Geothermal- What size heat pump is required

DA-LAD

After submitting plans to various companies for installation of geothermal underfloor heating, i have started recieving quotes and specs.
So far 1 company has stated that I will require a 17kw heat pump,another 14kw. Today I recieved a phone call from another company who propose to install a 11kw heatpump and that it will be sufficient for our house size.They also say that installing a 17kw pump would not be suitable (too powerfull)Another company say that they would install their largest pump (12kw) but that a supplementary heat source may be required.
After speaking to all these companies I now dont know who to believe.
Any advise or suggestions would be appreciated
Our house is about 3,400sq/ft. We plan to install insulated wall slabs.
Thanks,
Da Lad

muffler

Would you believe the shower who post here

Qwerty?

Thanks Muffler

We have a 3500 sq foot house and are using a 13kW Nibe HP. Working fine for this size of a house. We have no supplimentary heat supplies or Solar panels.

Hope this helps a bit,
Qwerty.

Do-more

From past experiance all these companies use a "rule of thumb" guide to sizing your heat pump. (And then probably give you the next available size up in their range)

For such a substaintial investment my advice would be to spend a few hundred euro in getting an energy auditor (or consultant) to do a proper assessment of the heating requirements for your new home.

Try PMing <SNIP> he could probably help you out on this.

Edit by muffler: Your intentions may have been harmless enough but we dont condone advertising in any shape or form - unless its being paid for

RJ75

I agree, Hire a BEr assessor from doing the DEAP he can see the our build and preformance of your build plus see the heat losses of your build.
by seeing the heat losses you can size the heat pump accuratly.
remember all/most! renewable companies just have a person in the office doing quotes and just do the normal rule of thumb 45w per sq meter!
so your built would be 14.635kW
when sizing your heat pump by rule of thumb!
where really most sales reps should be pushing for a DEAP BER on your house) probably is these guys want sell bigger heat pumps why! more commission! and also these sales guys/ladies have the talk but asked them so proper questions they will just fill u with bull s**t
then u have the probably of alot of ber assessor when i comes to renewables know nothing!!!!!! so pick one wisely and not just anyone!
plus be careful with what renewables size you from your heat loss.
so use temperature differential of 20 where i would recommend 24
plus another thing to remember is! sales repsm are trying to win jobs so, some down the heat pump hence cheaper to win the job!
what are u looking at air to water or ground source?
remember its all about the performance of your build!
future proof it! it pays to spend more money on insulation now! make air tight and in the long run! cut on heat losses hence reduce running cost of you HP.
you thinking of whole house heat mechanical ventialtion? or solar?
what ber rating u looking for on your house?

muffler

Moved to RE forum.

BadCharlie

All goes by size of heating area and KW needed. They should be able to work it out, i my self have i think a 9.5kw for a 1700sq feet downstairs & upstairs another 800 but does not need heating. They wanted to give me a smaller one but i asked for the 9.5kw maybe its over kill.

RJ75

a guess is your house is well insulated. your build is 232.3 sp meters
so rule of thumb hehe... 11kW
but thats taking 45w per sq meter worst case! 45w per sq meter is an over kill. but to accurately size! you need to know the the heat losses from the DEAP.

i believe by getting a good knowledgeable BER assessor, he will alone cover his cost and by probably sizing the HP and recommending a HP will save €€€€ in the long run. a job i was involved in lately i told the customer get a ber! he was not pushed! i told him the truth! by seeing the DEAP i can see the performance of the build plus heat losses and can properly size the HP.
cost of ber assessor €350 resulted in down sizing the HP saved him €1,270!
not a bad return! i think!

sinnerboy

Sorry to take this thread on a tangent but i posed a similar question on a more familiar subject - i.e. how do you size a gas fire boiler .

I sent this text below to a lot of the "big names" . Few responded .
Of the 2 that did - one said "we don't size boilers - ask your installer"

Now i consulted one or two trusted plumbers and they said they always followed the advice of the boiler manufacturer ..... ( merry go round ) .

