Air Source Heat Pumps

samtheman1k

I went for a 50% oversize in our lounge and a 100% oversize in our main bedroom. All others aren't oversized as the others seem good enough to warm the rest of the house too! Gledhill recommend a 20% oversize, but I'm not convinced that that's enough. I'm sure someone could work it out scientifically if they were so inclined!

Those COP figures seem to be pretty realistic in my eyes, 2 at -7degC and 4 at +15. It will average around 3 over the course of the year I think.

Cardew

Kev_Dale wrote: »

Do you think the COP values are realistic?

That is the $64,000 question!!

I suspect some of the COP figures quoted are in the "my V12 Aston Martin gets 46mpg" category. Well it might at a steady 25mph in 7th gear

I have read(no idea if it tells the whole story) that the 'killer' in cold weather are the defrost cycles.

I suspect 'in the real world' a COP between 2 to 3 is realistic in winter.

That said IMO it is a 'no brainer' if no gas is available, as getting heat one half to one third of the normal cost is excellent.

If the Government are really serious about us saving energy, it really is high time that the Government/Energy Saving Trust carried out some trials of heat pumps under controlled conditions and gave the results widespread publicity.*

Now we have to rely on claims from installers(with a vested interest) or people who have installed a system who used to pay '£5000 a year for CH and it now costs me tuppence hapenny'

*On the subject of publicity, how many people are aware that the Government sponsored a trial of several solar HW panels from most of the maufacturers?

They found that the average output was under 1000kWh a year - with virtually nothing in the winter.

Yet this report is buried away and hidden from the public. So people are still spending £thousands to install panels to save themselves £tens and these rogue firms are conning unsuspecting public out of £millions.

Kev_Dale

Cardew wrote: »

I suspect some of the COP figures quoted are in the "my V12 Aston Martin gets 46mpg" category. Well it might at a steady 25mph in 7th gear

Without a shadow of a doubt!

Cardew wrote: »

That is the $64,000 question!!
That said IMO it is a 'no brainer' if no gas is available, as getting heat one half to one third of the normal cost is excellent.

I guess this is what I wanted to hear.

Thanks

stevehead

Originally Posted by Cardew
I suspect some of the COP figures quoted are in the "my V12 Aston Martin gets 46mpg" category. Well it might at a steady 25mph in 7th gear

Kev_Dale wrote: »

Without a shadow of a doubt!

Originally Posted by Cardew
That is the $64,000 question!!
That said IMO it is a 'no brainer' if no gas is available, as getting heat one half to one third of the normal cost is excellent.

Kev_Dale wrote: »

I guess this is what I wanted to hear.

Thanks

Now then now then.. lets not get carried away dissing COP values again.
IF you compare the COP rating of all Japanese ASHP's they are all tested under the same conditions. This is an Japanese Industrial Standard test, and all units must legally test within 10% of their claimed performance.
The heat output and power input are sampled over a 1/2 hour period, after the system has been run for an hour. The outdoor temp is 7C, and the indoor set point is 22C.
When comparing the performance of any Japanese equipment, the COP value stated will be very accurate, it has to be by law.*

The point here that it's the real world UK official test that's missing; there's no SEDBUK for ASHP.
But even if there was, do you think a simple 'A' rating would be enough information to persuade you to use ASHP? It's a bit dumbed down compared to COP. We need SEUKASHPCOP... mmm... bit of a gobfull that one!
And the question is, what do we do 'till then?

*Enforcement Regulations for the Law Concerning Rational Use of Energy
(Enforcement Ordinance for the Household Goods Quality Labeling Law)

richardc1983

Heat_Pump_Wannabe wrote: »

Re the video illustrating noise levels - I haven't seen one of these things before and I am puzzled - in the video the fan appears stationary, and the noise levels appear to be acceptably low. But - is it noisier or quieter when the fan is running i.e. during normal operation? If noisier, I would appreciate a similar video with it running ...

Sorry for the delay in replying back but I didnt get an email reminder.

I will do a video tmrw of it running with the fan going. IT was in a defrost mode (fan doesnt spin) so the noise you hear there is the same level you hear in cooling mode as the fan rotates very slowly.

When in heating mode the unit is no louder than an ordinary boiler flu, you hear the fan but this is just the airflow you hear it is not very loud at all. The compressor runs faster too and is a slightly louder hum. However traffic noise is still very much louder.

richardc1983

mech wrote: »

That would be a bit of a fluke wouldn't it?

If you read the text it says it's in defrost mode and that the fan starts up again afterwards. If you skip to the end of the video you see it start up, though there isn't a lot time to then assess how loud it is. Seems pretty quiet though.

