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With their new herb
processing factory at Palmwoods,
Gourmet
Garden wanted to explore how far
they could go to achieve new benchmarks in
Australia for environmentally
sustainable development and it was ISECO’s task to come up with
green options for refrigeration.
The factory comprises a
series of medium temperature process and chiller rooms operating at
design temperature in the range of 4C to 18C and one medium size
coldstore with a design temperature of -25C.
ISECO Consulting Services
were engaged to investigate and design a refrigeration system to
address these issues, such as minimising energy consumption,
reducing greenhouse gas emissions, minimising water consumption and
eliminating trade wastes i.e. water treatment
chemicals.
ISECO investigated the
latest technologies available and how these could be
applied.
Firstly, a survey all the
different refrigerants available with natural refrigerants like
ammonia and CO2, all the Freon and the Freon substitutes
as well as a new azeotropic refrigerant blend of hydrocarbon and
ammonia. The azeotropic blend was too new and Gourmet had stipulated
that they did not want to use any Freon because of the ozone
depletion potential and unfavourable global warming potential.
Eventually, ammonia and CO2 were the preferred options,
both being natural refrigerants that are readily available with
system properties that provide very good energy efficiencies.
The next step was to decide
what kind of plant best suited the factory, taking into account its
size and future expansion.
From the energy efficiency
perspective, a two-stage ammonia system was considered along with
two-stage and single stage ammonia- CO2 cascade systems
and the annual expected energy costs compared. The ammonia/
CO2 cascade system provided the best solution with its
use of glycol as a secondary refrigerant. The glycol – a mix of
anti-freeze and water, is used to transport cooling to occupied
areas in the factory. Due to ammonia’s toxicity it was placed away
from workers for safety reasons. Ammonia is contained in the
refrigeration plant room and CO2 is used in the freezer
store. Ammonia was chosen because its ozone depletion and global
warning depletion potentials are zero.
The low temperature
CO2 freezer system is direct expansion, and at nearly
100kWR capacity it is one of the largest CO2 direct
expansion plants built.
The heat rejection
equipment uses Dricon condensers, which provides savings in water
consumption of 70% over equivalent cooling towers or evaporative
condensers while not compromising the energy efficiency of the
plant.
Also the plant incorporates
a heat recovery system, where high quality heat is continuously
recovered from the refrigeration plant to preheat the hot water
services for the factory.
Queensland Company, Scantec
Refrigeration Technologies were chosen for the refrigeration
contract. Site installation commenced in September 06 and the plant
was successfully commissioned in early
December.
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