GB2512129A

GB2512129A - Force-cooled air-conditioning system

Info

Publication number: GB2512129A
Application number: GB1305237.8A
Authority: GB
Inventors: Ian Anthony Bramwell Wrigley; Simon Turner
Original assignee: ENIGIN PLC
Current assignee: ENIGIN PLC
Priority date: 2013-03-21
Filing date: 2013-03-21
Publication date: 2014-09-24
Anticipated expiration: 2033-03-21
Also published as: GB2512129B; GB201305237D0

Abstract

An air conditioning system (100) cools air in an enclosure (110), such as a building. A cooling fluid is supplied by a compressor (120) to a coil (130) in a duct (106). A fan (102) forces air through the duct and is cooled by the coil to cool the enclosure. A logic module (154) drives a motor control subsystem (156) to: deactivate a motor (124) of the compressor, when a monitoring module (150) detects thermodynamic saturation of the cooled air 132 leaving the duct; maintain operation of the fan, until a target temperature in the enclosure has been reached; activate the motor when the monitoring module detects that the cooled air leaving the duct is no longer thermodynamically saturated and a time threshold has been exceeded since deactivation of the motor. The voltage applied to the motor is regulated to be the minimum voltage that allows enough current to flow to provide synchronous rotation of the motor.

Description

Force-cooled air-conditioning system

Field of the Invention

The invention concerns a compressor driven, force cooled air conditioning system.

Background

Air conditioning systems are designed to keep the temperature in an enclosure, such as the internal building temperature, cooler than the external ambient temperature at the location where the air-conditioning system is installed.

Common air-conditioning system systems have the following components, for cooling an enclosure such as a room: (i) A fan to move warm air from the room past cooling coils of the air conditioning system.

(ii) A compressor, providing cooling fluid/gasses for the cooling coils. As air passes around the coils, heat is extracted from the air through a heat transfer (diabatic) process.

(iU) A motor for driving the compressor.

(iv) A switching mechanism that turns the air conditioning system on, in response to a demand to lower the temperature in the room. The switching mechanism is typically triggered by a temperature sensor in the enclosure that is to be cooled. The control achieved is binary: if the temperature in the room is above a value set on a room thermostat, then the air conditioning system will be running, with the motor compressor switched on; if the temperature in the room falls to or below the value set on the room thermostat, then the air conditioning system will be off.

Compressors typically incorporate AC induction motors that have high current demands. Electrical energy drawn by the motor will be converted to either work' or heat'. In many phases of the cooling cycle, the motor can absorb more electrical energy than is required to do the job of work. In many known arrangements, some of the waste heat from the motor of the compressor tends to further heat up the cooling fluid or enter the cooled room/enclosure.

This heat itself then also has to be removed by further operation of the compressor. The resulting systems can be expensive to run, and may suffer high levels of compressor wear.

Air-conditioning systems are typically designed and sized for a given location or application, in order to ensure that there is adequate cooling, even on the very hottest days of the year. This means that these air-conditioning systems are specified to cope with the worst-case scenario'. It is generally known that, because air-conditioning systems often come in standard package sizes, the systems are engineered to cope with maximum temperatures that the system will rarely, if ever, encounter. In many applications, the air-conditioning system is either switched fully on or off, in a series of cycles, and often remains on continuously until demand from a timer clock or room thermostat (if fitted and operational) is satisfied.

Prior art systems have, therefore, sought ways to avoid the compressor running at full speed. One approach is the introduction of variable speed drives at the manufacturing stage. Variable speed drives can adjust the demand by means of motor speed control. These are typically part of the design that is engineered by the original equipment manufacturers. They are not suitable for applications where the compressor requires the motor to run at a constant operational speed.

Systems incorporating a reduction in voltage supplied to a motor to prevent the motor running at full power are known. One example is shown at: wLcywThcpruic. The voltage fed to a motor may be cut to zero many times per second. This approach, according to wwwsavawattco.uk, may be used in almost any application of an electric motor, and is not specific to air conditioning systems.

Other known systems have attempted to provide control over the amount of time the compressor cycles. This may be achieved by providing a time delay, during which the compressor is switched off, after the compressor has been operational for a given period. This time delay approach is based on the assumption (which is often the case) that the system has reached thermodynamic saturation. Detection of thermodynamic saturation is achieved by installing a sensor in the duct of the air-conditioning enclosure immediately after the cooling coils. Once a fixed preset temperature is achieved, the compressor will be switched off for a set period. During this set period, the fan can be allowed to run, to extract the latent cooling of the system. In the prior art, the set point for the temperature indicative of thermodynamic saturation, and the time delay imposed on the compressor, may be adjustable via a potentiometer.

The inventors have recognized turther shortcomings of known systems. The operation of hermetically sealed AC induction motor driven compressors is governed by specific laws of thermodynamics. For example, in order to remove heat energy from a designated space, a proportional amount of energy has to be expended to move the heat', heat being energy in motion.

This applies to an air-conditioning system for an air-conditioned room.

However, the expended energy in known systems is a problem, since it leads to that energy itself needing to be removed.

However, energy cannot be created or destroyed. So any excess current that is absorbed by the motor within the process will be converted to another form, which is primarily heat. The excess current is any energy or current over and above the absolute minimum that would be required to do the job of work in a perfectly efficient system. After being converted to heat, the excess current will in effect be reintroduced back into the system in the form of entirely counterproductive additional heat'. The more the compressor runs and draws excess current, the more heat is introduced back into the system, creating a further isentropic effect. In a hermetically sealed compressor, any excess current may then typically go into the coolant first in the form of heat, before more energy is then expended to remove it externally.

