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NOTE: The maximum discharge gas temperatures indicated in this chapter are valid for safe
operation within the approved application envelope. The discharge line thermostat has the
function of a compressor protection device; it is not designed to control the o perating
envelope. For compressor envelope control, an additional control device or regulation must
be used.
3.7.1 Excessive discharge gas temperatures
A f ew of the possible consequences of excessive discharge gas temperatures are listed below:
▪ Since the oil circulates in the system with the refrigerant, it is subjected to high d is charge gas
temperatures. If the discharge gas temperature becomes too high, the so-called "cooking" effect
will occur (heating of oil under exclusion of air). Carbon deposits c an f or m at p oint s of high
temperature, for example on the valves, oil channels, oil filters , et c. The o il lubricity will b e
reduced and a progressive wear process will occur which will prematurely damage the
compressor.
▪ The stability of the ref rigerant can also be affected, particularly if t rac es of cont aminant are
present.
The problems described above frequently occur simultaneously, particularly since t he c hemical
reaction speed approximately doubles with every 10 °C temperature rise. This d irec tly leads t o
chemical reactions of the oil with the refrigerant and the compounds extracted from s ealant s and
insulation material. As a consequence, contaminants of various types, among them acids, will form
inside the system.
NOTE: For more information, please refer to Technical Information C7.8.6 "Di scharge Gas
Temperature Protection for Copeland™ Heat Pump compressors".
3.8
Screens
CAUTION
Screen blocking! Compressor breakdown! Use screens with at least
0.6 mm openings.
The use of screens finer than 30 x 30 mesh (0.6 mm openings) anywhere in the system should b e
avoided with these compressors. Field experience has shown that f iner mes h sc reens us ed t o
protect thermal expansion valves, capillary tubes or accumulat ors c an becom e temporarily or
permanently plugged with normal system debris and block the flow of either oil or ref rigerant to t he
compressor. Such blockage can result in compressor failure.
3.9
Mufflers
External mufflers, normally applied to piston compressors in the p ast , may no t be req uired f or
Copeland scroll compressors.
Individual system tests should be performed to verif y ac ceptability of s ound perf ormance. If
adequate attenuation is not achieved, use a muffler with a larger cross-sectional area to inlet area
ratio. A ratio of 20:1 to 30:1 is recommended.
A hollow shell muffler will work quite well. Locate the muffler at minimum 15 t o maximum 45 c m
f rom the compressor f or the most effective operation. The f arther the muf fler is placed f rom t he
compressor within these ranges, the more effective. Choose a muffler with a length of 10 to 15 cm.
3.10 Reversing valves
Since Copeland scroll compressors have a very high volumetric efficiency their displacements ar e
lower than those of equivalent capacity reciprocating compressors. As a result, Emerson
recommends that the capacity rating on reversing valves be no more than 1.5 to 2 times the
nominal capacity of the compressor in order to ensure proper operat ion of t he rev ersing v alv e
under all operating conditions.
The reversing valve solenoid should be wired so that the valve does not reverse when the s ys tem
is shut off by the operating thermostat in the heating or cooling mode. If t he v alv e is allowed t o
reverse at system shut off, suction and discharge pressures are reversed to the compressor. This
results in a condition of system pressures equalising through the compressor which can cause t he
compressor to slowly rotate until the pressures equalise. This condition does not affect compressor
durability but can cause unexpected sound after the compressor is turned off.
14
AGL_HP_ST_ZHK1P_EN_Rev00
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