Cincinnati Sub-Zero ZP Series, Installation, Operation & Maintenance Manual, Page: 40 / 104

GENERAL DESCRIPTION
28
The second path is to the wet coil humidity solenoid (item H127) and into the capillary tube (item H123).
Two phase refrigerant exits the capillary tube and enters the evaporator (item H125). The wet coil is
cold enough to attract moisture from the chamber air, but not cold enough to freeze the moisture on
the evaporator. The temperature of the evaporator is regulated by an evaporator pressure regulator
valve (item H126) E.P.R. for short. This valve is intended to flood the coil to keep pressure higher than
the suction pressure. The E.P.R. valve is set at 68 PSIG (4.7 bar(g)), which corresponds to a 29°F (-1.6°C)
evaporator temperature. The warm chamber air keeps the moisture from freezing on the evaporator,
and keeps the refrigerant from migrating to the evaporator when the humidity mode is inactive. The
refrigerant leaves the evaporator and passes through a check valve (item H128) and enters the suction
line, where it remixes with rest of the refrigerant from the first path.
If the chamber is equipped with a Low RH package, the following description applies. When
dehumidification is called for, some of the liquid refrigerant is diverted to the humidity loop. The
refrigerant passes through a solenoid valve (item H131) and a Low RH thermostatic expansion valve
(item H130). Two phase refrigerant exits the thermostatic expansion valve and enters the evaporator
(item H125). The evaporator temperature is cold enough to freeze water out of the air where it collects,
and freezes on the surface of the evaporator. The temperature of the evaporator is able to drop below
freezing temperature due to the suction bypass solenoid (item H129) where it allows the suction vapor
to bypass the evaporator pressure regulator valve (item H126) this allows the chamber to achieve low
temperature dew points limited as previously discussed in this manual.
CASCADE UNIT - SYSTEM 2 (R-508B) DESCRIPTION
System 2 – Description (2 HP – 6 HP Systems)
The compressor (item 201) will pump compressed R-508B/R23 vapor through the discharge line where
the high pressure gauge (item 283) senses and displays the pressure of the refrigerant. The high
pressure switch (item 295) senses the discharge refrigerant pressure and will open a contact in the
event that discharge pressure exceeds 350 PSIG (24.1 bar(g)). This contact opening will serve to shut
down the unit, and will automatically reset when the pressure drops to 250 PSIG (17.2 bar(g)).
The discharge gas then enters the oil separator (item 245). The oil separator removes 90% of the oil in
the refrigerant vapor. It collects the oil and drains it back to the compressor crankcase. This prevents
oil logging in the evaporator.
The discharge refrigerant vapor passes a tee which diverts some of the refrigerant to the bypass loop
(see Bypass Loop description).
The residual discharge refrigerant vapor passes through the discharge desuperheater (item 244). The
discharge refrigerant vapor passes a tee, in the event that discharge pressure exceeds a range of 270
PSIG (18.6 bar(g)) to 300 PSIG (20.7 bar(g)), see unit specific refrigeration flow diagram for setting. Some
of the discharge refrigerant vapor will be diverted to the high pressure dump valves (item 253), and will
flow to the vapor tank (item 255) where the gas is siphoned back into the suction line to maintain
proper flow of the refrigerant. The residual discharge refrigerant vapor then enters the cascade
condenser.