System and method for improving efficiency of a refrigerant based system

The present invention is designed to reduce running costs in refrigerant based air-conditioning, refrigeration and heating systems by using a combination of thermodynamic and hydraulic control to manage the on and off states of the compressor, which is the main energy consuming component. Thermodynamic or temperature control is used to manage comfort levels within the room or space being cooled. Hydraulic control is used to determine when the compressor has completed its useful work in delivering a supply of high-pressure liquid refrigerant. Once temperature and hydraulic conditions are satisfied the compressor can be turned off; thereby delivering a significant reduction in running costs.

FIELD OF INVENTION

This invention relates to a refrigerant based system for controlling temperature of a medium in an enclosed space and a method for improving the efficiency of the refrigerant based system; in particular, this invention relates to refrigerant based air-conditioning, refrigeration and heating systems.

BACKGROUND OF INVENTION

A typical refrigerant based air-conditioning, refrigeration and heating system comprises a compressor and an associated condenser (or heat exchanger), which are used to convert low-pressure refrigerant vapor into high-pressure liquid refrigerant for cooling purposes. In this compression of vapor, a very large amount of heat is generated and this heat can be either dissipated externally to the space that will be cooled or used for heating in a reverse cycle system (also called a heat pump system). The high-pressure liquid refrigerant is then transported to an evaporator (or heat exchanger) and is allowed to decompress there back to a vapor. In this decompression phase change process, the evaporator/second heat exchanger temperature reduces significantly and the reduction in temperature is limited by a significant amount of heat which is absorbed from the air passing through the evaporator/second heat exchanger. The heat removed from the air passing through the evaporator/second heat exchanger produces a supply of very cold air into the room or area being cooled. A blower fan is used to drive air though the evaporator. The supply of low-pressure refrigerant is then returned to the compressor.

Air-conditioning, refrigeration and heating systems employing refrigerants can account for up to 60% of the energy demand in office and domestic/residential installations. However, despite recent technology improvements, refrigerant based systems have yet to benefit from a significant reduction in running costs and as a result this sector remains inefficient compared with other energy consuming areas. As an example, lighting typically accounts for only 10-20% of the total energy demand but recent energy reduction advances have reduced running costs by 80% or more compared with earlier designs.

SUMMARY OF INVENTION

In the light of the foregoing background, it is an object of the present invention to provide an improved system and/or method to reduce the running costs and enhance the efficiency of a refrigerant based system in controlling the temperature of a medium in an enclosed space.

Accordingly, the present invention, in one aspect, is a refrigerant based system for regulating temperature of a medium in an enclosed space comprising a heat exchanger, a heat exchanger temperature sensor adapted for measuring the temperature of the heat exchanger, at least one compressor, a microprocessor for controlling the compressor, a medium temperature sensor adapted for measuring the temperature of the medium of the enclosed space, and a computer-readable storage medium encoded with computer-readable instruction for causing the microprocessor to execute the following steps:

(i) a medium temperature determining step for checking if the temperature of the medium has reached a first predetermined value;

(ii) a time determining step for checking if the compressor has operated for a predetermined period of operation time;

(iii) a minimum heat exchanger temperature determining step for checking if the temperature of heat exchanger has reached a minimum heat exchanger temperature;

(iv) a heat exchanger temperature determining step for checking if the temperature of the heat exchanger has reached a value below a compressor control temperature; and

(v) a controlling step for controlling the compressor.

The compressor will be turned off in the controlling step if the following conditions are satisfied: (1) the temperature of the medium has reached the first predetermined value; (2) the temperature of the heat exchanger has reached a value below the compressor control temperature; (3) the compressor has operated for the predetermined period of operation time and; (4) the minimum heat exchanger temperature has been found.

In one exemplary embodiment, the predetermined period of operation time in the time determining step is at least 3 minutes; the first predetermined value is one degree Celsius below a setpoint temperature set by a user; and the compressor control temperature is two degrees Celsius below the setpoint temperature set by the user.

Another aspect of the present invention is a computer-readable storage medium, for use in a refrigerant based system for regulating the temperature of a medium of an enclosed space, encoded with computer-readable instruction for causing a microprocessor to execute the following steps:

(i) a medium temperature determining step for checking if the temperature of the medium has reached a first predetermined value;

(ii) a time determining step for checking if a compressor has operated for a predetermined period of operation time;

(iii) a minimum heat exchanger temperature determining step for checking if the temperature of a heat exchanger has reached a minimum heat exchanger temperature;

(iv) a heat exchanger temperature determining step for checking if the temperature of the heat exchanger has reached a value below a compressor control temperature; and

(v) a controlling step for controlling the compressor.

