thermodynamic heating, heat pump: financial and ecological balance

Is thermodynamic heating, heat pumps and geothermal energy an ecologically and economically acceptable solution?

Article freely inspired by the reflections of this topic

This article concerns thermodynamic heating, very "fashionable", especially for individuals who are wondering about the choice of their future means of heating because the information circulating is rather vague ... The purpose of this article is to see clearer.

Indeed; provided that the heat pump is powered by a renewable source located in your home (wind, photovoltaic, etc.) or by 100% green electricity (green contract), thermodynamic heating is far from being as clean as it is claims it!

It is, for example, untrue to speak of 100% renewable or 100% green or even free energy in connection with geothermal energy. However, this is what we can still read too often in many commercial documents.

Here's why: in France, electricity has a primary energy cost of 2.58 times the final consumer energy. Thus, for 1 kWh spent, it will have been necessary to spend 2.58 kWh at the source. Thus a heat pump that will consume 1 kWh will in fact consume 2.58 kWh in primary energy if we wanted to compare it to a gas or oil boiler.

Here are the different correction coefficients primary energy / final energy according to the different labels: RT2005, Minergie, Effinergie and Passive House.

Points of reflection regarding the choice of thermodynamic heating (water-water, ground-water, air-water, air-air heat pumps, etc.)

Some points of reflection for those who "hesitate" on the choice of their current heating:

A) By switching from an oil boiler to a heat pump, your electricity bill risks being multiplied by ... a certain coefficient! We better understand the promotion made by EdF and the electricity sellers for this solution!

A heat pump is not economical for your electricity bills.

B) If your electricity is produced from coal or fuel oil, the overall output on CO2 can be the same level as with a fuel oil boiler taking into account the outputs of thermal power stations, line losses and COP of your heat pump.

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Here are CO2 releases per kWh for several European countries.

Concrete example:

- Oil heating. 2.6 kg of CO2 per liter of fuel oil consumed for approximately 8.5 kWh of heat (85% efficiency).
CO2 releases: 2.6 / 8.5 = 0.3 kg / kWh heat.

- Heating by heat pump in Germany (little nuclear power): 0,60 kg CO2 / kWh el. If we have an average COP over the year of 2.5. CO2 rejection: 0.6 / 2.5 = 0.24 kG / kWh heat

The gain on CO2 in this case is therefore very low (20%) and the average COP over the year must really be 2.5. If it is less than 2, an oil boiler becomes cleaner!

A heat pump powered by an oil or coal plant is not clean in terms of CO2

C) If your electricity is nuclear, you will certainly reduce much more your CO2 emissions but you finance the maintenance and revival of the French nuclear fleet.

A heat pump finances and promotes the development of nuclear power or the construction of new power plants (gas, coal) for power peaks, is it environmentally friendly?

D) The maintenance costs are high and to add to your electric bill: 2 to 300 € per year or all 2 years!

A heat pump has a high maintenance cost. This is to be taken into account in the financial statement.

E) The return on investment (in the event of renovation) is generally 10 to 20 years without correction of the price of electricity which will necessarily rise. The works (horizontal soil-water, vertical drilling, etc.) are quite substantial in the event of renovation and generally very heavy financially.

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Financial risk is important

F) The performances given by the installers are generally the optimal laboratory performances (like the consumptions given by the car manufacturers rarely reached in real use ...)

Actual performance will be below announced performance

G) The lifespan of the equipment is limited: there are not many refrigerators that last 30 years. However, a heat pump is an inverted refrigerator, it is a complex system with moving parts and fluids that can "wear out" ... This goes against an adage well known to construction professionals: more it's simple longer it lasts.

A heat pump has a limited lifespan compared to other heating equipment, especially considering the installation costs!

H) In the case of a horizontal sensor, the deposit is not infinite since you are cooling your garden. And in some cases it can be annoying, for example, when there is a snow cover! Geothermal, surface energy is indirect solar energy! The volume average heat capacity of the earth is equivalent to that of water ... This remark is even more true with Air-X heat pumps: many icing up and no longer operating below 0 ° C (even if there are less and less).

Heat pumps are more sensitive than other means of heating to the weather

I) The development of thermodynamic heating (replacing gas or oil boilers) contributes to peaks in power on the electrical network. These power peaks are very bad for the environment in France and greatly increase CO2 emissions. See the figures of CO2 emissions in France according to the use of electricity.

The advantages of thermodynamic heating

To finish all the same on good points, there are some definite advantages to thermodynamic heating, here are a few ...

A) In the case of a water-X heat pump, that is to say vertical deposit (drawing from the water table) the hot spring is much more constant than the air or soil in your garden. But to do this, you have to be "well" geographically placed and the cost of drilling is significant!

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B) Compared to conventional electric heating (convectors), geothermal heating is much more efficient econologically!

But we must also compare the costs of return on investment. Convectors at 30 €, a DHW tank at 200 € is a house equipped with heating for 2000 €. That's € 10 less than a small heat pump ...

C) One heating with reversible air-to-air air conditioning is the most interesting to replace convectors because the investment cost is much lower… but watch out for low temperature performance! Heating by air-to-air heat pump is very interesting in addition to another heater!

D) Geothermal allows low temperature heating therefore the "overall" efficiency of the installation will be higher but low temperature heating is possible with any other heat source provided the installation is well done!


Thermodynamic heating has a lot of constraints and drawbacks (and there are others besides those mentioned in this article, for example, we have not talked about the noise of heat pumps, here is an example with a CIAT Caléo) which are, of course, not put forward by sellers and installers.

The development of thermodynamic heating is pushed by electricity producers who see here an economic boon. Exactly as electric heating was (and still is in part since more than 2 million new homes have been heated in France with electricity since 2000) ...

However, thermodynamic heating is a real ecological and economic advance when it precisely replaces this direct electric heating.

For any investment, it is necessary to make the balance sheet and to inquire before, our forums can help you ask your questions!

- Forum heating and thermal comfort
- Comparison of a professional study. Heat pump VS gas VS district heating.
- Feedback from geothermal heat pump users
- Discussion on the points mentioned in this article
- Information about thermodynamic heating and heat pumps

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