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Heating and cooling: Shouldn't A2A heat pumps be receiving more attention?

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      CommentAuthorSteamyTea
    • CommentTimeOct 13th 2013
     
    It is all to do with how close to the Carnot Cycle it can get.
    So the less temperature difference between input and the output the less 'extra' energy is needed.
    Not sure how hot an A2A heatpump gets the output temperature to, but probably no more than 55°C and possibly only 45°C, so that may only be a rise of 30 to 40°C. When they are used to heat water then they try and get the temp to 60°C, so needs more work done.
    There is also the amount of time they will run for. About 4.2 times longer to heat the same mass of water as air.
    Why I asked the question a while back somewhere as to just how important is the ambient air temperature really is (knowing that it very rare that it goes below 0°C in the UK (even accounting for the last two cold winters, even went below that down here)
    • CommentAuthorEd Davies
    • CommentTimeOct 13th 2013
     
    Posted By: SteamyTeaWhen they are used to heat water then they try and get the temp to 60°C, so needs more work done.
    But this discussion is specifically about space heating, not DHW, so such high temperatures are not needed.
  3.  
    A2A heatpumps are more efficient than A2W mainly because they can use a larger condenser. Plus they are much more common, worldwide, than A2W so there's more development done (I presume). At least, I believe that's the main reason. I think the "output" temp of most A2A heatpumps is the order of 40-50C (based on my W2A heatpump).

    Paul in Montreal.
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 14th 2013
     
    Ed
    Was replying to this
    Posted By: stonesTo again bring it back to topic, how does A2A stack up to A2W assuming that it is only being used to deliver heat
    • CommentAuthorGarethC
    • CommentTimeOct 14th 2013
     
    GaryB, that's very interesting. I might contact the local regulator to get more colour, especially how they got past the DECC's reservations. Sounds like quite a generous level of subsidy! Would be interested to see what take up is like.

    Stones et al, in addition to what's been mentioned (SteamyTea, Paul) won't there also be more system losses in A2W? i.e. with A2W (even if only for space heating), there's an extra heat transfer stage, as heat is transferred from the refrigerant to water, then water to air, isn't it? Whereas with A2A it goes straight from refrigerant to air (albeit via a fan coil).

    And if that water is stored in A2W, there will be some losses there too. I suspect that the fan coil in the indoor unit will transfer heat more effectively to the air than large radiators. And I'm not sure how losses is transmission between the heat emitters and outside units compare. We did talk about the efficiency point at some length in an earlier post in this section.

    -Really- need some rock solid research on this to back up the high COPs claimed by manufacturers. Particularly need to understand the impact of the defrost cycle in our humid climate. The EST's latest field trial indicated that 5 out of 6 new A2W heat pumps achieved an SPF of 2.5 or more (needed to be classed as renewable), clustered around 2.8 as far as I can tell, and managing up to 3.2 (with an outlier at 4). That's better than in their first study, but will still be below manufacturer's claims by about 1 I think.

    Still, if, as I suspect, A2A manage a bit better (say 3.3 on average at a complete guess), you're looking at it costing less than natural gas for heating and being a chunk greener (and of course -much- cheaper to buy and install).
    •  
      CommentAuthordjh
    • CommentTimeOct 14th 2013
     
    Posted By: GarethCStill, if, as I suspect, A2A manage a bit better (say 3.3 on average at a complete guess), you're looking at it costing less than natural gas for heating and being a chunk greener (and of course -much- cheaper to buy and install).

    How is it much cheaper? Especially given that you're still keeping a gas boiler for DHW?
    • CommentAuthorGarethC
    • CommentTimeOct 14th 2013
     
    £2k for A2A vs £8k for a similar output A2W. Remember I'm only thinking here of homes that already have natural gas boilers but want a way to cut carbon emissions and/or running costs.
    • CommentAuthorjamesingram
    • CommentTimeOct 14th 2013 edited
     
    Posted By: GarethCPosted By: jamesingram"To get back to my main points relative to the topic here is.
    2. If people switch to electric space heating before the grid has reached a certain level of renewable input.
    the new renewable generation entering the grid each year might not be able to keep up with this demand switch from gas to electric and the percentage of renewable to demand might even drop . Creating more potential pollution."