Summary of the Invention

In accordance with a first aspect of the invention, a force-cooled air-conditioning system is provided, having the features of appended claim 1. In accordance with a second aspect of the invention, a method of force-cooled air-conditioning of an enclosure is provided, having the steps of appended claim 9.

The method of the invention comprises controlling the compressor cycles, based on an intelligent feedback loop constantly measuring the cooling demand requirements and detecting thermodynamic saturation of air in the duct. Intelligent motor control circuitry constantly monitors the efficiency' of the motor itself. This approach ensures that the motor has just enough current to provide adequate excitation between the stator and the rotor, to enable the motor to run at full speed without drawing excess current. The inventors have provided a synergistic combination of two dynamic, intelligent, multimodal solutions to the varying duty cycles of a constant speed AC induction motor controlled compressor system. The invention addresses the problems of known arrangements in one synergistic solution.

The motor control subsystem regulates the voltage applied to the motor when the compressor is operating and a load on the compressor varies, whereby in operation the voltage applied to the motor is regulated to be the minimum voltage that allows enough current to flow to provide synchronous rotation of the motor. The voltage applied to the compressor just matches an instantaneous load on the compressor. This operating condition improves the power factor and efficiency of the motor, during the lightly loaded phase of each duty cycle.

Further preferred steps and features of the invention are provided, as detailed in the dependent claims.

Although the existing prior art may somewhat arbitrarily reduce the number of compressor starts, it has been shown that under heavy load, the performance of known systems is compromised. Furthermore, the known systems also have to immediately combat the isentropic effect resulting from excess current in the windings, all of which means the opportunity for maximum savings is very limited with known systems. In known systems, the available calibration range for the set point' on any duct sensor has to be minimal, so as to ensure the system can perform under occasional periods of higher demand.

With the present invention, each time the air-conditioning system is switched on in response to a demand from a time clock or thermostat, the motor control module will allow just enough current to flow into the windings of the motor to initially soft start the motor and subsequently enable the motor to run at a constant speed for the remainder of the cycle.

During the initial and each subsequent phase of the cooling cycle, the temperature control module will look for the point at which the system has achieved thermodynamic saturation. This is the point at which the temperature control module has received feedback from the sensor control loop showing that the temperature of the cooled air leaving the duct has stabilised and flatlined for a predetermined period, or is on course to do so. At this point, the compressor will be de-energised. However, the fan is still allowed to run, to extract the remaining latent cooling from the coils. Operation of the fan will be maintained, until a target temperature in the enclosure has been reached. The temperature control module will continue to monitor the duct temperature via the sensor. At the point that the duct temperature shows a consistent rise in the air temperature, the compressor will be re-energised by the motor control module. This re-energisation involves firstly soft starting the motor, and then dynamically controlling the flow of current, in response to the motor control feedback loop.

With known systems, compressor motors are routinely oversized, which exacerbates the problem. With the present invention, such penalties for oversizing of a motor may be avoided. The effective power of the motor may be reduced by electronically controlling the torque that it exerts, to dynamically size the motor exactly to the load at any time. The motor may therefore be electronically' reduced in effective power consumption, without physically replacing the motor.

The combined aspects of the multimodality approach of the present invention mean that during an operational period the compressor will only re-energise when the temperature control module detects a consistent rise in the temperature curve. The compressor will thereafter draw only the exact amount of current required to maintain effective operation of the air-conditioning system.

Some or all of the following advantages may result from the apparatus and methods of the invention: (i) An energy saving of potentially up to 50%.

(ii) Compressor noise and vibration are reduced, by ensuring that the compressor is soft started, and only energized when a real demand is detected.

(iii) The current drawn by the compressor motor can be controlled and optimized, to ensure that wasted energy is not converted to counterproductive heat.

(iv) Compressor life can be extended, and the maintenance costs reduced.

This is achieved by reducing the run-time, and removing damaging heat from the compressor.

Brief Description of the Drawings

Figure 1 illustrates a system in accordance with an embodiment of the invention.

Figure 2 illustrates the variation in duct air temperature that may be achieved in accordance with an embodiment of the invention.

Figure 3 illustrates a flowchart of a method in accordance with the invention.

Figure 4 is a schematic block diagram of components for implementing a system in accordance with an embodiment of the invention.

Figure 5 is a circuit diagram of components for implementing a system in accordance with an embodiment of the invention.

Figure 6 illustrates recorded variations in duct air temperature achieved by a system operating in accordance with an embodiment of the invention.

Detailed Description

The inventors have realized that prior art systems show several limitations.

The present invention provides an energy efficiency methodology for optimizing, constantly monitoring and improving the performance of compressors utilized operationally to provide force-cooled air-conditioning systems. The invention incorporates a combination of electronic microprocessor control circuitry with software algorithms designed to deliver improved energy efficiency and control.

The invention may significantly reduce the current absorbed by a compressor motor. This will lead to: (i) Improved performance; (ii) Extended equipment lifetimes; and (iii) Reduced energy consumption.

Figure 1 is a schematic diagram, illustrating an example of a system 100 in accordance with an embodiment of the invention.

The force-cooled air-conditioning system 100 of figure 1 comprises afan 102.

