For a 100% fresh air application where the air was to be used for pneumatic conveying and finally exhausted, the fresh air needed to be cooled down to 2OC dew point and subsequently reheated to supply at 14OC and 45% RH (see Figure 1). The customer did not wish to install a desiccant dehumidifier and was also unwilling to
Figure 1: Psychrometrics of case study 1 consider a glycol system. Another issue was that the location of the plant was in north India and the ambient wet bulb varied from 28.5OC in the monsoon to 5OC in the winter. As the air was not recirculated, it had to be cooled online. Cooling was required to be continuously ON and at the same time to modulate based on varying incoming air condition. Lower RH than the design condition of 45% was, however, acceptable to the customer. Chilled water was available.
The solution was to cool the air down to an intermediate level of 14OC using available chilled water. From 14OC to 2OC the air was cooled by passing over another DX coil. For frost prevention, the coil was artificially loaded with hot gas from the compressor to maintain the minimum evaporating temperature to prevent frost formation.