Heat pump cost to run

[slingshotjim]

Hi, Ive an ESP 11Kw heat pump installed correctly, I hope, only issue perhaps is that its a long way from the100l buffer, pipes fully insulated and thro the garage tho....
Its all connected to Wundafloor over panel ufh, not much insulation underneath cos of heights etc, something I regret now mind, the overpanel kit is designed for this, polystyrene and an aluminium foil.
Wen it kicks in, it uses 6 kw approx with temp 41 in 44 out approx, its that for 40 mins then goes to 1.5 kw for 5 mins then back to 6.5, basically in 2 hours at 5 deg outside temp, its at 6.5kw for1 hr and 15mins and at 1.6 for 45 mins, Wow thats expensive to run, does that sound right, i thort it would be a lot less than that..... Is the controller set ok Im thinking, It uses 6.5kw even if only the bedroom stat is on, It would be cheaper to use elecy rads! Any one any ideas, Cheers... Its set at 45deg, Ive got an Eccocent ashp 300l cylinder doing the dhw so not trying to hard with temp I thought, It loses about 7 degrees thro the pipes from pump to manifold but that wouldnt effect the KW Draw just the temp in the rooms... Any thing I can do..... I thought a cop of 3,9 I think they advertise ment at 7 deg outside it would take about3kw to reach an 11kw output, have I got it all wrong... is it to smallpraps...
any help appreciated, Jim 07980749925

 

[unguided1]

If you think there is a problem Jim the best thing to do is chat to your installer or go back to the manufacturer.

I am wondering why your heatpump is set at 45 deg, typically on underfloor I would be running it at around 35deg on the return

 

[slingshotjim]

Hi, thanks for your reply, Ive set it at 45 cos the house struggles at 35, the ufh kit we used, overlay wundafloor is used when floor heights are an issue and we didnt want to dig the floors up... big bungalow massive job. Ive had plumber/installer back, hes a friend and we ve gone thro all the install etc and cant find a problem, good and neat job, Its the electricity draw for the pump, Am I right in thinking if it say works at 2.5 cop on an average cold day and its output is 11 kw it shouldnt draw 7 kw that cop is 1.5 ish isnt it and that surely isnt right, it was doing 6kw when it was 6/7 outside, any advice/ help appreciated. If I had enough money id buy a well known make ashp and install it next to it to prove a point praps.

 

[slingshotjim]

Still costing a fortune, Left it off last night and heated our bedroom with 2 on low electric radiators, not only was it warmer but from midnight till 9 am was about 30 to 40% cheaper to do than with the ashp...... what a nightmare, It seems to nearly cost the same to run one room as half the whole house.....

 

[eaton]

Have 2 good examples

New build with underfloor both floors, big 4 bed using 35kwhs a day this week

Old bungalow well insulated with rads 2 beds 30kwhs a day in december

 

[slingshotjim]

Wow, this is using 26kw just overnight from 12 till 10am just ufh on in the bedroom at 19 and 2 1/2 hours of heating in the kitchen/living . we can use 80Kw in a day thats total use mind but only 3 of us, not mad on usage etc is mainly heating, any clues on an issue perhaps, Ive emailed the supplier, have you an email add and Ill foward it, any help is much appreciated, maybe Im just expecting too much, got nothing to compare it with...

 

[eaton]

I'm not keen on people who install these bigg units with higher flow temps, both mine are lower temp models, both hitachi yutaki, bungalow is a 6kw unit and the house is a 12kw unit, house has a buffer the bungalow has none, bungalow is set to 50c water and 45c heating, house is set 50c water and 40c heating, both are wrath compensated

 

[slingshotjim]

Big units with high flow,Mine is an 11kw and only does the heating, set at 45, and has a buffer to the ufh. Is there anything else that may make it draw that amont of electricity, does it sound wrong to you, Is mine a high temp one then what does that mean is it not suited to its purpose, getting worried ill never be able to go on holiday again!!

 

[eaton]

I'll admit I've never heard of your unit, I'd check they haven't used an immersion inside the unit to aid any heat needed, that would be a massive drain.

 

[slingshotjim]

Its from Earth Save Products, Funnily enough I asked that in my email to them before, Some put an element in the buffer I believe to help but Im sure we never ran an electric connection to mine so unless its actually in the heat pump itself , Is that a possibility, It would explain the draw though if it clicks that on at the same time and its a 3kw element praps it would put my consumption where I thought it would have been, Like I said, i never used the house on the lpg that it had when we bought it so nothing to compare it with, only a bungalow but its quite big, got cavity like a white dry powder stuff in and Ive done the loft and all the windows are new etc etc..

 

[eaton]

Yeah a lot can put an element in heat pump, fortunately with new rules that will be outlawed.

 

[slingshotjim]

Looking at the instructions... average to say the least , it doesnt mention an immersion in there, in the eccocent for the dhw ,yes but not the ashp...... wish there was, problem solved, cant understand it. does it sound wrong though, is there a reason or circumstance when one would use so much electricity, im constantly reading about people with tiny £800 a year bills.... mine will be nearly £3k at this rate.....

