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ASHP with CO2 refrigerant


jonM

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I am in the process of building a Passivhaus. As there is no gas, I will be using an ASHP for Heating and Hot Water. Heating will be via radiators located downstairs and upstairs. I am in the process of deciding between two Mitsubishi heat pumps - the 4KW QUHZ (CO2) which is matched with a Thermal store and the 5kw PUHZ which is matched with a Hot water cylinder. 
 
I have phoned up Mitsubishi and spoken to them about the QUHZ (CO2 air source heat pump). There is no additional maintenance required for the QUHZ. I also asked them about reliability and there view was that as they've had to increase the spec of the QUHZ in several areas to take into account that CO2 is the refrigerant so they expected the QUHZ to be as reliable or more reliable than the PUHZ. I think there is a big difference in the way that it heats up the water as the QUHZ uses a thermal store rather than a hot water cylinder used by the PUHZ. Not an expert in this area, but research I have carried out suggests thermal stores are less complex than hot water cylinders. Idiots guide from Mitsubishi was to use the QUHZ if your hot water energy requirement exceeds your energy requirement. 
 
Using the more detailed data for range of temperatures supplied by Mitsubishi the services engineer checked performance in PHPP  for specific loads and temperatures for our house. It indicated that the heating is indeed slightly better with the standard unit but hot water is considerably better with the QUHZ which correlates with the feedback from Mitsubishi. These were both modeled at 45 C heating design flow temp and 55 C DHW supply temp. 
 
So on the surface it would appear the QUHZ is better suited to my needs. The only caveat is that it is a relatively new technology for Mitsubishi (introduced 3 years ago) and I think in the market place in general. I had an early condensing boiler fitted to my current self build and it was always breaking down, so I am a little cautious of using anything new on the market because of that experience. Heat pumps seem to be tried and tested technology however so maybe I am worrying unnecessarily. I would welcome any thoughts / feedback on this.  
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To store DHW with a thermal store, you need the water in the tank hotter than your hot water temperature.  With an unvented cylinder you store water at the required use temperature.

 

I am using an ordinary ASHP providing DHW at 47 degrees and under floor heating at 37 degrees.  

 

Any reason you don't want under floor heating? It's very much lower working temperature suits a heat pump a lot better.

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13 minutes ago, ProDave said:

To store DHW with a thermal store, you need the water in the tank hotter than your hot water temperature.  With an unvented cylinder you store water at the required use temperature.

 

I am using an ordinary ASHP providing DHW at 47 degrees and under floor heating at 37 degrees.  

 

Any reason you don't want under floor heating? It's very much lower working temperature suits a heat pump a lot better.

 

Responsiveness, simplicity and a requirement to heat upstairs together with differences in floor surfaces downstairs (slab) and upstairs (IBeam). We will have to go with radiators now as the slab has been laid, but are looking into oversizing and using K2 radiators to allow us to reduce the heating flow temp and make the most of heat pump efficiency. 

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#1 - find an engineer qualified and with the right kit to service your CO2 ASHP. 

#2 - ask how much they charge

#3 - buy standard ASHP...

 

Not trying to knock this but my experience of owning and living with a Sanyo CO2 unit was painful as the kit is specialized to the point of if you connect a standard pressure tester to a CO2 unit you’ll be picking the bits up a hundred yards away...

 

They are a niche market for high temperature ASHP and have never really caught on. Go with standard, plan accordingly and boost using off peak E7 and then spend the rest on a nice kitchen. 

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My view is that if you don't have mains gas, and really need high temperature DHW, then the best option may well be a Daikin hybrid ASHP/LPG combi.  They have a good reputation for reliability, and use only a modest amount of LPG, as they use the ASHP to preheat to round 45 deg C or so, then boost this up to 55 to 65 deg C with the small LPG combi. 

 

I'm not convinced that any of the CO2 ASHPs are a mature enough product to invest in yet.