The compressor will be turned off in the controlling step if the following conditions are satisfied: (1) the temperature of the medium has reached the first predetermined value; (2) the temperature of the heat exchanger has reached a value below the compressor control temperature; (3) the compressor has operated for the predetermined period of operation time and; (4) the minimum heat exchanger temperature has been found.

In one exemplary embodiment, the predetermined period of operation time in the time determining step is at least 3 minutes; the first predetermined value is one degree Celsius below a setpoint temperature set by a user; and the compressor control temperature is two degrees Celsius below the setpoint temperature set by the user.

In yet another aspect of the present invention is an energy managing device for use in a system regulating the temperature of a medium of an enclosed space comprising a microprocessor for controlling a compressor and a computer-readable storage medium as mentioned above.

In another aspect of the present invention, a method for regulating the temperature of a medium of an enclosed space in a refrigerant based system comprising the following steps:

(a) providing within the system at least one compressor, a heat exchanger, a heat exchanger temperature sensor adapted for measuring the temperature of the heat exchanger, and a medium temperature sensor adapted for measuring the temperature of the medium of the enclosed space;

(b) a medium temperature determining step for checking if the temperature of the medium has reached a first predetermined value;

(c) a time determining step for checking if the compressor has operated for a predetermined period of operation time;

(d) a minimum heat exchanger temperature determining step for checking if the temperature of heat exchanger has reached a minimum heat exchanger temperature;

(e) a heat exchanger temperature checking step for checking if the temperature of the heat exchanger has reached a value below a compressor control temperature; and

(f) a controlling step for controlling said compressor.

The compressor will be turned off in the controlling step if the following conditions are satisfied: (1) the temperature of the medium has reached the first predetermined value; (2) the temperature of the heat exchanger has reached a value below the compressor control temperature; (3) the compressor has operated for the predetermined period of operation time and; (4) the minimum heat exchanger temperature has been found.

In one specific implementation, the predetermined period of operation time in the time determining step is at least 3 minutes; the first predetermined value is one degree Celsius below a setpoint temperature set by a user; and the compressor control temperature is two degrees Celsius below the setpoint temperature set by the user.

In another aspect of the present invention, there is provided a chiller comprising a heat exchanger, at least one compressor, a heat exchanger temperature sensor for measuring the temperature of the heat exchanger, a microprocessor for controlling the compressor, a computer-readable storage medium encoded with computer-readable instructions for causing the microprocessor to execute the following steps:

(i) a delaying step of waiting for three minutes on first powering up the chiller before switching on the compressor;

(ii) a monitoring step of measuring the temperature of the heat exchanger in order to find a minimum heat exchanger temperature;

(iii) a controlling step of turning off the compressor if the minimum heat exchanger temperature has been detected in the monitoring step;

(iv) a restarting step of measuring the temperature of the heat exchanger and restarting the compressor if the heat exchanger temperature has reached a predetermined value.

There are many advantages to the present invention. One of the advantages is that the running costs can be reduced and the efficiency in controlling the temperature of a medium of an enclosed space can be enhanced upon implementation of the present invention into a conventional refrigerant based air-conditioning, refrigeration and heating system. Also the present invention can help in protecting the environment by reducing the production of greenhouse gas with the use of less energy/electricity. Furthermore, the present invention can also reduce the heat emitted by a conventional air-conditioner to the ambient environment, thereby cooling off the ambient environment, particularly that in a crowded city.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein and in the claims, “comprising” means including the following elements but not excluding others.

Two embodiments of the invention are disclosed, mainly the first embodiment indicated by the numeral36shown inFIG. 1and the numeral64shown inFIG. 2, and the second embodiment designated by numeral136shown inFIG. 3and the numeral164shown inFIG. 4.

First Embodiment

Referring first toFIG. 1, the first embodiment of the present invention is a refrigerant based system36for controlling temperature of a medium (i.e. gas or liquid) in an enclosed space. The refrigerant based system36comprises an interior unit40and an exterior unit38. The interior unit40and the exterior unit38are connected by a pair of circulation pipes42. The interior unit40further comprises a heat exchanger30, a heat exchanger temperature sensor34, a medium temperature sensor32, an evaporator blower22, a cold medium outlet44and a space medium inlet46. The heat exchanger temperature sensor34is located in proximity to the heat exchanger30and configured to measure the temperature of the heat exchanger30. The medium temperature sensor32is located in proximity to the space medium inlet46and configured to measure the temperature of the medium in the enclosed space. The evaporator blower22drives the space medium from the enclosed space to the interior unit40through the space medium inlet46and the heat exchanger30, and then blows the cooled space medium through the cold medium outlet44back to the enclosed space.

