3, The term ventilation as used in this report Ventilation. includes the continuous supply of outside air at ambient temperature and relative humidity and the control of its movement either by forced or induced fans, In some cases, ventilation included the removal of dust by means of filters. DEHUMIDIFICATION In accordance with design requirements as stated in the Reconnais- sance Report the only building to be air conditioned was the photo laboratory, All other buildings were to be dehumidified only. In September 1949, H & N received information from J-Division that certain buildings for use of NRL on various experimental sites would be dehumidified, The question of dehumidifying the telephone equipment room located in the H & N Administration Building on Parry was discussed with the manufacturers of telephone equipment and H & N decided to dehumidify this area to safeguard the expensive equipment against moisture and fungus attack. The working drawings of the buildings to be dehumidified on Parry were being drawn when, in November 1949, H & N received design criteria from J-Division requesting a change in the design conditions from 50 percent to 40 per cent relative humidity for all dehumidification requirements throughout the Project, except for the photo laboratory. The details of the photo laboratory had not been firmed at that time, and H & N was advised that the extent of air conditioning that would be required for this building would be specified later, Because of this change in requirement, all work was stopped on drawings and all the calculations were revised. The new loads were compared with the capacity of equipment selected and the only change required was to increase the fan motors from lhp to lehp. After this, it was determined that for easier maintenance and replacement, all equipment should be kept as nearly alike as possible, The dehumidifier units each consisted of three major elements: the air drying unit, the dry coil condenser, and the compressor. The units were designed to be completely selfcontained and adaptable for installation either inside or outside of the conditioned space. They had a return plenum chamber through which air from the room was re- circulated and mixed with a small portion of fresh, outside air, The air was filtered, cooled, and dehumidified by a direct expansion freon cooling coil and then reheated by the reheat coil to maintain the proper temperature within the building. Inasmuch as steam or hot water was not available for this heating, hot refrigerant gas from the compressor was used. The refrigerating compressor was of the hermetically sealed type, with the compressor shaft directly connected to the electric motor and the entire equipment hermetically sealed so that corrosive effect of the atmosphere would not reach the vital parts, The dry condenser consisted of a condensing coil, condenser fan, and air filters. The controls were designed so that once the unit was started it would 9-257