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Graham's Gossip
by Graham Hendra

Heat pump consultant


Blog

Do heat pumps really work? What? Even when it is cold?

22/12/2009 13:27:04
I have been working on air conditioning systems for 20 years but am a relative newbie in the air source heat pump market.



In this incredibly cold weather, (it's currently -1C outside and snowing) the big question is - will my air source heat pump really work in these conditions?

Everyone knows a gas boiler will cope with these conditions easily but a heat pump is an unknown quantity.

One of my colleagues recently asked me the same thing. Will it really work when it is snowing outside. He's been in the industry longer than me.

This kind of talk makes me nervous. I start to think maybe it will be a problem.

Well good news everyone, its snowing and freezing cold and the heat pumps are working well.

After thinking about this issue for a while I've realized that this question is ridiculous.

This morning I arrived in our offices at 9am, the room temperature was 21 degrees C and the ambient was -1. Our building is heated with a VRV unit, there is no other provision for heating in this building.

It didn't even cross my mind that this place wouldn't be warm today. Everyone knows that a split system or VRV will heat like the clappers even in these extreme conditions. So why do we even question air source heat pumps?

We know they work, they are no different from splits except they heat water not air. So have a think about it and don't doubt them. Sing their praises, they are fantastic systems.

If you think I'm biased and am just singing the praises of the kit so my boss will think I'm towing the party line, then you don't know me well.

In fact I'm so confident about the technology that over Xmas I'm ripping out my old floor mounted gas boiler and replacing it, not with a combi but with an air source heat pump.


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Comments
Air Source Heat Pumps
By David Wright
Surely with external conditions approaching minus 5 degrees celcius, the efficiency and ability to extract heat from the air reduces as the temperatures of the refrigerant and air become closer?

The defrost cycle also means there are times (albeit short) when the units are busy defrosting the external units rather than heating the space. I know this as our units struggle to meet the unusually high heat demand as I type this!

Heat Pump Efficiency
By Jules Freeman
Yes air source heat pumps will work in freezing ambients but at what cost?

The COP will drop and input consumption will increase raising the cost of heating potentially above that of gas, and increasing carbon emissions adding to climate change.

Many installers quote a COP of between 3.0:1 - 3.6:1 but what parameters is this figure based upon? Many may find there systems are costing them more than they think when they really need to use their heating flat out, such as in the recent cold snap.


By Anonymous
Heat pumps do 'work' but they don't work quite as well during the very time you need them most. The COP drops like a stone and some even need electric heaters to prevent legionnaires. They need another 10 years of research and a eureka moment to make them worth the investment.

I have a Combi boiler and when it fails I will be replacing it an even more efficient combi boiler.

I have no want for a soddin great box on my outside wall nor an even bigger soddin tank taking up valuable space indoors.

Unless the government ban gas boilers (as the rumours suggest) then I will never fit a HP in my own house. Or at least not until the COP is up to 7+ at deg'c.

The initial cost is high and what the consumer hasn't been told is a dropped compressor is an easy 2k. that is going to hurt.

I also remain convinced that a phase of global cooling from 2015 will ensure they remain a poor return

"I'm ouuut!"

Richard Bartlett
Ambient Control


Re - air-to-air heat pumps
By paul skeet

I just came across your blog on A2A h/p's. I'm an advocate too, having been installing virtually nothing but for at least 15yrs, but it's common knowledge that despite inverter technology, the efficiency of an A2W h/p WILL drop off as the ambient gets colder.

It has to - that's the laws of physics. They will freeze up more often, go into defrost (automatically) more often, and consume more electrical power at lower ambient temp. than when higher ambient temps.

You should ask to see test data from one of the manufacturers that clearly shows what goes on at these lower conditions. I think you'll find that there's little available.

Sure they work, i can testify to that - I have a multi-split in my own place, which works well even at freezing levels, as I found out the other day, but I also have balanced-flue warm air gas heaters in each room, which are very efficient (85%) and can provide 3kw output at any ambient temperature.

Personally, domestically these days, I'd go for a combination system, and I don't mean a combi boiler, I mean different systems - like my own place - because this gives the best of both worlds, and allows customer the choice and diversity, whilst providing a degree of back-up, so that if one develops a problem, you have the other to do the work required. I would'nt rip out your old system just yet (unless its failing anyway).- PS

Heat Pumps
By Mike McCourts
I have a Daikin multi type heat pump serving my offices and no other form of heating.

