Summary

Condensor and evaporator of a common direct-expansion cooling system consist of shell-and-tube heat exchangers. A thermostatic expansion valve (TEV) controls the amount of refrigerant flowing into the evaporator in order to keep the superheating at the outlet of the evaporator constant. Due to the system's inertia the superheating amounts to approximately 10 °C thereby eliminating the risk of damaging the compressor by fluid droplets.
Energy-efficiency can be substantially improved by the application of plate heat exchangers and an electronic expansion valve (EEV). Based on these components Wijbenga bv, located in Beesd, the Netherlands, built a test facility. With refrigerants R22, R507, R407C and ammonia the cooling system was able to operate at stable conditions.
The applied compact heat exchangers (type Q-plate) decrease the system's inertia. Optimisation can be obtained by automatically matching the condensation temperature to the actual situation. This also allows the superheating to be set to a minimum of 5 °C. Based on the results of the experiments, this new system leads to an improvement of the coefficient of performance (COP). Depending on cooling demand and outside conditions (summer/winter) it can save typically up to around 47% of the electrical energy used by conventional cooling systems using a constant pressure TEV.
The refrigerant content of this system is also substantially smaller than that of the regular systems, thereby increasing safety.
Applications for the innovative system can be found mainly in industrial refrigerating plants in the food processing industry and companies that provide cold storage and refrigerated distribution services (up to 200 kW).