 

 

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Every bit of info I've had, even from the various manufacturers own tech / sales people has been so unclear and indecisive that I instantly removed myself from a position of quoting for such a system to a client who had expressed interest in one. I was being told of "how good they were in Japan", and thought...…"but I'm asking about the UK you nugget ?!?"

I'm all up for tasting new flavours, but this one went sour pretty damn fast. If you don't want to ( simply and relatively cheaply ) boost by electricity then go for the hybrid. 

PV would swing it to the electricity option afaic.

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  • 1 year later...
  • 7 months later...

bumping this topic as I've been informed by a potential installer about the CO2 refrigerant and was wondering if those that know have any more information or updated opinions in the 2 years since this topic was last raised? @Nickfromwales would you still not quote for it?

 

we're going for UFH so don't need the high temps for DHW so should I not even bother considering it?  or will it be Uber-efficient when running at UFH temps, even more so than an RC32 ASHP?

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41 minutes ago, MrMagic said:

May also be worth checking out the latest Vaillant arotherm+ HPs, they are getting positive reviews in the marketplace (from what I've seen) - https://www.vaillant.co.uk/for-installers/products/renewable-systems/arotherm-plus/

 

R290 / propane so slightly less bad than R32

thanks @MrMagic I'll take a look. I haven't started researching the different refrigerants yet but it is definitely on my list!

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  • 4 weeks later...
3 hours ago, DenkiJidousha said:

I'm optimistic about getting an R290 Vaillant aroTHERM plus installed soon - I short listed it specifically for the lower green house gas potential than R32, coupled with good performance and low noise.

 

This is also our current plan.  I haven't got any quotes yet though, and am interested in comparing it with Samsung/LG/Mitsubishi/Panasonic R32 models.   Have you got any prices and/or compared performance/noise/price with R32 model?  (R32 is still lot lower GWP than other other gases)

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  • 4 weeks later...
On 21/10/2020 at 10:06, DenkiJidousha said:

We had a quote with the Panasonic R32 which was cheaper that the R290 Vaillant aroTHERM plus. I've not checked the quoted noise levels, but the Vaillants do not seem to be the quietest out there.

 

Which model are you looking at?  The 7kW model does seem to be have one of the lowest "sound power" numbers on the market at 55dB.  The 10kW on the other hand which is 1.5m tall, has dual-fans and isn't anything special at 60dB.

 

I'm not sure how Mitsubishi get their "sound pressure" numbers as they don't seem to make sense.  Unless they are calculated with no reflective surfaces... i.e. suspended in the air.

 

 

 

 

 

Edited by Dan F
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Sadly our installation has been cancelled. The installers quoted a while ago (what with the pandemic etc), and in the interval did a couple of similar installations elsewhere. They concluded in hindsight our old boiler cupboard was simply too small to get all the gear in plus adequate access space to do all the pipe work. An alternative was taking over space from the adjacent built in wardrobe in the master bedroom, but not a popular idea. It was always going to be tight, but still rather a shame.

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37 minutes ago, DenkiJidousha said:

Sadly our installation has been cancelled. The installers quoted a while ago (what with the pandemic etc), and in the interval did a couple of similar installations elsewhere. They concluded in hindsight our old boiler cupboard was simply too small to get all the gear in plus adequate access space to do all the pipe work. An alternative was taking over space from the adjacent built in wardrobe in the master bedroom, but not a popular idea. It was always going to be tight, but still rather a shame.

 

What were they planning to install?  Was a unitower and small buffer not an option?  You could always check with another installer to be sure.

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I think I had posted details on another thread, but very tight on space replacing an existing combi boiler - the planned install would have used a Sunamp heat battery. I did have a couple of other quotes using a traditional slimline hot water cylinder, but with caveats - one firm thought they could use the existing cupboard but would have to cut a large side access panel via the master bedroom.

Fingers crossed things continue to improve in heat pump technology (CO2 maybe?), and I can try again in a year or two - assuming we haven't moved house in the interim.

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