Yes the fan starts up at the end of defrost again.

You hear the 4 way valve energise again and that point the fan starts up.

WIll do a video tmrw running in heat mode.

richardc1983

Cardew wrote: »

That is the $64,000 question!!

I have read(no idea if it tells the whole story) that the 'killer' in cold weather are the defrost cycles.

.

Cardew

The answer is yes and no. If your equipment is undersized then when its cold like it is at the moment it will run flat out. The unit running flat out means that the coil freezes up faster.

Make sure the equipment is correctly sized so the unit can handle the extra capacity in cold weather. Personally I would slightly oversize so when the cold spells come the unit can handle it even better.

Defrost cycles in colder weather can range from every half an hour for an undersized system to every 2 hours for an oversized system.

My system when its been off all night will run flat out for a few hours to get the room temp up however the benefits of inverters means you can set the temp lower on a night so the unit ticks over at a lower speed maintaining the room temperature, then when your in during the day you can crank it back up again.

I quote from Mitsubishi site:

On investigation 90% of all end user complaints
of excessive defrost and poor low ambient
performance on investigation have been due to
incorrect application and sizing.

All heat pumps need to defrost. It is simply the
laws of physics. Unfortunately in the majority of
cases end users have not been advised of this
process at the time of sale. Part of the sales
process must include educating the end user and
ensuring the end user understands how the unit
will operate.

DEFROST PERFORMANCE

Defrost performance and frequency is critical to the efficient operation of a heat pump.
The period of time as frost builds on the outdoor coil, during the defrost period and after defrost as the
pipe work and indoor coils heat up reduce the hourly heat transfer rate of heat pumps and this affects
the units performance. While the unit is defrosting it is not heating.
Many end users are unaware that their units defrost and this is the subject of many calls to our service
support centre. Part of the sales process must be to advise the customer what to expect
from the heat pump and ensure they understand that their unit will defrost.

Heat pumps also use a “Dry Fan” sequence at the end of the defrost cycle to remove
water and from the outdoor coil fins following completion of the reverse cycle defrost. This ensures that
the outdoor coil is dry and free from moisture on resumption of heating.

Undersized units will defrost at regular intervals as low as 30 minutes apart in low ambient conditions
when they are struggling to reach set point.

Correctly sized units will have shorter total compressor run times and lower frequency operation
speeds. These conditions combine to reduce defrost frequency from the minimum of 30 minutes to up
to 120 minutes or not at all depending on the load requirements.

richardc1983

Please also read my guide.

http://forums.moneysavingexpert.com/showthread.html?t=1464827

Spent half the night the other evening compiling this! No one has commented yet and same questions cropping up!

Where are the mods who run the forums I have messaged requesting it to be made sticky but had no response yet.

Hermann wrote: »

Have you read this thread .....
http://forums.moneysavingexpert.com/showthread.html?t=1310449

and have you seen Steveheads heat pump video ........
http://uk.youtube.com/watch?v=79UAPRI6p-M

All interesting stuff.

richardc1983

As requested, heres a video taken just now of my outdoor unit in heat mode.

Very quiet.

http://www.youtube.com/watch?v=-mUzYHEfQEY

Cardew

stevehead wrote: »

Now then now then.. lets not get carried away dissing COP values again.
IF you compare the COP rating of all Japanese ASHP's they are all tested under the same conditions. This is an Japanese Industrial Standard test, and all units must legally test within 10% of their claimed performance.
The heat output and power input are sampled over a 1/2 hour period, after the system has been run for an hour. The outdoor temp is 7C, and the indoor set point is 22C.
When comparing the performance of any Japanese equipment, the COP value stated will be very accurate, it has to be by law.*

The point here that it's the real world UK official test that's missing; there's no SEDBUK for ASHP.

I am not in any way 'dissing' ASHPs and indeed if I didn't have gas would seriously consider getting one in UK - and as said above an overall COP of 2 to 3 is excellent. Bear in mind I have an ASHP in a property abroad.

However I do believe the analogy of car manufacturer's mpg figures - which are equally rigourously tested - applies.

In fact this quote from Richard's post demonstrates that not all is sweetness and light, in that there obviously are dissatisfied customers.

I quote from Mitsubishi site:

On investigation 90% of all end user complaints
of excessive defrost and poor low ambient
performance on investigation have been due to
incorrect application and sizing.

On this forum there is unbridled enthusiasm for all things ASHP.

I am just urging a note of caution for prospective customers and suggesting that some research on more technical forums etc is carried out before committing to buying a system. Above all have realistic expectations of costs of installation and savings.