    Not if the electricity is used to heat space more greenly than using gas directly? i.e. if the gas that would have been used directly for space heating is instead burnt in a power station (i.e. incremental electricity is not met by renewables, but existing fossil fuels), but the electricity produced drives heat pumps with COPs higher than 2.4 (not 2.2 as I mentioned earlier - oops!), then there's a net carbon benefit even without more renewables isn't there? If the SPF manages 3.6, maybe reasonable for new systems, that would be a 33% reduction in carbon intensity, which sounds worthwhile to me.
    .
    Sounds fair
    So quick look at figures kgCO2/kWh
    Natural gas ( burnt in home boiler) 0.203 at 90% eff = 0.225 (edit forgot boiler eff. :) )

    UK grid electric additional fossil fuel load - COP require to achieve similar CO2 to above
    natural gas , existing plant 0.47 = 2.08
    LNG new CCGT 0.53 = 2.35
    Coal 1.11 = 4.93

    Other than coal it's looking good,
    Let just hope when all these heat pumps get turned on a dark December evening it's not Coal stations that fuels the additional demand :shamed: ( Anybody thoughts on what's most likely to be used (station type) over the next 10 years or so to cover this potential additional demand ? I'm presuming gas ( is there the capacity?) )

    lots of different figures for values but this was my source (current DEFRA carbon factors appear slightly lower for natural gas primary energy)
    http://www.zerocarbonhub.org/resourcefiles/Carbon_Emission_Factors_for_Fuels-methodology_and_values_for_2013_and_2016.pdf
    Natural gas
    feel free to correct me.
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 14th 2013
     
    Posted By: jamesingram0.225 (edit forgot boiler eff. :) )
    Would even the most efficient gas boiler get close to 90% when it is cycling a few times a day. For that matter would any heat pump get close to its stated CoP when you take a few on/off cycles into account.

    If anyone has a HP of any sort, can you check how long it takes from standstill until the output temp reaches the temp that is needed. If you could note down the ambient temp as well all the better.
    • CommentAuthorEd Davies
    • CommentTimeOct 14th 2013
     
    Posted By: jamesingramLet just hope when all these heat pumps get turned on a dark December evening it's not Coal stations that fuel the additional demand
    Precisely; it's not the overall grid emissions (total kgCOâ‚‚/h divided by kW being generated) that matter but the marginal emissions (extra kgCOâ‚‚/h for each additional kW).
  11.  
    Ed , put much better than my many previous attempts , thanks
    • CommentAuthorjamesingram
    • CommentTimeOct 14th 2013 edited
     
    Posted By: SteamyTea
    Posted By: jamesingram0.225 (edit forgot boiler eff. :) )
    Would even the most efficient gas boiler get close to 90% when it is cycling a few times a day. For that matter would any heat pump get close to its stated CoP when you take a few on/off cycles into account.
    If anyone has a HP of any sort, can you check how long it takes from standstill until the output temp reaches the temp that is needed. If you could note down the ambient temp as well all the better.

    Fair point re. gas boiler . Gareths EST info. gives real data on COP on A2W and his estimate for A2A seems reasonable ie. COP at least 1 below claimed
    • CommentAuthorjamesingram
    • CommentTimeOct 14th 2013 edited
     
    Posted By: GaryBA2A is the future for new build low carbon housing.
    I'm currently working with research driven manufacturers on the next generation systems.
    There are already A2A single room units on the market which can achieve CoPs of 6.0 and in a couple of years' time 8.0 is possible. My focus is on whole house systems which currently are around the 3.6 mark for CoP. In a few years' time these should improve to 5.0 or better.