Fan 102 is configured to move a stream of air 104 through a duct 106, towards an enclosure 110 to be cooled. Enclosure 110 may be a room within a building, for example.

A compressor 120 supplies cooling fluid to a coil 130 located in the duct 106, for cooling air passing through the duct 106. The stream of air 104 shown in figure 1 upstream of coil 130 will be cooled, and then exits duct 106 as cooled air stream 132. Compressor 120 is located in a housing 122, which is outside duct 106.

A temperature sensor 140 is located in duct 106, downstream of coil 130. A monitoring module 150 receives a signal from temperature sensor 140.

Monitoring module 150 is operable to monitor the temperature of stream of air 132 in duct 106. Monitoring module 150 is operable to detect thermodynamic saturation of the stream of air 132 leaving duct 106.

A second temperature sensor 162 may be located in enclosure 110. A timer 160 or clock may also be located in enclosure 110. Second temperature sensor 162 may include or be combined with a thermostat that can be set by an occupant of enclosure 110, or which may be set by a building control system not shown in figure 1. Second temperature sensor 162 may be a standard temperature sensor of a thermostatic control panel. Such a standard temperature sensor is typically mounted where occupants of enclosure 110 can change the temperature setting at will. However, with known systems, the temperature sensor in an air conditioned enclosure will provide a signal that causes continuous operation of the compressor motor, until the temperature within the enclosure has achieved a value set on the thermostat in the enclosure. Such a system is discussed further below, in relation to the recorded temperature profiles for a known system that are shown in the left graph on figure 6.

Monitoring module 150 is part of a control system 152 of figure 1. Control system 152 also comprises a logic module 154. Control system 152 further comprises a motor control subsystem 156 for controlling the operation of a motor 124 of the compressor 120. Motor 124 is illustrated within housing 122.

Control system 152 also comprises storage module 158. Storage module 158 stores one or more algorithms, which comprise predefined values for comparison against measured temperature values and other operating conditions of air-conditioning system 100. The algorithms allow the detection of thermodynamic saturation of stream of air 132 in duct 106. The algorithms and their predefined values are provided to, and used by, a logic module 154.

Motor control subsystem 156 controls the operation of motor 124 under control of logic module 154. Logic module 154 is configured to drive motor control subsystem 156, on the basis of one or more algorithms from storage modulels8,to: (i) deactivate motor 124, when monitoring module 150 detects thermodynamic saturation of the stream of air 132 leaving duct 106; (ii) maintain operation of fan 102, until a target temperature in the enclosure has been reached; and (iii) activate motor 124, when monitoring module 150 detects that the stream of air 132 leaving duct 106 is no longer thermodynamically saturated, and a time threshold has been exceeded since deactivation of motor 124.

As a result of (ii) above, fan 102 will remain operational throughout the whole cooling period, from when the system is switched on, for example by the time clocklprogrammer 160 discussed below. Fan 102 will only cease to be operational when either: a) Air conditioning system 100 is turned off; or b) The temperature in enclosure 110 has reached a target temperature. The device that determines this target temperature' may be the incumbent room thermostat, which may be integrated with second temperature sensor 162.

Motor control subsystem 156 is configured to regulate the voltage applied to motor 124, when compressor 120 is operating and a load on the compressor varies. This regulation is such that, in operation, the voltage applied to motor 124 is regulated to be the minimum voltage that allows enough current to flow to provide synchronous rotation of motor 124. The voltage regulation achieved with this approach minimizes power consumption by motor 124. This lower power consumption leads to less heat being generated in motor 124 itself, and less wear on motor 124. If the application of system 100 is one in which waste heat from motor 124 leaks into enclosure 110 to be cooled or the cooling fluid, there will therefore be less waste heat for motor 124 itself to remove from the enclosure.

Figure 2 illustrates the variation in the temperature I of the stream of air 132 exiting duct 106 that may be achieved in accordance with an embodiment of the invention. The temperature I is plotted against elapsed time t.

The curve 210 shown in figure 2 starts at a temperature Thigh. Temperature Thigh illustrates a situation where no cooling has been applied to the air in enclosure 110 for a long period of time.

When the system of figure 1 applies cooling to stream of air 104, the temperature of stream of air 132 drops towards a temperature Ttarget.

Temperature Ttjrget generally illustrates the temperature around which the decisions (U-OH) described above in connection with figure 1 are made. The time for curve 210 to reach temperature Ttarget from the initial temperature Thigh may be of the order of 30 minutes. This time depends on many variables, including the value of initial temperature Thigh, the size of compressor 120, the size of enclosure 110, and the heat sources operating within enclosure 110.

At time 212, the temperature I has reached a constant level. Essentially, curve 210 has flatlined'. This situation continues to time point 214. At timepoint 214, logic module 154 is configured to drive motor control subsystem 156 to deactivate motor 124. This is the action described as (i) above, in the discussion of figure 1. At point 214, monitoring module 150 has detected thermodynamic saturation of the stream of air 132 leaving duct 106.

The break in curve 210 from timepoint 214 to timepoint 218 indicates a minimum period 216 where motor 124 of compressor 120 is switched off.

Note however that fan 102 is still switched on during period 216. During period 216, the stream of air 132 will still be cooled by coil 130, as fan 102 moves air along duct 106. Thus the enclosure 110 will still be cooled, but without the expenditure of energy to drive motor 124.

Between timepoint 218 and timepoint 220, the temperature T will begin to rise.

