So, Air to Air heat pumps – or perpetual motion machine?

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  • So, Air to Air heat pumps – or perpetual motion machine?
  • ianfitz
    Member

    Had solar PV panels fitted earlier in the year and just had a marketing email from a company who quoted for the job. it contains the following claim

    “Heat pumps are many times more efficient than using a boiler to heat your home.

    Putting 1kW of energy in to a boiler will feed less than 1kW of heat in to the home. 1kW of energy fed in to a heat pump, however, will feed several kWs of heat in to the home, reducing energy bills accordingly.”

    So can 1kw by turned into more than 1kw?

    I have a reasonable understanding and interest in scientific principles and would be very interested if this is

    A: a real possibility. or,
    B: some form of eco-snake-oil

    I’d also like to know if A2A heat pumps are any good generally, irrespective any magic properties they may or may not have!

    wrecker
    Member

    Heat energy taken from outside.

    Premier Icon leffeboy
    Subscriber

    It’s slightly deceptive but probably accurate. Your 1kw will power the pump which will get more heat out of the ground that then heats the house

    ianfitz
    Member

    ah, so they are mean that 1kw of energy powering the heat pump will pump in more than 1kw of heat energy?

    the email and website are fairly simple and don’t ‘do the science bit’

    wrecker
    Member

    It’s air to air, not ground source. The refrigerant is a heat transfer medium, the power input is for the compressor and fans. It’s called a COP(coefficient of performance) or, more correctly;EER(energy efficiency ratio) in heating mode.
    Most quality manufacturers will have an EER of >4 meaning 4kW of heat power per 1Kw of electrical power input. The additional heat comes from the heat outside. Beware, EERs are taken at certain conditions. The more heat available outside, the more efficient the system. At colder OATs efficiency falls away, and if incorrectly sized heat output will fall too.
    Happy to email you some stuffs I think I have on the laptop.

    Murray
    Member

    But the heat pump will use expensive electricity rather than cheap gas to provide the energy. Heat pumps are a great solution if you’re replacing straight electric heating, less so for oil and not at all for gas.

    ianfitz
    Member

    Thanks as always STW! several knowledgable replies in <5minutes – fantastic…

    wrecker thanks that would be useful.

    we have a edwardian villa type house, large rooms high ceilings – usually freezing, especially in our lounge with 2.5 external walls. just considering options.

    wrecker
    Member

    If possible, I would always go for a gas solution. The running costs can be comparable elec is 4x higher than gas but kit is >4x more efficient (boiler efficiency is now around 95% for a good one) but boilers are more resilient, and most heat pump indoor units are pretty ugly and outdoor units aren’t as bad as they used to be but they still make noise. If I didn’t have a gas supply, I’d go for a heat pump over biomass or similar. But buy wisely, NIBE and similar is shit. Look at Mitsubishi kit, its rather good.

    http://domesticheating.mitsubishielectric.co.uk/about_ecodan

    Bear
    Member

    Don’t even consider a heat pump then.

    Only consider one if your house is insulated to part L or preferably better, you are using underfloor heating (preferably), and can also consider MVHR.

    If you are on mains gas that will probably still be your best option.
    If on oil, electricity, or LPG then consider other renewables, but capital outlay can be very expensive.

    Google heating costs per kW for a guide as to the different technologies.

    And before you do anything insulation is king BUT you have to consider the building and making sure you will not cause condensation issues.

    Bear
    Member

    Wrecker – never a heat pump over Biomass in older properties surely?

    And not for commercial either as RHI payments higher on commercial RHI too.

    wrecker
    Member

    Capital cost and reliability. I’ve encountered massive problems with biomass. Schools who have relied on their gas “back up” boilers rather than the unreliability of the biomass plant (but still took the BREAAM excellent rating 😀 ) deliveries not being made due to snow at a supermarket resulting in £££££££££s of lost trade. Not to mention sourcing the fuel (often not as green a fuel as it sounds). Also, renewability; is there really sufficient wood source in the UK for everyone to have one? I know electricity isn’t great on that front either, I suppose that all of the headaches I’ve had from biomass installations have tainted my view somewhat. Also, they still release carbons without expensive filtration units.

