engleski

Efficiency analysis of the air-to-air heat recovery system

Air-to-air heat recovery from the exhaust air stream improves the energy utilization level in the air-conditioning and ventilation systems. The heat recovery device lowers the enthalpy of the supply air during warm weather and raises it during cold weather by transferring energy between the supply and the exhaust air streams. By applying the heat recovery equipment in the air-conditioning systems, heating and cooling energy consumption for the supply air preparation, fuel consumption, size requirements for primary utility equipment, and indirectly the environment pollution (emission of the harmful flue gasses and waste heat of the burning process) are reduced. In this paper, both the energy and efficiency analysis of the coil energy recovery loop system in dependence of changing the operating conditions were performed. A coil energy recovery loop system operates for sensible heat recovery only, with seasonally reversible energy transfer. It consists of two finned tube air-to-water heat exchangers, placed in the supply and exhaust air streams and connected in a closed loop via counterflow piping through which an intermediate heat transfer fluid (typically water or freeze-preventive solution) is pumped. For the purpose of analysis, the original simulation model of the system was developed. This model enables the analysis of the system operation, together with monitoring of both consumption and recovery of heating or cooling energy, electricity consumption of the electrical appliances, and also the determination of system efficiency value for various operating conditions in the unsaturated area of moist air. It is also possible to integrate this model in the simulation model of a complex air-conditioning system. Besides the simulation model development, the extensive measurements on the coil energy recovery loop system with 12 tube rows in the flow direction were performed to determine heating, i.e. cooling capacity in different operating points. For this purpose, the experimental rig was designed and installed in order to conduct the measurements on the system in its real dimensions, placed in the air conditioning unit. Based on the measurement results, the system efficiencies were determined for the measured operating points set. With the developed simulation model of the coil energy recovery loop system, consistent and stabile results were obtained, and their reliability was proven by comparison with the measurement results. The aberrations between the simulation and measurement results were in the range of „b3%. The influences of the air streams volumes, the air streams velocities, the water flow mass and the operation seasons on the system efficiency were presented in the proper diagrams. The obtained results are the base for forming the set of parametric curves for the system characteristics determination in diverse operating points.

air-conditioning; air-to-air heat recovery; heating and cooling capacity; simulation model; system efficiency

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