France, Europe’s biggest user of heat pumps Since the birth of electric heating at the beginning

of the 1970s, EDF has encouraged and contributed

to the development of technologies that reduce

the amount of energy used to heat buildings.

This work, which initially focused on thermal

insulation, quickly shifted its attention to heating

technologies and their performance.

In response to rapidly-changing energy efficiency

requirements for buildings, the heat pump has

constantly evolved to become a reference for the

high-efficiency and low-carbon production of

heat. Furthermore, heat pumps use a large share of

renewable energy. EDF actively participates in the

development of the heat pump to respond to the

customer needs (comfort and energy performance)

and to industrial challenges (management of the

load curve and price changes). Today, 800,000

heat pumps are sold every year in Europe. With

more than 180,000 machines sold in 2014, France

leads this market.

A SMALL AMOUNT OF ENERGY CONSUMED FOR A LOT OF HEAT DELIVERED

For over 30 years, heat pumps have constantly improved their performance and reliability. The Coefficient of Performance (COP), which is the ratio between ‘thermal energy supplied and electricity consumed’, is used to define heat pump’s performance. Today, the best heat pumps have a COP around 5. These heat pumps provide five times more energy than they consume. The customer pays for 20 ‘units’ to get 100 and the remaining 80 are provided free of charge by the external environment! This green and free renewable energy can be taken from the air, water or ground. In recent years, the main innovations have concerned the heat pump’s performance: variable-speed compressors, permanent magnet motors, vapour injection, e lec tronic expansion valves, and h igh -per formance heat exchangers. R&D also includes issues regarding heat pump’s i n t e g r a t i o n i n t o b u i l d i n g s ( c o m p a c t n e s s , a c o u s t i c s , connections to cold source and heat emit ters, etc…) and it s interaction with the environment ( c o m m u n i c a t i o n w i t h t h e c u s to m e r, s e l f - a d j u s t m e n t in accordance with weather forecasts.).

Heat recovery from waste waterHeat pumps dedicated to the production of domestic hot water use ‘tepid water’ from our wash basins, sinks and showers as a cold reservoir. They thereby make use of a higher temperature energy source to reach a higher level of performance. These heat pumps, which are more suited to collective systems, have a COP up to 6 or even 7. Davy Merlet and Paul Garret, research engineers at EDF R&D

R&D DECEMBER 2015 chercheurs.edf.com

Technologyunveiled

Calypso Ambiance heat pump

Heat pumps in buildings

Alfea Extensa Duo heat pump

In the case of individual and collective housing, heat pumps are used to meet heating and air conditioning needs as well as to produce domestic hot water. The thermal comfort and energy per formance customer’s satisfaction depend on an accurate analysis of his needs (comfortable temperature set t ing, heat los t by the building), the selection of a suitable heat pump (minimum operating temperature, available thermal capacity, outlet temperature), installation in accordance with proper practices, and a setting that complies with regulations. Inverter technology constitutes an important step forward as it allows heat pumps to adapt to highly variable environmental conditions. The emergence of high-temperature heat pumps onto the market has meant that heat pumps can be installed in renovated buildings as well as new buildings.

Low-power heat pumps have been developed to meet nothing more than the domestic hot water needs of individual homes. Since 2010, the number of ‘hot-water heat pumps’ sold in France has risen by a factor of ten, reaching 72,500 units in 2014.

Cut your fuel bill with a heat pumpFor the user, the installation of a heat pump leads to a reduction in his energy bill as this type of system makes use of free and renewable energy. The amount of energy supplied is up to five times greater than the amount of electricity payed (depending on weather conditions). By drawing energy from a renewable cold source, the heat pump is one of the levers that will enable France to meet its renewable energy goals. Furthermore, the use of electrical energy contributes to the reduction of

greenhouse gas emissions as it cuts CO2 emissions by a factor four in comparison with boilers powered by a fossil fuel.

Inversion of the natural direction of heat transfer

The operating principle of a heat pump is to make use of free and renewable energy to heat the inside of a building. However, during cold spells, there is no reservoir near the building whose temperature is high enough to heat the building’s inside air directly. Heat is therefore automatically transferred from the inside (20°C) to the outside of the building (for example, 5°C), which is known as heat loss. But, even at a low temperature, outside air contains a high amount of energy. The heat pump’s role is therefore to invert the natural direction of heat transfer by taking energy from a cold reservoir and injecting it into the building.

KEY POINTS

1748: William Cullen demonstrates the principle of artificial refrigeration.

1824: The French physicist, Sadi Carnot, describes the fundamental principles of thermodynamics.

1834: J. Perkins builds the first refrigerator based on a vapour compression cycle.

1852: William Thomson (Lord Kelvin) presents the theory behind heat pumps and explains their benefits as a source of internal heating.

1920: The first individual reversible air conditioners are manufactured in the US.

1942/43: The first collective heat pumps are installed in Zurich to heat public buildings.

1973-74: The oil crisis triggers the launch of the PERCHE programme (boiler back-up heat pump); 52,000 installations in 1982.

Since 2000: There have been several heat-pump installation support schemes. High-performance technology has become widespread: variable-speed compressors, electronic expansion valves and permanent magnet motors.

2014: Every year, more than 180,000 units are sold in France, for an approximately 1,700,000 heat pumps stock.

