Jump to content

DIY Solar water heating for the pool


Recommended Posts

I was inspired by a post on here regarding a farmer who heated up his pool by just laying out black pvc piping. 

So I found a few youtube videos and instructables - most of the video's use dc pumps to pump the water through the black pipe. I'd like to use the pool pump which is on anyways.

So a couple things I need help with, I'm a software engineer, some of this physical stuff is a bit daunting! 

If I'm going to use my pool pump to push water through coils of irrigation or LDPE piping, do I need to worry about pressure and load on my pool pump - totally clueless here, might not even be the right question ???

Would I need to limit the amount of water that goes into the coils for any reason? We used to have one of those commercial types installed, panels of small black tubing, they sent all the water from the pump through those panels and back whilst the pool pump was on, so not sure if this is an issue - just one of the video's showed how he doesn't send all the water but didn't really explain it. 

So in the comments there are some debates on thermodynamics etc. and some conflict on whether it's better to push the water through the panels fast or slow. To me it's sounding like fast is better, although "common sense" seems to be slow. So if someone who understands heat exchange can weigh in here. 
Also how would one connect the coils in parallel - would that be a t-connector thingy - so some of the water goes to the first coil and some of it goes to the second coil (assuming 2 coils for now)/

Any other ideas or experience on this? 

List of video's etc that I watched:

https://www.youtube.com/watch?v=-3t04YEM3wE

https://www.youtube.com/watch?v=PyE9dJaqDnU

 

https://www.youtube.com/watch?v=EO8SyoGmWFw

https://www.instructables.com/DIY-Solar-Pool-Heater/

 

Link to post
Share on other sites
  • Replies 50
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Popular Posts

How does that make you feel?

The idea of letting the water "dwell" in the pipe is only useful if your intention is to just have a hot pipe - not if you want to maximise the heat transfer between the sun and your pool  The rate of

Thanks for testing and reporting results... talk is much easier to replicate than actual data, as we've seen 😛

Posted Images

A good existing and durable product for this  are pool heating panels. See link below. Do stay clear of the heating panels with thin tubes between the upper and lower main connecting pipes as the thin pipes thend to perish over time. The one below looks like corrugated cardboard where the water flows thru and is durable and stong.

https://swemgat.com/products/pool-heating-3-solar-panel-diy-complete-kit?_pos=9&_sid=d266cdfe5&_ss=r

 

Alternatively a Heat pump that is run from PV? Normally heat pumps for pools  will draw 3/4 of the power from the environment, and only 1/4 from eletricity?

 

 

Edited by Arandoza
Link to post
Share on other sites

I probably need to say why I want to do this DIY - do it yourself. Those panels are expensive and leak and break - been there done that. A heat pump with PV is probably going to be just as expensive.  And I want to do a DIY build.

So any advice on how to accomplish this as a DIY project?

Link to post
Share on other sites
1 hour ago, MKRandburg said:

Another thing, I  must make clear. I totally get that this set up will only give me a few degrees at the beginning and end of summer - I'm not trying to swim in 30deg water in the middle of winter. 

You don't need to run all the water through the heating system. I installed a T piece in the outlet pipe of the pool filter and use a watertap to control the amount of water going through to this heating system. There is some heating panels on the roof. This pipe feeds water to a old flat plate collector for extra heating. The normal black pipe wall thickness is very thin and only last a year or two. Try to get good black pipe with a thicker wall. 

20210418_123920.jpg

Link to post
Share on other sites
1 hour ago, Chris Louw said:

I installed a T piece in the outlet pipe of the pool filter and use a watertap to control the amount of water going through to this heating system.

I'm just wondering how does this work in terms of diverting flow away from the heating system and straight into the pool - I've been also trying to figure out the configuration of valves, to be able to isolate the heating system completely. Which wasn't done properly on our previous system, leaks were a nightmare. 

Link to post
Share on other sites

We had a friend in Cape Town area, the old man, had arthritis and he ran the water over his garage roof, I can't recall whether he had a coil of 40mm PVC pipe up there, I guess probably, all I know is, the pool was probably 8m X 2.5m by shallow on the one end and probably close to 2m on the deep end and I recall us visiting one Cape Town winter, where it was mostly cloudy, cold & raining on and off and the pool had a whispy layer of fog over it and us kids, probably 12 years old, swam and it felt like a warm bath, considering the weather it was flippin great 🙂

 

Link to post
Share on other sites
52 minutes ago, Kalahari Meerkat said:

We had a friend in Cape Town area, the old man, had arthritis and he ran the water over his garage roof, I can't recall whether he had a coil of 40mm PVC pipe up there, I guess probably, all I know is, the pool was probably 8m X 2.5m by shallow on the one end and probably close to 2m on the deep end and I recall us visiting one Cape Town winter, where it was mostly cloudy, cold & raining on and off and the pool had a whispy layer of fog over it and us kids, probably 12 years old, swam and it felt like a warm bath, considering the weather it was flippin great 🙂

 

That would be awesome! I am most definitely aiming for a whispy layer of fog! However having had 6 panels of the traditional kind I know not to be over optimistic. hehe but one can dream.

