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View Full Version : Which is the best Air to water ASHP currently available?







TiredGeek
29-01-2012, 07:59 PM
Shortly I'm going to be ripping out a pair of 14kw Ecodans fitted by...., well lets just say "not fitted well" shall we ;)

I'm thinking to replace them with something similar or even the same, but this time it's going to be done right. So, I'm wondering if there's currently anything out there that's better.

It's got to be able to operate down to -28'c and produce water flow at 50'c for the radiators at that ambient. When occupied I want the house at ~20'c, but it's a holiday home so for most of the winter I need it to keep the house at ~10'c to protect from frost and keep the damp off.
Ideally it'll be self contained like an Ecodan but I'm not totally averse to split systems. Also I need inverter control as the starting amps need to be kept under control for my electric supply not to overload. Heat load of the house is about 18kw with 33 oversized radiators, and I'd like a bit extra capacity for the colder months just in case.

Oil is also being considered, I know the running costs are likely to be higher but the install costs for an oil system comes in at a fraction of the price of two 14kw ASHP and oil may fit the bill better for a holiday home.

mad fridgie
29-01-2012, 08:34 PM
If you need 18Kw at your rated conditions, then you are going to need a nominal rated heat pump output of 46Kw (heat pump size), And that is using a vapour injected comp, R404a as the refrigerant choice. COP at -28C is about 2.
Is suspect this would be a bespoke unit.

install monkey
29-01-2012, 09:44 PM
mitsi do a chva 46kw unit- but it needs 3 phase 70amp supply

mad fridgie
29-01-2012, 09:48 PM
mitsi do a chva 46kw unit- but it needs 3 phase 70amp supply
Will it still operate down to -28C and produce 50C water?

Bigfreeze
29-01-2012, 09:51 PM
Shortly I'm going to be ripping out a pair of 14kw Ecodans fitted by...., well lets just say "not fitted well" shall we ;)I'm thinking to replace them with something similar or even the same, but this time it's going to be done right. So, I'm wondering if there's currently anything out there that's better. It's got to be able to operate down to -28'c and produce water flow at 50'c for the radiators at that ambient. When occupied I want the house at ~20'c, but it's a holiday home so for most of the winter I need it to keep the house at ~10'c to protect from frost and keep the damp off.Ideally it'll be self contained like an Ecodan but I'm not totally averse to split systems. Also I need inverter control as the starting amps need to be kept under control for my electric supply not to overload. Heat load of the house is about 18kw with 33 oversized radiators, and I'd like a bit extra capacity for the colder months just in case.Oil is also being considered, I know the running costs are likely to be higher but the install costs for an oil system comes in at a fraction of the price of two 14kw ASHP and oil may fit the bill better for a holiday home. No heat pump does what you are asking of it without employing immersion's to back it up. Cut your losses and go back to oil. Air source units are not suitable for your application. You won't get a better return from any unit than you will from oil in the application you have for them

mad fridgie
29-01-2012, 10:27 PM
Cut your losses and go back to oil. Air source units are not suitable for your application. You won't get a better return from any unit than you will from oil in the application you have for them

And that is good advice.

install monkey
29-01-2012, 10:30 PM
https://rapidshare.com/files/1377474847/Spec_CAHV.pdf;
https://rapidshare.com/files/3039566199/Flash_Inj_Circuit.pdf;
mad thought u might like these,especially thr flash inj circuit

Will it still operate down to -28C and produce 50C water?

TiredGeek
30-01-2012, 08:36 PM
Thanks for the replies guys :)

Oil is a significant saving on the hardware side and probably going to be roughly the same running costs by the sound of it.
Some serious thinking to be done ;)

frank
30-01-2012, 09:43 PM
where in the UK do we get -28C temperatures?

install monkey
30-01-2012, 09:58 PM
in a chest freezer with the fast freeze switch on!haha

where in the UK do we get -28C temperatures?

stufus
30-01-2012, 11:25 PM
BOOOOOMMMMMM
Cheers
Stu

in a chest freezer with the fast freeze switch on!haha

TiredGeek
01-02-2012, 07:42 PM
Actually it's not all that unusual for a small place in the highlands of Scotland called Altnaharra, it regularly gets down to -20'c, and my place is within spitting distance in the same valley.

