US3415076A - Liquid chiller - Google Patents

Description

E. RODAK LIQUID CHILLER Dec. 10, 196-8 2 Sheets-Sheet 2 Filed June 20, 1967 United States Patent 3,415,076 LIQUID CHILLER Edward Rodak, Mexico City, Mexico, assignor to Borg- Wamer Corporation, Chicago, Ill., a corporation of Illinois Filed June 20, 1967, Ser. No. 647,543 2 Claims. (Cl. 62-435) ABSTRACT OF THE DISCLOSURE A shell-and-coil liquid chiller which may be operated to chill water or other heat exchange medium at close to the freezing point thereof without danger that a freezeup would damage the shell, the piping, or the refrigeration system. This is accomplished by establishing and maintaining an air pocket in the upper portion of the shell to provide a compressible fluid permitting expansion of the water during freezing.

Summary and background of the invention This invention relates to improvements in liquid chillers and more particularly to a shell-and-coil chiller which is capable of withstanding a freeze-up without damaging the refrigerant coil, the piping or other components in the system.

A shell-and-coil chiller normally comprises a tank, or other suitable vessel, and a coil immersed in the fluid to be cooled, through which refrigerant is circulated under evaporating conditions. The heat exchange medium is circulated in a closed circuit from the chiller to the load and back again. For purposes of the specification, water will be considered the cooled medium since this is the usual application for shell-and-coil chillers of the type described herein. 'It should be understood, however, that any other heat exchange medium can be employed.

One of the disadvantages of a shell-and-coil chiller is that it cannot normally be operated at close to the freezing point of the medium being cooled. When a liquid chiller is operated at close to freezing point of water, there is always a danger of freezing up if the water fio w velocity is reduced or the temperature control on the refrigerant side does not operate correctly. When the water does freeze, it expands and often creates sufficient pressure to break open the shell, crack the refrigerant piping and connections, and permit vvater to contaminate the refrigeration system. When the latter happens, there is a very great chance of completely destroying the compressor; and at the very least, the system must be put through a costly and time consuming drying operation. The danger is further increased when a pump-down cycle is used to reduce the starting load on the compressor motor; and additional protective controls must be incorporated into the circuit to prevent freeze-up.

In the present invention, the shell is constructed so that a pocket or head of air is maintained at all times in the upper portion of the shell to take up the expansion due to ice formation during a freeze-up. One of the problems of maintaining this air pocket is that it is capable of being dissipated by either dissolution or entrainment of air in the water. When the air pocket has been dissipated, the tank -fills with water and the inherent dangers of a freeze-up are again created.

In the present invention, the air pocket is maintained along with effective flow of water over the refrigerant coil by providing a pair of standpipes in the shell having openings throughout their entire length. This prevents air from being entrapped in the liquid as it is removed from the shell since the entire column is filled with Water up to the upper level of the water of the tank. At the same time, good distribution is assured because the water ice is supplied and discharged along the entire length of the respective supply and discharge pipes, thereby effecting uniform flow of 'water along the length of the shell over the entire coil.

Accordingly, it is a principal object of the invention to provide an improved liquid chiller which can be operated safely at temperature close to the freezing point of the liquid being chilled.

Another object of the invention is to provide a chiller in which the above object can be. achieved while still maintaining good circulation of the liquid through the shell and without forming stratified layers of water flow.

Additional objects and advantages will be apparent from reading-=- e following detailed description taken in T he drawings FIGURE 1 is a schematic diagram of an improved liquid chiller embodying the principles of the invention;

FIGURE 2 is a cross-sectional view of the liquid chiller;

FIGURE 3 is a cross-sectional view taken along the plane of line 3-3 of FIGURE 2;

FIGURE 4 is a cross-sectional view taken along the plane of line 44 of FIGURE 3; and

FIGURE 5 is a circuit diagram of a control system which may be used in conjunction with the present invention.

Referring first to FIGURE 1, a liquid chiller 10 forms a part of a refrigeration system including a compressor A, a condenser C, a receiver R, an interchanger I, an expansion valve V, and a distributor D for supplying refrigerant to an evaporator coil E in the chiller 10. Water to be chilled circulates through the chiller 10 by means of a conduit 12 which includes a pump P, to continuously recirculate Water in a closed circuit between the load L and the chiller 10.

