Architect and Builder Magazine South Africa March/April 2014 | Page 65
Five chillers are located on
the roof of the building,
with total capacity of 3
megawatt, and are used
to generate chilled water
ROOF SERVICE LEVEL - CHILLERS
fluctuation, acoustic noise and vibration.
These requirements presented a challenge
with regard to selecting the method of air
conditioning the room, housing the high
performance microscope.
The four key environmental challenges are:
1. Electromagnetic fields to less than 0,01 T r.m.s.
2. oom set point temperature of 18°C to 20°C
R
with temperature changes to less than 0,2°C
per hour.
3. irflow across the microscope column to less
A
than 0,076 m/s (i.e. 15 feet per min).
4. ir pressure changes to less than a few Pascal
A
per min.
Conventional air conditioning systems
ultimately utilize air to either cool or heat the
conditioned space. The volume of air introduced
into the space is a function of the heat to be
removed from the room. To achieve even
temperature throughout a conditioned space,
using air as the cooling medium, requires high
air change rates and a very low temperature
difference between supply air and room set
point. The disadvantage of using traditional air
based conditioning, for election microscope
laboratories, is that air movement can create
noise and vibration as well as cold air streams.
To illustrate the point, if a 300mm x 60mm
strip of single ply toilet paper deflects more
than 25mm, the air flow exceeds 0,1 m/s.
In order to minimise the cooling load, as
much of the heat generating equipment must
be kept out the microscope room and housed in
an adjoining dedicated equipment room.
After extensive evaluation it was decided
to implement a system utilising chilled water
Sasol Infrachem
radiant panels mounted on the walls of the
microscope laboratory. These chilled panels act
as a heat sink by absorbing heat by radiation
(the reverse of radiant heating) and creating
very slow convective ai ȁ