TOPMACS - Thermally Operated Mobile Air Conditioning Systems
Overview
Background & policy context:
The State-of-the-Art of the Mobile Air Conditioning Systems (MACS) is represented by vapour compression cycles that use R134a as a refrigerant, which is a greenhouse gas with a high global warming potential (GWP, equal to 1 300). Due to the refrigerant leakages during usage, it has been estimated that in Europe, every year, between 750 and 2 500 tons of R134a are emitted in the atmosphere. Taking into account the GWP, this is equivalent to up to 3 millions of tons of CO2.
Europe is making a huge effort to reduce greenhouse gas emissions. The development of highly efficient air conditioning systems with a near-zero greenhouse gas emission and eliminating hydrofluorocarbon (HFC) are considered a priority. According to the new EC regulation, by 2011, no refrigerant having a GWP higher than 150 can be used on MACS.
At present two gases are being considered as options to replace the R134a. CO2 has a low GWP (equal to 1), but as it works at high pressure, it needs the development of new components. Moreover, its performance could be critical at high ambient air temperatures. The other option is R152a, which is still a HFC but with a GWP below 140. The drawback is its slight flammability.
Objectives:
The project aimed at:
- eliminating the environmental impact from refrigerant leakages. The refrigerants used (water, ammonia or hydrogen) are in agreement with new regulations;
- reducing indirect emissions. The MAC system's impact on fuel consumption will be minimised since the primary energy source will be waste heat, while the electric compressor-driven metal hydride system can have a COP of up to 3.4;
- decoupling the MAC systems from the engine. The availability of a low-consumption electrical powered cooling system could be the ideal solution for a vehicle with electrical traction architectures (stop&start vehicles, hybrid vehicles or fuel cells). These vehicle types risk serious commercial problems, and elimination of their environmental advantages, if a high efficiency solution for thermal comfort is not available;
- developing an auxiliary heating system. Since these systems are capable of a heat pumping operation, they can be a solution for the lack of waste heat of highly efficient diesel engines and also for vehicles not powered by an internal combustion engine;
- developing additional functions like pre-conditioning. The potential of these systems to provide energy storage or the presence of an APU, will allow pre-warming and pre-cooling, for which the car market demand is growing and it is considered all important in the truck;
- downsizing the system. To have pre-conditioning systems is also beneficial from an energy point of view, allowing a system design with lower peak power.
Methodology:
The section below lists the planned activities and the research methods employed in the TOPMACS project:
- Determining the following system requirement definitions:
- specifications for systems in trucks and cars (weight, size, operating temperatures, vibrations, noise, etc.);
- target performance expected from the systems (refrigerant power, efficiency, thermal comfort, quality of the air);
- reference truck and car on which the performances will be verified and the corresponding assessment method defined.
- Overall Systems Model development: lumped parameter models of the truck and car that include all the sub-systems having an interaction with the MAC system need to be developed. The models will allow the simulation of thermal performances (power and perceived comfort) and energy consumption.
- Development of a metal hydride system: investigations will be carried out with either waste heat (from the engine or APU) or electric energy (for hydrogen compression) as the primary energy source. A test bench prototype will be set up and the performance evaluated.
- Development of a sorption cooling system: the design, construction and testing of lab-scale solid sorption air conditioner and cold storage systems for automotive applications.
- Installing a second-generation prototype onboard the car/truck and testing it.
- Conducting an evaluation of the environmental benefits and a cost analysis.
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