Hi Everyone,

Some time ago I carried out some research on buffer tanks, LLH and PHE, and watched some quite interesting YouTube videos, posted by people in the heating industry.

The conclusion was that heat pumps, and any of the above items do not make a good combination. Let me explain.

Heat pumps come with their own water pump, which unless you have a particularly large or expansive system should be adequate to pump the heat energy around your home. Installing any of the above equipment necessitates the requirement for a secondary water pump.

For PHE to transfer sufficient heat energy from the primary circuit to the secondary requires the LWT from the heat pump to be higher than would be necessary, and hence reduces overall efficiency. You are also running a secondary pump.

Buffer tanks and LLH would work okay if the water flow rate going in, was matched by the water flow rate coming out. This is hardly likely to be the case, since the heat pump will probably be varying the speed of the internal water pump, and hence the flow rate, to maintain the specified DeltaT. The end result is probable mixing of the flows within the BT or LLH, with resultant loss of heat energy getting to the heat emitters, and the controller or user raising the LWT to compensate.

If you need to know if your system has sufficient volume to cope without a BT or LLH. Measure the size of each radiator and note how many panels, then go to the Screwfix or similar website and find a radiator of the same size and type, look up the specification to find the volume in litres. Add up the volume of all your radiators and compare it with the minimum volume requirement specified for your heat pump. If the system volume is too low than add a volume chamber, or if you already have a BT, then remove one inlet and one outlet pipe and fit a connection pipe in between. Then plug the two ports on the BT.

Hive….. poor you. Quite possibly the worst on/off stat you can get.

Whereabouts in the property is the Samsung controller? Please don’t say ‘in the loft’

@derek-m Thanks for your thoughts on buffer tanks. My research about them produced similar conclusions. The minimum volume for a Samsung 12kW ASHP is 50 litres and our radiators are well over 80 litres. This assumes that the heat pump can always access the secondary circuit during a defrost cycle, which Fergal claims it can't. If true, that sounds like a serious design fault. My concern with following your advice to bypass the buffer tank is that it may void my warranty, which Fergal says it will, even though the manual claims that a buffer tank is not required "...unless working on a very small house/flat..". Also my system suffers from short cycling which the buffer tank is supposed to eliminate.

Posted by: @mike-h

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@derek-m Thanks for your thoughts on buffer tanks. My research about them produced similar conclusions. The minimum volume for a Samsung 12kW ASHP is 50 litres and our radiators are well over 80 litres. This assumes that the heat pump can always access the secondary circuit during a defrost cycle, which Fergal claims it can't. If true, that sounds like a serious design fault. My concern with following your advice to bypass the buffer tank is that it may void my warranty, which Fergal says it will, even though the manual claims that a buffer tank is not required "...unless working on a very small house/flat..". Also my system suffers from short cycling which the buffer tank is supposed to eliminate.

Maybe you should ask Fergal why it is short cycling.

Posted by: @batalto

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it might be in the manual (or was) but they've [Freedom/Fergal] told me it doesn't void the warranty as long as the system can work without. They add the LLH as it saves doing any actual calculations on if the system needs one or not. By adding it they by default don't need to check if it's needed - they said almost all of their installers are plumbers, so they just don't have the knowledge or capability to do that kind of technical analysis beforehand.

Posted by: @mike-h

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My concern with following your advice to bypass the buffer tank is that it may void my warranty, which Fergal says it will, even though the manual claims that a buffer tank is not required

I rest my case. Not only do Freedom think their installers are thick (can't do sums), they think their end users are thick as well. It must be frightfully jolly being so clever when all around you are so thick.

I think the end result is we are are on our own here. Freedom clearly haven't got a clue. The manufacturers constantly hide and/or obfuscate information. No wonder 10% or less of installation are achieved without flaws. All credit due to @derek-m and all the others who have done their own research and made their findings available here for others to benefit from.

@cathoderay in fairness to freedom, they are B2B not B2C. They assume (I think correctly) that most installers don't actually understand what they are installing and make it as fool proof as possible for them to minimise call outs/troubleshooting for the end user. Is it the most efficient for the end user? No. Is it the easiest for the installers, yes. Actually trained people who understand these things are few and far between. Most fitters come from the world of gas boilers. Chuck it in, set it to 70 degrees and take the cash - no one cares about efficiency with gas (for some reason). The fact is my original fitter could have easily removed/not installed the LLH, but he didn't know what it did and wasn't sure what impact it might have. So in the end he refused to do it. It was Freedoms technical support who directed me to someone who would. They said themselves that pretty much every customer was ignorant of their system and how it worked. They wouldn't fit a LLH in an ideal world. An individual person is smart, but people are stupid. And people want hot rads and an easy life. Most couldn't tell you the flow rate or volumes of their rads and 99% of plumbers couldn't either. Most people with a gas boiler couldn't tell you their flow temperature and thats a problem.

