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Archdemon

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Posts: 25
Reply with quote  #51 
Question bout this

Btu*h = [V x Oa x Ad x (To - Ti) x Sa] x 60
where:
V = air flow velocity from the heater/collector in linear feet per minute (measured with an anemometer)
Oa = hot air exhaust outlet area in square feet
Ad = air density at sea level and 60°F = 0.065lb/cu.ft
To = temperature of hot air exhaust in degrees Fahrenheit
Ti = temperature of cold air intake in degrees Fahrenheit
Sa = specific heat of air; the amount of energy required to heat 1lb of air 1 degree fahreneit = 0.24btu/lb-F
60 = number of minutes in an hour


Oa is that the total m2 in which the heat will cover or the limited space where the exhaust is?
Sa is this a fixed thing or something i need to figure out?

Wanna pull all of this into a db and into grafana as a display on the wall translating into numbers my wife will understand [smile]

Rick H Parker

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Reply with quote  #52 
Oa is that the total m2 in which the heat will cover or the limited space where the exhaust is?

It is the cross section of the exhaust outlet in Ft² not M². For example: the exhaust outlet is circular with a radius of 4 inches . Oa = π 4 in² = π 0.333 Ft² = 1.047 Ft².

Sa is this a fixed thing or something i need to figure out?

The specific heat of air depends on the temperature, but treating it as a constant of 0.24btu/lb-F would be close enough for what your doing. 







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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
Archdemon

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Posts: 25
Reply with quote  #53 
So a 20cm radius pipe would land at 2.0599 ft2?
If i understand that correctly [smile]
Rick H Parker

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Reply with quote  #54 
20 centimeter = 0.656 ft.
π = pi = 3.141
Area = n radius²

Units are ft.
Area in f = 3.141 * (0.656 * 0.656)
Area in f = 3.141 * .430
Area in f = 1.351
20 cm radius = area of 1.351 f

or

Area = π radius²
Area = 3.141 * (0.656 ft)²
Area = 3.141 * (0.656 ft * 0.656 ft)
Area = 3.141 * 0.656 * 0.656  ft * ft
Area = 1.351 ft * ft
Area = 1.351  ft²




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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
gbwillson

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Reply with quote  #55 
OR for a quick estimate...

BTU's/hour =
CFMx1.065xDeltaT


The spreadsheet I posted only needs the 4 orange cells filled in. The answers you are looking for are in the yellow cells. Everything else is only there to confuse you.

Greg in MN
Archdemon

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Posts: 25
Reply with quote  #56 
Next idea, how bout a hybrid?
Thought of adding cpvc pipes in it? Somehow, sure itll restricr air and an overall loss in air temp.
stmbtwle

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Reply with quote  #57 
It's an interesting idea, and a lot of us have wondered about it.

Problem I can see, you're looking a two different temperature ranges. For air you want maybe 80, for water you want 120 or so.

If you restrict the air flow to bring the temperature up, you'll lose efficiency. If you don't, the water likely won't get any warmer than the air.

You could select one or the other on demand with a switch, but I don't think you can do both at the same time.

A collector can only capture so much heat. You can divide it up, but you won't get any more. I think you'd be better served by building a second, dedicated collector.

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Willie, Tampa Bay
Archdemon

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Posts: 25
Reply with quote  #58 

Running out of space thats the problem, on the S side atleast.
Hence the idea, flipping back and forth could be automated based on parameters.

Heard of anyone tried this before?

Would be interesting to see some numbers or even try it and get some numbers.

stmbtwle

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Reply with quote  #59 
Yes you could. When the water storage gets to temp, it would switch to air, or vice versa. In warm weather you could turn off the air and heat just water. You'd probably need an Arduino or other processor to control it, I don't think snap switches would be enough.

Another option would be to build a straight hot water collector, and use the stored hot water for a space heater when needed (this works at night too). Water storage could be an issue though.

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Willie, Tampa Bay
gbwillson

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Reply with quote  #60 
Archdemon-

Like you, I have no room for a collector on the South side of my house. My collectors have to be moved seasonally. They are on the East and West sides of the house, even with the South side as possible, so the house itself doesn't cast a shadow on the collector. It does make the far end of the collector farther away from the house than I'd like. But I still have no problem collecting lots of heat even with the long duct run.

Greg in MN
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