DIY GAS WATER HEATER

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calivette2003

0
Sep 11, 2010
31
San Diego
Re: DIY Solar heater questions

Last summer I installed two 500' coils on the roof last summer and on average got an 8 degree return in pool temp for a 12x24 above ground Intex. Never got over 72 degrees, but it was a cold summer here in Southern California. I have a new plan (in addition to the coils) and can scan attach the free-hand diagram if needed.
So how about if I use the existing solar coil inlet (connected off the main pool pump outlet to the auxiliary 1HP "coil" pump, to a 40', 1.5" underground PVC pipe going to the crawlspace under the house, where, an 80 gallon auxiliary water heater would be placed (right next to the existing house water heater) I then fabricate all appropriate gas connections and then run the water heater outlet PVC line back to the existing coil return line (pool pump return)
*note coil will be isolated by ball valves in this mode.
So when Mother Nature is not working with me I can AUGEMENT the solar energy with a natural gas heat source. No different than the $3000 professional gas heaters used for underground pools but 1/6th the cost. Natural gas is cheap and if the water heater was set for say 110 degrees, 80 gallons of 110 degree water would definitely raise the water temp of a small 8000+ gallon pool that is say 72 degrees. The water heater is designed for a pressurized water system so an inlet check valve and spring loaded pressure unloading outlet valve is required. Water heaters take time to heat the water in it so I would run this for say 15-20 minutes daily to cycle the hot water out, refill with cold pool then shut it down. The gas expense should be negligible, as it is used sparingly and the pilot light is pennies on the dollar. Estimated cost of entire system (with a used water heater $250-300).

This should augment the solar coils nicely, especially when I put up the pool again this summer and fill it with frigid water off the hose tap.

Your thoughts?
 
Posts merged. Please only ask a question in one place and never in someone else's topic. JasonLion

Last summer I installed two 500' coils on the roof last summer and on average got an 8 degree return in pool temp for a 12x24 above ground Intex. Never got over 72 degrees, but it was a cold summer here in Southern California. I have a new plan (in addition to the coils) and can scan attach the free-hand diagram if needed.
So how about if I use the existing solar coil inlet (connected off the main pool pump outlet to the auxiliary 1HP "coil" pump, to a 40', 1.5" underground PVC pipe going to the crawlspace under the house, where, an 80 gallon auxiliary water heater would be placed (right next to the existing house water heater) I then fabricate all appropriate gas connections and then run the water heater outlet PVC line back to the existing coil return line (pool pump return)
*note coil will be isolated by ball valves in this mode.
So when Mother Nature is not working with me I can AUGEMENT the solar energy with a natural gas heat source. No different than the $3000 professional gas heaters used for underground pools but 1/6th the cost. Natural gas is cheap and if the water heater was set for say 110 degrees, 80 gallons of 110 degree water would definitely raise the water temp of a small 8000+ gallon pool that is say 72 degrees. The water heater is designed for a pressurized water system so an inlet check valve and spring loaded pressure unloading outlet valve is required. Water heaters take time to heat the water in it so I would run this for say 15-20 minutes daily to cycle the hot water out, refill with cold pool then shut it down. The gas expense should be negligible, as it is used sparingly and the pilot light is pennies on the dollar. Estimated cost of entire system (with a used water heater $250-300).

This should augment the solar coils nicely, especially when I put up the pool again this summer and fill it with frigid water off the hose tap.

Your thoughts?
 
Adding 80 gallons of 110 degree water to 8000 gallons of 72 degree water will result in a water temperature of 72.38, at least under ideal conditions.

Swimming pools need huge amounts of heat, probably a couple of times as much as your entire house uses in the winter. A fairly large water heater might be 40,000 BTU, while the typical swimming pool heater is 200,000 to 400,000 BTU.

Another thing to keep in mind is that total heat is temperature increase times flow rate, while efficiency is higher at lower temperature increases. A large temperature increase at a low flow rate tends to be inefficient and doesn't provide much heat. Very small temperature increases, say 1 degree, at very high flow rates are much more efficient.
 