Last winter when we all had the cold spell we were speaking to our friends who live there full time and they hadn't had anything warmer than -17'c for nigh on three weeks!

http://en.wikipedia.org/wiki/Altnaharra

Beautiful area, loads of wildlife and mamba for us who like that sort of thing. Well worth a visit if you're heading into that part of the world.....

frank
01-02-2012, 08:15 PM
I'm going up to Kilmarnock on Saturday to do a job....could be there for a few days....

MikeHolm
01-02-2012, 10:39 PM
Frank, you are going to tthe tropical part of Scotland

frank
02-02-2012, 08:19 PM
Don't worry...I'm taking my sun specs and shorts..

Oh!...and my language translation book :D

TiredGeek
02-02-2012, 08:48 PM
LOL Frank.
According to Autoroute, Nottingham to Kilmarnock is 291 miles, from there to Altnaharra is a further 311 miles.
You're not even going half way!

Magoo
02-02-2012, 10:08 PM
Remind me to go to Scotland in the summer, if they have one. When I check out the old bones heritage. No wonder they moved to NZ.

MikeHolm
02-02-2012, 11:56 PM
Personally, i would love to live in Scotland....well....OK, visit a lot.

TiredGeek
03-02-2012, 08:39 PM
Personally, i would love to live in Scotland....well....OK, visit a lot.

Yeah, and I'd love to live in Canada. Visited Toronto only twice but they've been the best holidays I've had :)
If it wasn't for family I'd be seriously looking into moving....

MikeHolm
04-02-2012, 12:32 AM
Awww, bring em along. There is tonnes of room.

frank
04-02-2012, 08:55 PM
[QUOTE=TiredGeek;252357]LOL Frank. According to Autoroute, Nottingham to Kilmarnock is 291 miles, from there to Altnaharra is a further 311 miles.You're not even going half way![/QUOTEII used to rent a bungalow in 1970 at Dunnet Head while working on the construction of the Dounreay nuclear station so I'm used to a Scotish Summer lol

TiredGeek
05-02-2012, 04:42 PM
I used to rent a bungalow in 1970 at Dunnet Head while working on the construction of the Dounreay nuclear station so I'm used to a Scotish Summer lol

Now we're talking! Dunnet Head, know it well, lovely place for walks. The midges can be a swine though
Dounreay, now in the process of decommissioning :(

That's hurt a lot of the local communities hard with loss of jobs. There was talk at one time of a new reactor going on the site but that seems to have fallen through....

Wind farms are the new big thing up there. As you know it can be a tad breezy, the bloody things are on every hilltop now, the "unspoilt northern wilderness" as the tourist board like to call it is no longer quite as unspoiled as it once was. Locals are now talking of the marked reduction in tourism due to the visual impact.

TiredGeek
05-02-2012, 04:43 PM
Awww, bring em along. There is tonnes of room.

No chance, you lot wouldn't have 'em. Seriously, you wouldn't!

MikeHolm
05-02-2012, 10:09 PM
Oh, we take all sorts, you'd be surprised, unless they have something to hide.....;)

Karl Hofmann
06-02-2012, 08:43 PM
Geek, at the risk of asking a daft question, have you considered using a pellet boiler rather than a stinking old oil boiler to heat your home? ......

TiredGeek
07-02-2012, 08:53 PM
Karl, wood pellet wouldn't really do the job as it's a holiday home and has to work for up to a month at a time without anyone there to check it. I don't think I'd trust a pellet burner to look after itself for that long with no one there to keep an eye on the pellet stock and the feeder system. We've no idea if pellets would be available there as well as it's very remote....
Also not all that keen on having a big hopper in the garden.

Smelly old oil or ASHP are pretty much the only options open to us. We may yet combine the two - smallish oil boiler to do "frost stat" duties in winter and ASHP for when we're there.

GSHP with bore holes is the only other choice and that comes in very expensive and I have worries about starting currents overloading the supply.

