GB1605052A

GB1605052A - Air conditioning system

Info

Publication number: GB1605052A
Application number: GB15236/78A
Authority: GB
Original assignee: Trane Co
Current assignee: Trane Co
Priority date: 1977-04-21
Filing date: 1978-04-18
Publication date: 1981-12-16
Also published as: FR2388213A1; FR2388213B1

Description

(54) AIR CONDITIONING SYSTEM (71) We, THE TRANE COMPANY, a corporation of Wisconsin, United States of America, of La Crosse, Wisconsin 54601, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns air conditioning systems.

Historically, building air conditioning systems have employed several schemes of capacity control.

One such scheme is to supply air at a constant volume to the conditioned space.

As the building air conditioning load varies, the temperature of the air supply is varied.

While some systems provide precise humidity control via reheat, others provide no humidity control. The system is relatively low in cost and simple to design. Where humidity control via reheat is employed, operating costs may be expensive.

Another system which is in use is known as a variable air volume system. In this system, the volume of the air is infinitely and continuously varied on a room-by-room or zone-by-zone basis usually while the supply air temperature remains constant.

This requires that the volume of building supply air from its source will vary continuously in accordance with the total needs of the area served by the source. It will be evident that such systems can also provide zone temperature control flexibility.

Another advantage over the contant volume system that may be achieved in variable air volume systems is an energy savings resulting from reduced air flow during periods of reduced air conditioning demand. A major disadvantage of the variable air volume system is its initial cost. In many buildings a variable air volume system cannot be justified for one or more of several reasons. The absence of a need for individual zone temperature control may be one. The initial cost may be another. The complexity of designing the system and selecting the components may be still another.

The present invention from one aspect provides a system for conditioning air comprising a duct; inlet means for admitting air to said duct; outlet means for discharging air from said duct; blower means for circulating air through said duct; a blower motor drivingly connected to said blower means; a heat exchanger disposed within said duct for tempering air circulated therethrough by said blower means and having a plurality of refrigerant lines extending generally transversely of a flowpath through the heat exchanger for the air and extending generally transversely of a plurality of fins which are common to and in direct heat transfer relation with each of said lines, the lines being intertwined; means for supplying a refrigerant to each of said lines; and system control means responsive to the condition of the air admitted to said duct for preventing the supply of refrigerant to a proportion of the refrigerant lines and for operation of the blower motor at a commensurately reduced speed; said proportion of the refrigerant lines being less than all of the lines.

Additionally, the invention provides a refrigeration system for use in the above air conditioning system, the refrigeration system comprising a heat exchanger having a plurality of fins common to first and second refrigerant lines which extend generally transversely of the fins in direct heat exchange relation therewith and generally transversely of a flow path, through the heat exchanger, for a heat exchange medium and which are intertwined; means for supplying a refrigerant to each of the first and second lines; and control means for preventing the supply of refrigerant to one of the two lines.

The invention is described further, by way of example, with reference to the accompanying drawings in which like numerals have been used to designate like elements throughout and wherein; Figure 1 is a schematic of a rooftop air conditioning unit utilizing multiple refrigerant circuits and compressors arranged for cooling and heating; Figure 2 is a schematic of an air conditioning unit similar to the unit shown in Figure 1 and incorporating an embodiment of the invention wherein each of the separate refrigerant circuits of the units embraces the entire face of an outdoor heat exchanger; Figure 3 is a schematic of an air conditioning unit similar to the one of Figure 2 and including another embodiment of the invention wherein each of the separate refrigerant circuits of the unit embraces the entire face of an indoor heat exchanger;; Figure 4 shows a variation of the units illustrated in Figures 2 and 3 wherein the indoor heat exchanger blower is in a blowthrough position.

It should be noted that the unit illustrated in Figure 1 is not constructed in accordance with the invention. However, this unit is described below for assistance in understanding the units according to the invention illustrated in Figures 2 and 3.

