Air Source Heat Pumps Do Not Work

[Thedreamer]

7 minutes ago, SteamyTea said:

The efficiency is not set by the type of building, it is set by the load cycle.

So the question is wrong really.

 

 

I am interested in the financial efficiency? 

 

10 minutes ago, ProDave said:

Ours runs about 6 months of the year, October to March usually.  Annual heating cost about £250

 

Is that £250 for just heating and not including any contribution from your panels? That's still £40 a month for the six months.

 

My build is not to the levels of most on here, but the temperature has not gone below 18, usually around 20.

 

If I had installed a external air source heat pump I would not being using it now in November.

[SteamyTea]

2 minutes ago, Thedreamer said:

I am interested in the financial efficiency? 

This is a very hard one to generalise.

Mainly because houses are different, and the occupants live differently.

It does not change the underlying physics.

Another problem is 'what does a heat pump cost'.  Some people play top dollar, others buy off eBay.

[Thedreamer]

As well as the financial efficiency. 

 

I am also not sold on how they perform.

 

Even now, in the recent current topics here, two topics are concerning problems relating to pumps.

 

 

[Thedreamer]

5 minutes ago, SteamyTea said:

This is a very hard one to generalise.

Mainly because houses are different, and the occupants live differently.

It does not change the underlying physics.

Another problem is 'what does a heat pump cost'.  Some people play top dollar, others buy off eBay.

 

But what would be the all in average installation cost for a unit installed by a plumber/engineer?

[ProDave]

13 minutes ago, Thedreamer said:

 

Is that £250 for just heating and not including any contribution from your panels? That's still £40 a month for the six months.

 

My build is not to the levels of most on here, but the temperature has not gone below 18, usually around 20.

 

If I had installed a external air source heat pump I would not being using it now in November.

That is just the metered electricity to power the heat pump in heating mode.

 

I actually generate more with my solar PV in a year than I use heating the house, but of course it does not generate enough in the winter.

 

I am genuinely surprised if you can maintain 18 degrees inside with no heating?  How are you heating your house?  the average outside temperature here is presently about 6 degrees. There is no way it would be comfortable with no heating.

 

 

[SteamyTea]

1 minute ago, Thedreamer said:

I am also not sold on how they perform.

 

Even now, in the recent current topics here, two topics are concerning problems relating to pumps.

This is really what this thread is about.

I say that correctly designed systems work perfectly fine.  Badly designed systems will not work as expected.

There is also a slight difference in how they are opperated.

In the past we had basic boilers and controlled the output with a combination of on/off temperature control, and a timer.  This was because 'gas was expensive' in the days of town gas.

Natural or North Sea gas changed this, and technology/legislation moved on, so now we have quite sophisticated modulating and condensing gas boilers, with temperature control in each room.  Coupled to that the controllers can also adjust each room to have a different temperature, at different times, and different days of the week.  This can also be done without machine learning, saves RTFM.

But at the heart of any heating system is a machine that raises temperature and transfers it to a transfer medium, usually water.  This is what the sizing is so important, and like cars, you cannot always gauge the performance on engine power alone.  My bosses car is about the same power as mine, but faster.  How can that be.  Well it is three quarters of the mass, has a lower drag coefficient, and is petrol.

But my car does more miles to the gallon (not the best way to work out efficiency, should really be kJ/km), is quieter and more comfortable.

And cheaper. 

[Thedreamer]

1 minute ago, ProDave said:

That is just the metered electricity to power the heat pump in heating mode.

 

I actually generate more with my solar PV in a year than I use heating the house, but of course it does not generate enough in the winter.

 

I am genuinely surprised if you can maintain 18 degrees inside with no heating?  How are you heating your house?  the average outside temperature here is presently about 6 degrees. There is no way it would be comfortable with no heating.

 

 

 

I burn a small trug of logs from about 6pm to 10pm. Once the temperature gets to 23c in the house I stop and then it usually 21c in the morning, it might drop to 20c before we start the cycle again.

 

That then heats the house.

 

The stove in the morning is cold but the blocks around the stove are still warm.

 

The beauty with the stove is that it's uncomplicated technology. One sweep a year and it's sorted.

 

As I mentioned before I do have a small heat pump for the hot water doing a family four. 

 

The total electricity is currently still 10kw a day.

