Air Source Heat Pumps

Cardew

richardc1983 wrote: »

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@ Cardew... defrost cycle uses less electricity than the actual heating cycle, it just runs in reverse, mine uses about 300watts for a 5minute defrost cycle.

300 watts in 5 minutes? that implies a 3.6kW heater! Are you saying that your input is more than 3.6kW? Or what is the length of your heating cycle?

So that is 300W of 'wasted' heat.

Now could that take longer and use more electricity if it was very humid and more ice built up?

More important is how often these defrost cycles occur?

To give an example:

At x degees C the quoted COP is say, 3 and your input is 2kWh to produce a nominal 6kWh.

If it has one defrost cycle an hour it will use 1.7kWh of input heat to produce 5.1kWh of heat. So the effective COP is now 2.55 - (2kWh used for 5.1kWh heat)

I have no idea of how long and how frequent defrost cycles are - have you?

richardc1983

Cardew wrote: »

300 watts in 5 minutes? that implies a 3.6kW heater! Are you saying that your input is more than 3.6kW? Or what is the length of your heating cycle?

So that is 300W of 'wasted' heat.

Now could that take longer and use more electricity if it was very humid and more ice built up?

More important is how often these defrost cycles occur?

To give an example:

At x degees C the quoted COP is say, 3 and your input is 2kWh to produce a nominal 6kWh.

If it has one defrost cycle an hour it will use 1.7kWh of input heat to produce 5.1kWh of heat. So the effective COP is now 2.55 - (2kWh used for 5.1kWh heat)

I have no idea of how long and how frequent defrost cycles are - have you?

No 300watts per hour if it was running for an hour, as seen on energy meter. Sometimes the defrost cycle depending on outdoor humidity levels can be as little as 5 mins upto 10minutes if outdoor temps are below freezing.

When it is freezing outside the defrost cycle runs for longer than usual 5minutes but only goes upto 600watts per hour when running for the ten minute cycles when its freezing cold.

I quote the 300watts and 600watts per hour as if a defrost cycle ran for an hour which it never would run longer than ten minutes and by that time hot air would be blowing inside again. THe energy meter only reads out current drawn bases it on an hour.

richardc1983

thechippy wrote: »

I agree with most of this. I install these on a daily basis, but decided against in my own home when my boiler recently failed. My concern was hot water. You can install a gas powered on demand dhw, but our home did not lend itself to one.
All homes / layouts are different and ashp's are not suited to all.

I also agree with not having to leave doors open etc for heat distribution. However, this can be overcome by using multi splits and having an ahu in each room.

I'm not keen on air to water systems. Rads need to be changed, as the existing will be undersized and often the dhw temp is boosted by a 3kw inline heater. It's an expensive system and you're better off using an A rated condensing boiler.

Re; servicing.
The ahu filters can be user cleaned, BUT contrary to popular belief, just brushing the condensers is not good enough. They have a very close fin spacing and often have secondary fins. These need to be foam cleaned by a suitably qualified engineer twice a year. Cost about £40 per visit.
Reliabilty is certainly better than most combi's and service life is the same if not better.

I clean the coils myself with the coil cleaners, however the outdoor unit prefer to get the experts in. I have multisplits 2 one for bedroom and lounge, but I leave doors open as I like even temperature through house.

Hermann

Cardew wrote: »

What some of us are trying to determine is realistic overall efficiencies of ASHP systems and installation costs.

In comparisons people often compare the unit costs of electricity vs gas but this isn't the complete picture. Its all very well having a gas boiler with 90% efficiency but if it needs expensive servicing and is unreliable then that has an impact on the overall costs. I do agree the ASHP industry needs to sort itself out with regard to stated efficiencies and installation costs.

Cardew wrote: »

Additionally for some of us air to air ASHPs would not be acceptable - I want a discrete heat source in all my rooms - not have doors to bedrooms and bathrooms left open.

Couldn't agree more, they're fanatastic for some people in some situations but not for everyone. Also can you imagine a long terraced town street with 2 or 3 outdoor units mounted on the front of every house?