The second manufacturer that answered advised .... a rule of thumb .
For a B3/2 rated house - 100 watts/m2 - to provide a heat-up-from-cold time of 30mins . For B1 + rated house 80 watts/m2 . Then + 20% for DHW . ( I was grateful for this - at least they gave an answer )

Other guidance can be found here - based on simplified data inputs

http://www.energysavingtrust.org.uk/housingbuildings/calculators/boilersizing/

http://www.idhee.org.uk/calculator.html

But I failed to obtain an answer anywhere to the question I have made bold below .

So ...... if such a lack of clarity exists with the familiar old gas boiler - how do we ( i.e. non heating engineers ) size heat pumps ( or for that matter boilers)

Dear Sirs

Up until recently I have relied on (volume ft3 x 5 + 20% for DHW ) = BTU to arrive at a domestic boiler size

I think we need to get condensing boilers sized better than that for them to condense

Is there a ( non heating engineer friendly ) method to calculate ?

Or ...

If DEAP* tells me ( proposed B2 rated house , 300m2 , well insulated , i.e. to TGD L 2007 ) -

"energy required for main space heating"
13200 kwh/yr
and
"energy required for main water heater"
5945 kwh/yr

From that , can I select a ( gas ) boiler size ? How do I get from ( combined energy demand ) of 19145 kwh/yr to "X" Kw boiler ?


Any ( relevantly qualified ) poster able to assist ?

RJ75

hi sinnerboy,
as with fire gas boliers you size them like a HP etc. get a BER assessor and from the DEAP you can see the performance of the build and the heat losses.
then size you fire gas boiler from that!
why you going with a fire gas boiler???
is it dristict heating?

sinnerboy

Thanks for responding RJ75 , Snyper

I am not "looking" for gas - just posing a general question

I have entered data into DEAP - house 300m2 - and have a calculated heat demand of

of 19145 kwh/yr - as follows ( 13200 kwh/yr space heating + 5945 kwh/yr DHW )

So

What kW heat pump would one select to match that requirement ?

Rule of thumb 45w/m2 (13.5KW) ?

Or - if condensing gas

Rule of thumb (100w/m2) + 20% = (36KW) ?

Or put it another way , how do you get from a DEAP calculated demand expressed in kwh/year to an "X" KW heating appliance ?

muffler

Right lads. I have removed 2 posts - one from snyper and one from RJ75 - which were in direct response to "off boards" enquires made by sinnerboy.

If any of you get a PM or an email from someone (doesnt matter if they are posting in this forum or not) then please reply to it in in the same format as which you received it. Do not reply to it in a public forum.



Edit: after a wee bit of delving Im un-deleting one post but the other stays off the thread.

sourcebody

Before you decide on what heat pump to use, the most important info to look for is to determine what the COP is of the Heat Pump (Coefficient of Performance). Let's say for 12KW the COP specified by the Heat Pump Manifacturer is 5, then this means tha the electrical power requirement for the pump will be 12/5 = 2.4KW. On the other hand if for another Heat Pump Manufacturer the COP = 3, then the power requireemnt will be 12/3 = 4KW of electricity - BIG DIFFERENCE. Generally the higher the COP the dearer and better the Heat Pump is. Sizing of 12 or 15 or 17 KW is not really significant but just to consider the COP.;)

rayh

Can I suggest you should consider the wider implications of this system of heat source for your dwelling. In Ireland our electricity generation efficiency is currently just over 41% and transmission losses around 14%, so at your meter you receive an energy source of 3 primary units converted to 1 unit of electric energy. You now employ a heat pump with a COP of 3 to 1. I recently carried out test on an installation which had a COP of 1.8 to 1 and not because the heat pump it was incorrectly sized, but the collector was sized to suit the land space available. A sale at any cost.