That is a very useful reference. If I use the COP calculator referenced above and put in your average figures your flow outlet temperature is 35C for an outside temperature of 4.5C to achieve a COP of 3.8
I am currently having to operate at around 43C under these conditions and that gives me a COP of 3.2 . This means I need to aim to lower my flow temperature by 8C. This needs radiators that are approximately twice the emission rating using the calculator below.
That is a quite an expensive upgrade and returns less than 10% saving on my space heating costsā¦
Before you rush off to buy new radiators, you might want to double check a few of your assumptions first:
You used @johncantorās CoP estimator. This is a good model for scoping new projects and for getting a feel for how heat pump operation varies with LWT and outside temperature, but the numbers it gives donāt necessarily apply to your specific heat pump model.
If you havenāt seen this, more relevant figures for your model are available in the Samsung EHS Technical Data Book https://midsummerwholesale.co.uk/pdfs/-tdb--ehs-mono-ht-quiet-for-europe--r32--50hz--hp--ver.2.1-221005.pdf (see Table 2-9 on p30). These are based on Samsungās measurements on their (ideal) laboratory set-ups, and apply when the heat pump is operating at synchronous speed (i.e. compressor inverter output frequency is 50Hz) and at a DT i.e. (LWT ā RWT) of 5degC. Even so, these numbers are probably more realistic than those from a generic model such as Johnās.
One reason that a generic model may not give accurate CoP predictions in your case is that, unusually in domestic heat pumps, the compressor in the Samsung HT is 2-stage. It has a vapour injection (aka economiser) circuit, as you can see on the flow diagram on p27 of the above Data Book reference. Vapour injection improves the CoP of a heat pump compared with single-stage designs (though it costs more to build, so is more expensive to buy).
A better basis for CoP estimation (and thus the basis for economic decisions on system enhancement, such as replacement radiators) is your own operating data. Iām sure that you know how to obtain this from your controllerās remote display ā you can see the LWT, RWT, and water circulation rate in Service Mode, from which you can calculate your heat generated from Q = M.Cp.(LWT ā RWT), and the power consumed on the Settings screen. You could even construct your own personalised Table 2-9, based on these figures and your outdoor temperatures (displayed on the Home screen) and your LWTs.
But even these figures are only approximate ā the thermocouples in the heat pump are only surface-mounted, so LWT and RWT may each have an error (say +/-0.5degC) which can cause a larger % error in (LWT ā RWT) in the above equation, hence potentially a large error in the calculated Q. The only way to get an accurate CoP is to install a certified heat meter in the water flow/return piping, and a CT (current transformer) meter on the heat pump power supply. These are not cheap (several hundred Ā£ installed), so may be difficult to justify economically.
Finally, even if you do derive sufficiently reliable running cost numbers, remember that upsizing radiators is not necessarily the only option for reducing them ā for example you might be able to get more heat from your existing radiators by increasing the water circulation rate (which reduces their water DT, which increases their deltaT to the room they are in, or alternatively allows you to reduce the LWT a little to maintain the same deltaT, hence heat output), or increase heat to critical rooms (e.g. living room, shower room) by reducing heat to unused rooms, or timing room heating to coincide with occupancy, or even reducing roomstat setpoints and putting on a sweater on the coldest days (probably the most cost-effective thing you can do).
Feel free to ask questionsā¦
Hi Sarah,
That is great information. I had no idea that the Samsung HT 8kW was 2 stage. The capacity table is much higher than standard. In the case of 55C FT at 2c ambient the COP is 3.1 rather than 2.57 in the Cantor calculator which makes me less concerned about running high temperatures. And the output at 70C with 2C ambient is 11kW How do they do that? No wonder it heats my DHW tank so quickly. Does that match your monitoring?
