An energy efficient and cost effective solar pool heating system

[AUSpool]

Our pool is to cold even in summer so it's time for some solar heating. It only gets morning sun and is exposed to the wind. We have a flat (3-5degrees) metal roof with box gutters and parapets all round which leaves me concerned about possible leaks.


I'm still waiting for a few quotes to come in but to reduce the risk of leaks on the roof I'm most likely going for a one piece polypropylene panel system that are interconnected with barrel unions. I will need to cut into the existing filter system for a booster pump as there is no dedicated supply for the solar heating.


We have a PV system that feeds back to the grid at 52c a Kwh and when we're not producing our own power we purchase it from the grid at ~28c a Kwk. I've calculated our self consumption of the PV at ~10% which is great with such a high feed in tariff. I'm currently using a 3 speed eco pump on the low speed which is timed to run early morning and late afternoon to avoid using our PV power. Four hours on low is currently enough to manage our pools water quality. The booster pump for the solar heat collector will need to run during the day and I can use a discounted, timed, feed from the grid that does not draw from from our PV system.


From the schematics I've seen on the net a booster pump is normally plumbed into the existing system between the filter and chlorinator with a non-return between the inlet and outlet. This setup would mean that I need to run my main pump whenever the booster pump is required and it will probably need to run on the medium speed.


I would love to run both pumps independent but can this be done? The main pump can be run for four hours a day and the booster pump can be used only as required. Power wise the main pump would need to be on our main power feed and timed to run early morning and late afternoon as it's currently setup. The booster pump can go on the discounted feed that provides power during the day but cuts out during peak usage times, typically early morning and early afternoon or evening.


I guess the suction ends of both pumps can be connected to the same point with non-return valves to prevent each from sucking through the other. A simple relay switch can be used to avoid both pumps being on together. Due to the non-return on the booster pump I will need a solar heat collector bypass up near the roof line to ensure the panels drain out when the booster pump turns off.


My sticking point for this system is the return point where the booster pump and solar collector plumbing feeds back into the existing filter system just after the chlorinator. I would use a wee or a Y tee here but I think when the main pump is running and the booster pump is off with the panels drained out a venturi affect will suck air into the return line from the solar system. Would this be the case and is it something that I should be concerned about?


If I can successfully run both pumps off the same feed and return lines I will need a solar collector bypass to allow the panels to drain out via the hot return, but will a bypass work? I would be connecting the cold feed and hot return just below the roof line using a pair of 1.5 / 0.5" faucet tees and could reduce the 0.5" join a little more if required. In theory I think this should work but I've never seen it done before. When the booster pump is on the water will want to go strait ahead through the faucet tee with very little bypassing the collector but when the booster pump is off the non return will prevent flow back through the cold feed and water will drain out through the bypass, I hope. Has anyone used this application?


Sorry for such a long post and thanks in advance for and advice that is greatly appreciated.


Steve.

 

[Agent99]

Can you run your 3-speed pump on medium or high when you require solar water heating? It might have enough power to pump through the panels.

In my system, I have one pump for everything including solar. I need to run my pump at a higher speed to overcome the head loss pumping up to my solar panels on the second story of my roof (30 feet) but I can run my pump quite low for general filtering.

 

[atttech-2]

all the booster pumps I have seen require the main pump to be running or you risk burning them out. That being said most pumps will support solar. Do a search for Hydraulics-101 in the forums, lots of good info. As for valves most designs I have seen use 3 ball valves to isolate the solar from the pump for maint or winter and a 3-way valve to control the solar check out page 2 of this link for a good system diagram http://www.h2otsun.com/ps/tilemanual.pdf adding a power actuator and automatic control to the 3-way can be done for a couple hundred assuming you are doing the work yourself.

 

[AUSpool]

Can you run your 3-speed pump on medium or high when you require solar water heating? It might have enough power to pump through the panels.

In my system, I have one pump for everything including solar. I need to run my pump at a higher speed to overcome the head loss pumping up to my solar panels on the second story of my roof (30 feet) but I can run my pump quite low for general filtering.

Thanks Chris,

An actuated 3-way valve controlled by the solar controlar was always an option but I didn't think about it seriously. The controller can turn the pump on and off but I dont think it can change the speed. I will ask the supplier next I talk to him.

We go about 30" from pool to filter then will go another ~30 - ~40" to the panels. I'm only going up on story though so I think the existing pump will do it and the cost of an actuated valve is not much more than the booster pump. I wonder if there is much difference between running my existing pump on low for 4 hours a day, every day, plus a booster pump as required; as apposed to running the existing pump on medium 4 hours a day, every day, which includes the solar feed, plus a bit extra for the solar as required. There's probably not much difference.