    Do the units you're working on have a cooling function (cheap ones I've look into do) and if so what's the thoughts regarding effect on energy use.
    If it's there isn't it likely to be used and therefore detrimental to all it's potential benefits in terms of energy saving ?
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 14th 2013 edited
     
    Posted By: Ed DaviesPrecisely; it's not the overall grid emissions (total kgCOâ‚‚/h divided by kW being generated) that matter but the marginal emissions (extra kgCOâ‚‚/h for each additional kW).
    Coal tends to be scheduled, as does Nuclear. Gas is generally used to fill in any short comings. But if enough people use Heat Pumps (or electrical heating in general), then the coal becomes scheduled to supply that energy. Coal is a cheap fuel, about 20 quid a tonne still. Or about £0.003/kWh (primary) So even allowing for 30% efficiency it is under a penny per kWh.
    Why we use it :sad:
    • CommentAuthorSeret
    • CommentTimeOct 14th 2013
     
    Posted By: SteamyTeaCoal tends to be scheduled


    Indeed. Those coal plants are massive, they can't really follow demand.
    •  
      CommentAuthordjh
    • CommentTimeOct 14th 2013
     
    Posted By: GarethC£2k for A2A vs £8k for a similar output A2W. Remember I'm only thinking here of homes that already have natural gas boilers but want a way to cut carbon emissions and/or running costs.

    Ah sorry, I misunderstood. I thought you were comparing it against the costs of a gas system.
    • CommentAuthorTriassic
    • CommentTimeOct 15th 2013
     
    Posted By: SeretThose coal plants are massive, they can't really follow demand.
    wait didn't I just hear on the news that 6 of these coal fired stations are due to close in 2015/16 and brown outs and black outs could be the order of the day?
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 16th 2013 edited
     
    Yes you did, but don't worry, the Government is about to announce the price we are going to pay for the new Franco-Chino nuclear installation at Hinkley, so all is well.
    Going to be a shock to some PV owners when they find their PV is disconnected and not earning.:wink:
    • CommentAuthorSeret
    • CommentTimeOct 16th 2013
     
    Posted By: Triassicwait didn't I just hear on the news that 6 of these coal fired stations are due to close in 2015/16 and brown outs and black outs could be the order of the day?


    Yep, that'll be because of the Large Combustion Plant Directive. Power stations that don't want to comply with the new stricter emissions limits have been on borrowed time, limited to 20,000 hours of operation. Of the original plants affected most closed this year or last, but there are a few that have been eking out their hours. 2015 is the deadline, if they ain't used up their 20,000 hours by then they shut anyway.

    Harsh, but it'll certainly light a rocket under people to get some generation with lower emissions plugged into the grid.
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 16th 2013
     
    Posted By: SeretHarsh, but it'll certainly light a rocket under people to get some generation with lower emissions plugged into the grid.
    More details here
    http://en.wikipedia.org/wiki/List_of_power_stations_in_England
    • CommentAuthorjamesingram
    • CommentTimeOct 20th 2013 edited
     
    Posted By: Seret
    Posted By: SteamyTeaCoal tends to be scheduled


    Indeed. Those coal plants are massive, they can't really follow demand.
    So if heat demand switch to HP is powered by gas stations, CO2 has potential to drop. If Coal plants are scheduled to cover load switch then there's a problem ( but coals being potentially restricted as mentioned ( hence move to biomas being used at Draks etc.?)
    All a bit up in the air with these ASHP etc. :bigsmile:
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 20th 2013
     
    Yes, if we swapped to HPs of all sorts then out CO2 emissions would go up until we have 60% nuclear generation.

    I was thinking about the £14b that is goign to costs us about £90b on our bills.
    That would buy a lot of R&D and commission of CCS for out old coal plants. And less of a controversial than the EDF deal.
    • CommentAuthorcullym
    • CommentTimeOct 21st 2013
     
    I've been following this discussion with interest. Doing a bit more research online and I've come across this article http://www.carboncommentary.com/2013/10/03/3272 which should add to the discussion here. I'm working my way through it at the moment but the conclusion is that an A2A should be a lot more efficent to run and require less power than an A2W to achieve the same effect re. space heating.
  24.  
    Paul Dodgshun's argument seems to be based on the delivery temperature required by an air-to-water heat pump feeding radiators, the assumption that the air-to-air system will sit alongside a oil/gas fired boiler which will cover DHW demand & an ignorance of the fact that an A2A heat pump may get used for cooling.

    He assumes that an A2A heat pump can deliver heat at 30°C & that an A2W heat pump will need to provide 60°C. This may be the case when connecting to existing radiators, but is clearly not the case when connecting to underfloor heating in a well insulated, airtight property.

