Coaxial Condensers (Water/Glycol-Cooled Condensing Units)
Each water- or glycol-cooled condensing unit has a coaxial condenser consisting of an exterior steel tube
and an interior copper tube. If the water supply is clean, coaxial condensers do not normally require
maintenance or replacement. Should your system begin to operate at high head pressure with reduced
capacity and all other causes have been eliminated, the condenser may be obstructed or fouled and
should be replaced.
Regulating Valves (Water/Glycol Condensing Units)
The water regulating valve automatically regulate the amount of fluid necessary to remove the heat from
the refrigeration system, permitting more fluid to flow when load conditions are high and less fluid to flow
when load conditions are low.
The water regulating valve is designed to begin opening at 180 psi (1240 kPa) and to be fully opened at
240 psi (1655 kPa). The valve is factory-set and should not need adjustment.
Glycol Solution Maintenance
It is difficult to establish a specific schedule of inhibitor maintenance since the rate of inhibitor depletion
depends upon local water conditions. Analysis of water samples at time of installation and every six (6)
months should help to establish a pattern of depletion. A visual inspection of the solution and filter
residue is often helpful in judging whether or not active corrosion is occurring. The complexity of
problems caused by water requires expert advice from a water treatment specialist plus a regular
maintenance program schedule. It is important to note that improper use of water treatment chemicals
can cause severe problems.
Proper inhibitor maintenance must be performed in order to prevent corrosion of the glycol system.
Consult your glycol manufacturer for proper testing and maintenance procedures. Do not mix products
from different manufacturers.
Hot Gas Bypass
Operation
The hot gas bypass valve is installed between the compressor discharge piping and suction piping,
bypassing the condenser and evaporator coils. The discharge gas mixes with the suction gas, raising the
suction temperature and pressure and decreasing the mass flow through the evaporator. The higher
suction temperatures could cause compressor overheating, therefore a separate liquid quenching valve is
provided to mix refrigerant from the system liquid line with the discharge gas before mixing with the
suction gas entering the compressor.
During normal operation, when the evaporator is under full load the hot gas bypass equalizer pressure will
remain high enough to keep the valve port closed. If the evaporator load decreases, the evaporator
temperature and pressure will drop. When the suction pressure reduces below the hot gas bypass valve
setting the hot gas bypass valve opens diverting some of the refrigerant flow back to the compressor
suction. The liquid quenching valve bulb senses this increased superheat and opens, allowing liquid
refrigerant to mix with the discharge gas, desuperheating it.
Proper mixing of the three refrigerant paths ensures stable operation and system performance. The liquid
quenching valve bulb must be located downsteam of all these connections to control superheat at the
compressor inlet. Superheat settings for the liquid quenching valve are chosen to maintain consistency
with the system expansion valve. During hot gas bypass operation higher superheats, 50-60°F (19 to
15°C), may be observed at the compressor. The liquid quenching valve is internally equalized and
superheat is not adjustable.
Vertiv | Liebert Mini-Mate2—5 ton User Manual| 78
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