Operating Principles
CVHH-SVX001A-EN
71
RuptureGuard
The rupture disk m onitors the pressure inside the chiller. If
the pressure exceeds the disk’s burst setting, the disk
ruptures allow ing the chiller pressure to enter the valve
holder com partm ent upstream of the relief valve. If the
pressure is above the pressure setting of the relief valve,
the valve w ill open allow ing only the am ount of refrigerant
to escape to keep the pressure w ithin safe operating lim its.
The excess flow valve m aintains the dow nstream side of
the rupture disk at atm ospheric pressure to assure proper
operating conditions for the disk. When the disk bursts, the
rapid pressure increase causes the excess flow valve to
seal and the valve holder area becom es pressurized.
A disk rupture w ill be indicated by a pressure reading on
the gauge and the pressure sw itch contacts w ill close. The
pressure sw itch is an optional accessory and does not w ire
to the control panel. The pressure sw itch can be connected
to a custom er-supplied building autom ation system
(BAS).
EarthWise Purge
Centrifugal chillers that use low-pressure refrigerants,
such as R-1233
zd
(E), operate w ith areas of the chiller at less
than atm ospheric pressure. Non-condensables in the air,
such as water and nitrogen vapor, m ay leak into these low-
pressure areas and accum ulate in the condenser. If these
non-condensables are not rem oved, the condenser loses
its ability to condense refrigerant efficiently, and the
pressure of the condenser increases. Increased condenser
pressure low ers the chillers efficiency and capacity.
A purge system is required on low-pressure centrifugal
chillers. It is a device that is externally m ounted on the
chiller. Its purpose is to rem ove non-condensable
m aterials that have leaked into the m achine.
N ot e: For convenience, the term “ air” is often used in this
docum ent, although any other non-condensable
m aterials that m ay exist in the chiller are also
rem oved by the purge system .
How a Purge System Works
From a functional standpoint, the purge system can be
divided into subsystem s of com ponents. This section
identifies and describes the function of these subsystem s.
Refrigeration Circuit Subsystem
The purge evaporator of the refrigeration circuit is located
in the purge tank. The purge tank is connected to the chiller
condenser by supply and return lines through w hich chiller
refrigerant can freely flow.
The purge evaporator coil presents a cold condensing
surface to the chiller refrigerant entering the purge tank.
When the purge refrigeration system is running,
refrigerant from the chiller condenser is attracted to the
cold surface of the purge evaporator. When the gaseous
refrigerant contacts the surface of the purge evaporator
coil, it condenses into a liquid, leaving a partial vacuum
behind. M ore refrigerant vapor from the chiller condenser
m igrates to the purge tank to fill the vacuum .
The liquid refrigerant that has condensed in the purge tank
returns to the chiller condenser through the liquid return
line. The return line includes a filter-drier and a m oisture-
indicating sight glass.
The condensing unit is air-cooled, and is operable w hether
the chiller is running or not. No additional cooling source
is required.
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