Trying to heat the pool/spa.

This project has been going on for too long now. This week we installed 6 X 3 = 18 aluminum boxes on the roof each of which holds maybe 15 ft of coiled 1/2" copper tubing painted black. The boxes sit on the flat roof. The cold water line has an air escape valve and the 'hot' water line has 2.

At ground level the cold water line happens to have a flexible joint at the moment. When I turn the pump on the flexible joint flexes (as in bubbles) and there is pressure to the roof because if I remove the cold water valve water spouts but no water seems to be returning hot from the boxes. The input water is piling up.

If the spa is empty and I pull water from the pool to the roof and attempt to fill the spa, it takes about 4 hours. The other thing is there are always air bubbles going into the spa, At first I thought - ok a new system maybe it takes some time to force the air out... but after hours that doesn;t seem right,

I thought maybe I need to incline the panels some to let the possible air in the system elevate to the valves.
I thought maybe - and it would be a TON of work - to maybe send the cold water through 6 rows of 3 boxes rather than 3 rows of 6.

The PVC to the roof is 1 1/2". All the copper tubing is 1/2"

Any ideas greatly appreciated.

 

You won't get too much flow from 1/2" pipe but still if you are putting pressure/water into the loop something should be coming out. If nothing is coming out..... the system is plugged.
Does each panel disconnect from the next one ?

 

How many linear feet of 1/2" line are you trying to force the water through?

 

15 liner ft x 18 boxes = 2800 linear ft of 1/2" copper tubing.

WOW, that is a lot of pipe, too early to attempt the math but going to need some significant pump pressure to force water through a 1/2 mile of restrictive pipe!

 

In theory each of the 18 boxes is 'independant' in that each has a copper connection (underneath) with 1 or 2 neighbors (in line) but at each end (cold and hot) the boxes are joined with the 1.5" PVC.

I'm guessing here but each box has about 15' of copper tubing. So 6 X 15 = 90' of tubing in a line. Three lines.

I'll post some photos when we get back from grocery shopping, but so far this morning I tried ;
- shutting of the return line at the pump. I removed the two air release valves on the roof and water flowed (not robustly) out.
- I removed all the air release valves and capped the holes, basically closing the system. Air bubbles are still coming into the pool - but I don't know from where they are coming at this point.

Thank you all for your help.

Edit : Hmm - the system tells me I've run out of space for attachments. Anyone know how I can clean up old ones ? Looks like some go back to 2012...

 

One thing that will help is knowing the flow rate you are trying to get through your system. Flow rate has a huge impact on the flow resistance through piping, especially when you talk 90° fittings and small diameter tubing. As you try to move more water, resistance will have a greater and greater impact.

In theory each of the 18 boxes is 'independant' in that each has a copper connection (underneath) with 1 or 2 neighbors (in line) but at each end (cold and hot) the boxes are joined with the 1.5" PVC.
I'm not exactly sure what that means. Hooking each of your heater boxes up parallel to the trunk/manifold lines would help flow by reducing the flow rate through each heater. Any heater boxes plumbed in series will have higher flow resistance.

 

I'm sure that what I have is a flow rate issue but unfortunately I have no knowledge of how to determine what my current flow rate is nor what flow rate I am trying to acheive. As I mentioned at some point earlier, the bulging flexible coupling on the 1.5" PVC makes it obvious that some water is being deprived/delayed access to the boxes on the roof. What is worse - our filtering system which normally runs at 15 psi, runs at about 30 psi when I route the water to the roof AND the flow of cold water into the pump 'basket' is about half what it should be. (I'm glad I just wrote that out because I suspect THAT could be the source of some of the air in the system).

Each box is more or less 30" square and each has 1 cold inlet and 1 hot outlet.. The copper couplings screw together. The copper boxes sit on a custom metal base which is about 18" off the roof (tight working conditions).

Already I am coming to dread that I may have to change the orientation of the boxes such that rather than having 3 lines of 6 boxes I will need 6 lines of 3 boxes. (That change will probably take 2 people 2 days). The other (simpler ?) thought I had was given the current arrangement, intall a new 4th connection off the cold water 'trunk' and simply run a hose or pvc tube directly to a new 4th connection on the hot water trunk (bypassing all the boxes). In my naive mind that path might allow the restricted water to find a way up to the roof. That sounds like a 'hack' but I might learn something from it.