Now with reference to Figure 1, it will be seen that a rooftop air conditioner 10 is supported upon a roof 12 of a building containing a space 14 to be conditioned.

The air conditioner has a generally rectangular housing 20 which is divided by partition 26 into a conditioned space air tempering chamber 22 and a tempering fluid source chamber 24.

An air tempering heat exchanger or indoor air heat exchanger 28a, which is of the fin and tube type, is disposed in the air tempering chamber 22 between first 16 and second 18 apertures in housing 20. The apertures communicate through aligned openings in roof 12 with the conditioned space 14. An indoor air centrifugal blower 30 is arranged to circulate air from the space 14 through opening 16 into the chamber or duct 22, over the indoor air heat exchanger, and back to the conditioned space 14 via enclosure distribution conduit 19 and fixed registers 21. Partition 29 prevents air from bypassing the indoor heat exchanger. Blower 30 is drivingly connected to a four-andsix-pole blower motor 32 which operates at nominal speeds of 1750 or 1167 revolutions per minute, depending upon the number of activated poles when connected to a sixty cycle per second power source.It will be appreciated that these nominal speeds will be proportionately lower when the power source is at a low frequency as, for example, fifty cycles per second.

The indoor heat exchanger 28a has first 34a and second 36a portions each of which encompasses a separate facial area of the heat exchanger 28a and has a refrigerant circuit separate from the other portion. The air passing over the first portion 34a thus is in parallel flow relation to the air passing over the second portion 36a.

A damper 38 activated by an operator 39 is positioned to shut off the air flow over the second portion 36a. The energizing of the operator 39 opens the dampers 38.

The heat exchange fluid 28a or refrigerant for indoor air heat exchanger 28a is supplied from fluid source chamber 24 which contains first 40 and second 42 compressors each having a refrigerant accumulator 43.

Also associated with and preferably in chamber 24 is a source or outdoor heat exchanger 44a, also of the fin and tube type, having first 46a and second 48a portions, each of which covers a separate facial area of the heat exchanger and has a refrigerant circuit separate from the other portion.

Disposed within chamber 24 is a centrifugal blower 50 which is arranged to circulate atmospheric air over the outdoor heat exchanger 44a. Blower 50 is drivingly connected to a four-and-six-pole blower motor 52b. A damper 54, actuated by an operator 55, is positioned to shut off the air flow over the second portion 48a. The energizing of operator 55 opens the dampers 54.

In the air conditioner shown in Figure 1, the compressor and indoor and outdoor heat exchanger portions are shown connected in two separate circuits as reverse cycle heat pumps through reversing valves 56 which are actuated to the heating cycle by the energizing of actuators 58. A first liquid line 60 with appropriate throttling means and check valves connects heat exchanger portions 34a and 46a while liquid line 62 in similar manner connects heat exchanger portions 36a and 48a. The suction and discharge sides respectively of compressor 42 are connected through gas line 66 via a four-way reversing valve 56 to the first portions 34a and 46a of either indoor and outdoor heat exchangers 28a and 44a respectively thereby permitting one of the first portions to function as a refrigerant evaporator while the other first portion functions as a refrigerant condenser. Compressor 40 and the second portion 36a and 48a of the indoor and outdoor heat exchangers are similarly connected through gas line 64.

A control system 68a is shown for controlling the motors 32 and 52b, compressors 40 and 42, reversing valve actuators 58 and damper operators 39 and 55 in response to the sensible load.

The control system shown includes a two-stage heating-cooling thermostat 70, a cooling cycle relay 72, a heating cycle relay 74, and a staging relay 76. The bi-metallic temperature sensing element of thermostat 70 is positioned to sense the temperature of the air returning to the indoor heat exchanger so as to sense the sensible thermal load imposed upon the air conditioning system.