Current ambient temperature in Cheadle is minus 10 degC. Indoor fan coil unit supply air temperature is plus 32degC. De-frost periods imperceptable

Yes, dinosaurs, heat pumps DO work. Please pay me a visit to my offices this summer when the conditions will be cool and comfortable.

Air heat pumps
By Revor


I have looked at these for my build and have drawn the conclusion that they are not efficient when you need them most i.e when it is cold.

Most electricity is produced inefficiently by burning fossil fuels, far better to burn the fossil fuel at source.

I would have thought that by now we would be seeing a gas powered heat pump that would add I think at least a factor of 3x to the efficiency compared to electric. The one thing in favour of electric is that it is very convenient.

The above heat pump comments
By Graham Hendra

Blimey I'm impressed. Four good comments all of which show a full understanding of heat pumps. I couldn't agree more with what's said above, we all know this.

Sure heat pumps cost more to run when its really cold, the flip side is they are cheap to run when its warmer.

Generally COPs quoted are the average achieved over the heating season. Check with your supplier to confirm this though anything above 4 and I would check again.

Thanks for the comments makes it all worthwhile

Graham

Air heat pumps
By John Rosier

A few notes to add to the informed comments made:

a) When the COP reaches about 2.4 the air to air heat pump running costs are cheaper than the equivalent condensing boilers. The carbon emissions are also less.

b) Using a digital scroll VRF type air to air heat pump providing hot water and refrigerant based heating/cooling to the building typical, typical COP s are likely to be as follows (based on a water temp of 50c

Ambient (C) COP Ambient (C) COP
- 6.0 1.7 +16.0 4.0
0 2.3 +21.0 5.5
+ 7.O 2.8 +25.0 6.5
+13.0 3.3

c) The above COP figures will increase significantly when hot water is generated whilst air conditioning is also being provided.

At around 1 or 2 degrees ambient temp, the air to air heat pump running costs will probably be less than that of the equivalent condensing boiler.

d) Do you really want an explosive device mounted near your bedroom? Keep to heat pumps, they don't explode (at least not if they use conventional refrigerants).

Heat pumps in cold weather
By Alan Davey ( AD 2000 Air Conditioning )
Having worked in this industry for over 35 years, I remember when A/C Heat Pumps were first introduced.

They were greeted with great suspicion. They have had less than a fair press over the years and even today are not always the first product to be considered for all round heating and cooling applications.

We as an industry should be yelling from the roof tops about the benefits of Reverse Cycle Tecnology. We still have a largely untapped domestic market in this country.

Almost everyone enjoys the benefit of A/C in their cars these days, so why not point out the comfort benefit that A/C in the home can provide. Comfortable summer nights and winter heating with COP's as much as 3 to 1.

My family has enjoyed the benefit of A/C in our bedrooms for the last 5 years and we would now not be without it. Let us be positive about the green credentials of these systems as well.

Heat pumps

The comments are all very interesting as I have been selling the praises of heat pumps for many years but it is really over the past two or three years that things have got to a point where inverter technology has made it possible to get the COPs up to reasonable levels and small air to water systems that are ideal for the domestic market.

If used with other technologies such as solar thermal and PV, people will really start to see major savings in terms of cost and carbon.

-By Ian Willis

heat pumps
By berni page
Will the air to water pump work in outside temps of minus 15-20. I live in Austria and am building a new well insulated house. I am very confused which way to go with heating!!

Heat pumps
By Spot
Here in Australia, they just don't work below 5 or 6 degrees celcius. outside. Maybe they sell us the crappy ones.

air source heat pump
By C Robinson
It's cold in the UK. Don't get an air source heat pump - you will be a risk of hypothermia in cold conditions.
When its cold outside, below 5 degrees, it does not work! I have had one in my three bedroom house and it uses 690 Watts of power for no heat!
You're better off turning on the oven and leaving the oven door open to heat your house. Not only this, but it takes six hours to get the slightest bit of heat. You can't run the hot water and heating at the same time as the system crashes.
The hot water takes 2.5 hours to heat up and in that time you have NO HEATING!
The Government should scrap this scheme and spend money on things that actually work! I can't cope with getting huge electrical bills for 208 a month for a system that is useless.

Too expensive, too cold
By Julie Switsur
I just had one installed under the government grant scheme. Eleven months to install. Not warm enough in the winter. Very slow to heat up. Far too expensive to run. I have turned mine off and gone back to coal and wood. They are OK if you are rich but if you are on benefits or a low wage - forget it!


By Andrew
I'm in Canada and it's currently -22 C outside and my heatpump will still kick out enough heat to keep our house between 19 and 20 C


 
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