INTRODUCTION

The air-conditioning is that branch of engineering which deals with the study of supplying and maintaining desirable internal room atmospheric conditions of air for human comfort. The four important factors for human comfort are: temperature, humidity, purity and motion of air.

The working substance for air-conditioning is moist air, which a mixture of two gases. One of these is dry air, which itself is a mixture of a number of gases and the other is water vapour which may exist in a saturated or superheated state. Moist air is not a pure substance in any process in which condensation or evaporation of moisture occurs. Both dry air and water vapour can be considered as perfect gases since both exist in the atmosphere at low pressures. Hence, perfect gas laws to both and Dalton’s law of partial pressures for non-reactive mixture of gases can be applied to dry air part only.