Speaking of 'flow'. Given a 1.5" trunk with three 0.5" branches, is the flow equal through each branch or is the flow diminished as you go down the trunk ? And should a branch occur at a 45 degree angle or the easier 90 degrees ? One final thought - all the interbox copper (rigid) connections are beneath the boxes. They drop roughly 6 inches down from the tubing in the box. and run at 90 degrees to meet their mate at the next box. Perhaps those right angles need to be smoothed out as well.

Edit : another thought - surely the rate of flow of the water through the boxes also has a 'say' in the heating of the water as it passes along ? Water simply shot through the tubing is going to heat 'less' than water that takes a slower journey ? no ?

 

So you have an 1-1/2" line to the roof and the same coming back ?
A pool pump is considered a high flow low pressure pump.
Typically a separate pump is used to run the water thru the solar system.

 

Yes - I think ALL of the PVC tubing in this system is 1.5" - up and down.

Our 'copper boxes' are replacing very expensive hard plastic panels (from Germany) which were starting to leak all over the place (10+ years old). We have merely replaced panels with boxes - and cut down from something like 36 plastic panels across mutiple layers of roof down to (non-leaking) copper filled boxes in a small area. Also kind of expensive. I don't see the introduction of a second pump as an option at this point. And to be honest - I don't see how a second pump would address the flow issue.

Edit : another distasteful alternative I have is - when our water leave the sand filter there is something like an inverted K type situation. There are 3 valves. Two (1&2) allow the hot and cold lines to flow to the roof. The other (3) allows water to bypass the roof. I 'could' open the third valve somehat to simply bypas the roof and revieve the pressure throughtout the system. As I said - distasteful.

 

Given a 1.5" trunk with three 0.5" branches, is the flow equal through each branch or is the flow diminished as you go down the trunk ?

If you do the math a 1/2" pipe has an area of .196 square inches while a 1 1/2" pipe has an area of 1.767 square inches. The 1 1/2" pipe is actually about nine times bigger than 1/2" so... your three runs of 1/2" is a huge restriction.

 

So is it merely the area of the pipes that is important in the water flow ?

What about the fact that the water needs to run about 100 ft from the pool room to the place on the side of the house (with bends and curves) where it will rise perhaps 20 ft to reach the boxes ? What about the energy needed to move the water through the (let's say) (3) 100 ft of 0.5" copper tubing with its bends and curves ?

Surely the horsepower of the pump in the pool room also comes into play ?

 

This morning's experiment... As I mentioned yesterday, we have a set of valves which direct the water flow as it leaves our sand filter. They are in the shape of a large U, The pipes which make up the U appear to be 1.25" copper. The two 'arms' of the U are the hot and cold water to/from the roof. The base of the U controls the flow to the roof. All three pipes have valves.

So I powered up the pump with the 'base' valve wide open - very little if any water to the roof. System ran normally, no air anywhere, pressure gauge read like 18 psi. Then I started slowly closing the valve in the base - sending water to the roof and watching the pressure gauge at the same time. When I had that valve about 3/4 way closed the pressure gauge read 20 psi. The system seemed to be working fine. When I went beyond 3/4 way - the pressure started to spike.

So that is kind of a stinky solution to my problem. I suppose I could add more boxes (more lines of boxes) on the roof. $$$. Do you think it makes sense to try and restrict the 1.5" cold water line on the roof to something like 1" before entering the tubing ? Any other ideas ? Thanks.

 

No, it's not only about pipe size but it is a big part, and it's a big part of your system because you have so much tubing. If you chart how water flows through a pipe it's not linear. A small diameter pipe has a lot more interior surface area dragging on the water vs the amount of the water in the pipe while large diameter pipe has much less surface touching the water to cause turbulence and drag. Fittings are another killer of flow. A 90° fitting can have the flow resistance of several feet of pipe even though the water is in it for just a few inches. All of this gets worse as you try to run higher flow rates.

When you close off the valves to send water to the rooftop heaters I think the pressure spike you are seeing is the resistance of all that piping. If you try pumping 1 gal/minute through your heaters there wouldn't be much resistance but if you try to force 50 or 100 gal/min though the resistance spikes dramatically. Running your water through the heaters you might only get 5 or 10% the flow you do through your filter. It's not the end of the world as far as heating as it gives the water more time to absorb heat but it's probably not enough flow for filtration.

One solution is to get a second pump just to feed the heaters. This could be a pump optimized for higher pressure and a lower flow rate. The This way you heating the water won't hurt your filtration. Another option is to run each of your heater directly off the trunk line. That way all the heaters are working in parallel and you don't have any stacked together in series.

You can also do what you are doing now when you partially close valves. You can manually find a balance where you are sending enough water to the roof for heating while letting the rest go through the filters. You will have to keep an eye on it over time and occasionally tweak it to keep things balanced the way you like.

