The Oil Drum

Wow! I have never seen a figure remotely near to £1500 for the pipes and excavation!
I am not disputing it, but have you a link to your supplier?

Small quibble - the heat from the original gravitational collapse may have leaked away but the heat from continued gravitational pull (collapse, except that things are fairly dense liquids or solids) continues in conjunction with radioactive decay. In fact, this mechanism has been presented as one possible theory of terrestrial heat generation. As the paper referenced notes, there are aspects of this theory that are more consistent with observed statistical values than the fully radiogenic theory. Further, work published in the journal "Nature" also calls into question the radiogenic theory.

Thus, I would state that it is far from settled that radiogenic sources are the only or even primary source of terrestrial geothermal heat.

I agree with Nick Rouse above.

Ground source heat pumps are only sold as 'geothermal' because it sounds good. Basically the heat comes from the air by making the ground a bit colder than it would have been otherwise.

Air source heat pumps have a problem of the heat exchanger becoming coated with ice in damp climates like the UK. This means that their midwinter performance deteriorates rather seriously and at worst they may have to revert to plain resistance heating. There was interest in them in the UK in the 1970s but, as I understand it, the electricity industry dumped the air source technology when they realised that it would not reduce the peak winter load on the grid.

Ground source heat pumps get round this by using the thermal mass of the ground to coast through midwinter cold periods without performance dropping too much.

You have to be careful in assigning an EROI to heat pumps. Most are electrically operated, so they are really part of the electricity distribution network rather than an actual energy source. A true EROI calculation needs to start with the EROI of the fuel used to generate the electricity. Their advantage is that they can compensate for the efficiency loss at the power station. If 3 units of coal go in to make 1 unit of electricity, then the heat pump with a COP of 3 can convert this back to 3 units of heat.

The same applies to engine-driven heat pumps. The Festival Hall in London was originally designed to use diesel driven heat pumps sucking heat from the Thames. I'd guess at a diesel to heat COP of around 1.5 for this, so the overall EROI would be the EROI of the diesel fuel multiplied by 1.5 less a bit for the energy used to make the diesel heat pump.

Finally can I ask again -

Where is the EROI of building insulation as a potential generator of negawatts (i.e energy not used)? Surely this is just as valid as positive energy flows in the bubble diagram?

I reckon it has potential EROIs in the range 10-100 and potential equivalent negawatt flows in the US of the order of 5 quads or more.

BobE

Not only is the source of geothermal heat the energy generated by the decay of uranium and thorium atoms within the earth, but that decay produces radioisotopes which pose certain radiation dangers that might be associated with the use of geothermal power. I became aware of this while investigating radiation problems associated with the extraction of natural gas from the Barnett Shale of North Texas. The extraction of heated steam and water from subsurfaces sources will inevitably bring radioisotopes including radium and radon to the surface. These isotopes in tern have the potential for contaminating geothermal electrical generating systems, as well as releasing significant amounts of radioactive gas into the atmosphere. Thus the use of geothermal energy sources pose a hazard to human health, it the associated release of radioisotopes is not contained and cleaned up.

Secondly, in practical terms earth source heat pumps are far more expensive to install than air source heat pumps. They are also potentially very expensive to repair. A COP of over 6 is possible with air source heat pumps, and air source heat pumps capable of operating in Canada have been designed. Air source heat pumps are far more practical replacements for gas furnaces in the American South, because of their lower price, and because Air Conditioning contractors would already be familiar with many air source heat pump features. An air source heat pump is basically an air conditioner that can reverse its heating and cooling cycle.

Because they tend to level summer-winter electrical demand, electrical generating companies might well subsidize the installation of air source heat pumps. The Government could also offer tax incentives for switching from natural gas to ASHPs.

I would dispute the air sourced heat pumps are a better option then ground sources ones if you have the ground to install one. Any advance in working fluids, thermodynamic cycles and heat exchangers will apply equally to both types. Even a slight drop in the external temperature makes a big hit on the coefficient of performance. The link given says they have achieved a COP of 3. This will be under the best conditions. It would be unlikely to achieve better than 2.3 over the winter. I have instrumented my ground source system and it achieved a COP of better than 4 for nearly all the winter.

Hi Nick,

I keep detailed and I like to think fairly accurate records of my heat pump's operation and its seasonal COP averages between 2.4 and 2.5 over the course of our long, cold and surprisingly damp winters (colder than Buffalo, NY and about as damp as the Pacific North West!). I've crossed checked these numbers with my fuel oil consumption and daily meter readings and everything seems to mesh well. My heat pump is an older model that falls below current federal standards; its HSPF is 7.2 and the new minimum is 7.7. High end air source units such as those offered by Fujitsu, with HSPF ratings as high as 11.0, are 1.5 times more energy efficient than my own and generate far more heat at the low-end of the temperature band and continue to operate down to -15C and I'm told, anecdotally, as low -20C. The COP in this case is as high as 3.2, which is not all that far off from that of a typical GSHP, particularly if heating and cooling loads are not well balanced and taking into consideration additional fan and pump related losses.

I paid $2,100.00 CDN for my ductless unit, installed -- a GSHP would easily cost ten to fifteen times as much (likely more since my home has no existing duct work) and would at best save me another couple hundred dollars on my utility costs. As it stand now, my home's space heating costs are about $650.00 a year (electric + backup oil) and a Fujitsu high efficiency model could knock another $150.00 off that. I'm trying hard to understand how a GSHP can offer better overall value in moderately cold climates like mine (well, that is if you consider Buffalo, NY moderately cold) and for the life of me I'm just not getting it. And I'm not saying this to be argumentative -- I genuinely want to know if they are truly cost effective and offer superior value when compared to the other alternatives.

Cheers,
Paul