However, there will be no significant, immediate change to the temperature of the air in duct 106. At some time between time point 218 and timepoint 220, logic module 154 may switch off fan 102. This will only happen if the temperature in enclosure 110 has reached the target temperature.

At time point 220, the signal from temperature sensor 140 leads monitoring module 150 to make the decision outlined as (Hi) in the discussion of figure 1.

At time point 220, logic module 154 drives motor control subsystem 156 to switch on motor 124. Monitoring module 150 has detected, at timepoint 220, that the stream of air 132 leaving duct 106 is no longer thermodynamically saturated, and a time threshold has also been exceeded since deactivation of motor 124. In the example shown in figure 2, the time threshold may have been be set at any period between timepoint 218 and timepoint 220.

After timepoint 220, the temperature T of stream of air 132 again begins to fall. At timepoint 222, the temperature T flatlines once more. At timepoint 224, logic module 154 is configured to drive motor control subsystem 156 to once again deactivate motor 124. This is a repeat of the action described as (i) above in the discussion of figure 1, and the discussion of timepoint 214 in figure 2. At time point 224, monitoring module 150 has again detected thermodynamic saturation of the stream of air 132 leaving duct 106.

The break in curve 210 from timepoint 224 to timepoint 228 indicates a second period 226 where motor 124 of compressor 120 is switched off, but fan 102 is still switched on. During period 226, the stream of air 132 will still be cooled by coil 130, as fan 102 moves air along duct 106. Thus the enclosure 110 will still be cooled, but without the significant expenditure of energy to drive motor 124.

After timepoint 228, as shown by curved portion 230, the temperature Twill begin to rise. After time point 228, similarly to the situation immediately after timepoint 218, there will be no significant, immediate change to the temperature of the air in duct 106. However, the temperature Twill usually rise gradually, in most applications of air conditioning system 100.

At time point 232, logic module 154 once again drives motor control subsystem 156 to switch on tan 102 and motor 124. Monitoring module 150 has detected, at timepoint 232, that the stream of air 132 leaving duct 106 is once again no longer thermodynamically saturated, and that the time threshold has also been exceeded since deactivation of motor 124 at timepoint 224. After timepoint 232, therefore, the temperature Tot stream of air 132 again begins to fall.

During periods 216 and 226, no current is supplied to motor 124. Current will be drawn by fan 102, but the magnitude of the fan current is much less than that needed to drive motor 124. During the time periods between timepoints 214 and 220, and between timepoints 224 and 232, fan 102 will draw current unless the target temperature in enclosure 110 has been attained.

Recalling the description of figure 1 once more, when current does flow in motor 124, the voltage regulation ensures that the voltage applied to motor 124 is the minimum voltage that allows enough current to flow to provide synchronous rotation of motor 124. Considering this regulation together with the time periods between timepoints 214 and 220, and between timepoints 224 and 232, the arrangement of figure 1 shows a synergistic combination of: (i) The lowest possible voltage during operation of motor 124. Note that, in the embodiment of figure 2, motor 124 will not run at all between timepoints 214 and 220, and between timepoints 224 and 232.

(ii) Operation of motor 124 only when necessary.

(iii) Operation of fan 102 alone, without motor 124, when a cooling effect from cooling coil 130 can still be achieved without further operation of motor 124 during time periods 216 and 226.

The advantages that may be delivered may include the minimization of heat generation in motor 124 itself, a reduction in wear on motor 124 and compressor 120, and a reduction in electricity consumption and noise for any given thermostat settings in enclosure 110. The invention provides a combination of the two energy saving features of a duct temperature sensing module 140, and dynamic motor control for current minimization via logic module 154, storage module 158 and motor control subsystem. These two features reduce the current consumption very significantly over known air conditioning systems.

Optimisation of the voltage supplied to motor 124 together with sensing of the temperature in duct 106 with single sensor 140 can work synergistically to very significantly enhance the energy saving delivered by the arrangement of the invention. The invention offers the possibility to combine these separate technologies into a single system, in which the synergistic energy saving methodologies are embedded in software algorithms within a single compact microprocessor. Integration into a single microprocessor based package further simplifies manufacturing and installation. Optimisation of the motor voltage control and the switching of motor 124 will work reliably together, when a single microprocessor provides the commands for both aspects of this energy saving.

The energy saving performance is enhanced further by using intelligence to constantly monitor the air-conditioning system 100, and modify both the compressor cycles and the power supplied to motor 124 in a much more dynamic way than has been possible with known systems. At least one known system comprised a simple logic device with just preset temperature values.

In contrast to that known system, the present invention is microprocessor driven, with intelligent software algorithms. Those algorithms may in addition be adaptive, as is explained in more detail below. Other known systems provided a fixed voltage chopping device, which provided a constant reduction in voltage fed to the compressor motor. In contrast, the present invention constantly monitors the load on motor 124. The invention may then, for example, adjust the voltage and thereby current drawn by the motor as often as every half cycle.

Figure 3 illustrates a flowchart of a method in accordance with the invention.

At step 310, motor 124 of compressor 120 is activated to cool the stream of air 104 in duct 106, and hence reduce the temperature in enclosure 110. This phase may correspond to the leftmost portion of curve 210 in figure 2, as the temperature falls from initial temperature Thigh to temperature target.

At step 320, while motor 124 is in operation, monitoring module 150 monitors the temperature of stream of air 132 in duct 106, by means of the signal from temperature sensor 140 in duct 106. This monitoring is to detect the attainment of thermodynamic saturation of stream of air 132 leaving duct 106.

