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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorEd Davies
    • CommentTimeOct 27th 2016
     
    Posted By: Paul in MontrealAll refrigeration systems require a liquid<->gas phase transition as the latent heat of evaporation is what gives the energy transportation ability
    Maybe that's right for practical systems but I don't see why, in principle, you couldn't move heat around by just compressing and expanding a gas.
  1.  
    Posted By: Ed DaviesMaybe that's right for practical systems but I don't see why, in principle, you couldn't move heat around by just compressing and expanding a gas.


    Oh you can, but the latent heat of condensation makes it much more effective as it magnifies the effective heat capacity of the gas. The limiting factor in many refrigeration systems is the volume of refrigerant you can move - this is why, actually, the output of A2A heatpumps falls with temperature - the volume of gas produced in the evaporator declines. I think the very low critical temperature of R744 (CO2) helps mitigate this.

    Paul in Montreal.
    •  
      CommentAuthordjh
    • CommentTimeOct 27th 2016
     
    Posted By: Paul in Montreal
    Posted By: Ed DaviesMaybe that's right for practical systems but I don't see why, in principle, you couldn't move heat around by just compressing and expanding a gas.


    Oh you can, but the latent heat of condensation makes it much more effective as it magnifies the effective heat capacity of the gas.

    See also - heat pipes, as used in PCs or solar thermal tubes. See also - phase-change materials for heat storage. Just for two more examples.
    • CommentAuthortopher
    • CommentTimeNov 22nd 2018
     
    Just in case anyone is still there . . . . . .

    It is now 7 years since my GSHP was installed.

    In 2015 I added a heat output measuring device. It measures the flow rate of the water by ultrasound and taking the supply and return temperatures calculates the heat output produced.

    I measure the energy input with a standard kWh meter. I divide the output by the input to get the CoP (coefficient of performance.

    Here are recent readings with their dates . . . .

    7/5/18 - 3.74

    20/4/19 - 3.74

    10/4/18. - 4.23

    23/2/18. - 4.27

    I am constantly tweaking the parameters to get the compressor run time to be as long as possible. With the mild weather this is difficult.
    • CommentAuthorowlman
    • CommentTimeNov 22nd 2018
     
    That's interesting topher, and to me those figures seem good for a 7 year old install. How do those figures relate to the mfs. published COPs
    I'm well on with my own ASHP install ( A2A ) and I may look at somehow recording output in a similar manner.
    • CommentAuthortopher
    • CommentTimeNov 22nd 2018
     
    Owlman,

    I have been trying to find the spec for my heat pump, but can't. I remember a manufacturer's CoP of about 4.2 for 35 deg C output from 0 deg C primary. I sometimes get this.

    I bought a meter that records heat output. It has an internal battery. It needs to be put in the heat output and have small pockets to take thermocouples for supply and return temperatures. It was fun to install and use.
    • CommentAuthorowlman
    • CommentTimeNov 22nd 2018
     
    I've gone for a Toshiba SDI R32 outdoor unit and coupled it with a standard duct indoor unit. The mfs. say it'll produce a CoP of 5.52 for heating, with an A+++ efficiency rating. For me sampling warm air supply and return may be a bit more onerous. Maybe sampling the refrigerant loop may be easier and perhaps more accurate.
    •  
      CommentAuthordjh
    • CommentTimeNov 22nd 2018 edited
     
    Posted By: owlmanFor me sampling warm air supply and return may be a bit more onerous.

    Easy enough to measure the temperature. I'd suggest measuring the flowrate with a hooded anemometer for particular fan speed settings and then relying on realtime collection of the speed settings to infer the flowrate.
    • CommentAuthortopher
    • CommentTimeMar 6th 2019
     
    Owlman, That spec looks very impressive. When it has a CoP of 5.52 what is the air temperature, and what is the output temperature?
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