Now gas isn't cheap I think we'll see a change and a lot of flow temperatures come down. But even now the focus in all media is about lowering your thermostat AND NOT lowering your flow temperatures. Arguably the latter will save far more gas, cost less and deliver a better consumer outcome. I would easily take a punt that 90% of housing stock in this country with gas could run at a flow temperature of 50 or 55 degrees with NO issues. But one thing I've noticed is people like red hot radiators, the idea they wouldn't be scalding to touch seems to be an anathema to many.

@batalto - I respect Freedom's right to be B2B (they said the same thing to me, when they were telling me to get lost) but that doesn't mean I think it is enlightened. There are other fields I operate in that involve technical matters of varying degrees of complexity and I generally find things work best when manufacturers/suppliers are prepared to talk to informed end users. Elsewhere I said I considered Freedom are arrogant, and it doesn't get much more arrogant that 'pretty much every customer was ignorant of their system and how it worked'. That's every customer, so that includes me and you as well!

I have a theory about why people like hot rads, I suspect it may be because hot rads also radiate as well as convect heat, and so you feel a sun like warmth when near one, and who doesn't like the warmth of the sun. 

@cathoderay to be fair, I was pretty ignorant lol. It's only through self learning that I understand. I imagine most consumers wouldn't bother to understand the intricacies of weather compensation or low loss headers - nor would they want to, frankly.

For what it's worth, I managed to get through to Samsung technical support and had a call back from one of their engineers. The system volume that matters from a warranty point of view is the fixed volume - it does not include radiators with TRVs, only radiators that are on all the time plus the pipework. So he appears to back Fergal's stance. When I asked him how other manufacturers managed without buffer tanks, he said he used to work for one of those and they had lots of problems with their invertors breaking down. I think I will be keeping my buffer tank. Thanks for all the comments.

Just have to sort out the short cycling now......

@mike-h - none of this makes much sense. You might as well ask these 'engineers' what the best way to Tipperary is. I have a plate heat exchanger rather than a low loss header of buffer (and Freedom seem to think they are interchangeable, at least on Midea systems) and one of the 'good' points about a PHE is it keeps the clean primary circuit separate from the dirty secondary rad circuit. One consequence is that the ASHP primary circuit circulating volume is small, just ASHP to airing cupboard and back, maybe 6m each way, plus whatever is in the PHE or DHW heating coil. Go figure...  

And here are the figures: bore capacity of 28mm pipe (copper, mine is plastic, but will be near enough the same)= 0.54L/m x 12 = 6.48L plus whatever is in the PHE, which is in use >23 hours/day as DHW is on a 1300-1400 only timer, say 2L max, total 8.48L.    

@batalto (and others) - I've just had a look at Freedom's latest Midea installation manual, available here, only to find the kiss your warranty goodbye message is there, albeit with slightly different wording:

"Every system must have hydraulic separation between the primary (heat pump) and secondary (heating circuit) pipe work. This can be via a buffer tank, low loss header or plate heat exchanger. If you install the unit without hydraulic separation, you will void the warranty."

Arrgghh...  

Posted by: @cathoderay

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And here are the figures: bore capacity of 28mm pipe (copper, mine is plastic, but will be near enough the same)= 0.54L/m x 12 = 6.48L plus whatever is in the PHE, which is in use >23 hours/day as DHW is on a 1300-1400 only timer, say 2L max, total 8.48L.    

@batalto (and others) - I've just had a look at Freedom's latest Midea installation manual, available here, only to find the kiss your warranty goodbye message is there, albeit with slightly different wording:

"Every system must have hydraulic separation between the primary (heat pump) and secondary (heating circuit) pipe work. This can be via a buffer tank, low loss header or plate heat exchanger. If you install the unit without hydraulic separation, you will void the warranty."

Arrgghh...  

 

I think that you may need to ask Freedom to clarify exactly what they mean by 'hydraulic separation', since of the three items listed, only a PHE will provide true hydraulic separation, in that the liquid in the primary circuit is completely separate from the liquid in the secondary circuit. Both a buffer tank and a LLH use the same liquid.