To ERV or Not?
Hi, I’m having a house built in central VA (Zone 4)…2 floors and a basement (~3300 sq.ft.). Trying to build pretty tight and so we are concerned with proper ventilation. Each house in the community must meet certain standards which include fresh air ventilation to the ashrae standard. Btw…I’m pushing to get the hvac system within the conditioned space, so we are likely to have a single forced air ducted system for the entire house with manually set dampers for each floor.
Here are the options I’ve received on ventilation….
– Standard (no additional cost): Timed fresh air ventilation introduced into the return side of the air handler and using existing ducting. The ventilation and hvac blower will be linked so that both run together. (No idea yet the wattage of the hvac blower).
– Recuperator 200 ($3100): I requested a quote for the ERV. System would be installed as above for the standard with the exhaust also coming out of the return side ducting.
So….appreciate any thoughts on if the ERV is worth the extra $3k, or if I should I stick with the standard. Or perhaps…..ask that they do something different so that the HVAC blower and exterior ventilation are not linked. This site has been very helpful, but like everything else, creates as many questions as answers. Thanks.
– Bryan
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Replies
Bryan,
Neither proposed system is well designed.
The first system is called a "central-fan-integrated supply ventilation system." It sounds as if your HVAC contractor has omitted two essential components of such a system: namely, a FanCycler control (also called an AirCycler control) and a motorized damper. The function of these components is to avoid overventilation (by closing the motorized damper when the furnace fan operates for long periods of time) and underventilation (by energizing the furnace fan occasionally during the swing seasons of spring and fall).
When it comes to ERVs, I'm not a fan of systems that use foced-air ductwork to distribute ventilation air. Systems with dedicated ventilation ductwork are preferable.
For more information on designing a mechanical ventilation system, see Designing a Good Ventilation System.
Concerning your question -- "Is the ERV is worth the extra $3 K" -- I'd say, probably not, in your climate. I'd go for the central-fan-integrated supply ventilation system -- but only if your contractor includes the motorized damper and the FanCycler; and if they are properly installed; if the system is commissioned properly and the air flows measured; and if the furnace is equipped with an energy-efficient ECM blower rather than the typical energy-hog blower.
Martin-
Thanks so much for the well thought out response. I had read your recommended article some time ago, but reading again after talking to the HVAC guy was really helpful.
I know the HVAC contractor mentioned a damper on the fresh air intake and a timer to ensure the house was not underventilated during the swing season. However, I believe he said that the fresh air would always be activated if the HVAC system was on to heat or cool. So..that does not solve the overventilation issue. Also, since he couldn't specify the energy draw of the blower fan, I suspect it is not ECM.
I'd love to go the dedicated duct route, but I'm guessing that adding that on to the EVR cost will be hard to justify given my climate, etc.
As you suggest, I will specify the need for motorized damper and FanCyler to avoid overventilating and request the ECM and air flow validation.
In your opinion would this be a better route than an exhaust only system with a couple of Panasonic fans?
Thanks!
Bryan,
Q. "In your opinion would this be a better route than an exhaust only system with a couple of Panasonic fans?"
A. An exhaust-only ventilation system can work well, especially in a compact house with an open floor plan. However, you'll get better fresh air distribution in your bedrooms if you install a central-fan-integrated supply ventilation system.
In the past if you look back passive inlets added to bedrooms have been mentioned to go with a Panasonic bath fan. Also Panasonic makes an integrated HRV bath fan.
People all across the planet live in air that must be orders of magnitude less clean than the latest ASHRAE idea. So I think it boils down to personal choice and personal health issues.
Also, HRV is my choice here where we heat more than we cool.
Martin ERV is better choice in hot humid climate? Also somewhere back awhile two speed DC blowers or something else were the actual most efficient? ECMs under actual testing .... Could you point to that for us?