aircon?

Cardew

Just to eleborate, there are hundreds of websites with information on the pros and cons of ASHPs. You are best looking at the 'independent' site such as Energy Saving Trust etc.

One interesting theme that comes through is in this quote:

The biggest killer of the COP of an ASHP is the need to defrost the outdoor unit when the temperature is below about 7C as the coils freeze up.

You also need to consider how the heat is to be distributed around your house - ducted? doors left open? multiple units?

stevehead

deffinetly

Cardew wrote: »

I certainly don't want to be cast in the role of an anti-heat-pump campaigner - because I am a fan. I just want to get costs into perspective and have a balanced debate - and all the issues brought into the open.

I know you're pro heatpump Cadrew and I'm just giving you a heads-up that effiiciencies have improved recently, but only in a select few products.
If I could draw an analogy with cars......
You might own a horse, and ask how much fuel a replacement car would use. A general answer would range 25 - 40mpg, but there's 3 or 4 models that get over 60mpg in real world tests.
So I'm just feeding in results from a real world test of 2 of these select units that claim a performance significantly above the norm.

stevehead

deffinetly

Cardew wrote: »

Just to eleborate, there are hundreds of websites with information on the pros and cons of ASHPs. You are best looking at the 'independent' site such as Energy Saving Trust etc.

The Energy Saving Trust are well aware of the lack of info on their Website
I had a mail from them last week, and I quote:
" [FONT=&quot]We are aware that air source heat pumps are relatively cost effective, however, due to the lack of industry accreditation with the technology it has been difficult to incorporate them in any depth into our advice mechanisms. This situation is rapidly changing, and mail such as yours helps us force it up the agenda. In the new, soon to be released, RdSAP upgrade (the mathematical model that runs behind the HEC) ASHP technology will be fully represented. I imagine that these changes will also be reflected in the information presented on our website. [/FONT] "

Cardew

stevehead wrote: »

The Energy Saving Trust are well aware of the lack of info on their Website
I had a mail from them last week, and I quote:
" [FONT=&quot]We are aware that air source heat pumps are relatively cost effective, however, due to the lack of industry accreditation with the technology it has been difficult to incorporate them in any depth into our advice mechanisms. This situation is rapidly changing, and mail such as yours helps us force it up the agenda. In the new, soon to be released, RdSAP upgrade (the mathematical model that runs behind the HEC) ASHP technology will be fully represented. I imagine that these changes will also be reflected in the information presented on our website. [/FONT]"

EST have this page:

http://www.energysavingtrust.org.uk/Generate-your-own-energy/Types-of-renewables/Air-source-heat-pumps

This is another site.

http://www.csep.co.uk/page176g.html

stevehead

deffinetly

Cardew wrote: »

One interesting theme that comes through is in this quote:
"The biggest killer of the COP of an ASHP is the need to defrost the outdoor unit when the temperature is below about 7C as the coils freeze up."

This inference in this quote is misleading; ASHP's rated COP is normally stated at 7C ambient so this is where you get closest to acheiving the manufacturers claimed efficiency. As the outdoor temperature falls the COP will too, but not to the point where it can be described as "The biggest killer".

Some numbers:
From the COP Values stated for the Mitsubishi Ecodan Air-to-Water system refered to in Cadrews post #8
COP @ Ambient Air Temp 7C = 3.9
COP @ Ambient Air Temp 2C = 3.4

Applying the same performance envelope to the Mitsi SRK20ZGX
COP @ Ambient Air Temp 7C = 5.45 (Stated)
COP @ Ambient Air Temp 2C = 4.75 (Calculated)

So no big 'Killer' when operating in normal UK climate conditions - in fact negligible.

If the papers are anything to be believed, then we're in for a big chill next week with Siberian weather. I'm sure that if we hit -10C all day then efficiency will go out the window and the old gch will be cranked back into life.
So maybe I'll have 10 or so days a year when things aren't perfect, but the other 170 (6 months heating season) the COP'll be a good 'un.

thechippy

deffinetly

Cardew wrote: »

I assume that remark in bold is directed at myself as I had the temerity to challenge Stevehead's figures.

As I have said before I have had such a ASHP system in a property abroad for a while. I am a fan of the concept and if you look through posts I have made over the past few years I have been a constant advocate of heat pumps.

I believe they are the future for heating - particularly for properties without gas - so I don't need to be convinced.

However much as people with vested interests(like yourself) wish to heavily promote them, it is important to get the costs into perspective. Stevehead's figures in his original(unqualified) post of £30 a month for heating which would cost £120 with gas is just fantasy.

Everyone seems to bandy about a COP of 5 as if it is obtainable all the time - well it ain't. The Energy Saving Trust talks of a COP of 3.

Mitsubishi have an excellent website and this is an extract from a report(dated Oct 2008)




I also question why the hurry if the efficiency will increase as "technology develops"

Heat Pumps will certaintly figure prominently in highly insulated new build properties as they are far better incorporated into the design of the building than retrofit. Particularly using air to water with underfloor heating.

Good they are - but let us not go overboard!!

P.S.
For a more balanced view of ASHPs I suggest those interested read this thead:
http://forums.moneysavingexpert.com/showthread.html?t=702257

The OP has had his system a year now and hopefully he will post some objective figures soon.

P.P.S.
I particularly liked the comment in post#7

Hi Cardew,

The comments were not aimed at you at all, I respect your input on these matters. The comment was aimed at some of the info you find on the net!!

As Steve has said, the efficiency can vary widely between the different manufacturers and models. I didn't infer that systems HAVE a cop of 5, but rather that some of them are quite capable of 5+ under certain conditions.

The defrosting of the outdoor coil will only become quite frequent when the ambient falls below zero for any length of time. Even then, the cycle is quite short.

These things are changing all the time and the cops at low ambients are getting better and better. I'll be in receipt of the latest Mitsubishi data soon, so I will post the cop of thier latest units in this thread.

Happy new year guy's.......

stevehead

deffinetly

Now it's the 1st of a new month I've taken the KWh usage readings from my aircon and reset the counters to zero. So, here's the scores on the doors....

Downstairs Unit 165KWh
Upstairs Unit 139KWh
Total 304KWh for 31 days

Just to recap the scenario
2 X Mitsubishi SRK20ZGX-S ASHP Units costing £2,200 installed
End terrace 3 bed house in SW England
House kept at 20/22C upstairs 21/24C downstairs
House is occupied every day
No other form of heating used whatsoever

Is this cheaper to run than a gas combi?

richardc1983

Everyone should have these installed!!