The exterior unit38comprises an exterior blower26, an expansion valve28, a condenser24, and a compressor20. The pair of circulation pipes42is configured to transfer refrigerant between the condenser24in the exterior unit38and the heat exchanger30in the interior unit40. The exterior blower26is located in proximity to the condenser24and configured to remove the heat generated at the condenser24. The compressor20is located upstream of the condenser24, but downstream of the heat exchanger30. Conversely, the expansion valve28is located downstream of the condenser24, but upstream of the heat exchanger30. In a specific embodiment, the compressor20used in the present invention is an ON/OFF compressor20in which the compressor20can only operate at a full-speed mode or a complete-stop mode. A control48, connecting the compressor20, the medium temperature sensor32and the heat exchanger temperature sensor34, is configured to control the compressor20based on the inputs from the medium temperature sensor32and the heat exchanger temperature sensor34. The control48comprises a microprocessor52and a computer-readable storage medium50encoded with computer-readable instruction for causing the microprocessor52to execute the following steps:

(1) A medium temperature determining step for checking if the temperature of the medium has reached a first predetermined value. In one embodiment, the temperature of the medium is measured by the medium temperature sensor32and the detected medium temperature is sent to the microprocessor52for evaluating whether the first predetermined value has been reached. In another embodiment, the first predetermined value is at least one degree Celsius below a setpoint temperature; in one embodiment, the setpoint temperature is set by a user.

(2) A time determining step for checking if the compressor20has operated for a predetermined period of operation time. In one embodiment, the predetermined period of operation time in the time determining step is at least 3 mins.

(3) A minimum heat exchanger temperature determining step for checking if the heat exchanger30has reached a minimum heat exchanger temperature. In one embodiment, the temperature of the heat exchanger30is measured by the heat exchanger sensor34and the detected heat exchanger temperature is sent to the microprocessor52for determination of the minimum heat exchanger temperature. In another embodiment, the minimum heat exchanger temperature is determined by continuously comparing a newly measured heat exchanger temperature with a previously measured heat exchanger temperature. If the newly measured heat exchanger temperature is higher or equal to the previously measured heat exchanger temperature, the minimum heat exchanger temperature is reached.

(4) A heat exchanger temperature determining step for checking if the temperature of the heat exchanger30has reached a value below a compressor control temperature. In one embodiment, the temperature of the heat exchanger30is measured by the heat exchange sensor34and the detected heat exchanger temperature is sent to the microprocessor52for evaluating whether the compressor control temperature has been reached. In another embodiment, the compressor control temperature is two degrees Celsius below a setpoint temperature; in one specific embodiment, the setpoint temperature is set by a user; in one specific embodiment, the setpoint temperature is set by a user.

(5) A controlling step for controlling the compressor20. In one embodiment, the compressor20will be turned off in the controlling step if the following conditions have been satisfied: (1) the temperatures of the medium has reached the first predetermined value; (2) the temperature of the heat exchanger has reached a value below the compressor control temperature; (3) the compressor has operated for the predetermined period of operation time and; (4) the minimum heat exchanger temperature has been found.

In one embodiment, the steps listed above are executed in the aforesaid sequence.

In another embodiment, the computer-readable instruction50causes the microprocessor to further execute the following steps:

(i) An adjusting step for deciding a stable setpoint temperature if a setpoint temperature set by the user is lower than a second predetermined value. In one specific embodiment, the stable set point temperature is 23° C. whereas the second predetermined value is 18° C.;

(ii) A notifying step for issuing a notification for requiring service if the stable setpoint temperature in the adjusting step is above a third predetermined value. In one specific embodiment, the third predetermined value is 23° C.;

(iii) An alerting step of issuing a servicing alert if the minimum heat exchanger temperature is above a fourth predetermined value. In one specific embodiment, the fourth predetermined value is 10° C.; and

(iv) A restarting step of restarting the compressor20if the temperature of the heat exchanger30has reached a value above the compressor control temperature. In one specific embodiment, the compressor control temperature is two degrees Celsius below a setpoint temperature set by a user.

In one embodiment, the restarting step is performed after execution of the controlling step. In another embodiment, the temperatures in the above steps (i.e. the temperature of the medium, the temperature of the heat exchanger30) are measured once every predetermined interval. In one embodiment, the predetermined interval is 5 seconds. In another embodiment, the temperatures are measured at least every 5 seconds.