 

 

[ProDave]

1 minute ago, Thedreamer said:

 

 

I burn a small trug of logs from about 6pm to 10pm. Once the temperature gets to 23c in the house I stop and then it usually 21c in the morning, it might drop to 20c before we start the cycle again.

 

That then heats the house.

 

The stove in the morning is cold but the blocks around the stove are still warm.

 

The beauty with the stove is that it's uncomplicated technology. One sweep a year and it's sorted.

 

As I mentioned before I do have a small heat pump for the hot water doing a family four. 

 

The total electricity is currently still 10kw a day.

 

 

Ah yes, if I lit the stove every day I would not need the heat pump.

[SteamyTea]

12 minutes ago, Thedreamer said:

But what would be the all in average installation cost for a unit installed by a plumber/engineer?

Can't really be answered.

Like saying what is an average house, 60, 120, 180 m², 1, 2, 3, 4, 5 bedrooms, 1, 2 3 bathrooms, but only one actual bath.

 

Really comes down to discarding the cost of the common components i.e. cylinders, radiators, UFH pipe, then comparing gas, oil, and ASHP units that, and this is important, deliver the correct output.  That rated output may be different for the different technologies.

[SteamyTea]

8 minutes ago, Thedreamer said:

I burn a small trug of logs

Out of interest, could you weigh the logs you burn in a typical day, then we can work out the energy that is used.

Edited November 4, 2020 by SteamyTea

[Thedreamer]

5 minutes ago, SteamyTea said:

This is really what this thread is about.

I say that correctly designed systems work perfectly fine.  Badly designed systems will not work as expected.

There is also a slight difference in how they are opperated.

In the past we had basic boilers and controlled the output with a combination of on/off temperature control, and a timer.  This was because 'gas was expensive' in the days of town gas.

Natural or North Sea gas changed this, and technology/legislation moved on, so now we have quite sophisticated modulating and condensing gas boilers, with temperature control in each room.  Coupled to that the controllers can also adjust each room to have a different temperature, at different times, and different days of the week.  This can also be done without machine learning, saves RTFM.

But at the heart of any heating system is a machine that raises temperature and transfers it to a transfer medium, usually water.  This is what the sizing is so important, and like cars, you cannot always gauge the performance on engine power alone.  My bosses car is about the same power as mine, but faster.  How can that be.  Well it is three quarters of the mass, has a lower drag coefficient, and is petrol.

But my car does more miles to the gallon (not the best way to work out efficiency, should really be kJ/km), is quieter and more comfortable.

And cheaper. 

 

Most of the folks on here have a good skills, able to wire up panels or install heats pumps etc. I wish I could do this, but I have a lot to learn.

 

But I reckon most of the population can't do the installation,  the technology or maintain the unit.

 

As I am getting the older the more I realise that technology like heat pumps/underfloor heating are great but are more complicated then a gas boiler.

 

Just now, ProDave said:

Ah yes, if I lit the stove every day I would not need the heat pump.

 

Why not? Does it come down to just the cutting, splitting logs etc? 

 

I spend a hour splitting logs on Saturday and that's my heating sort the week. 

 

I enjoy having that control.

[Thedreamer]

7 minutes ago, SteamyTea said:

Can't really be answered.

Like saying what is an average house, 60, 120, 180 m², 1, 2, 3, 4, 5 bedrooms, 1, 2 3 bathrooms, but only one actual bath.

 

Really comes down to discarding the cost of the common components i.e. cylinders, radiators, UFH pipe, then comparing gas, oil, and ASHP units that, and this is important, deliver the correct output.  That rated output may be different for the different technologies.

 

We are 140 m2 and have three bedrooms, bathroom and ensuite.

 

Would I be looking at £5k, £7.5K or more?

[Thedreamer]

5 minutes ago, SteamyTea said:

Out of interest, could you weigh the logs you burn in a typical day, then we can work out the energy that is used.

 

The weight might not be the best way to measure a trug of logs.

 

As I could be attempting to burn wet heavy wood.

 

The wood we burn is well seasoned and measured with a moisture meter, so tends to be quite light and provides an efficient burn. It tends to be spruce at the moment, so not a hardwood but it's free.

 

 

 

 

[Temp]

40 minutes ago, Thedreamer said:

 

I am interested in the financial efficiency? 