At step 330, logic module 154 causes motor control subsystem 156 to deactivate motor 124 when thermodynamic saturation has been detected.

However, at this point, logic module 156 continues fan operation unless and until a target temperature has been attained in enclosure 110.

At step 340, logic module 156 causes motor control subsystem 156 to activate motor 124 to cool air in duct 106, when: (i) monitoring module 150 detects that stream of air 132 leaving duct 106 is no longer thermodynamically saturated; and also (ii)a time threshold has been exceeded since deactivation of the motor 124.

Once motor 124 has been re-activated at step 340, the method usually returns to step 320. However, step 350 indicates that various changes may be made to the algorithms employed by logic module 156. The air conditioning system 100 may operate in an evolving environment, such as when heat sources are added to, or removed from enclosure 110. In response, a different algorithm may then be selected, which then provides optimised motor and fan control under the new conditions. Additionally or instead, changes to the thermostat settings within enclosure 110 may lead to the selection of a different algorithm, which then provides optimised motor and tan control under the new thermostat settings. As another alternative, the performance of motor 124 or cooling coils 130 may vary, for example with ageing or the adherence of material to cooling coils 130 or the walls of duct 106, and a different algorithm may then be selected.

The term adjust' in step 350 may involve the selection of a different, predetermined algorithm from storage module 158. However, adjust' may also and/or instead involve altering parts of an existing algorithm. Such an approach effectively creates a new algorithm, such as by creating an evolution of the algorithm that was previously in use. The algorithms in use with the invention may therefore be considered to be intelligent adaptive software algorithms'. Newly created or altered algorithms can be stored back in storage module 158 of control system 152.

In summary, therefore, one embodiment of the invention facilitates monitoring the temperature of air stream 132 in duct 106, as it falls. Once the temperature has levelled out for a set period of time, the assumption can be made that thermodynamic saturation has been achieved, and compressor 120 can be switched off. Fan 102 continues to run as long as a target temperature in enclosure 110 has not yet been reached, and during this time may provide significant cooling. Compressor 120 remains switched off for a minimum set period of time, and then may start the cycle again. If there is no significant increase in the temperature of air in duct 106 after the end of the minimum set period of time, then compressor 120 remains switch off until the temperature of the stream of air 132 reaches a pre-set point. Only when the minimum set period of time has elapsed and the air temperature in the duct has risen significantly, will compressor 120 be re-started. Each time compressor 120 is re-energised, the control algorithms will look for the same flatlining of the temperature of stream of air 132, as a sign that thermodynamic saturation has been achieved.

Figure 4 shows an alternative control arrangement 400 for the air conditioning system 100. Control arrangement 400 includes a separate storage module 410 and a control system 450.

Storage module 410 stores multiple sets of predefined values, each as part of an algorithm that may be used to control air conditioning system 100. Each of the sets of predefined values stipulates the temperature thresholds and time thresholds for use in steps 320 and 340 of figure 3. Values appropriate to different algorithms are shown schematically as curves 412 and 414.

Control system 450 comprises a motor control subsystem 460 for controlling the operation of motor 124 of compressor 120. Motor 124 may be a hermetically sealed AC induction motor, with waste heat from the motor at least partially either entering enclosure 110, or leaking to the coolant fluid flowing to cooling coils 130.

Control system 450 also comprises logic module 470. Logic module 470 of the control system 450 is configured to drive the motor control subsystem 460 to activate or deactivate the motor 424 on the basis of the signal from temperature sensor 140, temperature signals from second temperature sensor 162, and time signals from logic module 470.

The particular algorithm 412 or set of predefined values is selected to ensure optimum switching of motor 124. In addition, logic module 470 ensures soft-start of each motor cycle. Motor control subsystem 460 provides only sufficient voltage to motor 124 to keep the coolant fluid moving in the cooling coils 130 of the air conditioning system 100, after an optimum suction gas pressure has been attained in the coolant loop.

Motor control subsystem 460 is configured to regulate the voltage applied to motor 124 when the compressor is operating and a load on compressor 120 varies. This regulation is such that, in operation, the voltage applied to motor 124 is regulated to be the minimum value that provides synchronous rotation of motor 124.

Metering subsystem 480 receives data from motor 124 and motor control subsystem 460. Comparison module 482 may receive data from metering subsystem 480. Metering subsystem 480 may carry out all or some of: (i) Capturing data, the data comprising a record of various temperature measurements, and times when compressor 120 is active; (ii) Exporting the data to a remote monitoring unit for verification of equipment use and/or energy use.

Metering subsystem 480 may develop a historical record of operating characteristics of motor 124. The historical record comprises a proportion of time for which motor 124 is switched on, and the signal indicative of temperature T of the stream of air 132 in duct 106.

Metering subsystem 480 may detect an abnormal function of motor 124, based on an increase in the proportion of time for which motor 124 is switched on, above an expected' proportion of time. The expected proportion of time is predicted from the historical record of the proportion of time for which motor 124 is switched on for various values of temperature sensor 140.

Metering subsystem 480 may be configured to capture data on voltage, current, power factor and power quality for the motor operation. Comparison module 482 provides summary information based on at least one of voltage, current, power factor and power quality for the operation of motor 124.

Comparison module 482 derives the number of motor cycles, motor run time, and power consumption of motor 124.