The thermostat 70 may either energize the cooling relay 72 or heating relay 74, respectively, depending upon whether the load demands cooling or heating. Thermostat 70 also may position the staging relay into the de-energized position shown for low capacity operation or energized position, shown by dashed line, for high capacity operation.

The operation of the system is as follows.

Upon closure of switch 78, electric power flows from an alternating current source 80, through switch 78, through contacts C2 of relay 76 to energise the six pole winding of motor 32 thereby driving blower 30 to circulate air at low volume. Should the temperature as sensed by thermostat 70 rise above the first stage cooling set point, contact C1 of thermostat 70 closes completing a circuit including source 80, switch 78, bimetal element of thermostat 70, contact C1 of thermostat 70, and the winding of relay 72 to thereby energize the winding of cooling relay 72 thereby closing the contact C1 and opening contact C2 or relay 72. A circuit is thus completed which includes power source 80, switch 78, contact C1 of relay 72, and compressor 42 to energize the low stage compressor.Another circuit is completed which includes power source 80, switch 78, contact C1 of relay 72, contact C4 of relay 76 to the six pole winding of motor 52b thereby energizing blower 50 at low speed. Dampers 38 and 54 remain closed so that the air moved by blowers 30 and 50 passes only over first portions 34a and 46a of the indoor and outdoor heat exchangers, respectively.

Should the temperature as sensed by thermostat 70 rise to the second stage cooling set point, contact C2 thereof will also close thereby energizing a circuit including power source 80, switch 78, contact C2 of thermostat 70, and the winding of relay 76 thereby energizing relay 76 to the dashed line position. The energizing of relay 76 establishes a circuit including power source 80, switch 78, contact C1 of relay 76 and the four pole winding of motor 32 which is then energized to drive blower 30 at high speed. It will also be noted that contact C2 of relay 76 is opened. Energizing of relay 76 also establishes a circuit including power source 80, switch 78, contact C1 of relay 72, contact C3 of relay 76 and the four pole winding of second blower motor 52b to drive blower 50 at high speed.Again it will be noted that the contact C4 of relay 76 is opened. Energizing of relay 76 also closes a circuit including power source 80, switch 78, contact C1 of relay 72, contact C5 of relay 76 and compressor 40 to thereby activate the refrigeration circuit associated with the second portions 36a and 48a of the indoor and outdoor heat exchangers, respectively.

Energizing of relay 76 still further establishes a circuit including, power source 80, switch 78, contact C1 of relay 72, contact C11 of relay 76 and each of damper actuators 39 and 55 to actuate dampers 38 and 54 to the open position.

It will thus be seen that the system when operated at the second stage cooling produces about twice the capacity as upon the first stage and has about twice the air flow through the unit. The balance between sensible and latent cooling remains substantially the same whether the system is operated at high or low capacity. Furthermore, because the air flowing over the heat exchanger portion 34a remains generally in proportion to the amount of refrigerant flow, i.e., one-half the full air flow is heat exchanged with the refrigerant circulated by one-half the compressors, the heat exchanger portion 34a will not have any more tendency to frost up at low capacity than at high capacity.

Should the temperature as sensed by thermostat 70 fall below the second stage cooling set point, contacts C2 of thermostat 70 will open thereby placing the system into the low capacity cooling mode as hereinbefore described.

Should the temperature as sensed by thermostat 70 fall below the first stage cooling set point, contact C1 of thermostat 70 will open to de-energize relay 72 thereby shutting the system off except for operation of the blower motor 32 under six pole operation as hereinbefore described.

Should the temperature as sensed by thermostat 70 fall below the first stage heating set point, contact H1 of thermostat 70 will be closed to energize relay 74 thereby closing contacts H1 and H2 of relay 74.

Closure of contact H1 of relay 74 completes the same circuits as did closure of contact C1 of relay 72. However closure of contact H2 of relay 74 establishes a circuit including power source 80, switch 78, contact H2 of relay 74 and reversing valve actuators 58 thereby causing the refrigerant to flow in the indoor and outdoor heat exchangers in the reverse direction as a heat pump thereby causing the air circulated by blower 30 to be the heated rather than cooled.

