We have shown that Solar PV is of no value to the house that has it installed or the planet, so are GSHPs our salvation?

Well, let’s take a detailed look at them as there is a lot of controversy that we might be able to sort out.  I have spoken on them publicly several times but was ‘invited’ not to explain the true situation when lecturing on them at what is meant to be an independent venue.  I therefore refused to continue with the presentation.  For me it is the truth or nothing and I will not be party to deception.  Incidentally nobody could argue against what I said or say.

Do they produce hot water – well yes they do.  So what could be the problem?  Let’s see how they work.

They are exactly a backwards fridge, so whereas a fridge takes heat from inside the fridge (making it cold) putting it into the room the fridge is in (through the evaporator on the back) a GSHP takes heat from the ground and puts it into the house.  But the GSHP has a powerful compressor which has to push the primary refrigerant round the circuit, and this uses electricity. [The industry likes to install what they call ‘Ground Source Heat Pumps’ – it probably sounds better - but they are only compressors!]  But that will be OK if it uses very little electricity to make a lot of heat, so what does it produce for what it uses?

Now we have to be very careful as the relationship between the heat output and the electricity input is called the ‘Efficiency’, and generally we can take about 300% for that efficiency.  Some manufacturers claim a slightly higher figure, but please challenge them if you want an installation.  The truth is the efficiency depends absolutely and critically on the temperature difference between the flow and return on the system – so the higher you want the water temperature – the lower the efficiency – and the efficiency crashes as that temperature difference increases.   Of course any reputable supplier will know their efficiency curve (efficiency against temperature difference) but it is close to impossible to get them to release them, so here I will guesstimate one purely to demonstrate this visually.  Even calling the GSHP Association has not yielded a curve!


But let’s start by just using the 300% efficiency figure. This means that 3KW.hrs of heat is produced by 1KW.hr of electricity so let’s check the financial implications of GSHPs against using your own boiler.

Producing that 3KW.hrs of heat from a gas boiler requires about 3½ KW.hrs of gas (the boiler should be about 85% efficient) so at first sight a GSHP seems extremely efficient.  However, generally the cost of electricity/kw.hr today is at least 3 times the cost of gas/kw.hr, and forward prices tend to a 4 times multiplier.  My costs are 7.77p for electricity and 2.57p for gas, a multiplier of 3.02. Of course you can test this for yourselves but you will find it is correct.

A Basic Analysis: So with the 3 times multiplier the GSHP could save about 14% of the energy bills but at the 4 times multiplier it would cost about 14% more.  I would therefore argue there is no effective financial saving even at this level of analysis. But a GSHP installation tends to be between £10k and £20k so that huge ‘investment’ frankly makes no sense at all.

But we might also need to save planet earth and reduce carbon so how does a GSHP fare here? There is a strange belief that electricity comes free of all pollution, but on the other end of the system from the plug there are umpteen power stations almost all burning fossil fuel, and many still burning coal.  As a rough guide a power station burns 3kw.hrs of fossil fuel to get 1kw.hr to your plug (just think cooling towers, generation losses, transmission losses, transformer losses etc).  So here are the figures to compare the carbon emitted from both:

1 kw.hr of gas emits 0.194kg of CO2

1 kw.hr of electricity emits 0.568kg of CO2 (annual average)

So electricity emits 0.568/0.194 = 2.93 times as much CO2 as gas does per KW.hr.

[These are government figures though my ratio is slightly higher at just over 3.  But it is 3 or thereabouts.]

A GSHP working at 300% efficiency therefore emits almost as much CO2 as using a gas boiler (the same 14% less) and one costs maybe £800 and the other £15,000.  It doesn’t therefore seem to make a lot of sense on any account and certainly does not have a useful impact on greenhouse gas emissions (for a gas boiler).  Burning oil emits about 40% more CO2 but we needn’t concern ourselves with this too much as there are other factors to consider first.

A further analysis: If we want to properly compare the CO2 emissions we have to understand that GSHPs used for heating buildings are doing so through the winter, and at this time much of the electricity is being produced by coal burning power stations, and these emit up to 0.80kgs/kw.hr.  Far from using the annual average, we do need to use a more representative figure, and I will take 0.645 as a better estimate. Using this figure:

A gas boiler system emits 0.194 ÷ 85% = 0.228kg of CO2/kw.hr of heat used.

A GSHP even at 300% emits 0.645 ÷ 300% = 0.215kg of CO2/kw.hr of heat used.

But a GSHP at 250% emits 0.645 ÷ 250% = 0.258kg of CO2/kw.hr of heat used.

So in reality, unless you have much better information and use your system very carefully, you are not going to save carbon and therefore not going to help planet earth.  You would need to use the GSHP during non peak hours in order not to cause coal fired power stations to be supplying the power.

An even deeper analysis:

So far we have assumed that both a conventional boiler and a GSHP deliver the same amount of energy, but maybe that isn’t right either.  I know of some installations where they use GSHP to heat domestic water, but as domestic hot water is almost useless below 50°C (unless the system heating the water runs continuously which is hugely inefficient in itself) the flow temperature to heat it needs to be at least 60°C yet GSHPs cannot really deliver higher than 50° to 55°C  so they will be running either continuously or very frequently.  Horribly inefficient.

