(06-02-2020, 09:43 AM)Wild Turkey Wrote: [ -> ]LOML wants a whole-house fan for those days when it's very pleasant outside but no wind -- we have quite a few days like that -- or when Fescue cooks something and fills house with smoke or pepper fog
I'm having a hard time choosing between direct and belt drive. Belt drives will eventually need maintainence but I'm afraid a direct drive will burn out the motor.
Anyone with much experience?
I've had a number of whole house fans. My last house was the best with a 36" Chelsea panel fan, which hung on chains on springs with a cloth plenum to the outside wall. It had a single-speed motor, but I replaced it with a 3-speed (which is now in my air filter in the basement
). Normal rated speed was only 400 rpm, so it was very quiet. The motor I put on was 1800/1200/900 rpm, and at 200 rpm fan speed you couldn't hear it run at all, and it was in the gable end of the house right over my head in the attic and pulled a nice gentle breeze through all the upstairs windows for sleeping.
One big advantage of belt-driven designs is that you can change max speed simply by changing sheaves. For a fan like that, cheap die-cast sheaves are fine. If you go that way, get a 2-speed model, as it'll have an 1800/1200 rpm induction motor (super common), and running at 2/3 speed is a lot quieter than at full speed. But you can always slow it even more with a sheave change.
I'm guessing you're considering putting it into an upstairs hall ceiling. Mine was in the gable wall, so it had two shutters. I added a shutter motor to the outside wall shutter, and the ceiling shutter already had one. If mounting the fan in the ceiling, you probably won't need a shutter motor unless you slow the fan down to where it can't pull it open.
I have pics of the installation somewhere but can't find it right now. Below is some generic pic of the same unit, and my old house with the shutter visible.
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If you do ceiling mount it, the blades will made a good bit of noise simply because they're close to the shutter. You can quiet it down by either building a chimney to raise it up, or better, a right-angle duct elbow (out of plywood) and mounting it so the shaft is horizontal. It'll be much farther from the shutter, and you can use some interior duct insulation to dampen some noise. If you have the room, mounting it another 8 ft away at the end of a big square duct (since it's plywood) would be even better. And use resilient mounts, as the sound will travel through the structure.
Speaking in general terms, for the same air flow, larger and slower is quieter than smaller and faster. And by the affinity laws (aka 'fan laws' or 'pump laws'), the air flow varies with the speed, the sound generated varies as the square of the speed, and the power required varies with the cube of the speed. So if quiet is a primary concern, get a large one and slow it down if it's too loud.