    He is not concerned by an A2A heat pumps inability to deliver DHW because he assumes the A2A heat pump will sit alongside an existing oil/gas fired boiler. This would be very wasteful in a new build & ignores the fact that in well insulated airtight properties the DHW load is very significant compared to the space heat load.

    Any benefit in COP from the A2A heat pumps ability to operate at lower flow temperatures need to be balanced against the fact that many people will use them for cooling, significantly increasing energy consumption & carbon emissions.

    In a well insulated airtight house,there is a lot to be said for a properly design A2W system which is directly connected to underfloor heating & delivers DHW via a separate cylinder/thermal store. Heat can be delivered where it is needed when it is needed at temperatures just above room air temperature without the horrible sickly smell of warm air from an air conditioning unit.

    David
  25.  
    Posted By: davidfreeboroughAny benefit in COP from the A2A heat pumps ability to operate at lower flow temperatures need to be balanced against the fact that many people will use them for cooling, significantly increasing energy consumption & carbon emissions.David
    Very important point and shouldn't be over looked
  26.  
    Posted By: jamesingramVery important point and shouldn't be over looked


    Entirely a red-herring in a climate like the UK where there's 20x more heating-degree-days than cooling-degree-days. Even here in Montreal with hot and humid summers, we still have, on average, about 14x more HDD load than CDD.

    The linked blog discussing A2A heatpumps does have some fatal flaws in reasoning though - the worst being the belief that an A2A heatpump can keep a house at 20C with a supply temperature of only 25C. It's extremely unlikely unless the insulation levels are so high that virtually no heating is required - otherwise enormous volumes of air would have to be circulated. The main reason why air-to-air systems (or water-to-air for that matter) are not used in the UK is the absence of anywhere to run the ductwork needed. Over here, most houses have basements where it's supremely easy to run the main duct trunk lines. That's just not feasible in UK-style house construction. I guess everything could be put in the attic, but that is definitely sub-optimal.

    Paul in Montreal.
    • CommentAuthorEd Davies
    • CommentTimeOct 22nd 2013
     
    Also, on the few days in the UK where cooling helps PV is likely to be doing well.
    • CommentAuthorjamesingram
    • CommentTimeOct 22nd 2013 edited
     
    cant see why it's a red herring Paul ? if it's there they'll use it , if not, they wont, degree days or not :cool:
    Fit something to save energy then use more on it's additional functions previously unrequired.
    I cant see any reason for domestic cooling in the UK , but it's become more desirable . All modern cars have it ?

    Another similar point would be the slow increase in desired internal temp. over the last few decades in the UK.
    I've worked at many homes 22+ deg C with windows left open and occupants moaning on about the size of their bills. Offer the suggestion that they might consider closing some windows, knocking the stat down a couple of degree and putting on a light additional layer and the look at you like you've just abused a recently dead relative . No they'd much rather spend their money on the latest 'eco' tech. gadget to absolve their middle class guilt. It's like buying partial indulgences :wink:
  29.  
    Posted By: jamesingramcant see why it's a red herring Paul ? if it's there they'll use it , if not, they wont, degree days or not


    But if the argument is valid that an A2A heatpump is much more efficient than an A2W, even if they use A/C, they could still end up using less energy than if they just had the A2W unit. Plus the capital cost is also quite a bit less. My argument is that there is such a low cooling load that the additional energy used by A/C would be much less than that saved by A2A in the first place. Plus it might encourage people to be of the mindset that interior comfort is highest when the windows are kept closed all the time!

    Paul in Montreal.
    • CommentAuthorjamesingram
    • CommentTimeOct 22nd 2013 edited
     
    Point taken Paul , but the thrust of this thread is A2A being potentially more efficient and cost saving if used as an alternative to existing wet/gas central heating system in the UK . If A/C comes into play then the marginal benefits (depending on additional load generation type) may be lost.
    Fitting A/C in UK home would be an unnecessary additional load. My point was using theoretical degree days
    to estimate load isn't the entire picture. Peoples inconsistencies need to be aloud for. It's adaptive thermal comfort , but in a negative way with regard to reduction in overall energy usage.

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