Electric heating of pool - Just a touch but still is it practical?

[l00semarble]

So I'm building a house in Costa Rica and plan to make it "off grid" with a large PV array, large battery, and larger inverters. This is not a frugal living situation but a independence choice. I will have the local GRID as a backup for if my PV does not keep up in an extended poor solar period.

Anyway - my house will have a pool of about 15,000 gallons. This is a tropical climate but we are at about 1,500ft elevation where it is just perfect nearly year round to have an open house without HVAC. We have a current house with pool in same area. The pool temperature is "refreshing". It feels good if you are hot and want to cool off but it is just a touch too cold to lounge around in for long periods. I would like to be able to raise the temperature just 2-3 degrees to make it just a little more comfortable for all.

So in my new home design I was thinking about installing a 11kw electric inline pool heater something like this one from Raypak. Then, I would configure our electrical system to use this pool heater as a dump load each day once the batteries are fully charged and we have excess PV. And if we don't have excess - no harm no foul as we don't consider pool heating to be critical.

But now that I am looking more seriously at the numbers I'm not sure how well this will work. 11kw is a lot of power obviously but a pool full of water laughs at 11kw. If we have a 20-30kw array we may have it to waste once batteries are charged. But...the RayPak manual states that you can calculate degrees per hour of temperature gain by: (kw * 410)/gallons.

(11kw * 410)/15,000gal = 0.3 deg/hr

It takes a lot of energy to heat water. Now I'm wondering if this is will be effective. I guess if I have a couple of hours a day with power to waste I may get some gains. I guess it also depends on how quickly any heat gain is lost. It is hard to tell if this is going to be worth it.

I could also do passive solar heat collectors for the pool which is the more common solution or I could do both.

Thoughts?

 

[hwy17]

My thoughts are that you understand it correctly. It takes a shitload of BTUs to heat a pool.

I use solar collectors, 2x Fafco Solar Bear plumbed in parallel and my main pool pump goes through them. I use a very simple single diverter valve to manually turn the system on or off, and then just time my pump runtime to coincide with solar hours.

The most relevant ratio for pool solar thermal is the pool surface area to solar surface area. I have about 60% collector area to pool surface (160 / 250 sq ft). My pool is 90 degrees now after a sunny week with the bubble cover on. Soon I will be able to take the cover off all the time and it will stay in the 80's all summer.

If you're not already using a bubble cover that is easily the most affordable and most effective gain. But it's a huge convenience to get enough solar that you don't have to bother with them anymore.

 

[GravelRider]

Are you looking to raise temps by 2-3 degrees F or C?

Have you considered using a solar pool cover? If 2-3 F, a solar cover would easily do this without any other energy input. If in Celsius, a solar cover may not quite cut it, though might depending upon how much sunlight you get. This would be a FAR less costly and time-consuming option.

 

[houseofancients]

i wouldnt even consider a pool that large for electric heat....
either use a heatpump, but better yet, use direct solar water heating, maybe a heat pipe system...

the amount of electricity to heat a pool that size would be staggering

 

[l00semarble]

Sorry I shoudl know to include units. I was talking F. 2-3 deg is not much but the range for comfortable pool temps is quite narrow. A couple of degrees F makes a difference I think.

I've thought about a cover but it is a pain in the ass and the pool is an architectural/design feature so the ambiance of the pool is critical to the house vibe. A cover would spoil that.

 

[hwy17]

Considering solar thermal and the resistive heater are similar in installation cost, and the electric heater comes with supply constraints while the solar thermal only adds slightly to running and maintenance costs, I would say it comes down to space. If you are constrained for solar space the resistive is worth consideration, if you're not constrained and have plenty of solar thermal space, I think solar thermal wins out.

In the continental US solar thermal only works during summer though, maybe 3/4 of the year in Florida or Arizona. I don't know if it's a year round solution in Costa Rica or not. Might be.

 

[Nobodybusiness]

So I'm building a house in Costa Rica and plan to make it "off grid" with a large PV array, large battery, and larger inverters. This is not a frugal living situation but a independence choice. I will have the local GRID as a backup for if my PV does not keep up in an extended poor solar period.

Anyway - my house will have a pool of about 15,000 gallons. This is a tropical climate but we are at about 1,500ft elevation where it is just perfect nearly year round to have an open house without HVAC. We have a current house with pool in same area. The pool temperature is "refreshing". It feels good if you are hot and want to cool off but it is just a touch too cold to lounge around in for long periods. I would like to be able to raise the temperature just 2-3 degrees to make it just a little more comfortable for all.

