FEATURE
INCORPORATING COLD CHAIN
Why is your cold store
floor rising?
By James Cunningham of Barpro Storage
fter some initial panic, it was found
that the obstacle was a ridge in
the concrete floor. As the floor had
been checked for level after initial curing,
the newly formed ridge was surprising.
The floor had a glycol heater mat
beneath the underfloor insulation, and
every circuit had a flow meter outside the
building so that movement of the glycol
mixture heated by the refrigeration system
condensers could be easily checked.
A bumblebee had become lodged
in a flow meter, obstructing the flow of
glycol and allowing ice to form in the
subfloor, which created the problematic
ridge through ‘frost heave’. The bee
was removed, the ice melted, and the
ridge disappeared without cracking the
concrete floor.
In Australia, 200mm pipes are laid
under freezer floors and air pumped
through them to stop ice from forming in
the subfloor. At one freezer, the pipe did
not have sufficient fall, so condensation
puddled and froze, obstructing the pipe
and eventually causing the cold store floor
to rise. At one local store, similar air vents
were blocked to prevent rat ingress. That
floor rose by 900mm.
The glycol heating circuit is installed
without flow meters, and the heat
exchangers are placed next to the
where the heater mat control panel is
situated and how it works. Just the other
day we had to help a customer who
realised that his heater mat control panel
needed fixing.
This was only identified after the floor
had begun to rise.
It is critical that heater mats
get checked regularly and that
management understands the purpose
thereof. In freezer stores, especially those
with mobile racking systems, keeping the
floor level is so essential that annual floor
level checks are recommended. CLA
condensers on the cold store roof when
heating the glycol.
LOCAL CONTEXT
In South Africa, while some recent stores
have installed glycol systems, most rely
on electrical heater mats, which normally
consist of three circuits of wire — a bit like
a hot blanket on a bed. The wires lie in a
sand bed, which may or may not be held
together with a weak cement mix. The
circuits end in a control box that activates
them only if the temperature beneath the
cold store floor dips beneath 4°C.
This 4°C temperature is interesting, as
water with impurities can freeze at higher
temperatures than zero. Some chill stores
have discovered this to their cost, as heater
mats were considered unnecessary. As
the business changed, temperatures were
dropped to minus 0.5°C and the rooms
kept running year round instead of being
switched off in the summer months. After
several stores experienced frost heave,
heater mats and underfloor insulation have
now become part of the building design.
While it may sound obvious, check that
the heater mats are on when the chamber
is commissioned. We have seen at least
three stores where the floor rose through
frost heave because the heater mats had
not been switched on. In one instance, the
A
In a newly commissioned Danish freezer some years ago,
a Storax mobile refused to move. What went wrong?
Heat exchangers next to the condensers on
the cold store roof when heating the glycol.
floor subsided. In the others, the movement
had already cut the wires.
I visited one store where the heat
mat cables had been cut by accident
and attempts had been made to drill
right under the floor in the insulation to
replace the wires. I do not know if the
plan worked.
What I have found somewhat
surprising is the number of times when
management did not immediately know
COLD LINK AFRICA • July/August 2018
Glycol heating circuit without flow meters.
www.coldlinkafrica.co.za
33