Heat Pumps, the great deception?

[Cornish Ian]

https://www.vaillant.co.uk/downloads/aproducts/renewables-1/flexotherm/flexotherm-230-v-tech-spec-1-2-web-1057063.pdf

This is a data sheet for a valiant set of heat pumps

If you look at the 11Kw system you’ll see that it is made up of a compressor that uses a maximum of 4.1KW and an additional electric heater which is 5.5KW do a bit of maths around the current use, the rest of the electronics uses another ~2Kw That’s where the 11KW comes from it is the energy the actual heat pump uses, that is not the energy it is extracting from the ground

The compressor doesn’t run at max all the time. Min is 2.6kW so somewhere in between.
I don’t see why the auxiliary heater would be needed if there is a decent hot water storage that the house can draw from.
Generally you can reckon of around 1 kW in to 3 kW out perhaps a little more depending on temperatures.

 

[AndyRKett]

The compressor doesn’t run at max all the time. Min is 2.6kW so somewhere in between.
I don’t see why the auxiliary heater would be needed if there is a decent hot water storage that the house can draw from.
Generally you can reckon of around 1 kW in to 3 kW out perhaps a little more depending on temperatures.

I posted this to test a theory which is that you’re literally going to argue the toss over everything at this point, you’ve no evidence of what you’re saying, just making assumptions at this point, but just can’t bare to let it drop


This is the link to where your graph comes from which talks about the mean earth temperature https://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm

And here is a link that talks of how deeper systems are more efficient because they are not subject to the changes in temperature that surface systems are https://www.imsheatpumps.co.uk/blog/how-much-space-needed-for-ground-source-heat-pump-gshp/

Literally the whole discussion is that the ground source systems are not dependent on the heat of the sun.

You would need the lag in between the ground and the surface temp to be considerably more than a month which your graph shows.

For a ground system you need to circulate it across 600+ square meters

A deeper system which is drilled vertically into the ground still needs the same run of pipe work but there is considerably less surface area influenced by the sun.

“Ground source” takes heat energy from the ground, but the shallow systems become less efficient because of the influence of the weather above and are not made more efficient by the heat of the sun

 

[vexorg]

@AndyRKett just a final one on this, how much power do you get per metre (or from 1 metre) of pipe in the ground roughly and a 1m nomimal depth.

Is there a duty cycle tied to the systems? as in it works because it's only on 6 hours a day and has 18 hours to "recharge" (your favorite word!)

 

[AndyRKett]

@AndyRKett just a final one on this, how much power do you get per metre (or from 1 metre) of pipe in the ground roughly and a 1m nomimal depth.

Is there a duty cycle tied to the systems? as in it works because it's only on 6 hours a day and has 18 hours to "recharge" (your favorite word!)

The “power” is energy the energy is heat and that can vary depending on a whole host of variables I’m sure the designers of these systems could tell you exactly how much energy they can expect to gain from the ground if you know all the other variables.

As for “recharge” being my favourite word? I’m sure it was/is you who is hung up on the ground getting recharged. But no there is no requirement to rest the system or only be able to run it for a few hours a day then have to turn it off

 

[vexorg]

I did mean power, as energy per second, so how many watts can you extract from a metre of pipe.

The recharge might have an effect, depends on the limits of of how much power () you extract. If you pull too much from it by pushing more cold fluid/gas though the pipes then the soil gets colder. There will come a point when the ground cant pass enough heat up to the pipes. As that happens, maybe it's hidden as the fluid just gets colder to match, but there will be critical point where you cant get more heat out.

Because off that there must be a thermal lag between you extracting energy and the soil returning to the ambient (assuming no pipe was there). This is what I mean by recharge, the soil around the pipe will go up and down in temp depending how much and how long the system has been running. The warmer the soil then more energy you can pull out, but thermodynamically, there must be a blip as the stored heat in used as the system is turned on, then it's get cooler around the pipes.

 

[AndyRKett]

I did mean power, as energy per second, so how many watts can you extract from a metre of pipe.

The recharge might have an effect, depends on the limits of of how much power () you extract. If you pull too much from it by pushing more cold fluid/gas though the pipes then the soil gets colder. There will come a point when the ground cant pass enough heat up to the pipes. As that happens, maybe it's hidden as the fluid just gets colder to match, but there will be critical point where you cant get more heat out.

Because off that there must be a thermal lag between you extracting energy and the soil returning to the ambient (assuming no pipe was there). This is what I mean by recharge, the soil around the pipe will go up and down in temp depending how much and how long the system has been running. The warmer the soil then more energy you can pull out, but thermodynamically, there must be a blip as the stored heat in used as the system is turned on, then it's get cooler around the pipes.

Really what you’re saying proves that the sun isn’t involved in this process, in the summer it takes a month for the soil to warm back up to the Temperature at the surface, so if you drop the temperature of the soil then it’s going to be a month before your heating system works again.

As I said before the amount of energy you can pull out of the ground depends on a whole host of variables I’m not a heating designer I’m not going to go searching for all the equations, but basically because of temperature gradients the ground will always be colder than the fluid in the system and so it will always extract some heat.

 

[vexorg]

Really what you’re saying proves that the sun isn’t involved in this process

Not really since I'm not stating a source for the heat, equally valid from above or below. We'll leave that there.

