Can air source heatpumps lose efficiency?

[Vortex2]

We have had an air source het pump for three yrears.

We change the air filters when required - but do no other maintenance.

This year the house seems a bit colder .... can the air source heat pump get 'tired'?

[adam2]

Yes they can.
Firstly the refrigerant gas may leak out, partial loss of this gas will reduce effectiveness, it might need topping up, and if this is needed more often than every few years then the leak must be located and mended.

Secondly, the outdoor heat exchanger may become dirty, some cleaning is possible but some loss is permanent. It can not realistically be restored to showroom condition.

And finally general mechanical wear takes its toll, perhaps slightly reducing effectiveness of moving parts, only slightly with a good design.

[adam2]

Do of course consider other possibilities including,

That you have become more sensitive to cold, it tends to happen in time.

That if the SAME warm clothing is being worn as in previous winters, that it will become less warm with time. A pullover or sweatshirt might last several winters but wont be as warm as when new. Long underwear, depending on quality and pattern of use might last for 100 uses/launderings, but near the end of its life will be thinner and less warm than when new. If in any doubt purchase new garments, don't discard the old items but wear them in moderately cool weather, keeping the newer garments for more severe weather.

Bedding likewise, a reasonable quality wool bed blanket should last at least ten years of daily use but by year nine will be a lot less warm than when new. Duvets likewise, polyester or other fake stuff soon looses bulk and therefore insulating value. Feather lasts a bit better, but steadily looses warmth as the feathers compress, break up or wear away. Down is more durable but still gradually looses bulk and warmth. If in doubt buy new, and keep the old bedding for use in milder weather. Down or feather duvets that have lost bulk can be partly restored by washing and tumble drying. Only do this if the ticking is in good condition or you know what will happen !

Brushed cotton sheets, duvet covers and nightwear are warm when new but soon loose this warmth, again buy new for winter and "use up" the older articles in mild weather.

Consider also that minor and unnoticed deterioration in your home may be leading to loss of heat. Apparently trivial structural settlement or shrinkage of timbers may admit cold air through previously sealed areas.

Have you replaced any domestic appliances with more efficient versions ? Use of a modern laptop PC instead of an older desktop unit might save 100 watts or more but of course that is 100 watts less heat into your home. Fridges, TVs, and lighting likewise.

[PS_RalphW]

The more I read about air source heat pumps, the less I like them. We are thinking of moving to a modern 3 bed semi and I am wondering if upgrading to passivhaus or similar standard of insulation would be a better investment than replacing the heating system, in terms of reducing carbon footprint and future heating costs. I do not know how the relative costs of the upgrades compare.

[adam2]

I would in general favour passive haus or similar standards of thermal insulation rather than a heat pump.
The modest heating demand can be affordably met from electricity.

In a long term emergency the supper insulated home will remain tolerable without electricity.

The home with the heat ump will become intolerably cold in a few days.

[Vortex2]

Very small Passive Houses have a special 'reduced' standard, as they are hard to make efficient.

We have excellent insulation and a heat pump and we still need 1kw heating on cold days.
(The computer model predicted this quite accurately)

[Vortex2]

Some excellent ideas here- thanks!

[kenneal - lagger]

You can never stop all heat loss from a house - it's just pure physics - and the more you try to stop it the more ridiculous the insulation thickness gets as the laws of diminishing returns rapidly kick in. To halve the heat loss you have to just over double the insulation thickness. So a heat source, be it the sun, a wood burning stove or electricity, will always be necessary. In a rural area I would specify a room sealed wood burning stove as a back up heat source to any electrical or solar heating provided.

And to any one who says that global warming/heating will make insulation unnecessary in the UK you could well point out that if the AMOC keeps on slowing the climate of northern Europe will be a lot colder, more like North Eastern Canada, than it is now even with warming. And because of our position in the Atlantic we are at the confluence of three air masses: the cold Arctic; the hot/cold, depending on the season, continental European; and the, at present mild/warming, Atlantic air mass. Depending on the meanderings of the jet stream any of those can govern our weather at any time of the year so we can't guarantee what temperatures we are likely to enjoy/suffer at any time of the year. A sustainable heat source that we might use once in a year one year but for several weeks/months in another year is a requirement for any home in the UK going into the future.