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JBF
09-08-2006, 09:55 AM
Has anyone considered ducting the output of the condenser exhaust into the attic?

I understand the temperature of the condenser exhaust is several degrees above the ambient temperature.

The temperature of the condenser exhaust is many degrees cooler than the temperature of an unventilated attic.

It is almost free and much better than nothing....

I live in Texas where attic temperatures exceed 140 degrees F in the summer. 110 degree air is cool compared to what I have otherwise.

[Edited by JBF on 09-08-2006 at 10:02 AM]

dash
09-08-2006, 10:29 AM
The blades used on outdoor units,will move the correct amount of air,if you try to connect a "duct".To be ducted the fan and motor would need to be changed,and operating cost would increase.

09-08-2006, 10:34 AM

HeyBob
09-08-2006, 10:36 AM
How about some attic vent fans? What you want to do is a real bad idea.

JBF
09-08-2006, 10:38 AM
I bought a foil/spun-bonded-polyolefin/foil radiant barrier that I stapled to the underside of my rafters. That helped a lot. My attic looks like a mirror now.

I did my whole attic for less than \$300.00 (1500 ft^2).

JBF
09-08-2006, 10:51 AM
Originally posted by dash
The blades used on outdoor units,will move the correct amount of air,if you try to connect a "duct".To be ducted the fan and motor would need to be changed,and operating cost would increase.

That makes sense. The fan and the pitch of the blades of the fan are designed for a given back pressure. My point is: if you combined the two functions, the the energy cost of the combined functions would be less than the cost of the individual functions of the condenser plus attic fan.

I am looking at the problem from a systems point of view.

The functions should be integrated.

troyorr
09-08-2006, 11:16 AM
JBF, there seems to be a small hole in your logic. Your condenser is built to operate in an approximately 95 degree environment. The 110 degree air you referrence is in relation to this. When you expose the condensing unit to the 140 degree attic temperature, which is pulled through the condenser coil for cooling, your discharge temperature will increase accordingly. You will experience higher than normal head pressure and possibly have a unit that will cycle off on high temperatures. Use attic exhaust fans.

JBF
09-08-2006, 11:45 AM
Originally posted by JBF

Originally posted by dash
The blades used on outdoor units,will move the correct amount of air,if you try to connect a "duct".To be ducted the fan and motor would need to be changed,and operating cost would increase.

That makes sense. The fan and the pitch of the blades of the fan are designed for a given back pressure. My point is: if you combined the two functions, the the energy cost of the combined functions would be less than the cost of the individual functions of the condenser plus attic fan.

I am looking at the problem from a systems point of view.

The functions should be integrated.

You could put the condenser in the attic but you would want to pull air from the outside for the condenser and exhaust that air into the attic. In no way would you want to use 140F air to cool the Freon in the condenser.

You might be able to put the condenser in the attic, but you would have to use outside air, otherwise the functions would not work synergistically.

JBF
09-08-2006, 11:51 AM
The condenser is moving a lot of air. The vast majority of the condensers in this world accomplish nothing with their exhaust.

MAKE IT DO SOMETHING. USE IT TWICE. IT IS ALMOST FREE.

docholiday
09-08-2006, 11:52 AM
Originally posted by dash
The blades used on outdoor units,will move the correct amount of air,if you try to connect a "duct".To be ducted the fan and motor would need to be changed,and operating cost would increase.

As dash said, propellar type fans are not designed to offer much in the way of ability to overcome static. For this reason we use blower wheels when ducting is involved. If an attic is a problem, ventilate it, insulate the cieling and the ductwork. A radiant barrier is also a good idea.

I can appricate thinking "outside the box" and kudos for that, but it's probably best to know whats inside the box before you start working on things outside the box.

JBF
09-08-2006, 12:10 PM
If I was going to design a condenser, I would put it in the attic. I would use outside air to chill the coolant, and I would exhaust the air into the attic.

The condenser would be more difficult to install and to service. I agree.

I would bet that the long-term benefit would be phenominal.

The condenser would be far from vegetation, dog pee, hail, hot near-ground air, baseballs and other toys, weedwhackers, and God-knows what else.

And the exhaust air could push that hot attic air out of whatever vents there are.

paul42
09-08-2006, 12:24 PM
From an engineering point of view, your idea makes sense. Froma practical point of view, problems arise.

Very few homes have a good seal between the attic and the house. There are just too many penetrations and unless you have a very unusual house, they are not well sealed. So, running the air from the condensor into the attic would presurise the attic, which would force hot attic air into the house.

You are better off to foam the inside of the roof, and remove all vents from the attic. It is much easier to seal off everything at the roof line that it is at the ceiling.

JBF
09-08-2006, 12:35 PM
Originally posted by paul42
From an engineering point of view, your idea makes sense. Froma practical point of view, problems arise.

Very few homes have a good seal between the attic and the house. There are just too many penetrations and unless you have a very unusual house, they are not well sealed. So, running the air from the condenser into the attic would pressurize the attic, which would force hot attic air into the house.

You are better off to foam the inside of the roof, and remove all vents from the attic. It is much easier to seal off everything at the roof line that it is at the ceiling.

God knows foam is wonderful. I would kill for foam insulation in my attic. If you have good eave, soffit, and ridge/turbine vents, you shouldn't have to worry about attic pressurization. Overpressure might even reduce the leakage from the ducts in your attic. Let us hope that is not the case.

Gunnery Sergeant Hartman
09-08-2006, 12:44 PM
Originally posted by JBF

Originally posted by paul42
From an engineering point of view, your idea makes sense. Froma practical point of view, problems arise.

Very few homes have a good seal between the attic and the house. There are just too many penetrations and unless you have a very unusual house, they are not well sealed. So, running the air from the condenser into the attic would pressurize the attic, which would force hot attic air into the house.

You are better off to foam the inside of the roof, and remove all vents from the attic. It is much easier to seal off everything at the roof line that it is at the ceiling.

God knows foam is wonderful. I would kill for foam insulation in my attic. If you have good eave, soffit, and ridge/turbine vents, you shouldn't have to worry about attic pressurization. Overpressure might even reduce the leakage from the ducts in your attic. Let us hope that is not the case.

Sounds like you should present your idea to the different manufacturer's since it is so good.