Using outdoor air for cooling


  #1  
Old 07-10-13, 10:55 AM
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Question Using outdoor air for cooling

Hi, our house only has a heating furnace. During the summer more often than not the outside temperature at night is significantly lower outside than inside. What I'd like to do is use the existing system to pump outside air in much like the warm air is forced around the house during winter. Is this feasible?

Thanks,
Nick
 
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Old 07-10-13, 11:08 AM
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Why not just install a whole house fan in the ceiling and open up some windows.
That's what there made for.
 
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Old 07-10-13, 12:31 PM
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The fan on your furnace may not be the most energy efficient to run, but the approach you are suggesting is often used to meet the fresh air needs of modern homes. A duct from the return side connected to the outside will pull in that cool air and circulate it throughout the house.

However, moisture issues may come with that fresh air. There are many climate zones in CA, so you will have to judge whether the new air is acceptable. In addition, as the air is pulled in, the same amount of air needs to find its way out and that will often be through the leaks in the exterior of your home. It will carry with it the moisture from inside.

The whole house fan Joe suggested works in reverse by exhausting the inside air and pulling the outside air in through the leaks.

I'm on the other side of our country where we also enjoy cool evenings and we use a couple of window fans and open other windows as needed.

Bud
 
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Old 07-10-13, 02:02 PM
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I'd like to do is use the existing system to pump outside air in much like the warm air is forced around the house during winter. Is this feasible?
Depends- on the furnace type, and on the house layout.

Most furnaces will only to turn on the fan when the heat is running.
To have the returns and vents work without the heat being on, you may need an A/C controller addition which would allow you to circulate the air INSIDE the house. There are a few threads about that under "furnace as fan" etc. But, even if that works, since the vents and returns are INSIDE the house, you'll see no net pull of exterior air into the house.

Next, as to the house layout. I'm east coast, hot humid days, generally cool nights, 3 story masonry house with basement. I've found that having a single box fan in one attic window helps dramatically. I actually leave the fan on 24/7.

During the day, the fan pulls outside air through the uninsulated attic, preventing a buildup of heat. With one large A/C unit on the first floor you can use fans to pull the cool air throughout the house by having exhaust fans in the windows of the rooms.

You also get a bit of a "evaporative fountain effect" by allowing the hottest air to rise up the staircases and into the attic and out via fan, which takes the heat with it and passively leaves the cooler air below.

At night, just flip the fans around to bring the cooler night air into the house.
Just remember to leave a window open for each window that has a fan in it.

To use the furnace fan for cooling, you'll likely need an A/C adapter to allow the fan on independant of the furnace. You'll also need a way to bring in outside air into the furnace system.
I have occasionally run the basement furnace with the the air-filter access panel removed so that the furnace draws the air from the basement, but that was more about dealing with seasonal dampness in a basement than an attempt to cool the house.

I have thought about it, but found that the fan in the attic and A/C works reasonably well.
 
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Old 07-10-13, 11:01 PM
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Thanks for all the replies so far.

Here's so more information. The house is a single level ranch-style in San Jose, CA. I don't think humidity is much of an issue here (at least in spring/summer/fall). We do keep the windows open at night but unfortunately there isn't much of a breeze and it take a long time for the cooler air to make its way in. So the house cools down eventually but by then it's morning.

I was hoping that the forcing the outside air through the floor vents that are throughout the house and pulling the warm air from the ceiling vents would speed up the process. I would just need to make sure that the intake is from outside and the exhaust is also going outside. I don't know much about furnaces but as an engineer when I see I problem I tend to look for a solution.

Nick
 
  #6  
Old 07-11-13, 07:48 AM
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I'm guessing your furnace runs on natural gas, so the question of avoiding a back draft issue with your furnace needs to be answered. Tell us about your furnace, sealed combustion, power vent, or natural draft. Also, your water heater or any other combustion devices vented to the outside like a fireplace. When you start pressurizing or depressurizing a house you need to consider the effects on combustion and chimney draft. In some homes, even a big window fan can be an issue.

How old is the house? Does it have a traditional attic? How well is that attic insulated? Is the attic well vented to the outside, soffit vents, ridge vent, and/or gable vents.

Bud
 
 

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