Solar heater fan speed

[trdat]

I have a small computer fan pulling air out of the top of my collector. It is hooked to snap disk to come on at a certain temp. Is there a speed you guys suggest for this type of application?

[PNPmacnab]

Speed or temperature? Is it a 4 wire computer fan? Normally you want to control speed with temperature.

[J.P.M.]

I have a small computer fan pulling air out of the top of my collector. It is hooked to snap disk to come on at a certain temp. Is there a speed you guys suggest for this type of application?

For starters, what are the collector dimensions and what does the collector do - produce heated air/water , or electricity ?

[Mike90250]

Sounds like an air heater using a fan to move the air out.
There are two sides to the sword.
Low air movement, feels like warm air, but higher losses in the collection box from re-radiation,
High air movement, harvests more BTU's but moving air in your house feels cold.
Dammed if you do, dammed if you don't

And, the fan goes at the COLD end and blows into the box. otherwise, you roast the fan and buy new ones often

[J.P.M.]

Sounds like an air heater using a fan to move the air out.
There are two sides to the sword.
Low air movement, feels like warm air, but higher losses in the collection box from re-radiation,
High air movement, harvests more BTU's but moving air in your house feels cold.
Dammed if you do, dammed if you don't

And, the fan goes at the COLD end and blows into the box. otherwise, you roast the fan and buy new ones often

Hence my purpose in asking the questions about size and collector purpose. Sometimes folks come here and ask about keeping a PV panel cool by blowing air over/around/through it. That was not clear to me in the OP's original post. More information is needed before I'd feel comfortable or spend/waste the effort based on incorrect assumptions. That's one of the types of situation for which the Almighty created the question.

If the collector is an air cooled thermal type, and it's of any size more than a science toy, and if the "computer fan" is of a size I'm familiar with, my SWAG is it'll mostly be a waste of time, or at least very inefficient, pretty much for the reasons you cite.

To give a qualified answer the OP's question, and perhaps not quite as satisfying as the OP may want and no more than FWIW, and if this is an air cooled application, and not much more than a rough rule of thumb (those being best, depending on required accuracy, for measuring thumbs and not much else), an air cooled collector will need something like 6 - 8 ft.^3 of air per minute per ft.^2 of collector glazing area for about a 10 deg. F. temp. rise of the air, inlet/outlet with what's probably a higher pressure drop than most computer fans are designed to accommodate.

Bottom line, and at the risk of being accused of condescension, I can't answer the question the way it was asked. However, and notwithstanding the lack of information, my guess is the air mover under consideration is way too small for the collector size probably being considered. Based on the information supplied and it's quantity, my ignorance requires more information before I can make a better guess.

OP: See builitsolar.com for more info. if interested.

[trdat]

The collector is 4' wide by 8' tall. It is made out of steel studs for the frame and has galvanized metal on the inside. It works the air back and forth inside with channels. It has another layer of steel painted black on the outside. There is a poly carbonate sheet that covers the unit. I purchased the prints online and like the unit so far. Thanks for all the help guys this is my first try at solar heating. Unit is heating a small room we keep materials from freezing for work 8x10.

[PNPmacnab]

On ebay search for 12V temperature controller. There is a board you can buy for about $3 shipped. I've bought a few of them and they are an ideal controller with time delays, differentials, digital display,and other stuff with a relay output for heating or cooling. The temp sensor lead can be extended. Highly suggest you use this to get data and adjust fan operation. Nearly an ideal temp controller (if it could do F instead if C, blame Jimmy Carter).

[J.P.M.]

The collector is 4' wide by 8' tall. It is made out of steel studs for the frame and has galvanized metal on the inside. It works the air back and forth inside with channels. It has another layer of steel painted black on the outside. There is a poly carbonate sheet that covers the unit. I purchased the prints online and like the unit so far. Thanks for all the help guys this is my first try at solar heating. Unit is heating a small room we keep materials from freezing for work 8x10.

Sounds similar to some of my DIY attempts back in the day. For that size, I'd suggest considering a blower that will move about 300 CFM free air volume (before pressure drop) or maybe a bit larger. If you haven't done so yet, put a backflow damper on the outlet and keep the ducting runs to/from the room as short as possible, and insulate them - that's more important for air ducts than water piping. For winter heating applications, orient the collector toward the equator at a tilt of about your local latitude plus ~ 15 deg., maybe a bit more. Also, rig some way to throttle the flow rate and thus provide some temp. regulation, and some comfort, or at least options on temp. ranges/drafts.

Add some thermostatic control or something thing called differential thermostatic control as your familiarity of the equipment and how it works increases.

Good luck. Hope you have as much fun and learn as much as I did.

[bcroe]

Sounds similar to some of my DIY attempts back in the day. For that size, I'd suggest considering a blower that will move about 300 CFM free air volume (before pressure drop) or maybe a bit larger. If you haven't done so yet, put a backflow damper on the outlet and keep the ducting runs to/from the room as short as possible, and insulate them - that's more important for air ducts than water piping. For winter heating applications, orient the collector toward the equator at a tilt of about your local latitude plus ~ 15 deg., maybe a bit more. Also, rig some way to throttle the flow rate and thus provide some temp. regulation, and some comfort, or at least options on temp. ranges/drafts.

Add some thermostatic control or something thing called differential thermostatic control as your familiarity of the equipment and how it works increases.

Good luck. Hope you have as much fun and learn as much as I did.

I have a few 300 CFM free flow fans that operate at 28VDC or 56VDC max, with speed control. Have bird names.
They are a lot more powerful than home computer stuff. Bruce Roe

[trdat]

OK a few questions. Should the fan be pushing cold air into heater at bottom or hot air out at the top? I have a snapdisk that turns on at 110 and off at 90 for the fan is this setup ok

[trdat]

Also my runs are 4in insulated pipe and 2ft long at max at bottom and 1ft at the top

[Brian53713]

My solar space heaters fan is on the hot side but there is about 8 feet of pipe between the panel and the air exchanger blower. And is approximately 30 years old.

[inetdog]

OK a few questions. Should the fan be pushing cold air into heater at bottom or hot air out at the top? I have a snapdisk that turns on at 110 and off at 90 for the fan is this setup ok

Depends on whether you want to suck cold air in through the leaks or blow warm air out.
As noted, a fan at the cold side pushing in will run cooler.

[trdat]

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

[Brian53713]

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