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The cost of using heat pumps.


studiot
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On 3/3/2021 at 12:42 AM, studiot said:

For the first 3 years the combined electricity and gas costs were lower with the heat pump. This year has been the first with the pump markedly more expensive.

@Danijel Gorupec

Up to 2016 the principal consumer in the house was the gas boiler, but we also have a gas hob.
Now the heat pump is the principal energy consumer and I only need about 10 cubic feet of gas a year.

It is actually rather galling to receive a gas bill bot £1.50 worth of gas plus £28.50 worth of standing charge.
 

 

studiot, Before I approach your thoughts I should state that I am currently installing major heat pump installations in a large Hospital in Brisbane as part of a project that is removing an old coal burning system. As I have said here on other occasions I am not a scientist (though I have returned to study science at Uni) but do deal with engineering, installation and commissioning loosely in air-conditioning and building services - the technology side of construction, if you will.

I would agree that an air-cooled heat pump may not match a gas boiler in the residential environment.  Also that the tech data published regarding "efficiencies" of heat pumps is used to suggest otherwise. Even engineers get confused on that. But it's like using a truck as a taxi, it's just not where the device is strong.

Any refrigerant cycle will produce heat on one side and cold on the other. If you only harness one side you've missed half the benefit. Quite literally. Worse - in most air-conditioning systems that unused heat needs an additional heat rejection system which costs additional energy. If you have a need for cooling and heating, at the same time, NOTHING will match the efficiency of a heat pump. If you don't, then more investigation is required before you commit if you want the optimum solution.

We've had to be creative in the hospital with dispersed plant rooms, having to tap in to the existing systems that are available as we spread from one end of the campus to the other. And we are competing with a very efficient centralised coal burning steam system. Tough gig to match that let alone beat it. In part it works like this:

The huge coal burning boiler (which run a large steam system) are to be decommissioned. The coal burner, which all things being equal will not be beaten on efficiency by anything, will be replaced by smaller dispersed gas or electric fired steam generators.  Coal is better than, gas, which is better than electric. <Don't trust those words, do the engineering, but mostly it is adequate as a generalisation>But all things are not equal. Overall capacity is reduced by a combination of thermal heat pumps (driving air-conditioning) and potable hot water heat pumps. And where we had to, we use residential style electric Hot Water Units just to get load down to make the rest of the system work. It's a negative on efficiency but against the full system one we could cope with. There is the obligatory and pointless but visible PV system thrown in - a green sticker slapped on the building as these days to be virtuous must be signalled to the world. They have their place (I have them at home) but this is not really it.

The thermal heat pumps, on the hot side, feed thermal or potable hot water. On the cold side they feed whatever we could find - chilled water (on the return leg hence "pre-conditioning" the return water before it gets to the chillers); - condensate water (on the flow side giving additional cooling to equipment that needs it).

It would have been pointless to install heat pumps that simply wasted the cold generated.

On a personal basis I am now investigating heat pumps at home for pool heating combined with air-conditioning. It's problematic as we don't necessarily need to heat the pool in summer, when the air-conditioning is running. But I'm working on it. The trick on this one will be performance on "the shoulders", ie not either peak summer or winter but the messy bits between where the engineering is more tricky and much more experience is required.

Your experience with efficiency measured as operational cost (and that is actually a very good indicator) comparing a heat pump (where half of the benefit simply goes to waste) compared with a gas boiler does not surprise me in the slightest. Your maintenance cost will increase as well, by the way.

But it is wrong to call these systems twaddle. 

 

PS At home my hot water is an instantaneous gas system. I'd consider solar but there is not enough roof real estate once the extensive PV system was installed, it's a three phase system to cope with air-conditioning and pool pumping. It's working fabulously well. And I like my gas hot water.

Edited by druS
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35 minutes ago, druS said:

 

 

studiot, Before I approach your thoughts I should state that I am currently installing major heat pump installations in a large Hospital in Brisbane as part of a project that is removing an old coal burning system. As I have said here on other occasions I am not a scientist (though I have returned to study science at Uni) but do deal with engineering, installation and commissioning loosely in air-conditioning and building services - the technology side of construction, if you will.

