Crazy Kitchen Hoods

[khc]

Help ! Suggestion or idea appreciated.
6500sqft house with 2 wood chimmenys with 80,000btu gas logs and get this one 1200cfm kitchen hood. New house so tight construction. Between an engineer and the wholesaler they designed a system using an air handler and electic heater in the attic. Had the ductwork design and install according to cfm and place outlets in the rooms where the chimmeys are and of course the kichen. Last thing to do was hang the air handler and install motorized damper.Reading instruction with airhandler air coming into cannot be less than 65F otherwise condenstation will form on electric coil (buzz). I am in Canada and temp gets considerably less than 65F.

Thanks

[vern p]

Check with the designer of the system. Maybe you are supposed to install that electric heater ahead of the air handler to keep that temp up above 65.

[Carnak]

Originally posted by khc
Help ! Suggestion or idea appreciated.
Reading instruction with airhandler air coming into cannot be less than 65F otherwise condenstation will form on electric coil (buzz). I am in Canada and temp gets considerably less than 65F.

Thanks

Do you have a make and model number of this air handler?

[khc]

The unit is made by Unitary Products Group (york) and the I beleive is a N1AH is an airhandler with the option of add on electric coils. I contacted the Manufacture directly and the issue is that when cold air (0F) hits a 20kilowatt heater it will create condensation on the coils and cause them to shortout. Which to me seems a real possibility..

[Carnak]

Are you trying to use this as a heated make up air system?

I am confused now you are saying 0F and before it was 65F.

Are you using this 20 kw residential system as make up air heater for 1200 CFM?

Maybe keep the blower and get an electric coil by thermolec. They may have a releatively inexpensive SCR controller?

What is the design outdoor air temp?

What do you want it to discharge at?

20 kW will heat that air by almost 53 degrees.

What's up with the gas logs?

[khc]

I am bringing fresh air from the outside that could be a low as 0F or as hot as 90F. The information I got from the manufacture was that when the cold air coming from outside will hit the electic coil and condense on them. We are trying to get the temp to be as close to room temp as possible to avoid cold or draty spots in the house when returning the fresh air. The gas logs are in the masonary chimmenys which have the dampers welded 60 percent open.

[khc]

src controller ?

[Carnak]

The SCR is a solid state controller that modulates the electric heat. It turns the heat on and off many times to maintain a discharge air set point. You set the discharge temperature you want and it will not use any more electric than necessary to heat that air.

Thermolec in Quebec makes a lot of duct heaters for make up air, using a residential furnace sounds like a bad idea to me.

With 20 kW you will be able to heat that 1200 CFM up by 53 degrees F (with a little help from the fan/blower). So if it is 0F entering its going to be supplied at 53F. Not going to freeze water lines but will feel drafty. 25 kw will heat that air up by about 66 degrees. Thermolec could make you 26.6 kW one to give you a 70F rise. With the SCR, you would always have 70F coming out as long as the air was not colder than what it was designed for.

I can see a ski chalet at a fancy resort having these logs, but I think they are a bad idea for a house. Obviously the owners have money if they have a 6500 square foot home. Not even sure if they have direct vent inserts or how 'big' they are. It has been 7 years since I did anything with a gas fireplace, but a lot of guys in the fireplace forum may know.

How does combustion air get to these gas logs?

What actually heats this big shack?

I would make sure my a$$ was covered on this one if I were you. Get that engineer to stamp some design drawings.

[khc]

Combustion air is coming from the air inside the house !! There is three forced air furnaces, one each floor. The basement is a seperate area as it is all fire rated and gas proof. There is a garage door and car lift for the owner to store his antique cars in the basement. So the basement is also equiped with co2 sensors which are interlocked with 2 20" prop fans and also the garage door for make up air. You know your average house !!!!

What about condensation on the electric coils? Is this a real possibility?

[pstu]

If anyone could explain how condensation is possible on electric heating coils, that would be most enlightening.

I am just recently learning the basics of psychrometrics but think I understand the principles. It would seem to me condensation could only occur when the coils are below ambient temperature, and that any heating whatsoever would make this impossible. But perhaps I am missing something basic. I do understand that Carnak has both education and long experience that is very relevant to the question at hand. I don't want to overlook the other gurus on this board, but it's clear to me he has been a major help to the rest of us.

Best wishes -- P.Student

[Edited by perpetual_student on 01-21-2005 at 09:51 AM]

[Carnak]

The york residential air handler with electric heat option is not made to be a 100% outside air unit. They publish limits of 57-72F wb and 65-95 db, to define the limits of entering air to electric heat, cooling coils and condensing units. Sounds like a vague all encompassing weasel clause disclaimer to me.

The only condensation scenario I can see is as follows.

The unit is up in a cold attic and has been off for a while. Even with a tightly sealed outside air damper, with down time, that air handler will be cold inside. The air handler will cool down, heat will conduct out of it.

Without a tightly sealed damper in the supply, Warm, relatively humid air will 'want' to rise up into the duct work when the system was off. Just like a leaky pot light the warm air would have a path out as the cabinets on that air handler are not well sealed, neither is the cover where the filter etc would be, electrical knockouts etc.

So relatively humid air would condense on all cold surfaces including the electric coil.

Just rationalizing out something to come up with how condensation could happen. There are many electric make up air heaters out there.

The only other thing I could think of would be horfrost, but I would expect that at an air intake inlet.

The condensation issue to me sounds like they are indirectly telling you that the operating conditions will void any warranty.

[Carnak]

If the system recirculated some return air to mix with the outside air and then heated it, there would be some moisture available to condense on the heating elements on start up, before they heated.

Flame rods on gas fired units ice up.

[Carnak]

Originally posted by khc
Combustion air is coming from the air inside the house !! There is three forced air furnaces, one each floor. The basement is a seperate area as it is all fire rated and gas proof. There is a garage door and car lift for the owner to store his antique cars in the basement. So the basement is also equiped with co2 sensors which are interlocked with 2 20" prop fans and also the garage door for make up air. You know your average house !!!!

What about condensation on the electric coils? Is this a real possibility?

That's quite the shack! Some rich guy in TO?

I hope that engineer has dealt with all the combustion air.

[khc]

Burlington Lakeshore not far from T.O.

Make-up was designed by heatloss duct designer with the co-operation of a mecahical engineer. But NO stamp !!!! Makes me nervous right there. Thanks for all the help and info thinkk I am on the right track now.

[DocHVAC]

Ditch the electric make up air and go with a water coil and a continous water heater.

[khc]

will the hot water have the ability to give that great of a temperature rise, and if so how would you modulate the output with the outdoor temperature? I guess you would have to use a glycol brine solution ?

[Carnak]

Glycol, with a mixing valve or outdoor reset

[Edited by Carnak on 01-22-2005 at 10:21 PM]

[khc]

Is possible to get a 70F temp rise out of a water coil ?

[Carnak]

Yes,

Call Engineered Air

[khc]

Do you know where they operate out of , would like to talk to them and see what they could offer. Thanks for all your help.

[Carnak]

Head Office is in Calgary, here is a link to some sales offices

http://www.engineeredair.com/locations.asp?RegionID=2

[khc]

Turns out they have an office 20 mins away from me. Thanks for your help..

[Carnak]

You're welcome, they will probably try to sell you an expensive air handler too.

I used to work for them in a previous life :)