Application Study On R404a Evaporative Low Temperature Refrigerant Units

To develop air conditioning units operating under conditions of low temperature, high humidity is the urgent need of development for food processing industry. Different with the traditional food processing system, how to solve the frost problems of unit during operation, how to match machine reasonable, and how to control the temperature of food workshop from a technical point of view for achieving the maximization of energy saving and improving the COP of the low temperature refrigeration system, is an urgent problem as because of the low evaporation temperature and high humidity..The heat transfer performance of evaporative condenser is greatly increased compared with the air cooling condenser, and the load of the fan and the energy consumption are reduced. At the same heat load, the heat transfer area needed of the evaporative condenser is smaller. Compared with the cooling system using traditional shell and tube condenser and cooling tower, the condensing temperature is decreased significantly. In addition, the evaporative condenser exerts the effects of the cooling tower fully, and its structure is simple compact, the install area is greatly reduced. Also the costs of connected pipes and valves of the condenser and cooling tower and the maintenance costs are reduced. Therefore, utilization of the energy saving and efficient evaporative condenser on the air conditioning unit system of the food processing room is urgent and necessary.This research adopts the direct evaporation cooling refrigerant, and the problems such as energy dissipation, heat transfer efficiency, safety and system simplification, and many other problems are solved fundamentally. R404a is used as refrigerants, which is non-azeotropic, non-toxic, odorless, colorless gas under atmospheric pressure. It is a kind of mixed refrigerant which can’t bring destruction to ozone and is an alternative of R502and R22in the field of refrigeration system.For food processing workshops working at10℃or2℃and high humidity, the heat transfer mode of large temperature difference and small flow rate can reduce the heat transfer and increase the air resistance, also the evaporator would froze. In addition, a large amount of moisture load would produced, which is not conducive to workshop cooling and energy-saving. But the heat transfer form using small temperature difference and mass flow, although the thermal efficiency is not high, but the problem of condensation and frost can be solved if the appropriate temperature and wind speed are selected. To find a suitable supply air temperature which can not only increase thermal efficiency, and can solve the problem of condensation or frost, is one of the aspects of this subject research.The following innovations are mainly completed on the basis of fully considering the advanced refrigeration technology:(1) Outdoor unit using the evaporative condenser, saving energy, space and reducing the need of fan, water pump, pipes, valves, control system and other facilities for the air-cooled, water-cooled condensers. Many aspects have been saved such as the investment, operation cost, and management difficulty. Compared with the water-cooled condenser system at the same load, the COP increased by25%. And compared with the air-cooling condenser system, the COP increases by35%.(2) The indoor machine uses direct evaporation evaporator of R404a. Compared with ethylene glycol cooling system, the system is simplified, the water pump, control system and other facilities are saved, and the investment and operation cost are reduced.(3) The air supply using the method of3～5℃temperature difference, reduces the effects of the moisture load on the workshop air conditioning. The evaporation temperature and cooling efficiency are both improved, and energy can be saved at the same time. Using the method of delaying to stop indoor air to defrost or heat recovery from refrigerant to defrost is a better solution of frosting problem of heat exchanger for food processing workshops, which work at the low temperature and high humidity environment.