Motivation

Development of equipment specifically designed for natural fluids could lead to even higher efficiencies than the ones obtained with synthetic refrigerants, contributing at the same time to the reduction of the energy consumption and to the practical elimination of direct emissions, resulting in a double reduction of the global environmental impact of heat pumps.

The barriers for the wide-spread use of natural refrigerants are twofold: non-technical and technical.

Non technical barriers:

There is practically no barrier to the development of CO2 equipment except for their cost. The issue of the cost is of course also technical, being essential to look for cost effective solutions. Furthermore, the cost is strongly dependent on the production so this could only be finally solved if the developed solutions evolve into industrial products.

With regard to hydrocarbons, the most important barrier to their utilization is the fear of the OEMs to produce components and equipment for flammable refrigerants and then being eventually involved in legal claims for accidents related with their flammability. However, the long experience gained now with small systems in domestic or in light commercial applications, proves that the equipment employing hydrocarbons as the refrigerant is safe, and engineers, installers and technicians have become very experience to avoid the associated risks along the manufacturing, handling and maintenance of the equipment. On the other hand, in the field of commercial units for heating and cooling or industrial applications, it could be even easier to avoid risks than in the domestic or small commercial sectors, since the equipment is always installed in restricted areas where only trained people have access, and placing the units in the open air or in machinery rooms is perfectly possible.

The public in general is very open to solutions with natural refrigerants. They understand the advantages of employing a natural fluid instead of a new synthetic one, and if they perform even more efficiently, why not? It should be pointed out that there has been no adverse public reaction at all to the huge penetration of the isobutane technology in refrigerators almost all over the world.

Technical barriers:

On the technical side, the barriers are logically different for Hydrocarbons than for CO2.

Hydrocarbons (HCs):

There are already in the market components and technology available for the use of flammable refrigerants.

Additionally, after many years of discussion, the relevant standards now finally include the set of requirements and measurements that must be followed in order to safely employ flammable refrigerants in refrigeration and heat pump equipment. This set of requirements constitutes of course a certain cost barrier that must be overcome but guarantees the intrinsic safety of the equipment. Therefore, the key point for the development of HCs equipment is to look for applications in which the extra cost involved in the safety measures is low and can be in fact compensated by the lower energy consumption. This is particularly possible for the equipment targeted in this project, since high capacity units are located either in open air (rooftop units) or in a special machinery room with restricted access.

CO2:

The efficiency of transcritical CO2 systems is more sensitive to ambient temperature than HC or HFC systems. For cooling purposes at high ambient temperatures, i.e. in hot climates, CO2 is not the best choice. Similarly, for space heating, where the temperature increase of the heat sink fluid is low, it is difficult to design a highly efficient CO2 system, but for refrigeration in supermarkets or heating of sanitary hot water, CO2 may be a very efficient refrigerant, additionally offering its excellent characteristics from the point of view of the global warming potential. Therefore, the important thing is to develop improved components and systems for the applications in which the transcritical CO2 cycle may be integrated and utilized to advantage.

Of course, for both HCs and CO2, the cost is a very important barrier too. HCs do not require any special measure from the refrigeration point of view that could imply a higher cost. On the contrary, the components could, in general, be equal or less expensive than for synthetic fluids and the cost of the refrigerant itself much lower. However, the incorporation of safety measures could lead to a slight increase in cost of this technology. Therefore, it is essential to try to look for a reduction in all possible costs of the unit in order to compensate the extra cost of the necessary safety measures. On one hand, CO2’s high operating pressure requires heavier thicknesses and different design of some components. But, on the other hand, it also requires smaller size of the components, so in principle the development of CO2 equipment with a cost similar to the conventional refrigerants could be possible if the production is large enough. This is especially true for the compressors, which at the moment are more expensive than for conventional refrigerants.

This project strives to give a definitive step forward to overcome the barriers impeding the spread of natural refrigerants and usher in a new generation of heat pumps based on HCs and CO2 that are perfectly feasible and commercially competitive.