COMPRESSOR COOLING SYSTEM
The closed cycle of the most standard compressor cooling systems is
composed of 4 main elements, combined with each other by a pipeline.
The system includes circulation of a cooling agent in the form of liquid or
steam, the agent is moved by a compressor (1) with an electric engine
Compressor Cooling System
1. Compressor, 2. Condenser, 3. EXV velve
The compressor takes the cooling agent steam and compresses
it, simultaneously performing the work of the electric engine. The
work turns into heat, by heating the steam it raises the temperature.
The steam temperature increases above the environment (ambient)
temperature and amounts to between 60 and 90°C. Now, the steam
enters the condenser (2). The condenser is washed by external air.
As result, the cooling agent steam gives away heat and is condensed,
i.e. turns into liquid. The condensation process occurs at a fixed
temperature and pressure (which was created by the compressor).
Now it is time to lower the liquid’s temperature, the process of damping
(reduction) is used for this purpose.
The liquid goes through the valve (3), called the thermostatic expansion
valve (EXV), and as result, the freon pressure and temperature are
lowered. During this process, the freon liquid turns into a humid
saturated steam (a mixture of dry steam and liquid drops).
The thermostatic expansion valve (3) can be opened more or less by
regulating in a small range the temperature of the cooling agent.
In point (4), the humid saturated steam enters the evaporator, where
it starts to heat up and the drops of liquid freon start to vaporise by
taking the heat of the cooled object – in case of an air conditioner or air
handling unit with direct vaporisation coil, it is air, while in the case of
water chiller it is water.
The temperature of freon vaporisation cannot by lower than 0°C due to
the risk of freezing the water condensate, therefore the temperature
of the agent’s vaporisation is usually set between 3 and 11°C. Next, the
cycle is repeated.
INVERTER COMPRESSOR COOLING SYSTEM
Regulation of the cooling power in a classic cooling system is
performed with the use of a compressor, which is periodically
operational with the maximum cooling power or is turned off entirely.
Since 1990, other solution has been used for regulation of the cooling
power. The compressor was equipped with an inverter, allowing for
change of rotation speed of the compressor’s engine and as result – a
smooth change of the cooling power.
The benefits of such a system are as follows:
• high comfort in the air-conditioned room – air temperature set point
is maintained with a higher accuracy , air temperatures fluctuation in
air-conditioned room is minimal
• lower noise level – decrease of the rotation speed of a compressor
which is not working at full capacity, especially noticeable at night
• energy consumption savings in comparison to the ON/OFF cooling
system during 24 hours even 50%
• Elimination of the number of stop-start cycles extends the lifetime of
the cooling system’s components
• low start electric currency
• the possibility of operation at low ambient temperature of the condenser,
even below -20°C in cooling mode
In water chiller, freon during its vaporisation cools the water .
Cold water use as a cooling agent for such systems as air handling
units, fan coils and other terminal units
In order to prevent freezing during a winter period, these systems most
often include a cooling agent in the form of not pure water, but its mixture
with glycol – propylene or ethylen.
The type of used glycol and its concentration in the water mixture determine
the temperature of solidification and other physical and chemical
properties of the liquid. While specifying the required concentration of
the glycol mixture, it is necessary to remember that the temperature of
solidification of the used mixture must be lower almost 3 degrees from
the ambient temperature.
Despite high popularity of both types of glycol, ethylene glycol is most
often used. This is due to the lower viscosity coefficient in comparison
to propylene glycol (30% of propylene glycol and water mixture has
100% higher hydraulic flow resistance in comparison to pure water),
and lower costs.
However, ethylene glycol is a toxic substance. Propylene glycol in this
case is characterised by significantly lower toxicity. Due to this fact, it is
used in the food industry and in places where a potential leak could get
in contact with drinks or food.
The figure presents the change of solidification temperature depending
on the concentration of glycol in the water and glycol mixture.
Water and glycol mixture have a stronger corrosiveness than water.
Inhibitors are used in order to protect the installation from damage and
protect the liquid itself from glycol degradation.
Dosage of inhibitors can be performed directly into the installation and
act as an element of the developed water treatment station. It is also
possible to use ready-to-use mixtures of water, glycol and inhibitors,
where the inhibitors comprise 4÷6% of the mixture.