Daily Archives: April 24, 2011

Some HRV advice

Here is some quick HRV/ERV advice based on our experience so far:

– Do ASHRAE 62.2 stuff so you get the right flows to right rooms and size the unit appropriately. We run ours on setting 3 of 5, but maybe it would be preferrable to have the slightly larger unit running on 2. Quieter?
– Have duct routes planned out. Don’t leave it to the HVAC contractor to wing
– Keep duct runs short. use Ys not Ts, etc. Generally follow advice from the David Hansen article in JLC LINK
– Ideally get a contractor who has done HRVs before because it seems to me that not everyone is very experienced in balancing using pitot tubes, adjusting registers, taping calerfully, etc, etc, etc, etc. Basically it would be nice for someone who is good at measuring/verifying the installation. In our case, I’ve been left to do most of that.
– Choose a model that has good CFM per watt. Our Lifebreath 155ECM is good on that front, but there are some with even better “efficiency” in terms of heat recovery apparently?
– It’s no joke: having flexible ducting for the first foot or so is KEY in keeping the system quiet. It’s really amazing (ours didn’t at first).

Other random notes:
– We have the typical — exhaust bathrooms, fresh air to bedrooms — setup and find that it works pretty well in the bathrooms, but I’m not convinced it can handle when it’s like a sauna in there all that well. I will have to do some RH measurements. Occasionally we open a window. Once (on a winter day) a window was left 1/4 open and wasn’t noticed for 1/2 a day(?) because the house is so tight that it doesn’t cause much of a draft . Which really means another windows should have been opened if someone wanted to dry it out quickly.
– When it’s like 0F out, our system goes into defrost mode pretty regularly (I will have to check how often) which only affects you in that the fan speed is set to 5, so it will be louder off and on, on very cold winter nights. Maybe some units are better about needing this less? Who knows.
– I’ve also experimented with using a portable… DEHUMIDIFIER… same effect (the air is dried out) but you get to keep the heat you make! If you have space, this is a nice way to go in heating season.
– Consider exhaust-only ventilation with a whispergreen fan and make-up-air hole. There is discussion on GreenBuildingAdvisor.com about which is “better”. You got me! LINK

– I am going to add some “solar preheating” of the intake air. But according to the PHPP, this would not be enough in our cold new england climate to be able to heat the house. That’s fine.


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