PROJECT
INCORPORATING COLD CHAIN
The system cools the one tank to 5°C, while at the same time heating the other tank to 55°C. Chiller pumps.
landscapers, and the like, to be used as a
wonderful soil additive for gardens, putting
nutrition back into the earth. winter they do start running out of heating.
That is why they have recently added a
boiler to boost the system.
CLIENT BRIEF
The new Medallion site required about
1 200kW of cooling at 7°C and heating
to keep a tank at 55°C, all with full
heat recovery.
Wynroete Verkoeling, who has worked
with the client before, was appointed and
got to work putting together a suitable
system design with the help of the
AERSA team.
SYSTEM DESCRIPTION
Initially, an ammonia-HFC cascade system
was considered, but with ammonia, full heat
recovery would not have been possible
and the overall plant efficiency would
have been lower when accounting for the
heating elements as well.
So in the end, a water-cooled chiller
system was selected. Two Aermec chillers
were supplied by AERSA and two closed
circuit BAC coolers were added, with
four 4kW fans. Each fan cycles separately
according to the water temperature, and
when the heat recovery system is bypassed
and the cooling towers function normally,
the four-stage thermostat will put each fan
on/off individually.
The system runs with dual set point control
for the hot water side to keep the system
operating at a high efficiency. This is
achieved by diverting the hot water
between the hot water tank at 55°C, and
once it has achieved temperature set point,
it is diverted to the cooling towers.
Basically, the system cools the one tank
to 5°C, while at the same time heating the
other tank to 55°C. As soon as the tank
reaches 55°C, the tank is bypassed via the
three-way valve and functions as normal
through the evaporative cooling tower.
Although the cooling towers still consume
a lot of water, they are much more efficient
than air-cooled alternatives and it would be
impossible to do the same heat recovery
on an air-cooled system. Also, with the
incredibly high ambient temperatures in the
area (sometimes above 40°C), an air-cooled
system simply wouldn’t be as efficient.
As soon as ‘normal’ mode is activated,
the cooling tower will work to bring the
condenser water temperature down to
24°C. However, as soon as it switches over
to heat recovery mode, the Schneider
TAC Xenta system will monitor the hot
water temperature and three-way valve
accordingly.
With the heat reclaim, they produce
more hot water than they need in summer.
In autumn and spring they are on par, but in
A crop failure
because of a
cooling failure
can wipe you out
completely. It is
something we
could not take a
chance on.
The new plant has been set up to run at a
lower temperature when compared to its
ammonia plants. This means that the coils
had to be bigger. They also have much
bigger pipes feeding heating and cooling
to the rooms than they would normally
have. It is four times the size of normal pipes.
But although it is a bigger volume of water,
less pressure is required (only running at 1.5
bar). This means the friction losses become
less and the pumps do not use as much
electricity.
COLD LINK AFRICA • May 2018
EQUIPMENT CHOICE
Once decided to go the chiller route, Koorts
did a lot of research before selecting a
particular supplier. Service levels were essential,
as this was quite a large capital investment.
As they wanted full heat recovery, this
already ruled out quite a few suppliers. What
sold them on Aermec in the end, was the
fact that these chillers come with standard
Bitzer compressors and Carel making spares
easily available. Although Aermec fully
supports the client with spare parts and
service delivery, the equipment components
are also supported locally through the OEMs
such as Carel and Bitzer. They previously had
issues with compressors going down and
they could not afford to wait for spares.
“The chiller plant is our lifeline,” explains
Koorts. That is why they have two chillers
now, to build in redundancy. “Mushrooms
are very sensitive to temperature control
and we are helpless without the chiller.”
At Medallion, they are working with a
five- to six-week stock pile at any given time
in a cycle. So if the chiller goes, they lose all
of it. “All of that is cost sitting in the system,”
explains Baring Richardson. “A crop failure
because of a cooling failure can wipe you
out completely. It’s something we could not
take a chance on.”
That is why there are two chiller plants.
The entire system is duplicated. “Having a
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