Moving off the Grid - Part Two - Heat Pumps

This will be part of an on-going series  on how and why people choose their source of energy.

Heat Pumps

Heat pumps move ‘heat’ from one point to another. Refrigerators are the most common example of a heat pump system. In our context we are looking at a system that takes heat  energy from a lower temperature body and by mechanical means extracts the heat energy which is then released at a higher temperature. The power  necessary to  enable this is usually electrical and one would normally expect to use 1kW of electrical power to produce 3kW of heat energy. Mostly the source for the heat pump is either the ground or the air but if available in sufficient quantity, water.

Practical and beautiful - one of the two lakes on the property.

 The Lady of the Lake – 35 years of heat pumps

Some necessary maintenance - cleaning the exchanger.
Anne-Marie and Jean-Louis have always used heat pumps as their principal source of energy. Their first system was installed when they lived in a riverside property, where they had the right of use not only of the section of river which fronted their property but also an ancient lavoir (communal laundry). This latter gave them ample place in which to accommodate the exchanger. Thirty-five years ago this type of system was so new here in France that the technician who installed the pump didn’t actually have either the belief in, nor knowledge of, the system, just the technical competence to do the work. Anne-Marie and Jean-Louis were so pleased with the system that when they moved, some twenty years ago, to their present home they decided to go with the system again, this time with Jean-Louis building the exchanger himself. Their present system was built from scratch, as they had managed to find a beautiful piece of land with two lakes and a small dwelling, thus giving them scope to build their new home around its heating system. This is perhaps one of the drawbacks with this form of heating in that it is best installed in a newbuild as it requires pipes to be laid within the flooring. However, it is possible to retrofit the system, if one can break through the flooring or use a system of wall-mounted radiators. For Anne-Marie and Jean-Louis, who mostly worked from or at home it has been the perfect solution. The house is kept at a constant  ambient 19°C, except in the bathrooms where additional piping adds to the heating capacity and give a temperature of 23°C.

The constant temperature allows Anne-Marie to grow a whole range of orchids and succulents. A great and avid gardener she uses the heating system to its full advantage when growing some of the many difficult members of these plant families.

This brings us to another consideration with heat pumps, in that they require volumetric calculations for the designs and costings of the whole installation. This could add to the costs of start up, in that you may need to engage a professional to undertake such a study. However, some of the companies selling and installing heat pumps also include a feasibility study within the package – it pays to shop around. All in all this sort of system requires a physical mass, whether a body of water or area of land in which to install the exchanger and a significant initial outlay in time, money and possibly inconvenience for start-up. Anne-Marie and Jean-Louis found and then preserved a beautiful natural environment, which is home to a wide variety of rare and beautiful wildlife. The little grebe, frogs and moorhen paddle about the water lily pads oblivious to the system beneath.

It is also to be considered that the system they have heats a very large volume of living space. Anne-Marie’s original intent was to run a Bed and Breakfast, so their heat pump actually provides a constant 19°C and 23°C in six bedrooms and bathrooms respectively, as the system was also installed in the floorspaces on the upper floors. According to Jean-Louis many people opt for a system which heats just the lower floor and uses radiators above.

The Layout

The lake is some 50m from the house, the feed and return pipes to the exchanger were buried in a trench. Jean-Louis made the 3m x 1m exchanger himself, the tubes arranged in two layers to give a total exchanger area of 6m².

From left to right;-  150l hot water tank, heat pump for heating and hot water and heat pump for heating only.

There are two heat pumps in their system the first solely for heating the second for heating and hot water. Recirculating pumps deliver the anti-freeze laden water from the heat exchanger in the lake to the heat pump where some of its heat energy is absorbed prior to returning to the exchanger. The heat from the heat pump is then used to warm the water in the hot water tank, the system from then on being similar to any conventional wet  central heating system. Central heating pumps move the heated water around the matrix of underfloor pipes throughout the house. In the bathrooms the pipes are laid closer together to provide the elevated temperatures required (9cm apart as opposed to 14cm for the rest of the house). The floors act as massive heat sinks, if there is no heating supplied to the system for a 24 hr period, the temperature of the floor drops by only 1°C. The heat pump system is programmed to only run from midnight to 7a.m. thus taking advantage of the lower rate tariff. The financial implication of this is that their total energy bill for this whole house (floor area of 200m²) amounts to 1 350 Euros per annum.

The circulation pumps supplying the water from the exchanger in the lake. A well spaced out system like this is essential for ease of access in case of maintenance.

Upstairs feed manifold supplies heating water to the bedrooms and bathrooms. A similar arrangement exists for the ground floor.


Reliable heating system furnishing comfortable temperatures throughout a large house.

Low maintenance costs.

No fuel storage necessary.

High level of reliability – few moving parts, no exposure to weather.

Long life expectancy

No pollution provided the integrity of the source loop (heat exchanger in lake) is not compromised.


Initial capital costs high.

Underfloor installation work is messy in a retro-fit operation.

Electricity supply needed to make system work. Hence you have to have a backup source if there is a possibility of outages and you are still on the grid.
For example, in 1999 the hurricane we had here took down pylons with a resulting 7 day power outage.

Any leak in the heat exchanger will lead to system failure but also to contamination of the water source or land, although use of ecological anti-freeze reduces risk.

Repairs to heat pump requires specialist know-how.

Care has to be taken to ensure no corrosion to pipes and fittings arises from the water in the heating side of  the system.  Jean-Louis has had to change the fittings in the hot water feed manifold to stainless steel due to the acidity of the potable water. He also cites chemical attack from the concrete has caused further deterioration in some fittings.

Jean-Louis and Anne-Marie are so sure that this system is the right one for them that having put their house on the market they have already chosen their new house with a heat pump system as the prime consideration.

A heating system which takes full advantage of the landscape  but which has no visible presence within it.    

All the best and thanks for dropping by. Please feel free to share this article, comment and/or ask questions.

Cheers, Andy

© Andy Colley 2014


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