nel5on
West Midlands
Posts: 270 
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Apr 30, 2019 16:48:52 GMT
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Hi Guys,
I made a solar heated Spa pool last year.
Got a broken spa, removed the heater, fixed the pump, then added 4 solar flat panel collectors, on my garage roof and plumbed it to a Central heating pump.
It a "vented" heating system so the pump pumps spa water into the panels and it drains back into the spa.
This work until the end of Sept, then the central heating pump stopped. Last weekend I pulled the pump and got it going again....and it started pumping again. but it has stopped again.
How much HEAD should a central heating pump reach? My garage roof is only around 3mtrs off the ground.
I don't need volume, I need 15mm supply to keep a small flow all day and its controlled by a £10 temp differential controller.
Last year it was often the Spa was over 40 and sometimes over 50Deg!!....and I would need to open the cover to cool it down for a few hours. 38-40deg seems to be perfect for me.
This weekend it went from 9deg to 26deg in 12hrs of cloudy weather
Thanks in advance
Nelson
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Covin
996.2
Tucson
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I would think that most central heating pumps can manage more than 3m head. Having said that, most heating systems are fully filled so the static head will be balanced (suction head + discharge head when the pump is off) and any working head will come from friction losses in the system.
On your system it sounds as though you are recirculating the actual spa water? This means it has to handle the static lift from spa to roof as well as any friction losses from the pipework (probably quite low). This isn't likely to be a problem from the lift point of view but increases the potential for gas-locking and getting jammed by picking up "human debris" (dunno how heating pumps feel about hair, but there will be hair in the water!). Long term it would be better to keep the heating loop separate from the spa water and use a heat exchanger as that way the static heads can be balanced and the recirc. water kept clean.
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Hi, Yes it should be able to pump up, it's pulling up that pumps struggle with if it's too high. So where is the pump in relation to the water level in the spa? I agree with vitesseefi it would be better to keep the two lots of water separate as they do in central heating systems in regards to indirect hot water tanks, although for different reasons.
Colin
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nel5on
West Midlands
Posts: 270
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1st of all... the central heating pump (solar)takes from the "filtered" side of the system, just before the main spa pump. When used the main pump rand for an hour a day...and the solar pump is only when the panels are 10deg hotter than the spa.
Another problem I had last year was thermosyphon, when the spa water was drawn and cooled in the panels overnight, cold spa every morning...tried an electric dishwasher valve but the restriction on flow was too much....so removed the spa water return to above the waterline to stop any reverse flow at night. Then it would be 26-30deg each morning. Would be better to find a low restriction way to stop the back flow at night...then that will help solve the pump "head" problems too.
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Covin
996.2
Tucson
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I would be careful with any form of valve on the system, at the moment it will thermosyphon if the pump fails or is turned off in the heat of the day, thus avoiding catastrophic failure if the water stops circulating and starts boiling in the panels, normally they run a pressurised expansion vessel with a strong antifreeze solution to help prevent this.
Control valves are forbidden on solid fuel fired bookers for the same reason - you can't just turn off the heat source in the event of failure.
All I could think of would be a motorised valve on a light sensor but pipe in a 15mm bypass so some water can still flow, bigger is better when it comes to thermosyphon systems, they perform noticeably better on 1" pipe rather than 22mm.
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nel5on
West Midlands
Posts: 270
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I would be careful with any form of valve on the system, at the moment it will thermosyphon if the pump fails or is turned off in the heat of the day, thus avoiding catastrophic failure if the water stops circulating and starts boiling in the panels, normally they run a pressurised expansion vessel with a strong antifreeze solution to help prevent this. Control valves are forbidden on solid fuel fired bookers for the same reason - you can't just turn off the heat source in the event of failure. All I could think of would be a motorised valve on a light sensor but pipe in a 15mm bypass so some water can still flow, bigger is better when it comes to thermosyphon systems, they perform noticeably better on 1" pipe rather than 22mm. Currently I have the panels "self draining" but that is something to consider if I add a valve. Will try a new pump and keep the vented system and see if that works ok. |
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Covin
996.2
Tucson
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Standard central heating pumps are all just cast iron so tend to corrode around the impellor area stopping the pump when not in use if you don't have a suitable corrosion inhibitor, they do make a bronze body pump specifically for pumping clean water to stop the corrosion problems
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