Metering subsystem 480 and comparison module 482 together may comprise part of a motor monitoring subsystem. However, the separate functions of metering subsystem 480 and comparison module 482 may be combined into a single subsystem, and they are illustrated as separate elements in figure 4 for ease of explanation.

A communication module 484 may send reports via the internet to a remote monitoring station for display, any or all of: (i) The data from metering subsystem 480; (ii) At least one of the summary information, the voltage, current, power factor or power quality for the motor operation.

The remote monitoring station may then display instantaneous and historical values for the reported parameters.

Figure 5 is a circuit diagram of components for implementing an air-conditioning system 500 in accordance with an embodiment of the invention.

Figure 5 illustrates a complete air-conditioning system 500. Air-conditioning system 500 may use only a single air temperature sensor 540 for cooled air that has passed through the cooling coils, as in the arrangement of figure 1 for stream of air 132. However, air-conditioning system 500 may use up to four temperature sensors. These are described below with reference to figure 5.

The four temperature sensors each monitor one of four temperature variables Ti -T4. Measurements of all or some of temperatures T2-T4 may be used together with the air temperature sensor 540 that provides a signal indicating the temperature Ti for the cooled air 132 that has passed through the cooling coils.

First temperature sensor 540 provides a first signal as a measurement of first temperature Ti of air downstream of fan 502 and cooling coils 530. Duct 106 shown in figure 1 has been omitted from figure 5, to simplify and enhance the clarity of figures.

Second temperature sensor 542 provides a second signal, which is indicative of the temperature T2 of air drawn from the air-conditioned enclosure towards cooling coils 530. Second temperature sensor 542 acts as an air intake sensor.

Compressor motor 524 is provided with a motor temperature sensor 522.

Motor temperature sensor 522 provides a third signal, which is indicative of the motor temperature T3. Temperature T3 may be a temperature of the windings of motor 524.

An ambient temperature sensor 562 provides a fourth signal, which is indicative of an ambient temperature T4 within the air-conditioned enclosure.

The signals indicative of each of T1-T4 are supplied to temperature control logic 530. Control strategy logic 532 may store one or more sets of stored values, as explained in relation to storage module 158 of figure 1. Metering subsystem 554 provides additional inputs to control strategy logic 532. Control strategy logic 532 provides overall motor control, via motor control logic 534 and relay 550.

Motor control logic 534 may also receive an input from energy sensing circuitry 536. Energy sensing circuitry 536 may be connected to a motor driving coil, which is not shown in figure 5 but which implements intelligent motor energy control (iMEC') in motor 524. By means of energy sensing circuitry 536, motor control logic 534 can ensure that the voltage applied to motor 524 is regulated to be the minimum voltage that allows enough current to flow to provide synchronous rotation of motor 524, under varying load conditions on the compressor 220.

A bypass relay 550 may be connected in parallel to energy sensing circuitry 536. Bypass relay 550, if used, allows motor control logic 534 to directly switch motor 524. Fan control logic 552 is also fed from control strategy logic 532. Fan control logic 552 controls fan 502 via relay 556.

In the embodiment of figure 5, therefore, the control system of the invention may therefore comprise the temperature control logic 530, control strategy logic 532, motor control logic 534, fan control logic 552, relay 550, relay 556 and energy sensing circuitry 536. The various additional components that make up the control system of figure 5 may enhance the operation of the control system relative to that of control system 156 of figure 1.

In the arrangement according to figure 5, air-conditioning system 500 exports data to Enigin's Eniscope' system. Enigin's Eniscope' connection 580 leads to an Eniscope hub, which exports data to the internet for remote surveillance.

Thus metering subsystem 554 and control strategy logic 532 contain within them on-board metering elements with the ability to connect directly to an Eniscope Real-time Energy Management System via connection 580 and the hub. See also communication module 484 in figure 4. This configuration allows information relating to the operation of the compressor 220 and other components to be exported to the world wide web. An air-conditioning system 500 anywhere in the world can thus be monitored and analysed from any location where Enigin's Eniscope' system is installed.

Figure 6 illustrates recorded variations in duct air temperature achieved by an air-conditioning system operating in accordance with an embodiment of the invention. In figure 6, the enclosure 110 is a room' in a building. The upper curve on each of the left and right graphs in figure 6 shows the development of the room temperature. The lower curve on each of the left and right graphs in figure 6 shows the development of the temperature I of stream of air 132 in duct 106.

In the embodiment of the invention that provided the lower curve of figure 6, motor 124 is deactivated before the temperature from temperature sensor 140 has flatlined. Instead, the algorithm selected from storage module 158 deactivates motor 124 whilst temperature T is still falling. Seethe right half of figure 6.

In the lower curve of the right graph of figure 6, motor 124 is only active during the three time periods marked as Compressor On'. During these three periods, motor control subsystem 156 regulates the voltage applied to motor 124, when a load on compressor 120 varies. This regulation ensures that the minimum voltage, which allows enough current to flow to provide synchronous rotation of motor 124, is supplied to motor 124. The voltage regulation achieved with this approach reduces power consumption by motor 124, compared to the known system illustrated in the lower curve of the left graph of figure 6.

Following each period of operation of motor 124, latent cooling is achieved by continuing to operate fan 102 whilst motor 124 of compressor 120 is deactivated. The periods of latent cooling are shown with diagonal stripes and marked Compressor off' in the right graph of figure 6. Following each of the three periods marked as Compressor off' in the right graph of figure 6 is a period during which motor 124 is switched off, and fan 102 may or may not be switched off.