Cardew wrote: »

This means an air to water system and existing radiators are not suitable as the water does not get hot enough.

There are solutions to this although it will usually increase installation costs.

Cardew wrote: »

The Mitsubishi Eco dan, which I understand is one of the leading systems, claims a COP of "up to" 3.5. Normally if a manufacturer includes the phrase 'up to' it is a fair bet that it will be considerably less in the real world.

I believe COP of 3.5 is entirely realistic with decent equipment for a significant portion of the year in the UK.

Cardew wrote: »

The problem is that there is no reliable data available.

I tend to find real life experiences such as those reported in this thread quite useful.

Cardew wrote: »

I don't understand your point on tax.Why is there more scope for taxing gas rather than electricity?

Its a long term thing.
Imagine the country is succesful at seriously reducing energy usage through efficiency and improved technologies.
The tax revenue from energy usage and oil industry plummets as the efficiencies kick in.

Now consider two different routes.

Option 1)
The technologies rely on reliable units that last a long time and need little in the way of servicing. They are powered by an electricity supply that has taken full advantage of renewables and green 'tax breaks'.

The tax revenue generated by this route is minimal and diminishes the more its adopted.

Option 2)
Industry and government push forward a technology as 'very efficient' and cost effective. They'll even supply and fit it for free for the qualifying low income households.
This technology requires expensive annual servicing throughout its life. It is also unreliable often requiring replacement before its expected life is up. This creates a whole new industry of 'service contracts/breakdown insurance'.
Safety concerns mean an annual certificate is needed for rented/commercial properties.
The tax revenue generated by this system is substantial.
All that servicing creates taxable revenue.
That new service contract industry creates taxable revenue.
The early failure and need for replacement units increases manufacturing levels which in turn creates increased tax revenue.
The whole certification industry creates taxable revenue.

The tax revenue generated by this system increases the more its adopted.


A great deal of generalisation but hopefully you get the jist.

As far as I can see the Gas boiler industry falls into Option 2 and provides some security of tax revenue even if the total energy used decreases.

Heat pumps fall into Option 1 and result in decreasing tax revenues.

If you were a hard pressed Government committed to improving energy efficiency which route would you take?

Cardew

Hermann,
On Tax, I simply don't accept your hypothesis! So there really is no point in speculating further.

The increased costs of air to water ASHPs was exactly the point I was making e.g. larger/more radiators, underfloor heating, boosting water temperature etc.

Ditto the costs of servicing/replacement for gas boilers. Although you might note in post #121 above that someone who installs ASHPs states that they need 6 monthly servicing by a qualified engineer.

You might be correct about a COP of 3.5 being entirely realistic for most(how long is most?) of the year. However, what you or I 'believe' is not the point - we should have reliable, realistic data for systems.

The Energy Saving Trust which is as near as you get to an Government body has a rather pathetic page on ASHPs but states:

The efficiency of air source systems is measured by a coefficient of performance (CoP). CoPs for air source systems are almost comparable with ground-source heat pumps, and generally range between 2 and 3. This means that for every unit of electricity used to power the pump, 2-3 units of heat are produced, making it an efficient way of heating a building.
A typical 6kW domestic system, suitable for a well insulated detached property, costs in the range of £7,000 to £10,000 installed.

Lastly on real life experiences, I may be more cynical than you but these are simply not reliable! Read through the various forums on MSE.

People strap a magnet on their car fuel pipe and post that it has decreased their mpg by 20% - ditto the same magnet to oil CH fuel lines has a similar effect. - and they have convinced themselves that it is true.

Claims by people for the Hot water Solar panels they fitted are simply outrageous - impossible.

They buy an expensive heater to replace an existing heater and convince themselves that it has halved their heating costs - despite the fact that both old and new heaters give out exactly the same amount of heat.

Specifically on ASHPs it is just not possible, without trials under controlled conditions, to state an overall COP for a system.

Personally I believe that the future of ASHP will be in new build properties with underfloor heating or ducted warm air to each room.

At current gas/electricity prices I am not convinced there is much of an advantage in running costs for either system.
Certainly I don't think there is much of a case to change an existing Gas CH system for an ASHP in most properties.