I would agree that an air-cooled heat pump may not match a gas boiler in the residential environment.  Also that the tech data published regarding "efficiencies" of heat pumps is used to suggest otherwise. Even engineers get confused on that. But it's like using a truck as a taxi, it's just not where the device is strong.

Any refrigerant cycle will produce heat on one side and cold on the other. If you only harness one side you've missed half the benefit. Quite literally. Worse - in most air-conditioning systems that unused heat needs an additional heat rejection system which costs additional energy. If you have a need for cooling and heating, at the same time, NOTHING will match the efficiency of a heat pump. If you don't, then more investigation is required before you commit if you want the optimum solution.

We've had to be creative in the hospital with dispersed plant rooms, having to tap in to the existing systems that are available as we spread from one end of the campus to the other. And we are competing with a very efficient centralised coal burning steam system. Tough gig to match that let alone beat it. In part it works like this:

The huge coal burning boiler (which run a large steam system) are to be decommissioned. The coal burner, which all things being equal will not be beaten on efficiency by anything, will be replaced by smaller dispersed gas or electric fired steam generators.  Coal is better than, gas, which is better than electric. <Don't trust those words, do the engineering, but mostly it is adequate as a generalisation>But all things are not equal. Overall capacity is reduced by a combination of thermal heat pumps (driving air-conditioning) and potable hot water heat pumps. And where we had to, we use residential style electric Hot Water Units just to get load down to make the rest of the system work. It's a negative on efficiency but against the full system one we could cope with. There is the obligatory and pointless but visible PV system thrown in - a green sticker slapped on the building as these days to be virtuous must be signalled to the world. They have their place (I have them at home) but this is not really it.

The thermal heat pumps, on the hot side, feed thermal or potable hot water. On the cold side they feed whatever we could find - chilled water (on the return leg hence "pre-conditioning" the return water before it gets to the chillers); - condensate water (on the flow side giving additional cooling to equipment that needs it).

It would have been pointless to install heat pumps that simply wasted the cold generated.

On a personal basis I am now investigating heat pumps at home for pool heating combined with air-conditioning. It's problematic as we don't necessarily need to heat the pool in summer, when the air-conditioning is running. But I'm working on it. The trick on this one will be performance on "the shoulders", ie not either peak summer or winter but the messy bits between where the engineering is more tricky and much more experience is required.

Your experience with efficiency measured as operational cost (and that is actually a very good indicator) comparing a heat pump (where half of the benefit simply goes to waste) compared with a gas boiler does not surprise me in the slightest. Your maintenance cost will increase as well, by the way.

But it is wrong to call these systems twaddle. 

 

PS At home my hot water is an instantaneous gas system. I'd consider solar but there is not enough roof real estate once the extensive PV system was installed, it's a three phase system to cope with air-conditioning and pool pumping. It's working fabulously well. And I like my gas hot water.

 

Thank you for observing the purpose of this thread which was to relate exchange exeriences involving heat pumps, for the benefit of all.

A very interesting contribution, probably more in line with the commercial calculations I posted in the previous post.

+1

 

I'm gald you have a good experience of instantaneous gas water heaters.
Mine was nothing but trouble from installation in 1989 to replacement in 2016 and never met its advertised specifications.

A few minor corrections to your post are in order however.

Firstly I did not call the systms twaddle.
I said that a lot of twaddle is being talked about them  -  I might have added "In order to sell them like a car salesman promised the Sun the Moon and The Stars".

Secondly my experience of maintenance is that heat pump maintenance is far cheaper than hi tech domestic gas boilers.
Since heat pumps are actually also somewhat hi tech there are old fashioned systems lo tech gas systems, such as I enjoyed in my previous house, that were indeed cheaper to maintain. Sadly our glorious government had chosen to declare these illegal, in preference to highly flammable building cladding, leading to significant loss of life and untold misery in the UK.

 

A couple of points perhaps not made explicitly before.

