IEA issues report on Retrofit Heat Pumps for Buildings in Europe

In Europe, about 40% of the primary energy use relates to the building sector, while 80% of the energy demand in houses and utility buildings relates to space heating and hot water generation.

Heat pump potential lies in “small scale” renovations

With the annual replacement of the existing building stock with new built constructions being very low, the renovation of the existing building stock presents the largest potential for energy saving and renewable technologies such as heat pumps.

This is especially true given that for privately owned buildings the main renovation measures that take place hardly ever go as far as demolishing and rebuilding or completely renovating the interior while keeping the main skeleton. Indeed, in privately owned buildings the main renovation measures lie in the replacement of the existing heating boiler at the end of its life time or at best in the large scale replacement and renovation of the energy system with small renovation on the envelope.

The challenge for retrofitting with renewable energies systems such as heat pumps hence lies in this area of “small scale” types of renovation.


Existing buildings require high distribution temperatures that CO₂ can deliver

The present market for heating-only heat pumps with water distribution systems (hydronic systems) is dominated by heat pumps with low temperature distribution systems. However, conventional radiator systems, which still dominate in the existing building stock, require high distribution temperatures, typically 60 - 90°C for the supply, as opposed to today’s modern low temperature systems (e.g. floor or wall heating) that are designed for 35/28 °C supply/return temperatures.

The main technological barrier for retrofitting with heat pumps noted in the International Energy Agency (IEA) study, is the limited availability of heat pump technology fit for retrofitting existing buildings and finding solutions for coping with the high design temperature of conventional heating systems in existing residential buildings with distribution temperatures up to 70 - 90°C.

Economic competitive and energy-efficient heat pumps for the retrofit of high temperature heating systems in existing buildings are still in the development stage. The aim is mainly directed to economic ground-coupled and air-to-water systems with around 60 °C heating temperature and high COP. Possible solutions are CO₂ as working fluid, multi-cycle systems or speed regulated compressors.

Heating & cooling air-to-air heat pumps of growing interest for retrofits in S. Europe

“Heating and cooling air-to-air heat pumps, the most common types in residential applications in the mature heat pump markets of Japan and the USA, are of increasing interest for the retrofit market in Europe, especially in the southern parts of the region. The air is either passed directly into a room by the space-conditioning unit or distributed through a forced-air ducted system. The output temperature of an air distribution system is usually in the range of 30-50°C”.

CO₂ research in Europe

The report provides an overview of the CO₂ heat pump research conducted in different European countries:

Austria

• CO₂ heat pump for combined space heating and tap water production (Arsenal Research)
• Ground coupled horizontal CO₂-loop with forced circulation as a heat source for heat pumps (Arsenal research)

Germany

• CO₂ heat pump with ejector (Stiebel Eltron)
• CO₂ domestic hot water heat pump (Stiebel Eltron - CH)
• CO₂ compressor (University Braunschweig)
• CO₂ retrofit heat pump with high energy- efficiency and an eco-friendly refrigerant (R&D project from Viessmann)
• CO₂ heat pipe as earth probe for geothermal heat pumps (FKW)
• Investigating a 250m deep FKW-CO₂-earth heat pipe for providing earth heat to an old existing building from only one individual deep borehole (EIfER, European Institute for Energy Research in Karlsruhe)

Norway

• Trans-critical CO₂ heat pumping systems for space heating (SINTEF Energy Research)