I just finished my hot air collector 32" wide 6.5' tall flows through polyester felt and I'm looking for fan and panel ideas. flow rates and such. i was planing on twin 4" fans in top duct. Any ideas?
pv fan and panel source and sizing?
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You need a CFM high enough to keep the temp in the collector down. If not, then you will lose more out the glazing and drop your collection eff and output. That is, imagine your house is 70°F, and it is 30°F outside. If you let the collector get to 110°F, you will lose 2x as much through the glazing as if you blew enough air to keep the collector close to 70°F (that is 80F across the glazing rather than 40).
Heat delivery for forced air is given by BTU/hr = 1.08 * Delta_T(°F) * CFM. Since your collector has a vertical area a little less than 2 m^2, the max power you would collect is say 1500 W. 1500 W*3.412 = 5100 BTU/hr. So, at a flow of 500 CFM, your Delta_T will be less than 10°F. 1.5 kW is likely too optimistic--I suspect a CFM of a few hundred will suffice. Running such a blower off a PV panel is likely not cost effective, but would eliminate the need for a controller or a snap disk.
The felt idea is neat, but you might look at getting some cheap 'selective emission' paint to boost eff.
Heat delivery for forced air is given by BTU/hr = 1.08 * Delta_T(°F) * CFM. Since your collector has a vertical area a little less than 2 m^2, the max power you would collect is say 1500 W. 1500 W*3.412 = 5100 BTU/hr. So, at a flow of 500 CFM, your Delta_T will be less than 10°F. 1.5 kW is likely too optimistic--I suspect a CFM of a few hundred will suffice. Running such a blower off a PV panel is likely not cost effective, but would eliminate the need for a controller or a snap disk.
The felt idea is neat, but you might look at getting some cheap 'selective emission' paint to boost eff.
Thanks both of you. i wank to put fan on top so I so mess with flap and convenient access. The duct is 4'x8' Hence the two fans. Why pv not effective? cost of panel? I could run power and snap disc, but I figured with this small collector I would not need much flow so pv would be the way to go. I am planning a much larger pannel for another part of the house, 20 something feet in length with a fan and snapdisc (90-70). would selective paint work on felt? spray on? Thanks again.
The pv panel is dealer's choice....I was just saying a payback analysis might show the pv panel to cost more than running conventional elec. Overall, though, the cost is likely to be small--I bet you can find a fan to move several hundred CFM for 5W or so, and it would eliminate a control issue AND work during a heat emergency, etc. I'd probably go that route too, and pay a little more $$.
IIRC you are blowing air through the felt? If so, it will make your fan work harder for no clear benefit. If I'm confused, and it is just a nice dark collector, then you might replace it with a spectrally selective surface.
Let's see....maybe the thurmalox paint:
http://www.solar-components.com/batchheat.htm
might be a little pricey for a small project, but worthwhile if you building a bigger panel in the future.
IIRC you are blowing air through the felt? If so, it will make your fan work harder for no clear benefit. If I'm confused, and it is just a nice dark collector, then you might replace it with a spectrally selective surface.
Let's see....maybe the thurmalox paint:
http://www.solar-components.com/batchheat.htm
might be a little pricey for a small project, but worthwhile if you building a bigger panel in the future.
I am blowing air through the felt. not sure how it will perform, I've heard of people doing this and also using furnace air filters. The idea is as the felt absorbs the heat it is instantly carried off. I also figure that since the cooler air is on the outside of the felt and the warmer air is on the inside it might reduce heat loss. this panel heats my master bath 50sf. today it is 5 degrees warmer than attached bedroom with no fan. I have no idea of how this translates to winter conditions.
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