Newbie question about rated heat pump output

I’d suggest that ASHPs are roughly the same, as they use the same refrigerants and are governed by the same laws of physics. I don’t think you’d see vastly different heat outputs.

What really sets them apart is the quality of the controls, and how well designed the overall heating system is. What really matters is finding a great installer who really understands low-temperature heating, and let them worry about which heat pump to fit.

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Is the info from MCS wrong then, or at least out of date? Unless I have misunderstood, the MCS guide seems to be saying that many heat pumps will only give 60% of their rated output at the not particularly low temperature of -2C. Whereas other heat pumps, as you demonstrated, will give 100% of their rated output right down to below -10C. That seems like a pretty major difference to me.

MCS seems to be somewhat out of date, both with that 60% figure and expecting to need 55°C flow temperatures when it’s below freezing. Heatpump technology and system design has evolved considerably; MCS has not.

You may find this topic interesting, which discusses how much to oversize a heatpump to ensure it can provide enough heat to compensate for regular defrosts. It includes data from several manufacturers, as well as real-world measurements from real systems:

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Thanks, that’s really interesting. I think what the OP is hinting at is that the 11kW and 16kW models are mechanically identical, but the 11kW has been hobbled with software. So, when you look at the -7/8C output for the 16kW, you see it is only 66% of the rated output. That is probably closer to the heat pump’s inherent mechanical performance and more in line with what MCS says. Whereas for the 11kW model, the equivalent figure is 82% because mechanically it is a bigger heat pump than 11kW. That’s just my own interpretation and may, of course, be complete nonsense :laughing:

The 60% figure is for an old school (state of the ark) fixed speed unit; or an inverter drive unit that runs without any software restrictions

The units that give “100% of nameplate down to -10C” are throttled at higher ambient temperatures. It is a rational thing to do. (throttling output at higher temperatures)

Ignore the badge. Looks at the rating at design condition AND the minimum output at say +7C or +12C. Better yet don’t buy a unit that you don’t see is capable of working well on the OEM dashbaord.

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Thanks, that’s really clear. But how do you actually get that information? In the thread linked by @Timbones, the OP said the Daikin rep showed him a page in a book but wouldn’t give him a copy. I thought that was very strange.

The datasheets I have read don’t make a lot of sense. They talk about Tj values and pdh values at partial load but without any explanation. I think most people would just like a simple graph or table to show output against temperature, like the one above for the Ecodan. I am surprised that manufacturers don’t provide this information as a matter of course in the brochure or on the website. Surely, it’s the most basic information that a consumer needs i.e. will this heat pump actually provide enough power when it’s cold outside? It seems to be treated like a state secret!

All manufacturer’s do indeed provide the data you are looking for.
Granted, it can often be difficult to find, sometimes you have to go as far as contacting their technical departments and request it.
More often than not, it is within the installation manuals.

Regards,

Derry

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Some manufacturers have it in the installation manual, but even then it is often presented in a very obscure way and is extremely difficult to understand for a layperson.

But why should consumers, who are often paying upwards of £15K, have to hunt for this most basic information? Until I started looking into heat pumps properly, the main thing I had heard was that they didn’t work as well when the outside temperature was low. So, the first bit of information I wanted to know was how well will my heat pump work when it is cold outside. I am sure many others are in the same position, and would appreciate this basic information being presented in an easy to understand manner in the consumer materials.

It is all very well being told we need to just trust the installer. But bearing in mind most heating engineers still struggle to specify a gas boiler of appropriate size, I think it is more than reasonable for consumers making a large investment to have easy access to this information. Not just to be given a glimpse of a table, as was the experience with the Daikin rep as recounted above.

Consumers are not expected to understand. Nor are the installers in the UK. That’s why all the marketing and the installation instructions in the UK are dumbed down.

On the continent the information you’re asking for is on the first page after the contents…

“Plan Your Work! - here are all the grapshs howing the maximum outputs for the 3.5 / 5 / 7 / 10 / 12 kW units at various combinations of outdoor temperature/flow temperature”

kurzanleitung-arotherm-plus-2105-2146405.pdf (5.4 MB)

Followed by size, noise, and restricttions on locations due to propane.

Then how much hot water you get for each tank size and what the available pressure is for puping the water around the heating circuit.

Then what you need to know about soakaways for the defrost water.

Fairly simple; but considered WAY beyond your average thicko in a colourful van working for a major utility company. And WAY beyond most of your average sales reps in the UK.

Then there’s also a full spec sheet:

kl-06-e2-verze-01-01062021-2108745.pdf (6.0 MB)

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They shouldn’t have to.

The first step any installer will do is a heat loss survey and calculate how much heat is required at “design temperature” (typically -3°C in UK). (You can do this yourself using HeatPunk, if you’re interested.) This will determine the flow temperature, radiator sizes for each room, and which heat pump will be best suited. This is required by MCS.

The point is, the heat pump will work well when it’s cold. The most common issue with installs is the heat pump being oversized, resulting in less good performance when weather is mild.

If you want a high quality, super efficient system, Find A Heat Geek.