In yet another embodiment, the control48acts as an energy managing device for use in the refrigerant based system36comprising the aforementioned components mentioned and performing the aforementioned steps.

Now turning to the operation of the refrigerant based system36described above. The instant embodiment of invention makes use of two temperature sensors (32and34) to deliver significantly reduced running costs in which the heat exchanger temperature sensor34is used for hydraulic control in detecting when the compressor20has filled available space with high pressure liquid refrigerant and hence has completed its useful work.FIG. 2shows a flowchart describing how the control48works according to one embodiment of the present invention.

Referring toFIG. 2, at step66, the refrigerant based system36is switched on with the compressor20being turned off before the start of the control process. Next, at step68, the compressor20is turned on and starts running with the medium temperature being measured at a predetermined frequency. In one embodiment, the medium temperature measurement is made at least every five seconds. The control48will first seek to establish the first predetermined value around a setpoint temperature desirable by a user. In one embodiment, the first predetermined value is 1 degree Celsius below the setpoint temperature to minimize any subsequent temperature variations once the compressor20is switched OFF later on. If the setpoint temperature has been set lower than a second predetermined value, then the control48will determine a stable setpoint temperature for use in on-going control. In one embodiment, the stable setpoint temperature is 23° C. whereas the second predetermined value is 18° C. If this stable setpoint temperature is above a third predetermined value, then the control48will issue a notification that the refrigerant based system36requires servicing. In one embodiment, the third predetermined value is 23° C.

Having satisfied the medium temperature requirements described above, at step70, the control48will next verify whether the compressor20has completed its useful work in filling the available space with high pressure liquid refrigerant. This hydraulic control assessment is carried out by seeking a minimum heat exchanger temperature as extensive modeling has indicated that this is a good measure to use with regard to hydraulic performance. Once the control48has verified that (1) the compressor20has been running for a predetermined period of time, (2) that the medium temperature has reached the first predetermined value and (3) that the minimum heat exchanger temperature has indeed been reached, then the control48will proceed to step72. In one embodiment, the predetermined period of time in step70is at least 3 minutes. Ensuring the compressor20has been running for a minimum of 3 minutes by the control48can prevent short cycling of the compressor20. In another embodiment, the first predetermined value in step70is 1 degree Celsius below the setpoint temperature. In yet another embodiment, in order to determine whether the minimum heat exchanger temperature has indeed been reached, the control48continuously compares a newly measured heat exchanger temperature and a previously measured heat exchanger temperature. If the newly measured heat exchanger temperature is higher or equal to the previously measured heat exchanger temperature, the minimum heat exchanger temperature has then been reached. In another embodiment, the present invention takes one temperature measurement every five seconds on the medium temperature and the heat exchanger temperature.

At step72, the control48will de-energize a relay to stop the compressor20if the heat exchanger temperature has reached a value below a compressor control temperature. In one embodiment, the compressor control temperature in step72is 2 degrees Celsius below the setpoint temperature. If the control48detects that the minimum heat exchanger temperature is above a fourth predetermined value, then a notification will be issued indicating that the refrigerant based system36requires servicing. On stopping the compressor20, the evaporator blower22will continue to run and the heat exchanger temperature will remain at the minimum heat exchanger temperature for a short time, unit all high pressure refrigerant liquid has been used up. In one embodiment, the fourth predetermined value is 10° C. When all of the high pressure liquid refrigerant has been exhausted the heat exchanger temperature will rise, initially quickly and then at a reducing rate proportional to the difference between the medium temperature and the heat exchanger temperature. While the heat exchanger temperature is increasing the medium is still being cooled; albeit at a reducing rate. Once the heat exchanger temperature has reached the compressor control temperature, the control48will restart the compressor20and the control cycle will repeat itself. In one embodiment, the compressor control temperature is two degrees below the setpoint temperature. In another embodiment, the present invention takes one temperature measurement every five seconds on the medium temperature and the heat exchanger temperature.

The present invention is designed to reduce running costs in refrigerant based air-conditioning, refrigeration and heating systems by using a combination of thermodynamic and hydraulic control to manage the on and off states of the compressor20which is the main energy consuming component. Thermodynamic or temperature control is used to manage comfort levels within medium being cooled. Hydraulic control is used to determine when the compressor20has completed its useful work in delivering a supply of high-pressure liquid refrigerant. As discussed above, once temperature and hydraulic conditions are satisfied the compressor20can be turned off; thereby delivering a significant reduction in running costs.

