@davidalgarve

Oh, I forgot to add, that we will all need to come and stay with you for a couple of weeks this Summer, to check that any modifications have been done correctly and confirm that your system is working at its optimum. 😋 

I am most grateful to both Derek M and JamesPa for their advice, and I would just like to confirm how the tank is used as a volumiser, only in the return line.

I should confirm that at present, the pipe from ASHP to the buffer tank is connected to the top left tank connection via the 3 way valve which alternatively feeds the DHW tank.

Is the following correct?

The ASHP pipe after the 3 way valve, (which is currently connected to the tank), should be replaced by one that connects the 3 way valve to the CH pipework at the point where secondary pump discharge is now connected.

The top left tank connection (currently ASHP flow) and the top right (currently radiator flow) to be plugged, whilst the bottom left (ASHP return) and bottom right (Radiator return) are to remain as installed.

The secondary pump appears to be connected to the mains feed (running whenever the heat pump power is on), but will any electrical changes be required in the Ecodan?    

@derek-m 

You would be most welcome and 3 bedrooms available. I would consider it good value!

Posted by: @davidalgarve

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The ASHP pipe after the 3 way valve, (which is currently connected to the tank), should be replaced by one that connects the 3 way valve to the CH pipework at the point where secondary pump discharge is now connected.

   

Correct

Posted by: @davidalgarve

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The top left tank connection (currently ASHP flow) and the top right (currently radiator flow) to be plugged, whilst the bottom left (ASHP return) and bottom right (Radiator return) are to remain as installed.

It would be better to connect the radiator return to top right, leave the ASHP return bottom left, then plug the remaining two ports.  This ensures that the volume in the tank is engaged by forcing water to flow top to bottom through the tank.

With 15 radiators its quite probable that you don't actually need the volumizer, but since you have it... 

Posted by: @davidalgarve

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The secondary pump appears to be connected to the mains feed (running whenever the heat pump power is on), but will any electrical changes be required in the Ecodan?    

If its currently running constantly (indicating that the Ecodan doesn't control it in any way) then probably not, but without going through all the system settings I couldn't be sure.

Posted by: @davidalgarve

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@derek-m 

You would be most welcome and 3 bedrooms available. I would consider it good value!

Thank you for the very kind offer, but it was my feeble attempt at a joke. If my wife and I were to visit Portugal in the not too distant future, which we are not planning to do, we could maybe get together for a meal, and bore the ladies with tales of heat pump disasters.

After discovering yesterday that all buffer tanks would appear to not be created equal, I would add to the excellent advice supplied by James, that you should check for arrows on the buffer tank indicating direction of flow. With reference to the photo bellow, the return pipe from the radiators would need to be moved from the bottom left connection and connected at the top right connection. The present bottom right connection remains the same, and the two now open connections would need to be plugged.

With regard to the electrics for the secondary water pump, the manual shows that the power for the water pumps is switched on and off via relay contacts within the control unit. It should therefore only be necessary to disconnect at the local power supply feeding to pump.

Thanks Derek M for the further update. I have approached the contractor that installed the DHW system (including the 3 way valve) and he will make the changes as confirmed by JamesPa and I believe that this complies with your description above regarding the radiator return.

One last point: The towns water supply is connected to the buffer tank via a pressure regulator and is always on (currently set to about 1.9 Bar).  Is the connection at that point acceptable or must I move it?

I am attaching a photo and the connection referred to is middle front.

I can't think of any reason why the mains water connection would need to be moved.

Posted by: @derek-m

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Posted by: @davidalgarve

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Thanks Derek M for the further update. I have approached the contractor that installed the DHW system (including the 3 way valve) and he will make the changes as confirmed by JamesPa and I believe that this complies with your description above regarding the radiator return.

One last point: The towns water supply is connected to the buffer tank via a pressure regulator and is always on (currently set to about 1.9 Bar).  Is the connection at that point acceptable or must I move it?

I am attaching a photo and the connection referred to is middle front.

-- Attachment is not available --

 

I can't think of any reason why the mains water connection would need to be moved.

 

Agree, although in the UK, at least according to my understanding, this would have to be demountable via double check valves etc (assuming its effectively the 'filling loop'

Thanks JamesPa - have only just picked this up.

I have the contractor visiting who is primarily a solar installer but he added the DHW system and I have a lot of respect for him, although he has some fixed ideas.

I have started to explain the perceived benefits of taking the buffer tank out of circulation, but it occurred to me that I am uncertain how I will decide on the speed of the built in Ecodan pump.

What method will I use to evaluate the performance at the available speeds? 

By "taking the buffer tank out of circulation" I mean removing the secondary pump and using the buffer tank just as a volumiser

@davidalgarve If the heat pump is capable of modulating the pump speed (via a pwm cable) I would let it do so.

Otherwise you will have to look in the installation manual unless someone here is familiar with the specifics of ecodan.  Or just set it at the middle speed, and see if you get a DT flow-return of roughly 5C at the design OAT (or in proportion to Room temp - outside temp at higher OAts unless the heat pump modulates the water pump speed), with all emitter valves open.  Its not particularly critical ASFAIK so long as its sufficient.

Posted by: @davidalgarve

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Thanks JamesPa - have only just picked this up.

I have the contractor visiting who is primarily a solar installer but he added the DHW system and I have a lot of respect for him, although he has some fixed ideas.

I have started to explain the perceived benefits of taking the buffer tank out of circulation, but it occurred to me that I am uncertain how I will decide on the speed of the built in Ecodan pump.

What method will I use to evaluate the performance at the available speeds? 

I agree with James. I think that I am correct in saying that the water pump speed on the Ecodan can be varied from 1 to 5, so probably start with the pump set at 3 and see what DT you get. You may find that you need the pump speed lower in Summer and higher in Winter.