INGENIEUR
Picture 10 : Typical Thermal Wheel
Picture 8 : Typical Boiler and Heat Pump Chiller
processes , circulate through the Hot water coil as shown in Picture 8 .
For hot and humid countries like Malaysia , the hot water reheat system as a separate hot water system just for OT applications would be a poor return on investment and cannot be justified .
Reheat plus a Desiccant Wheel Heat Recovery System
when it passes through the desiccant wheel and comes into contact with the “ cold ” wheel surface . As the wheel turns , the “ hot ” wheel surface is cooled by the return air from the chilled water cooling coil before discharging to the outside atmosphere . Picture 10 shows the location of the heat wheel .
Normal operating theatre design requires 100 % fresh air , and no return air is allowed to circulate in the system , as this would introduce bacteria , viruses , micro-organisms into the OT . However , it would be a waste of energy by simply discharging cool air to the atmosphere .
An energy efficient method includes a Desiccant / Thermal Wheel ( see Picture 10 ) which is cooled by the exit air from the chilled water-cooling coil before it is discharged into the atmosphere . The cold wheel rotates and precools the incoming outside fresh air to 22 ° C before it passes to the chiller . With the introduction of an energy efficient system such as a thermal wheel , the initial cost of the system goes up .
Picture 9 : Typical Heat Recovery Wheel Air Handling Unit System
Outside fresh air at 34 ° C passes through the desiccant wheel which contains crystals to remove moisture and at the same time cools the air to 28 ° C . The cooled air is then passed through the chilled water cooling coil to reach the 10 ° C to 12 ° C dew point temperature .
As can be seen in Picture 9 , outside fresh air comes in to the lower section , and is cooled down
Double Chilled Water Coils plus Heat Pipe System
A Heat Pipe is a thermal transfer device that is basically a sealed tube filled with a refrigerant . It typically spans the supply air and exhaust air sides of a system . Energy is transferred – with no moving parts – from one air stream to the other ( as long as there is a temperature difference ). The refrigerant is evaporated on the hot side of the heat pipe and moves to the other side of the pipe
30 VOL 86 APRIL-JUNE 2021