hot water coil in unconditioned space

steve novak

I am putting a hot water coil into a attic that is not heated. I wanted some opions on what to do to keep it from freezing. I was going to put a T stat in the attic and if it went below 32 degrees kick the pump on the let water circulate but I think that it would be on for most of the winter. My other though was to install a small heat exchanger and glycol the system. If the exchanger is the way to go then does anyone have any manufactures that they can recommend.

ed wallace

water coil

why use a heat exchanger just add glycol to the system

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Mark Hunt

HX


Flat Plate.

Better idea.

Mark H

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Constantin

Glycol does the trick but consider insulation

However, glycol is somewhat expensive and has some side effects regarding thermal efficiency, IIRC.

Depending on where you live, you may consider having someone come in and insulate the space between rafters with foam insulation. Not the least expensive solution, but it should raise the temps in that space and it will give you additional space in the house. See the attached PDF from Building Sciences for a house they did in Portland, ME.

I would encourage everyone to take a look at the Building Science Corporation web site that I got the above PDF from. BSC exemplify the original spirit of the web by publishing a lot of information for free, without banner ads, etc. If I were building a new house, I'd follow their guidelines to a T and/or hire them to safely maximize efficieny and comfort within the structure.

Robert O'Connor_3

Agree on insulation

Even with a dark shingle roof, an attic will warm above freezing durring the day. Probably circulation would only be needed at night and in severe cold, but the hydrocoil would have to have to be cycling frequently anyway. Loss of power durring the winter might be the only concern.

Ed_13

Coil in unheated attic.

> I am putting a hot water coil into a attic that

> is not heated. I wanted some opions on what to

> do to keep it from freezing. I was going to put

> a T stat in the attic and if it went below 32

> degrees kick the pump on the let water circulate

> but I think that it would be on for most of the

> winter. My other though was to install a small

> heat exchanger and glycol the system. If the

> exchanger is the way to go then does anyone have

> any manufactures that they can recommend.

Ed_13

Coil in unheated attic.

Steve,

Remember not to oversize the coil. If it is too large the coil will heat the conditioned space quickly, and the pump will shut off stopping the circulation throught he coil. It will have longer off cycles which would expose it to the cold temperatures longer.

If you have a no heat problem, the coil would be the first casualty. I think that glycol is a good option, then you wont have any chance of freezing.

If you are still concerned about it you could change the controls to run the pump for the coil constantly when the COIL temperature (not attic temp) gets below 35 degrees, and cycle the fan as a function of the room stat.

You would waste a little heat if the coil cabinet is not well insulated, however, with the fluid in motion you will never freeze the coil or feed pipes.

Good Luck
Ed Carey

Ed_13

Coil in unheated attic.

Steve,

Remember not to oversize the coil. If it is too large the coil will heat the conditioned space quickly, and the pump will shut off stopping the circulation through he coil. It will have longer off cycles, which would expose it to the cold temperatures longer.

If you have a no heat problem, the coil would be the first casualty. I think that glycol is a good option, and then you will not have any chance of freezing.

If you are still concerned about it, you could change the controls to run the pump for the coil constantly when the COIL temperature (not attic temp) gets below 35 degrees, and cycle the fan as a function of the room stat.

You would waste a little heat if the coil cabinet is not well insulated and if the system is prone to long off cycles of the AHU, however, with the fluid in motion you will never freeze the coil or feed pipes. If it not prone to long off cycles, (conditioned space only used intermittently), then the coil temp control would only act a freeze stat protection for the coil.

Good Luck
Ed Carey

Ed_13

Coil in unheated attic.

Steve,

Remember not to oversize the coil. If it is too large the coil will heat the conditioned space quickly, and the pump will shut off stopping the circulation through he coil. It will have longer off cycles, which would expose it to the cold temperatures longer.

If you have a no heat problem in the building, the coil would be the first casualty. I think that glycol is a good option, and then you will not have any chance of freezing.

If you are still concerned about it, you could change the controls to run the pump for the coil constantly when the COIL temperature (not attic temp) gets below 35 degrees, and cycle the fan as a function of the room stat.

You would waste a little heat if the coil cabinet is not well insulated and if the system is prone to long off cycles of the AHU, however, with the fluid in motion you will never freeze the coil or feed pipes.

If it not prone to long off cycles and the conditioned space is constantly heated in the winter, then the coil temp control would only act a freeze stat protection for the coil. The AHU would probably cycle enough that the coil would usually be warm.

Good Luck

Ed Carey

Al Letellier

attic coil

It may be a given to you, but just in case....which ever way you go, make sure the unit has a self.contained drain or pan to collect the leak when it happens. Use anti-freeze and a plate exhanger for best protection.

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Rudy

No problems so far....

Steve, I put an air handler in my attic about 14 years ago, piped to an oil fired hot water tank. I insulated the cabinet and piping and have had no problems with it freezing - been down to -20 here several times since.

I've noticed that the copper line going to it is always warm whether the pump is running or not so I'm assumed there is a thermosyphoning effect going on.

There are ALOT of things I plan on changing (flat plate, drain pan, priority flow switch, etc) but worring about freeze protection hasn't been a concern.

Bob Murray

Flat plate oversized to about 120% of demand and glycol that side of system. We all know what putting glycol in the whole system can do...don't we...

Ed_13

attic coil

Don't forget to consider a prolonged power outage. Depending where you live a bad ice storm could mean no power for days. No power - no circulation