So in my new home design I was thinking about installing a 11kw electric inline pool heater something like this one from Raypak. Then, I would configure our electrical system to use this pool heater as a dump load each day once the batteries are fully charged and we have excess PV. And if we don't have excess - no harm no foul as we don't consider pool heating to be critical.

But now that I am looking more seriously at the numbers I'm not sure how well this will work. 11kw is a lot of power obviously but a pool full of water laughs at 11kw. If we have a 20-30kw array we may have it to waste once batteries are charged. But...the RayPak manual states that you can calculate degrees per hour of temperature gain by: (kw * 410)/gallons.

(11kw * 410)/15,000gal = 0.3 deg/hr

It takes a lot of energy to heat water. Now I'm wondering if this is will be effective. I guess if I have a couple of hours a day with power to waste I may get some gains. I guess it also depends on how quickly any heat gain is lost. It is hard to tell if this is going to be worth it.

I could also do passive solar heat collectors for the pool which is the more common solution or I could do both.

Thoughts?

Lot of electricity to do that.

Not sure if cheaper to use PV or Thermal panels.

I’m sure some of these smart folks on here will let you know.

 

[Checkthisout]

So I'm building a house in Costa Rica and plan to make it "off grid" with a large PV array, large battery, and larger inverters. This is not a frugal living situation but a independence choice. I will have the local GRID as a backup for if my PV does not keep up in an extended poor solar period.

Anyway - my house will have a pool of about 15,000 gallons. This is a tropical climate but we are at about 1,500ft elevation where it is just perfect nearly year round to have an open house without HVAC. We have a current house with pool in same area. The pool temperature is "refreshing". It feels good if you are hot and want to cool off but it is just a touch too cold to lounge around in for long periods. I would like to be able to raise the temperature just 2-3 degrees to make it just a little more comfortable for all.

So in my new home design I was thinking about installing a 11kw electric inline pool heater something like this one from Raypak. Then, I would configure our electrical system to use this pool heater as a dump load each day once the batteries are fully charged and we have excess PV. And if we don't have excess - no harm no foul as we don't consider pool heating to be critical.

But now that I am looking more seriously at the numbers I'm not sure how well this will work. 11kw is a lot of power obviously but a pool full of water laughs at 11kw. If we have a 20-30kw array we may have it to waste once batteries are charged. But...the RayPak manual states that you can calculate degrees per hour of temperature gain by: (kw * 410)/gallons.

(11kw * 410)/15,000gal = 0.3 deg/hr

It takes a lot of energy to heat water. Now I'm wondering if this is will be effective. I guess if I have a couple of hours a day with power to waste I may get some gains. I guess it also depends on how quickly any heat gain is lost. It is hard to tell if this is going to be worth it.

I could also do passive solar heat collectors for the pool which is the more common solution or I could do both.

Thoughts?

Can you share some pictures of the house?

Do you feel safe down there or do you need walls/gates etc?

 

[time2roll]

I would use a heat pump heater over resistance heat any day. Especially in a warm climate.

Then of course I have always thought about running tubing in the concrete decking to circulate the heat into the pool. Cooler decking, warmer pool is a win, win. I assume some of that radiant heating tubing could be used when pouring the cement. Easy to pump the water without going to the roof.

 

[Ampster]

I would use a heat pump heater over resistance heat any day. Especially in a warm climate.

Yes, it is more efficient to move heat rather than.create it using resistance.

 

[time2roll]

Heat pump may need to run all day so instead of a dump as the battery is full it would be such that the battery gets full later in the day or only 90%. Or heat pump could start at battery 60% full or some value that capacity overnight will not be an issue.

If the solar is 20-30 kW and the dump load is 11kW there is still plenty left on the table.

 

[l00semarble]

In the continental US solar thermal only works during summer though, maybe 3/4 of the year in Florida or Arizona. I don't know if it's a year round solution in Costa Rica or not. Might be.

Our rainy season is what they refer to as "winter" around here where temps are cooler due to less sun. This would be when heating would be most appreciated but whether resistive or direct solar it will be the worst solar conditions during this time. But we live fine without it. This is just a nice to have little addition.

 

[l00semarble]

Yes, it is more efficient to move heat rather than.create it using resistance.