 

See the table column "Pence per kWh (after boiler efficiency)".

 

https://nottenergy.com/resources/energy-cost-comparison/

 

They still reckon oil or gas is cheaper than an ASHP but its possible to argue with their figures. How much do you pay for electricity? They assume 19.4p/kwh.

 

[ProDave]

19 minutes ago, Thedreamer said:

Why not? Does it come down to just the cutting, splitting logs etc? 

 

I spend a hour splitting logs on Saturday and that's my heating sort the week. 

 

I enjoy having that control.

I am not self sufficient in wood, I have to scavenge and collect a lot of it.  The cold winter we were in the static caravan we had a stove in that and it hardly went out from November to March.  Keeping it fed with wood was a challenge and we burned coal over night.  But it is nice to have the stove knowing each time I light it, that's less electricity the HP will use.

[Thedreamer]

3 minutes ago, Temp said:

 

See the table column "Pence per kWh (after boiler efficiency)".

 

https://nottenergy.com/resources/energy-cost-comparison/

 

They still reckon oil or gas is cheaper than an ASHP but its possible to argue with their figures. How much do you pay for electricity? They assume 19.4p/kwh.

 

 

I'm on bulb, I think around 15 to 16p kwh, it went up slightly a month ago.

[SteamyTea]

1 hour ago, Thedreamer said:

The weight might not be the best way to measure a trug of logs.

I is easier than working out the volume.

Timber has a specific energy of ~4.5 kWh/kg.

Another thing worth looking at is the number of rings showing on logs, that gives a good indication how long it takes to replenish that resource, quite frightening that you can burn a ten year old log in a few minutes.

But that is another topic.

1 hour ago, Thedreamer said:

We are 140 m2 and have three bedrooms, bathroom and ensuite.

 

Would I be looking at £5k, £7.5K or more?

Without knowing the heat losses of the building, it is hard to work out the cot of any type of heating system.

You can do a simplified calculation by working out the U-Value and areas of all the exposed components, then find some local weather data, that will give a fairly good estimate of what is needed.  Then you can look at different technologies and how they compare on capital and running costs.

 

1 hour ago, Thedreamer said:

As I am getting the older the more I realise that technology like heat pumps/underfloor heating are great but are more complicated then a gas boiler.

Which do you think is more complicated, your gas oven or your fridge?

Heat pumps are really very basic and have been around, unchanged, for about 50 years (the first heat pump was about 1940).

The only major change is the transition from reciprocating 'piston' compressors to rotary 'scroll' compressors.  Though is some CO₂ HPs they are going back to reciprocating pumps.

The reason for this is that even the 'best' R32 refrigerant gas is still several hundred times worse that CO₂. This is legislation driven, not a technology change as such.  Heat pumps can use tap water as the refrigerant, but as water is 'the universal solvent' it does not have the longevity desired, though the performance is very good.

 

1 hour ago, Temp said:

See the table column "Pence per kWh (after boiler efficiency)".

While a useful basic comparison of technologies, the running costs can vary way too much in individual households i.e. the standard deviation is very great.

When looking at the technology side, it is easy to get side tracked by the fuel costs.  These vary, and vary greatly around the world.  Japan, which has no naturally occurring coal, oil or gas, uses heat pumps.  Russia has about 150 year worth of natural gas at current consumption rates, so uses basic technology and they control temperature by opening windows.

The running costs do not change the efficiency of a system and can very easily be a distraction when trying to work out the best there is.

[Oz07]

Gas is just a lot more straightforward for Neanderthals like me 

[SteamyTea]

1 hour ago, Oz07 said:

Gas is just a lot more straightforward for Neanderthals like me 

In what way, operation, design, installation, maintenance?

[Hobbiniho]

I had a ASHP installed in my house replacing storage heaters. my house is 85m2 and i have a 7kw panasonic heatpump feeding 2 air rads downstairs (living room, kitchen) and conventional rads upstairs (3 bedroom's) and in the lean too extension at the back ( utility, master bedroom*) these conventional rads are controlled by TRV'S.

 

My system was designed by someone who has a lot of experience in doing so, i provided him with the information he required to work out the heat loss, this included plans showing the size of rooms as well as the wall make up, floor make up roof make up and what insulation installed as well as size of windows and size of double glazing as well as how "draughty" i felt the house was, i also inputed all the info into jsharris spreadsheet and the figures that i got were almost exactly what the same as he had come up with.

