Air Source Heat Pumps

richardc1983

andy2308 wrote: »

Hi,

I've been living with a Mitsubishi Ecodan system now for nearly 3 years, our house was a new build with this system installed.

After weighing up the pro's and con's, I'm seriously considering ripping the system out and going back to a combi.

Pro's:

Running costs, when running in its eco mode and not having to work hard it does save money - particularly in summer months when you're only using hot water. However the running costs could also be attributed to the fact that the house was built and insulated to a very high standard to accommodate the parameters of the system.

And now the cons as I see them:

1. Space - lack of. Bloomin' massive storage tank in the airing cupboard means there's absolutely no room for any storage and can't be used as an airing cupboard. Also factor in that you'll need to locate the outdoor unit somewhere and it needs to be spaced away from the property to allow adequate airflow around it. It's not small either and the larger the house, the bigger the outside unit.

2. Noise - I can honestly say it drives me nuts! The outdoor unit is outside the patio door to the living room. The compressor & fan are variable speed. When it's not working too hard it's not obtrusive but when it cranks up it really drones at a pitch that really goes through you! I have it set for a hot water cycle in the early hours and if I'm awake I can even hear it in bed, and our bedroom is the opposite side of the house!

3. Performance - Use it in its ECO mode and it'll just about manage 22C provided it's not too cold outside, when the outside temperature drops it makes the rads hotter, the upstairs rooms are actually warmer on colder days. You can override ECO, if you do it costs a bomb to run.

4. Lukewarm radiators - Now that doesn't bother me but it really bothers the lady of the house who likes to warm herself on the rads on a cold day. You can't really do that! You see the radiators are all oversized to accommodate the lower running temperatures so forget having a quick warm up.

5. Timings - This is a right pain in the *rse. You see you can't have hot water and heating at the same time. Priority goes to hot water first. This means that when it's really, really cold and you happen to be at home all day, you've got to allow sufficient time with no heating on so that it can heat the water sufficiently. Budget for an hour or so at least to top up the hot water before you get your heating back, by which time the temperature has dropped!

If you've got friends or relatives staying then make sure you program in extra time for hot water or you'll be using the booster immersion, or bathing in cold water!

6. Anti-legionella - This has been a total and utter nightmare on ours from day one. After much tweaking of settings the legionella control seems to work but the immersion has a mind of its own. Basically the system will just switch over to immersion heating after about 30 minutes of heat pump. I know this because when I'm at home working I'm suddenly alerted to the sound akin to a large kettle trying to boil in the cupboard behind me. Turn off and on again and it reverts to heat pump control. Basically any savings I make on the heat pump system I lose through use of the immersion. You can of course isolate the immersion - then it just sits and waits, then you end up showering in lukewarm water.

As a trained refrigeration engineer and gadget freak I wanted to love this system. The principle is sound, I just don't think the technology - based on this system - is there just yet. There's been more than a few visits from various people to look at this thing and lots of head scratching.

We've been told that these work better with underfloor heating.

Cheers,

Andy.

My friends system they leave the hot water on 24/7 so it just keeps coming on to top the tank up rather than doing a hot water cycle have you tried that?

TiredGeek

Our you could go with a gas boiler AND the EcoDan and let the FTC decide which is best at any given time.

Personally I think you have some installation and setting issues. Some of your problems sound very familiar to me, so much so that I'm betting I know who supplied your system

If you want to PM me I'll give you the name of a company who can sort things out, but obviously they're not going to work for free, and if you're already in the mind set of ripping out then the investment in having someone in to look over the system and suggest how to make it better may not be your first choice.

What I can say is we did rip out an EcoDan system, then put another one straight back in and now we love it

Cardew

TiredGeek wrote: »

What I can say is we did rip out an EcoDan system, then put another one straight back in and now we love it

For new readers you should perhaps inform them of the costs of your installation, and the atypical demands you place upon the ASHP's. Also why your Ecodan was ripped out after spending £14,000?


Every time someone posts of a disappointing experience with an ASHP, we get post after post suggesting it is a faulty installation, or needs setting up, or shouldn't be used for hot water, or the noise can be masked etc etc.


My point is that Mr and Mrs Joe Average shouldn't have to pay many thousands of pounds(often over £10,000) to a firm who could well be cowboys and get a rubbish set up that might well be in an unsuitable house.


The manufacturers seem to wash their hands of any responsibility for their systems, these customers do not have the knowledge to seek redress from the installer. Indeed other than huge bills, and poor heating, how do you prove your system is unsatisfactory?


I note Mitsubishi are now quoting the Phase 2 EST trial of heat pumps - their Ecodans apparently achieved a better average on the 'system COP'(SPFH4) than the average for all ASHPs which they give as 2.43. (I believe it should be 2.45) IIRC that figure includes some systems that do not heat domestic hot water(which is the least efficient aspect of heat pump performance)


Prospective buyers of a heat pump would do well to read the report.


http://www.energysavingtrust.org.uk/Organisations/Working-with-Energy-Saving-Trust/The-Foundation/Our-pioneering-research/The-heat-is-on-heat-pump-field-trials


IMO the most relevant point was that after the 'disappointing' Phase 1 trial, the experts from the manufacturers were allowed to examine the systems and make improvements(termed 'interventions') some of these interventions were major - including replacement of the heat pump itself.


They also added new systems to the trial - presumably hand picked to increase the overall average COP.


