Refrigeration System Including Head Pressure Control Means

Abstract

A refrigeration system comprising an air cooled condenser, fan means for passing outdoor air over the condenser including a first fan operative only at higher outdoor temperatures, a second, multi-speed fan and control means responsive to the system high side pressure for controlling the second fan speed; the control means including a time delay relay means for assuring a high speed operation of the fan upon initial operation of the system regardless of outdoor temperatures.

Description

BACKGROUND OF THE INVENTION

In the operation of modern refrigeration systems, such as those employed for cooling an enclosure, it is not uncommon for cooling to be required even when the outdoor temperatures are relatively low. When outdoor air is used to cool the system condenser, low outdoor air ambient termperature conditions may result in over cooling so that the high side pressure of the system is at an extremely low level thereby reducing the amount of refrigerant flow from the condenser through the expansion means to the evaporator which in turn reduces the system capacity.

In order to maintain the required high side pressure in the system at low ambient temperatures so that the expansion means can properly control the refrigerant flow and maintain capacity, it has been a common practice to provide means for decreasing the air flow across the condenser when the outdoor temperature falls below a predetermined minimum. Various means for decreasing the total air cooling of the condenser at low ambient temperatures are described and shown, for example, in U.S. Pat. Nos. 2,952,991-Pierre; 3,112,620-Steward; 3,152,455-Ware and 3,293,876 -Geisler. These known systems involving either means for varying the number of fans operating or the speed of one of the fans have decreased the air flow under conditions which, with full air flow, would result in unacceptably low high side pressures, but under some conditions they fail to provide the constant air flow required for optimum cooling operation.

For example, in the initial start up of these known systems, under low ambient temperature conditions, the air flow called for by the controls is low. If the air flow is controlled only by ambient temperature, the head pressure may become too high for optimum cooling operation. If it is controlled by head or high side pressure or temperature, the air will increase as the head pressure and temperature increase but may hunt or oscillate due to the system pressure or temperature lag at start up and still level off at a lower fan speed than that giving optimum cooling operation. Thus the system may continue to operate at either a lower or higher head pressure than its design is intended for so that it will operate for a longer or shorter optimum time. Substantial icing of the system evaporator may take place due to such inefficient operation of the system.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a refrigeration system including an air flow control means designed to quickly enable the system to find its optimum cooling operating level under various ambient temperature conditions.

Another object of the invention is to provide a refrigeration system including an improved head pressure control means which during the initial start up causes the system to quickly operate at a higher system high side pressure level than will be required and thereafter regulating to the desired air flow and high side pressure for proper cooling operation of the system.

In accordance with the illustrated embodiment, the present invention provides a refrigeration system comprising a compressor, a condenser, expansion means and evaporator series connected to form a closed refrigerant circuit and air flow control means which is responsive to both outdoor ambient air temperature and system high side pressure or single fan air flow control responsive to system high side pressure and which assures a maximum air flow for optimum cooling operation. To this end, the illustrated system is provided with two fans for passing a cooling stream of outdoor air over the condenser. The operation of one of the fans is controlled by an outdoor thermostat which de-energizes the fan whenever the outdoor temperature falls below a predetermined temperature. The second fan on a dual fan system or the only fan on a single fan system is a multi-speed fan, the speed of which is controlled through an autotransformer having high, medium and low voltage taps and first and second time-delay relays operated by the first and second pressure actuated switch means responsive to different high side pressures for connecting the fan to one of these three taps. The time delay provided by the relay means is sufficient so that during initial energization or start-up of the compressor the increase in fan speed will lag behind that actually called for by the pressure actuated switch means so as to permit the high side pressure to reach a level higher than that at which it will ultimately be required to operate the fan to maintain optimum high side pressure. This will provide the highest fan speed operation and hence maximum cooling under the existing ambient conditions.

BRIEF DESCRIPTION OF THE DRAWING

In the accompanying drawing:

The single FIGURE is a schematic view of a refrigeration system including the control circuitry of the present invention. The FIGURE denotes a dual outdoor condenser fan system and is considered to illustrate a single outdoor condenser fan system using high side system pressures in the same manner as described.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the accompanying drawing, there is illustrated a refrigeration system comprising a motor driven compressor 1, a condenser 2, a capillary flow restrictor 3, and an evaporator 4 series connected to form a closed refrigerant circuit. The refrigerant compressed by the compressor 1 is discharged at high pressure through the discharge conduit 5 to the condenser where it is condensed into liquid form. The liquid refrigerant then passes through the expansion device in the form of the capillary 3 to the evaporator 4 where at a lower pressure it evaporates to extract heat from indoor air passed over the evaporator by means of fan 7. In terms of refrigerant pressure conditions, such a system is frequently described as having a head or high side or high pressure side extending from the compressor outlet to the expansion means and a suction or low side or low pressure side from the expansion means to the compressor.

