Energy conservation needs prime consideration during design and operation stages of any facilitites.;but equally air what we breath is also important..Quality air is fundamental to people's health and well-being. Indoor air quality is an important issue from both a social and economic point of view. The US Environmental Protection Agency (EPA) concedes that about 30% of new or renovated buildings have serious indoor air quality problems, and ranks IAQ as the most prominent environmental problem (Roodman, 1995). It is reported in the report titled "Causes of Indoor Air Quality Problems in Schools"(ASHRAE Journal, P16, 1999) that as many as 20% of U.S. Schools have indoor air quality problems.ASHRAE has created new standards particularly for IAQ.. The new standards require more fresh air and exhaust large volumes of conditioned air which in turn raises energy cost. Engineers and owners of facilities are facing a major challenge to find solution without tripling the cost of building operation and maintenance system. Installation of suitable heat exchangers used to recycle the energy from the exhaust to the supply air stream, is one option to reduce the energy cost. During recent years Demand Controlled Ventilation (DCV) concept is being used in HVAC system design.DCV is a strategy that attempts to reduce the energy used by ventilation systems while maintaining required levels of indoor air quality (IAQ). During the last few decades variable air volume (VAV) systems that were conceived to alter the volume flow rate to match thermal demand has became popular among air conditioning engineers. By regulating the flow rate of air through a properly designed system, significant energy savings could be achieved with the help of VAV systems. The concept has been developed and refined to produce the modern DCV systems that frequently not only control temperature (and humidity) but also optimize the supply of air volumes, and particularly outdoor air, so that appropriate levels of IAQ are maintained whilst minimizing energy costs. Humidity plays a vital role in defining comfort and also it adds latent heat load and therefore maximum limit is there.