The known system in the left graph of figure 6 shows continuous operation of the motor, as indicated by the diagonal stripes across the entire width of the left graph of figure 6.

A review of figures 1-6 allows an overview of the force-cooled air-conditioning system of the invention. The force-cooled air-conditioning system comprises a compressor for supplying cooling fluid to coils, which cools the internal air fed to an enclosure of the air-conditioning system, such as a room or warehouse.

A module for measuring the internal duct temperature is located in the enclosure, the module being configured to provide a signal indicative of the air temperature moving through the enclosure.

A logic module of the control system is configured to drive the motor control subsystem to activate or deactivate the motor on the basis of the signal indicative of the cooling coils having reached thermodynamic saturation over a minimum measured time period.

The motor control subsystem is configured to regulate the voltage applied to the motor when the compressor is operating and a load on the compressor varies, whereby in operation the voltage applied to the motor is regulated to be the minimum value that provides synchronous rotation of the motor.

The voltage applied to the compressor just matches an instantaneous load on the compressor. This operating condition improves the power factor and efficiency of the motor, during its lightly loaded phase of each duty cycle.

The air-conditioning system may be applied in a wide variety of settings.

These may include commercial air-conditioning systems and compressor driven refrigeration cabinets, such as those found in supermarkets, convenience stores, freezer centres, public houses, restaurants, hotels and garage forecourts. High specification domestic air-conditioning systems may also benefit from the invention.

Various aspects of the air-conditioning system solves the specific disadvantages that the inventors have identified with prior art systems by dynamically and intelligently learning from and reacting to demand changes.

The reactions may include both varying air temperature, as detected by a temperature sensor downstream of the cooling coils, and varying duty cycle on the compressor motor. A series of software options can be formulated from measuring and recording the thermal characteristics of differing systems and the internal building temperatures in real-time.

None of the known systems enables direct switching of the compressor combined with optimizing of the current drawn by the compressor. So, in prior art systems, the compressor is either switched on or off by the incumbent analogue thermostat, with no intelligent digital control being provided.

In the field of motor control technology, it is known that a reduction of the terminal voltage by a fixed amount on an AC induction motor that is less than 70% loaded will typically achieve a beneficial reduction in the amount of current drawn. Also, it is known that if the current being drawn can be reduced without slowing the motor down, this will ensure that a greater amount of the current being absorbed will be converted to a job of work' rather than being dissipated as heat'. The problem with existing technologies when applied to air-conditioning systems is that a hermetically sealed air-conditioning system compressor is housed within the refrigerant coolant. The compressor has unique operational characteristics during its duty cycle, which prior art systems cannot detect or respond to. The inventors have realized that the compressor motor should only be optimized at specific stages within the cooling cycle. The optimization within the invention is therefore dynamic, rather than employing an arbitrary time delay or fixed reduction in current,

voltage or speed as in prior art systems.

Both the electricity supply on the National Grid and the load on the motor may alter continually, based on a large number of variables. So an arbitrary fixed reduction in the current supplied does not deliver optimum benefits.

Furthermore, there is also great cost in providing prior art motor control systems, which involve high production and installation costs in relation to the energy savings that they can deliver.

The air-conditioning system of the invention provides a significantly better level of control. The motor control achieved takes into account the varying duty cycle of the compressor motor. This is achieved by constantly calculating the demand on the system and delivering the appropriate amount of current.

The current is that which maintains the correct amount of excitation between the motor stator and rotor, so as to maintain full motor speed throughout the duty cycle. The voltage supplied to the motor may be varied as often as each half cycle. Another significant benefit is that, by eliminating excess current that would otherwise convert to heat' within the hermetically sealed compressor casing, further isentropic benefits are delivered.

The invention therefore addresses two distinct problems with just one turnkey solution. The advantages achieved may be some or all of: (i) The compressor cycles less often, to maintain any given target temperature; and (ii) The compressor consumes the minimum necessary current at each stage of every cooling cycle, unlike known systems.

In summary, the invention comprises of a single air-conditioning system that may be web-enabled' via Enigin's Eniscope'. It is a unique total solution for air-conditioning system equipment. The invention may provides: (i) An intelligent dynamic motor optimizer, with specific design features to maximize efficiency on hermetically sealed compressors; (ii) An accurate internal duct temperature digital thermostat; and (iii) A single set of circuitry to implement the above functionality.

The algorithms for acting on the temperature reference points (intelligence) may be embedded in software within the invention, or provided in an application specific integrated circuit (ASIC).

Because the compressor is controlled, in effect, by an intelligent electronic switch', the compressor motor can be started and stopped via an on-board triac. This on/off switching is based on monitored temperature calculated by the microprocessor and sensed by the temperature sensor, which may be a thermistor. The motor control logic will also automatically soft-start the compressor, thereby reducing peak demand. In addition, the approach results in cooler and quieter running of the motor, with a much improved power factor. This reduces any reactive power charges. By reducing waste heat, the invention also potentially reduces the external ambient temperature around the enclosure, which further lightens the load on the compressor (isentropic effect).

As explained above with reference to figures 1-6, the air-conditioning system

is notable for:

(i) Digital software programed to calculate the point at which thermodynamic saturation is achieved; (ii) Control hardware circuitry and unique software algorithms designed to optimize the efficiency of a hermetically sealed compressor motor, during each phase of the cooling cycle; and (Ui) The combined synergistic benefits of both these energy saving technologies in one simple turnkey solution providing a unique synergistic combination of advantages.

