Life after Heat Pump-Cold

[Deleted User]

Kopthat wrote: »

Al, thanks for the depressing info. So what about other heat pumps or are they all of a similar output? Maybe this explains why the RHI may not apply to domestic heat pumps, as from what I have seen, they are not now looking as good as stated.
Would a different heat pump of better design do any better. (Size of property is 230sq m, and insulation is to a high standard).
Kopthat

We've had lot's of snow and freezing temps over the last week and the 14 kw EcoDan has performed perfectly. House heated exatly to temp with zero icing on the outside unit. Tis the first time in my life the winter duvet has stayed in the loft Your house sounds a lot more insulated that mine too...

Hope you get this sorted.

[Deleted User]

Kopthat wrote: »

The company who we contracted the system with were MCS credited, and seemed/were a big company.
Whilst it is fine to say just turn the the system off at 5C, and install a wood burner.....this surely cannot be the point.
Our house is H shaped with the middle linking section single storey and the other legs two storey, so, maybe we should have four wood burning stoves.

The question then, can we get a heat pump to work for our dwelling to a -15deg temperature?
What happens where similar units are installed in other European countries where they have been used more commonly?

And if they don't work, why are they being sold at all?

WBS's are great but to do the whole house, like you, i'd need several and that would cost more than a heat pump at £3-4k a pop installed It'd be a full time job fuelling all these stoves and cleaning them to...

Perhaps in a two up two down a single WBS would take the chill off...

I'm not knocking stoves but it only heats one to two rooms and ours being a cast one takes an age to warm up but once it gets there...phew! Nice to have on in the evening but having relied on one during the last winter as the main source of heat it not something i'd want to do again.

paceinternet

We've had lot's of snow and freezing temps over the last week and the 14 kw EcoDan has performed perfectly. House heated exatly to temp with zero icing on the outside unit.

# 43
jeepjunkie, why doesn't your EcoDan require defrost cycles in sub zero temperatures?

Are you in a very low humidity environment, or maybe getting a lot of sun on it?

Blowing wet or moist air over the outside coil. which could be at -5 or even lower, normally causes icing.

Last year, photos of some EcoDan installations were posted very heavily iced up, so they are not immune to icing, but if you have some experience of avoiding icing, it would be good to share info.

grahamc2003

jeepjunkie wrote: »

We've had lot's of snow and freezing temps over the last week and the 14 kw EcoDan has performed perfectly. House heated exatly to temp with zero icing on the outside unit. Tis the first time in my life the winter duvet has stayed in the loft Your house sounds a lot more insulated that mine too...

Hope you get this sorted.

Great to get the feedback in cold weather, and good to see the ecodan is up to it (as expected when installed correctly).

Supplying heat in cold weather is one thing. What is more interesting is how much it costs to do that. Have you been taking meter readings? (Even crap hps can supply lots of heat in the cold weather, simply by turning on 12kw of heating elements)

You can't escape these things costing more as the temp drops - it'd be really interesting to get some idea of the real cop at sub zero temps for the ecodan.. I'd also say that surely it's impossible to escape defrost cyles in the uk too - be great if you could monitor how frequently they happen (I assume the ecodan will indicate when defrosting?).

(as an aside form the post above, As to the temp of the outside coils - I've heard they are around minus 60C, and I expect they must be something like that to extract heat from -15c air in great qunatities).

[Deleted User]

paceinternet wrote: »

# 43
jeepjunkie, why doesn't your EcoDan require defrost cycles in sub zero temperatures?

Are you in a very low humidity environment, or maybe getting a lot of sun on it?

Blowing wet or moist air over the outside coil. which could be at -5 or even lower, normally causes icing.

Last year, photos of some EcoDan installations were posted very heavily iced up, so they are not immune to icing, but if you have some experience of avoiding icing, it would be good to share info.

I'll be honest... with everthing I read about icing up it was a concern. All I can say is the unit gets afternoon sun, is sheltered from winds/rain, minimal snow landed on it and the air has been pretty dry. Checked the unit regularly with absolutely no sign of ice anywhere on it or in it It is freezing if you stand in front of it

It is running for longer periods than say in November and there has been an increase in electricity consumption. My total electric consumption is now in the region of £110pm during this winter period which for an old house to be always warm, all lighting, oven and washing machine [the latter two never off:mad:] is great.

Not to mention the dozen outside lights to help me see in the dark when doing all the fun jobs the wife doesn't do like cat trays, bins, recycling, WBS ash, logs and coal etc

The EcoDan is rated to -25c and has no electric boost. Even if the -25c is a tad otimistic the system should have more than enough grunt to cope which so far it seems to.

I'm still waiting to hear from Mitsubishi if the system will be chosen to be monitored as aprt of a group test. If it is I'll be able to login to a website to view COP etc...

EDIT: Yes we have PV but it is about as much use as a chocolate teapot at this time of year so is not skewing the figures.

Swipe

Must be down to the conditions so far this winter. I too have yet to have a defrost cycle so far and I normally get lots (every hour) when it's cold. It must not be cold enough yet during the daytime. By the time it has gone frosty the house is warm and the units are only ticking over.

bernithebiker

I think one of the key things re.defrosting is not to push the units too hard.

For example, coming back from holiday, it's -5 outside, the house is cold, so you push the HP to max. The compressor will run as hard as it can and the coils will get super cold, and no break to allow for a warm up. Classic icing conditions.

If, however, the system is well sized, (err on the side of too big, not too small), and is allowed to run all the time at low to medium demand, then you should be pretty much OK.

2 interesting things I've heard;

a) moist, humid air at say +5, has more energy in it than dry air at +5. So as long as the system doesn't ice up, humid air can improve the COP.

b) humidity tends to decrease at very low temps like -10, -15, so icing can be less of a problem. Prime icing temps are from +3ish down to -5.

Correct me if I'm wrong!

lovesgshp

bernithebiker wrote: »

I think one of the key things re.defrosting is not to push the units too hard.

For example, coming back from holiday, it's -5 outside, the house is cold, so you push the HP to max. The compressor will run as hard as it can and the coils will get super cold, and no break to allow for a warm up. Classic icing conditions.

If, however, the system is well sized, (err on the side of too big, not too small), and is allowed to run all the time at low to medium demand, then you should be pretty much OK.

2 interesting things I've heard;

a) moist, humid air at say +5, has more energy in it than dry air at +5. So as long as the system doesn't ice up, humid air can improve the COP.

b) humidity tends to decrease at very low temps like -10, -15, so icing can be less of a problem. Prime icing temps are from +3ish down to -5.

Correct me if I'm wrong!

Without going into detail on specific models, some units have a holiday function where a ambient temperature is kept for x number of days. You program to have the unit reheat to normal level say 24hrs before you return.
Yes damp air is better, as is damp ground for a GSHP.

Cardew

bernithebiker wrote: »

If, however, the system is well sized, (err on the side of too big, not too small), and is allowed to run all the time at low to medium demand, then you should be pretty much OK.

Well everything I have read states it is just as bad to oversize a heat pump as undersize.

This from a Government publication:

Oversizing will significantly increase the installed cost for little operational saving and will mean that the period of operation under part load is increased. Frequent cycling reduces equipment life and operating efficiency.

lovesgshp

Cardew wrote: »

Well everything I have read states it is just as bad to oversize a heat pump as undersize.

This from a Government publication:

That is totally correct Cardew