Responding to PM questions here so everyone can see them:
1) Do you know any pool builders that you recommend?
2) We will live in Livermore. If we only used the cover and solar (and no gas heating) how many months do you think we could have 80 degree water midday and at 8pm? Could it be from May to Oct?
3) How quickly does the pool lose heat from 5 pm to 10pm? Does it quickly get down to 72 (which is cold to me)?
4) Do you know anyone that has an undertrack system with a non rectangular pool?
Our pool builder,
Janssen Pool Construction, is good but for the North Bay so not quite your area.
As shown in
this post, heating is about getting above the average day/night temperature of the air. A bubble-type mostly clear insulating cover will usually increase the temperature 10-15ºF above this average day/night temp. A solar system used in conjunction with a cover will usually get 20-25ºF above average day/night temps, but this depends on the number and type of solar panels and on the type of cover (I have 12 black flat mat panels with 10 mostly in sun facing SSW). Automatic covers are only about half as insulating as bubble-type covers. So let's look at some data for Livermore (the solar insolation is using San Francisco area numbers):
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
.56..61..66...71..77..83...89..88..86...77..64..56 ... Avg. High Temp
.39..42..44...46..50..54...57..57..55...50..43..39 ... Avg. Low Temp
.48..52..56...59..64..69...74..73..71...64..54..48 ... Average Temp (slightly more weight to daytime temp)
2.0 3.0 2.4 1.0 . 0.5 0.1 0.0 0.1 . 0.2 0.9 1.8 2.6 ... Average monthly rainfall in inches
3.1 3.9 5.0 6.2 . 6.8 7.0 7.3 6.9 . 6.2 5.0 3.5 2.9 ... kWh/m2/day from the sun (30-year average for month; panels facing south tilted at 38-15=23 degrees)
So with a solar system and an automatic pool cover, you should easily be able to have 80ºF water from May to October and might be able to have part of April as well, depending on your system. I am unable to do that with my pool without gas (except for July and August) because we keep it warmer at 88ºF. Also note that if you get some cloudy days, then you won't get the same amount of heating which is why we have to use gas at least some in June and September. So if you don't have a gas heater, then you'll have some days where you won't reach your temperature target. Note also that the typical pattern is that the pool is coldest in the morning and hottest in the late afternoon with a temperature swing of up to 4-6ºF in the outside months. Note that I am talking about a 16,000 gallon pool -- smaller pools tend to lose heat more quickly since they have a higher surface area to volume ratio.
From 5 to 10 PM, you may lose a degree or two. Most of the loss is during the colder nighttime temperatures. The loss during peak summer is only 2-3ºF with the electric cover, but increases to 4-6ºF in the outer months of the season. A bubble-type cover would cut such losses almost in half, but that would have to be manually put on and off.
My system is an undertrack from
Pool Covers, Inc., but it's a rectangular pool. You can use an undertrack with a freeform pool that is designed to use it (probably has a "shelf"), but a beach entry would seem problematic as others have noted in your
other thread.
Also, I am trying to understand the difference if I had an auto cover or not in regards to pool temp. On a sunny spring or summer day would the pool be warmer with the pool uncovered or covered? Seems that the cover keeps the pool warm overnight but then prevents it from warming during sun.
So if my main goal is to get 5 or 6 months of 80 plus pool water and I have solar (and didnt use gas heater), would I definitely need an auto cover (as opposed to no cover)? I wouldnt want a manual cover.
You most definitely need a cover so an automatic cover in your case. Without a cover, you will have roughly twice the temperature drop at night compared to an electric cover while a bubble-type cover cuts that loss in half again. What this means is that you won't get a 20ºF gain in temperature though you are right that having the sun on the pool does help. The problem is that evaporation cools the water. In our area which isn't terribly dry, the sun does add some net heating to the pool but not a whole lot since you have elevated the temperature using solar. What kills you is nighttime where evaporation continues with no sun to heat the pool. I'm just guessing, but I'd be surprised if you could gain more than 15ºF with the solar if you don't use a cover. So while June through September may be OK, May and October are probably not. When you hear about many people opening their pools on Memorial Day and others on the 4th of July and closing the pools on Labor Day, it's either in climates with shorter summer seasons or people who don't use pool covers.