My heat pump system suffers from the same difficulty experience by the previous instantaneous gas boiler.

It cannot provide both domestic hot water and central heating at the same time.

Also in the UK domestic situation there is no use for the 'cooling output' as you put it.
I can well see a use in Brisbane, where there is a much warmer climate.

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31 minutes ago, studiot said:

 

Thank you for observing the purpose of this thread which was to relate exchange exeriences involving heat pumps, for the benefit of all.

A very interesting contribution, probably more in line with the commercial calculations I posted in the previous post.

+1

 

I'm gald you have a good experience of instantaneous gas water heaters.
Mine was nothing but trouble from installation in 1989 to replacement in 2016 and never met its advertised specifications.

A few minor corrections to your post are in order however.

Firstly I did not call the systms twaddle.
I said that a lot of twaddle is being talked about them  -  I might have added "In order to sell them like a car salesman promised the Sun the Moon and The Stars".

Secondly my experience of maintenance is that heat pump maintenance is far cheaper than hi tech domestic gas boilers.
Since heat pumps are actually also somewhat hi tech there are old fashioned systems lo tech gas systems, such as I enjoyed in my previous house, that were indeed cheaper to maintain. Sadly our glorious government had chosen to declare these illegal, in preference to highly flammable building cladding, leading to significant loss of life and untold misery in the UK.

 

A couple of points perhaps not made explicitly before.

My heat pump system suffers from the same difficulty experience by the previous instantaneous gas boiler.

It cannot provide both domestic hot water and central heating at the same time.

Also in the UK domestic situation there is no use for the 'cooling output' as you put it.
I can well see a use in Brisbane, where there is a much warmer climate.

 Hey studiot.

Not managing both hot water and heating suggests a capacity issue. Or it could be overcome (or at least ameliorated) with the additional of thermal storage.

Yes it's rare to need cooling in residential in the UK. It's why I never installed a condensing boiler at home when I lived there. Gas fired boilers have been declared a risk, wow. Does that extend to other firing systems and other fuels? Geez there would be a lot of country houses regretting loosing the Aga.

Commercial is a different matter and I was comfortably able to apply my trade in England for 10 years before returning home to Aus.

To be honest, in the hospital Environment I was talking about earlier, I'm surprised at the campus use of steam. Seems excessive. They do need it for sterilisation but that is nominal load at best. I wouldn't have expected potable hot water to justify the installation and steam to the air handlers 24/7/365 suggests other problems in the plant operation. Buildings in Brisbane do not usually require that much heat. Possibly for dehumidification which is required to operating theatres - again nominal load.

Back to the thread - I would always question heat pumps unless there was a requirement for both heat and cooling. Gas burners are wonderfully efficient, even if they are demonised on the basis of carbon these days.

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12 minutes ago, druS said:

Gas fired boilers have been declared a risk, wow. Does that extend to other firing systems and other fuels? Geez there would be a lot of country houses regretting loosing the Aga.

No I didn't say they were a risk.

I said the government chose to ban baxi bermuda style back boilers as 'inefficient'. And yes they are planning to ban the AGA and gas boilers in new build properties.

I also said that the inflammable cladding that they did not ban, led to major tragedy.

12 minutes ago, druS said:

Not managing both hot water and heating suggests a capacity issue. Or it could be overcome (or at least ameliorated) with the additional of thermal storage.

Or alternatively control issues.

And yes the salesmen of this world claim that storage cures all known ills.

But the reality is rather different.

We can discuss this at length for the benfit of others if you like.

 

13 minutes ago, druS said:

Gas burners are wonderfully efficient

 

As a member of 'the trade', surely you realise that all gas burners are less than 100% efficient in that you receive less than 100% of the combustion heat.

However heat pumps deliver heat out using work in and can deliver well over 100% ( up to 400% depending upon conditions) heat out equivalent using the work in as the  base.

 

Edited by studiot
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1 hour ago, studiot said:

As a member of 'the trade', surely you realise that all gas burners are less than 100% efficient in that you receive less than 100% of the combustion heat.