The reason for the power question was a random thought, if you can convert the heat back to electricity, and it's more than needed for the pump, then free electricity too (free as in not paid for, rather than free energy)

 

[AndyRKett]

The reason for the power question was a random thought, if you can convert the heat back to electricity, and it's more than needed for the pump, then free electricity too (free as in not paid for, rather than free energy)

You can convert heat into electricity via something like a peltier device which works by having a difference in temperature from one side to another, you might gain a few watts this way but the gains would be minimal and any electricity you generate would be far outweighed by that used by the coolant pump.
In something like a power station you boil the water into steam and then push the steam though a turbine to make electricity, these systems would not provide enough heat and would not harvest enough energy from the ground to make it worth while, bearing in mind the system could be using 10+kw of power which is like running more than 3 fast boil kettles constantly

 

[vexorg]

I know how power stations work, I work in the power industry. These ground source supplier are quoting 4:1 for the heat out to power in, so for a 10kW input then they'd be expecting 40kW out. I'd have thought the pump would be near 1 or 2kW for that kind of system.

I'm wondering now if these companies are using fake numbers, that are equivalent to gas boilers. The average boiler maybe 10kW or 20kW, but probably spends most of it only life at 1kW due to the duty cycle once the house warms up.
It would be good to see some real world numbers for power used and heat gained.

 

[timmycm850]

Real numbers. Well I will let you know. We currently run an18 year old gas combi boiler and have no hot water tank and we run an electric shower. Currently the last year we have used 10900kwh gas units and 2200kwh electric units from the grid and about 2400kwh from our solar panels/ battery. Four bed detached house

We have signed up for an air source heat pump and tank to be fitted and will be removing the electric shower and fitting a thermostatic shower. We are getting the £5000 government grant to assist with the conversion.

It will be a while before I can give some long term numbers but will periodically update on how it performs.

Tim

 

[timmycm850]

If I buy my electric from a renewable supplier my home will be carbon neutral by the end of the summer so thats 25 years before the governments 2050 commitment.
My van is adblue diesel 2017 and we have a 2021 Panda hybrid sport so they are both as low emmission as possible without making the step to electric.

So where can I get my Francis Lombardi GP and OT1000 Replica converted to electric.

Tim

 

[portland_bill]

Real numbers. Well I will let you know. We currently run an18 year old gas combi boiler and have no hot water tank and we run an electric shower. Currently the last year we have used 10900kwh gas units and 2200kwh electric units from the grid and about 2400kwh from our solar panels/ battery. Four bed detached house

We have signed up for an air source heat pump and tank to be fitted and will be removing the electric shower and fitting a thermostatic shower. We are getting the £5000 government grant to assist with the conversion.

It will be a while before I can give some long term numbers but will periodically update on how it performs.

Tim

But how much will this installation cost, and how long to break even?

 

[timmycm850]

Hi Bill.

As our gas boiler is due for replacement anyway the cost of that will have to be taken into account anyway. I estimate the combi replacement to be 4 to 4.5k and the ASHP to be £6.2k taking the grant into account so its 2k more. With the tarrif I can get into with the ASHP at 20p per leccy unit for 6hrs a day running the system sensibly I can save myself between £500 and £600 per year so 3 to 4 years to pay for itself. Thats just the financial numbers that I always got asked about when we fitted solar panels 2 years ago.

We must remember that the carbon output is the area we should be looking at not the financial.

Tim

 

[timmycm850]

Once I'm past the 3 to 4 years break even point I'm quids in to the tune of £500 to £600 per year

and this is the big surprise.

It will be cheaper to run a carbon neutral home than a global warming/ polluting one

 

[timmycm850]

I'm trying to work out why I often get the question over when is break even point.

Buy a big German car instead and work out the break even point,

oh that'll be eeerrrr.

Never!

 

[vexorg]

The general view is that air source isn't great for the UK. You might need additional heating and the running costs could be higher than predicted, especially with the current prices.

 

[timmycm850]

I think with 100mm cavity wall insulation. 8 inches of loft insulation and boarded out to cap it and triple glazing i think I've got the basics in place.

Our gas energy consumption at 10900kwh per year is less than the government prescribed average house at 12000kwh in a 2 or 3 bed semi. We are an extended four bed detached with 4 outside walls so it looks like we are in the right place to me.

 

[chris3234]

Heat pumps would work in a well insulation house especially with under floor heating and insulation under ground floors if you have solar pv and a timed traffic for cheeper overnight power to run the pump for. Awhile to warm up for the morning

Allthough a battery system would also be recommended to charge up on cheep overnight traffic's



If you have Facebook there a bloke called Alen heart on there who had. A huge ov battery and heat pump system and gets very cheep bills now and uses virtually no gas



But sticking a heat pump in your average house is unlikely to work well I'm my opinion

The general view is that air source isn't great for the UK. You might need additional heating and the running costs could be higher than predicted, especially with the current prices.

 

[timmycm850]

We have solar and battery but not the type where you can charge it at cheap periods.

I will however be going onto a tarrif where certain timeable periods are discounted by 40% so running hot water during those periods and raising and lowering the home temperature to benefit from them. Dishwasher can be timer delayed into the cheaper periods along with tumble dryer and washing machine.

We find that if the outside temperature is above 9 degrees then our gas heating never comes on due to minimal heat loss

 

[s130]

Hi Bill.

As our gas boiler is due for replacement anyway the cost of that will have to be taken into account anyway. I estimate the combi replacement to be 4 to 4.5k

We must remember that the carbon output is the area we should be looking at not the financial.

Tim

Had a new combi, Bosch/Worcester ,10 Year Warranty, Wifi full control thermostat & timer, full flush, filter, inhibitor, removal of old etc. for £2976 in Oct 2022. I was dreading having to replace the old floor standing combi in the house we moved to as I too had heard of these £4K to £5K+ prices. Was pleasantly surprised.

Updated date to Oct 2022 not 2020.