INTRODUCTION:

Air conditioning systems using mechanical refrigeration have high initial cost and consumes significant amount of energy. A cheaper system of cooling is Evaporative Cooling used extensively in hot and arid climates. However, this process has its own limitations that it cannot be used effectively if the wet bulb depression is low (Wet bulb temperature is high).

It has therefore been considered that an economical system, involving both mechanical refrigeration and evaporative cooling may be evolved to cater to Indian conditions consuming less power and providing the same indoor conditions as in refrigerated air conditioning.

A DBT of 32șC (±2șC) and relative Humidity of 50-75% in different section of textile industry can be achieved by above combination.

SYSTEM EXPLANATION:

A two stage hybrid air conditioning system consists of a first stage of a Dry Surface Type Indirect Evaporative Cooling System and a second stage of Chilled Water Spray System.

Cooling of air by chilled water spray using a refrigerated air conditioning system is a costly and energy consuming system. The cost of refrigerated cooling system comes to about 1.00 kW per TR (50 Kcal/min or 3.5 kW of cooling).

Pre cooling inlet air using cold water from cooling tower does not consume that much power. Power required to pre cool air will depend on ambient wet bulb temperature however, under worst climatic conditions (say 29șC WBT) the power requirement may be 300 Watt per TR of heat removed from air in pre cooler as compared to 1 KW/TR for refrigerated air-conditioning. At lower wet bulb temperature the power requirement will be still lower as has been shown subsequently.

TWO STAGE HYBRID AIR CONDITIONING SYSTEM:

 When the indirect evaporative cooler is placed in series (upstream) with a conventional refrigerated system, it reduces the sensible heat load on refrigeration system. Energy required for the indirect cooling stage includes the pump and cooling tower fan as well as some additional fan energy to over come resistance in the supply air system due to heat exchanger. The energy consumed by indirect evaporative cooling stage is much less than the energy saved from reducing the load on refrigeration system. As a result, the overall energy consumption of the system will reduce. Another saving could result from the reduction in size of the refrigeration equipment required. Indirect evaporative cooling may also reduce the total time the refrigeration equipment must be operated during a year.

It has been found that the load on chilled water system can be reduced by pre cooling of air, thereby reducing the power consumption by more than 30% during the period of worst ambient conditions.

CONCLUSION:

 A hybrid air conditioning system will yield the same indoor design conditions as a refrigerated air conditioning system as the second stage comprises of the refrigeration stage. The initial cost incurred on first indirect evaporative cooling stage is also compensated by reduction in the size of the refrigeration plant as its load is partially transferred on the first stage. The first stage cools the air evaporatively and hence consumes less power as compared to the refrigeration plant and so the hybrid system is more power efficient as compared to the refrigerated air conditioning.