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Green Building Bible, Fourth Edition
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Products: Heat Pumps- 3 out : 1 in : 3 out

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    • CommentAuthorally.gill
    • CommentTimeDec 19th 2007
     
    I'm producing a uni paper on env design and want to consider the incorporation of heat pumps to achieve csh. i'm not content with the concept of 3 parts energy to 1 part electric feed to 3 parts heat. i cant see the benefit especially with the reliance on energy security through centralised supply. So,
    1. How often would the pump need power and to what quantity?
    2. Can rooftop supply (pv array/turbines) provide the electrical energy required at reasonable cost/payback? (based on avge uk wind and solar figures)
    3. Could a 100 dwelling development provide localised renewable heat and energy within achievable cost parameters to omit reliance on gas and centralsied power, provide an oversupply of electric feeding the grid to fund maintenance costs, and provide affordable homes with the required level of profit margin to satisfy shareholders.

    And as an aside if we are in an energy crisis can the government introduce a power ban (similar to a hosepipe ban) to prevent this ridiculous waste of electricity on christmas lights outside peoples houses?
    •  
      CommentAuthorOlly
    • CommentTimeDec 19th 2007
     
    Posted By: ally.gillheat pumps to achieve csh.

    Are you referring to air source or ground source heat pumps?
    By CSH, do you mean the Code for Sustainable Homes, if so, then which level?

    1. Too little information to say.

    2. The short answer is no.
    You're unlikely to see your money back on PV, outputs are fairly predictable, but the only way you'll make/save money is if electricity prices shoot up, which isn't inconceivable. Micro wind will perform poorly in all but the windiest locations, so installing one in an average location in the UK is not generally speaking a good idea. You can of course sell the ROCs from renewables, but it's a PITA having spoken to people who've tried to do it. Although with the possible introduction of banding for ROCs, PV's will score 2 ROCS/MWh, whereas onshore wind will only score 1ROC/MWh. (See table 5.3.1 in the DTI Energy White Paper) this is because PV is classed as an "Emerging technology". I'm not 100% sure about the thinking there, I guess we'll have to wait and see what happens.

    3. Not at present. I'm working on a CSH code level 6 "net zero carbon" development, however this is only financially viable due to significant funding.
    • CommentAuthorally.gill
    • CommentTimeDec 19th 2007
     
    yes i mean code for sustainable homes and in terms of achieving points at any level.

    1. pump energy i'm just thinking in general rule of thumb terms; eg 60% of the time in winter 40% o fthe time in summer.
    3. so 3. is only achievable with major subsidies and the money is being pumped into nuclear power instead, at ten times what goes into the renewables industry.

    4. so heat pumps use electricity to create the heat. their demand cannot be met on-site, but could be met by regional development if heavily subsidised leading to more efficient supply, maybe 1.5 : 1 : 3 ?

    olly, could you set up a discussion on real life solution to meeting the low water demand requirements of csh6. would be interested to hear how this is being addressed.
    • CommentAuthorCWatters
    • CommentTimeDec 19th 2007
     
    Not quite sure we understand your question 1 but here goes...

    The amount of power required to maintain a set temperature depends on just four things:

    a) The temperature difference between inside and out.
    b) The thermal resistance between inside and out (eg insulation)
    c) Amount of ventilation (the amount of cold fresh air that has to be heated)
    d) The efficiency of the energy converter (Boiler, heat pump etc)

    Heat pumps can be 300% or more efficient so they use 1KW to move 3KW indoors. That's the benefit compared to other systems. It's not easy to put a percentage figure on the time the pump will run. If it's only used for heating it might be off all summer. The rest of the time it would depend how correctly specified/sized it was. If undersize it will run for a greater percentage of the time than if overspecified.
    • CommentAuthorally.gill
    • CommentTimeDec 20th 2007
     
    Thanks CW. my point is that to get the 300% out you need to put 100% in and this only comes from generating 300% in the first place at the power station. That is unless micro-generation can be used on site to adequately supply the pumps electrical demand. By knowing the demand, we can size the supply (eg pv array/turbine) but the demand is diurnal and will fluctuate with the seasons (out of sync with pv) so is the supply able to meet the demand and if not then the pump system is reliant on nuclear power, energy security to power stations, continuity of inefficient centralised supply and if thats the case then where is the benefit.
    if we were talking about a stove being really really efficient at burning tropical hardwood, would that justify cutting down essential forests ?
    also how much energy is required to drill the borehole, remove the spoil, grout the hole, i.e the embodied energy of the scheme itself.
    • CommentAuthorchuckey
    • CommentTimeDec 23rd 2007
     
    Ally.gill
    "this only comes from generating 300% in the first place at the power station." This is a typo?, to re-iterate, using a 1 kW motor you shift 3kW of heat out of the soil into your house. The heat from the motor is dissipated inside your house so you get 4 kW of heat with electricity bills for 1kW.
    "and if thats the case then where is the benefit" - see above.
    Why are you not considering air source heat pumps?
    Have you ANY idea about the likely heating load of your development? Even allowing for the thermal gains of GSHP, the pumping power requirements are going to be in the 10s of kW, so unless you have onsite (battery?) storage of this power for at least 10 days the scheme will come to a shuddering and frozen halt. We could not get fully 100% 24/7 support for a 500W load using solar and turbine to charge a 24V 1000A/Hr battery in Cornwall.
    Frank
  7.  
    Chukey,
    I think that Ally's 300% refers to the fact that, in broad terms, you use 3 units of primary energy to generate 1 unit of delivered energy. This 1 unit of delivered energy is that converted to 3 units of space heating.

    Ally,
    Have a look at this and see if it helps you address some of your queries.
    http://www.heatpumpnet.org.uk/files/gir72.pdf

    Air sources heat pumps have an even worse COP than a ground source pumps; thus the CO2 emissions are worse also. Why bother with Heat Pumps? Gas has lower CO2 emissions and if far cheaper. I'd be of mind to consider using the additional capital to far more effect by purchasing more insulation, airtightness and MVHR.

    Mark

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