    Bear
    Member

    Wrecker – are these wood chip installs then?

    These are problems that should not really be happening either, poor planning of deliveries for instance.

    No there wouldn’t be enough wood to support them but we are miles away from that, and there isn’t enough gas, oil, nuclear fuel to support any one technology 100%. More crops will be planted to provide a good source of biomass.

    Yes the emmisions aren’t great but the idea is carbon neutral as the trees that are planted should absorb the CO produced. I realise delivery etc that it isn’t a complete cycle but it helps.

    How green is electricity anyway? Emissions from power stations coupled with poor efficiencies on the grid make for a very poor green fuel?

    Out of interest what job do you do?

    maxtorque
    Member

    Basically the air-conditioning cycle, which uses a phase change in the working fluid acts effectively as a “wheel barrow” to move large quanities of energy around. it doesn’t break any fundamental laws of physics. For example, i could use a real wheel barrow to bring in say 50kg of burning coal into my living room, That would probably need me to expend a couple of hundred watts over about 3min, but would release many tens of kW into the room as heat. In that case, fundamental laws aren’t broken because i am just releasing the chemical energy locked up in the coal, and i can do this easily with just a wheelbarrow and a match. In the A/C cycle, the system relies on the specific heat of evaporation of the working fluid being higher in effect that the work done on that fluid to compress and move it. So the system uses 1kW to suck in say 4kW of heat outside and move it inside.

    wrecker
    Member

    Never mind crops, we don’t have the landmass to support it. I’m an engineer (although some designers would sneeringly deprive me of that title), I deal with operational buildings particularly where there are problems of a technical nature and also energy reduction. Have worked for very large M&E consultants, contractors, manufacturers.
    I’m in agreement with you about electricity and gas, neither are ideal. In theory, biomass is fantastic. Living with it can be very painful. The very large supermarket we deal with are not rolling it out following trials.
    Also, I know that industry are using biomass (including the grants and incentives) essentially as incinerators for their waste to save money.

    Premier Icon footflaps
    Subscriber

    More crops will be planted to provide a good source of biomass.

    That’s the bit I don’t get – it just puts more competition on arable land space and pushes up food prices. Higher prices for grain force more people to go hungry in the third world. It doesn’t seem very ‘green’ at all.

    Bear
    Member

    But we do have land mass to support growing some more fuel.

    So are they all wood chip plants that have caused the problems?

    Where are you based?

    wrecker
    Member

    Bear, some chip, some pellet. As I expect you’re aware, it’s the delivery systems which are the weak link. Augers in particular are problematic. My point was that we don’t have the landmass for all of us to have biomass, its not viable which leaves shipping it in, and some are doing this from Eastern Europe already which is against the spirit of biomass. Maybe arable land will be future reasons for invasions? Of course we do this with gas as well!
    Biomass is already affecting the price of things. The UK furniture industry has a campaign for the removal of the subsidy as its pushing up the cost of timber.
    As I’ve admitted, my experiences have coloured my opinion of biomass, of course it doesn’t help that I only generally see plant where there are problems, there must be many many more operating very well!
    I’m SW based by the way.

    Bear
    Member

    Wrecker, next time I’m down that way would love a nose round some big biomass sites.

    Maybe a chat over a beer or coffee to hopefully learn a bit more as I’m increasingly finding work advising customers about things such as you are doing but on a smaller scale! Anything yo further my knowledge is good.

    wrecker
    Member

    I’m no expert in biomass by any means but I’d be happy to join you for a coffee!
    Ill have a rummage for any technical docs I have and get them over to you. Drop me a mail to remind me?