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Heat pump - a renewable energy Heat pumps blow hot and cold

A thermodynamic cycle based on four components

To fulfill its function, a heat pump comprises a thermodynamic cycle in which a refrigerant circulates. Energy is captured in the cold reservoir by an evaporator in which a low-pressure and low-temperature (lower than the temperature of the cold reservoir) refrigerant circulates. Heat is therefore transferred from the cold reservoir to the refrigerant, which changes from a diphasic state (simultaneous gaseous and liquid state) to gas state. The compressor then channels this gas to high-pressure and high-temperature to deliver the energy drawn from the cold reservoir at the temperature desired. The heat transfer process takes place inside the condenser, where the fluid delivers its energy to the hot reservoir by changing from gas to liquid. Finally, the refrigerant travels through the expansion valve, which lowers it s pressure and temperature and thereby makes the refrigerant turn into a low-pressure diphasic state (liquid/gas).

This cycle is beneficial in terms of

energy consumption when the energy is

drawn from a free and renewable cold

reservoir. The electricity used by the

compressor represents the only cost for

the user. The thermal energy supplied to

the building is several times greater than

the electrical energy used by the system,

as shown by the heat pump’s Coefficient

of Performance (COP).

Reservoirs available in the vicinity of a building

This process therefore allows any source

of renewable energy that is available

in the vicinity of a building to be used,

even if its temperature is far lower than

that of the building’s inside air. However,

the higher the reservoir’s temperature,

the higher the system’s COP. It is for this

reason that a ground -or water- based

heat pump, which runs at around 12°C

throughout the heating season, will

perform better than a heat pump that

uses outside air whose temperature can

fall below -20°C.

unveiledTechnology

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DID YOU KNOW?

Energy can be withdrawn f r o m a n e n v i r o n m e n t w h e r e t e m p e r a t u r e i s down to -273.15°C. In fact, a t e m p e r a t u r e r e a d i n g quantifies the agitation of molecules in an environment. The absence of any molecular agitation, also known as absolute zero, corresponds to -273.15°C. Whenever there is molecular agitation within an environment, energy can be withdrawn from it. This means that, even in the planet ’s coldest regions where the temperature is close to -100°C, energy can be withdrawn from the air.

Technological developments made over the past 15 years have allowed heat pumps to become reliable and efficient heating systems. Today, high-temperature heat pumps are suitable solutions for renovated homes. The widespread adoption of Inverter technology has significantly improved the products’ performance and versatility.

New, less-polluting refrigerantsThe European regulation regarding refrigerants, known as the F-Gas Regulation, was revised in 2014. In light of the reduction of greenhouse gas emissions, the revised regulation imposes, for the period 2015-2030, increasingly restrictive Hydrofluorocarbons (HFC) sale quotas; HFCs are the main refrigerants currently being used. Low-GWP (Global Warming Potential) fluids will therefore become the fluids of the future. These fluids include ‘natural’ fluids such as CO2, which is already used in some heat pumps, propane and many other blends.

Refrigerant: a fluid that circulates in

a closed cycle within the heat pump. It

captures and releases energy in the desired

environment by modifying the pressure and

temperature at which it changes state.

Compressor: the element that increases

the pressure of the refrigerant when it is in

gaseous state.

Condenser: a heat exchanger in which

the refrigerant changes from a gaseous to

a liquid state by transferring heat to the hot

reservoir.

Evaporator: a heat exchanger in which

the refrigerant changes from a liquid to a

gaseous state by incorporating heat from

the cold reservoir.

Cold reservoir: the environment in

which the heat pump withdraws energy.

This is usually the outside air or the ground.

Inverter: a variable-speed compressor

which improves the heat pump’s performance

by adapting power to the heat pump’s

requirements, thereby reducing the number

of ‘on/off’ cycles and the amount of

energy used.

High-temperature heat pump: a heat pump that can reach a heating

temperature up to 80°C; it can therefore

be connected to a conventional central

heating installation.

GWP (Global Warming Potential): Greenhouse gas comparison

index of different gases over a given period.

The GWP of carbon dioxide (CO2) is 1 and

serves as a reference.

Hybrid heat pump: the combination

of a heat pump with a fossil-fuel boiler. When

managed correctly, this combination is very

effective and saves energy.

Hybrid energy sourcesFor a part of the housing stock, so-called ‘hybrid’ heat pumps have proven to be particularly suitable for heating. A hybrid heat pump comprises an ‘electric heat pump’ and a ‘fossil fuel boiler’. The combination of the two systems has been around for a long time (boiler back-up heat pump) but ‘hybrid heat pumps’, which recently came on to the market, go further thanks to a high-tech control system that is implemented between the two systems. The performance of these new-generation hybrid machines is optimal in every aspect: in terms of CO2 emissions, customer’s energy bills and balancing supply and demand across the national grid. This last point, hardly known by the general public, is crucial as it helps to secure the supply of electricity in the country and to retain a high-quality network. The performance of these hybrid heat pumps remains high both in terms of energy (high COP) and in terms of the environment (low CO2 emissions) thanks to the heat pump’s high operating rate (> 70%).

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www.edf.fr

Please do not print this document unless you need to.Publication EDF R&D - 1 av Général de Gaulle 92141 Clamart CedexPublishing Director: Jean-Paul ChabardEditorial secretary: Florence Metge-LaymajouxThe author, not EDF, is responsible for the content of this publication.

© 2015 EDFReproduction is forbidden without authorisation from the author.Photo credits: Atlantic, IDE - Robin Sarian

EDF Group is ISO 14001 certified.

> for more informationAssociation Française pour les Pompes A Chaleur: http://afpac.org/

European Heat Pump Association: http://www.ehpa.org/

Technology unveiled, ‘The industrial heat pump’: http://chercheurs.edf.com

unveiledTechnology

Contact:

communication-rd@edf.frhttp://chercheurs.edf.com

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