We've got all summer to figure this out :)

mad fridgie
07-02-2012, 09:12 PM
I recently did, something very similar to a very large house.
He already had a oil boiler, but this was costing a fortune to run,(56Kw)
We added a heat pump (20kw), increase the flow through the floor (reducing flow temps from 48C to 31C)
The boiler only comes on when the return temp drops below a set point.
His boiler now only uses about 7% of what it did. The total savings were about 70%. (original oil - new oil plus power)

MikeHolm
07-02-2012, 11:16 PM
Mad, what was the floor tubing length and diameter to be able to decrease the temp so much. The pump head must be quite high:eek:

mad fridgie
08-02-2012, 12:02 AM
The actual overall temp of the house was much better. They could not believe that by running low water temps the house could be warmer.
The areas around the manifolds previously were always very warm, but the living areas were some distance away, so originally the energy was lost in the passages.
Yes i had to change the pump. (I did not have the design of the piping). I changed the 2 inline pumps (which in my opinion were way to small anyway) for a single open pump, this id have a dead head pressure of 20 meters. I did not take measurements, because I do not care! I suspect based upon flow and return temps, that the whole system pressure drop was about 12meters (includes heat pump heat exchanger).
I can say of the many system s that I have been asked to look at (heat pumps mainly systems), That just changing the pump for the underfloor, fixed all but a couple.

MikeHolm
08-02-2012, 02:24 AM
That's pretty high head pressure but guess the reduced overall bills make up for the higher pumping power. Can you hear any noise? What brand/model of pump and Dt over the floor loops (approx)?

mad fridgie
08-02-2012, 06:50 AM
Dt across the loops is around 4C.The pump some Chinese make. (Cheap as)This not an inline pump, just a close couple pump. Efficiency is higher as not such a big gap between the stator and rotor.No water noise (inside).The pump is louder than a normal (air noise from the fan at the end), but the pump was next to the heat pump.???

MikeHolm
08-02-2012, 11:09 AM
Right, 4C would be fast if it was designed for 10-12C. I know that type of pump but why not a wet rotor? Because it is cheap?

mad fridgie
08-02-2012, 07:41 PM
the original was running close to 25C, (to small in my opinion)
Wet pumps only have limited head (well what we can buy as standard in NZ)

Jon Glanfield
09-02-2012, 06:49 AM
MF why does increasing the flow through the floor work so effectively, were you matching the delta t across the floor closer to that of the heat source?

mad fridgie
09-02-2012, 09:36 AM
Hi Jon,
good question.
First i better explain a tiny bit about the systems, no buffer tank, and no controlled areas (apart form original balancing) So always total flow or nothing.
I could say that the increased flow gives better heat transfer, which is sort of true, but really is not the case as the concrete itself is the limiting factor.
What I have found that comfort levels are increased due to the more even temperature of the floor, and I suspect (I have not proved it) that natural air fows are evenly more consistent and even, so very little wind chill effect. I have found that the increased flow also helps with boilers, so not always a heat pump problem.
How ever the higher flows and lower Tds are very much suited to heat pumpss, ensuring low condensing pressures, low power draw, high levels of heat of rejection. (Increased energy absorbed for evap)
The problems may have been that the original piping lay out could well have just been wrong.
I cam across one system, where a single circuit was 300meters long (16mm) The heat was lost, before it even got to the main area. The heat pump was knocking itself to death. And the house was cold. The hall way was hot.
The only fix available to me was to install a pump that gave upto 40meters of head, Td was a bit hard to measure originally, as the return was in close proximity to the supply in the hall, so it warmed back up.
The new pump did fix the problem, the area did become warm. No perfect, but better than ripping up the floor.

MikeHolm
09-02-2012, 11:32 AM
Logical, mad.

I have to stop people all the time from using long, long tubing lengths. There is no operational benefit to it, just a cheaper install. Ideally, I would make the lengths 60m if possible but 80m is normal. Most 50-60w circs can easily give the flow rate for a 8-10 loops if the head loss is reasonable and then give a close dT.