Yes, I get that, but how large is that loss percentage-wise? The throttling effect reduces say 11kW to 8kW - a 27% reduction. I suspect the blockage is the main problem, not the agreed but possibly not very large drop in efficiency. Again, I am distinguishing between throughput on the one hand and efficiency on the other.
As stated upthread about 2-3% per deg C, but if you want an accurate number check your systems data tables.
Throttling is a different phenomenon which may (will) in addition cause a further loss in efficiency because water is being recirculated through the heat pump without doing anything useful and you cant get owt for nowt. However I don't have a figure for this effect and as you say its probably not the main downside of throttling.
This post was modified 4 months ago 2 times by JamesPa
I'm still sure about this, I think we might be mixing up throughput with efficiency. Consider the PHE as a form of obstruction: it restricts throughput. Even if the heat pump can produce 11kW, and the PHE can only throughput 8kW, then you have, in effect, my situation, with the heat pump reacting by only producing 8kW. A bit like trying to blow down a very small bore pipe. Your lungs can produce enough airflow to blow out candles six feet away, but the small bore pipe restricts the flow, and you only can only blow out one candle three feet away. But does that mean your lungs are now less efficient? Less capable, certainly, but less efficient? I can imagine something similar with a heat pump: its output is restricted, but it can still produce that lower output efficiently.
and I am still sure also. we just need to be clear we are talking about the right things:
your system has a throughput problem, because of the undersized PHE.
because it has a PHE in it, it has an efficiency loss due to the temp drop across the PHE. Thats physics, it can't not be there. But that isn't your main issue because that problem is almost entirely masked by the first one.
Any system with a PHE (or llh, or buffer) in it will have problem #2. To varying levels depending on the quality of the engineering. In some systems its awful. In some , its acceptable.
An open loop system would also have a throughput problem if the pipes were too small and it wouldn't work properly. that'd be equivalent to problem 1 above. But it would never have the "efficiency loss due to enforced temperature drop" problem (2).
I don't think you need a degree in physics (although it probably helps), but you do need engineering skills to do the system design and problem solving. Many plumbers are essentially fitters, very skilled at what they do but not able to do the engineering. Unfortunately the system engineering and problem solving associated with plumbing, which I think is inherently interesting, comes with the requirement to bend yourself double in a confined space, whilst being looked down upon by a sector of the British public. Not the greatest incentive for a bright young graduate.
agree. I've always thought a mandatory qualification for a plumber is to be wiry, with very strong but thin arms. had one once who was my build (flanker) and he always sent his scrum-half build apprentice into the tight spots. very skilled fitters as you say. But none of them was ever what I'd call a heating engineer, always at a loss when I wanted to discuss detailed system design . They would rely on vendor supplied information... which is where the likes of Freedom, Midsummer, Joule etc come in . The conjoining of it with the role of bathroom fitter doesn't make for an interesting path for an technical graduate either.
digressing but I've pondered several times if there's a way to combine my engineering/physics/system design skills with those of the young plumber down the road who is merrily servicing / fitting combi's all day every day. can't think of a way that actually works though.
But that isn't your main issue because that problem is almost entirely masked by the first one.
Which is the point I was trying to make using lay language. The throttle effect (at 11 down to 8 kW) is around 27%, the efficiency losses are (much?) less. Taking @jamespa's 2-3% per degrees C (between primary in and secondary out, I presume, which most of the time was between 1 and 2 degrees last time I took measurements) then the efficiency losses are say 2.5-5%.
An open loop system would also have a throughput problem if the pipes were too small
This is the same as my blowing through a small bore pipe analogy. It is not a loss as such, or an efficiency question, but rather simply a failure to deliver.
I do get it, but in my non-physics trained mind I see two problems (as you do) but conceptualise them slightly differently: the first, and more important problem is an obstruction to flow, the second is efficiency losses that arise from the heat pump having to work harder to get the same water temp at the rads.
Still no reply from Freedom Heat Pumps on details of my PHE.
Midea 14kW (for now...) ASHP heating both building and DHW
digressing but I've pondered several times if there's a way to combine my engineering/physics/system design skills with those of the young plumber down the road who is merrily servicing / fitting combi's all day every day. can't think of a way that actually works though.
To some extent you are doing that by contributing to this forum. I have also wondered the same (but am enjoying being retired too much to want to commit at the present time). There are a couple pf people out there who are doing exactly that, albeit doing some plumbing as well, but trying to find ways to outsource this bit.