Link to post
Share on other sites
2 hours ago, MKRandburg said:

Thanks @Chris Louw, is there a reason you don't let all the water through to the heating system? Or is it just to control the heat of the pool without having to turn the pump on and off?

What kind of pipe would you recommend? 

We run most off the water through 50mm pipe to the main heating panels on the roof and the rest of the water through this 20mm pipe connected to the flat panel heat collector . This way we benefit from both heaters and have a balance in the water flow. 

Link to post
Share on other sites

The way I have done it is on the outlet that goes back to the pool, after going through the pump and filer, I have a T piece with a valve that I can partially close and direct some of the water flow through a loop of black pipe (various sizes, just joined all the odd pieces I have into a long one). So most of the water goes directly back to the pool, but an amount of it goes through the black pipe and is heated. 

Link to post
Share on other sites

Hi

I suppose If you let all the water go through the black pipe the flow will be  such that there will be very little heat transfer because the water flow will be too much and the water will not have time to heat up and only the hot water initially in the pipe will have any effect.  In some some solar geysers the water only flows when the is a a few degrees difference and the pumps are very small.

Link to post
Share on other sites
On 2021/04/19 at 5:11 PM, MKRandburg said:

Thanks @DeepBass9 is there a reason you did it this way, instead of sending it all through the black pipe? 

Because the pipe was a lot of different diameters, with the smallest being 25mm, and because I didn't want to load the pump with pushing the water through a few 100m of pipe. Even if the pipe is all the same diameter as your pump outlet, there is still extra work to be done to overcome the friction in such a long pipe. The way it is I can control the amount of water going through the pipe. I generally adjust it so the water is being warmed to about 30 odd degrees (finger thermometer) as it exits the pipe. 

Link to post
Share on other sites
1 minute ago, DeepBass9 said:

Because the pipe was a lot of different diameters, with the smallest being 25mm, and because I didn't want to load the pump with pushing the water through a few 100m of pipe. Even if the pipe is all the same diameter as your pump outlet, there is still extra work to be done to overcome the friction in such a long pipe. The way it is I can control the amount of water going through the pipe. I generally adjust it so the water is being warmed to about 30 odd degrees (finger thermometer) as it exits the pipe. 

There was also the risk that one of the pipe fittings would pop off under the full pressure of the pump and my swimming pool would be pumped away into the veld!

Link to post
Share on other sites
8 hours ago, Peter Topp said:

Hi

I suppose If you let all the water go through the black pipe the flow will be  such that there will be very little heat transfer because the water flow will be too much and the water will not have time to heat up and only the hot water initially in the pipe will have any effect.  In some some solar geysers the water only flows when the is a a few degrees difference and the pumps are very small.

Yeah this seems to be big debate and I don't understand the arguments,  I've been seeing. Let the water dwell in the black pipes and heat up really high before it comes back into the pool, or heat up a lot of water a small amount but do it often by letting it flow fast. I suppose I can experiment with it and make sure I can control the flow when I set up the system. I was hoping to avoid the rabbit hole of thermodynamics.

Link to post
Share on other sites
2 hours ago, DeepBass9 said:

There was also the risk that one of the pipe fittings would pop off under the full pressure of the pump and my swimming pool would be pumped away into the veld!

Yip! We had endless trouble without bought system of things popping off and pumping our water away. The guy who installed it, also didn't think through the isolation valve, so it wasn't really an isolation valve.

Link to post
Share on other sites
4 hours ago, MKRandburg said:

Let the water dwell in the black pipes and heat up really high before it comes back into the pool, or heat up a lot of water a small amount but do it often by letting it flow fast

The idea of letting the water "dwell" in the pipe is only useful if your intention is to just have a hot pipe - not if you want to maximise the heat transfer between the sun and your pool :) The rate of energy transferred to the water is proportional to the Area of the heated surface, as well as the temperature differential between the hot pipe wall and the water. 

Understand it like this: The water can't get hotter than the outside of the pipe, right? You're not expecting that somehow, you'll have water at 80 deg if the hottest part of the pipe is only at 65 deg? This would be creating energy, which I'm told is a big scientific no-no. So if the rate of energy transfer to the water is 0 when it gets to the same temperature as the pipe, then the energy transfer must be decreasing the closer you get to this temperature. Therefore the heat transfer is slowing down the smaller the temperature difference between the hot and cold objects. So the best way to make sure you get the maximum amount of energy into the water, is to always have the water as cold as possible - IE, have it flowing fast.

