Air to water heatpump/back boiler

FGK

Im thinking of getting an air to water heatpump installed in my new build two storey house, but i also want to put in a solid fuel stove with a back boiler. i was told one way to do this is to have the heatpump heat the underfloor up and down and the domestic water, and to have the boiler heat the domestic water as well and install a few rads upstairs to take the excess hot water from the boiler. having the heat of the rads upstairs should stop the heat pump kicking in as much.
is this the best way to do it or should i leave the stove normal without a boiler?
i still might go back to my original plan of oil condensing boiler, stove with back boiler, underfloor downstairs and rads upstairs with a mixing tank to bring the back boiler temp down for the underfloor.

any thoughts would be very much appreciated

heinbloed

Better get a professional in to check your plans.

air to water heatpump

plus

solid fuel stove with a back boiler

or

original plan of oil condensing boiler

plus

stove with back boiler

The thermal energy demand must be calculated. How much is this?

Get all calculations signed.

FGK

Hello Heinbloed

the company im talking to are advising a 14kw heat pump ,and not to bother with the back boiler at all. but i find it hard to do away with the back boiler and just have an ordinary stove after having one in my present house for years.
financially i dont think im going to be able to go for the heat pump as i got prices back this morning
and supply only of 14kw heat pump, 300l stainless steel cylinder, all piping for underfloor up and down including associated stats and pipes is coming in at 14,000 euros inc vat, i wasnt expecting it to be as expensive i was hoping for something around 10,000, but its not to be:(

heinbloed

Hi!
How high is the thermal energy demand?
Divided into domestic hot water and space heating.

Expressed in kWh per year and kW per m2.

Without numbers any recommendation is like playing lotto.
How did the company get to their recommendation (14 kW)? They might have issued a calculation sheet to you.

For a normal house(-hold) the max. energy demand is well below 8 kW. For the entire house(-hold) that is. The 14 kW output of the suggested thermal supply system seems to be very high. But a large house with bad insulation will get you there.

So: how high is the demand?

FGK

hi heinbloed
sorry for taking so long to get back to you.
the company im dealing with said that the space heating is 7.27kw and water heating is 5.83kw.the area to be heated is 293m2.
also when i brought up the subject of the cost they said i could run rads upstairs instead of uf and this would save money by not having to have insulate the floor upstairs.also the rads would be less cost than uf.i would have my doubts about the heat pump running rads but they claim having warm rads instead of hot will suffice to heat the upstairs?

i was going over all the remaining costs to be able to move in and i dont think i am going to have enough money in the budget to put it in the air to water unless i really start scrimping on other things like the stairs and kitchen which my better half does not want me to do!

FGK

actually forgot to write a few things

emitted heat per surface is 93.1kwh/m2
total thermal energy is 27174.9kwh
yearly energy consumption 6399.4kwh
primary energy use 15998.6
these are all figures from the company

heinbloed

Well done to get some numbers!
One important number still missing is the maximum energy demand per square meter, expressed im kW/m2.
7.25 kW max. demand for the whole house (293m2) is around 25 Watts per m2.

The number of 25 Watts per m2 max. space heating is very low, are you sure about this? What is the designer saying? Are the ventilation losses included ?


What makes me wonder is why they ad the anual space heating demand to the anual domestic hot water demand. 7kW+5kW.
If 1 thermal source is employed (heat pump) there would be no need to ad the both (space heating + DHW) for a total sum. Esp. since a thermal storage - the SS cylinder - is planned.
This DHW demand would only be called for for a few minutes per day, maybe an hour.
In the meantime the UFH/space heating can be covered fully by the HP.
Since DHW would be needed only for a very short period per day.
The house must be very well insulated (25 Watts/m2 space heating) and since it has a high thermal mass (UFH) this adition would be obsolete, selling a HP larger than necessary.Oversized.

Better contact your architect/civil engineer/heating engineer for a check.

