Heat pump / inverter DIY

A question about : Heat pump / inverter DIY

I've just ordered a single inverter aircon unit to heat the open plan area of my house.

Ј450 for a 13000BTU unit which I should be able to fit myself, the savings over storage heaters sounds sensational - 1kw in = up to 4kw out (I know 1:6 units exist but they are too expensive to ever make them worth it).

I was given advice to hire a air vac pump to get any moisture out the system but on phoning a couple of local aircon engineers they have advised me I don't need to do that, just to run it on full heat and it will burn of any moisture - one actually said he would come and vac it but that I was wasting my money!

Does this sound right? Does anyone else run one of these air to air inverter systems?

Best answers:

• Hi
  Sorry I don't have any knowledge of these units but it sounds interesting and I wondered where you bought it from and do they have a website?
  Thanks.
• Sure, I got it from these guys, but there are more on ebay + web.
  https://cgi.ebay.co.uk/FREE-UK-SHIP-I...742.m153.l1262
  The other one I'm ordering heats the hot water + radiators.
  The reason I got two was that I plan to heat the open plan area with one and the rest of the house via radiators with the other - maybe I don't need two, maybe the hot water one will do it all, if so I'll put the other one in my holiday cabin.
  I'll report back once I finish installing this first one on how well it works.
• I have air conditioners/heat pumps, but I got them installed professionally.
  If you do not use a vacuum pump, then you will not know if you have a leak (the pump evacuates the system & is left for a while to ensure the vacuum holds) & if the refrigerant disappears then you have to get an air-con engineer anyway - you can't re-gas as a DIY'er.
• bobmedley. how are your heat pumps performing now we are getting regular temperatures in the -something to 5 deg C ?
• Absolutely fine - the temperature is 4c and they are pushing out heat in prodigious quantities.
  According to the documentation they are running at 80% of their COP which is 3.45 therefore the cost is 2.86p per kw.
  Mind you oil has dropped so much that I'm only paying 4.3p per kw for that, but it's still a saving I suppose.
• And which models are you running?
  If they are air source, are they going through defrosting cycles yet?
  At temeperatures above zero I guess they don't (or not very often) but we have been having some periods below zero?
  Many thanks
• I use 2 9000BTU Mitsubushi Units (SRK20-ZGX) to heat my 3 bed end terrace with loft. I decomissioned my old gsh at the end of last winter after getting a Ј270 gas bill. So far, house is warmer (22 in loft, 23 living room) and last 4 weeks cost Ј17 for just heat. I work from home, so the house is kept comfortable waking hours. It's easy to measure as I have an energy use monitor on each unit.
  Outside temp tonight is 0, and they're still pumping out toasty heat.
  I must add that I'm located in SW England which had a mild climate, and frost is a rarity. These ashp's perform amazingly well for me, I'm just bowled over by how cheap they are to run. It's worth noting that the cost of running these units is less than the cost of a service contract for GSH without using any gas at all.
  With better insulation, it even looks feasable to micro-generate enough electricity to heat your own home!
  ASHP's ROCK, and if you live in a mild climate, are cheaper than GSHP's; cheaper than the best gas, cheaper than chips even.
  Oh... and they're useful in the summer too
• DOnt under any circumstances even attempt to install these units yourselve. The same as to handle Gas boilers you have to be corgi registered for Air con you have to have refrigerant handling certificates and qualifications. How do you know how to vac it, how long for? What pressures you should be running to, how much gas to put in the system? Testing and commisioning of the system. Tell these cowboys who are trying to sell them to you where to go and get a proper installer to do it. YOu will end up breaking the equipment because you dont know what your doing and this will cost more to put right in the long run.
  On the other hand I have 2 x LG Multisplit system installed consisting of 1 x outdoor unit FM25AH and 2 indoor convertible MV12AH units. The system was installed in June and cools the whole flat perfectly sometimes only needing 1 unit on.
  Now its winter currentlly -2 outside and im getting air off temps from the units of 35C which is making my house a lovely 23c throughout. I find that when I go to bed it uses less electric to leave the system on but set to 18C as it doesnt have to work as hard and for as long when I put it back upto 23c the next day.
  IN regards to defrosting the unit because it is cycling on and off happily maintaining indoor temps it doesnt defrost much at all however when the units have been switched off and the indoor temps drop to 13c the system will run for about 4hrs to get indoor temps up, in this time the outdoor coil will go white with ice and the unit will defrost mode about twice during this period.
  Excellent systems. We had it installed as we cannot control our heating in our flat as the landlord runs it so when its off we had to rely on electric heaters. This way the house is always warm.
• as the UK air is damp i would expect units to frost up even at above freezing air temps, as the compressor will drop below freezing and the moisture in the air will freeze on it. As long as the unit has an additional reverse defrost cycle on the outside unit it should be ok.
  not all units for sale here have that, so check before buying.
• Regarding DIY install... it is straightforwad to install the ashp's described as such because they come precharged. An aircon engineer is not required as you just drill the big holes in your property, mount the units and hook up the pipes - job done. Seen it, a mate did his own - it was inspirational.
  The problem arises if you get it wrong. You need good diy skills to get the mounting, pipework & electrics right, and if you get a refrigerant gas leak you're screwed with out professional help. BTW there's a Ј5,000 fine for letting the gas escape.
  I went for a professional install for 2 reasons:
