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Author Topic: Gas driven heat pumps  (Read 2447 times)
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« on: September 06, 2016, 05:58:38 PM »

Does anyone have one? Either gas engine driven or absorption.   I've been doing some work on markets for them in China and elsewhere, and I can't quite understand why they're so uncommon here.  Is it just that the RHI design didn't promote them, or that relative price of electricity is low enough. Or simply that the grid is so good why not use leccy (ie the only reason there's a market elsewhere is that people want heating in powercuts).   

I know DECC's grand plan was always electrification of heat, but I'm pretty sure there'll be some back-peddling from that as winter evening peaks get worse and worse.  Using a bit of gas for heating makes just as much (probably more) sense as using a bit of gas for meeting daily electricity peaks, which pretty much all sensible energy people assume will be necessary for a long while yet.   

Following is from an (old) decc paper:
Seasonal COPís of present gas-fired systems range from 1.1 to 1.5, and the theoretical limit could exceed 3 but keeping within what might be possible in systems we an envisage now, a   seasonal   COP  in   the   UK   of 2.0 [Gross   CV,   air   to   water   at  50C] is   certainly  not unreasonable. Machines  that  can  achieve  these  efficiencies  will  use  thermodynamic  cycles that are more complex, with cascaded temperature levels, improved heat regeneration, etc. and will probably be larger per unit of heat delivered. At the moment gas heat pumps must compete with gas boilers rather than electric heat pumps, but in the future we can imagine that  they  will  have  to  compete  more  with  advanced  electric  heat  pumps  and  a  COP  of  2.0 might be necessary as well as desirable.
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« Reply #1 on: September 07, 2016, 12:06:45 PM »

The Warwick University report says it all, gas powered units are too expensive and gains  over condensing  gas boiler  too small.   

Heat pumps are  probably more popular in areas where there is no gas supply.   If cost savings are to be made compared to gas   then electricity  needs to be at off peak rates and of course subsidies help as well.   If anything the surprising thing is that there aren't more  electric powered heat pumps installed in the UK and they are mainly air source, 66,000 in 2015.   


DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
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« Reply #2 on: September 07, 2016, 12:49:09 PM »

I think mains gas CHP would be a better option in the mid term.
If premium rate energy pricing becomes available, small scale CHP plants could run during times of peak demand when customers are likely to require heat also.

PV - 2.75kW East, 1.5kW South, 2.5kW West. 3 x Flat Plate Solar Thermal with side arm FPHE on 268L cylinder
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South West London

« Reply #3 on: September 07, 2016, 10:40:46 PM »

One of the on-going issues in the UK is our very weak building regs for new builds, Energy efficiency is not currently high on the list. So installing a low cost (to purchase) gas boiler that can run 30Kw is a valid option, all the other options have a much higher upfront purchase cost.

All the government forecasts 10+ years ago showed that gas costs would start to rise drastically, so electrification of heating became a focus (as did HPC and other stations). Between the drop in oil prices (and so gas prices) and the availability caused by things like fracking the whole 'plan' was put on the shelf.   

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