The refrigerant based system36can be a commercial and residential air conditioning system employing one or more compressors and refrigerants where air is the delivered cooled medium; or a commercial and residential air conditioning unit with reverse cycle (heat pump) heating functions employing one or more compressors and refrigerants where air is the delivered cooled medium; or a commercial refrigeration unit employing one or more compressors and refrigerants where air is the delivered cooled medium; or a centralized chiller unit employing one or more compressors and refrigerants where water is the delivered cooled medium.

Second Embodiment

Now referring toFIG. 3, the second embodiment of the present invention is specifically designed and used for chillers. The chiller as illustrated in the embodiment shown inFIG. 3comprises an interior unit140and an exterior unit138. The interior unit140and the exterior unit138are connected by a pair of circulation pipes142. The interior unit140further comprises a heat exchanger130, a heat exchanger temperature sensor134, an evaporator blower122, a cold medium outlet144and a space medium inlet146. The heat exchanger temperature sensor134is located in proximity to the heat exchanger130and configured to measure the temperature of the heat exchanger130. The evaporator blower122drives the space medium from the enclosed space to the interior unit40through the space medium inlet146and the heat exchanger130, and then blows the cooled space medium through the cold medium outlet144back to the enclosed space.

The exterior unit138comprises an exterior blower126, an expansion valve128, a condenser124, and a compressor120. The pair of circulation pipes142is configured to transfer refrigerant between the condenser124in the exterior unit138and the heat exchanger130in the interior unit140. The exterior blower126is located in proximity to the condenser124and configured to remove the heat at the condenser124. The compressor120is located upstream of the condenser124, but downstream of the heat exchanger130. Conversely, and the expansion valve128is located downstream of the condenser124, but upstream of the heat exchanger130. In a specific embodiment, the compressor120used in the present invention is an ON/OFF compressor in which the compressor120can only operate at a full-speed mode or complete-stop mode. A control148, connecting to the compressor120and the heat exchanger temperature sensor134, is configured to control the compressor120based on the input from the heat exchanger temperature sensor134. The control148comprises a microprocessor152and a computer-readable storage medium150encoded with computer-readable instructions for causing said microprocessor152to execute the following steps:

(1) A delaying step of waiting for a first delaying time period on first powering up the chiller before switching on the compressor120. In one embodiment, the first delaying time period is at least three minutes;

(2) A monitoring step of measuring the temperature of the heat exchanger130in order to find a minimum heat exchanger temperature. In another embodiment, the minimum heat exchanger temperature is determined by continuously comparing a newly measured heat exchanger temperature and a previously measured heat exchanger temperature. If the newly measured heat exchanger temperature is higher or equal to the previously measured heat exchanger temperature, the minimum heat exchanger temperature has been reached;

(3) A controlling step of turning off the compressor120if the minimum heat exchanger temperature has been detected in the monitoring step;

(4) a restarting step of measuring the temperature of the heat exchanger130and restarting the compressor120if the heat exchanger temperature has reached a compressor control temperature. In one embodiment, the compressor control temperature in the restarting step is one degree Celsius below a setpoint temperature set by a user.

In another embodiment, the steps listed above are executed in the aforesaid sequence.

Now turning to the operation of the chiller as mentioned in the second embodiment as shown inFIG. 4. In the first step166, in which the chiller136was switched on. Next, at step168, the control148will wait for a first delay time period on first powering up the chiller136before switching on the compressor120. In one implementation, the first delay time period is at least three minutes.

At step170, the heat exchanger temperature sensor134will then monitor the heat exchanger temperature once every predetermined time period until it detects a minimum heat exchanger temperature. In one implementation, the predetermined time is at least 5 seconds; in another implementation, the minimum heat exchanger temperature is −8 degrees Celsius. The chiller136will then turn off the compressor120. Then at step172, the chiller continues to monitor the heat exchanger temperature once every predetermined time period until the heat exchanger temperature has reached a compressor control temperature; by then, it will switch the compressor120on and the cycle will continue. In one implementation, the predetermined time is at least 5 seconds.

In another implementation, the compressor control temperature is at least 1 degree Celsius below the setpoint temperature

In yet another embodiment, the control148acts as an energy managing device for use in the refrigerant based system136comprising the aforementioned components mentioned and performing the aforementioned steps.

The exemplary embodiments of the present invention are thus fully described. Although the description referred to particular embodiments, it will be clear to one skilled in the art that the present invention may be practiced with variation of these specific details. Hence this invention should not be construed as limited to the embodiments set forth herein.