Heat recovery ventilation unit 2

[camago]

Hi ,

I am designing the ventilation system for a condo building, I am using a heat recovery ventilation unit to recover the energy from the bathroom. Do you think I need to add an electric duct heater for the cold air, or is enough using the heat exchanger? Is it better to put the heater after the recovery unit?

Thanks

 

[AmanDeol]

You can put a duct heating coil after the ERV depending upon the temperature you required to raise. You can utilize any free available energy in the building through this heating coil, which I doubt in your case.

 

[Drazen]

Duct heater mostly comes after recovery, except if you have two-stage heater, where first, pre-heater has anti-freeze protection as primary function.

Otherwise, you cannot have recovery, isn't it? Heater will lower temp. difference "killing" recovery efficiency.

Actually, using bathroom heat is not something I fully grasp. Bathroom has latent heat mostly, and only on ocassional basis, while all regenerating recovery system have problems with undesired pollution transfer.

 

[ChrisConley]

Drazen:

I think you are thinking about a different form of heat recover. An HRV would be a plate type heat exchanger than recovers heat from the exhaust air stream and transfers to the incoming make-up air stream. Pollution transfer is negligible.

These are used heavily in cold climates.

http://www.venmarces.com/products/

 

[317069]

you are using HRV to exhaust from WC that mean you have small amount of cfm, you don't need duct heater(think about the operation cost not only about a fancy design)

residential HRV's is designed as per manufucturers to exhaust air from wet areas such as kitchens, bathrooms ..etc

 

[317069]

Also check with the HRV maker for the place of the unit, in condo some makers don't recomend to install unit under the bedroom of the higher floor

 

[Drazen]

Chris, I was thinking exactly about cross-plate exchanger, the most commonly used in residential application.

Pollution transfer is non-existant, but latent heat transfer as well, which renders it useless for bathroom-only application.

Normally, bathroom air is mixed with all other exhaust, so its influence is small.

Speaking of kitchen exhaust, I would never put it in there, that is even fire hazard. Some Swedish manufacturers offer residential recovery units with spigot for kitchen exhaust which bypasses exchanger, which does make sense, as grease condensation makes much more trouble than anything else, and completely different filtering is needed.

 

[camago]

Actually I have 75 CFM, I decided to put a 0.5 kw heater after the HRV to raise the temperature of the ventilation air in the winter.
Thanks 317069, do you think we can make the design without the duct heater even with -23 C in the winter?

Thanks

 

[ChrisConley]

I just reread your post again Drazen and realize where I made my error.

Have you seen/used the cross plate HX that allows latent transfer? I call it the soggy cardboard HX (which they hate) but the HX really does look like a waxed coated piece of cardboard.

http://www.lifebreath.com/en/consumer/products/residential/erv/

camago

If you are exhausting warm humid bathroom air, and replacing with -23C air you'll have to consider a defrost strategy.

For a low volume non critical application I'd recommend exhaust only defrost, but there are several ways to skin this particular cat.

 

[317069]

Thank you for your question

- My answare would be yes we can use 75 cfm without duct heater after the HRV.
- HRV usually gives up to 50F raise and after that the air will mix with the return air which is about 22C or 72F.
- if we mix a 20% fresh air(-23C)with 80% return air(22C) (even without HRV)the result would be about 13C, So with using an HRV unit it would be higher than 13C.
- what if someone open a window in the winter for one minut?

 

[Drazen]

I saw several manufacturers offer that, and indeed, they look like some biscuit on the inside, never saw it installed.

Noone talks much about pollution transfer, this "washable by water" is probably meant to be overall solution for cleanliness.

What I did not see by now is a unit designed specifically for cooling recovery.

 

[chicopee]

Heat recovery for a 75 CFM exhaust. Why bother waste of money and what doyou think will happen when moisture ladden exhaust cooler air is about to be exhausted to an ambient temperature of -23 dC. Ice up of course

 

[cry22]

Drazen,
You mention some swedich manufacturer including kitchen exhaust with general exhaust.
I would caution all in using these "fancy" european designs, most of them are conceived for their own local codes in mind AND for their own climate. Their codes and climates are Way different than ours, most of their systems are not applicable to us.
Check IMC, pantries and kitchens, etc, cannot connect to bathroom exhaust, they require their own dedicated exhaust systems.
when it comes to HVAC, I say stay away from european designs, they are not to be copied, especially when codes and life safety are involved. I just read today that it is only now that they are requiring smoke detectors in houses (by... 2015).

No ofense to Europeans of course.