PhilT

It is absolutely definitely worth installing. Heat pumps are key to solving the energy crisis AND saving cost. My stats. MCS heat loss 16,213kWh p.a. Energy consumption in previous year before ASHP was 21,134kWh gas plus 3,274kWh electricity = 24,408kWh total. Energy consumption with ASHP in first full year was 200kWh gas (cooking only) plus 6,533kWh electricity = 6,733kWh total i.e. a whopping 72% reduction in energy consumption! ASHP gave rise to additional 3,259kWh electricity which, simplistically and very roughly, gives a SCOP of 5 - seems almost absurdly good but them's the numbers! This translates into actual savings for me of at least £600p.a. at current energy prices, on a net outlay of £6,000, so simple payback = 10 years.

To be clear - much lower than gas boiler fed radiators. I considered UFH but in the end went for properly sized rads with my heat pump, and I'm very glad I did, they work brilliantly, always within a temperature range of 35 - 50degC, similar to UFH.

Yes it's in the technical information (R290 clearances). My copy is from early last year - it may have been updated - worth checking for any changes

In March last year I was faced with a similar choice. After a lot of research and analysis I wanted to go with the Vaillant Arotherm Plus (featuring the R290 Propane refrigerant) but could not find a suitable and safe place to put it anywhere around my house without breaching fire regulations. So in the end I went with the latest Mitsubishi Ecodan R32 single phase model. My electricity usage went up from 3,274kWh pa to 6,542kWh pa vs. an MCS heat loss calc of 16,213kWh implying a SCOP of well over 4. I was using around 21,000kWh of gas in the previous full year! So for me it has been an astonishing success story, but I have no reason to doubt that the Vaillant is capable of at least as good performance. As for the so called "vampire load" although initially I had a concern, after extensive monitoring my Ecodan R32 only consumes around 40-45W when idle so it's just not an issue for me.

Seems reasonable. I plead guilty for my early contribution to the apparently high power draw. My house was using around 7kWh per day back in April while I was away with no heating or DHW left on. One reason was a very inefficient 30 year old fridge/freezer which has been replaced saving around 2kWh a day. The other reason is the 1.4kWh per day of power consumed by all the "idling" devices in my house - TV/box standby, internet router, land line phones, power line adaptors etc, some of which will be culled as a result. All in all a useful learning curve! "Idling" Appliances W hrs/day kWh/day Router 12 24 0.288 Power line adaptor 3 24 0.072 Phone/base station 2 24 0.048 Night light 9 8 0.072 TV standby 11 24 0.264 BT box 7 24 0.168 Power line adaptor 3 24 0.072 Kitchen phone 2 24 0.048 Study phone/printer 2 24 0.048 Bedroom phone 2 14 0.028 Landing night light 12 8 0.096 Spare PLA (now disconnected) 3 24 0.072 Aerial amplifier (loft) 5 24 0.12 1.396 Fridge/Freezer (saved 2kWh/day) 35 24 0.85 2.246 Heat Pump Idle max 45 24 1.08 (PDF data guess) min 37 24 0.888 TOTAL IDLE max 3.326 min 3.134

I've called them so many times now. Each time I get a different answer, the latest being an admission that they don't have actual measured data on the latest R32 models. While away from home all of last week my house consumed 3.2kWh per day, of which all the mains plug appliances, measured by watt meter, totalled 2.2kWh per day, leaving 1kWh per day for the heat pump compressor AND controller. That is for a PUZ-WM112VAA which is the latest 11.2kW R32 model

For the latest R32 models they don't yet know. Hopefully the calls they are getting as a result of this thread will motivate them to find out. My best guess after many weeks of monitoring is around 1kWh per day in summer (11.2kW single phase model). I'm OK with that - it's a star performer for the year as a whole

Up front cost is cited as the main barrier to the widespread adoption of heat pumps. The grant recently dropped to £5k so heat pump installations have gone up by between £4k and £6k plus accelerating inflation (evidence the £17k price mentioned by richo106), possibly as much as doubling the overall cost of installation. That is a big issue.

Seems very high indeed. Last year we got 11.2kW ashp, dhw tank, expansion tanks and 6 new rads for £15k, less RHI £9k over 7 years. Suppliers should be moderating their huge margins to fit the new £5k grant otherwise ashp sales will dry up.

The excess usage is so high there might be a fault with the compressor (is it running most of the time?), or the refrigerant circulation has been compromised somehow. In summer it should only be using a tiny amount for DHW. My 11kW heat pump runs each day for 30min at 3pm (when daily outside temps are at max.) and only uses around 1kW to do so, for 2 people. In summer we get enough hot water for a couple of showers and other domestic chores at a set temperature of only 40degC on ECO mode

According to the data sheet I attached above yours is only 54W when on and 15W when off, so average only 35W (or 28W >21degC). Which precise full model description is yours? The mystery is why LA322's 8.5 (a VAA?) and my 11.2 (PUZ-WM112VAA) consume a lot more. I can't get a clear answer from Mitsubishi tech help but I'm not going to worry too much as the overall annual performance of my unit is spectacularly good and way better than my expectations.

