tight house and not provide some kind of mechanical--hopefully balanced--ventilation. The comparison should be something like a code-compliant house without an HRV, so more like 3-5ach. The HERS score for that leakier house would be higher than the HERS score for the tight house + ERV. Net of the energy cost of the HRV, which is real, the higher performance envelope is still providing a more efficient end result.


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