Heat pumps are a terribly important technology, but we run the risk of being indiscriminate in their use. Not every heat application is environmentally suitable to operate with a heat pump. We have to choose the best horse for each course when it comes to microgeneration and renewable energy.
A heat pump works by exploiting ground or air temperature differentials to make the use of electricity more efficient, when electricity is turned to heat. This can be very effective in saving carbon emissions in homes that are off the gas grid network. Typically heat pumps can make the electricity twice or three times more efficient.There are different kinds of heat pumps; some exploit ground temperatures, some exploit underground water temperatures and some exploit air temperatures. The heat pumps use electricity to drive the heat up from the ground (or in the air) into the places where it is needed.
When there is a big temperature differential between the outside and the inside the electrical energy used to drive the heat is very high; at around −18 °C outside an air source heat pump will not be at all efficient (I do not use that term in a technical sense) or worthwhile. The lower the temperature differentials the less “work” the heat pump has to do (using less electricity) making it operate in a much more “efficient” way. When the air is warm outside and not too cold inside you can get up to four and a half times the equivalent electricity use from a heat pump.
That means that if you install a heat pump you can get better benefits by using lower heat requiring underfloor heating than by using traditional radiators, in almost every application. Connect a heat pump to steel radiators in a very cold place the efficiencies will be much lower.
Overall the carbon dioxide savings of heat pumps are very variable, depending on many factors but I would suggest that a UK average would put the overall emissions of an average home with a heat pump heating system about the same as a typical homes’ average natural gas emissions. It makes no sense to me to build an “eco town” using heat pumps driven by electricity rather than natural gas; you will get better emissions savings if you use natural gas powering super condensing boilers supported by solar panels in virtually every place in the United Kingdom.
If electricity is the only source of grid energy then the carbon dioxide emission savings from a heat pump would be between a half and two thirds of an electrically heated home; use a heat pump rather than electricity for home heating then I think that you will reduce your home’s carbon footprint by two thirds.
There is increasing use of heat pumps to provide heat for swimming pools. This trend developed in the United States where electrical energy is still much cheaper than in Europe and solar thermal technology still relatively unsophisticated compared with Europe. Heat pumps in the USA are installed for reasons of cost economy in swimming pools, because they make the electricity go further.
In Europe, however, for the low grade heat application in high volumes that swimming pools require give heat pumps about the same carbon footprint as natural gas for swimming pool heating. I therefore find it strange, that in the name of carbon emission savings heat pumps are being installed for pool heating when they are in overall carbon footprint terms they will deliver the same as natural gas – quite a large rate of annual emissions especially when you consider the energy needed to heat a pool.
Not every swimming pool is on the natural gas network but there is a technology that can heat pools which has a tiny carbon footprint compared with a heat pump and natural gas and where the electricity costs around 3% of the heat pump electricity usage.
Of course, I am talking about solar thermal technology where the source of energy is light, not electricity, and instead of digging deep into the ground you raise solar panels to the sky.
Ground source heat pumps means digging deep to lay pipes to exploit heat differentials is usually done by digging vertical or horizontal boreholes into which a sealed pipe containing polypropylene glycol is filled, which is used as a heat exchange medium, just as in solar thermal systems.
In winter the temperature of these pipes has been observed in the Netherlands to become very low, and in large heat pump systems (for example if there are more than 40 homes served by heat pumps in a hectare) some recommend that the subsoil is regenerated every summer.
The sub soil can be regenerated quite easily by pumping heat back into it, in the summer.
If you do not regenerate the subsoil, you can get lower than normal temperatures of subsoil which affects the heat pump coefficient of performance under peak load conditions. There is still not enough known about how underground aquifers can change or subsoil stability is affected by long term operation of heat pumps in a concentrated area.
These subsoil points are all probably solvable by excellent installation so a properly installed heat pump will probably work well for many years. However, it will only work by consuming electricity which is expensive and has a high carbon footprint even with the help of a heat pump. Getting a constant supply of electricity from renewable sources is very hard because we have not yet solved the problem of storing electricity.
Solar thermal has one distinct disadvantage over a heat pump; it works better by far in the middle six months of the year, when light is abundant and long lasting but it is not terribly helpful in the winter.
If the pool is to be heating for the winter months then natural gas remains the next best option in the United Kingdom, but if that is not available a heat pump installation as winter back up for those who swim in winter would work provided the outside is not too cold, and by using solar thermal in summer and a heat pump in winter you can make the highest carbon emission savings that you can get by heating pool off the gas grid network.
Filed under: carbon emissions, climate change, electricity, energy, gas, heat, microgeneration, natural gas, renewables, solar, solar energy, solar panels | Tagged: eco towns, efficiency, gas network, heat pumps, heat pumps carbon footprint, regenerating subsoil, swimming pools and heat pumps, underfloor heating, USA
Yes, quite of lot of our electricity comes from France, but not all of it ven in the South East. I do not think that it is right to consider nucler as a carbon free source, but rather as a low carbon source; there are meissions in minging and in processing and more importnatly in waste disposal whch should be taken into account.
Robert
In the south east of the UK, electricity is used from France which has no carbon emissions so the carbon emissions is drastically reduced using the heat from air system.
Peter
I suspect that the Middle East Nations would prefer to eek out their reserves for as long as possible in order to make them last.
I think ultra insualted homes might not need any heat in the UK, except for water heating.
Robert
Excellent analysis, I guess that the benefits of solar thermal could possibly be crystalized by situating a holding tank/pipes in the soil below the basement of a house where it could be pre-heated/conserved by the sub-soil, maybe in Canada heat pumps alone are a really nice idea with its abundent supply of Electricity from its hydro-electricty and not much solar energy availability in the winter. The pumps they are using may be the problem, one way is to have a small pipe pushing water down a high pressure and returning up a a lower pressure inside a larger pipe a, this method is used for extracting water from wells, so a larger amount of water will return upwards but the function of extracting heat is a closed system requiring only an equal amount of water to return, which is less work than pulling up more.
Also what would be the ground temperature underneath an ECOBLOCK ultra-insulated ICF home would that hold more heat causing a tighter heat differential making a heat pump more efficient if it was tapping into this comparitively close temperature to the air temperature of the building than the su-ground outside?
People are too reluctant to move first, Maybe it would be easier to ask Middle eastern countries if they might think about using all the solar energy that they get to use as solar thermal to then generate Electricity, but with an abundent supply of oil and gas there is no incentive!