Refrigeration – Processes – Circulating external gas
Reexamination Certificate
2002-04-08
2003-11-04
Jones, Melvin (Department: 3744)
Refrigeration
Processes
Circulating external gas
C062S434000
Reexamination Certificate
active
06640561
ABSTRACT:
DESCRIPTION
The present invention refers to the field of refrigerating or chilling systems of the so-called “free-cooling” type.
Refrigerators or chillers with free-cooling are currently available on the market and are generally used for technological sites (data banks, telephone exchanges, etc.). There follows a brief explanation with reference to
FIG. 1
, which shows a currently known typical free-cooling system. The system is designated as a whole by reference number
1
and comprises a primary circuit
10
, a secondary or user's circuit
20
, and a refrigerating or cooling circuit
30
. The refrigerating circuit comprises a compressor
31
, a condenser or condenser battery C, an expansion valve
34
, and an evaporator E. It further comprises a line
32
between the compressor and the condenser, a line
33
between the condenser and the expansion valve, a line
35
between the expansion valve and the evaporator, and a line
36
between the evaporator and the compressor, all these being indicated in the figures with dash lines.
The secondary circuit
20
generally comprises a disconnector line referenced
21
, a delivery line
22
with pump P
2
; a number of users' appliances or terminals referenced U, U′, each on a respective user's line
23
,
23
′, the lines
23
,
23
′ etc. being generally connected in parallel, and each having a bypass line
25
,
25
′; and a return line
26
.
The primary circuit
10
comprises a free-cooling battery EC, a delivery line
12
at outlet from the evaporator, a return line
13
with pump P
1
, a bypass line
14
for bypassing the free-cooling battery, said line extending to a three-way valve referenced V, a line
15
extending to the free-cooling battery FC, a line
16
extending between the free-cooling battery FC and the three-way valve, and a line
18
extending between the three-way valve and the evaporator.
The free-cooling battery FC is a finned-tube battery. In the tubes thereof a fluid of the primary circuit (generally water) circulates. Air circulates around the tubes, so as to obtain, if the air temperature allows, a “free” cooling of water. The free-cooling battery FC is generally set upstream of the condenser, with respect to the air flow.
The assembly shown in the box of FIG.
1
and referenced
50
is generally supplied as a single or self-contained apparatus called “refrigerator or chiller with free cooling” or “free-cooling chiller” intended for being connected to the user's circuit.
Free cooling chillers are able to exploit the low temperature of outdoor air for cooling water to be sent to a user's system or secondary circuit
20
and are used in systems that require cooling energy also at low temperatures, as in the case of technological systems. They differ from normal chillers in that the finned battery FC is provided, which operates as an air-water heat exchanger, and is located upstream of the condenser battery C, of the refrigerating circuit
30
. Air moved by fans traverses in series, first, the air-water battery FC, and then, the condenser C of the refrigerating circuit.
The purpose of the additional battery FC is to take advantage of a low air temperature for cooling the return water coming from the system before sending it to the evaporator of the machine. In this way, a free cooling is obtained which leads to a saving in terms of electrical energy, in that less compressor work is required.
Free-cooling chillers have, therefore, two different operating regimes: normal operation and free-cooling operation.
Switching from normal operation to free-cooling operation is controlled by a microprocessor control system (not shown): when air temperature at the batteries inlet is lower than water temperature at the unit inlet, the free-cooling system is activated.
Under normal operating conditions, the valve V has the way to the line
14
open and the way to the line
16
closed : the free-cooling battery FC is therefore bypassed or excluded. As soon as air temperature, measured by the probe TA, drops below the return water temperature, measured by probe TW
2
, the valve V opens the way to the line
16
and closes the way to the line
14
. In such a way, the return water is cooled by outdoor air in the additional battery FC before entering the evaporator.
In this way, the consumption of electricity by the compressors is reduced. The purpose of the refrigerator or chiller is to produce refrigerated water at a desired temperature, measured by the probe TW
1
. Obviously, if water is pre-cooled by the free-cooling battery, the amount of refrigerating energy to be supplied, by means of the compressors, to the evaporator decreases, with consequent reduction in the consumption of electricity.
Free-cooling is said to be partial when water is cooled in part freely by the exchange battery and in part in the evaporator, thanks to the operation of the compressor/s; it is said to be total when the entire refrigerating load is supplied freely by the exchange battery.
The percentage of free-cooling as compared to the total refrigerating load required depends upon outdoor air temperature, upon the refrigerating load required from the system, upon refrigerated water temperature desired at outlet from the refrigerator, and upon water inlet temperature in the free-cooling battery.
FIG. 2
shows, as a function of outdoor air temperature, how the load is divided between the free-cooling battery and the compressors in the case of power (capacity) linearly decreasing with external temperature: 100% at 35° C., 40% at 5° C. The temperature at the delivery side to the system, measured by the probe TW
1
, is 10° C. In the diagram of
FIG. 2
, the grey area indicates the power (capacity) from the free-cooling battery.
As may be seen, when outdoor air temperature drops below 13° C., the free-cooling battery starts to supply part of the power required by the system. The entire power is supplied by the free-cooling battery for temperatures below 7° C.
The system described has constant flow rate.
The user's terminals or batteries U, U′ in fact, are controlled by three-way valves VU, VU′. At full load, all the water passes through the user's batteries U, U′ whilst, as the required power is reduced, an increasingly greater part of the water flow bypasses the user's batteries through the lines
25
,
25
′. Downstream of the valves VU, VU′ however, the flow rate remains constant whatever the load required by the system.
Also known are systems in which the user's terminals U, U′ of the system may be controlled with two-way valves which directly choke the flow of water to the user's batteries U. U′. The pump P
2
varies the number of revolutions to adapt to the new flow rate of the system. The secondary circuit thus operates with variable flow rate. Systems with variable flow rate are becoming increasingly common because they enable a considerable saving on the pumping expenses and because the cost of regulators or controllers with inverter for the pumps is markedly decreasing.
In known systems the flow rate variation, however, must be limited to the secondary or user's circuit alone and cannot take place in the primary circuit
10
, a portion of which passes through the evaporator. The primary circuit, in fact, cannot undergo flow rate variations in operation, because a flow rate variation through the evaporator would lead to failure of the compressor
31
. In known systems, it is therefore not possible to use a free-cooling battery with variable flow rate.
In systems with constant flow rate the return temperature measured by probe TW
2
of
FIG. 1
is directly proportional to the load required by the system. For example, if water leaves the chiller assembly
50
at 10° C., at 100% of the load it returns at 15° C. At 75% of the load, the return temperature drops to 13.7° C.; at 50% it becomes 12.5° C.; at 25% it becomes 11.3° C.; and at zero load, it becomes equal to outlet temperature, i.e.,
The situation is different in the case of a syst
Jones Melvin
RC Group S.P.A.
Young & Thompson
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