However heat pumps deliver heat out using work in and can deliver well over 100% ( up to 400% depending upon conditions) heat out equivalent using the work in as the  base.

 

 

Yes - relates to how "efficiency" is measured on a scientific basis which does provide useful comparators and necessary for engineering. It's also what I was referring to when data is quoted for sales purposes. It's bit like COP (coefficient of performance) figures quoted for equipment. It's not the specific equipment data that determines efficiency but the entire system/plantroom along with the way the equipment is harnessed in installation, commissioning and operation. So my use of the word "efficiency" there would be technically incorrect. But those efficiency figures are not, I think, the full story when you are considering things. I would use efficiency figures comparing two heat pumps, or two burners. But I would add other measures when comparing across different systems. 

As I said, I think your measurement of energy usage in operation is a very good indicator for this. It works just as well in commercial as residential or any other environment.

Amazed that the Aga is outlawed - there will be plenty of people unhappy about that.

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It's obvious really that if you are running air conditioning in a very hot country, then a heat pump will give you some free hot water in the process. But you have to store it, as has been said. And you are getting it at a time of year that it's of least use. Even here in England, I find myself showering in water that's almost mains temperature, just to cool off in summer.

That's the trouble with air source in a nutshell. It's at it's most efficient at exactly the hottest time of year. And struggles at the coldest times when you really need it most. If you could find a way to reverse that, you would be able to outspend Bill Gates. 

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On 11/28/2021 at 1:45 AM, druS said:

Amazed that the Aga is outlawed - there will be plenty of people unhappy about that.

Actually I was a bit overdramatic there because you can still install an electric AGA, its just the gas ones at the moment.

Interestingly folks come from all over the world (even Oz) to visit the splendid country kitchen showrooms near me.

You can see not only AGA, but many other European and American manufacturers rages there.

Some of these are absolutely enormous.

We sometimes take our visitors there as it provides a good half day out.

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You can still buy AGAs that run on oil, gas and dual fuel, as well as electric. It's wood burners that have some restictions these days. AGAs don't burn wood or coal any more, but they make the Rayburn Range as well, and these can still burn wood and coal. The restrictions are on the sale of the fuel. "Wet wood" sales are to be restricted to larger volumes, with advice on how to dry it. Coal in bags will be banned, but loose coal still allowed. 

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6 minutes ago, mistermack said:

You can still buy AGAs that run on oil, gas and dual fuel, as well as electric. It's wood burners that have some restictions these days. AGAs don't burn wood or coal any more, but they make the Rayburn Range as well, and these can still burn wood and coal. The restrictions are on the sale of the fuel. "Wet wood" sales are to be restricted to larger volumes, with advice on how to dry it. Coal in bags will be banned, but loose coal still allowed. 

 

On 11/28/2021 at 12:30 AM, studiot said:

And yes they are planning to ban the AGA and gas boilers in new build properties.

 

I am using the AGA, as I think druS did, to represent cast iron ranges which often had/have a domestic hot water capacity as well, not to represent any particular brand.

 

I should perhaps take this opportunity to note that building owners in the UK,  have a statutory duty to inform Building Control if they change the form of heating (water and I think space) in their property.

I had to do this when I changed from oil to gas and again from gas to an electrically driven heat pump.

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I tried to do a calculation of what I suggested earlier, storing solar heated water in the summer, and chilled water in the winter, for use with a heat pump. 

The resulting volume of water needed to store all the heat needed for an average house came out rather bigger than I thought, a 20ft cube. (Although my maths is probably way out). That's assuming that you raise the temp of the water by 50 deg c.  

You would need a fair bit of land to build that, but actually a ground source heat pump needs a similar area. Dunno about the cost. It's about the size of a small swimming pool, but it wouldn't need all of the fancy finishing so it might be a lot cheaper. I think it would deifinitely be viable for two or three houses sharing one tank, because to double or treble the volume doesn't actually increase the dimensions by much. 

