Solar heater fan speed

[J.P.M.]

In general, the cold air returning from the space should enter at the lower end of the air cooled collector and exit at the opposite side of the top of the collector.

The blower is usually at the inlet end of the collector meaning a slightly higher mass volume of air will be passed due to a lower air temp./higher air density at the inlet.

More importantly, the blower will see a lower air temp. Under normal operation, and depending on the design, this probably won't matter much given a delta T for inlet/outlet of 20-30 deg. F. or so, just a consideration of perhaps better design. Bottom inlet is also sometimes easier to design for with respect to support considerations.

However, if, for some reason, the power fails/someone forgets something, or some restriction causes the flowrate to drop and temps. go up, the situation with the blower at the top could possibly harm the blower due to elevated temps., particularly on startup under stagnation conditions of high irradiance and no flow. It will happen. Plan for it.

The Blower at inlet configuration does mean that the collector will be operating at a slight positive pressure with respect to the atmosphere, and as Inetdog notes, leaks, or poor collector envelope integrity will reduce how much of the heated flow gets to the dwelling as f(system leaks), not blower location, which will only change the direction of the leak as f(pressure differential). Having built several similar type air cooled collectors back in the '70's, one of which could be disassembled/reassembled for changeout of absorbers and glazing configurations, I found that collector air leaks are easy to spot and seal, often discovered with a good ear and/or some plastic wrap if it's not too windy.

[bcroe]

Found a couple new Maltese Falcon 300 CFM fans, looking for a home. Bruce

[J.P.M.]

Or if your using solar-powered fans put them on both openings.

Mostly a waste of fan power.

[Brian53713]

They may not have been playing in God's country, but they were certainly looked out for .
GO PACKERS !! My 30 year old solar space heater, has the fan on the hot side because there's at least 8 maybe 18 feet of insulated pipe going to the outlet of a 16 foot wide 4 foot tall two pieces of glass collector which blows into 1st floor main level living space and pulls it from the upper Second Story Cape Cod 2nd story .

[J.P.M.]

The fan I have is inside the building pushing the hot air out not in the box outside. If you guys think it would benefit being at the bottom let me know. I'm new to all of this

It probably shouldn't be IN the collector anyway. Just pay attention to the duct sealing and everything else that the air passes through for that matter. And - Do NOT use cloth duct tape. It won't last. get a roll of 2" wide or so paper backed aluminum tape w/ adhesive on the back side. It has little structural use but that's not what it's for. Used outside, I've had some in place and exposed to the elements, including sunlight for 8+ yrs. and still going strong and leak tight.

[trdat]

I have the inlet at the bottom of the wall and outlet near the top. So from what I'm getting I should move the fan to the bottom pushing cold air in. Any other tips or suggestions guys this helps a ton

[trdat]

This is the heater

[J.P.M.]

This is the heater

Looks pretty standard. Is there a data sheet for it ?

[trdat]

Not sure what you mean by data sheet. All there was was instructions to build. No heat output or anything

[J.P.M.]

I have the inlet at the bottom of the wall and outlet near the top. So from what I'm getting I should move the fan to the bottom pushing cold air in. Any other tips or suggestions guys this helps a ton

Provided the system is reasonably tight, meaning the collector and the ducting to/from it, including transitions at wall and collector attachments, the likely place to put the blower is either at the collector inlet (preferable, provided that location is out of the weather, and maybe not possible or practical, depending on exposure to cold/the elements) or where it will be pumping the cold(er) air - so, as you say, pushing the cold air "in" to the collector from the house interior. Or, a third location, again, depending on exposure to the elements, perhaps on the outside of the dwelling wall to perhaps help keep the noise to the inside of the dwelling down. A lot of times, pumps/blowers don't care much for low ambient temps. any more than very high temps.

Regardless of where the blower is located, the flow to the collector should be from the coldest part of the room, and that's probably near the floor. That inlet from the house to the collector should most probably be at the lower end of the collector., with the outlet at the top on the opposite side, but in any case always follow instructions from the manufacturer.

Put a damper on the high wall penetration (the return from the collector) to help prevent thermosiphoning and seal it with some foam weatherstripping.

An aside on dampers: I had a 12" penetration high on the wall from my sunspace to the house I retrofitted in Buffalo and a 2' thk. rigid foam damper that was gravity controlled and light enough that it didn't impede air flow (too much) when a thermostat in the sunspace called for a 1000 CFM blower ( that pumped probably ~ 800 CFM after pressure drop losses) to fire up and blow air from the cold air return in the house into the sunspace. The damper worked great. The blower was a bit noisy, but no one was home during the day except 2 cats.

[LucMan]

The proper fan would be a centrifugal type blower that would be able to over come the high static of the panel. A propeller type fan is not meant to be used in a high static system such as a solar panel.
A fan rated for approximately 100-200 cfm at 1.5 inch static should do the job. Use a manual rheostat in series with the wiring to adjust your speed to 10-15 degree delta T.

something like this http://www.ebay.com/p/Fasco-B24220-1...wer/1000494412

[bcroe]

A centrifugal fan will tend to be quieter for a give ap. Ac fans can be more of a problem, but DC fans don't
have to have a hot inefficient rheostat for speed control. Many have a control input, or a buck converter
can be used to efficiently vary the DC voltage. I used this method for a set of 27VDC 300CFM axial fans
on a 48V nominal TelCo battery. Bruce Roe

[trdat]

I didnt know something like Lucman suggested would work. I thought it would cool the air to quickly. I bought a 4in inline fan thats 90 cfm. Do you guys think this is ok or should i go something way bigger like Lucman. Also can you guys show me a pic of your damper system. The fan i have wouldnt push out enough iar to move a damper i dont think. Thanks again guys

[LucMan]

If the fan you have uses a centrifugal blower wheel try it, 90 cfm is close enough. As far as the damper goes you can use a piece of aluminum step flashing cut to size attached to a piece of coat hanger 1/4 of the way from the top to make the hinge. If you are using 4" pipe for your connection stick the coathanger end through 2 holes you drill in the pipe to make the damper swing down when the fan is off, and up out of the way when the fan is running.

[J.P.M.]

If the fan you have uses a centrifugal blower wheel try it, 90 cfm is close enough. As far as the damper goes you can use a piece of aluminum step flashing cut to size attached to a piece of coat hanger 1/4 of the way from the top to make the hinge. If you are using 4" pipe for your connection stick the coathanger end through 2 holes you drill in the pipe to make the damper swing down when the fan is off, and up out of the way when the fan is running.

FWIW, I used a dryer outlet vent with an aluminum flapper on it. As I seem to recall from the late '70's, pressure drop/flow rate decrease seemed reasonable and not very noticeable to a good eyeball and a wet finger, or produce any decrease in flow rate as indicated by no noticeable change in the in/out delta T of the air through the collector.