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Author Topic: WRB09 buffer tank config help  (Read 2129 times)
wrigpm
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« on: September 26, 2010, 11:06:25 AM »

I have a Range tribune HE cylinder as the buffer tank for my heatpump.  Currently the heatpump drives the indirect coil and the UFH comes from the main body of water.  However, I think the heatpump is cycling too much so am thinking of driving the heatpump into the main body of water and taking the UFH from the coil (mid coil as bottom coil is where the solar goes).  However, I have some questions:-

1. I think the flow from the heatpump should go in the top (where the DHW extract would be) and return from the bottom - not sure though!?
2. Will the heatpump circulating pump destratify the tank? And do I want it too!?
3. 'Standard' coils on tanks seem to be capable of taking 15kW in from a boiler - can I also extract 15kW?

Any help and advice greatly appreciated.

Paul
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welshboy
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« Reply #1 on: September 26, 2010, 08:17:32 PM »

I started with a similar configuration but abandoned it rightly or wrongly for the following reasons
1 - the heat pump output temperature needs to be higher than the water temperature used to heat the underfloor pipes.
  This is inefficient as the heatpump efficiency drops off rapidly when you run it at higher temps .
2 -The overhead running cost of the circulating pump from the heatstore to the underfloor is a parasitic load.

I now run it direct to the underfloor switched on and off with a timer (judgement) which does away with one circulating pump and also cuts out the parasitic load of the  output circulating pump on the heatpump.
Altogether a more efficient use of input electric I think. No doubt someone will point out my mistakes though.
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ecogeorge
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« Reply #2 on: September 26, 2010, 09:09:51 PM »

I have a Range tribune HE cylinder as the buffer tank for my heatpump.  Currently the heatpump drives the indirect coil and the UFH comes from the main body of water.  However, I think the heatpump is cycling too much so am thinking of driving the heatpump into the main body of water and taking the UFH from the coil (mid coil as bottom coil is where the solar goes).  However, I have some questions:-

1. I think the flow from the heatpump should go in the top (where the DHW extract would be) and return from the bottom - not sure though!?
Correct - that is how I did mine. Hottest water is then at the top.
2. Will the heatpump circulating pump destratify the tank? And do I want it too!?
Yes it will and you want it to!  The buffer tank will heat from the top down to the max temp of the heat pump. If you extract heat from the top for your heating the tank will take longer to heat and slower to cool -reducing cycling. Also the heat pump will always be fed the coldest water keeping it running efficiently.
3. 'Standard' coils on tanks seem to be capable of taking 15kW in from a boiler - can I also extract 15kW?
Can't help you on this one ! but would always go direct for max effeciency.
- Use the "boiler " coil for solar input.
-Connect wood burner to buffer tank via same connections as heat pump (use a nrv) to maximise available heat inputs.Heat pump will only run if buffer tank gets below set temp. Move return temp senor for WR09 to top of buffer tank to use all other free heat first. Set circ' pump on WR09 to come on with ground loop(move wires) other wise it runs continuously.
I have had to pump my woodburner as when the heat pump runs the pump stops the thermal siphon and the stove boils  Grin Grin
Used a budget solar panel controller with sensors on woodburner inlet and outlet- if outlet 5c above inlet it pumps to buffer tank. Combined with loading valve on woodburner to keeptemps up. -Works a treat.

Any help and advice greatly appreciated.
Future plans include addition of waste oil burning boiler to use free oil as well an an extra 30 x 58mm tubes on roof.. Although heat pumps are efficient they still use electric.

Paul

Rgds George.
« Last Edit: September 26, 2010, 09:12:08 PM by ecogeorge » Logged
wrigpm
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« Reply #3 on: September 27, 2010, 12:25:55 AM »

Guys

Thanks for the responses so far - good to know I am not that far off with my thinking!!

How about another idea:-

Ignore the coils in the cylinder (apart from the solar/wood input).  i.e put a 'T' on the top of the cylinder and run the WRB09 into one side and the UFH from the other.  As the flow of the UFH changes (due to zones opening/closing) then the 'excess flow' would go into the cylinder instead of to the UFH.  I have my WRB09 configured so I can switch it on/off like a normal boiler (with a closing pair contact) so I can put a stat at the top of the tank to turn it (and the continuous running loop pump) off if the cylinder is to temp.

Further thoughts?

P
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