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/

 

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 April 18, 20215 yr by Arandoza

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?

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. 

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. 

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? 

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. 

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 🙂

 

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.

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. 

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. 

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

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.

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. 

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!

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.

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.

Much to consider. Thank you for this.

4 minutes ago, ThatGuy said:

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

Made my day!

@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.

38 minutes ago, MKRandburg said:

@ThatGuy 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!

How does that make you feel?

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.

 

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.

45 minutes ago, MKRandburg said:

Sigh. I wish I knew what this means.

Apologies - too technical.

Bottom line: you pool's pump uses less power when the filter is dirty than when the filter is clean.

13 minutes ago, Calvin said:

Bottom line: you pool's pump uses less power when the filter is dirty than when the filter is clean.

Oh cool. So sending some water round black pipes (I'm thinking LDPE by the by) might save me a few pennies on power. hehe