I am building a new house (2000 sf and probably 30000 cf with vaulted ceilings) and want to install an exhaust fan in the attached garage. My idea is that it will get rid of welding smoke, saw dust etc.. but mainly I want it for cooling the house in the summer. Open the a window at opposite end of house, open window in the door between garage and turn on fan. I have no idea what CFM to get but was thinking about an 18" model rated at 3200 cfm. It uses a 1/3 hp motor. Can these be slowed down if to much air is moving. Can any motor be slowed with a speed control or are certain motors only designed for this. I guess I could put a smaller fan blade on to reduce flow. Thanks
If you've got decent wind, windows and draft can do a very good job without power.
Look at options for heat exchangers, and see what gets you the right number of changes of air per unit of time. I forget how many changes of air you're supposed to have per day to have good ventilation, but it's a surprisingly high number.
It also might help if you say what climate you live in.
"habbi" wrote: (clip) Can any motor be slowed with a speed control (clip) ^^^^^^^^^^^^^^^^ No. Undoubtedly, your fan will be driven by an induction motor. They do not respond to the usual speed control methods. The easiest way to reduce the volume of air would be to partially close the open windows. Think of the windows as valves.
6 changes per hour is considered about right. Don't bother fitting a sped controller. Just put a damper in the exhaust from the fan and adjust it to what you want.
I thought about that but the velocity of the air would increase creating more noise. the other option would be to bend the fan blades to reduce the pitch.
Better check the building code carefully before you put much money into this scheme. Most places want a fire-rated wall and door between the garage and living-space. They might not allow the window in the door.
If you can figure out how to pull the air from close to the top of the vaulted ceiling. The air there will be warmer. It would be really nice if you could design it so the fan will pull the air from the top of the valted ceiling and either direct it into the garage or back into the house. Then you could use it in the winter to prevent the air from stratifying and to cool the house in the summer. Blowing air into the garage will get rid of welding smoke. Probably not sawdust.
We do this at our 1300 sq ft. house, we have a 24 inch fan with two speeds, and basically use the slow speed all the time. Our fan moves air from the garage to the attic.
During the day, we open the big garage door an inch, and turn on the fan. This keeps the attic and garage cooler. The windows in the house are kept closed. When the sun goes down, we close the garage door and open the door between the garage and the house. We then open some windows in other parts of the house to cool down the house. (We live in a dry climate with typically 30 degree day-night temperature swings). In HVAC terminology, this is a night cooling system. My spouse does not really understand how to use the system to best advantage. For example, if you want to cool the bedroom, you open the bedroom windows and close all the other windows in the house. She just doesn't grasp that closing windows in one room cools another room more quickly. The airflow in the one bedroom can be pretty substantial if all the other windows are closed. I doubt if you will need to or want to slow the fan down.
The system works well for us, except on the hottest days.
As someone else said, this is almost certainly a code violation, due to the requirement of a 45 minute firewall between the attached garage and the house. As soon as you prop the door open between the garage and house you are in violation.
If you are designing a new house, build in an exhaust fan for the attic that comes on automatically whenever the attic gets hot. You can build in a separate fan between the house and the attic or the house and the outside for night cooling. If you want to automate it you will need something called a differential thermostat that compares inside and outside temperatures. (We have an inside-outside thermometer which lets us determine when to start night cooling). Then you would have a separate exhaust fan for the garage. Note that window fans will also work for night cooling of the house, but you might need more than one fan. That is the code way, and the best way to do it.
My two cents, or maybe a dime since I actually do what you say you want to do, practice being worth more than theory.
Almost forgot. We quieted the fan considerably by mounting it on foam rubber, prevented the fan vibration from transmitting noise to the rafters. Well worth the trouble.
It depends on how the motor syarts but some fan motors are speed variable by voltage reduction. If the motor has a centrifigul starting switch then you cannot lower the speed. If however, it does not then you can try supplying lower voltaand see what happens. The motor may heat up too much. But you can feel the motor and tell way before any damage can occur. ERS
As others have said, this can be a bad idea for fire reasons.
If I was doing it, I'd want to make the inlet from the house through a couple of meter conduit, with a couple of doors set to fall on 45 degree closures, at the failure of a fusible link (both doors at once) at 50C or so.
I would be more tempted to seperate out the two fans.
On Tue, 08 Feb 2005 04:16:57 GMT, Richard Ferguson vaguely proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email
Hehe! I would advise "Buy and airconditioner, then!" but my SWMBO cannot even handle that. There are all these complex bits, like louvres that actually make the air cooler near you, and controls for temperature. I just go by these days and fix it after she has turned it on. I used to tell her, and we would argue, then I would correct it, and we would argue. Now I just check it. After 5 years it's right _most_ of the time.
She is not dumb by any means. She is an uppermiddle level exective. She has degrees and left high school with good marks. But things are supposed to be there to _work_, just as they are.
I fly trick kiste ( that typo s why I don't call them stunt kites )just to relax from time to time. One time I let my mother have a go. She managed to stop pounding it into the ground, but then it got to the top of its flight and she said "What does it do now?". "Whatever you want. Pull a string gently, and it will go that way" sez I. "But what does it _do_?". The tone was one of almost panic. IT was supposed to _do_ something.
She _asked_ to use it after she had seen what it did.....
Real non-PC comment. I reckon the glass ceiling cuts both ways.
I have no doubt that my balls will not end up in my court after this!
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.