Some central AC systems NOT good for HRV/ERV?

D107

I've lately been thinking more in terms of heating/ac, ventilation, insulation as a single system in my old house. We have a 1992 3-ton central AC with ceiling registers and I have always assumed once I foam-insulated I could drop in an HRV to the existing system, but now I'm not so sure. What kind of system lends itself to an HRV? and who's writing the best not-overly-technical books these days on the latest AC/HRV systems?

thanks,

David

Unknown

What is

an HRV? If you want an excellent book on heat pumps....the book Heat Pumps by Siberstein is the best I ever read. It is sold on this site.

D107

I believe it stands for 'heat recovery ventilator'

but the idea is it brings fresh air into the house while simultaneously exhausting stale air. There is an exchanger box where the incoming and outgoing air modify each other--in winter incoming cold air is modified by warmer outgoing air--so energy is saved. summer it's the reverse. This allows ventilation in a controlled way according to whatever schedule you set. I think it's called an ERV if a humidifier (or dehumifdiier?) is added. My hope is that such a system can work through an existing AC duct and register system.

thanks for the book info.

Thanks,

David

Unknown

Your right David,

up here they are a building code requirement on every new house constructed.

Dave

don_205

It sure can

It depend on what your goal is.Is it bc the house is so tight that you need to bring in cold dry outside air to get
the humdity down.Is it used to assure enough combustion air.Or simply used to change the 02 inside the envelope.

One should have a blower door test before running out and spending any money.You never know you may find that your house leaks enough that none of the above would be a issue.

And yes..depending on your needs bringing fresh air thru a
existing ac duct system can be a option.

D107

thanks.....

I had heard that some AC's are not adaptable to HRV so I wondered what are the criteria--when couldn't you do it. Currently my house is not tight enough to need one, but with foam insulation in attic and basement rim joists, (and blown in cellulose insulation already done) it would seem like the smart thing to do.

I suppose a tight building in NY might build up humidity in winter and periodically changing 02 is always a good idea. As for FAI i'd always assumed it had to be dedicated to the heating system in the mechanical room, otherwise the cold air would be travelin throughout the entire house just to get to the boiler room. Anyway my next boiler better be sealed combustion or at least with a FAI routed right into a burner boot.

David

Unknown

I will add that

to my acronym list. Sorry, I am unfamiliar with those units.

don_205

I understand

I understand David.It can be very confusing.But just like a hvac system you have to design around load and building envelope.

Asked yourself if I lived in a area that has high dewpoint in the summer how does a hrv help me.

Believe it or not there is alot of advantage of piping in the fresh air to your returns of your ac distribution system.

One I can think of right off the back.It not untreated ventilation air.

Its time to get out the psychrometrics charts and start plotting the what ifs.

Now it looks like you wethead have to start thinking more about AIR then ever before.I know how much you guys hate to discuss anything about air,but here we are.

I'm loving life right about now.

singh

David

Go with an ERV in your area. (Hudson Valley, NY)

A HRV has condensate and could freeze, an ERV is direct exchange only and does not provide any dehumidifcation. Leave that for the AC.

I had installed into existing duct work. No problem, just check control sequence when the air handler comes the ERV/HRV should operate simultaneously.

A per hour timer unit can also be used, run the ERV/HRV longer in winter.

don_205

Just keep

Just keep in mind erv/hrv are known as a balance ventilation system.It will be of no help to you if you want to try and reduce infiltration loads.

Only bringing the fresh air to the return of your hvac system can do that.

Just alittle more to think about.

Chris S

hrv

I took a class that adressed hrvs in December. With very tight construction such as SIPS panels, or ICFS an HRV is definitely needed. Combination foam systems also can make a home very tight. In my opinion though a remodel with 2x 4 walls will be very hard to achieve air tightness to make this a concern.

The info I have says that moisture from perspiration, cooking & showering will bring the humidity in a home ( such as those described above) above 40% without an hrv.

D107

perhaps you're right

thanks Chris. in a 1924 home with balloon construction with 4" blown cellulose plus 3/4" styrofoam on outside that's not a high R; even with 4" corbond in roof rafters and gable walls and basement rim joists that's what R25 unless you throw in some styrofoam above sheathing when you install a new roof.

First blower test before any weatherstripping, wall cellulose, chimney damper was .9ACH. My guess now maybe .6 or .7. What's the tipping point with blower test numbers before you need an HRV/ERV? (assuming proper fresh air intake into boiler room) and NO makeup air for small bathroom fan, oven exhaust (spring summer fall crack a window.) or drier, hwh in boiler room.

I guess fresh air's not a bad thing, depending on the price I guess.

thanks,

David