The chiller 10 comprises generally elongated, rectangular shell 20 which is completely enclosed on all six sides to form a hermetically sealed chamber. Preferably, the dimensions are chosen so that it has a relatively narrow width to effect uniform velocity of the water being circulated therethrou-gh and avoid stagnant zones within the shell.

The refrigerant side of the chiller (i.e., the evaporator) comprises a plurality of serpentine coils 22 extending along the length of the shell. Refrigerant is supplied to each coil from the distributor D through tubes 24; and refrigerant gas flows from the coils through a corresponding number of tubes 26 which are connected to the interchanger I. The interchanger is used to increase the superheat of the gas being returned to the compressor and to subcool the liquid refrigerant being supplied to the expansion valve. Such interchangers are well-known in the art and do not require a more detailed description.

An important aspect of the invention resides in the means for circulating the water to be chilled through the shell. As best shown in FIGURE 2, water is supplied from the load L into the shell 20 by a standpipe 30 which has a cap 32 on the upper end and is provided with a series of openings 34 throughout the entire length thereof. A discharge standpipe 36 is constructed in substantially the same manner and has a cap 38 and plurality of openings 40. If desired, a liquid level sight glass 42 may be provided to permit inspection of the level during operation; and a purge plug 44 is conveniently associated with the sight glass.

The system described so far may also be readily adapted for a pump-down operation to reduce the starting power requirements on the compressor. A solenoid valve 46 (FIGURE 1) is located between the interchanger I and the expansion valve V to terminate flow of refrigerant to the evaporator. When the solenoid valve is closed, the compressor continues to operate to evacuate any refrigerant remaining in the evaporator. As the refrigerant is evaporated, suction pressure is reduced which reduces the pressure in the evaporator. In the conventional system, an extremely cold evaporator can freeze the liquid and burst the shell; while in the proposed system, the liquid can freeze with no danger that the chiller can be damaged. The pump-down system is advantageous because the compressor can start under greatly reduced load and thereby reduce the in-rush current required to bring the motor up to normal running speed.

Another advantage of the present system is that overall pumping costs are reduced. As a general rule, the quantity of refrigerant to be circulated is much less than the quantity of the liquid to be cooled. Pumping power required increases as the cube of velocity, i.e.,

Therefore, any reduction in the velocity of flow results in a great reduction in the power requirement. By passing the liquid to be cooled through the normally greater cross sectional area of the tank spaces around the outside of the tubes, the velocity necessary to move a given amount of liquid to be cooled is less than it would be if it were passed through the tubes.

In a conventional system, many safeguards must be provided to prevent freezing up of the system; and in the liquid chiller provided by the present invention, these specialized controls may be eliminated. Moreover, compressor lubrication problems are materially reduced. In the conventional system, a tube bundle is position in a tank. The liquid to be cooled is generally in the tubes. The refrigerant is fed into the tank space around the tubes. The volume of this space is such that, upon entering the space, the velocity of the refrigerating medium is greatly reduced. Oil, entrained in the refrigerant during high velocity flow through the other parts of the system, has a tendency to separate from the refrigerating medium and become entrapped in this space and does not return to the compressor. This reduces the heat exchange efficiency and may result in compressor failure due to lack of lubrication. In the proposed system, velocity of the refrigerant/ oil mixture is maintained at a high level through the coil sections and oil return to the compressor is assured. Also, in the conventional system, the large volume in the tank into which the refrigerating medium is fed necessitates a large amount of refrigerant to operate efficiently. The large refrigerant charge further complicates compressor lubrication as well as contributing to higher initial cost. The charge necessary to operate the proposed system is very small due to the small volume within the tubes which make up the coil sections. The high velocity of the refrigerant in this system also insures a turbulent fiow for maximum heat exchange.