Should the temperature as sensed by thermostat 70 fall below the second stage heating set point, contact H2 of thermostat 70 will also be closed thereby placing the system in the high capacity mode just as did closure of contact C2 of thermostat 70 as hereinbefore described. Further, as the heating demand drops, the thermostat contacts H2 and H1 will successively open to bring the system back to the original condition with only the indoor heat exchanger blower 30 operating at low speed.

An air conditioner embodying the invention is shown in Figure 2 and is similar to that of Figure 1. It differs from the Figure 1 conditioner insofar as the separate portions 46e and 48c each embrace the entire face of the heat exchanger 44c. The blower motor 52b is of the four-and-six-pole type.

The embodiment of Figure 3 is similar to the embodiment of Figure 2 except that the separate portions 34c and 36c are each arranged to embrace the entire face of the heat exchanger 2 & No dampers are required to prevent air from bypassing through a portion of the heat exchanger 28c.

Blower motor 32c having four-and-eightpoles effects an air reduction commensurate with the reduction in refrigerant flow.

Figure 4 shows a variation applicable to both of the embodiments shown in Figures 2 and 3. This variation repositions the blower 30 in upstream relation to the indoor heat exchanger.

The systems described are basically constant volume systems from the standpoint of design complexity and initial low costs.

They have, however, certain advantages over conventional constant volume systems in the areas of reduced operating costs and energy consumption. Satisfactory humidity control may be achieved without reheat and evaporator frosting is avoided by a stepped reduction in blower capacity and a stepped change in heat exchange fluid flow at the air tempering heat exchanger.

Thus, It is possible to operate these air conditioning systems with improved energy efficiency by reducing the blower capacity, and to prevent frosting of the evaporator heat exchanger when the air conditioning system is operated at low blower capacity.

And finally, it will be observed that even with lower capacity operation, the cooling heat exchanger may be operated at low or lower temperatures so that the system may reach low wet bulb temperatures.

In these systems, the air volume is controlled at its source in response to the air tempering loads rather than in response to the sum of the volume demanded by several zones as in a variable air volume system.

More specifically, the blower capacity is staged at discrete levels of constant air volume. The staging does not alter the ability of the system to produce a conditioned air having a wet bulb temperature as low as may be obtained at other levels of operation. Under most operating conditions a lower wet bulb temperature will be achieved by use of these systems. A multispeed motor is employed to effect reduction of blower speed with consequent reduction in air flow at the air tempering or indoor heat exchanger.

The reduced but steady air volume mode is simultaneously accompanied by a reduced flow of tempering heat exchange fluid to the air tem rating heat exchangers.

The flow of heat exchange fluid is reduced to that which is commensurate with the reduced air volume which causes the air temperating heat exchanger to affect the sensible and latent heat load in generally similar proportions as it did when the system was operated at a higher capacity level.

And, the change in tempering heat exchange fluid flow is accompanied by a reduction in compressor capacity, which may be accomplished by selective compressor operation, compressor unloading or compressor speed reduction.

Various modifications to the described systems may be devised. Thus, in some instances it may be desirable to forego the use of a multispeed motor and use a single speed motor for the blower at the outdoor heat exchanger. The system might be staged for more than two levels of operation. The system might be operated strictly as a cooling system or as a heating system. Still further, it will be appreciated that the controls have been shown in a simplified and schematic manner to illustrate the basic manner of operation. Many refinements and variations of the controls are possible. For example, a time delay device might be added to delay energization of the low speed winding of the multispeed motors after the high speed winding is disconnected so as to avoid damage to the motor and avoid objectionable noise. The temperature sensing element may be located in the enclosure.

