Some basic info please

[devlin maguire]

A customer of mine has had 7 12m x 16m 3 bed houses all en-suite 2 storey all built with air to water heat pumps for underfloor, rads, and hot water, as a requirement of planning this was the only option as far as meeting requirements was concerned, however it now costs 12k per annum more than the other 20 houses built in the 80s, and 90s, to heat, I was not involved in the planning or installation however I at the time expressed concerns over air source given our geographical locale, Isle of Arran on the west coast of Scotland and the size of the outdoor units looked "small" given what was required units are Mitsubishi PUHZW85UHAZBS,OF00405, cop 3.17, 11.8A A2/W85 if you guys could shed some light on any issues you can see, and the main contractor has had engineers over a few times but has now walked away from this,
Dev

[TiredGeek]

Do you happen to know the heat load for the houses? It will be possible to give some idea of running costs if you can find out that bit of info....

[devlin maguire]

Thank,s thats info I do not have, bearing in mind the this was supposed to be a all singing and dancing super economical build project with all the latest in energy saving glazing and insulation but broadly speaking its a 3 bed 5x4 each and a open plan upstairs lounge dining and kitchen of about 12x5 with ufh every where, but like I said the outdoor unit looks way to small,l any ideas how I can compare the unit capabilities with the house requirements
Dev

[al]

The insulation levels would be the first place to start.
Is the 12000 per house or for the whole development?
is every house suffering the same problems or do they vary house to house?

al

[devlin maguire]

All of the new builds are suffering the same running costs, I have read some other threads on this and I will suggest they carry out this To calculate the delivery from the heat-pump do a simple test on the water buffer tank:
1. Make sure that water circulates only heat-pump to/from buffer tank;
2. Measure the time taken to heat up the water from start temp to top temp;
3. Calculate the average heating power into the water as follows:
Q = 1000*(Volume [m3])*(4186.8)*(T,end - T,start)/(time taken in seconds) = heating power in Watts (/1000 => kW)
(temps in 'C, or K)

Cant remember whos thread this is but thanks any way would this be a good starting point
Dev

[mad fridgie]

Firstly your rating is A2 W35 not 85C.
Simply question what is the average water temperature entering and leaving the heat pump, forget everything else first

[chillerman2006]

Hi Devlin

I am just getting into if i should fit ashp to my home, not far north of London where ambient temps is higher than yours and rain is a lot less

with my requirements for the equivelant of boiler temps in my rads, ashp is not suitable for me as the cop will likely fall close to or below 1.0 and it looks like my current condensor boiler will perform better than a ashp for my needs

the reason being with low ambients (lowered further by rain evaporation) and the requirement for 60*c water, at least 50*c...... to achieve this the compression ratio is too great and is in-efficient

after checking insulation is adequate, I would be looking into what mitsi claim is the operating temps for this cop 3.17, as in what ambient and what water temps can be reached, your probaly find once water temps reach 35*c the cop starts to fall

from what I am understanding so far, the property occupants can have hot rads at high cost, or warm rads at low cost, you cant have your cake and eat it

R's chillerman

[devlin maguire]

Excuse the lack of knowledge, what does the A2 W53 actually mean, and where exactly is the heat pump is that the outside unit if so are the two lines water as I am used to them being refrigerant lines, or are they inside the same cupboard as the boiler, like I say excuse the total lack of knowledge here as I am just not up on this
Dev

[chillerman2006]

Hi Devlin

the model you listed I could not find but found

mitsi PUHZ W85 HERBS http://domesticheating.mitsubishielectric.co.uk/

http://domesticheating.mitsubishielectric.co.uk/home/ecodan_video

does this look similar ?

R's chillerman

[chillerman2006]

Hi Devlin

this link shows their claims are based upon 35*c water delivery temp (under floor heating)

http://domesticheating.mitsubishielectric.co.uk/about_ecodan/benefits

R's chillerman

[r.bartlett]

Hi Devlin

Last edited by chillerman2006; 18-10-2011 at 01:16 PM. Reason: grammer/spelling again



Always makes me giggle :-)

[chillerman2006]

Always makes me giggle :-)

Haha RB

:off topic:you got me at it then thinking after all that I spelt 'grammer' wrong:)

R's chillerman

[Bigfreeze]

Excuse the lack of knowledge, what does the A2 W53 actually mean, and where exactly is the heat pump is that the outside unit if so are the two lines water as I am used to them being refrigerant lines, or are they inside the same cupboard as the boiler, like I say excuse the total lack of knowledge here as I am just not up on this
Dev

A2/W35 means that the heatpumps COP is being rated at an air on temp of 2C at the outdoor unit and the water leaving the heatpump would be 35C. The COP for that unit would be most likely just above 3 at those temps. For every degree the outdoor temp decrease the COP will drop 2-3% and for every degree the water outlet temp increases the COP will also drop 2-3%.
Therefore if your outdoor temp is -5 and the temp you need for the rads is 45C the COP will have dropped at least 34% from the rated COP at A2/W35.

The main problem you have is with the temps that rads require so the COP will always be low. In cold weather the effect would be magnified and would be akin to heating the house with an immersion. You may also have problems with defrost as if the piping is 3/4" throughout the building its unlikely you'll have enough flow to complete defrost correctly which will have knock on effects on running.

The refrigerant lines will be running from the outdoor to the indoor unit. Heat transfer takes place at the indoor

[devlin maguire]

I think I need a idiots guide to how these systems work as I cannot for the life of figure out how they are put together AC I understand,fridges I understand, but not this ashp set up what heats the water. the HS discharge line ? how ? is it pumped into the water tank in a coil, or ist it the plate HEX ??
Dev

[devlin maguire]

Bigfreeze thanks I was posting as you were replying makes a bit moe sense now
Dev

[Bigfreeze]

Going by the info you've supplied the area of the houses are 384sqm. No air to water system should ever be fitted to a building that size, especially one with rads. I'd suspect the units are drasticly undersized and depending on the back up immersions just to make temp in cold weather. So you probably have multiple problems, all contributing to the high running costs. Wrong application is the biggest problem out there when it comes to heat pumps and its definitely the case here.

[Bigfreeze]

I think I need a idiots guide to how these systems work as I cannot for the life of figure out how they are put together AC I understand,fridges I understand, but not this ashp set up what heats the water. the HS discharge line ? how ? is it pumped into the water tank in a coil, or ist it the plate HEX ??
Dev

Its the exact same as a refrigeration system, because it is a fridge system. Instead of transfering the discharge energy to air, its transferred to water. Low temp gas picks up energy while travelling through the outdoor unit for the air passing through. Gas is compressed, raised in pressure, raised in temp. Hot gas travels to indoor unit and passed through heat exchanger. Depending on demand at the time, either water from the heating or the DHW will be passing through the heat exchanger and absorbs the energy from the gas. The higher the water temp, the higher the condensing temp will be and therefore the lower the efficiency.

[RSTC]

As big freeze points out these are 384sqm houses, so maybe 12K per annum for 7 houses is not all that crazy.

If this is the electricity bill it includes the normal electricity as well so take away that (what is average elec bill in Skye? £800? I'm guessing if they need a 384sqm house they're not exactly frugal people). So £900ish a house.

UK & Ireland is littered with people (and local governments is seems) who were sold this idea of 'free heat'. Sad really - because the tech is fine, but the application will give it a bad name for years to come.

My advice? ... find out how much you are going to get paid. Ensure the units are working ok. Get paid. Get out.