Producing delivered 27,000 kWh per year with an electricity demand of 6,4000 kWh demands a system COP of 4.2 (the heatpump's anual COP would have to be around 4.4 !).
Reason: The COP of a HP is always less than the system's COP, distribution costs (circulation pumps + controls) have to be included to get the entire system's COP.

THIS would be very high for an air to water heat pump, I say this is impossible.


In my opinion a very dubious calculation.

A normal UFH would not emitt more than 30-70 Watts per m2. With only half the house equipped with UFH and the other half with wet radiators (how many m2 surface?) the thermal distribution is to small. The house would stay cold. Unless the flow temperature, the output from downstairs is doubled.



Doubling the thermal output of the UFH to warm up the upstairs floor demands more than a doubling, nearly tripling of the flow temperature in the UFH. This kills any reasonable HP COP. And gives hot feet, hot heels (smiley).

So invest some hundred €s for a proper calculation (engineer, energy advisor etc.) to check this. And signed please, better check the professional indemnity insurance of all parties involved.

Outkast_IRE

are you sure you want to go with an air to water heatpump , i know plently of people who found them brutal in the last 2 winters.
One of these got us to rip it out and install oil for him cause he was sick of how the air to water heat pump works worst when you need it most .

I the performance of these decreases with the colder the air temp gets outside.

FGK

hi heinbloed

i checked out the COP and the company actually say it is 4.4
as for the 25wm2 i dont know if it is accurate but the insulation will be fairly good.
100mm cavity getting pumped
all exterior walls are getting drylined with 25mm insulation 12mm plasterboard and these are getting set on 22mm battens as i was told that this is warmer than sticking the boards on the wall.
groung floor is getting 100mm board on the ground.
the attic insulation is still being debated i will probably have to wait and see what money is left,as i can always add to it over a year or two.

FGK

hi outkast

i dont think it matters if i want the air to water i cant see me affording it
im probably going to put in an oil condensing boiler.
that person that changed to oil after paying a lot of money for the air to water must have been having big problems to go to that extreme.
i presume that they changed because their electric bill must have been surpassing the cost of heating by oil?
thanks for giving me another side of the issue of awhp.the sales rep dosent tell you those kind of stories!

heinbloed

An independant institute should back up the COPs.
Here at Buchs the results are published (press the flag symbol), see

https://institute.ntb.ch/ies/waermepumpen-testzentrum-wpz/pruefreglement.html

A COP of 4.4 (see below) for an air-to-water HP in cold winter time isn't heard of, unless a luke warm result is wanted. But this wouldn't be enough to keep a house warm running 1m2 UFH warming 2m2 of total surface.
Would you mind to tell us which type of HP was recommended? Brand and type of model?
The older Buchs test reports are available in German only, I could translate the test results - if wanted.

Outkast_IRE

FGK wrote: »

hi outkast

i dont think it matters if i want the air to water i cant see me affording it
im probably going to put in an oil condensing boiler.
that person that changed to oil after paying a lot of money for the air to water must have been having big problems to go to that extreme.
i presume that they changed because their electric bill must have been surpassing the cost of heating by oil?
thanks for giving me another side of the issue of awhp.the sales rep dosent tell you those kind of stories!

Yeah we did the install , of that air to water heat pump , and had the manufacturer out to inspect and the company it was bought from and neither could fault the installation side of things, it worked well during mild winter temps but as soon as air temps went below 0 it was only keeping the house barely warm , i wouldnt call it comfortable , the unit spent a lot of its time in defrost mode apparently !!!

Basically it was 8 grand down the toilet for them , they got us back to install the oil condensing back in september and we were talking to them in janurary and they were delighted they changed .

Your money would be best spent installing the oil , ensuring your system is zoned well and has good quality digital thermostats ,and your house is well insulated and as airtight as possible.

FGK

thanks outkast i think that is the route i will be going down!

heinboeld the unit is a
daikin altherma 14kw monobloc unit c/w 6kw backup.

heinbloed

Hi FKG!