 

When we lived in Florida we had a single pump that sat outside in the weather (no room). Today our house (in Mexico) has at least FIVE different pumps. In the pool room we have our simple 1hp pump. Then we have a pump that is engaged if you want bubbles in the spa. Finally there is a dedicated pump for a 'waterfall' type thing. We have a pump that directs water around if there is no water pressure at the street (every other day). We also have a pump on the roof to provide enough water pressure in the shower to make it comparable to the US. I'm not sure I can handle yet another pump, and I'm not sure how it would fit in with the current plumbing.

Tomorrow morning (today is a holiday) our good friend, who is kind of the architect of our system (she has a similar one), is going to stop by to review where we stand. She had to go through a few adjustments to get her system to her liking. As I write this her comparably sized system/pool is about 86 degress. Ours at the moment is around 60 !. We have lived in this house for going on 8 years and we have never gone in the pool - the spa yes, but not the pool.

I sure would like a better understanding of all this water flow stuff. Have you ever seen a "Fluid dynamics for dummies" type book ? Is that would you would search on - Fluid Dynamics ?

Edit : Make that SIX pumps. I forgot the one for the sprinkler system.

 

You could use one of your existing pumps for the heat. You can plumb it with valves so you can have the pump for the waterfall or for heat. That way no new pump and you can turn the waterfall back on when you have guests.

 

We had 3 people stop by this morning to review our solar heater installation. The overwhelming consensus was that everything was perfect. Someone did make the suggestion of a second pump. There was a disagrement as to whether if we installed another 'row' of boxes if they would just be able to absorb more of the pressure (if that would let us open up the restraining valve to allow more water to the roof). Everyone said we MUST insulate all the plumbing AND get covers for the spa/pool.

There were a couple of places where we could add some 45 degree PVC fittings rather than 90 degree. One idea I had overnight was to replace the hard angled (90 degree) copper connections under our boxes with flexible couplings (like you would see on a toilet). We would be giving up some copper for I don't know what kind of metal (zinc ?). But we should improve flow. That would probably be a day's work. Any thoughts on that ?

I watched some YouTube related videos earlier today and I must say, our installation looks pretty spiffy in comparison.

 

A lot also depends on the fittings you use but I don't think you will see a noticeable improvement by removing a few 90 degree fittings.

 

There are at least 36 instances of 90 degree right angles under our boxes. Just in the 1/2 copper tubing alone.
I think I will put a pressure gauge somewhere (maybe where the cold water goes to the roof and then start to make some adjustments.

Later today I'll create a new userid on this forum so I can get a new storage allotment to post some photos.

Thanks for all your ideas by the way,

 

Yes, photos have been a continuing problem. I host my pictures online somewhere else like Imgur. I upload the photos to that site (free). Then I copy a link for that photo and post it in this forum. That way your photos don't contribute to your maximum allowance here.

 

I'm still wrestling with this some.

We have purchased a plastic bubble cover for the spa and it works great. Just using the cover, not running the pump, it increases the spa temp about 10 degrees and it only loses a few degrees over a cool night. I think the high temp this far is 86.

When I turn on the pump and send the water to the heater boxes on the roof it doesn't seem to make much difference. At this point I think it might be an air blockage. The boxes, while elevated about a foot or so, are lying flat. It almost looks like the area where the cold water enters the boxes might be higher than where the 'hot' water leaves. There are three air release valves. One on the cold water pipe and two on the hot water pipe. Yesterday I ran the system for a short while after turning it off I removed the air release valve at the cold water pipe. There was a noticable noise as air foreablly was released.

The metal frame on which the boxes sit is rather heavy. I am going to need another pair of hands to lift it so I can slip some bricks under the frame at the 'hot' end. (I thought of maybe using the car jack).

I did purchase a PSI pressure gauge. In the pump room the pressure gauge reads 25 psi. At the point where the cold water has reached the roof the gauge read 10 psi. The pressure was 0 psi at the hot end.

 

Stating the obvious.

25 psi at pump discharge and 10 psi at the roof after running through 1 1/2" pipe? That seems high but I could not find how long of run that was.

10 psi at the roof and 0 psi through the boxes, blockage or so much restriction within the boxes that more pressure is needed!

 

First, air is not and does not "cause a blockage". In fact it's easier to push through a pipe than water so it's the opposite of a blockage. The only time air is bad is on the intake side of the pump where it could cause the pump to loose prime. Other than that air in the lines will NOT stop the flow of water.

