Hot Air Collectors

Hot Air solar collectors can be used to supplement the heating requirements of a house in a cold climate. As long as the house is well insulated and one side of the house has adequate sunlight exposure a home made solar hot air heating system could be a good investment. The price of oil will continue to rise, but the wise use of sunlight energy may be used to reduce the consumption fossil fuel concentrates. Hydronic solar collectors have the advantage of supplying heat and hot water all year long, but the simplicity of hot air collectors has a special appeal to home owners with limited time for projects. Hot air collectors do not require storage tanks to store heat or radiant floors to distribute heat. Instead household furnishings and interior walls are used to store daytime solar heat and release it gradually at night.



"Pop Can Collectors" have become a bit of a fad. They look cool and I do believe they provide an excellent "double green" method of recycling, and if you're patient and keep saving those cans you may decide to build one. They are very portable and they may be attached to the south side of a house to collect solar heat and pump that heat into a house with the help of a fan.   

An alternative to the pop-can collector is the aluminum flashing collector. Notice how the aluminum is bent like an accordion. This is done to increase the surface area of the aluminum in contact with the air that's blown through it. 

Aluminum soffits and aluminum screens may also be used to transform light into heat. 

In the video below I'll be passing air through a sheet of polyester felt to collect  heat. 


Data Analysis: T1 is the temperature of air at the top of the heat storage chamber and T2 is the temperature of air toward the bottom of the heat storage chamber. When the fan is off T1 reaches 135*F by 3:30PM and T2 remains at 50*F. This is what we would expect since heated air from the collector in not circulating through the heat storage chamber. After the fan comes on the T1 (temperature of air from collector) drops and T2( temperature of air returning to collector ) increases. By 4 PM the the temperature differential between incoming and outgoing air stabilizes at 22*F. This differential temperature is used to measure the heat gain of the collector. To estimate the efficiency of heat collection we will need to know: the vertical sunlight intensity at 4 PM, the surface area of the glazing surface and the flow rate of the circulated air. 

GLAZING SURFACE                        7 sq ft
FLOW RATE OF FAN                    20 CFM
SOLAR FLUX                                200 BTU/sq ft
MASS OF AIR (m)                        .075 lbs/ft^3
Qc   =    heat gain/hr  from collector
Qs    =    heat energy available from sunlight  ( assumption 200 BTU/sq ft)
Qc    =    20 CFM    x    60 min    x     .075lbs./ft^3    x    .24 BTU/*F    x    (T1-T2)
Qc    =    475 BTU/hr

Qs    =    200BTU/sq ft     x    7 sq ft.             =            1,400 BTU/hr
Efficiency    =    Qc/Qs    =    475/1400        =             34%

* This is the basic method of estimating efficiency of a solar hot air collector... The flow rate of the fan and the estimated solar energy available is only an estimate. This hot air collector is experimental. If you decide to build one please let me know what you discover. One feature that I have not explored is the filtering capacity of the felt. I was thinking it would be nice to design the felt absorber so that it may be removed and washed every three years.. This would be an nice way of keeping household air clean. Thank you for your interest in the polyester felt solar hot air collector. 


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