    T1000
    Member

    we do however have lots of wasted Biomass… that could be harvested….

    in Forestry lots of the plantations are not properly thinned and managed (never been much of an incentive)… why bother with the inheritance tax loophole……

    if properly managed theres a lot of thinings and brash that can be recovered and chipped (and used in properly designed plant)

    additionallly when felled at harvest theres a large portion which is left as historiacally its not been worth the effort

    wrecker
    Member

    That was the original idea for biomass was it not? Waste product being used effectively. Then they made it profitable via subsidy and due to the high capital expenditure required, its generally used by wealthy organisations………..reminds me, I need to brush up on biomass CHP.

    Premier Icon igm
    Subscriber

    I suspect available biomass is going to become more scare once Drax complete their refit – they’re going to be running 1800 MW of biomass (which is quite a lot).

    No subsidy for biomass heating yet I think, but there will be one for biomass generation.

    mefty
    Member

    Drax is already out there buying

    Premier Icon igm
    Subscriber

    Indeed. But only for one unit this year. Two next and three the year after IIRC.

    globalti
    Member

    Not an air source but a ground source… my neighbour sucks heat out of a 400m plastic pipe buried under his field, he puts in about 1 kw to move the refrigerant around and gets about 4 kw of heat out, so a net gain of 3 kw if you like. House is heavily insulated and toasty warm.

    His total energy bill last year was £75.00.

    His only regret? He put the compressor in the utility room adjacent to the house and despite lots of insulation it is still quite noisy. He says he should have put it at the far end of the barn.

    wrecker
    Member

    If its a recip, he could investigate replacing it with a scroll compressor. Much quieter.

    mefty
    Member

    Air to Air is widely used in residential property in Sweden but they have relatively cheap electricity there due to hydro etc. Its performance does vary with outside temperatures but I would suggest if there can get it to work in Sweden it will work here. I have never looked at it in detail but CoP of 4 sounds quite optimistic. But as others have said, if mains gas is available, it will be the best option financially as generally you need to hit a CoP of more than 4 before any run cost savings are achieved, let alone the repayment of the additional upfront expenditure. Bear is right that they are more efficient (and cheaper) if they are producing at a relatively low temperature which is all that is required in a well insulated home or building.

    If you are looking at ground source, CoPs are higher and more consistent but installation cost is higher. There are a number of reasons why they work very well in the commercial sector. First, they can provide cooling as well as heating where they are replacing existing electricity usage. Secondly, they can be used to recondition heat that is being emitted as a result of other processes in the building, plus of course there is the subsidy in the form of the RHI. Subsidy for Ground Source can be higher than Biomass dependent upon total energy use. The other benefits of Ground Source is that the installation should last a lot longer than a boiler. Loops should be good or 50 years and heat pumps for 20. Maintenance costs should also be less but this is not yet the case in the UK, but is in countries with greater adoption rates such as the US.

    As regards how clean is electricity to gas, the ratio of CO2 produced per 1 kWh is approximately 2.5 times so providing you have a CoP of more than 2.5 times the CoP of the gas boiler, you are saving carbon.

    Biomass has its place and I don’t see local producers of pellets being effected by huge requirements of the Biomass Power Stations in the UK, Denmark etc. These guys are only interested in people who can provide significant levels of fuel which rules out most local producers in the UK and therefore I can’t see a huge impact on their prices where I imagine logistics of delivery is the key driver.

    I’ve been looking into this for our new build and have come to the conclusion that it’s likely madness not to use an efficient gas boiler if mains gas is available.

    There are two things to consider – running costs and installation costs

    Installation – £GSHP>£ASHP>£Gas boiler. Gas boiler *should* be serviced annually at c£100 whereas in theory the other two you can do yourself. Gas boilers seem to have a life of a little over 10 years. GSHP meant to be c20, ASHP likely c15. That evens up AS vs Gas

    Running costs
    GSHP COP hopefully 3-4 average over the year. ASHP maybe 2.5 in real use. ASHP’s do work well below 0C (becoming less efficient) but they don’t like cold and damp weather which we get a lot of in the UK. Then they’re prone to icing of the heat exchanger and use up power to defrost it. Likewise I suspect the damp means they’ll not last as long in the UK as they do in somewhere cold and dry.