A time delay may be associated with the dampers to avoid momentary unduly low suction pressure which may cause the refrigerant system low pressure cutout to be actuated. It is entirely possible to combine many of the desirable features of the prior art with those features detailed herein. Such an example would be to make provision for circulating at times only fresh air and exhausting all return air during which time the dampers on the indoor heat exchanger would be opened.

Thus it will be understood that many variations are possible without departing from the scope of the invention.

WHAT WE CLAIM IS: 1. A refrigeration system comprising a heat exchanger having a plurality of fins common to first and second refrigerant lines which extend generally transversely of the fins in direct heat exchange relation therewith and generally transversely of a flow path, through the heat exchanger, for a heat exchange medium and which are intertwined; means for supplying a refrigerant to each of the first and second lines; and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. bring the system back to the original condition with only the indoor heat exchanger blower 30 operating at low speed. An air conditioner embodying the invention is shown in Figure 2 and is similar to that of Figure 1. It differs from the Figure 1 conditioner insofar as the separate portions 46e and 48c each embrace the entire face of the heat exchanger 44c. The blower motor 52b is of the four-and-six-pole type. The embodiment of Figure 3 is similar to the embodiment of Figure 2 except that the separate portions 34c and 36c are each arranged to embrace the entire face of the heat exchanger 2 & No dampers are required to prevent air from bypassing through a portion of the heat exchanger 28c. Blower motor 32c having four-and-eightpoles effects an air reduction commensurate with the reduction in refrigerant flow. Figure 4 shows a variation applicable to both of the embodiments shown in Figures 2 and 3. This variation repositions the blower 30 in upstream relation to the indoor heat exchanger. The systems described are basically constant volume systems from the standpoint of design complexity and initial low costs. They have, however, certain advantages over conventional constant volume systems in the areas of reduced operating costs and energy consumption. Satisfactory humidity control may be achieved without reheat and evaporator frosting is avoided by a stepped reduction in blower capacity and a stepped change in heat exchange fluid flow at the air tempering heat exchanger. Thus, It is possible to operate these air conditioning systems with improved energy efficiency by reducing the blower capacity, and to prevent frosting of the evaporator heat exchanger when the air conditioning system is operated at low blower capacity. And finally, it will be observed that even with lower capacity operation, the cooling heat exchanger may be operated at low or lower temperatures so that the system may reach low wet bulb temperatures. In these systems, the air volume is controlled at its source in response to the air tempering loads rather than in response to the sum of the volume demanded by several zones as in a variable air volume system. More specifically, the blower capacity is staged at discrete levels of constant air volume. The staging does not alter the ability of the system to produce a conditioned air having a wet bulb temperature as low as may be obtained at other levels of operation. Under most operating conditions a lower wet bulb temperature will be achieved by use of these systems. A multispeed motor is employed to effect reduction of blower speed with consequent reduction in air flow at the air tempering or indoor heat exchanger. The reduced but steady air volume mode is simultaneously accompanied by a reduced flow of tempering heat exchange fluid to the air tem rating heat exchangers. The flow of heat exchange fluid is reduced to that which is commensurate with the reduced air volume which causes the air temperating heat exchanger to affect the sensible and latent heat load in generally similar proportions as it did when the system was operated at a higher capacity level. And, the change in tempering heat exchange fluid flow is accompanied by a reduction in compressor capacity, which may be accomplished by selective compressor operation, compressor unloading or compressor speed reduction. Various modifications to the described systems may be devised. Thus, in some instances it may be desirable to forego the use of a multispeed motor and use a single speed motor for the blower at the outdoor heat exchanger. The system might be staged for more than two levels of operation. The system might be operated strictly as a cooling system or as a heating system. Still further, it will be appreciated that the controls have been shown in a simplified and schematic manner to illustrate the basic manner of operation. Many refinements and variations of the controls are possible. For example, a time delay device might be added to delay energization of the low speed winding of the multispeed motors after the high speed winding is disconnected so as to avoid damage to the motor and avoid objectionable noise. The temperature sensing element may be located in the enclosure. A time delay may be associated with the dampers to avoid momentary unduly low suction pressure which may cause the refrigerant system low pressure cutout to be actuated. It is entirely possible to combine many of the desirable features of the prior art with those features detailed herein. Such an example would be to make provision for circulating at times only fresh air and exhausting all return air during which time the dampers on the indoor heat exchanger would be opened. Thus it will be understood that many variations are possible without departing from the scope of the invention. WHAT WE CLAIM IS:

