Hot water closed loop at 135 degrees F
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| Posted in Mechanicals on
Hi , I have set up an anaerobic digester at my horse property , I have made a solar heater ( black hosepipe behind some upvc ) to heat it ,for best results I need to get the digester up to max temp 135 deg F , just had my first pump seize up , what of off the shelf pump can cope with that kind of temp , its running water around a closed loop of hosepipes
any and all suggestions welcome
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Replies
David,
Go to a plumbing supply distributor and buy a circulator designed for a hydronic heating system (a heating system with a boiler). You can also look online for a circulator designed for a solar thermal system.
As long as you are circulating water (or a solution of water and antifreeze), not a slurry of horse manure, one of these circulators will work fine.
Many hydronic circulators are cast iron. The reason they don't rust is that they are in a closed-loop system where the small amount of oxygen in the water gets quickly depleted, and there's no more oxygen available to corrode the iron. In order for that to work, the pipes can't allow oxygen to diffuse through them, so any plastic pipes have to be special versions that inhibit oxygen diffusion. That's why there are different grades of PEX tubing for hydronic systems vs. potable water.
I think that means you have two choices:
1) Pipe your whole system with metal or oxygen-barrier plastic, and use a cast iron circulator, or
2) Get a more expensive bronze or stainless pump, and then you can use any tubing.
Plastic pumps are cheaper and also don't rust, but finding one rated for 135 F might be hard.
If you will be running the pump a lot, it would be worth getting one with an "ECM" motor which uses about 2X to 4X less electric power compared to traditional induction motor circulators.