 

[AUSpool]

all the booster pumps I have seen require the main pump to be running or you risk burning them out. That being said most pumps will support solar. Do a search for Hydraulics-101 in the forums, lots of good info. As for valves most designs I have seen use 3 ball valves to isolate the solar from the pump for maint or winter and a 3-way valve to control the solar check out page 2 of this link for a good system diagram http://www.h2otsun.com/ps/tilemanual.pdf adding a power actuator and automatic control to the 3-way can be done for a couple hundred assuming you are doing the work yourself.

Thanks for that, I'm leaning towards the power actuated 3 way valve and I notice that second scematic with the spa included has a by-pass but it doesn't say what its for or how it works. And I wonder how the (dv) drains vales work. I want to avoid pool water draining onto the roof but I could provide a little plumbing to take it off the roof.

 

[atttech-2]

There is a link to their full install manual in that doc too that has more detail. It's not all that clear in the drawing but my PB said the drain valves "DV" are just normal hose spigots or ball valves you put near ground level so you can fully manually drain the system for winter. During normal operation much but not all of the water will drain into the pool when the pump turns off. The check valves make sure the water goes to the return side and doesn't put back pressure on the filter. We had our builder stub out the solar so most of the work on the ground will be done I just have to get the panels, controller and run the pipe up the wall to the roof. As for the spa bypass that one has me confused to but we are not putting in a spa on our build so I think I will save my brain the space on that one.

 

[AUSpool]

There is a link to their full install manual in that doc too that has more detail. It's not all that clear in the drawing but my PB said the drain valves "DV" are just normal hose spigots or ball valves you put near ground level so you can fully manually drain the system for winter. During normal operation much but not all of the water will drain into the pool when the pump turns off. The check valves make sure the water goes to the return side and doesn't put back pressure on the filter. We had our builder stub out the solar so most of the work on the ground will be done I just have to get the panels, controller and run the pipe up the wall to the roof. As for the spa bypass that one has me confused to but we are not putting in a spa on our build so I think I will save my brain the space on that one.

Thanks again,


That site is very helpful, I've had a bit of a look and will make some time to look some more and a bit deeper look hear. I don't think I'll need to drain out the panels in winter, the winter mode on the controllers I can get run water through the system once a month for a short time just to make sure it's kept clean. I guess in winter I could do this manually and leave the pump in the low setting.


I spoke with the supplier this afternoon and he said that their actuated valves can't change the pump settings but will recognise when the pump is stable in the medium mode so the system doesn't over pressurise at start up. When the flow to the solar panels is not needed but the filter needs more time the valve and pump cycle through a close sequence. The pump goes off with the valve open for 10 minutes to allow the panels to drain out then the valve closes the solar feed before the pump starts again.


The plumbing schematics from h20thot differ slightly in that my supplier minimises the hot return and puts the vacuum brake on the top or beginning of the hot return. He also suggests to add a 2' loop at the input and output of the panels for expansion. I've tried to add a pic of my very rough sketch. I guess there are a number of ways to do it.

Thanks again, Steve.

 

[atttech-2]

I have seen the VB at the top in other designs as well, not sure it makes a difference but for some reason it seems more logical to me to put it at the top as you have it in your drawing.

 

[Agent99]

Here is a schematic of my system. Maybe it'll help you visualize things to see where automation can help you.

A lot of the higher priced variable speed pumps provide a lot of flexibility and communication so that you can dial in things like speed and operating times. Very powerful.

 

[AUSpool]

Thanks again Chris,
Your schematics look great, very helpfull. We looked a house for sale yesterday (not for me) with a pool/spa combo, 4 pumps, 2 filters, multiple control gear and more plumbing then a hardware store!

 

[AUSpool]

I had a chat with one of my potential suppliers and when pressed on the actuated valve idea he suggested that the actuated valves have a relatively short life span when compared to a pump. Two and a half to three years was the turm. Does anyone have any life span experience with these valves?

My existing plumbing is all in 2" so do I keep all my plumbing within the filter area in 2" and continue in 2" for the 30' underground bit changing to 1.5" up and back to the panels or change to 1.5" within the filter area and continue that under ground?

 

[mas985]

Many pools have actuated valves especially those with solar and spas/water features and I could not imagine my pool without them. It would be a lot of back and forth to the equipment pad. But I have had mine for 10 years now without any failures so I really don't know what the PB is talking about.


Also a booster for solar is only really needed for very high installations (over 2-3 stories). Most pool pumps today can easily support solar on a two story house. I had been running my solar on a second story with a 1/2 HP pump.

 

[Agent99]

I have Jandy valves and a Jandy actuator on the solar valve (hence why I colored it black although I should make that clear on the schematic) and it's been running fine since 2005 when the solar panels were installed. All my solar is 2". In fact everything is 2" in my system EXCEPT the return pipe and that is 1.5". It was done that way the pool was originally built way before I bought the house. Doing it over, I would make everything 2" and call it good.

 

[AUSpool]

Thanks again for all your help Chris.

10 years for an actuated valve, I think the guy I spoke with wasn't being completly honest.

I was always leaning toward the 2" for within the filter area and under ground.