The invention may be provided as a bespoke air-conditioning system.

However, the invention may be used as a retro fit' on existing equipment. The invention could be incorporated, by an original equipment manufacturer, as an enhancement to control circuitry on generic equipment, e.g. motor compressors.

Claims

Claims 1. A force-cooled air-conditioning system, comprising: a fan configured to move air through a duct, towards an enclosure to be cooled; a compressor for supplying cooling fluid to a coil located in the duct, for cooling air passing through the duct; a temperature sensor located in the duct, downstream of the coil; a monitoring module for monitoring the temperature of air in the duct, the monitoring module configured to receive a signal from the temperature sensor, the monitoring module operable to detect thermodynamic saturation of the air leaving the duct; a control system, comprising a logic module and a motor control subsystem for controlling the operation of a motor of the compressor, wherein: a) the logic module is configured to drive the motor control subsystem to: (i) deactivate the motor, when the monitoring module detects thermodynamic saturation of the air leaving the duct; (H) maintain operation of the fan, until a target temperature in the enclosure has been reached; (Hi) activate the motor, when the monitoring module detects that the air leaving the duct is no longer thermodynamically saturated and a time threshold has been exceeded since deactivation of the motor; b) the motor control subsystem is configured to regulate the voltage applied to the motor when the compressor is operating and a load on the compressor varies, whereby in operation the voltage applied to the motor is regulated to be the minimum voltage that allows enough current to flow to provide synchronous rotation of the motor.
2. The air-conditioning system of claim 1, wherein: the motor control subsystem is configured to regulate the voltage applied to the motor to allow just sufficient current to flow in windings of the motor to ensure adequate torque for synchronous rotation of the motor, thereby matching the instantaneous load on the compressor.
3. The air-conditioning system of claim 1 or claim 2, wherein the logic module is configured to ensure soft-start of a motor cycle, and the motor control subsystem is configured to provide only sufficient voltage and current to the motor to keep a coolant fluid moving in a coolant loop of the air-conditioning system, after an optimum suction gas pressure has been attained in the coolant loop.
4. The air-conditioning system of any previous claim, wherein the motor is a hermetically sealed AC induction motor, with waste heat from the motor at least partially entering the enclosure and/or leaking to the coolant fluid.
5. The air-conditioning system of any previous claim, wherein the monitoring module is part of the control system.
6. The air-conditioning system of any previous claim, wherein the temperature sensor comprises a thermistor-type digital sensor.
7. The air-conditioning system of any previous claim, wherein: (i) the monitoring module, the logic module and the motor control subsystem are combined into functional elements of a single microprocessor; and (H) wherein the motor control subsystem is operable to adjust the voltage at least every half second.
8. The air-conditioning system of any previous claim, further comprising: (i) a second temperature sensor configured to measure the temperature of air entering the duct from the enclosure; (H) a third temperature sensor configured to measure the temperature of the motor; and (Hi) a fourth temperature sensor configured to measure the temperature of ambient air at a location within the enclosure.
9. A method of force-cooled air-conditioning of an enclosure, comprising: moving air through a duct, towards an enclosure to be cooled; supplying cooling fluid to a coil located in the duct by means of a compressor, for cooling air passing through the duct; measuring the temperature of the air in the duct, downstream of the coil, by a temperature sensor; monitoring the temperature of the air in the duct, by a monitoring module receiving a signal from the temperature sensor, the module thereby detecting thermodynamic saturation of the air leaving the duct; a) a logic module of a control system driving a motor control subsystem of the control system to: (i) deactivate a motor of the compressor, when the monitoring module detects thermodynamic saturation of the air leaving the duct; (H) maintain operation of the fan, until a target temperature in the enclosure has been reached; (Hi) activate the motor, when the monitoring module detects that the air leaving the duct is no longer thermodynamically saturated and a time threshold has been exceeded since deactivation of the motor; b) the motor control subsystem regulating the voltage applied to the motor when the compressor is operating and a load on the compressor varies, whereby in operation the voltage applied to the motor is regulated to be the minimum voltage that allows enough current to flow to provide synchronous rotation of the motor.
10. The method of claim 9, wherein: the motor control subsystem regulates the voltage applied to the motor to allow just sufficient current to flow in windings of the motor to ensure adequate torque for synchronous rotation of the motor, thereby matching the instantaneous load on the compressor.
11. The method of claim 9 or claim 10, wherein: the logic module ensures soft-start of a motor cycle; and after an optimum suction gas pressure has been attained in the coolant loop, the motor control subsystem provides only sufficient voltage and current to the motor to keep a coolant fluid moving in a coolant loop of the air-conditioning system.
12. The method of any of claims 9-11, wherein waste heat from the motor at least partially enters the enclosure and/or leaks to the coolant fluid, the motor being a hermetically sealed AC induction motor.
13. The method of any of claims 9-12, wherein the logic module of the control system drives the motor control subsystem to adjust the voltage supplied to the motor, and thereby the current drawn by the motor, every half cycle.
14. The method of any of claims 9-13, wherein the logic module employs intelligent adaptive software algorithms to optimize: (i) the time threshold that must be exceeded before re-activation of the motor; and/or (H) the temperature at which thermodynamic saturation of the stream of air leaving the duct is ascertained.
15. A force-cooled air-conditioning system in accordance with, or as described with reference to, any of figures

1-6.