PROJECT
INCORPORATING COLD CHAIN
are connected to the discharge of the
medium-temperature rack and heat
produced from the refrigeration cycle is
used to heat up a secondary water cycle
for use within the store area.
The adiabatic gas coolers are situated
in a properly ventilated area. In high-
ambient conditions, the gas cooler
may use water to maintain acceptable
discharge pressures and temperatures. The
water is evaporated, thereby lowering the
dew point temperature below ambient
temperatures, allowing the system to
continue to run within acceptable limits.
Woolworths is now working with CRS to
use dry gas coolers instead of adiabatic to
help preserve the use of water.
All high-pressure piping is done
with stainless-steel tubing, fittings, and
components, where necessary copper
piping is used for all the low-pressure and
suction line piping. Where copper piping is
used, it is ensured that high-pressure copper
piping is fitted.
It is important to note that all lines are
fitted with relief valves:
• Medium-temperature suction: 48 bar
• Low-temperature suction: 30 bar
• Medium-temperature discharge:
130 bar
• Low-temperature discharge: 48 bar
• Liquid line: 48 bar
• Receiver: 48 bar.
The receiver (or flash tank) is also fitted with
a purge valve; this is operated through a
pulse timer and controlled by a pressure
switch to relieve pressure from the receiver
should the pressure rise uncontrollably for
whatever reason. This pre-emptive safety
feature is to help prevent the total loss of
the refrigerant charge.
All electrical components are linked
with an array of cables, and the racks are
operated by switch gear and protected
by various electrical and mechanical
safety switches.
Chilled water pump.
A Danfoss system manager, case, and
pack controllers have been used to ensure
that the refrigeration cycle is continuously
run at optimum performance.
UNDERFLOOR HEATING
There are two heat exchangers on the
CO 2 discharge line, which heat up the
water to the required 55°C. This is then
circulated through two 250ℓ storage vessels.
It is controlled by a hot water pump and
variable speed drive (VSD) to maintain
the required temperature. This was part of
CRS’s scope.
WSP’s scope involved pumping water
from two storage vessels through the heat
pump if further heating is required, or
bypassing directly to a series of manifold
stations positioned in the store. This split up
the hot water supply into various underfloor
water heating pipes that were cast into the
surface bed at the stage of construction.
The heat exchangers were manufactured by HC Heat.
PLANT OPERATION
The refrigerant used within the refrigeration
cycle is CO 2 (R744) and is a natural
refrigerant that is odourless, non-flammable,
food safe, and heavier than air.
Leak detectors are therefore essential in
particular areas of low ventilation; that is,
cold rooms, and are required to be situated
close to the ground.
Each rack consists of more than one
compressor, where the first compressor
is controlled by a VSD — this is used to
control the suction temperature as close
as possible to set-point. The rest of the
compressors will start up direct on line as
needed when the required capacity of the
cycle increases. The compressors that are
not driven will switch on in a cyclic manner
to ensure that running time is spread
between each non-driven compressor.
The Danfoss pack controllers will
always attempt to operate to the best
coefficient of performance (COP)
possible, unless set-up is altered for heat
The open display cases at Woolworths Kyalami.
The Danfoss variable frequency drive.
Inside the custom-built control panel for the refrigeration
packs.
COLD LINK AFRICA • January/February 2019
www.coldlinkafrica.co.za
39