Increasing energy efficiency of refrigeration and freezing applications
Michael Beck, Karsten Müller, Wolfgang Arlt,
Friedrich-Alexander-University of Erlangen-Nürnberg, Germany
Institute of Separation Science and Technology
Refrigeration and freezing applications are responsible for about 17 % of the electrical energy demand in the residential sector. The electrically driven compression chiller is by far the most widely used technology to supply cooling. The cycle process, which is installed in most refrigerators and freezers, works with the aim to transfer heat from a lower to a higher temperature level. The topic of this work is to present and compare several innovative concepts to increase the energy efficiency for providing refrigeration in residential as well as in commercial cooling and freezing applications.
The first approach discussed in this work evaluates the possibility to achieve higher energy efficiency for cooling processes by using the environment as an infinite thermal heat sink. With the help of heat pipes as efficient heat exchangers and the integration of a cold storage, it is possible to cover a part of the energy demand by passive cooling. Thus, the overall energy demand for the cooling unit can be significantly reduced. The modeling of the energy storage loading based on outside temperature data, as well as the design of the heat pipes are important for the efficiency of the concept.
The second approach is based on a possible form of load management for photovoltaic energy (PV), by using the surplus electricity to load a low temperature thermal storage with a compression chiller. This cold storage can be used to cover the required cooling capacity. The concept requires the operation of the refrigeration process in a way that fits to the generation profile of the PV system. A meaningful implementation of the system concept is possible only with the help of a suitable cold storage, for example a phase change material.
The operational behavior and the controlling of the storage system considering several boundary conditions, such as the radiation profile and the cooling demand, is modelled in this work. Based on a sensitivity analysis the influence of various system parameters on the efficiency is investigated. Furthermore, the described concept of storing excess solar energy by using a low temperature thermal storage system is compared to the state of the art technologies to store electrical energy. At last a comparison between all evaluated concepts is presented.