 

I had the option of going for a complex "smart" control system with different zones etc but decided that as downstairs was open plan that it was pretty much pointless it was decided that a simple cheap "clicky" rotart thermostat at the top of the stairs was all that was needed to control the heat downstairs, with the TRV'S taking care of the bedrooms, in hindsight this would have been better being downstairs somewhere as there is about a 1.5degree difference between what the thermostat says and the downstairs temp, i originally had the heatpump set in "weather compensating" mode but found that it was coming on hard and fast which effected the COP i changed this to "direct" at 38degrees and it seems to work well.

 

I think that as has been said there is no one fits all aproach and every house is different and everyones level of comfort is different and the way everyone expects the heating to function is different, i personally heat my house to 18/19 degrees and my heating system copes fine, it may not be able to cope with someone who likes there house heated to 28 degrees, but this should be factored in at the design stage, if you have an old house that you are retro fitting with an ASHP you really need a well thought out system that is designed by someone who has the necessary experience.

[ToughButterCup]

18 hours ago, SteamyTea said:

....

And could everyone stop getting temperature, energy and power confused, they are different thing.

 

If we wanted to follow your advice,  could you please recommend an online resource that would help us read up for ourselves? Thanks .

 

Or maybe a brief explanation from you...?

[joe90]

As said above. ASHP,s are basic technology (fridge) it’s the operating systems that get complicated. Someone on this forum was clever enough to design a control system that even predicted the weather to control his system!. He removed it after a while and had one simple room stat and it worked well (as does mine).

[SteamyTea]

21 minutes ago, ToughButterCup said:

Or maybe a brief explanation from you

Energy is the ability to do work.  It can take one of two forms.  Potential or kinetic. Those words just mean stored or moving. The unit of energy is the joule [J] and the definition of that, in SI units is kg.m-².s-².

 

Power is the actual work done, and is the rate that the energy is being used.  The unit is the watt [W] kg.m^-2.s^-3 or is simpler English, a joule per second j/s.

 

Temperature is a relative value with the 0 point set where there is no kinetic movement within an atom.  This is known as 'absolute zero'. Temperature can be thought of as how fast atoms are allowed to move when unimpeded.  The hotter they are, the faster they can move.

 

So taking a very simple example, if you have a box with sided each 1 metre long, with lots of smaller cubes in it, 1000 of them, that have a mass of 1 kg each, and you move each smaller cube out of the box and place then on a table 1 metre away, if you disregard friction and gravity, for each mass you move you have used a J of energy.  The temperature of the masses has not changed (though the person, or machine doing the work will get warmer.

Now if you move each mass at a rate of 1 a second, the power you are moving those masses is 1 W.

It will take 1000 seconds to empty the large box and 1 kJ of energy will have been used.

 

For some reason we do not use joule as a unit of energy, we use the kilowatt hour.  But that can be easily broken down in derived SI units. kilo = 1000, W = J/s and hour is 3600 seconds.

 

Writing out in long hand.

 

1000 x  1J.s^-1 x 3600s = 0.00027777777777778 kWh.

[ToughButterCup]

Thank you very much indeed @SteamyTea

[SteamyTea]

23 minutes ago, ToughButterCup said:

Thank you very much indeed

If only this forum had a way to easily direct people to decent static resources.

 

There is a second part to the whole energy, power and temperature bit that is more relevant to heat pumps and that is phase change materials.

This is how heat pumps work efficiently, but also gives that looks like a deficiency.

 

As the gas used in the units has a fixed temperature, like all gases, at phase change, this puts an upper limit on how high it can raise the temperature, off say, water.

The gasses are chosen to be as high as possible, without causing other problems i.e. extremely high, or low pressure, too large a difference in temperature between liquid and gas states, power need to change the state via the compressor etc, and other things like the need to lubricate moving parts, not so cold that they instantaneously free the moisture out of the air.

 

It is the differences in specific energy capacity, and reversibility, of gasses and liquids that allow heat pumps to run with high efficient.

 

Oddly, combustion can also be thought of as a phase change, from gas to plasma and back to a gas, but not the same gas, it is not easily reversible though, and this causes pollution problems.  The efficiency cannot be as high as a heat pump, ever.