    As regards how clean is electricity to gas, the ratio of CO2 produced per 1 kWh is approximately 2.5 times so providing you have a CoP of more than 2.5 times the CoP of the gas boiler, you are saving carbon.

    Is that for the UK? The reality is that much UK electricity is generated using gas. My understanding was that production/distribution losses are about 2/3 so, given boilers are >90% efficient now you need to hitting a COP of 3 to break even in carbon terms (and cost – electricity is about 3 x the price of gas per kw and unlikely to change while much of our generation capacity is using gas).

    With an ASHP you might just about break even on cost and carbon if your system is set up perfectly and works at peak efficiency (but up front costs higher). UK grid electricity MAY get greener over time but unlikely to be a material change in the life of your installation.

    mefty
    Member

    Is that for the UK?

    Yes, it is based on the factors used to calculate carbon tax. If you are on mains gas, gas is generally cheapest and I will replace my existing oil boiler with a gas one when the time comes.

    I think you need to look at your tariffs as you should be able to get gas at closer to a quarter of your electricity costs per KWh.

    I’d not looked at pricing in detail – UK billing seems designed to make comparisons as difficult as possible.

    Anything you’d disagree with in my assessment? No final decision made yet but all pointing to a small gas boiler for us (in a new build ultra low energy house). Still willing to consider alternatives.

    Also to confirm Solar Thermal/PV. Consensus seems to be that PV now has a better return. For us would occupy usable roof space so tempted to install ST and have larger roof garden.

    mefty
    Member

    No disagreement, sorry if not clear, the tariff should make the decision even clearer. I have not looked at pv recently, without subsidy solar thermal makes much more sense but you can’t ignore the subsidy. I will probably look at solar thermal when I replace my oil boiler, which is imminent.

    Premier Icon molgrips
    Subscriber

    The running costs can be comparable

    I was going to ask about the CO2 footprint but mefty answered that nicely – ta.

    I like the ground source set-up that globalti’s neighbour has. I wonder how much it costs and if you can do similar with a smaller area and a more effective heatsink in the ground?

    bobalong
    Member

    Wrecker, you obviously don’t like them, but I have a Nibe air to water heat pump and it’s great.

    We have a good sized 4 bed house, some dating from 1860’s, but well insulated and dry lined where there are no cavities. The roof insulation is ok, but needs to be improved as its just about the minimum.

    We have underfloor heating downstairs and radiators upstairs.

    The heat pump works really well. We have the house at a constant 20c and our combined heating lighting and cooking works out to be around £90/month.

    We had no option for gas, so it was oil or lpg and heat pumps are much better long term choices than either of those.

    The payback is not crazy quick, but it works and works really well.

    Wrecker, why don’t you like Nibe?

    mefty
    Member

    A vertical loop is much more expensive than horizontal loop because you need a drilling rig (and access for one).

    A vertical loop is much more expensive than horizontal loop because you need a drilling rig (and access for one).

    We’d been given 10k as a guide price for a borehole. That buys an awful lot of gas for a well insulated house. If you’ve got a field and your own JCB then you can dig your own trenches for slinkies and it’s mostly just time.

    globalti
    Member

    ….especially if you’ve got friendly neighbours around to help you with the laying and careful burying of the pipe.

    Premier Icon nickc
    Subscriber

    Got a Mitsubishi air pump, it’s noisy ( small back garden, right by window) but low level rather really really annoying. No gas in village. House is very well insulated ( stone terraced cottage with new build extensions) almost too well in the extensions as we’ve a bit of a condensation issue ( not helped by really bad weather over last 9 months). Also rads are about 25% larger than normal and they run a bit cooler. Couldn’t tell you if we’re saving money on it, as we have leccy for everything, but we are pretty careful about costs anyway, running laundry at night that sort of thing.

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