 

[eaton]

I wouldn't touch your unit to be honest having a quick look at what I've seen. Amateur to say the least

 

[slingshotjim]

Doesnt really help me that, but noted. Thanks.

Does that mean it would cost that much to run though, are you saying they are no good, there are always better, and hinesight etc etc.... any help with what Ive already got much appreciated.

 

[eaton]

It's impossible to say, we don't know what your unit is really, or the exact flow rate, flow temps, internal sensor set up, the list goes on, your asking an impossible question

 

[slingshotjim]

Oh ok, I just thought someone may think it was much too much usage for just ufh and there must be an issue. With you saying you wouldnt touch one and they were amateur I thought you may know these type quite well, no worries.

 

[Gray0689]

I was always led to believe with heat pumps the house needs to be very very well insulated

 

[MattWeth]

I was always led to believe with heat pumps the house needs to be very very well insulated

It does.

'Fabric first' is vitally important with heat pumps otherwise they'll be very expensive to run.

I've worked for 20 years in industrial refrigeration and HVAC design with the last 5 years working at a university in research on domestic renewable heating. For what it's worth, a few points to consider:

As above 'Fabric first': take care of building efficiency before even starting to consider adding energy in the form of a heat pump (or indeed any heating system).

HP sizing: Very accurate sizing and selection of the pump is essential. They need to be working at their peak efficiency in order to see the best economy (which means they'll be working quite hard). It's no good to err on the side of caution and put an oversized unit in 'just in case' - it'll end up working very inefficiently - it must be accurately matched to the building heat losses (which should have been accurately calculated). High flow temperatures nail efficiency unless using a sophisticated twin stage pump - selection of pump and emitters should be based on the manufacturers peak efficiency (usually 35 - 40 C ish)

COP: In the real world, a coefficient of performance of above 3 is nigh on impossible to achieve - manufacturers claims of above 3 should be treated with a pinch of salt (or indeed a bucket full of suspicion) - they will quoting lab performance in ideal conditions with a perfectly sized HP. The big manufacturers (eg Daikin and Mitsubishi) are quite honest and specify realistic COP's, some of the lesser known manufacturers are less scrupulous.

Underfloor heating is another can of worms: When well matched to a HP in a suitable dwelling, it can work very well but when poorly specified it can be a nightmare. UF relies on the heating of a large thermal mass which is well insulated from the ambient ground temperatures. If you can't get at least 100mm of high performance insulation underneath a 100 mm slab then you really need to be considering different emitters (low temp rads, fan coil units etc) and if you haven't got 100mm of insulation under your floor, you shouldn't be considering any HP. Overlay UF systems with no thermal mass are never going to be efficient when used with a HP - the pump will end up cycling continuously due to the lack of thermal mass. Buffer tanks can help but it's still an inefficient way of using a HP / UF.

Then, assuming you've got everything right with your slab and insulation, the way it's used can have a huge impact on efficiency - because of the high thermal mass, the slab takes a long time to heat up and cool down. During heat-up the HP will be running flat out to raise the temperature of the slab but once it's up to temp, it'll run efficiently just taking care of the heat losses (assuming it's properly sized). This is why UF is best suited to high occupancy buildings where it will rarely be switched off - using it for 'on-demand' heat when everyone is back from work / school in the evening is never going to be efficient - the HP will still be bringing the slab up to temperature when everyone has gone to bed.

Sorry to paint a bleak picture but from the information provided, it doesn't sound like the system in question has a much chance of running efficiently.

 

[eaton]

Just a quick one, is your pump invertor or scroll, I'd say in your situation you'd be best with an invertor

 

[slingshotjim]

Typical........ guess....... its a scroll...... brill. Got some more info to check etc. but if the worst case shall I start checking out some new style alloy gel filled rads or something... sounds like it may be my ufh system not having mass aswell as the ashp so not worth doing another type of boiler etc praps... not got mains gas obviously......

 

[eaton]

You really need to answer above question, what is your insulation like, floor, walls, loft etc, also was the underfloor designed for heat pumps? Many are not and designed for gas/oil boilers, this would make a massive differance

 

[MattWeth]

Just a quick one, is your pump invertor or scroll, I'd say in your situation you'd be best with an invertor

The two aren't mutually exclusive. Inverter control is just a away of speed controlling a compressor and getting it to modulate (within pretty a pretty narrow range). Many inverter controlled heat pumps use scroll compressors but some use screws or indeed good old recips.

A well sized scroll compressor HP is capable of good efficiency (with or without inverter control).

 

[eaton]

With a heat source that isnt all that stable invertors would be my first choice

 

[eaton]

Don't get your point?

 

[slingshotjim]

Its a bungalow, so no second floor... Cheers for all the ideas keep em coming. shame no one near, would nt mind paying if necessary to maybe do some heat loss calcs etc to recheck size of pump etc, just to see if I may need to have a new idea, just trying to heat the house the cheapest way poss, didnt go heat pump for the green.... just got no gas supply in the road and looked at oil n lpg and ended up at ashp and ufh.....