  Firstly, there is an extremely limited range of units described 'DIY Install'. The most desirable units are pro install only - ie not pre-gassed.
  Secondly.. I didn't want the layout of the units limited by my own technical abilities. By using pro installers, I got the unilts neatly mounted in the correct & difficult to reach locations.
  What I really don't understand is why these ashp's are so ignored as an amazing way to heat your home sooooo cheaply. This country is hypnotised by decades of cheap North Sea Gas, so we're all buying condensing burners. Why?? The Gas industry's established, huge and influential; the (mainly) Japaneese aircon manufacturers are invisible. Ever seen an aircon ad on TV?
  Thank god for Google. I now know that I can heat my home to just-a-shirt comfort for peanuts by using electricity.
  More specifically... I have a wallmounted unit in the (open plan) living room and one at the top of the stairs. They are set to 25/24 degrees (low power). Whilst on, they pull between 8 and 360 watts each. Thats 720 watts heating my whole house!
  This is far greener / cheaper than any gas anywhere, and is feasably user-generatable.
  But nobody I know gets it. A typical reaction would be "I bet they're expensive to run" or "had those on holiday to keep cool". I'll just smile a lot this winter when I look at my credit-crunched heating bill.
• The fact the user is not aware of how to install these, is the concern, if it was a precharged unit (i assume you mean flexible pipeworks b&q jobbie) then fair enough but the user is saying he has been recommended to use a vacuum pump. Also all air con units come precharged with a certain weight of refrigerant.
• Yup, they're the Mitsubushti Hyperinverter's with a COP of 5.45. In low mode, they cycle between 320w - 360w whilst pumping heat, and 8 w when just idling (outdoor unit off / indoor unit flaps up and gentle air filtration) which they do when they've reached the desired temprature. I was just indicating that my units are not in compress mode all of the time.
  I set the downstairs unit to 25 because it is not an enclosed space. The temp at seating level is 23 and that's how I like it. I've checked the temp adjacent to the aircon unit and it is indeed 25.
  I agree that if you set these units to 'Auto' Mode, they will ramp up and down a lot more than the restricted 'low' mode; Boost Mode (mega blast of hot air for 10 mins) will pull 1350w!
  But that's not needed to heat my house. In low mode they're not allowed to work hard and they don't need to. The most important thing of all... insulate FIRST, then add heat.
• Steve, sorry mate I completly understand when you put it in HVAC terms that I understand, most people will not understand the 2nd reply you put but I completly understand now.
  So your saying that to run the indoor unit on fan mode is just using 8w, that is great I think mine are the same the motors are the new style motors that use very little power even when on high speeds.
  I also understand now the reasons you put set points at 25, obviously a lot of heat is going to be lost in the open space so you have to set a higher temperature in order to heat the areas furthest from the units.
  We had a similar problem in heating mode only, we would set 22C on the controller in heat mode, and the units are low wall mounted so mounted at radiator height just aboveskirting board, the air flap would point air at an angle towards the floor and the unit would heat the floor area quick and reach setpoint and the return air sensor would read 22C however where the seats are in the lounge would only read 20C so still chilly, we had to set the controller to 24C to compensate for the distance furthest from the unit.
  We found that areas nearest the unit were overheated to 24C and the seating area was comfortable 22C.
  We spoke to the installer who has now installed remote air sensors which has extended the temp sensor inside the unit into a little box that is mounted on the wall near our seating area so if we set 22c on the controller the unit will heat until the remote sensor senses 22c on it, we have also found this has made the inverter units work much more efficiently as the sensor feeds temperature info back to the outdoor unit so for instance in your case your unit is set at 25C, if the unit senses a 3C difference below the setpoint the outdoor unit will run at full speed to bring the room temp up, as it starts approaching the set point of 25c the inverter will start to ramp down. So because your room is cooler at the point where you want 23C the sensor is thinking that its above 23C because its reading it from the unit so slows down. if you had the unit measuring the temperature from the area where you want 23C it would be much more accurate in reaching that temperature as it would be specific to the area your wanting heating. Basically your unit will run for longer to achieve 25C when really if you had it measuring the temp from the location where you want 23C you would be able to set 23C and get an even temperature through the room. Also have the flaps set on auto in heat mode so they move up and down to distribute heat.
  Hope that makes sense ive had quite a few beers tonight! IN cool mode we have no problem at all as the air is circulated up from the unit around the ceiling area and blankets the room in cool air, whereas heating mode it has to force it to the floor area and for it to rise, but because the units are so powerful it doesnt rise quick enough for it not to affect the sensor inside.
  Rich.
• Steve were talking 2 indoor units running off 1 outdoor unit. Combined duty is 7kw at a push we get 7.5kw.
  Max power usage at fully duty is 2.3kw winding down to 600w.
  Not sure what the cop is of that as the multisplits i have are not given a COP marking as its a mix and match system. There are many different combinations of indoor units to attach to the outdoor unit you see so depending on what units are attached to the outdoor unit affects the cop.
• Ah if your units are wall mounted then it makes sense that the air is already being blown down anyway, its harder for my unit to get the air flow down without it sucking it back in..
  The remote sensors work very well, basically all it is a longer cable with the thermister on the end of the wire.