I notice that you dont have a bypass under the actuated valve as in the pic below. I've seen many schematics that don't but do you think I should?

 

[AUSpool]

Many pools have actuated valves especially those with solar and spas/water features and I could not imagine my pool without them. It would be a lot of back and forth to the equipment pad. But I have had mine for 10 years now without any failures so I really don't know what the PB is talking about.


Also a booster for solar is only really needed for very high installations (over 2-3 stories). Most pool pumps today can easily support solar on a two story house. I had been running my solar on a second story with a 1/2 HP pump.

Thanks Mark, another 10years for an actuated valve, thats great news for me. I think the PB I spoke with wasn't being completely honest.


Love all the info in your signature, I'm still trying to get through the hydraulics 101 and haven't really started on the pump ed yet. I saved a copy of the run tim study a few weeks ago and it really supports the way I've been managing my pool for ages. Good work.

 

[AUSpool]

I finally decided to use the actuated valve and started with buying the Jandy 3 way valve but have had problems trying to find a suitable controller. I want a controller to control everything, chlorinator, pump and valve with battery backup as its all going to run off a controlled power supply. My problem is that my existing Davey eco series 3 speed pump always starts up on high flow for 5 minutes before defaulting to the selected flow setting. High flow is too much for the solar collector and any controller I use must be able to detect that the pump is stable in mid flow before cycling the valve.


The controller must also be able to allow the collector to drain out when shutting off the water supply to the roof, to turn the pump off with the valve open until the collector drains, then close the valve and turn the pump back on to maintain the normal filter run time if needed. I think there is a controller that will do this but I haven't found one yet and assume it will be quite expensive. So I think I'm going to go back to using two pumps independently off the same feed and return from the pool.


I have taken the time to figure out the annual running costs of the various installation options and probably should have done that first up. I've based the calculations on my existing pump, a Davey Eco series* and an Astral E170*, both are Aussie 240V pumps. All $ values in Australian dollars and based on a peak tariff (T11) at $0.27kWh and a controlled tariff (T33) at $0.20kWh. I used an Ausgrid calculator that uses watts and Hours to produce an annual cost based on a $27kWh tariff.


http://www.ausgrid.com.au/Common/Customer-Services/Homes/Energy-efficiency/Energy-efficiency-at-home-tips/Energy-usage-calculators/SmallApplianceCalculator.aspx


My existing Davey pump running for 4 hours a day for a year on a peak tariff costs me $70 year.


Two pumps running independent, AUD$260 year. The Davey eco on low for 4 hours a day for 12 months on tariff 11, and the Astral 170 for the solar heating at 6 hours a day for 6 months over summer on tariff 33.


One pump plus an actuated valve, AUD$262 year. The Davey eco on mid flow for 4 hours a day, six months and the same pump on mid flow for 6 hours a day for 6 months over summer on tariff 33.


Main pump plus booster, AUD$451 year. The Davey eco on mid flow for 4 hours a day, for 6 months on tariff 33 plus the Davey Eco on mid flow and the Astral 170 both for 6 hours a day for 6 months both on tariff 33. The Davey has to be left on mid flow so the Astral solar pump can do it's winter program thing.


*Both pumps are Aussie pumps at 240V.
Davey Eco Series, low flow - 180Watts / 0.24Hp / 0.75Amps, mid flow - 720Watts / 0.92Hp / 2.88Amps, hi flow - 990Watts / 1.32Hp / 3.96Amps.


Astral E 170, 850Watts / 0.75Hp / 3.5Amps.

 

[mas985]

Two pumps running independent, AUD$260 year. The Davey eco on low for 4 hours a day for 12 months on tariff 11, and the Astral 170 for the solar heating at 6 hours a day for 6 months over summer on tariff 33.


One pump plus an actuated valve, AUD$262 year. The Davey eco on mid flow for 4 hours a day, six months and the same pump on mid flow for 6 hours a day for 6 months over summer on tariff 33.

Why not run a single pump on low flow for 4 hours a day in winter and on mid flow for 6 hours a day for summer? Doesn't seem like a fair comparison the way you have it now.

 

[AUSpool]

Thanks again Mark,
I set it up like that for the comparison so that both systems were both set and forget. When using the one pump and an actuated valve the pump needs to be left in the mid flow setting so the controller can do it's winter mode thing and come on automatically for 5 minutes a day. The solar pump controller that I'd use for two pumps indepenandly has a similar feature.

I stopped by another pool shop today and both Davey and Zodiac have controllers that fit the bill but at around $2000 each there not for me when a simple controller for a pump will come in just under $300. Sometimes things cost a bit more in Aussie. I think I could get away with a .5Hp pump but we just cant get them here, a 0.75Hp pump is going to have to be it.

Can I use a Jandy 3 way valve to divert just a little of the flow (ie. 20 / 80 split) or are they normally used for all or nothing?

Cheers, Steve.

 

[mas985]

The valve can be set to any flow. The actuator has cams that allow you to stop anywhere as well.