For the purpose of cooling the condenser 2, outdoor air is passed over the condenser by the operation of one or the other of two fans 11 and 12 respectively driven by motors 14 and 15.

Power for the operation and control of the compressor and fans is supplied through leads L.sub.1 and L.sub.2 connected to a suitable source of electrical power. The control circuitry includes a plurality of switches operated by a thermostat 17 responsive to indoor temperatures. These switches include compressor switch means 18 for connecting the compressor across the leads L.sub.1 and L.sub.2 when the thermostat 17 calls for cooling and switches 19 and 20 respectively connecting the first fan motor 14 and the second fan motor 15 to the lead L.sub.2. The circuit for the fan motor 14 is completed by an outdoor thermostat switch 21 for connecting motor 14 to the lead L.sub.1 ; this switch 21 being closed at higher outdoor temperatures and being open at lower outdoor temperatures. Preferably, this outdoor thermostat 21 opens to de-energize the motor 14 when the outdoor temperature falls to a predetermined temperature, as for example 50.degree. F, and resets or closes to energize the fan motor 14 when the temperature again increases.

During operation of the compressor 1, the operating speed of the fan 12, or more specifically, its motor 15 is controlled by the head or high side pressures in the system. This control circuitry includes a first time delay relay 22 comprising a two-pole switch 23 and a relay coil 24, the energization of which is controlled by a pressure responsive switch 25 sensing pressure in the discharge line 5. A second time delay relay 26, a two-pole switch 27 and a coil 28 is operated by a second pressure sensitive switch 29 which is also operated by the pressures within the discharge line 5. Depending upon the operating positions of the switches 23 and 27, the fan motor 15 is connected either to a low voltage terminal tap 31, an intermediate voltage tap 32 or a high voltage tap 33 of an autotransformer 34 connected across the supply lines L.sub.1 and L.sub.2. Low voltage power for operation of the relay coils 24 and 28 is provided through a transformer 35 the primary of which is connected across supply lines L.sub.1 and L.sub.2.

As previously indicated, the first and second relays 22 and 26 include time delay means for delaying the operation of the switches 23 and 27 following operation of the pressure responsive switch means 25 and 29. Such time delay relays are well known, and include, for example, a heated bimetal switch means delaying the actual operation of the relay switch following energization or de-energization of the relay coil. In addition, pressure operated or actuated switches 24 and 28 are responsive to different high side pressures, the switch 24 closing at a lower pressure than switch 28. However, both of these pressures are preferably higher than the lowest non-operating pressure within the discharge line 5.

The amount of cooling air circulated over the condenser 2 depends upon whether one or both of the fan motors 14 and 15 are energized as well as the speed in which the motor 15 is operating. After an idle period, that is, at a time when the room thermostat 17 first calls for cooling, refrigerant pressures within the system are substantially equalized or, in other words, the high side pressure is at a low level. If the outdoor temperature is above the operating temperature range of the outdoor thermostat 21, fan motor 14 will be energized. If the temperature is below that value, motor 14 will not be energized and fan 11 will not be operating.

In either case, the high side pressure in the discharge line 5 is usually below operating pressure for either of the pressure switches 25 and 29, both of these switches will be open so that relay coils 24 and 28 are not energized. Under these conditions, switches 23 and 27 will be in their illustrated positions with switch 23 completing an energizing circuit for the notor 15 through contact 37 to the low voltage tap 31 with the result that the fan motor 15 will operate at its lowest speed providing a minimum air flow over the condenser 2. The operation of the compressor 1 then continuously increases the head pressure or high side pressure, and this increase initially closes pressure switch 25 to complete the energizing circuit for the relay coil 24. Due to the time delay built into the operation of this relay, there will be a short delay, as for example about 45 seconds, before the switch 22 operates to engage contact 39 and allows the pressure switch 29 to complete the energizing of time delay relay coil 28. At this time, fan motor 15 is energized through a circuit including contact 39 of switch 22, contact 40 of switch 26, and the medium voltage tap 32 so that the motor 15 runs at an intermediate speed thereby with an increase in the air flow over the condenser 2.

The high side pressure continued to increase, depending upon the outdoor air temperatures, the pressure switch 29 closed to complete a circuit to the relay coil 28 forming part of the second time delay relay 26 and after a short period of time, as for example 10 to 15 seconds after the time delay relay 22 had been energized, switch 27 engages contact 41 to connect the fan motor to the high voltage tap 33 for operation of the fan motor 15 at maximum speed.

