Posted by: @toodles

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At the risk of being drummed out for heretical thoughts ( ;-))) ) No, I’m sure I wouldn’t be, … would I?! Suppose this LLH is losing some efficiency - where is the loss taken place and where is the wasted energy going please? If the loss is in the form of heat that doesn’t make it across the interior of the LLH, does it radiate into the surrounding area? In my case, this will be the airing cupboard where such heat will be ‘always useful’, (harking back to the topic of uninsulated pipe runs within the home again!). If the unharnessed energy is being deflected back out into the return pipe-run to the heat pump outside, I can see that this might well be wasted heat though. Regards, Toodles.

The principal reason that LLH reduces efficiency is if there is a temperature drop flow to flow across it (which there almost inevitably is unless it is particularly well set up).  This means that the heat pump operates less efficiently, because it must operate at a higher flow temperature to achieve the same temperature at the emitters.  Part of the reduction in efficiency will be that the compressor (which is usually outside) has to work harder, and part of the loss will be that not as much energy is extracted from the outside air.  So no, the 'lost' efficiency does not result in an increased radiation into the house (nor is it the case that a 'loss' of energy takes place in the LLH, albeit that it is the cause of the reduced efficiency - the reduction in efficiency occurs even if the LLH is lossless)

There will also of course be some actual loss of energy from the system at the LLH, due to convection.  Depending on the location of the LLH that might get radiated into the house.  This can be ignored if the LLH is within the heated envelope, and generally is ignored in these discussions.

Posted by: @toodles

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At the risk of being drummed out for heretical thoughts ( ;-))) ) No, I’m sure I wouldn’t be, … would I?! Suppose this LLH is losing some efficiency - where is the loss taken place and where is the wasted energy going please? If the loss is in the form of heat that doesn’t make it across the interior of the LLH, does it radiate into the surrounding area? In my case, this will be the airing cupboard where such heat will be ‘always useful’, (harking back to the topic of uninsulated pipe runs within the home again!). If the unharnessed energy is being deflected back out into the return pipe-run to the heat pump outside, I can see that this might well be wasted heat though. Regards, Toodles.

If you have any more heretical thoughts then please let me know, so that I can send the Inquisitor round. 😋 

The loss isn't actual thermal energy as such, the loss is due to reduced efficiency (lower COP). Because of possible temperature reduction from primary circuit to secondary circuit, the LWT may have to be higher to ensure the heat emitters receive the required quantity of thermal energy.

To produce a higher LWT the compressor has to work harder, using more electrical energy, and in turn the heat pump absorbs less free energy from the OAT.

The overall thermal energy supply to the home should be approximately the same, just less free energy and more expensive energy.

@derek-m Just for ‘fun’, I placed strips of matt black insulting tape on the four pipes to and from the LLH and used my IR thermometer to obtain these approximate readings; I measured the four points a number of times to attempt to obtain steady readings and my best attempts tend to suggest the following temperatures.

Input to LLH from heat pump: 29.8 deg. C

Output to emitters: 29.0 deg. C

Return from emitters: 28.0 deg. C

Return to heat pump: 28.8 deg. C

Do these readings look as if they may be true? I’ll take another set of readings another day when time permits (don’t get older if you can help it, you spend more time than you might like draining the NHS facilities!) meanwhile without placing ‘proper’ sensors on the pipes, I’m not sure I can increase the accuracy. I wonder if there is also room to improve the Delta T by adjusting the secondary pump? Regards, Toodles.

I can't remember ever having used an IR thermometer, but then I've always had access to what I would term correct test equipment. I do believe that one of the other forum members found difficulty getting accurate readings using an IR thermometer. What is the specified operating range and tolerance?

The actual readings obtained could be appropriate for a mild day like today, but again without other values to compare it is difficult to know for certain.

The DT does look low, but again without comparing with values measured during colder weather conditions, I cannot say for certain.

Without further data, I would suggest that you just monitor, without making changes, especially if you are warm and it is not costing you an arm and a leg to operate.

I keep advising people not to grow older, but they will insist upon doing so. 🙄 

@toodles I've tried IR with black tape, doesn't work very well . Other forum members have had good results for very little spend with a set of these from amazon. tape them tightly to the pipes, pipe insulation over the top to isolate from ambient.

@iancalderbank Oh Ian, I couldn’t see a link or any product details - please could you detail the goods again? My current attempts have been with a non-contact IR Thermometer with a spec. Of  0 ~ 550 C. +/- 1.5 %. Probably indicative but the tape covered pipe might be causing all sorts of errors I would imagine. Regards, Toodles.

@derek-m The system seems to be working well, we are warm and at approx. 450-500 W/h in this present warm weather, I feel all is goodness and light. (COP shows as 4.5 plus), when it was - 6 or -7, the COP was approx. 2.6 I think. As Ian has mentioned, an alternative means of measuring the actual LLH adjoining pipe temperatures would be better though. Regards, Toodles.

@toodles I put a link in the word "these" in the previous post. this type of thing. others on here have used them successfully.

@iancalderbank Thank you Ian, Regards, Toodles.

@iancalderbank Amazon delivered the four thermometers today; shame that there was not insulating material interposed between the contact and the button cells; flat cells in three of them and a faint glow only from the other! Did extended battle with Amazon help line / suppliers site and now await replacements. Ho-hum more grey hairs (well, actually, they are white already) and time I won’t get back!;-) Regards, Toodles.

@toodles You were unlucky. I got the same 4 digital sensors over a year ago and all batteries are still going strong. Great devices across the low loss header to check primary and secondary flow and return temperatures. Make sure the sensor is touching the pipe and well insulated. Cable tie sensor to pipe, and then cable tie insulation completely over it. They would probably benefit from heat sink compound, but my memory of that stuff from my apprenticeship days is it ruins clothes instantly!

@allyfish I had a reply from the supplier, requesting a photo or video the the product!!! I sent a phot of the four displays; one was readable, one was feint and the other two were blank. I asked if they didn’t trust me? Anyhow, I orderedmsome LR44’s that should arrive today so that I can put the ‘kit’ together. Perhaps the supplier will send me another 4 units, I doubt they sell the cells anyway! Regards, Toodles.