Roundtable on climate-friendly refrigeration technologies

Roundtable on climate & ozone-friendly technologies in refrigeration & air-conditioning

ANNUAL MEETING OF THE
REGIONAL OZONE NETWORK
FOR EUROPE & CENTRAL ASIA
BELGRADE, SERBIA, 10-13 MAY 2011

Belgrade, May 10, 2011 Slobodan Pejković 1
Ammonia as a Refrigerant in the Water Chiller for apple storage cooling


Case study:
Ammonia as a Refrigerant in the Water
Chiller for apple storage cooling
(cold storage capacity is 8000 t)

Dipl.-Ing. Slobodan Pejković
Filter Frigo - Serbia
E-mail=filfrigo@EUnet.rs



For chilling and storing apples, cooling installation
has been planned with water chiller using Freon 404A
as a refrigerant, and cools secondary fluid, mix of water
and glycol to -6ºC temperature and lower. Advantage
of the secondary fluid is the possibility of temperature
control in cold storages with small difference between
the air and secondary fluid’s temperature. In this way
loss in weight of products is decreased. Besides that, it
is also important that the quantity of a refrigerant in
such cooling systems is small.

Necessary cooling capacity for cooling and storing
8000 tons of apples is around 1.1 MW.



Freon 404A as three component mixture of a
refrigerants R143a / R125 / R134a has high global
warming potential (GWP=3780). Therefore in the
European Union measures are contemplated which
would lead to decreased use of this refrigerant. The
first of the measures introduced by Denmark since
2011 is ecological tax for use of Freon 404A
amounting to 79€/kg, which shall be collected during
Freon procurement.

That made us think of envisaging some of the
natural refrigerants for this cold storage. The choice
was ammonia.



Ammonia as a natural refrigerant has GWP=0,
meaning that it does not influence global warming of
the Earth, therefore its use is being stimulated.
Advantages in using ammonia with strong smell is that
during leakage which happens occasionally in cooling
installations is that you can immediately sense it,
remedy the failure and top-up the installation with
refrigerant without stopping. Differently from that,
Freons, even R404A are without smell and its leakage
from the cooling installation can not be observed until
pressure drops, that is, capacity decreases.



Because R404A is three-component mixture of
different Freons, in case of leakage one must
discharge the whole quantity from the installation
(installation charge is around 300 kg), the failure must
be remedied, than the installation should be vacuumed
and refilled. This procedure requires several hours
work and during that period the cooling installation can
not operate.



Ammonia as a refrigerant is cheaper. Exploitation
costs and maintenance costs of modern ammonia
installations are lower than for Freon installations.

Installations with ammonia as a refrigerant are
more energy efficient, meaning that for achieving the
same cooling capacity they shall spend less
electricity. Due to poor mixing with oils for lubricating
compressor, ammonia can be used in flooded
evaporators at higher evaporating temperatures in
relation to Freons, simultaneously using less
electricity.



In order to achieve the necessary glycol
temperature of -6ºC with ammonia as a refrigerant,
the compressors can work with evaporation
temperature of -10ºC in flooded plate&shell
evaporator and with suction gas superheat of 1K.

In order to achieve the same conditions (glycol
temperature and capacity) with Freon R404A as a
refrigerant, the installation must have an direct
expansion evaporator where the evaporation
temperature can not exceed -12ºC while suction gas
superheat must be from 6 to 10K.



In order to present real difference between the ammonia and Freon
404A installations, we shall present table with the cooling capacity and power
consumption of screw compressor, product of Bitzer.

Ammonia R717 Freon R404A
Bitzer Energy Energy
Cooling Power Cooling Power
screw Efficiency Efficiency
compressor capacity Consumption Ratio capacity Consumption Ratio
[kW] [kW] EER [kW] [kW] EER
Model
324 83.4 3.88 293 94.7 3.09
OSKA8581-K

Operating regimes
Bitzer Ammonia R717 Freon R404A
screw compressor OSKA8581-K OSKA8581-K
Evaporation Temperature [°
C] -10 -12
Condensing Temperature [°
C] 35 35
Liquid Subcooling [K] 3 3
Suction Gas Superheat [K] 1 10



Tables show that in installations using ammonia
as a refrigerant for the same compressor model,
cooling capacity is 10% higher in relation to R404A
with smaller absorbed power for 11.3 kW.
During the first 27 days of work of the cold
storage with full capacity, when the daily apple intake
exceeds 300 t/day, electricity savings during work of
4 screw compressors, products of Bitzer, model
OSKA8581-K with ammonia as a refrigerant would be
29 MWh. Simultaneously, these compressors would
have 10% higher cooling capacity than the Freon
ones, and would enable quicker cooling of apples,
which is very important for apple quality.



Analyses of different solutions using ammonia
have been made. One of the solutions was a chiller
with one screw compressor of 1150 kW cooling
capacity. Maximum cooling capacity for this type of
cold storage is necessary during the first 30 days of
work, from start of apple picking. After that, needs for
cooling decrease, as well as the external temperature,
and the water chiller has better condensing conditions.
Therefore a solution with three water chillers has been
discussed – chillers in variant 1 with water cooled
condenser, and in the variant 2 with air cooled
condenser. Both solutions have their advantages and
shortcomings.



Advantage of the chiller with air cooled
condenser is installed in the container outside the cold
storage facility, so no special safety measures are
required. Besides that, apples are stored in the period
from October to June, when we don’t have extremely
high air temperatures, and the condensing
temperatures are such that they render sufficiently high
Energy Efficiency Ratio – EER.



Microchannel Condenser



AUTOMATIC OIL RECOVERY SYSTEM

For a regular, efficient and continuous operation
of a chiller, it’s necessary to guarantee oil recovery to
the compressor.
Oil often collects in the bottom part of the
evaporator, with the risk to compromise efficiency and
heat exchange of the evaporator. For this reason an oil
recovery system has been introduced; thanks to an
ejector, oil at low pressure is conveyed from evaporator,
with high pressure ammonia to the compressor suction.



Unit prices for the equpment:

Ammonia water chiller; piston compressor,
water cooled condenser - - - - - - - - - - - - - - € 135.000

R134a water chiller; 2 Turbocor compressors,

R134a water chiller; 2 screw compressors,

Cooling capacity 400 kW



Price for the cooling system:

R404a glycol chiller system;
cooling capacity – 1.200 kW
4 screw compressors,
1 evaporative condenser
for 4 compressors € 260.000



CONCLUSION
Advantages of ammonia as a refrigerant:
Ammonia as a natural refrigerant does not influence global warming of
Earth.
Ammonia as a refrigerant is cheaper than Freon.
Exploitation costs and maintenance costs of modern ammonia installations
are lower than for Freon ones.
Installations with ammonia as a refrigerant are more energy efficient.

Shortcomings of ammonia as a refrigerant:
Investment costs in making ammonia installations significantly exceed the
costs of making Freon installations.
Safety measures that should be undertook in using ammonia installations
due to its explosiveness cause fear with investors and influence the final
price of the installation.



Thank You For Your Attention

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Roundtable on climate-friendly refrigeration technologies

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