Still, it sounds like you have too much resistance in the piping or possibly even a blockage.
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Scientifically air and water are both fluids. Water is about 50 times more viscous than air but they are both fluids and they flow through pipes just the same. Just for fun get a 50' long coil of 1/4" tubing and try blowing through it as hard as you can. With all your might you will barely be able to feel the air coming out the other end. Yet, blow in a soda straw and you can force a lot of air through. The same thing happens with water except it's 50 times worse.
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If you have a valve on the outlet end of your hot water pipe you can do an experiment. Install your pressure gauge at the end of your hot water line but upstream of the shutoff valve. Turn on the pump that feeds the solar collectors AND close the valve on the hot water outlet. Give it time. Eventually you should see the pressure rise and given enough time it should equal the pressure at the beginning of the system. If the outlet pressure does eventually rise and get pretty close to the input pressure than you've proven that the pipe is not blocked and it is very likely that the resistance in the pipes is the problem.

Now that your solar collectors and piping are fully pressurized open the shutoff valve at the end of the hot water piping. You will probably see the pressure plummet. You may see an initial flow of water but if it soon slows to a trickle it further points to too much resistance in the piping.

 

The only shutoff valve on the hot side is back in the pool room - something close to 120 feet away. But I can do as you suggest and watch if the pressure gauge changes. One interesting thing is that there is no air at the pool filter's skimmer basket. Not even a buble. Yet bubbles are continually going into the spa or pool (depending on where I direct the return flow).

If I do not send the water to the roof (simply back to the pool/spa directly) the sand filter's pressure gauge reads 17. If I send 'most' of the water to the roof that gauge reads 25. If I send all the water to the roof that gauge reads like 29.

So - what exactly happens inside the series of 6 heater boxes if there is too much resistance ? Let's say at box 5 the water runs out of umpf. The system should be closed. What goes on inside box 6 ? Does the resistance 'create' air ? Where are the bubbles coming from ?

I hope some of my silly question make you smile :-)

 

Heating pools is always a challenge. They have so much mass that in some ways you want a massive heater (no matter what the type) to heat the pool up fast, but once it is warmed up, then all that heat stays, and you never really needed a big heater after all.

I would be suspect of people that say you situation is ideal however if it does not work. A lot of times people look at the set-up in terms of aesthetics and make determinations on whether it should work or not by that.

To me, it seems the glazing is not adequate for the amount of mass it is trying to heat, but that is just a guess.

 

Today I was lazy and just turned the pump on sending the water 100% to the roof. Maybe 15 minutes later I looked outside and the spa had dropped about a foot because the pressure had ripped (?) the flexible connector off the pipe to the roof, and the water was flooding the lawn.

I am going to do the aforementioned experiment BUT - in terms of 'physics' (which I was never any good at) - if I were to convert our existing 3 lines of 6 boxes into a 6 lines of 3 boxes might that cut down on the resistance issues ??

 

Yes, if done correctly that could reduce the resistance and lower the back pressure. You want your heater boxes in parallel not series.

 

A year later and this is still a project for me - although it is a little better.

Originally I had 3 rows of 6 heater boxes on the roof and I was not happy with the flow. If I drained the spa (ideally I would like to use our heater boxes for the pool as well) and then refilled the spa directly from the pool's main drain it took around 30 minutes to refill the spa. In the 3 rows of 6 heater box scenario - when I repeat the above experiment it took around 2 hours to refill the spa. (Very little water flow ).

So now I have cut the runs in half. I cut the connections between boxes 3 and 4 on the three lines. (Thank goodness for sharkbite, and flexible hot water tubing). So now I am sending the hot water from row three back and sending the cold water into boxes at row 4. Now when I re-run the above experiment it takes around 1 hour to refill the spa. I have a lot more playing to do and I still may need to separate the filter pump from the heater pump.

Today - at 3pm (our peak heat time) - I went out to the (covered) spa and checked the temp (on a gauge about 3 inches from the surface). It read about 89 degrees. I removed the cover and turned the pump on sending the water to the roof. Shortly thereafter the thermometer read 82 degrees. (I assume that is the proper recirculation of the spa). I sat in the spa letting the system run for a while and maybe it reached 84 degrees.

I did not check (I should have) but I would venture that today the pool water itself would have been in the low 70s.

So - what are realistic expectations for pool/spa heating using solar heaters ? There was a time when we lived in Texas where we heated the spa (nat gas) and in the winter steam would come off the spa. I'm not expecting that - but what sort of temps should be possible ? (Of course when we lived in Florida heating was never an issue).

Thanks