MIL-HDBK-1191
Additional Note - Compressed Air Systems:
MECHANICAL REFRIGERATION VERSUS DESICCANT COMPRESSED AIR DRYERS.
There are definite advantages and disadvantages for each dryer
technology, and type selection must consider the individual requirements
and characteristics of each project. While there seems to be a trend
toward greater utilization of desiccant systems, refrigerated dryers
continue to represent the bulk of the systems sold. The principle
concern with the refrigerated type is the presence in the air of
excessive moisture. However, research does not clearly establish that
high moisture levels are a pervasive or unavoidable problem in U.S.
military MTF's. There are also concerns in our community with desiccant
systems, including excessive air dryness and higher first cost. The
concerns with each system are described below:
Refrigerated Dryers.
Advantages:
a. Typically lower cost.
b. Lower space requirements.
c. Presence of higher moisture level in air (higher dewpoint) is better
for some procedures.
d. Lower compressor capacity required than desiccant systems.
Disadvantages:
a. Limited minimum dewpoint level of 35-39 F; higher dewpoint means
greater potential for system condensation.
b. Moisture carryover potential due to evaporator icing, or failure of
automatic receiver drainage equipment. (May be correctable by cycling
controls and proper specification of components.)
c. Requires regular maintenance.
Desiccant Dryers.
Advantages:
a. Drier air (as low as 40F dewpoint) leads to lower probability of
condensate formation or carry-over in the supply system.
b. Relatively lower maintenance required.
Disadvantages:
a. Very low dewpoint can cause problems with some dental procedures
(upward adjustment available in some capacity ranges from some
manufacturers but required competitive procurement eliminates ability to
specify).
b. Larger compressor capacity required than refrigerated system (to
supply additional air for desiccant regeneration).
c. Higher cost.
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