Domestic Heat Pumps

[asymptote]

Hi Forum. This question may be ABC for you guys but I am interested in installing a domestic air/air heat pump in the UK (latitude 52N). While there seems to be lots of manufacturers in the wide world there seems to be very little activity here. This is an initial probe in this area and would welcome advice/input/direction/experience on this subject.

 

[friartuck]

I believe B&Q sell a domestic heat pump package. The system needs a power supply and I believe the refrigerant pipework is pre-charged with push fit connections to make installation easier.

Alternatively, there are plenty of small AC companies (yellow pages) and get a quote.

I had three quotes recently to install a 6kW heat pump in a kitchen. The quotes varied from 3k to 4k. That included a Mitsi unit made from stainless steel (Kitchen unit)

A std unit would set you back a total of around 2K fitted and wired.

Cheap AC units (but still good quality) are Fujitsu and possibly Haier (I think I spelt that right). I have never used a Haier unit but I am told they are very competitive (Made in China).

My son recently started work at an AC company and within 3 weeks he can install them, so its not rocket science.

At worst, you need to be able to braze copper.

Friar Tuck of Sherwood

 

[smckennz]

Hi Asymptote

I live in NZ and because of our cheap electricity, heat pumps are not so common here because its cheaper to have a heater in winter and open the windows in summer.
Some of the older (retirement age) folk buy them because of the promise of lower monthly power bills.
If you intend buying to save long term money, be sure to do your lifecycle cost sums first.
If you want a brand, I have a soft spot for Daikin. Mainly because of their good reputation as aircon units in poor but hot climates.
If you are looking at one, dont forget the cost of ducting which can cost more than the unit. Also look carefully at the COP, which can be a little sad on a cold day. Finally, remember that they are normally on-off units and will be trying to heat your whole house which can be expensive if you only want one room heated. Yes you can get round it with dampers and the like, but always at extra cost. Be extra careful in deciding what areas you want heated and when. The final issues to watch out for are drafts, noise, and how you control the thing.
Tread warily but dont give up.

Cheers

Steve

 

[asymptote]

Hi smkennz (Steve)& Friar Tuck
Thanks for you input. I have been interested in these devices for a long time but always seem to get diverted. I first ran into them c1962 with imported equipment. The rising cost of energy has again raised my interest as I am in the pension bracket now. My house is heated with a 15kW 3 phase electric ducted hot air system and it would seem the ideal solution to go for an air/air Heat Pump. The last time I obtained any details the COP was 3 and heat pump compressors were not considered very reliable(as opposed to refrigeration compressors) so it all was put on the back burner. Questions that now come to mind are has the COP been inproved, now CFC's are out what COP can I expect at a latitude of 52N, whats the capital cost going to be and as we are a keen DIY family can we do it our selves. In the intervening years technology must have move on.
Any further input would be welcome.

 

[friartuck]

Toshiba now claim COPs over 4 up to 5 in some instances. Inverter technology has moved on, as has reliability. Theres little to choose between Mitsubishi, Toshiba and the market leaders (and Worlds biggest) Daikin.

I take it your unit is 15kW heater is all direct electric???

If so, the heat pump sounds like the ideal solution as running costs will be a fraction.You will nee a low ambient kit if your winters are cold. Daikin operate to as low as -15C I believe.

Just make sure a quality company fits it as any moisture in the fridge pipe or any contaminants will cause you loads of problems.



Friar Tuck of Sherwood

 

[chicopee]

If you have a constant temperature heat source for the evaporator to function properly in the winter so that no liquid enters the compressor (ie, about 5 to 10 degree F superheat entering the compressor), a domestic heat pump will do fine.

 

[imok2]

You may find this web site informative:

http://search.nrel.gov/query.html?qp=url:

http://www.eere.energy.gov/femp/&qs...lk=1&rf=0&oq=&col=eren&qt=heat+pumps&x=30&y=8

 

[saxon]

asymptote, I once owned a house that had a heat pump installed (don't own it now!)located on the southern shores of the Great Lakes, N.A. Although the thing kept the house at 68-72 F in the winter time; the place always felt cold and in order to compensate, the fire place burned all winter. Used close to three cords of wood (so much for the energy/cost savings these things were supposed to effect).

There is just something about the human body/mind that craves blasts of warm air that a furnace supplies during the winter as opposed to the "cool" air that heat pumps supply.

Hope this helps.
saxon

 

[smckennz]

Hi Asymptote

Unfortunately things have not moved on as far as you might expect, apart from misleading advertising which knows no bounds.
The biggest problem with heat pumps is that they are very efficient when indoor and outdoor temperatures are about the same (i.e. when you dont need them). This is when the advertisers COPs kick in. However most people want about 15-20C inside regardless of outdoor temperature.

Saxon says something that I strongly agree with although I dont know how to measure it.

I am a great believer in doors to shuts off parts of the house that dont need heat/cold. Unfortunately with a ducted system, some mods may be required.

There is no way I would assess and unknown system with a COP greater than 2 and thats being very kind.

If you want some help in choosing the best system for you, some further information about location would help. No need for size because you have already indicated 13kW does the job. Would be interested to know about insulation though.

Cheers

Steve

 

[Cooky]

Hi Asymptote,

Steve is right-on with his comments about the performance of the heat pump falling away as the outside temperature drops below freezing (just when you need it most!). To get your 15kW heating capacity with an outside air temperature of, say, -5 deg.C, you would need to oversize the equipment.

You will also need to consider the defrost cycle for the heat pump system. When the system is operating in heat pump mode, the coil on the outdoor unit will be below freezing. To prevent ice forming on the coil, the system will switch into defrost mode for a couple of minutes, this will result in a cold blast of air from the indoor unit. So you'll need to keep your existing electrical heaters to counter the cold air, when the system enters the defrost mode.

Unless your familiar with refrigeration systems and you have the correct equipment, I would recommend you get a qualified refrigeration technician to install the pipework and commission the refrigeration system.

Good luck

Cooky (in the UK)

 

[asymptote]

Hi Forum. My computer has been down for a week so I am just catching up with all this valuable information and comment from the Forum, thanks for the input.

 

[crysta1c1ear]

Heat pumps are sold in France, and I think you'll find they are common around the mediteranean, where it doesn't get too cold in winter. Maybe for the reasons stated above, they don't get installed too much in central France where the winters are colder.

If all your heating is currently electrical then it should cut the fuel bill once installed, but are you sure you'd not be better off with something else.

I visited a house a few months ago where they had black solar panels containing liquid, not solar cells, and if the liquid outside was warmer than the liquid inside, the pump would turn on and bring the heat into the house. The house had underfloor heating. They could also heat water for showers, washing up, etc from the panels too.

There are newer evacuated tube designs where a black blade about 4 inches by a yard warm up with light (even on cloudy days to some extent). A tube runs down the centre of the blade, taking the heat from it, and the tube contains just a few cc's of water. So water temperatures are pretty darn hot. Since the tubes have a vacuum in them the black blades won't get affected by cool rain like normal solar panels.

=

Okay, the UK has the gulf stream to keep it warm, but I think you need to check how well the heat pumps work when it gets cold.

I've rejected the idea for my girlfriend's house in central France and it has 2500m2 of garden to run tubes round underground to capture heat, and a constant ground temperature of about 13°C if you go down a bit, like wine cellar depth.