Homemade solar heater

[jeremyweber]

Hi All,

Ive been thinking about building some sort of solar heater for the last month or so, just kind of doing the math and thinking about ideas. I think the general idea I am formulating is something like the following...

Building a shallow rectangled box filled with irrigation pipe. Size of the box is unknown as of yet. Box is covered with plexiglass and sits in southern exposure. Water flows in, circulates in the pipe and comes out warm.

The questions I have are basically:

* How many btus will this thing generate if its a 4x8 foot box?
* How hot do i need to water to get when coming out of the pipe to raise the pool temp by 1 degree ( 16x32 / approximately 150000 gallons)?
* Im stumped at flow rate, so I havent considered that at all really. Any thoughts?

Other ideas I am potentially considering:

* Using a peltier chip somehow to get the water up to temp.
* Using a chiminea to heat the water.
* some sort of fresnal lense contraption ( although this sounds a bit scary )

I'd be curious to hear any thoughts suggestions. I know buying heater is much easier, efficient, etc but its out of the budget and doesnt allow me to experiment as much as a home made one would.

Thanks in advance,

Jeremy

[mas985]

Here are some rules of thumb:

Most solar panels deliver on average about 1000 BTU/Day/Sq-ft of panel. That is for a standard solar panel without insulating glass. With the glass, the efficiency is actually less during hot weather but could be more during colder weather because they do prevent heat loss but sacrifice heat gain.

The peak heat transfer is related to the solar irradiance and the efficiency of the panel. So you can get your latitude and panel tilt from here vs time of year and then multiply it by about 80% for the efficiency.

As for flow rates, most manufactures recommend about 0.1 GPM per sq-ft of panel. That makes sure that the input to output temperatures are lower than about 8 degrees to minimize the heat loss.

[Poconos]

Hi Jeremy,

With Peltier heating/cooling your electric bill and the cost of the things would put a dent in Bill Gates wealth. Joking of course but the cost and implementation would be prohibitive.

Would take a pretty big chiminea to generate enough heat.

One BTU raises 1 pound of wate r1 deg F. Therefore 15000 gal at 7.5 pounds per gallon takes about 112,000 BTU assuming no heat loss due to evaporation or other factors.

I have about a 22,000 gal IG pool and a homebew solar in the back field. Made some PVC manifolds to split the feeds for 12 100' sections of 1/2" black poly pipe layed out on about an 8x50 base made of black rolled roofing. If I remember right I think I can get 40,000 BTU/Hr from the thing. It's nowhere near the theoretical heat output because the pipes aren't spaced tightly as would be the case of a solar mat. But....it was CHEAP and I have the space and when the grass grows you can't see it.

Another source of heat is the home air conditioner. You could add a water-freon heat exchanger to capture the heat removed from the house. However, the bad part if usually when you have to cool the house the pool is already warm enough you don't need to add heat.

Sounds like you want to experiment and I can assure you it can be fun.
Al

[jeremyweber]

With Peltier heating/cooling your electric bill and the cost of the things would put a dent in Bill Gates wealth. Joking of course but the cost and implementation would be prohibitive.

Its my understanding that these chips can generate electricity by applying heat/cold on one side or the other. I was thinking about running a length of copper piping pipe on one side to draw the heat into the solar box. The other side would be in the shade... Just an idea, I am not married to it and kinda just want want to play with the chips.

I have about a 22,000 gal IG pool and a homebew solar in the back field. Made some PVC manifolds to split the feeds for 12 100' sections of 1/2" black poly pipe layed out on about an 8x50 base made of black rolled roofing. If I remember right I think I can get 40,000 BTU/Hr from the thing. It's nowhere near the theoretical heat output because the pipes aren't spaced tightly as would be the case of a solar mat. But....it was CHEAP and I have the space and when the grass grows you can't see it.

How did you measure the 40000 BTU's?

I dont have nearly as much space as you Since thats the case, I am wondering if I will need to superheat the water someway in order to get a meaningful temp increase in the pool. If so, any ideas how....

[jeremyweber]

Mas985 - thanks for providing the average btus and flow rate recommendation... Also checking out the link you provided.

[Poconos]

I haven't played with Peltier devices in a long long time but as I recall they weren't the most efficient devices in the world. I believe they're used in some solid state coolers now and in some electronics for very local cooling. Enough of that.

I have two solar things. One a 4x20' mat and the other the pipes I mentioned. Flow is split three ways. To returns, mat, and field. The mat and field have their outputs going through separate hoses I drop in the deep end so it makes it easy to measure GPM using a timer and calibrated bucket. Measure the water temp at the skimmer inlet and the temp of the water out of the hose and that's all you need. Delta F and GPM. Convert GPM to pounds per hour and multiply by delta F = BTU per hour. I'm not where my records and notes are but rethinking this the 40 KBTU was for BOTH heaters. Something like 10 GPM through each and a 4 deg rise. Haven't looked at this in more than a few years so my memory is a little cloudy....like pool water sometimes.
Al