Yes of course but at the same time the resistive load is nice and easy on the inverters

 

[l00semarble]

Can you share some pictures of the house?

Do you feel safe down there or do you need walls/gates etc?

Our current house (Photos are old before landscaping matured. Looks quite different to me now!)






And our new house is going to look something like this. The render is far from perfectly correct but this is the general idea. Construction is by board formed concrete using the trees from lot that we have to cut down. We have decided to change the pool liner tiles to a dark volcanic stone to help with heat absorption.



Anyway - to answer the question about feeling safe and about walls and such. There are issues here and they are getting worse but it generally isn't about personal safety but about your stuff. Petty theft is common so you have to be careful about leaving valuables in a car or on the beach etc.

Generally the MO of most thieves in our area is to hit a house full of renters when they go out to dinner. Vacationers are often very gullible relative to residents and they leave a mountain of laptops, ipads, cameras, binoculars, and sometimes cash etc. But lately there have been more aggressive incidents including armed home invasion. This gets kind of scary.

Both our homes are high on the mounting on a long difficult 4x4 road which dead ends. We have a 24hour security guy at the bottom of the road. This is a better spot to be in as a bad guy is just likely to pick an easier target. Our houses are behind a gate at the driveway but it doesn't stop anyone who wants to sneak in. Fences and etc don't do much to a determined thief. We leave the house "open" meaning nothign but screens to stop a bad guy but there is a security system so at least there will be a loud alarm and notifications if someone did "break" in. We do lock our valuables in a safe.

You have to maintain vigilance here but even some effort puts you into the less easy target category.

 

[Checkthisout]

Our current house (Photos are old before landscaping matured. Looks quite different to me now!)

View attachment 150376

View attachment 150377


And our new house is going to look something like this. The render is far from perfectly correct but this is the general idea. Construction is by board formed concrete using the trees from lot that we have to cut down. We have decided to change the pool liner tiles to a dark volcanic stone to help with heat absorption.

View attachment 150378

Anyway - to answer the question about feeling safe and about walls and such. There are issues here and they are getting worse but it generally isn't about personal safety but about your stuff. Petty theft is common so you have to be careful about leaving valuables in a car or on the beach etc.

Generally the MO of most thieves in our area is to hit a house full of renters when they go out to dinner. Vacationers are often very gullible relative to residents and they leave a mountain of laptops, ipads, cameras, binoculars, and sometimes cash etc. But lately there have been more aggressive incidents including armed home invasion. This gets kind of scary.

Both our homes are high on the mounting on a long difficult 4x4 road which dead ends. We have a 24hour security guy at the bottom of the road. This is a better spot to be in as a bad guy is just likely to pick an easier target. Our houses are behind a gate at the driveway but it doesn't stop anyone who wants to sneak in. Fences and etc don't do much to a determined thief. We leave the house "open" meaning nothign but screens to stop a bad guy but there is a security system so at least there will be a loud alarm and notifications if someone did "break" in. We do lock our valuables in a safe.

You have to maintain vigilance here but even some effort puts you into the less easy target category.

Thank you for the run down.

What an absolutely gorgeous place!

 

[Ampster]

Yes of course but at the same time the resistive load is nice and easy on the inverters

I presume that is because of the motor load? My inverter has no issue because it is only 500 Watts compared to 4000 Watts for resistive load.

 

[Quattrohead]

Solar powered pool pump and passive solar heating system seems like the best approach to me.

Absolutely beautiful homes, both the old and the new.

 

[l00semarble]

I think I am convinced that I should just go with high quality solar collectors. I want the type that are enclosed in glass for durability and aesthetics. Some of those roll out black tube-matt things look chinsy as hell. I can just imagine a Costa Rican critter munching through the thin plastic or any other number of hazards of a jungle deployment.

I'm not doing something that looks like this:

 

[Ampster]

I think I am convinced that I should just go with high quality solar collectors.

Have you found them to be cost effective? Those plastic ones work well because the temperature differentials are small for heating pools.
A friend of mine who throws away money like it is water used evacuated tube collectors to heat his hot tub. They were mounted on a structure so they looked like a Pergola in the garden. He has experienced some of the tubes failing.

 

[l00semarble]

Have you found them to be cost effective?

I haven't found out anything yet. But I will make whatever investment is necessary for a set and forget solution that will last hopefully decades. Those roll out type look almost disposable after a couple seasons. I'm just going on looks alone. I dont' know shit....yet.