Project not sound like much but when one considers that the ceiling height is around 14m , this equates to a lot of outside air . With this volume of fresh air input , the design is dominated by the need to condition this air adequately , this then meant dealing with vast differences in on-coil conditions - both from a diurnal and a seasonal annual perspective .
It is important to remember that no amount of positive pressurisation within the space can stop the inflow of vapour pressure . Vapour pressure is only interrupted by vapour barriers , in the case of a building this means impervious building materials and very limited airgaps . Moisture will move against airflow if there is a vapour pressure differential . The existing building construction was very well sealed and relatively air tight , which assisted in limiting the inflow of moisture .
It can thus be seen that the constant flow of conditioned fresh air into the building is the critical factor in maintaining low relative humidities . To this end it is also important to note that the system is operated at as high a dry bulb ( DB ) temperature as possible , within the prescribed limits , in order to reduce the relative humidity and save on cooling energy requirements .
The other benefit of constantly maintaining a positive pressure within the controlled space is that there is very little dust ingress since intake air is filtered through primary and secondary filter banks .
The AHUs were designed to cool the conditioned air down to a leaving coil condition of 11.5 ° C DB and 11.3 ° C wet buld ( WB ). This “ overcooling ” drops the absolute humidity to the
The AHU and condenser units were mounted on steel platforms with sufficient space for maintenance .
EC plug fans were used for supply air .
Condenser units with neatly installed refrigerant piping .
www . refrigerationandaircon . co . za RACA Journal I September 2022 33