Speedheating a Pool

Weather here in NorCal is somewhat inclement, despite it being the end of May (damn you El Nino!), and the pool at my grandparents, solely heated by a solar pool cover, is obviously not up to swimming for this Memorial Day weekend (unless it heats it up by 2F a day for the next ten days - highs are forcast in the low 80s).

Since there’s no pool heater, I was wondering if there are any ways to speed up the heating process. I suppose it would be asking to much for a tablet that you drop in and bing there it is. But, being an engineer, my motto is “There’s always a way”…

As a side note, my grandparents do have a hot tub (heated by solar panels), but I don’t know what the tempurature of that is or if any water will be in it come Memorial Day.

Greek fire? Hot stones from a bonfire? Plenty of ways but I shouldn’t have to tell an engineer there is no free lunch.

If I was given this task I’d setup a big steel washtub full of water over some big propane burners. Coil some copper tubing and hose with one of those inline pumps powered by a drill motor and use it to pull cold water out of the bottom of the pool, heat in the tub and dump back in. Kind of a junkyard wars solution but it was the first thing that popped into my mind.

I have used a solar cover in the past on my pool successfully. It’s a big sheet of blue bubble wrap and will heat the pool up pretty quickly if it’s sunny. It also insulates and keeps the pool from cooling down overnight. Cost about $75 at a pool supply store, depending on the size of your pool.

Did you even read the OP?

The solar panels are all you have. Are the pool and hot tub hydraulicaly connected? If not, adding solar panels to the pool would be a good idea. Otherwise, heat water in the hot tub and trasnfer the water to the pool.

How many gallons in the pool?

Some physics guy can figure how many of these would be needed to do the job in the time allotted.

p.s. I just googled 1000 watt cause it seemed like a nice round number. I’m sure there are much bigger ones but the price is right.

This tip is marginal but it does work to some extent: leave the filter on during the day to mix up the water. There is a tendency for the hot water near the surface to form a warm layer which doesn’t mix. Then, at night, the same hot water is near the surface and so cools fastest.

When I was a kid we used to do the opposite trick because pools here tend to get too hot in mid summer. We’d try not to use the filter routinely during the heat of the day but only in the early hours of the morning when the air was coolest.

I have a solar heater that is just a black 4X20’ panel with a bunch of thin tubes in it the pool water runs through. With a couple sunny days in a row it can make a big difference in the water temperature. IIRC it cost less then $200, it hooks up to the filter system so the only other thing you might have to buy are a few hoses.

http://www.fafco.com/WarmWater/Solar-Technology.html

Otherwise trying to route the pool water through the solar panels you have for the hot tub seems like a good option.

Get a cheap pump (harbor freight) A roll of 1/2"-3/4" black polyethylene irrigation (underground lawn sprinkler) tubing, and some clear PE sheeting (extra havy duty drop cloths).

Form the irrigation pipe into a scroll (AKA a flat coil, and no it is not called a spiral). Maybe use some plywood, or even cardboard under it for insulation from the pool deck…get fancy and use some black foam sheathing. It’s late enough spring that it is probably not worth the trouble to prop up the north end.

Cover with a layer of PE sheeting in an improvised frame. You want to keep any wind or other air circulation from the tubing. the sheet should not touch the tubing. The temperature differntial should be pretty low, so “double glazing” probably won’t gain you a lot. That is for collectors that are attempting to achieve higher temperatures.

Use the pump to push water through the tubing, so it doesn’t see the hot side.

I’m am not an enginer, and I’m just doing some napkin math, and I may make a few mistakes here, but here’s what I get running things through convert.exe and a calculator:

Assuming a 25 by 35 foot pool that is five feet deep, you would have about 125 metric tons, or 280,000 pounds of water. To raise the temp by twenty degrees you will need to add 5,600,000 BTUs of heat, also known as “a little more than 5,900,000,000 joules.”

5.9 billion joules divided by 777,600 seconds (nine days) looks to me like 7590 watts. You need eight of the heaters that Eleusis linked to. They will draw about 70 Amps, assuming a perfect resistive load. You could plug them, two each, into four dedicated 110v circuits, but I’d try to put each one on a separate circuit from the house (i.e., one from the master bedroom circuit, one from the kitchen, etc., etc…) Since you’re working around water, I’d put a GFCI on every line to minimize the risk of electrocution.

Seriously though, I’d try to heat the pool using a solar heater. My guess is that it would be a lot cheaper and simple. Also, being simpler, any safety risks would be minimized.

…And all of the above is just meant as a mathematical exercise. If you have five hundred dollars to spend to heat the pool it would be better spent by having a pool maintenance company do the job for you.

Short-term memory loss. :smack:

Would getting some thin BLACK plastic sheeting and using it instead of the solar cover help? I would imagine you could run it over the sides of the pool, but make it so it just sits on the surface of the water.

Unless your solar cover is already a dark color.

A trick I’ve seen used before is to paint the bottom of the pool a dark color (usually a navy-ish shade, since black would be too hot) so that it absorbs more heat on its own.

The downside is that by the end of the summer, the pool is usually about the temperature of bathwater and isn’t very refreshing on a hot day.