1. A refrigeration system comprising a heat exchanger having a plurality of fins common to first and second refrigerant lines which extend generally transversely of the fins in direct heat exchange relation therewith and generally transversely of a flow path, through the heat exchanger, for a heat exchange medium and which are intertwined; means for supplying a refrigerant to each of the first and second lines; and

control means for preventing the supply of refrigerant to one of the two lines.

2. A refrigeration system as claimed in claim 1, wherein the means for supplying refrigerant to the two lines comprise first and second compressors which are each connected to a respective one of the lines, and wherein the control means are arranged to render one of the compressors inactive for preventing the supply of refrigerant to one of the two refrigerant lines.

3. A refrigeration system comprising an evaporator, compression means, a condensor, and two refrigerant circuits, each of which is arranged to pass through the evaporator, the compression means and the condensor, at least one of the evaporator and the condensor including a plurality of heat exchange fins common to first and second refrigerant lines each forming part of a respective one of the refrigerant circuits, which lines extend generally transversely of the fins in direct heat exchange relation therewith and generally transversely of a flow path for a heat exchange medium through said one of the evaporator and condensor and which lines are intertwined, and control means being provided for preventing the flow of refrigerant through one of the first and second refrigerant lines.

4. A refrigeration system as claimed in claim 3, wherein the compression means include two compressors and wherein the control means are arranged to render one of the compressors inactive for preventing the flow of refrigerant through one of the first and second refrigerant lines.

5. A system for conditioning air comprising a duct; inlet means for admitting air to said duct; outlet means for discharging air from said duct; blower means for circulating air through said duct; a blower motor drivingly connected to said blower means; a heat exchanger disposed within said duct for tempering air circulated therethrough by said blower means and having a plurality of refrigerant lines extending generally transversely of a flowpath through the heat exchanger for the air and extending generally transversely of a plurality of fins which are common to and in direct heat transfer relation with each of said lines, the lines being intertwined; means for supplying a refrigerant to each of said lines; and system control means responsive to the condition of the air admitted to said duct for preventing the supply of refrigerant to a proportion of the refrigerant lines and for operating the blower motor at a commensurately reduced speed; said proportion of the refrigerant lines being less than all of the lines.

6. A system as claimed in claim 5, wherein the heat exchanger comprises an evaporator for cooling and dehumidifying air circulated through the duct by the blower means.

7. A system as claimed in claim 5 or 6 further comprising a first compressor; a second compressor; a second heat exchanger; a first refrigerant circuit interconnecting said proportion of the refrigerant lines of the first heat exchanger, the first compressor and the second heat exchanger in a first closed refrigerant loop; and a second refrigerant circuit interconnecting the remainder of the refrigerant lines of the first heat exchanger, the second compressor, and the second heat exchanger in a second closed refrigerant loop, the control means being operable to maintain the first compressor inactive while the second compressor is in operation.

8. A system as claimed in any of claims 5 to 7, wherein the blower motor is arranged for four- and eight-pole operation, the control means being arranged to switch the blower motor from four-pole to eight-pole operation for reducing the speed of said motor.

9. A refrigeration system substantially as herein particularly described with reference to and as illustrated in Figure 2, or in Figure 3 of the accompanying drawings.

10. A system for conditioning air substantially as herein particularly described with reference to and as illustrated in Figure 2, or in Figure 3 of the accompanying drawings, or in Figure 2 or 3 when modified by Figure 4 of the accompanying drawings.