Refrigeration – Refrigeration producer – Compressor-condenser-evaporator circuit
Reexamination Certificate
2001-03-27
2002-12-10
Doerrler, William C. (Department: 3744)
Refrigeration
Refrigeration producer
Compressor-condenser-evaporator circuit
C062S467000, C062S324100
Reexamination Certificate
active
06490882
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a method of preventing refrigerant condensation in a discharge volume or discharge line of a compressor, and, more particularly to the application of one or more heaters to a cooling circuit to prevent condensed refrigerant from migrating into the discharge line and/or discharge volume of a compressor.
Electronic equipment in a computer or telecommunication room requires precise, reliable control of room temperature, humidity and airflow. Excessive heat or humidity can damage or impair the operation of critical computer systems and other components. For this reason, precision cooling systems are operated to provide cooling in these situations.
A typical cooling system
10
is schematically illustrated in FIG.
1
. The cooling system
10
includes compressor
20
, condenser
30
, expansion valve
50
and evaporator
60
. Refrigerant for use in the cooling system
10
may be any chemical refrigerant, such as chloroflourocarbons (CFCs), hydroflourocarbons (HFCS) or hydrochloroflourocarbons (HCFCs) such as R-22.
Operation of cooling system
10
is as follows. Refrigerant is compressed in a compressor
20
, which may be a reciprocating or scroll compressor or other compressor type. After the refrigerant is compressed, it travels through a discharge line
12
to a condenser
30
. A high head pressure switch
24
is attached to discharge line
12
. High head pressure switch
24
shuts down the compressor if the discharge pressure exceeds a predetermined level.
In condenser
30
, heat from the refrigerant is dissipated to an external heat sink, e.g., the outdoor environment. Upon leaving condenser
30
, refrigerant passes through a liquid line solenoid valve
40
and travels through a first liquid line
14
to expansion mechanism
50
. Expansion mechanism
50
may comprise a valve, orifice or other possible expansion apparatus known to those of ordinary skill in the art. The expansion mechanism
50
causes a pressure drop in the refrigerant, as the refrigerant passes through the mechanism.
Upon leaving the expansion mechanism, the refrigerant travels through second liquid line
16
, arriving at evaporator
60
, which comprises a heat exchanger coil. Refrigerant passing through evaporator
60
absorbs heat from the environment to be cooled. Specifically, air from the environment to be cooled circulates through evaporator coil, where it is cooled by heat exchange with the refrigerant. Refrigerant carrying the heat extracted from the environment then returns to compressor
20
by suction line
18
, completing the refrigeration cycle.
The precision cooling systems, such as that outlined above for a computer or telecommunications room, are typically operated year round, even when the outdoor ambient temperature is below 40° F. Certain operating conditions produce a high head pressure within the cooling system
10
and particularly in discharge line
12
. As a result, high head pressure switch
24
shuts down compressor
20
if the discharge pressure exceeds a predetermined level. In particular, when the environment in which the condenser is situated is 30° F. or cooler than the environment in which the evaporator is situated (i.e., the environment to be cooled), condenser
30
is significantly cooler than the evaporator.
With the cooling system
10
shut down for an extended period of time, refrigerant is in liquid line expands through evaporator
60
and draws through compressor
20
. The refrigerant then condenses in the cold condenser
30
. The condenser fills with liquid refrigerant, and refrigerant may begin to condense in discharge line
12
and compressor
20
. Starting compressor
20
with liquid refrigerant present in the discharge line
12
and/or the discharge volume of compressor
20
is likely to cause pressure excursion incidents. Condensation-induced shock (CIS) and vapor-propelled liquid slugging (VPLS) are phenomena that can produce dangerous high-pressure excursion incidents in the discharge lines.
To describe the occurrence of CIS and VPLS, operation of cooling system
10
is described after refrigerant has migrated from the liquid lines and condensed in the discharge line
12
and/or discharge volume of compressor
20
. During start up of compressor
20
, the refrigerant mass flow rate may increase from zero to the normal operating conditions in less than 10 seconds. To transfer momentum to the liquid in discharge line
12
, the refrigerant vapor being pumped by compressor
20
undergoes a pressure surge.
Any volume of liquid in discharge line
12
decreases the volume available for the vapor from compressor
20
. The less vapor volume available to absorb the pressure surge, the greater is the peak of the pressure surge to provide the necessary transfer of momentum. The condensation in line
12
or the discharge volume of compressor
20
induces a shock or pressure surge. If the vapor discharge volume is too small at startup, the peak of the pressure surge will exceed the predetermined setting of high head pressure switch
24
(which is chosen to prevent damage to the components of the cooling system).
High head pressure switch
24
will trip and shut down compressor
20
. Multiple attempts to restart cooling system
10
will eventually result in successful operation. With repeated starts of the compressor, the liquid slugging the line is eventually propelled by the vapor along the line
12
, and the volume available to the vapor increases. In other words, the liquid condensate in discharge line
12
can be forced through the line, allowing for enough volume in the discharge line to accommodate the compressed vapor without tripping high head pressure switch
24
.
Field reports indicate high-pressure pulses in discharge line
12
in close proximity to the location of pressure switch
24
. In some cases this pulse is high enough to peg and bend the needle on the gauge used to perform the measurement. Therefore, damage and wear to compressor
20
and other components of cooling system
10
can result from repeated occurrences of the high head pressure at startup.
It is to be understood that the formation of high-pressure excursion incidents can result from a number of other factors or conditions not listed herein. Furthermore, those conditions cited in the present disclosure as contributing to the possible occurrences of high-pressure excursion incidents may vary with the given design characteristics or installation conditions of a cooling system. The conditions cited are presented as exemplary of those conditions that may lead to high-pressure excursion incidents for a given cooling system in a conventional field setting.
One prior art solution to the refrigerant migration and condensation problem is to move liquid line solenoid valve
40
from the outdoor unit, i.e., condenser unit
30
, to the other end of the liquid line
14
just ahead of expansion mechanism
50
. Adding a liquid line solenoid valve to all evaporator units in production would prove costly. The circumstances associated with high-pressure excursion incidents as discussed herein occur in only a few installations of cooling system. Furthermore, the problems associated with liquid line slugging and high head pressures at startup are not usually discovered until after installation of a cooling system. Moving or inserting a liquid line solenoid
40
to just ahead of the expansion valve
50
involves a complicated retrofitting procedure. Typically, the procedure involves cutting the liquid line
14
and installing the liquid line solenoid
40
in the new location
42
, which can be cost prohibitive.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In view of the foregoing and other considerations, the present invention relates to the application of one or more heaters to a cooling circuit to prevent condensed refrigerant from migrating into the discharge line and/or discharge volume of a compressor.
In accordance with one aspect of t
Doerrler William C.
Howrey Simon Arnold & White , LLP
Liebert Corporation
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