ERV temperature settings?
Tommy Barrett| Posted inEnergy Efficiency and Durabilityon
I recently purchased an energy-efficient home with many upgrades on that front. One of them is an EVR. While I understand and felt like we have benefited from the EVR, I am confused as to what temperature I should have the lock-outs set to.
Currently the builder put them to 30 degrees and 95 degrees. That seems cold/hot to have that air being pushed into the house. Can anyone share some thoughts logic on those settings and if there are different settings please advise why?
Thank you!
Replies
Tommy,
EVR = ERV? What model? What climate zone are you in?
Tommy,
Bill nailed it -- there are three questions that we need answers to in order to help you.
Sorry about the ERV.. :)
S&P TR130
I am in North Carolina. I am sure you know but we have maybe 45-60 days of below 35-40 degrees in winter and then 3 +/- months of 85-100 degrees. Thanks for the help!
Tommy,
It took some sleuthing, because I had never heard of a company named S&P. It turns out that your energy-recovery ventilator (ERV) was manufactured by Soler & Palau, a manufacturer in Barcelona, Spain. Evidently a U.S. distributor in Jacksonville, Florida is now importing and selling these Spanish ERVs.
I'm not sure whether these Spanish ERVs operate well in North American climates, and I don't know anything about their control algorithms. And GBA readers have any information?
John,
Thanks for the comments. I appreciate learning more about S&P.
The S&P ERV's are re-branded units manufactured by Renewaire in Madison, WI. S&P, a large multi-national company focused on ventilation products, acquired a majority stake (100%?) in Renewaire a couple of years ago. Here's the identical Renewaire unit -http://www.renewaire.com/products/residential-products/ev130
The specs on the EV130 are decent, but certainly not great. They use the same core size as the EV90, but the heat + moisture transfer efficiency goes down in comparison since they're pushing more air through the core. Fan efficiency is mediocre as well, in part for the same reason.
In my experience, it's uncommon to use temperature-based lockout controls on ERVs. These units do not ship with this kind of control. From strictly a heat-transfer efficiency standpoint, the greater the temperature difference, the greater their heat transfer rate....one of the few kinds of products that perform better the worse the conditions are (up until frost point, which is something well below 0 on these units, I suspect). Typical practice is to let an ERV or HRV run during all conditions, and to size the heating/cooling system to handle the load during extreme conditions (usually 99% winter and 1% summer design temperatures). Indoor air quality trumps low energy use...or, it should anyway. In my opinion, if you're not going to ventilate under 30 and over 95, then the builder probably should have just skipped the ventilation system in the first place.
Some arguments for reducing or eliminating ERV operation during very cold weather are:
1) When it's very cold, your heating system might have trouble keeping up, so you might want to go into "emergency mode", and stop caring about air quality.
2) Infiltration driven by stack effect is greater when it's cold out. If your envelope has non-zero leakage (which all do), you are getting outside air during cold weather even without the ERV, more so than you would in mild weather. Whether this is enough depends on your envelope tightness and many other details.
3) If part of your goal is dehumidification, it takes less outside air to do that when it's colder outside.
4) The ERV might get clogged with frost. Most have defrost cycles, but a cheap alternative is shutting it off. And some defrost cycles waste energy. And some ERVs can be damaged by frost.
Analogies to 1) and 2) are also arguments for hot-weather lockout.
Whether any of these apply and how the tradeoffs work out will vary with the application, so I'm deliberately avoiding saying whether I think it's a good idea because I think it is sometimes and is not in other situations.
Bang-bang controls as seem to be the norm for HRVs and ERVs make a lot of sense for most tight home applications. There are some of us whose VCR clock isn't flashing 12:00 though, and it would be nice to have more granularity of control. Examples could be managing an HRV via CO2 levels, switching between HRV and ERV functionality by indoor humidity requirements, etc. One can dream anyhow.
(This rant has little to do with the original poster's question, just venting...)
Andrew,
If you want an ERV that responds to CO2 levels, you can buy one. The appliance is called the CERV. Here is a link to an article that describes the CERV:A Balanced Ventilation System With a Built-In Heat Pump.