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Posts: 37
Reply with quote  #1 
Hi, I have different requirements than most members. All I want to do is collect the excess heat in the air in a greenhouse (typically the air can get too hot from noon till 5 pm and needs to be vented) and store it in water. So the ideal heat collector/transferer for me might be very different than what you want.   So I learned yesterday that water has over 4000 times the volumetric heat capacity of air and that if you drip water down insect screen it will mostly drip down the screen to the bottom even if the screen is held at quite an angle. This probably means your screen can be angled close to  an optimum for your latitude.   So the idea might be (in my case) a little fan in the greenhouse that blows air through the screen and the water dripping at 4 inch or 8 inch intervals takes heat away to be stored in a container. Then at night when heat is needed, it radiates out and lowers the nightly dip in temperature.  I did video and the water stays going along the same route.  I think this might eventually be useful for the hydronic people too. I will run it for a few days. (The water I am running is also irrigating the plants so it is not clean).   


Posts: 37
Reply with quote  #2 
I did a quick test and today (miserable cold cloudy  damp day) it gets a 1.3 C degree rise as the water drips down. From about 8.4 C to 9.7 C  The air temp in the greenhouse is probably in the 10 or 11 degrees range and I have no idea what the solar radiation flux is.   If you imagine a liter per hour per tube at a slow setting, this is quite a hopeful result for greenhouse cooling situations.  Don't let my tiny airlift pump fool you. I use it for trickle irrigation of plants so it is tiny for a reason.  Airlift pumps are adaptable.   My old pulser pump (powered by a small stream) was pumping 3 to 4 liters per minute at 10 ft high depending on how fast the stream was running.  The stream  0.5 meter high, 300 liters per minute flow contained 0.5m by 5 l per second by 9.8 ms-2 (gravity) about 25 watts of power according to my calculations.      Thanks Brian

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Posts: 2,897
Reply with quote  #3 
Sounds like a great idea!  Any energy you can capture in the morning to use in the evening and thus use less heating fuel, is going to save you money.  Looking forward to more news on it!
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay

Posts: 243
Reply with quote  #4 
Interesting idea -- it will be interesting to see how your test comes out.

One thing to consider is that some of the water running down the screen will evaporate and the evaporation process takes a lot of heat to drive it (about 1000 BTU per lb of water evaporated)  -- this will tend to cool the water.  

Its hard to beat the simplicity of your setup, but if it turns out to be disappointing in stored heat, another option to try is an air to water heat exchanger up near the peak of the GH: http://www.builditsolar.com/Projects/Sunspace/LowCostHtStorageNathan.pdf


Posts: 37
Reply with quote  #5 
It seems to be working well.  The most I have got is about a 3 degree rise in the soil temp (about 6 inches down)    I have a playlist and a gardening group will probably put it in "field trials".  I run it day and night to see what goes wrong but it should probably be turned off at night (I think).   At night it cools the water (warms the air or radiates heat, don't know which).    I don't know how much it is acting as a solar collector and how much it is acting as an air cooler.   Time will tell.  Brian
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