But to heat the water delivered by the GSHP to these higher temperatures means the compressor efficiency has dropped significantly.  Therefore both the cost of heating the water and the emissions resulting from the process are much higher than if conventional boilers were used.  So that is a big LOSE LOSE situation.

And if there is a need to run any underfloor heating (a conventional use for GSHP’s) at a higher temperature, then both the cost and environmental penalty increase as well as shown above.

So at best they basically achieve next to nothing and if you move the flow temperature up at all you would be better advised to find another energy source.

An even more detailed analysis: The trouble with industries and businesses is that they only want to sell product, so at best you get half truths and at worst surely they have to know they are misleading you.

There is yet another issue with the GSHP system as there are huge lengths of pipe both in the ground and probably in the house, so every time it is started up, a really significant amount of energy is used just to get it to an operational state.  It is the same with Air conditioning systems.  And all this costs you money and the planet – carbon.  Given that it can only react so slowly, the convention requires it to be turned on and off very infrequently which is one reason why it is extremely horrible for domestic hot water, and tedious for heating buildings.

Given the above, we can understand why GSHP is almost always matched with Under Floor heating, so we need to consider this building heating system here though I will write about it separately.

Before we peek at Underfloor heating we should also recognise that by taking heat out of the ground we are cooling it down, and constantly removing heat will make the ground around the ground loop colder that it normally is.  Over a heating season therefore, the ground temperature must drop and with it the efficiency – which is so crucial.

Underfloor Heating: When coupled with a GSHP system, the conventional wisdom is that an underfloor heating system is turned on in the autumn [when on one day the house needs heat], and off again in the spring when it is no longer needed.   So it runs continuously for between 6 and 8 months guided only by a house thermostat or room thermostats.

Now, in Tranquility House I did install underfloor heating as it is argued that a room can be a degree or two colder for the same level of comfort, as a warm floor firstly keeps your feet warm and secondly – it heats the zone of the room we inhabit rather than the ceiling.  These are both true, so it is installed here and works well in the way it is designed and expected to work. BUT:

As the house is one big research centre, each room has a different configuration of underfloor heating under it which I will discuss in the White Paper on the subject.  This is to compare how well they work with much lower installation materials, so pipe centres are even stretched to 900mm under two rooms instead of the conventional 150mm with no ill effect.  It seems all the design computers only have the 150mm pipe centre option, so if you ask for a design – that is what you will get.

But for a very low energy house, frankly underfloor heating is a big mistake and it is only used here for demonstration purposes.  But why?

Well its reaction time is horrible, so in reality if I want to heat the house a little for any reason for an evening, I need to put it on the evening before.  And then the sun comes out the following morning and I didn’t need it – but the energy has been spent and the heat will come up regardless, so it actually increases the temperature oscillation in the house.  And maybe the visitors didn’t arrive but still the energy is spent.

My solution is to have ‘unconventional’ radiators in the important rooms.  Unconventional just because they don’t mostly look like radiators and visitors often have to be told what they are!  After all, with thermostats on all but one – exactly the right amount of heat is delivered as and when necessary and only when necessary.  But in the case of this house, it is only required on about 40 days a year – in a normal year!  So if we considered the cost of installing an underfloor system, it really is a no-brainer.

But even for less efficient houses, the response time to a signal from a thermostat to reduce the heat will take ages to take effect, during which time the rooms are warming well above the thermostat setting.  And the notion it should be turned on in the autumn and left on through the winter could not remotely be considered energy efficient.  It will keep the house nice and warm – but energy efficient it is not.

IF you already have it installed I would suggest setting the thermostats extremely low – not above 16° and probably at 14° – so a small amount of additional heat is applied to any room really needing it when it needs it.  THAT is more energy efficient.

A further issue is that bedrooms really do not need to be anything like as warm as living rooms in the evening, but if the downstairs is running at a constant 20° or more, then it is likely the upstairs will be warmer than necessary as there is conventionally no insulation between ground and first floors.

Conclusion:  Installing a GSHP is not going to save anybody or the planet anything of value, but may indeed cost all of us a great deal.  It is sad that this technology is marketed with so much incorrect information as we do find it difficult to sort the ‘wood from the trees’. The idea that such an enormous expenditure couldn’t be better spent elsewhere is difficult to imagine, and here we turn to one of my golden principles.  “Spend money saving energy until it is cheaper to spend that money generating it”.

You can replicate all the work done here and prove it for yourselves, but beware incorrect ‘information’ posted on the web or given out by suppliers.  I could publish that silver is gold – but it wouldn’t be true.  I have found incorrect values for a number of the figures used here, so remember that a supplier will select figures that work for them.

It is surely useful to know what the ‘break even’ cost of a system needs to be to make economic sense for a buyer, and this is not too difficult. It needs to be a lower cost that the alternative of using a conventional boiler with conventional radiators – so for most houses that would be less than £3,000.