By this built in time delay in the switching of the variable speed motor 15 from its low to higher speeds, the head or high side pressure is allowed to go to the highest level that the system will experience under ambient conditions before regulating to the desired motor speed required, predetermined by the opening and closing pressure setting of the pressure switches 25 and 29, for the proper operation of the system. This assures continuing operation of the highest fan speed, or in other words, the highest air flow required for the operation of the system under the existing ambient temperature conditions. As a result, the system will operate at maximum efficiency insofar as cooling rate is concerned. Unless the head pressure and outside ambient temperature conditions require high speed operation of the fan motor 15, the motor will modulate to the next lower speed. In other words, during initial start up, the fan speed will normally be increased at least one step beyond that ultimately required to maintain the proper operating head pressure for the existing conditions thus assuring that the system does not level off at an air flow below that needed for maximum cooling efficiency. Under these conditions, minimum icing or frosting of the evaporator is also obtained as well as allowing the expansion means to properly control and provide maximum efficiency.

A further advantage in the use of time delay relays is the substantial elimination of false signals effecting a change in air flow. With known systems, gusts of wind which materially change the amount of condenser cooling can cause an undesired decrease or increase in fan speed particularly when the controls are operating close to a change over pressure condition. With the time delay, the false signal will usually disappear before an actual change over to a different fan speed has taken place.

While there has been shown and described a specific embodiment of the present invention, it is not limited thereto and it is intended by the accompanying claims to cover all modifications falling within the spirit and scope of the invention. For example, the head pressure control means of the present invention obviously could also be used to provide head pressure control in cooling operation for an air conditioner of the heat pump variety.

Claims

I claim:

1. A refrigeration system comprising in combination:

a compressor, condenser, capillary flow restrictor and evaporator series connected to form a closed refrigerant circuit in which the portion of said circuit from said compressor to said expansion means defines the high pressure side of said refrigerant circuit;

fans respectively driven by separate fan motors for passing a cooling stream of outdoor air over said condenser, one of said fan motors being a multi-speed motor;

a circuit for controlling the energization of said second multi-speed motor including an autotransformer having high, medium and low voltage taps, first and second time delay relays each including two position switches, and first and second pressure actuated switch means respectively responsive to lower and higher operating pressures in said high pressure side of said refrigerant circuit;

said first switch connecting said second multi-speed motor to said low voltage tap at a high side pressure sensed by said first pressure actuated switch means which is below said lower pressure and to said second switch at pressures above said lower pressure;

said second switch connecting said second multi-speed motor to said medium voltage tap at pressures below said higher high side pressure and to said high voltage tap at pressures above said higher high side pressure;

said time delay relays having time delays sufficient that upon initial energization of said compressor, said multi-speed fan motor will be sequentially connected to said low, medium and high voltage taps with sufficient delay while connected to said low voltage tap to permit the high side pressure to reach the highest level for the existing outdoor temperature.

2. A refrigeration system comprising in combination:

a compressor, condenser, expansion means and evaporator series connected to form a closed refrigerant circuit in which the portion of said circuit from said compressor to said expansion means defines a high pressure side of said refrigerant circuit;

first and second fans respectively driven by first and second fan motors for passing outdoor air over said condenser, said second fan motor being a multi-speed motor;

control circuitry for controlling the operation of said fan motors comprising:

means for energizing said first fan motor only when the outdoor temperature is above a predetermined temperature;

a circuit for operating said second fan motor at high, medium and low speeds, including first and second time delay relays and first abd second pressure actuated switch means respectively responsive to lower and higher pressures in said high pressure side of said refrigerant circuit for respectively energizing said first and second relays;

said time-delay relays having time delays sufficient that upon initial energization of said compressor, with said second fan motor operating at low speed, the system high side pressure will go to the highest level the system will experience at existing outdoor temperatures before said second fan motor operates at its higher speed.

3. A refrigeration system comprising in combination:

a compressor, condenser, capillary flow restrictor and evaporator series connected to form a closed refrigerant circuit in which the portion of said circuit from said compressor to said expansion means defines the high pressure side of said refrigerant circuit;

first and second fans respectively driven by first and second fan motors for passing a cooling stream of outdoor air over said condenser, said second fan motor being a multi-speed motor;

control circuitry for controlling the operation of said fan motors comprising:

an outdoor thermostat for energizing said first fan motor when the outdoor temperature is above a predetermined temperature and for de-energizing said first fan motor when the temperature falls below said predetermined temperature;

a circuit for controlling the energization of said second fan motor including an autotransformer having high, medium and low voltage taps, first and second time delay relays each including two position switches, and first and second pressure actuated switch means respectively responsive to lower and higher operating pressures in said high pressure side of said refrigerant circuit;

said first switch connecting said second fan motor to said low voltage tap at a high side pressure sensed by said first pressure actuated switch means which is below said lower pressure and to said second switch at pressures above said lower pressure;

said second switch connecting said second fan motor to said medium voltage tap at pressures below said higher high side pressure and to said high voltage tap at pressures above said higher high side pressure;

said time delay relays having time delays sufficient that upon initial energization of said compressor, said second fan motor will be sequentially connected to said low, medium and high voltage taps with sufficient delay while connected to said low voltage tap to permit the high side pressure to reach the highest level for the existing outdoor temperature.