Posted by: @broadsman

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I may need to have a volumiser fitted to stop short cycling in my system, a Gen 7 Samsung 12Kwh ASHP.  I have read comments on here about how to plumb them in correctly, but have lost the thread. Could I please ask for comments from those that know how. I believe they should be on the flow side and not on the return. Thanks.

This was debated at length about a year ago on here.  It doens't make an enormous difference but yes in the flow and after the diverter valve, so that the volumiser is only engaged for space heating not DHW.  In at the bottom and out at the top to ensure that the whole tank is engaged even if the water in the tank starts to stratify.

Posted by: @jamespa

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Posted by: @broadsman

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I may need to have a volumiser fitted to stop short cycling in my system, a Gen 7 Samsung 12Kwh ASHP.  I have read comments on here about how to plumb them in correctly, but have lost the thread. Could I please ask for comments from those that know how. I believe they should be on the flow side and not on the return. Thanks.

This was debated at length about a year ago on here.  It doens't make an enormous difference but yes in the flow and after the diverter valve, so that the volumiser is only engaged for space heating not DHW.  In at the bottom and out at the top to ensure that the whole tank is engaged even if the water in the tank starts to stratify.

Whilst I generally agree with the above, it can be manufacturer specific.

For example, my Samsung heat pump will take heat from whichever cycle is active, space heating or DHW, when a defrost cycle is triggered.

If a defrost cycle commences when the system has just switched from space heating to DHW cycle and the DHW tank is cold, there may be insufficient heat in the system to perform the defrost unless the volumiser is fitted to the common flow or return pipes (before the 3-way diverter valve). Just something to consider, that there is no simple one size fits all recommendation. My volumiser is fitted on the primary return so affects both DHW and space heating, which is the correct location for Samsung heat pumps (flow or return debates aside).

Posted by: @old_scientist

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Whilst I generally agree with the above, it can be manufacturer specific.

For example, my Samsung heat pump will take heat from whichever cycle is active, space heating or DHW, when a defrost cycle is triggered.

If a defrost cycle commences when the system has just switched from space heating to DHW cycle and the DHW tank is cold, there may be insufficient heat in the system to perform the defrost unless the volumiser is fitted to the common flow or return pipes (before the 3-way diverter valve). Just something to consider, that there is no simple one size fits all recommendation. My volumiser is fitted on the primary return so affects both DHW and space heating, which is the correct location for Samsung heat pumps (flow or return debates aside).

 

Can you quote a reference for that requirement for the requirement on volumiser location in a Samsung system, Im struggling with the logic.

Whilst I can see the argument in principle, I cant see how it makes sense in practice.  That is unless Samsung require a volumiser in every system, which they dont in any manual I have seen, or alternatively provide a minimum specification for the contents of the DHW circuit, which again they dont so far as I can recall from the manuals I have seen.  If there were a material risk that the energy in the DHW circuit is insufficient for defrost, then that risk occurs irrespective of space heating system volume, hence every system would require a volumiser. But they don't and this must be because they are assuming that the energy engaged through the DHW tank even if its cold is pretty much guaranteed to be sufficient.  This is a very plausible assumption given that a DHW tank will typically be several times larger than minimum system volume, and minimum system volume must be calculated with the system water at 20C or thereabouts, because a defrost could occur shortly after the heating starts up or just after the system has switched back to space heating from a DHW cycle.

So far as I am aware many, perhaps most, heat pumps will take heat from whichever cycle is active, space heating or DHW, when a defrost cycle is triggered, so the 'Samsung' argument, if it is valid, would apply to those also, yet apparently it doesn't.   

The reason not to put the volumiser in the common parts of the system BTW is that, if you do, then in Summer, you heat it to the DHW temperature on every DHW cycle and that heat is completely wasted or worse contributes to overheating of your house.

@jamespa Sorry, I've checked and am unable to find a system schematic showing a volumiser in any of my Samsung documentation (I thought it did).

The only relevant reference is to the minimum system volume of 50L which must be achieved, and that a volumiser should be fitted if required to achieve this. Without a volumiser fitted, my DHW circuit would not contain 50L (18m of primary 28mm pipework only gives a ~10L system volume plus maybe another few litres in the cylinder coil), and if the tank temperature is cold, the water covering the coil could easily be at winter inlet temps of around 10C. It's difficult to see how there would be sufficient heat in the system to effect a defrost cycle in DHW mode.

I do take your point though, and wish I'd asked the plumbers to plumb in a bypass for the volumiser that I could open in summer as I'm no doubt heating an additional 50L volume to 55C in summer to reheat the DHW tank. In winter it's less of an issue as that slug of hot water gets fed into the radiators and quickly dissipated into the rooms as a welcome boost of heat given the heating has just been off for 30mins whilst the DHW cycle ran.