So after these improvements, and monitoring the ASHPs on the 12 month trial, they averaged a COP of 2.45 - which you may or may not consider satisfactory. However these results were achieved with manufacturer involvement. On the initial 12 month trial several ASHPs were in the range of 1.2 to 1.6 for their COP. What is to say there are not many systems in use with similar performance?


The question to ask is what will happen if you spend your £10,000 and you get a duff system in an unsuitable house? Will the manufacturers come and make interventions to your system?


How many firms, when asked for an installation quote, will refuse on the grounds that your property is unsuitable??

andy2308

With regard to our system, it's been checked, by both the installer and Mitsubishi over the time we've been living here.

The outdoor unit does appear to be correctly mounted on its platform with rubber mounts.

We tried running the hot water permanently when we first moved in but were advised against doing that, the instructions with the system also state that this will result in high running costs.

To be honest, I get about the efficiency of the system, as I said I'm a refrigeration engineer by trade so I fully understand the characteristics of the heat pump system but don't see the gains in having to run the immersion every day.

We installed a combi in our last property, I have to say that we run the taps for longer with this system than we did with the Vailant we installed. As there's only the two of us here the issue of lots of taps running together isn't a problem.

If it had been up to the other half, it would have been ripped out long ago!

We're now at a stage where one of the twin port valve's internal switches keeps jamming on and the pressure relief valve is dripping water constantly through the waste pipe. Having done the checks suggested by Mitsubishi it would appear that the valve itself will require replacement. My mindset at the moment is not to throw money this thing and just change the lot!

Appreciate all the comments, just wanted to share my experiences.

Cardew

andy2308 wrote: »

We installed a combi in our last property, I have to say that we run the taps for longer with this system than we did with the Vailant we installed. As there's only the two of us here the issue of lots of taps running together isn't a problem.

As there are only two of you(presumably working during the day?), it raises another important issue on the running costs of heat pumps.


If you get an annual overall COP of, say, 2.5 then 5,000kWh will produce 12,500kWh. However because of the low water temperature for radiators(typically 35 to 40C), an ASHP must be kept running for long periods - sometimes 24/7 - to keep the house heated. Thus the ASHP is producing heat when occupants are out or in bed.


With gas/oil/LPG CH the water for radiators can be as high as 80+C. You can set the heating to come on, say, 20 mins before you return from work/get up in morning and the house is warm.


So if a house requires 12,500kWh for heating with an ASHP, the same effect will be achieved with a conventional CH system using considerably less kWh. This was acknowledged by an EST representative in a thread on MSE.

Smiley_Dan

I also wonder whether the construction styles of different houses lend themselves to lower grade heat. Modern timber framed houses heat up quickly but may lose heat quickly too whereas higher thermal mass houses may retain heat and lend themselves better to the type of heat that hear pumps generate (lower grade).

deano72_2

Turn the pasteurisation cycle off, you won't find many installers with it on. Aslong as your have a weekly turn over of water then legionella can not occur and can only occur at temps between 20c-50c so if the dhw is set to 55c no worries, or if your worried and want pasteurisation, set it to come on 150 cycles instead of 15 or every cycle.

If you can get your hands on a infra heat camera you may have significant heat loss, I bet it's not air tight

andy2308

deano72 wrote: »

Turn the pasteurisation cycle off, you won't find many installers with it on. Aslong as your have a weekly turn over of water then legionella can not occur and can only occur at temps between 20c-50c so if the dhw is set to 55c no worries, or if your worried and want pasteurisation, set it to come on 150 cycles instead of 15 or every cycle.

If you can get your hands on a infra heat camera you may have significant heat loss, I bet it's not air tight

It's already set to 150 cycles. At the moment if I turn off the immersion we get little or no hot water the next morning. Can't see any reason why, there are no error codes and it happily reaches 55C on HP alone. The FTC unit seems to think that it needs to switch over because it hasn't reached the desired temperature change in time but having checked, the hot water comes on at 16:30, by 16:45 it's switched to immersion heating, switch off and back on and off it goes happily on HP until it reaches 55.

TiredGeek

Cardew wrote: »

For new readers you should perhaps inform them of the costs of your installation, and the atypical demands you place upon the ASHP's. Also why your Ecodan was ripped out after spending £14,000?

Oh, don't get me wrong, I'm not saying they're right for everyone and absolutely they should be much much easier to fit and set up, and the cost of ours ended up being frankly horrendous (and will never pay for itself) but IF you get it all right then they can be great.
I was trying to make the point that I think it's not a fundamental heat pump problem Andy has, more a probably relatively easy fix.

I have great respect for your advice Cardew, I tend to agree with you particularly when it comes to working out the costings of installation versus saving the money and getting the interest.
Keep up the good work

lovesgshp

andy2308 wrote: »

It's already set to 150 cycles. At the moment if I turn off the immersion we get little or no hot water the next morning. Can't see any reason why, there are no error codes and it happily reaches 55C on HP alone. The FTC unit seems to think that it needs to switch over because it hasn't reached the desired temperature change in time but having checked, the hot water comes on at 16:30, by 16:45 it's switched to immersion heating, switch off and back on and off it goes happily on HP until it reaches 55.

I don't know the Ecodan at all, but maybe check the immersion heater timer countdown. It could be too short. Also, what timer settings on the DHW, size of tank, DHW hot water temp.