The area of heat transfer is the other big factor: The Sun only shines from one direction (at least where I live). And like a solar panel the more area you have for the sun to "hit", the more energy you can absorb (Watts / m^2). So 3x 20mm pipes next to each other present an effective 60mm "width" that the sun shines down on, and will have a better energy transfer area than 1x 50mm pipe. Additionally, the bigger diameter pipe requires thick walls to resist increased internal pressure, and the PVC the pipe is made from is a good insulator (which insulates well against electricity as well as heat). So the thicker the wall of the pipe, the less heat will be transferred through the PVC through conduction. Therefore it usually makes more sense to have many thin pipes in parallel, rather than just one big pipe. However - The 50mm pipe has a bigger internal cross-section than the 3x 20mm pipes, so it will allow you to move the water faster and with less pressure loss, and less work done by your pump.

Basically my point is: Engineering is hard, just use the pipe you can get the cheapest 🤣

Link to post
Share on other sites

@ThatGuy thank you so much for your post though. This is exactly the information I was looking for, presented in an easily understandable and useful way! It definitely confirms what I've been reading. And is logical! 

I wish I had the whole long weekend for the build but sadly I'm doing a Masters in Psychology so will be working on a proposal but building solar heating for my pool sounds like much more fun! 

Still not 100% clear on whether I need to worry about pressure and resistance in terms of my pump motor? It's something ancient, I recall it was measured in HP but those stickers are long gone. I'd hate to blow it.

Link to post
Share on other sites
16 minutes ago, MKRandburg said:

Still not 100% clear on whether I need to worry about pressure and resistance in terms of my pump motor? It's something ancient, I recall it was measured in HP but those stickers are long gone. I'd hate to blow it.

Ancient is sometimes better where motors are concerned... Newer ones from Chyynaa usually have a lot less copper in them and are less resistant to overloading. I don't think you have to worry too much about burning it out (it is water cooled after all), you just mustn't make the pipes so long that you don't get circulation!

Before you add anything, suggest you let your pump run for about 30min (preferably before you've cleaned it and before backwashing so the load is as high as it'll normally get) and feel the heat on the fins of the motor: If it's more than 65 deg already (uncomfortable to touch for more than a few seconds), then the pump is already struggling and you'll need a different circulating pump. If it's just warm to the touch, then have at it :)

I suggest this with no experience and at your own peril: Get 1 long length of pipe and run it as-is. Repeat the heat check after 30 min running and check the flow in your pool. If the load is too much or flow is too little, cut that pipe in half and add fittings to make 2 parallel paths (double the flow area). You can repeat as many times as necessary, while having the same effective heating area. Don't add too many runs though: Eventually the pump won't be able to keep enough flow to fill the pipes, and your heat transfer will suffer because the water won't be making contact with the top of the pipe (where the heat is).

Please don't tell anyone about my bed-wetting when you're a famous head shrinker.  

 

Link to post
Share on other sites
1 hour ago, ThatGuy said:

preferably before you've cleaned it and before backwashing so the load is as high as it'll normally get

Positive displacement pumps are similar to constant current sources - as load resistance goes up so does power.  On the other hand a centrifugal pump is similar to a constant voltage source - as load resistance increases the flow rate/current decreases and power goes down.  A dirty filter is essentially a higher load resistance, meaning less flow and hence reduced power.

I did a quick test on my own pool pump to confirm what I remember from fluid dynamics classes 40 years ago and found to my relief that my tuition fees had not been completely wasted.  Partially closing the return valve increased the pump speed by about 1%.  Motor slip changed from about 6.7% to 5.8%.  I did not measure the power, but the reduction in slip means that it certainly decreased.

 

Link to post
Share on other sites
59 minutes ago, Calvin said:

Positive displacement pumps are similar to constant current sources - as load resistance goes up so does power.  On the other hand a centrifugal pump is similar to a constant voltage source - as load resistance increases the flow rate/current decreases and power goes down.  A dirty filter is essentially a higher load resistance, meaning less flow and hence reduced power.

I did a quick test on my own pool pump to confirm what I remember from fluid dynamics classes 40 years ago and found to my relief that my tuition fees had not been completely wasted.  Partially closing the return valve increased the pump speed by about 1%.  Motor slip changed from about 6.7% to 5.8%.  I did not measure the power, but the reduction in slip means that it certainly decreased.

 

Sigh. I wish I knew what this means.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...