18,000 kwh for average annual house heating 

one watt = 1 joule per second 
= 3,600 joules per hour 
1 kw = 3,600,000 joules per hour 
1kwhr = 3,600,000 joules 
1 joule = 1/3,600,000 kwh 
18,000 kwh = 18,000 x 3,600,000 joules 

 
The specific heat capacity of water is 4,200 Joules per kilogram per degree Celsius (J/kg°C). This means that it takes 4,200 J to raise the temperature of 1 kg of water by 1°C 
So it takes 4,200/3,600,000 kwh for 1kg by 1°C or 0.0011666666666667 kwh.
Or 1.1666666666667 kwh per metric ton
Or 11.6666666667 kwh per metric ton for 10°C  
So 1/11.6666667 x 18,000 tons for annual house heating = 1,543 tons
So needs 1,543 cu metres of water. Or 11.5m cube 
For 20°C 771.5 cu metres or about 9.2m cube 
For 50°C 308.6 cu metres or about 6.7 m cube or 20 feet approx.

It's probably wrong, maths is my pet hate.      

 

 

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1 hour ago, mistermack said:

I tried to do a calculation of what I suggested earlier, storing solar heated water in the summer, and chilled water in the winter, for use with a heat pump. 

The resulting volume of water needed to store all the heat needed for an average house came out rather bigger than I thought, a 20ft cube. (Although my maths is probably way out). That's assuming that you raise the temp of the water by 50 deg c.  

You would need a fair bit of land to build that, but actually a ground source heat pump needs a similar area. Dunno about the cost. It's about the size of a small swimming pool, but it wouldn't need all of the fancy finishing so it might be a lot cheaper. I think it would deifinitely be viable for two or three houses sharing one tank, because to double or treble the volume doesn't actually increase the dimensions by much. 

18,000 kwh for average annual house heating 

one watt = 1 joule per second 
= 3,600 joules per hour 
1 kw = 3,600,000 joules per hour 
1kwhr = 3,600,000 joules 
1 joule = 1/3,600,000 kwh 
18,000 kwh = 18,000 x 3,600,000 joules 

 
The specific heat capacity of water is 4,200 Joules per kilogram per degree Celsius (J/kg°C). This means that it takes 4,200 J to raise the temperature of 1 kg of water by 1°C 
So it takes 4,200/3,600,000 kwh for 1kg by 1°C or 0.0011666666666667 kwh.
Or 1.1666666666667 kwh per metric ton
Or 11.6666666667 kwh per metric ton for 10°C  
So 1/11.6666667 x 18,000 tons for annual house heating = 1,543 tons
So needs 1,543 cu metres of water. Or 11.5m cube 
For 20°C 771.5 cu metres or about 9.2m cube 
For 50°C 308.6 cu metres or about 6.7 m cube or 20 feet approx.

It's probably wrong, maths is my pet hate.      

 

 

 

I haven't checked the arithmetic but some practical comments may be in order.

1 How would you heat the water ?

2) How would you extract the energy from your supertank ?
Assuming 50oC, as soon as you had extracted half the energy the tank water would be down to 25oC.
If you simply ran water from than tank through a domestic radiator system the system would cease to heat the house at about this point.
Radiators at 25oC are of little use.

3) Very large houses for very rich people in the past had 'ice houses' capable of preserving winter ice during the summer heat against a temperature differential of perhaps 30oC.
With modern insulation we could perhaps contemplate the larger differential, but it would still ad considerable bulk to any installation.
Not a prospect available to most.

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45 minutes ago, studiot said:

1 How would you heat the water ?

2 How would you extract the energy from your supertank ?

3) Not a prospect available to most.

1) Solar thermal collectors to heat the water during summer.

2) Direct to radiators when hot enough, then heat pump when needed. If you could heat the water 50 deg over ambient, it would need very little electricity, even when it had cooled quite a bit. 

3) For one tank feeding three houses, it could be very cost-efficient I think. To increase the volume by a factor of five, you would only need to go from a 6.7 metre cube to an 11.5 m cube. With all the economies of scale to go with it. With the promise of very low bills over fifty years or more, it could pay off. 

 

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