This only adds to the mystery. We have contributors with 85's, one of whom (the OP) is consuming large quantities of energy on standby, the other is not. My 112 is using around 5Kw a day on standby based on actual mains meter readings, and your 14 is hardly using anything. Mitsubishi Ecodan tech help sent me this attachment on "Standby Power Consumtion" - would be interested to hear peoples views on this Standby Power Consumption (1).pdf

Good point. What would be a reasonable % efficiency to assume? A few years ago we had 2 large extra radiators installed with the same boiler so return temperatures should have dropped significantly. A brief look online suggests ideal efficiency of 95% translates to real world efficiency nearer 80%. My EPS/MCS estimate of 16MWh gives 76% so seems reasonable? Still a very impressive SCOP of 4.8 including that annoying idle power usage.

Yes exactly. I had chapter and verse specs and quotes from 2 different installers for the two different models. I had almost made up my mind to go with the Vaillant when the installer drew my attention to the requirement - respect to him.

Yes that's possible although the installer surveyor's estimate was even higher at 18,000kWh p.a. which looked reasonable vs. my condensing gas boiler usage of 21,000kWh p.a. at around 85% efficiency

Agreed. The SCOP is amazing in spite of the ridiculous idle power draw. I also considered the Vaillant Arotherm Plus which on paper looks really good but there was nowhere to put it around my house without contravening the fire prevention rule minimum distance from windows, doors and drain covers and, as you hinted, the Mitsu size and shape is so compact for the power.

Just had an interesting conversation with Liam at Mitsubishi UK Technical. The compressor on the PUZ-WM85VAA and PUZ-WM112VAA models is a scroll compressor. It is definitely working correctly in having a heater keeping the compressor warm, using up to 6kWh per day if idle 24/7 but, depending on the time of year/% of time working, not drawing power all the time, and none at all if working 24/7. The quoted SCOP of 3.6 or whatever, takes this power draw into account, which my first year data suggests is very conservative as my heat pump usage of 3,300kWh on an estimated EPC space heating/hot water (MCS certified) heat loss of 16,000 kWh gives a SCOP of 4.8 which is phenomenal. It was a very warm winter and I did get some extra insulation put in so may be a bit top side. As both a tech and a fitter Liam suggests that if you can put up with the hassle you can switch it off every day as long as you switch it on at least 2 or preferably 3 hours to be safe, to warm up before use. However if you get this wrong it cannot be damaged as it will prevent itself from starting unless the compressor is up to temperature, you will just have to wait.

Mine is R32. I just looked at the plate on the side and it says PUZ-WM112VAA. The original quote spec said PUHZ-W112VAA

Isn't your heat pump massively over-capacity based on that peak usage - that's a jaw dropper - which model number is yours? Mine is a PUHZ-W112VAA. It's all very puzzling - the mission to understand goes on...

Logical but really needs a definitive answer from a Mitsubishi designer. Till then I'll buy the idea that the c. 5kWh per day compressor preheating is doing extremely useful work in making the heat pump much more efficient during winter months, and in summer months the wasted energy drags the SCOP down to a lower figure than it should be if it were to use some kind of automated summer energy saving switch off scheme.

thanks for your constructive and useful comment

From this and other threads and based on my discussions with Mitsubishi techs it would seem that there is a big trade off between the "wasted" standby energy consumption in the summer months and the stunning efficiencies achieved by the pre-heated compressor in the regular use winter months. My 11.2kW Ecodan R32 heat pump energy consumption in its first full year is c. 3,300kWh which is almost unbelievable given that my (not very old and working perfectly) condensing boiler consumed 21,000kWh in its last full year. There needs to be some way of automating a controlled, damage preventing, energy saving, switch off.

Presumably you mean 0013kW which would be 24 x 0.013 = 0.312kWh per day which is very low indeed compared to the Ecodan R32

Seems I was completely wrong about this I must have taken a measurement when the compressor heating was at that moment not required. The compressor temperature is maintained while idle and my heat pump uses between 4 and 6 kWh per day when switched on but not heating either radiators or DHW. Mitsubishi tech support say although the manual specifies a 12 hour wait between switching on and use this can in fact be as little as 4 hours without any problem. TBH I can't see why it should take 12 or even 4 hours to simply heat up the compressor - anyone know why it has to be such a long wait?

I have an Ecodan 11.2kW. I switched off my main consumer unit leaving just the dedicated supply for the Ecodan pump and control system running at 24W background idle, agreeing with previous posts. Must be the control system. Whatever the standby consumtion may be, all I know is that in its first full year it has produced absolutely stunning results - 3,600kWh of electricity consumption for the year compared to 21,000kWh worth of gas the previous year. I'm having trouble believing the figures but if real that's certainly one way to help solve the energy crisis!!!