Air Source Heat Pumps

stevehead

bobmedley wrote: »

If I do get a COP of c5 then I'm hoping to swap some oil kw's @ 5.29p for ASHP kw's @ 1.88p at current (excuse the pun) prices.

Bob... if you have access to any info on the air flow rate of the indoor unit then you can work out the COP you're getting.

http://forums.moneysavingexpert.com/showpost.php?p=26378941&postcount=400

sadgran

I am about to plunge into buying an ecodan asp. The 14 Kw is sold with a compatible cylinder which costs around £2k extra. This appears to have a couple of pumps and 3 zone valves. I reckon I can get a similar cylinder for about £1k including valves and pumps. Does the ecodan tank unit include anything else to justify the extra £1k other than a bit of copper pipe?
Thanks in anticipation.

albyota

Yes, the bracket to fix the ftc controller where all the motorised valves, pumps, safety stat, tank sensor and immersion heater control, and lcd programmer, all pre-wired and pre-connected, the flow setter valve, filter, etc.....if you can fit all this and save yourself £50 then go for it. trials have been done between engineers to see who can install quicker/cheaper....there is honestly £50 in it.

Are you an accredited Ecodan installer?, are you MCS registered?, if not, you or your customer won't qualify for the RHI. ...Or the CERT Funding!!

bobmedley

Cardew wrote: »

Any advance on a COP of 6;)

Hey even with the outside temp at 30C and used to heat water for a swimming pool at 32C you ain't going to get a COP of 6.

If you get a year round COP in the region of 3 it will be good.

http://www.heatpumps4pools.com/Heat-Perfector/Single-Phase/Heat-Perfector-Model-5-32kw-Swimming-Pool-Heat-Pump-Heater

Heat Perfector Model 9 has a COP of 6.3

thechippy

At what ambient?

Cardew

bobmedley wrote: »

http://www.heatpumps4pools.com/Heat-Perfector/Single-Phase/Heat-Perfector-Model-5-32kw-Swimming-Pool-Heat-Pump-Heater

Heat Perfector Model 9 has a COP of 6.3

Heat pumps are at their most efficient when raising the temperature of a lot of water a few degrees.

e.g with outside temperatures in the low 20's C and getting a pool to 25C or so.

Meaningless in central heating terms.

bobmedley

Cardew wrote: »

Heat pumps are at their most efficient when raising the temperature of a lot of water a few degrees.

e.g with outside temperatures in the low 20's C and getting a pool to 25C or so.

Meaningless in central heating terms.

Yes, I know. I was just pointing out that your original assertion was 5% inaccurate

TiredGeek

Hi guys, new to the forum, and please bear with me if I ask something here that's already been asked, I read everything up to post 830 and thought I'd skip ahead for some advice

Ok, quick run down of my install:
2 x 14kw EcoDans heating a 170m/2 house with 31 radiators, mostly doubles (!, yes I know), if you count a hall or a landing as a room then 17 rooms, no buffer tank fitted (as Mitsubishi say no need),
2 x 210 litre DHW tanks,
28mm, 22mm and some 15mm pipe, 4 x 15/60 Grundfos Alpha pumps (2 pull, 2 push).
No seperate zones, most rads have TRV, but all turned to "max on",
400mm loft insulation, 600mm solid stone walls uninsulated due to listing. Full double glazing.
SAP report said 15kw required, and walls have a U value of 1.9.
House is undergoing refurb and not lived in. Heating was set to 10'c, water from Ecodans 22'c @ 17'c ambient ramping to 38'c @ -10'c ambient. No DHW generating set at the moment.
House is an old croft in northern Scotland (KW11 6UA, near Altnaharra, you may have heard of it recently) Recent temps dropped to -16'c and hovered around -10'c for several days.

Last winter the units iced up and failed due to inadequate water flow. Replumbed and sorted that. Both Mitsubishi and the install company are now happy with the water flow. Last winter it got down to -22'c, but the heating was off due to the failures.

This year they have again iced up to the point that the air flow is completely blocked. They try to defrost but fail, go back to heating and build up more ice, try to defrost etc....
Honestly, the ice was a solid sheet 10mm thick covering the back and sides of both units, last year it did this so thickly the fan blades sheared off due to the build up. Caught it this year before that happened.

When we're there and the room stat is set at 18'c the Ecodans easily manage to hit target temp within an hour of a cold start (31 out, 31 return) and the house is up to temp in about 3 hours, so I don't think it's a problem of sizing. They get the DHW tanks up to 58'c in 30 mins when we need it.

When they do a defrost it can be as frequent as 10 mins apart, or as long as 45, I'm sure they've never run for 2 hours without one. It lasts about 2 mins, though I haven't timed it. Interestingly Mitsubishi website says 30 to 120 mins apart, definitely more frequent than that.

When it fails it's different: it says "defrost" on the indoor unit, the outdoor shuts down, then you can hear the compressor start, then it makes a huffing sound and stops. The indoor still says "defrost" but the outdoor is doing nothing. After a couple of mins they then go back to heating mode and the cycle starts again.....it doesn't throw any codes or warnings on the indoor units, and I don't want to take the covers off outside to check as I don't want them to say I've voided my warranty by doing so. Sometimes after several failed defrosts it does a good one and then dumps loads of water out. It seems to fail more over night than during the day for some reason.