In general building we have Structural engineers, Architects and Builders. They manage to work together. The customer often contracts separately with them (for very good reason).
MCS mandates that your contract for the design and installation is with a single person (just saying!).
This post was modified 4 months ago 2 times by JamesPa
It may take two separate people. In building we have Structural engineers, Architects and Builders. They manage to work together. The customer often contracts separately with them (for very good reason). MCS mandates that your contract for the design and installation is with a single person (just saying!).
I think it's called market forces, the efficiency of markets, or whatever those who work in the field that makes astrology look reputable call it these days. There's nothing to stop firms that have an engineering department and a fitting department providing both sides of the equation - I'm not sure you really need the added complexity of multiple contracts - except that the engineering department is an unnecessary expense if Freedom et al are willing to step in provide a quasi-engineering department, in the form of their spreadsheet, along with their training, handy videos and installation kits.
I can't think of another household or other purchase that requires potentially a lot of engineering input at the design stage, and then a considerable amount of fitting work to be done at the installation stage. Maybe the industry needs to think about new ways of working, though I have to add that in medicine any medical report that has new ways of working in the title usually means new ways of putting your feet up.
Midea 14kW (for now...) ASHP heating both building and DHW
Hi @toodles don't know if you've seen them before but there a couple of articles which may be of interest from Protons for Breakfast regarding his system performance before and after removal of the LLH (I have a LLH on my Daikin ASHP) - links here and here
Having looked at the two articles, I think that the author seems to be arriving at conclusions on very limited data.
I also note with interest that he appears to have failed to appreciate the reason why the IAT increased to 22C after the LLH was removed, the transfer of thermal energy was much improved, so the LWT was now higher than required. Had he lowered the WC curve to lower the IAT, I think that he would achieved an increase in efficiency and higher COP.
@editor Here is a graph of temperatures taken from my 4 pipe buffer tank ( before it was removed). You can see that Delta T between Buffer in (LWT) and Buffer return (RWT) is similar to the Delta T between Buffer out (to the radiators) and Radiator return (back to the buffer from the radiators). I take that to suggest that the flow rates in the primary and secondary circuits are similar. Nevertheless, there is a 4-5 degC difference between LWT from the Samsung and the temperature of the water going to the radiators. That in itself reduces efficiency and increases costs by around 12%.
Protons for breakfast found that removal of his LLH didn't make much difference, but I wonder if his LLH was tall and thin as opposed to my buffer tank which was short and stout. There is only a couple of inches between the pipes in my buffer tank, so mixing is inevitable.
A simple remedy would be to re-pipe your buffer to make it into a volumiser in the return leg to the heat pump.
This leads us to a critical point regarding the testing practices of heat pump manufacturers in the UK. While the performance and efficiency numbers they publish are derived from standardised testing conditions for consistency and reliability in comparing various models, the specifics of whether these tests include LLHs and buffer tanks are often not detailed in the general product literature.
According to information I've received from sources well-informed about the industry, most of these test setups do not incorporate LLHs or buffer tanks. Despite this, manufacturers frequently recommend their inclusion in actual installations. This discrepancy suggests that the performance results achieved in real-world settings may not align precisely with the published data, as the test conditions under which these figures are obtained do not fully mirror the recommended installation setups.
I think this may be one of the problems encountered when modelling heat pump behaviour based on manufacturer data. The manufacturers quote efficacy (what can be achieved in ideal circs eg in a lab/RCT), whereas in the real world we get effectiveness (what can be achieved in practice, in the real world, where 'stuff happens'). In medicine, the two are often very different, and I think the same might apply to heat pumps: what the labs predict is not what you get. And that's before incorporating the PHE throttling effect (which is after all just another what you get in practice effect).
That is precisely why when modelling heating systems, not just the heat pump data should be part of the overall equation. It is also necessary to incorporate the effect from additional equipment and the limitations of the overall system design.
Really it’s system dependent, as we learn how few KWS we really need there are going to be proportionately bigger pipe layouts that the heat pump pump can’t cope with..1200 lph just won’t satisfy a system need 1800 lph
And it’s a brave person who poo poos system designs from manufacturers, and it’s cynical to think global manufacturers add things unnecessaryily. But I will grant you this, the very same manufacturers are doing a piss poor job educating installers and the public..