Check out HeatGeek website or YouTube channel for consumer advice on heat pumps.

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Samsung offer peak output tables (enough for “Planen SieIhre Arbeit” purposes) to all distributors as part of the “EHS Technical Data Book”



Their authors are not as installer minded as Vaillant though (there isn’t a quick summary of just what you’re affter presented in a nice easy way in the booklet with the appliance; there’s just a huffing great PDF with the info buried halfway through)

Fun stuff you can see in this?

All of them run the compressor incrementally harder at lower outdoor temperatures in order to maintain capacity at the expense of COP (there are some internal re-injection ports and control valves that make this possible without burning up the compressor that are not fitted to other models)

8 kW @ -25C with a leaving water temperature of 55C sounds impressive / is genuinely impressive and the COPs when it’s genuinely cold outside are impressive. Irrelevant in a UK context - but useful to you if you are trying to make hot water in -25C with a COP of over 1.75, and heat your house via underlfoor heating in -25C with a COP of over 2.0.

The highlighted numbers at +7C (where all their efficiency labels are tested) are also impressive. It’s not quite as blow your socks off impressive as you might first think though. The Samsung rep will compare against others using max ouptut. COP 5 at 35Cthey will say. Vaillant is only 3.9; 3.9 at 45C but Vaillant is only 3.0; COP 3.2 at 55C but Vaillant is only 3.8 etc.

That’s missing the point though. Houses don’t need 8 kW at 35, 45, and 55C. They need less heat the warmer it gets. Compare the outputs at either minimum or the best efficiency point at each outdoor temperature and it’s much closer (5.0/4.9, 3.9/3.8, 3.2/3.0)

Compare.xlsx (11.4 KB)

The Vaillant can turn down usefully lower than the Samsung. The latter unit gets those high “max output” efficiencies by actually being a MUCH bigger unit that’s then software limited ot only run at a “max” output" that is pretty much the best efficiency point.

You need to know this when designing.

The Vaillant “7 kW” means about 7 kW (net of defrost) at about -7C; and it is designed to run at less than this by being conencted to rads/underfloor and allowed to “tickle along” at a relatively low output of it’s own managing.

The Samsung “8 kW” means about 8 kW (net of defrost) down to -25C; and it appears* pretty much designed to run with “on / off” controls with their software artifically imiting the output of the unit to just 8 kW at +7C. (they don’t bother limiting it some much above this because…drumroll…that doesn’t affect the score they get on the efficiecy label)

I guess what I’m saying here is…this is not simple. Any data that you do will be misrepresented against you by marketing asshats from the other brands…so it’s easier not to play the game and to rely on the installers to specify something appropriate / rely on independently verified results for how the units perform in the field with various designs.

*Though it’s far from obvious because nothing useful is published in terms of part load capability; and the internal controls appear to be as dumb as a rock with respect to managing output. (run as hard as you can and keep running until setpoint is breached and you can’t turn down any more?)

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I did ask Samsung UK Helpline for Gen 7 part load data, and was told bluntly “not available”. Pity, because my ASHP spends most of its time at half speed. I can only estimate part load compressor characteristics by assuming that both energy developed and power consumed vary linearly with speed (roughly true for scroll compressors in general, but who knows whether the Gen 7 is typical?)

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One of the Dutch techies.confirmed that the highlighted figures were as good as the best efficiency point on the performance map.

I don’t think you can use pure compressor maps with this unit; given all the bypasses and cycle economising etc that are going on in the background. (not a simple compressor with variable orifice type setup)

I’m sure you’re right, Marko, I was just reflecting the published data from a couple of Daikin scroll compressors:

If you plot Qo (energy generated in BTU/h) or Pe (input power in kW) against the three given speeds (at any given ambient temp To and LWT Tc) you’ll see that they are pretty linear.

Thanks, Tim. It makes sense to me now.

Also, I’ve realised now that heat pumps are much more complicated than I had imagined. I knew they were complicated, just not how complicated. I can see why it is not possible to present the information I wanted simply in a meaningful way.

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Thank you for all the amazing information and explanations. It has been so helpful and I have found it fascinating and it has really helped me understand the point you are making here.

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More viarbales than boilers, yes!

Imitating a setup / recipe that you know does the job is a good option. Experimenting is for those with the luxury of being able to get away with it though I think!

I hear you!

However the Samsung really is quite the unit internally…

  • Intercooled
  • Vapour injected
  • Liquid injected
  • Hot gas byapssed

Some of which improve efficiency; some of which harm efficiency. (hot gas bypass in particular is a way to provide less heat whilst using the same input power)

I don’t think you can draw the same conclusions on linearity as you might on a more basic unit without all the gubbins.

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I’d love to reverse engineer that circuit, but without a MIM-C02N hooked up I can’t access real time conditions/valve status etc, and the £200 price tag wouldn’t pass the rigid tests imposed by my Chief Finance Officer… :face_with_diagonal_mouth:

Think howmuch time it would occupy though @SarahH and how much peace and quiet the CFO could enjoy!

(that’s the line I use with my wife when toy shopping anyhow!)

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