While the failures are bad enough it's the electric consumption we're more concerned about. To keep the house at 18'c (overnight 14'c) when outdoors it's ~8'c took roughly 100 kwh / 24hrs. At our rate that's about £11. When people nearby in similar houses with similar insulation are spending about £6 / 24hr heating to 22'c and DHW we're more than a bit concerned! In the temps we've just been having I imagine it would have been substantially higher. At that sort of rate we'd be better off burning £5 notes to keep warm

The only thing I can think of is high humidity causing very frequent defrosts using more electric and dragging the COP right down as a result. We share the valley with a river and according to my weather station thingy humidity is always around the 90% area outdoors (30% indoors). Other than that I can't see any reason why our system doesn't work as promised, and neither can the engineers who have been.

The install company has passed all the info I give them to Mitsubishi, data from my weather station showing indoor & outdoor temps, humidity and wind speed, loads of photo's, and all my observations, and all they said was basically "they're working within parameters, stop bothering us, not our problem".
Real helpful.
The install company is baffled and we're getting a bit worried about our £14k system. I think the next thing they're going to try is to put a buffer tank in but I don't see how that's going to help.

Have any of you gurus got anything to suggest to help find the problems?

Thank you for reading this much, sorry, it did get a bit rambling in places, I tried to keep it short while putting all the info down

richardc1983

Hi TiredGeek.

It could be a couple of things, I started to have snow build up on the floor around the back of my outdoor unit,now as this started defrosting and thawing due to the unit going into deforst cycles it turned into ice so after a few days we had maybe about 10mm of ice at the back of the unit up at the first 1Cm of the coil. It was never touching the coil though. All I can put the massive build up of ice to is snow being sucked into the back, however on a defrost cycle this should clear fully. My defrost cycle on my unit when there is a large ice build up can be nearlly 5minutes before it switches back into heating... 2 minutes is not enough.

Defrost cycle length and timing and compressor speed etc is determined by sensor mounted on the coil. These will put the unit into defrost when the refrigerant circulating is below certain values etc. It could be that these sensors are not readinig properly so defrost cycles are not lasting long enough. It also should not be defrosting after 10minutes if it had done it properly the first time round.

I understand the very low temps you have up there but are you aware that at -20C you are not going to get anywhere near the 14KW per unit that you need to heat the house. What outdoor ambient did they base the sizing on. You should always design the system at worse conditions so if you regulary get to -20C in winter then the system size should have been calculated based on this.

You really need to see the performance figures at various outdoor temps you will see for yourself then that as it gets colder outside your performance drops off. The fact you are only able to get higher than 18C indoors is a concern as it says to me that you dont have enough heating (however you say it reaches 18C very quickly). Your defrost cycles are not working properly and you are wasting energy there that you could be heating the house with as it is not able to collect heat from the air due to the coil being blocked. YOU NEED TO ADDRESS THIS FIRST. What are the installers/manufacturers explanation of the defrost cycles not clearing the coil etc.

Also what flow temp do you have the system set to. 38C flow temp is really only suitable for underfloor heating. Double radiators even if oversized do not have the same surface area as the floor in your room so you really will probably needing flow temps of 50C. Have you tried playing with the flow temps (when there is no ice build up) to see if this makes any difference. Is the system able to achieve a higher flow temp if you set it.

Its got to be one of the things mentioned above. Defrost is not working properly I can tell you that now. For a Mitsubishi system you have paid top dollar for do not get off the phone until it is rectified. This is one of the market leaders.

I think you should also copy and paste this over at http://www.refrigeration-engineer.com/forums/forumdisplay.php?f=78 many many skilled engineers on there who will be able to advise as well.

Hope that helps.

grahamc2003

TiredGeek wrote: »

Hi guys, new to the forum, and please bear with me if I ask something here that's already been asked, I read everything up to post 830 and thought I'd skip ahead for some advice

The only thing I can think of is high humidity causing very frequent defrosts using more electric and dragging the COP right down as a result. We share the valley with a river and according to my weather station thingy humidity is always around the 90% area outdoors (30% indoors). Other than that I can't see any reason why our system doesn't work as promised, and neither can the engineers who have been.

The install company has passed all the info I give them to Mitsubishi, data from my weather station showing indoor & outdoor temps, humidity and wind speed, loads of photo's, and all my observations, and all they said was basically "they're working within parameters, stop bothering us, not our problem".
Real helpful.
The install company is baffled and we're getting a bit worried about our £14k system. I think the next thing they're going to try is to put a buffer tank in but I don't see how that's going to help.

Have any of you gurus got anything to suggest to help find the problems?

Thank you for reading this much, sorry, it did get a bit rambling in places, I tried to keep it short while putting all the info down

I don't claim to be anything like a guru, in fact I'm just a beginner with ashps, although I do understand the theory. I'm reluctant to think I could add anything when your system has been given the once over by Misterbushi engineers, but I will do anyway, so please see my input in those respects.

But one thing which cropped up in another thread is ingress of water into the outside unit. Obviously, the quality unit you have has been tested and almost certainly meets it's operational specs, including operating at 100% humidity and low ambient temperatures.

But is there a possibility here that in your location, the air is often misted, or foggy? If so, then not only are the fans sucking in 100% humid air (which I would imagine they can handle easily with their defrost strategies), but also lots of liquid water (the mist or fog is water droplets in air) - which possibly is beyond the specs of the unit (only possibly - I have no idea - does the documentation mention water ingress?). Obviously throwing gallons of saturated air plus water droplets each second at the very cold heat exchanger will cause plenty of ice, and certainly a lot more than just saturated air (in fact saturated air at low temperatures contains very little water).

So the situation may be (I'm certainly not saying it is) mist causes ice production beyond the limit the implemented defrost strategy can handle. That at least is a possible explanation of the unit cycling between
- going into defrost mode
- not fully clearing the ice, yet going into heating mode (for a short period) because the defrost strategy says it's cleared the ice, buiding up more ice
- going into defrost mode
etc etc.

which looks like a cop of zero to me!