I've checked the Buchs results on the Daikin Altherma 14.9kW units. These 14.9kW units are refered to as ERHQ 014 and EKHBX 016, Buchs test number is 124-08-5 . The results are published here:

https://institute.ntb.ch/fileadmin/Institute/IES/pdf/Pr%C3%BCfResLW110125.pdf
page1/8

and here again

https://institute.ntb.ch/fileadmin/Institute/IES/pdf/WPZ%20Bulletin%2001-2009%20DE.pdf
page 5/24

The only way this HP delivers a COP of 4.5 is when it delivers 35 degrees warm water during an outside(air-) temperature of +7 degrees Celsius.

If the outside temperature drops to -7 degrees Celsius in winter the COP will be a barmharty 2.9. At a flow temperature (coming from the HP going into the UFH) of 35 degrees Celsius and a return temperature of 30 degrees Celsius (going back to the HP).

But since only half the floor's surface will be equipped with UFH in your situation the flow temperature would have to be raised to keep the house warm with the radiators in the 1st floor, 35 degrees Celsius won't do.

So at - 7 degrees Celsius outside temperature and a flow temperature of 45 degrees Celsius the COP drops to 2.3.

And at - 7 degrees Celsius and a flow temperature 55 degrees Celsius (typical wet radiator temperature) the COP drops to 1.5.

Distribution energy (circulation pump) and controlling equipment (thermostats) will cut further into these low COPs.

This might have been the problem with the person you have refered to who riped out the HP and went for the oil boiler instead.

HPs make sense only where a low DeltaT Kelvin has to be bridged - a low increase of the available (outside) temperature has to be achieved.
A pitty that the salesmen wheren't honest to you, they slander the name of a technology which could make sense provided the parameters limiting the economics are being met.

Get a heating engineer to figure out the flow and return temperature of your heating system. Then you can decide if you go for an oil or gas condensing boiler, maybe solid fuel is economic as well.
Note that the return temperature for an oilboiler to run in the condensing modus must be lower than for a gas condensing boiler.
It makes no sense to purchase a condensing boiler if the condensing modus can't be achieved.

FGK

thanks heinbloed for all the info it is very much appreciated!

galsy

hi there, if u insulate house as described, the heatpump with underfloor up an down will work perfectly, ive got the same setup in my house, which is a 2 story,290 sq/m ufh up and down, air to water heat pump provides all heating and hot water, even through the past 2 winters, at -17 no problem, <snip>

heinbloed

Hi galsy!
As an owner of the exploding and recalled Ecodan HPs:
How did Mitsubishi handle your case?
See

http://www.acr-news.com/news/news.asp?id=2180

How much compensation did they offer? Where it the same 'trained' staff handling the replacement that comissioned the installation/ i.e. you ?

Did you have to hear about the risks from the news or was it Mitsubishi who informed you to stop using their HP until further notice? What source of heating did you use instead in the mean time?
Was the guarantee renewed or just extended for the time standing idle? Who contacted you and when ?

Thanks....

galsy

hey there, as you are probably aware, mitsubishi compensated all ecodan users for the cost of providing alternative heating/ ie electric radiators/ immersion for hot water in the form of a inital cheuque the day after being informed of the one unit out of six thousand that had a problem, and if you have been on the industry forums u will have seen the pic of said unit, which didnt explode, it blew a panel off lol, anyway a new unit was delived within a fortnight and fiited, warrenty running from date of install of new unit. all in great customer service, what other manufacturer would have done that.

heinbloed

Thanks, galsy.

A "cash-and-carry" client , how would he/she then be contacted by Mitsubishi? No adress, no contact number?

galsy

hey there.... <snip>


Galsy has time to think about this comment and make himself aware of the charter. This arguement needs to end now its now the place.

Thanks

danny555

hello fgk , can you tell me how much your oil boiler cost ?

The First Guru

I have heard of many people who spend thousands on oil and could reduce thier bills by using a heat pump but at leat they have a warm house with expensive oil.
Make a fair comparison and ralise that if the capacity matches the house there are big savings with a heat pump