In reality I think it is going to be difficult for me unless I invest in the fully certified heat monitor. I will tabulate my CoP as best as I can for now for comparison purposes. ( cannot find RWT though in settings screen)
The system works so well right now for so little cost compared to the oil system it replaced I am inclined to think I am grossly underestimating the heat output into the house.
Would be interested to hear what numbers you get for your house putting it through this simple heat loss calculator Super Simple Heat Loss and what youāre using for electric and what the Samsung suggests itās outputting in terms of heat on the coldest days?
Could you also list the radiators and standard DT50 outputs that you have, E.g:
6x 1200x600 K2 @ 2080W each = 12480W
4x 1000x400 K2 @ 1260W each = 5040W
Total = 17520W
I wonder what you would get plugging the numbers from the simple heat loss calculator and the total radiator rated output into the Weather Compensation tool? and how those numbers reflect the settings that you mentioned in the first post.
Easy-peasy. If you look at Table 2-1 on p10 of the Data Book you will see that the same compressor is installed in the 8kW unit as in the 12/14kW units (even though the evaporator is slightly smaller). Iām guessing that 90% of the kit in the Outdoor Unit is too (I havenāt actually looked - my OU is on an elevated platform to prevent cold air recirculation and I have no head for heights). Iāve often measured over 10kW from my 8kW nameplate HTQ. Also, your compressor inverter output frequency is not constrained to 50Hz (the basis of the Data Book capacity table). Iāve measured up to 60Hz output (and scroll compressor duties theoretically vary linearly with speed per affinity laws for positive displacement machines, so 8kW x 60/50 gives a fairly consistent 9.6kW).
You can do an 80/20 for about fifty quid. Have a quick read of Monitoring Your Samsung ASHP Controller. I can sit at my laptop and watch whatās going on around my Outdoor Unit (as well as water circulation/DHW data), live on the screen and/or recorded as an Excel spreadsheet for later study. (The advantage of the spreadsheet is that you can use Excelās powerful graphical and regression capabilities, if you want to dig a little deeper and know a bit about sums). Installation is easy (I know nothing of data transmission techniques - I just followed a step-by-step email from my son-in-law, who does). Edit: I should have added that I can also inspect/update all the controller factory settings (āFSVsā) from my laptop using the same monitor software - another little bonusā¦
Itās buried in the Service Mode settings (up+down then 0202), under Self-Test Mode/Self-Test Mode Display. Unfortunately itās only given to the nearest integer degC (no decimal) so not really accurate enough with a single reading (before I installed the above monitor - which does give the first place decimal for LWT/RWT - I would average the remote display readings over a few minutes). The water flow reading (lpm) is given under Indoor Zone Option/Indoor Zone Status Information. You need to convert to kg/s (via density) to do the CoP calculation, of course.
When I had my HTQ installed, I did upsize a couple of living room radiators but all the rest do a good job of keeping the house warm, without modification.
You may actually have a better HP than you realise - you should congratulate yourself for choosing an above average one!
Thanks Sarah , I chose the Samsung HTQ after a recommendation that it is designed to replace a fossil fuel burner with DT50 radiators and standard DHW tank with no internal changes required, just a new pump and a better filter. I have proved it works fine like this achieving the target temperatures just as they say.
I have some experience with monitoring solar energy systems on the RPI so will try out the very useful guide you have posted and see how efficient it is running with such a simple low impact installation. (but I already know it is much cheaper to run than oil so very happy!)
I am in about the same position, although my design temp is 45ish at -3. i do find that after balancing the system and using honeywell valves to stop solar gain I find that my living room is lacking in heat and I am compensating with a higher flow temp. open plan and leaving the doors open for the heat to rise in the house makes this situation worse. I think its definitely worth doing just a couple of DIY radiator upgrades to increase the output in the colder rooms , this will automatically allow a lower design flow temp without a big cost. my self install 7kw Vaillant system will have some rad increases to see if I can lower another 5 deg. Some insulation on the suspended timber floor and then i think thatās effectively where the investment for ROI will stop.