Interesting idea, I thought about doing something like this with my 50gal gas hot water heater and a water-to-water heat exchanger (transfers heat but keeps the domestic water separate from the pool water) I would have to run about 50 each way and insulate the pipes. Then I found out it takes days for a 200k-400k BTU pool heater to raise the pool 20 deg. when I looked at my hotwater heaers BTU rating I see why it would be just too low of an output for my 20k pool. THat also explains why the pool heaters are such fuel hogs. SO I started looking into evacuated tube solar collectors and how to build them out of PVC. They will heat even in the winter and under snow! DOn't know that a home made would be that effecient but would be cool. I Have one proto type half built.
I like your idea still, so I'd say change the tank to a tankless that can generate hot water on the fly contitiously and definatly insulate the pipes with the premium foam wrap (feels rubbery and cost $5-6 per 5 ft. length) and I could work for that size pool. obviously a solar cover is a must, as you be loosing heat as you try to heat the body of water. I can tell you in my digging that the selling point of a 400k vs a 200k pool heater wasn't just the conveicence of a faster heatup time but it cost less to run the 400k to hit the target temp vs. the smaller units. thats due to less time for the heat to excape DURING the heating. So bigger is better baby!
I would look at ebay and online for a gas tankless to play with. Home Depot and Lowes charge $1000+ and don't stock anyway.
-Jason what are your thoughts on this?
 
Calivette

From Jason:
Swimming pools need huge amounts of heat, probably a couple of times as much as your entire house uses in the winter.
Click to expand...
Think about that gas bill. Even if you can stand the price, you don't have enough btu's to make a difference.

You will be very depressed (as I was after learning the hard way) if you attempt this. I found my 200,000 btu woodstove couldn't touch my rather large pool. While your pool and btu requirements are smaller, you do not have a chance of producing btu's fast enough with the setup you are talking about.
 
Swimming pool heaters are specifically designed for maximum efficiency at heating large volumes of water, with high flow rates and small temperature differentials. Domestic hot water heaters are designed to heat low flow rates by large temperature differentials, which has a much lower inherent efficiency. If you can afford the gas bill, you are much better off going with a pool heater.
 
JasonLion said:
Adding 80 gallons of 110 degree water to 8000 gallons of 72 degree water will result in a water temperature of 72.38, at least under ideal conditions.

Swimming pools need huge amounts of heat, probably a couple of times as much as your entire house uses in the winter. A fairly large water heater might be 40,000 BTU, while the typical swimming pool heater is 200,000 to 400,000 BTU.

Another thing to keep in mind is that total heat is temperature increase times flow rate, while efficiency is higher at lower temperature increases. A large temperature increase at a low flow rate tends to be inefficient and doesn't provide much heat. Very small temperature increases, say 1 degree, at very high flow rates are much more efficient.
Click to expand...

Jason, you are absolutely correct. I looked up your numbers and you are correct the average water heater is less than 30000 BTU and it will not work. Thanks.
 
I think your better off using a Fresnel lens to heat the hot water heater that has a small pump in it to recirculate the water. I know it sounds funny but if you have never used one of these lens they are pretty cool to mess around with. By the way they are also dangerous. I just dont know how exactly you could do it without making sure you dont burn up the plumbing or the hot water.
 

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The total available energy goes by the size of the collecting area. There just isn't that much heat in sunlight, so you need a large collector area to get enough heat. Heating a focused pin prick a lot doesn't give you any more total heat than heating a flat panel with the same area as the lens by a much smaller amount.

Conventional pool solar panels are already very efficient. No use of lenses can improve that efficiency by any useful amount unless they increase the total collecting area. You could make a small water heating tank, but the lenses still have to be large. Given the complexity and size of such a setup, conventional solar panels are easier, less expensive, and probably just as efficient. Even if the lens system was 100% efficient, it would only improve a tiny bit over conventional solar panels of the same size as the lens.
 
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