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HRV selection

user-4310370 | Posted in Mechanicals on

Finishing up a zone 5 pretty good house ~4000 sq foot home with a wall stackup of (exterior to interior) 2″ XPS (taped/staggered seams) -> 1/2 inch plywood -> 2×4 wall with R-15 roxul. Heating with traditional forced air. We have separate ducting for an HRV pulling air from bathrooms and mostly returning in bedroom closets and a few other spaces. The original plan was to use a Fantech 2005R 82/204 CFM with approximately 75% apparent sensible effectiveness. I have an option to use their higher efficiency unit the SHR 3005R (95 to 238 CFM) with dual cores leading to about 90% apparent sensible effectiveness. This unit is about $500 more.

I am just looking for any practical pros and cons on the choice to move to the more efficient unit at that cost? I understand one is more efficient but practically speaking will the extra 15% make a noticeable positive difference?

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  1. GBA Editor
    Martin Holladay | | #1

    According to one study, the difference in operating costs between an HRV with efficiency that is OK and an HRV with very high efficiency is about $100 per year in Chicago. So you might see an energy payback for your $500 incremental cost in about 5 years (plus or minus a few years).

    To read more about the study I'm referring to, see Are HRVs Cost-Effective?

  2. user-4310370 | | #2

    Thanks for the fast and clear response. It has a reasonable payback period and the increase in comfort from the higher temperature of the incoming air is certainly worth a few bucks a month. So all in all it looks like the higher efficiency is the way to go.

  3. charlie_sullivan | | #3

    You might want to also consider the electric power consumption. At 117 CFM, the 2005R consumes 154 W, whereas the 3005R consumes 212 W, according to the spec sheet. The 58 W difference might cost you $50/year in electricity (if your electric rate is around $0.1/kWh), so that cuts the $100 savings in half. Better would be to choose an HRV with an ECM fan motor that might use only 60 W or so. Venmar, Lifebreath, Zehnder, Ultimate Aire (ERV only, as I recall) are some of the brands that have ECM standard or as an option.

  4. user-4310370 | | #4

    Thanks Charlie -

    A quick look at the lifebreath 195ECM and it does have significantly better power consumption particularly at its lowest speed and I do like that they have 5 speeds and includes 1 control.

    I also looked at Zehnder earlier and they wanted 3X my current total price to install a system which is above my budget.

    Venmar was an option but I can't find a dealer who sells them without also being the installer which is not an option at this time.

  5. SwitchgrassFarmer | | #5

    Michael, will you be installing any sort of boost switches or sensors on your system?

    It looks like your chosen Fantech has three speed ranges including a "high" setting; I find that quite appealing. I too have a fully ducted HRV system, but my Honeywell HRV only has two settings, let's call them "normal" and "twice normal" (boost). What I really need is something like "normal", and then "3 or 4x normal" when a bathroom timer switch calls for extra ventilation. That way I could back off the HRV a bit during its normal 24 hour operation.

    Another nice thing about that Fantech "R" unit is the way it appears to handle defrost through its five port design. My "dumber" Honeywell just unbalances itself a few minutes each hour during cold winter days. I learned this the hard way, when I was unlucky enough to open up the door to our masonry heater at the same time it was in defrost mode. (I am mulling over some sort of heater or bleed air system to prevent the Honeywell from ever going into defrost.)

    Agreed on how nice it would be to have five speed settings like the Lifebreath, that is indoor air quality fine tuning!

  6. GBA Editor
    Martin Holladay | | #6

    What makes you think that the John Semmelhack study I referred to didn't consider electricity use? As far as I can determine, it did. (That's where the estimate of $100/year savings came from -- the Semmelhack study.)

    In my report on Semmelhack's paper, I wrote, "he modeled the performance of the house with three different ventilation systems: an Ultimate Air 200DX ERV, a Zehnder Comfo 350 HRV, and a Panasonic FV-08VKS3 exhaust fan with variable airflow settings and passive air inlets. The electricity use of each appliance was assumed to be as follows: 0.58 W/cfm for the Ultimate Air ERV, 0.30 W/cfm for the Zehnder HRV, 0.12 W/cfm for the Panasonic exhaust fan. ..."

    Of course, you can criticize my response to Michael by noting that Semmelhack's study looked at different HRV models than those being considered by Michael. But you can't criticize my response based on the false premise that Semmelhack didn't take electricity consumption into account.

    If you are willing to accept (for the sake of argument) that the savings derived from the Semmelhack paper are a reasonable ballpark estimate for Michael's annual savings, then there is no need to "cut the $100 savings in half" because of electricity use differences. Semmelhack assumed that the more efficient HRV used less electricity than the less efficient HRV.

  7. charlie_sullivan | | #7

    Martin, I didn't look at the report--I only assumed that you were quoting a number that was a good answer to the question as posed--the savings from a unit with higher thermal efficiency.

    Michael, if you want us to, we could estimate the cost savings for a given 15% thermal efficiency difference, if you told us your heating system type and fuel costs, and the ventilation rate you expect to use.

    But it sounds like we might have already talked you into the Lifebreath ECM, if the quote on that comes back looking better than the Zehnder, which I think it will. Yes, the efficiency advantage will be greatest at low speed. Single-phase induction motors often have pathetic efficiency at low speeds--that's where ECMs shine the most.

  8. user-4310370 | | #8

    Andrew -

    I will definitely have boost switches - 1 in each bath. I also do like the defrost method of the Fantech , it would be terrible to have an HRV freeze up on you. I'll update things after we live with it for a bit.

    Charlie I do like the lifebreath but actually had ordered the Fantech before your response. I may end up with that because a) its on order and b) we don't have the extra room required for the ducting of the Lifebreath that is required for a recirculating defrost since it has to be external.

  9. Poliana | | #9

    Why an HRV would freeze up on you? How?

    1. this_page_left_blank | | #11

      The air inside your house has a lot of moisture. If the outside temperature gets low enough, it can lower the outgoing airstream to below freezing temperature, at which point frost can build up in the core. The exact outside temperature this might happen at depends on interior temperature and humidity, HRV flow rate and HRV efficiency. All HRVs require some kind of frost prevention strategy in cold climates. Some ERVs claim to not to require it, a claim some find dubious.

  10. calum_wilde | | #12

    I've had a fantech for 14 years now. I replaced the original unit that unbalanced its ventilation to defrost for one that recircs for defrost about 3 years ago. The old unit still worked great after a decade though.

    I've had to replace two controllers over the years. Presently the "Eco-touch" central controller isn't functioning correctly; it allows manual speed changes but won't go into automatic "eco" mode. I'm not sure why, but I'm fine with it as it still allows me to set 20m or 40m/hour run time on the lowest fan speed setting, which is about right for my house. I also replaced a boost switch and a humidastat.

    As an aside, I have humidastats in the bathrooms along with boost switches. They get set to max humidity in the summer but in the winter they're set about 10% higher than the main unit to help control humidity at its source. It's a secondary purpose for the HRV, but it's effective at it so I figured 'why not?' .

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