 

[Gray0689]

Its a bungalow, so no second floor... Cheers for all the ideas keep em coming. shame no one near, would nt mind paying if necessary to maybe do some heat loss calcs etc to recheck size of pump etc, just to see if I may need to have a new idea, just trying to heat the house the cheapest way poss, didnt go heat pump for the green.... just got no gas supply in the road and looked at oil n lpg and ended up at ashp and ufh.....

Get whoever designed the system back

 

[MattWeth]

Agreed - I think the installer should be your first port of call.
How was it sized / specified? Were any heat loss calcs done?

 

[slingshotjim]

Well, stuck here really, When I did the looking about for ashps ufh etc never went that far, I know I know, Gave all house sizes etc to ashp provider and they aimed me towards wundafloor as I was stuck with the floor height and fitted overlay panels..... insulation underneath an issue, Yes, I know.... And was told 11kw thats the one, and off I went, I m not complaining about the heat of the house or anything like that although the non thermal mass ufh definitely has an effect, in the tiled room heat much better than bedroom on 6mm of ply n carpet, Its the electricity draw, 6 plus kw a lot of the time when the water in is 42 and out 45, dont get that wether its all loss calcs done or not, is that totally wrong, the heat pump does what its supposed to, heats the house, just uses lots of electric, Could I praps have used a much smaller ashp maybe although its a big bungalow its all insulated, cavity, argon glass,roof etc..
Or its too small and overworking all the time praps, I know i need to do all the calcs and theres not a quick fix it seems, thanks for all advice. it seems to me that its maybe not too bad when heating the whole house the electric used, but at night when the stats are all off except in our bedroom it seems to use nearly the same amount, be cheaper to use a good spec alloy electric rad for that praps n leave ufh off unless its all on...... make sense?

 

[MattWeth]

I don't think you can think about 'quick fixes' until you've established a baseline heating load.

You need to do some heat loss calculations for your house before thinking about remedial work.

Try working through the heatloss calculator which you can download from here: Domestic heating sizing method (2010 edition) / Heating systems / Housing professionals / Publications / Home (United Kingdom) - Energy Saving Trust

It's a fairly crude 'whole house' method but should provide you with a starting point and you can use the method to do individual rooms if need be. You can search for more in-depth calculations if you need them.

Once you've done the calcs you can start to think about how to improve the efficiency of your HP installation but you do need to establish a starting point before spending more money.

Really, your HP supplier should never really have sold you your pump without recommending that you do some calculations - as I've said before, you really can't afford to take a flyer on heat pump sizing in the way that you can with boilers - they are too dependent on accurate sizing in order to maximise the efficiency but that's water under the bridge now...

 

[eaton]

Any of the bigger manufacturers wouldn't have sold him one without telling him they take responsibility unles he provided a full heat loss

 

[slingshotjim]

Matt, Thanks very much for your comments, Ive downloaded that and Ill get on it over the next few days, Itll be interesting to say the least, wonder what Itll say, probably 11 and Its just that thats how much it costs to run the house!! We'll see, Thanks again. I know it only gives a ball park figure but like you say its a starting figure I need, Ta

 

[slingshotjim]

Ok, Im back, I downloaded the sap calc sheets and did them today, just finished, now, I measured all the windows etc instead of using the guide etc , my bungalow is like a sort of offset L shape so I did the 2 parts independantly and called the wall that attatched the 2 a 1 and a half in the exterior wall bit, anyway, I think I did it all ok, in 2 parts its 93 sq ms and 88 sq ms so 181 sq ms in all. its got about 18 sq m of windows in each bit (got 2 sets of bifolders in one and a set in the other plus all normal windows if that sounds a bit high) . The calcs work out at Heat req 12.97 Boiler size 11.27 in one part and Heat req 12.89 Boiler size 11.21 in the other.
When I use the adding of one side to the other at the end I get a heat requirement of over 22 KW. Have I done this correctly, if I have im undersize by 11Kw! Oh dear, Any advice taken...... Oh and the.... should ve done this first routine that I expect from someone no doubt doesnt help.... Have I done the calcs right, do I add one to the other... Ta . Jim.

 

[eaton]

You need to work out every room individually,

 

[dontknowitall]

The 22Kw sounds about right though.

 

[slingshotjim]

Would It not come to the same if I did all the rooms individually, Ive already underfloor heated it. Im checking the heat input for the whole house ,is that not what you do when your sizing radiators,
If its right and my ashp is way way too small would putting the right one in means it ll use less electric, this is the bit I dont get, will it not use more as its a 22kw not an 11 version, as Ive said the house gets warm just takes ages cos of the ufh not the ashp, This is the bit I dont get.... If the house never got warm enough Id understand or is it that a bigger unit doesnt work as hard ,all I see is it producing 45 deg water for the buffer then to the manifolds, Ho hum, glad I sell Race bikes for a living and not this! Cheers Jim