Hermann

Cardew wrote: »

Hermann,
On Tax, I simply don't accept your hypothesis! So there really is no point in speculating further.

Well I suppose it does rather fail at the first sentence! ....

"Imagine the country is succesful at seriously reducing energy usage through efficiency and improved technologies."

Cardew wrote: »

Ditto the costs of servicing/replacement for gas boilers. Although you might note in post #121 above that someone who installs ASHPs states that they need 6 monthly servicing by a qualified engineer.

My current understanding is that the servicing could be carried out DIY if one was fit, capable and wished to. Installing outdoor unit at ground level would remove the danger of working at height. This would reduce the cost and indeed the tax burden on the homeowners who chose that route.
This isn't a realistic possibility with gas boilers.

TBH I think we're largely in agreement, with regard to Heat pumps at least!

richardc1983

I clean the coils myself, I use a foam which expands and pulls the dirt out of the coil ready to be flushed away with clean water.

Any other servicing is pretty much at my own discrection and would be really for a trained person to come out and check everything over in the outdoor unit

I clean the filters once a month depending on how much the units have been on.

THe outdoor unit is also at ground level so easy to get to, any higher and would not feel comfortable doing it.

Cardew

Hermann wrote: »

My current understanding is that the servicing could be carried out DIY if one was fit, capable and wished to. Installing outdoor unit at ground level would remove the danger of working at height. This would reduce the cost and indeed the tax burden on the homeowners who chose that route.
This isn't a realistic possibility with gas boilers.

TBH I think we're largely in agreement, with regard to Heat pumps at least!

I suspect you are correct about DIY servicing, although the input in post #121 contradicts that view.

The cynic in me suggests that the warrany will be invalid unless it is serviced by a 'qualified' [STRIKE]cleaner[/STRIKE]engineer.

What other reason can we think of? I know, you could damage a refrigerant pipe and release the gas - thus causing global warming on a massive scale;)

However as I have posted previously, IMO the servicing of most gas boilers is a simple DIY job - cleaning in the main. However the 'Safety Card' is played and we have to pay silly sums for a qualified Corgi man to clean.

thechippy

Cardew wrote: »

I suspect you are correct about DIY servicing, although the input in post #121 contradicts that view.

The cynic in me suggests that the warrany will be invalid unless it is serviced by a 'qualified' [strike]cleaner[/strike]engineer.

What other reason can we think of? I know, you could damage a refrigerant pipe and release the gas - thus causing global warming on a massive scale;)

However as I have posted previously, IMO the servicing of most gas boilers is a simple DIY job - cleaning in the main. However the 'Safety Card' is played and we have to pay silly sums for a qualified Corgi man to clean.

Hmmm……

Yes, the manufacturers do indeed have the right to void the warranty unless it can be shown that the equipment has been serviced by a suitably qualified engineer, and rightly so!

Would they honour a warranty on your new car if it was serviced by John Smith next door who knows a “bit” about cars??

The good quality condenser cleaners are caustic, not only that, you can’t just spray the stuff through the condenser willy nilly! There are delicate electronic components nearby, not to mention the condenser fan motor right behind the condenser. All can be easily damaged.

The engineer will also leak test the system and take temperature measurements. The measurements will be used alongside a comparitor to ensure the condenser is clean internally. Just because it “looks” clean - it doesn’t mean it is! This is the most crucial part of the system to keep thoroughly clean, unless you want a lack of performance, increase in running costs and burnt out compressors.
A decent engineer will also check the system for any fault codes that have arisen and take the appropriate action, or advise the client.

I won’t comment about CORGI, but I certainly don’t “play the card” - I treat clients how I expect to be treated myself!

Cardew

thechippy wrote: »

Hmmm……

Yes, the manufacturers do indeed have the right to void the warranty unless it can be shown that the equipment has been serviced by a suitably qualified engineer, and rightly so!

You quoted 6 monthly inspections at £40 each.

Well in most places I doubt if you will ever get anyone to service anything for under £60 - so add a mandatory £120 to your annual bill!!!