@jamespa

Posted by: @jamespa

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In at the bottom and out at the top

James, could you advise how much would be lost if I use in at the top out at the bottom, please? I am planning my changes for the end of the heating season and "in at the bottom...." will require more new pipework and rather more elbows, which I am trying to minimise to optimise flow.

Posted by: @old_scientist

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@jamespa Sorry, I've checked and am unable to find a system schematic showing a volumiser in any of my Samsung documentation (I thought it did).

The only relevant reference is to the minimum system volume of 50L which must be achieved, and that a volumiser should be fitted if required to achieve this. Without a volumiser fitted, my DHW circuit would not contain 50L (18m of primary 28mm pipework only gives a ~10L system volume plus maybe another few litres in the cylinder coil), and if the tank temperature is cold, the water covering the coil could easily be at winter inlet temps of around 10C. It's difficult to see how there would be sufficient heat in the system to effect a defrost cycle in DHW mode.

I do take your point though, and wish I'd asked the plumbers to plumb in a bypass for the volumiser that I could open in summer as I'm no doubt heating an additional 50L volume to 55C in summer to reheat the DHW tank. In winter it's less of an issue as that slug of hot water gets fed into the radiators and quickly dissipated into the rooms as a welcome boost of heat given the heating has just been off for 30mins whilst the DHW cycle ran.

 

I cant argue with your logic. 

I think most installers, rightly or wrongly, assume the DHW circuit will be OK or alternatively include the volume in the tank (not just the coil) in the calculated system volume (and thus conclude that the DHW circuit is OK). 

I think including the volume in the tank is a very reasonable assumption given that there is a pretty good heat exchanger, but I take your point that, in theory, it could be at 10C, in which case perhaps there would not be sufficient energy stored.  On the other hand, since this seems to be normal practice and since we haven't had a single case here of 'defrost death spiral' due to system being in DHW mode, I'm minded to think that the unstated assumption is actually a reasonable one.  Even water at 10C contains energy after all, and if you have 200l that's quite a lot of energy (roughly enough to melt 25kg of ice). 

A volumiser bypass with the volumiser in the DHW circuit is of course the 'ultimate' solution and as you say it matters materially only when the space heating is 'off'.  Most homeowners wont remember to flip the valves though, so it would have to be automated to deploy as a mass solution.  Given the lack of reports of 'defrost death spiral' its probably a very reasonable call just to ignore the risk!

Posted by: @jamespa

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Posted by: @old_scientist

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@jamespa Sorry, I've checked and am unable to find a system schematic showing a volumiser in any of my Samsung documentation (I thought it did).

The only relevant reference is to the minimum system volume of 50L which must be achieved, and that a volumiser should be fitted if required to achieve this. Without a volumiser fitted, my DHW circuit would not contain 50L (18m of primary 28mm pipework only gives a ~10L system volume plus maybe another few litres in the cylinder coil), and if the tank temperature is cold, the water covering the coil could easily be at winter inlet temps of around 10C. It's difficult to see how there would be sufficient heat in the system to effect a defrost cycle in DHW mode.

I do take your point though, and wish I'd asked the plumbers to plumb in a bypass for the volumiser that I could open in summer as I'm no doubt heating an additional 50L volume to 55C in summer to reheat the DHW tank. In winter it's less of an issue as that slug of hot water gets fed into the radiators and quickly dissipated into the rooms as a welcome boost of heat given the heating has just been off for 30mins whilst the DHW cycle ran.

 

I cant argue with your logic. 

I think most installers, rightly or wrongly, assume the DHW circuit will be OK or alternatively include the volume in the tank (not just the coil) in the calculated system volume (and thus conclude that the DHW circuit is OK). 

I think including the volume in the tank is a very reasonable assumption given that there is a pretty good heat exchanger, but I take your point that, in theory, it could be at 10C, in which case perhaps there would not be sufficient energy stored.  On the other hand, since this seems to be normal practice and since we haven't had a single case here of 'defrost death spiral' due to system being in DHW mode, I'm minded to think that the unstated assumption is actually a reasonable one.  Even water at 10C contains energy after all, and if you have 200l that's quite a lot of energy (roughly enough to melt 25kg of ice). 

A volumiser bypass with the volumiser in the DHW circuit is of course the 'ultimate' solution and as you say it matters materially only when the space heating is 'off'.  Most homeowners wont remember to flip the valves though, so it would have to be automated to deploy as a mass solution.  Given the lack of reports of 'defrost death spiral' its probably a very reasonable call just to ignore the risk!

All very reasonable. During 2 winter's of usage, I only recall 1 defrost cycle occurring during the DHW cycle, probably a result of always trying to run our daily DHW cycle at the warmest part of the day for maximum efficiency.

It never really occurred to me before, but I should also note that on our Joule Kodiak pre-plumbed cylinder, there is no option to fit a volumiser after the 3-way diverter valve as it's all 'built' in on the front of the cylinder, so the only place to physically plumb it is in the primary flow or return.