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Author Topic: Sizing Circullation Pump In Wetback To HWC With Coil  (Read 2989 times)

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Offline Squirrel

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Sizing Circullation Pump In Wetback To HWC With Coil
« on: November 20, 2014, 07:39:07 PM »
Hi there

- Is someone experienced in finding the correct size of circullation pump for a wet back to HWC connection?
Which brand / type can you recommend?
- Do I need to vent as well on the stove because it sitts about 250mm higher than Inlet on the HWC? There is going to be a vent on the highest point on the HWC anyway.
Horizontal distance Woddburner to HWC 1.7m, Woodburner 9Kw to water, HWC coil 10Kw, heating system is filled with 3.6m reducing valve, containing aprox. 20L water.

Regards
Ben

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Offline Plumber

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Re: Sizing Circullation Pump In Wetback To HWC With Coil
« Reply #1 on: November 21, 2014, 08:32:52 AM »
Hi Ben, I have seen attempted installations such as the one you are describing end very badly, its OK to ask for advise here but I would be very careful attempting to do this yourself if you dont have the experience or are appropriately licensed. Your systems sound very common and a basic high temp bronze body circulation pump such as a 10 AMP Grundoss or Wilo should suffice. Pumps are not the ideal solution for wetback circulation when natural thermal movement is not available, the most common way to circulate would be to use a pulse valve. You can view more information on this here >> http://www.plumbers.co.nz/forum/codes-standards-health-and-safety/10/wetback-installation-guidelines-how-to-install-a-wetback/1137/       
Please note that the advice I am giving is only my opinion and not necessarily a fact.  Please refer to our terms and conditions.

Offline Squirrel

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Re: Sizing Circullation Pump In Wetback To HWC With Coil
« Reply #2 on: November 21, 2014, 02:48:40 PM »
Hi There

Thanks for your reply. I am with a plumber, all legal, registered and so on. But at the moment he is busy az, so I'm doing a bit of research in the meentime.
The Woodrange we got comes from Italy and does need a pump to run it. Thermosiphon won't work according to manufacturar.
But If you dig a bit, proper heating systems can be tricky....
Reading pump manuals: 'Minimum suction head at suction port for avoiding cavitation' what's your experience on this? We intend to use a 3.6m Reducing valve, so we would have 3.6m head on the suction port. Just enough?
How about corrosion? The waterjacket in the woodrange is steel, the piping will be copper, the heat exchanger in the HWC is stainless. I have heard of anodes in HWC, but they are long and thick. I would need a small one to fit into the pipes and because there is only around 20L of water in the heating loop it wouldn't need to be such a big one.
What is your thought about this?
Cheers

Offline Plumber

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Re: Sizing Circullation Pump In Wetback To HWC With Coil
« Reply #3 on: November 27, 2014, 02:29:20 PM »
I think the first thing you need accept is that any pump you install will most likely have to be replaced between 2-5 years. I have done some of these in the past and the distances you are describing should be no issue at all for a 10 AMP, just make sure you get a bronze body one that can cope with the temps (avoid traps when running pipework). We used a solarstat to control the pump but there are several controllers out there you can use, make sure the sensor pocket is on the return. Yes you will still need an open vent, make sure you place the pump correctly to prevent overflow when the pump fires up, the shorter the circuit the higher the risk. Also just set the pump on the slowest setting usually 1. In regards to your HWC is it an open system or will you be using a heat exchanger? I wouldn't worry too much about corrosion to be honest but if you are concerned you can retrofit the HWC with one from the top by using a T or asking your cylinder supplier to weld in a connection.


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