UPDATED: Air Source Heat Pumps/Air Con - Full Info & Guide, is it cheaper to run than mains gas?

albyota

thills, sorry to here about your ASHP planning application refusal, :mad: I hope you manage to find a decent heating system that will suit your requirements.
Al

toerag33

We are currently looking up the suggestions from Albyota and anticipate we may ask for some further guidance.

Paceinternet: thank you for your input. we don't understand the heat load assessment - is this something we ask someone to do independently? What is it? The rest of your posting we feel we have a vague idea understanding about but will in all likelihood come back here for further advice.

We have wondered why ground source heat pumps weren't suggested?

:AThis has been extrememly helpful - our thanks for the information.

albyota

the engineer/advisor/surveyor does the heat load assessment, which is a calculation made by length, width, height, U values of walls, windows, ceilings, floor, insulation levels in roof / cavity etc, where in the UK you are, solar gain vs north facing rooms, external walls. this creates the heat loss of the house and from here the heat load from a heating source, boiler, ASHP etc...check size of radiators at delta t50 against lower temp from heat pump or better still underfloor heating for higher efficiencies as paceinternet said, if increasing size of radiators is not an option then you are better to go with the higher temp Sanyo or Daikin kit, hope this helps.

arty68

Although the sanyo and daikin kit do produce higher temperatures they are still subject to the rule 'the higher the water temp the lower the COP'.

GSHP are good but it's the set up costs that are prohibative especially if you are talking about a bore hole. They would be the way to go if you have an acre or 2 and access to a man with a digger and put the pipes in yourself.

With the radiators if they are old it maybe they simply need replacing with modern higher output versions using the same pipework.

You could use a rad sizing tool from the net and add 30% for lower temperatures ti see what sizes you need.

http://www.hamiltonit.co.uk/Tools/RadiatorSizeCalculator.aspx

paceinternet

Just to add to the replies above, albyota describes the heat load assessment, but you need to add your hot water requirements. Tell the person doing it how much you need and over what time period. Example; 3 * 10 minute showers every day within an hour plus whatever else you use it for.
Central heating engineers or heat pump installers should give you a quote for the work which should include this. You can then compare and question why they are different.

Beware of radiator outputs at lower temperatures. The Stelrad web site has a very good specification sheet showing reduced outputs from the standard delta t50. Going to delta t30 means output is halved (50% less). so, as I said above, if you run your heat pump at 50 deg C output water temperature and want a room temperature of 20 deg C, the delta t is 30.
To get the best COP from the heat pump and run it at 35 deg C, radiator outputs are reduced even more, so be careful.
And beware of the way the heat pump specification describes the output, because some use return water temperature and others use output temperature. Output is generally about 5 deg C higher that input when running correctly.

Finally if you haven't recognised the importance of these temparatures and COP (Coefficient of Performance), it is all about the kw output being higher if the temperature you try to achieve is lower, hence underfloor is so much better, but not essential.
Just to exagerate this, you might get 10kw at 35 deg C, but 6kw at 50 deg C. So if you can run the system at 35 deg C and have enough surface area of underfloor or radiator to distribute the heat, you can get more output and efficiency from the heat pump.
With Air source, you have further reductions in output as the ambient temperature reduces.

But, don't let all this put you off, I believe albyota has a very effective ASHP installation and is very very satisfied.
You just need to get the spec right.

Cardew

Just a further factor to add to the excellent posts above.

You do need to appreciate that the maximum output of heatpumps do not come close to that of conventional Gas/Oil CH boilers.

When returning to a cold house it doesn't take long for rooms to warm when the radiators can be heated to 80C by a gas/oil boiler blasting out 30+ kW even when it is freezing outside.

Not so with radiators heated at 35C-40C by a heat pump pushing out perhaps 6kW.

For this reason you need to allow plenty of time to warm rooms or preferably not let rooms drop too low during the day.

rhubarbe

But with the Feed in Tariffs for renewable heat coming in in April 2011, a properly specified ASHP system installed in a well insulated house may cost you nothing to leave running 24/7....

As long as you specify an MCS approved product and an MCS accredited installer...

peat

Could one of you enlightened folks tell me how to determine the output of radiators of a known size (now that paceinternet has kindly explained delta t 50 etc.)
For example what would be the output of a single panel 1000 mm by 600 at delta t 50?

paceinternet

http://www.stelrad.com/UK/docs/elite.pdf

Standard outputs at delta t50 on page 4
Factors for different temperatures on page 7 to multiply the standard output by.

richardc1983

paceinternet wrote: »

http://www.stelrad.com/UK/docs/elite.pdf

Standard outputs at delta t50 on page 4
Factors for different temperatures on page 7 to multiply the standard output by.

It states outputs at 75, 65 & 20C but not sure where it shows the results for 65 & 20c. yes I know page 7 shows these factors but the chart gives the impression that these have already worked out these.

So is delta t50 50C flow temp?