SRL Service Manual
Revision 00
July 2007
Page 4 of 56
1. General Description
The Sullair SRL Refrigerated Air Dryer reduces the dew point
(1)
of a compressed air stream by
reducing the temperature causing water and oil vapour (along with other evaporated contaminants) to
condense into liquids. These liquids are then separated from the air and discharged from the system.
The dry air is then re-heated before continuing downstream.
Air streams are measured in terms of their flow, temperature and
pressure. These variables fluctuate continuously throughout the
day and can change drastically throughout the year, depending on
the climate, conditions, and application. As they change, so does
the amount of heat in the air (called the “heat load”) and the
amount of moisture the air stream can carry.
Every refrigerated air dryer is designed to handle a maximum
incoming heat load. At any heat load below the maximum there is
the potential for energy savings as the dryer is absorbing less heat
than it is designed for.
The SRL is unique in that it can be operated either as a traditional
direct expansion dryer or a cycling dryer depending on the needs
and wishes of the end user.*
In direct expansion (a.k.a. “continuous”) mode the refrigerant compressor runs continuously, and the
dryer handles reduced heat loads by redirecting refrigerant away from the heat exchanger using a
bypass valve to maintain a constant outlet dewpoint. This is the simplest mode of operation, however
does not save any energy at part load.
In cycling mode the refrigerant compressor is cycled on and off depending on the temperature within
the heat exchanger. When there is less heat load, the heat exchanger absorbs less heat, and the
refrigerant system is cycled on and off only as necessary to keep the heat exchanger cold.*
* Cycling mode is not available on the SRL-250.
(1) Dew point – a measurement of the amount of moisture in a gas, indicated as the temperature at which
the air would be saturated (i.e. the relative humidity would be 100%) and liquid condensate would begin
to form. It is commonly shown as
o
F or
o
C. It is important when discussing dew point to specify if you are
referring to the “pressure dew point” (the dew point at the pressure of the system) or “atmospheric dew
point” (the equivalent dew point at atmospheric pressure) as the two are significantly different. For the
purposes of this manual, “dew point” should be considered synonymous with “pressure dew point".
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