Temporary Solar Heater Idea

Ever noticed how hot the water is when it comes out of a black water hose thats been laying in the sun? Why not remove one of the eyeball return jets and replace it with a PVC male adapter and downsize that to make it fit a 3/4 inch garden hose. At the beginning of the season, when the water is cold, hook up the black garden hose and snake it through the grass or on the concrete. Run the other end back to the pool of course. It seems to me that the sun would heat the water at least a few degrees even though it is moving water. The only question is how many feet of hose would it take to make a difference in the water temp. As we all know, only a few degrees can make a huge difference. Anyone tried this before?

Temperature rise is proportional to the area of the solar panel and the efficiency of the device. A garden hose will be much less efficient than a solar panels so you will need more area to get the same temperature rise. Assuming the hose is 3/4" wide, for every 100 sq-ft of hose area, you will need 1600 feet of hose. My panels are 450 sq-ft which would require 7200 feet of hose. Not very practical.

Al has a homemade solar mat made with black hose. He also has a commercial solar mat. Between the two of them, his pool water gets hot! (And I mean in the 90s sometimes. WAY too hot.) I'll ask him to pop in here on this thread.

If I ever can figure how to upload pics with this new VBulleting software I'll post a couple. Back in 1999 I first experimented with 400' of green garden hose. Was tightly coiled on a 4x8 sheet of plywood, painted black, covered in plastic wrap, and configured in 4x 100' sections. I built the 1x4 manifolds out of PVC. That was a proof of concept for what followed. Final heater was 1200' of black poly pipe in a 12x100' configuration, again with PVC manifolds in and out, layed in the back field on black rolled roofing that occupied roughly 8x50 feet. I diverted some of the return flow through the heater and just dumped the heater output in the deep end. Yeah, they work, not as efficient as a mat, but a lot cheaper, not as pretty, but probably more rugged. Space is the thing to have and I have plenty of it. When the grass grows in my uncut back field you can't even see it. The feed pipes are 1.25" buried black poly.
Al

Al, thanks for the info. I don't think I am prepared to do all that work. I live in Georgia and the swimming season is pretty long already. I just thought I could eek out a few extra degrees by using this the day before an early season party. I still think a couple hundred feet of hose stretched out in direct sunlight would gain possibly 5 degrees, say from 70 to 75 or so. Do you think this is possible? It seems to me that the hose in a coiled state would serve to block the sunlight from hitting the majority of the hose, unless you have it coiled in a single layer configuration.

In order to get 5 degrees of temperature rise, you need 42 BTU per Gallon of pool water. Not sure what your pool size is but the best panels on the market will deliver about 1000 BTU/sqft/day of heat which means you would need 42 sq-ft of panels per 1000 gallons of pool water to get a 5 degree rise per day.

200' of 3/4" hose is 12.5 sq-ft. In a 10000 gallon pool, at the very most you could expect 0.15 degree rise per day and I am being generous. It is even less at the beginning and end of season because of air temperature.

If you were to use a fairly clear (at least to visible and infrared light) pool cover, then you would have the entire area of your pool heating the water and eliminating heat loss from evaporation. As you can see from calculations in this thread, in a white plaster pool around 60% of the sunlight gets absorbed by the water and heats it. In a darker pool, even more gets absorbed. If the average depth is 4.5 feet, then this translates to peak noontime heating of around 0.7ºF per hour. If there were no pool cover, then evaporation can significantly cool the water where 1/4" of evaporation would cool that same 4.5 foot average depth pool by about 5ºF (per day, if evaporation is 1/4" per day).

Generally speaking, use of a fairly clear solar cover is the most economical way to raise the temperature of pool water. The downside is that most solar covers that are clear also let UV light through so you don't get much benefit of reduced chlorine usage. With a darker cover, less UV gets through and one gets a lower chlorine loss as a result. Getting a dark mostly opaque cover will block UV and absorb sunlight that can heat the surface of the water, but you have to have good surface circulation to remove that heat from the surface efficiently -- it's not nearly as good at heating the pool compared to a clear cover. At the other extreme, a white cover would reflect most sunlight and prevent heating of the pool which would be useful in very hot desert climates in order to prevent evaporation (i.e. save water), reduce chlorine usage, yet not get the pool too hot.

As usual, you were right. I hooked up about 100 feet of hose on a hot day and could not feel any difference at all in the temp of the water coming out of the hose compared to the pool water. Oh, well, it seemed like a good idea. Thanks for all the information though.