The heat pump a revolutionary and natural idea
A heating system that makes use of the heat of the sun stored in the air, in the ground or in the water, available all year round.
A heat pump that transfers to the water the heat recovered from the ground, the air or the water available in the external environment. This energy is used to heat and cool the environment and to produce domestic hot water.
There are four phases in the thermodynamic cycle of the refrigerant fluid in a heat pump: compression, condensation, expansion and evaporation. In the compression phase of the fluid - in a gaseous state - pressure and temperature increase, absorbing heat. In the next phase, it passes through a condenser and the heat is released to the water or air used as carriers for heating the environments or the domestic hot water. In the third phase, the fluid - now returned to a liquid state - passes through an expansion valve (lamination process) which causes a drop in pressure and temperature. In the fourth and final phase, which is evaporation, it goes into a vaporous state, absorbing energy from the heat source.
The energy used is mainly the electricity required to run the compressor, but the system on a whole is capable of providing more energy (in the form of heat) than it consumes.
The environment is rich with energy. In theory, you would have to reach absolute zero (-273.15ºC) to eliminate the last residue of energy. With the help of a heat pump, part of this natural energy can be collected and transformed to provide domestic hot water and heat.
Installation of this type of system also provides economic benefits. Thermal energy can be extracted even at temperatures below -15ºC. On average, in the course of a year, the return of natural energy at zero cost will be equal to about half of normal heating costs.
Operation of a heat pumpThe energy which can be obtained from the environment provides about 75%of the energy required by a heat pump. The addition of just 25% of external energy (normally electricity) provides 100%of the needs of the heating system.
Energy can be extracted from outside air, from water (groundwater, river, or lake) and from the ground, using heat exchangers. This heat then enters in the cycle of the heat pump, where it is brought up to a temperature that meets heating needs.
Recovery of energy from the ground
These heat pumps are capable of recovering the environmental energy in the ground in two ways: horizontally and vertically.
Recovery of energy from the ground using horizontal tubing
A geo-thermal collector is located horizontally in the garden (horizontal coils made of PE synthetic material) absorbs the heat from the ground and transmits it to a heat carrier fluid (water with glycol). This liquid then reaches the heat pump which, in winter operation, absorbs the heat contained in the water to release it, via the refrigeration circuit, to the system in the house (through radiators, fan coil units or radiant panels). This system requires a surface area of ground that is two to three times larger than the surface to be heated.
Recovery of energy from the ground using vertical tubing
The principle of operation of the geo-thermal tubing is similar to that of the geothermal collectors buried in a horizontal surface. The geothermal pipes are inserted at a depth of 30-100 m. They consist of one or more pipes in synthetic material, through which a water and glycol mixture flows. The vertical geothermal pipes require a limited amount of space. The absorption capacity varies depending on the characteristics of the terrain and varies between 30 and 100 watts per metre of geothermal pipe.
Recovery of energy from the water
Energy can be drawn from water, using the natural warmth of lakes, wells and groundwater. Groundwater is especially suited for a heat pump. It is capable of storing heat from the sun for long periods of time and to maintain generally constant temperatures of 9-12° C. With these temperatures, the heat pumps offer better performance (hence lower operating costs) than those based on the principle of geothermal probes. Here's how it works. A supply pump draws groundwater, which is carried to the heat pump, which recovers its heat. An absorbing well then carries the water back to the groundwater. The distance between the supply pump and the absorbing well must be at least 10 metres, to prevent short circuits. The available volumes and the quality of the water should be checked in advance through pumping tests.
Recovery of energy from the air
The most widely used application is still however based on recovery of ambient energy from outside air. Outside air is always available and there are no limits on it. The benefits of this system include easy installation, since all that is needed is an external unit capable of recovering the warmth in the air, resulting in low system costs. In addition, modern air cooled heat pumps offer extremely high energy efficiency even at very low temperatures.
Modern electric heat pump systems that make use of the energy stored in the environment present clear advantages in terms of ecology and annual energy costs, even when compared to the most efficient heating systems that burn gas or some other fuel.
The benefits of a heat pump include:
- Energy savings through the use of energy stored in the environment
- Reduction of emissions of CO2
- Use of only electrical energy which, in the future, will increasingly be produced using alternative sources
- Reliable operation and reduced maintenance
- No expulsion of combustible gas, thus no need for a flue pipe and periodic checks on emissions into the environment.
The heat pump as a source of renewable energyThe EU commission published, on 23 January 2008, the proposed directive RES (Renewable Energy Sources) on the promotion of the use of energy from renewable sources The proposed directive includes heat pumps as technology that uses renewable energy from the air, water, and earth. Heat pumps are a mature technology that have significant potential to make a contribution to energy savings and the climate protection objectives of the EU. Heat pumps are one of the few technologies that can cover all needs for heating, cooling, and production of domestic hot water with the use of renewable sources. Heat pumps can be successfully used in residential and commercial buildings, and in industrial applications. Heating and cooling consume at least 40% of all primary energy consumed in the EU. Widespread installation of heat pumps should bring the total number of units installed to nearly 70 million by 2020. The installed units would make a contribution of 21.5% to the targeted reduction in CO2 by 2020. In 2020 heat pumps would produce more than 770 TWh (approximately 30% of the EU target) of renewable energy, saving more than 900 TWh of primary energy.
EfficiencyThe efficiency of an electric heat pump is measured by the "C.O.P.", or coefficient of performance. This is the relationship between energy provided (heat released to the item to be heated) and consumed electrical energy.
A heat pump recovers about 75% of the energy that it demands of the environment (air, water, earth). This means that for 1 kWh of electrical energy consumed, it will provide 2.5 kWh of heat to the item to be heated. The C.O.P. varies depending on the type of heat pump and the operating conditions.
The most evident benefit of a heat pump, in addition to the high energy efficiency, is the complete elimination of local emissions of combustion by-products. The only emissions of CO2 are those resulting from the production of electricity at power plants. However, power plants are responsible for fewer emissions than small domestic heating systems. Replacement of out-of-date, inefficient gas or oil boilers is therefore a priority.
Comparison of emissions of CO2
The "Primary Energy Ratio" index (PER)The estimate of CO2 emissions is essential in evaluating environmental efficiency. There are however other indexes to verify the actual efficiency of the various available systems.
The PER (Primary Energy Ratio) is the ratio between usable thermal energy released to the environment and the primary energy which is consumed. This indicator makes it possible to analyze the energy benefits offered by various solutions, in order to identify the one that is most advantageous in terms of consumption of primary energy, which is the concept of energy savings.