ASHP – Should do better - Must Do Better

Cardew

Geotherm wrote: »

You cannot really take data from someone in Finland, which has much more temperature extremes than the UK. The readings for the first chart are based on -5.1C so the cop will be much lower. His hot water temps are steady, showing the heat delta is working, with hot water priority, otherwise DHW production would not be kicking in as much.

The 2010 average temperature for Southern Finland is 5.0C and for UK is 8.0C.

Would you be happy with an expensive ASHP system that for the last month gave a COP of 1.2?

To achieve that from the graphs it appears the system is running 24/7. As stated above much of that heat is wasted when occupants are out/in bed.

If you used straight electrical heating(not even storage heating) you would be able to set a very high output for say 1 hour in the morning before you went to work.

Then have it come on, say 1 hour before you returned and off again when you went to bed.

Would you not think that with a COP of 1.0 against the ASHP COP of 1.2, a case could be made for 'straight' electrical heating?

lovesgshp

http://weather.uk.msn.com/monthly_averages.aspx

for London UK

If the guy in Finland is using UFH then to turn it up and down would be unproductive. On a normal underfloor system you need up to 24 hrs to feel the effect of a heat increase. I will quite happily give you the flow temperature requirements for UHF here set with indoor temp at 19C, indoor temp sensor @ 70% influence over external temp and down to -35C outside in 5C increments. Heating delta at 5C.

rhiwfield

Live ASHP air-water cop data per site posted above (reposted)

Figures are for HW, CH and total

site 1: -, 3.4, 3.4
site 2: 1.3, 3.2, 2.9
site 3: 1.7, 3.8, 3.6
site 4: 1.9, 3.1, 2.9
site 5 1.9, 2.7, 2.3

Cardew

Geotherm wrote: »

If the guy in Finland is using UFH then to turn it up and down would be unproductive. On a normal underfloor system you need up to 24 hrs to feel the effect of a heat increase.

That is exactly the point I am making.

Say, for the sake of this discussion, an ASHP is producing a constant 5kW and is operating 24/7.

In 24 hours it will have produced 120kWh and with a COP of 1.2 used 100kWh.

Someone out at work could have the heating on in the morning for an hour using, say 10kWh and then say 3 hours in the Afternoon/evening @10kWh followed by a further 3 hours @ 5kWh before going to bed. Therefore using 55kWh in the 24 hours. There being no point in heating while out at work or in bed.

* the figures are only to illustrate the principle.

lovesgshp

Agree in principle Cardew, but you should never set a flow rate return difference of more than 1.5C for a underfloor system. Up to 4.0C for radiators is okay. I have 1.5 below set for 10.00 pm to 6.00 am.
I looked at the Sanyo site for the 4.5KW air/water and they state a COP at 4.1,with outside temp 25C, inlet water temp 30C/outlet 50C. I could not find the standard European detail EN255 for 7C input /35C out for ASHPs

muckybutt

Ill add a bit about our ashp.

We were given it as a fuel poverty grant fully funded so didnt have owt to pay, we were on oil before which supposedly cost more than the ashp would.

The house was measured up and design done by the manufacturers agent and all the pipe work and rads replaced.

Now we live in a 1850's terraced with no double glazing as we are listed and cant have it and we have solid walls.

The system itself is ok I cant complain it was well installed and comissioned by heatking themself's so we know everything is ok with it. However as stated it costs an effing fortune to run, our comparable leccy bill the year before was £110 for the quarter, the same quarter a year later cost us over £800. Our oil bill the year before was only £320 and that lasted us some 5 months so we're well out of pocket.

How has it coped with the cold ? water output even on the coldest of days has been 42 - 47 deg, when the weather warms up between 46 - 56 deg, cant say weve been roasting inside and werent expecting to be but I like my hot water hot ! which sadly some days it just isnt so we then have to top it up with the immersion heater.

Noise wise when running it is quite quiet you can easily have a conversation in front of it, defrost is a little noisier as my neighbours informed me via the council noise enforcement officer ( thanks ! ) :mad:.

Well we had it installed Sept 09 and are soon getting it ripped out as it cant be said its cost effective for our house, back to basics for us with a multi fuel stove.

lovesgshp

OK,size of house, heat pump size, room temperature settings. Do you have the thermal analysis for the property?

muckybutt

Size of house two up two down 4m x 4m rooms and a kitchen and bathroom approx 4m x 2m, all rads are stat controlled set to 3 - 4, main stat set to 19 deg, dont have thermal analysis, unit is a heatking 9000i 9Kw output 3kw input rated down to -20 http://www.renewablesireland.com/uploaded_files/File/Heatking_leaflet.pdf
same name but 9kw version for some reason heatking site wont load.

ra200

Well guy's i have a nibe 360p exhaust air source heat pump with ufh and it is usless in my 95m2 new build house it eats electric and when it is below 9c outside it relies on the immersion heater most of the time the other night it was -3 outside and the nibe was on the immersion heater most of the time and even with that it was cold upstairs in our house,

thechippy

Just to clarify....

I don't and never have installed either ashp's / gshp's. (to water)
These days they tend to be installed by plumbers / heating engineers as the refrigeration side is self contained, They are just plumbed into the water circuit.

I've only ever been called out to them when the heat pump itself is assumed to not be working.

By and large, the hp is actually working ok, it's my experience that they do not perform, as they are often undersized for the application. The heat load calcs seem to be incorrect regularly.

Some "seem" to be sized ok, in that the space air and hot water requirements have been calculated correctly, but the building heat loss characteristics have not - therefore it remains undersized.

My industry experience is vast - from huge water chillers that cool an entire office block, to helicoper a/c, to freezer coldstores that you could do handbrake turns in a double decker bus.

I don't look in here too often and my posts are often brief, as I've had enough of this subject all day at work....;)

...I could ramble forever if I wanted...:D, although I'm happier on the DFW board helping the poor souls on there....:cool:

Some will debate this, but gshp's will eventually suffer reduced efficiency as the hp will remove heat faster than mother nature can replace it. The only possible exception to this, is where the ground is quite wet all the time and the moving water table can replenish the heat. It can take a few years before the reduced efficiency is noticed, but once it starts, it won't get any better - just worse!!

Air to air however, I love - the best source of space heating by far. I've installed hundreds of these and see how well they operate all the time. I still have contact with all the clients and have no complaints on either efficiency or running costs.

So, despite being in the trade, I agree with Cardew on these things, they need to improve considerably.

I would only even "consider" one on the following basis...

1. The property is VERY well insulated
2. Heat calcs done correctly
3. No access to mains gas.
4. Property unsuitable for air to air hp's