Referring to FIGURE 5, which shows preferred circuit for controlling the operation of the liquid chiller, power is supplied through lines L and L The low oil pressure cut-out OP is bypassed on start up through timed opening contacts ITR-TO. Switching the ON-OFF switch to the ON position energizes time delay relay ITR; and it remains energized through the make-lo terminal of the low oil pressure cut-out OP as long as net oil pressure is below the setting of the low pressure cut-out OP. If oil pressure remains below this setting for the period of time fixed for the time delay relay ITR, timed opening contact ITR-TO will open, breaking the circuit to the compressor motor contactor IM and stop the compressor. If net oil pressure rises to the setting on the oil pressure cut-out P within the time interval set on time delay relay ITR, the low pressure cut-out OP will open, breaking the circuit to time delay relay ITR; and timed opening contacts ITR-TO will remain closed to complete the circuit to compressor motor contactor IM. When the compressor motor contactor IM is closed, the compressor motor is running and the normally closed auxiliary contact MAC is open, deenergizing the crankcase heater. When the compressor motor contactor TM i deactivated, auxiliary contacts MAC are closed and the crankcase heater is energized.

Compressor cycling is controlled by action of the low pressure cut-out LP set to cut out at 2 p.s.i.g (or at compressor manufacturers minimum recommendation). This setting allows practically complete pump-down of system on each off cycle and permits a wide differential between cut-out and cut-in to prevent destructive shortcycling. Also, it precludes liquid slugging of the compressor on start up and, depending on cut-in setting, compressor start up is accomplished under minimum loading conditions. During this pump-down period, some icing may occur in the chiller but no harm is done.

It will be noted that no freeze protection control is required because the liquid in the chiller can freeze without doing any damage. It is desirable, however, to provide an oil pressure cut-out which comprises a pressure switch actuated by a pressure differential between lubricating oil pressure and crankcase (suction) pressure. Normally, it is factory set to open at 40 p.s.i.g. and close above 45 p.s.i.g. Any oil pressure failure will stop the compressor and close liquid line solenoid LS, which presents liquid refrigerant migration to the evaporator when the compressor is not running.

A high pressure cut-out HP comprises a pressure switch, sensitive to discharge pressure which will open if the compressor discharge pressure becomes too high, breaking the circuit to compressor motor contactor IM and also breaking the circuit to the liquid line solenoid LS allowing it to close .and prevent liquid refrigerant migration to the evaporator when compressor is not running.

For the protection of the motor, hermetically sealed thermostats, shown at IMP, a-re imbedded in each of the three phase windings. Should any winding reach an unsafe temperature, motor contactor IM and the liquid line solenoid LS are immediately deenergized.

While this invention has been described in connection with a certain specific embodiment thereof, it is to be understood that this is by way of illustration and not by way of limitation; and the scope of the appended claims should be construed as broadly as the prior art will permit.

What is claimed is:

1. In a liquid chiller including a shell, means for circulating a liquid medium to be cooled through said shell, a coil disposed in said shell, and means for circulating a coolant through said coil, the improvement comprising: a first, substantially vertically arranged supply conduit in said shell for supplying said liquid medium, means defining a plurality of openings along the entire length of said conduit; a second, substantially vertically arranged discharge conduit for discharging said liquid medium from said shell; and means defining a plurality of openings along substantially the entire length of said second conduit, whereby during normal operation of said chiller a head of air is trapped above the level of liquid medium in said shell to provide a compressible fluid capable of absorbing expansion of said liquid medium in the event of freeze up.

2. A shell adapted for use in a liquid chiller comprising: means defining a closed, substantially rectangular chamber including side walls, a top wall, and a bottom wall; a substantially vertical supply standpipe at one end of said shell, said standpipe having a plurality of distribution openings along the length thereof for supplying a liquid medium to said shell; a substantially vertical discharge standpipe located at the opposite end of said shell, said standpipe having a plurality of discharge openings along the length thereof; a refrigerant coil arranged in said shell extending along the major flow path of the liquid medium 5 6 to be chilled; and means for supplying refrigerant cool- 2,286,618 6/1942 Hiller 62310 X ant to said coils. 2,722,108 11/1955 Hailey 62--7 References Cited 3,090,212 5/ 1963 Anderson et a1 62310 UNITED STATES PATENTS 5 LLOYD L. KING, Primary Examiner. 2,101,953 12/1937 Oman 62-118 2,182,174 12/1939 Finnemore 62-310 X US. Cl. X.R. 2,278,242 3/1942 Chapman 62310X 62-118

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