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TOPMACS
Thermally Operated Mobile Air Conditioning Systems

The goal of the project is to develop mobile air conditioning systems (MACS) with a reduced impact on the environment. The systems will be considered for two vehicle applications: passenger cars and trucks.

Tags: Road

Background

The state of the art of the 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) have been 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 aims 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.

Description of work

The following system requirement definitions need to be determined:

  1. specifications for systems in trucks and cars (weight, size, operating temperatures, vibrations, noise, etc)
  2. target performance expected from the systems, (refrigerant power, efficiency, thermal comfort, quality of the air)
  3. reference truck and car on which the performances will be verified and the corresponding assessment method defined.
Overall Systems Model: 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)
  • 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 sorption cooling system: the design, construction and testing of lab-scale solid sorption air conditioner and cold storage systems for automotive applications.

A second-generation prototype will be installed onboard the car/truck and tested.

An evaluation of the environmental benefits and cost analysis will be carried out.

Results

An assessment methodology will be developed to evaluate both the fuel over-consumption due to the MACS and the thermal comfort. This methodology could be a useful base for a procedure proposal about the measurement of the over-consumption/emission due to MACS.

An overall model of the truck and car and the subsystems will allow a simulation of the thermal performance and predict the energy consumption of the systems.

There will be four test bench prototypes (three of sorption, one of metal hydride).

A prototype car and truck, equipped with the best innovative systems, will be developed. The prototypes will be compatible with the incoming EU regulations on fluids, and will also allow a lower impact of the MACS during the phase of use, lowering the additional fuel consumption generated by MACS. The MAC systems can be decoupled from the engine, offering a solution for vehicles powered by non-conventional powertrains and for truck air conditioning in parking conditions.

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