Patent Publication Number: US-2011054701-A1

Title: Energy saving method and system for climate control system

Description:
BACKGROUND OF THE PRESENT INVENTION 
     1. Field of Invention 
     The present invention relates to a climate control system, and more particularly to energy saving system and method for climate control system, which reduces climate control system energy use while providing a thermal comfort at every thermal zone. 
     2. Description of Related Arts 
     Climate control system is particularly designed for a large building, such as office structure, hotel, hospital, skyscrapers or shopping mall, where an indoor ambient temperature thereof must be regulated. In order to maximize comfort and energy efficiency, the climate control system is able to regulate the indoor ambient temperatures of different thermal zones in the building so as to provide a thermal comfort at each of the thermal zones. 
     The conventional climate control system generally comprises a thermal station, such as a chiller unit and/or a heat pump, for supplying a medium at a predetermined temperature, a duct system circulating the medium to each of the thermal zones by means of a circulating pump device, heat exchangers located at each of the thermal zones to heat-exchange the medium with the air at the respective thermal zone until the ambient temperature of the thermal zone reaches the desired temperature preset by the user. 
     Accordingly, water is generally used as a medium to be circulated within the duct system for heat exchanging with the air in the thermal zones. In other words, a circulating pump (or group) pumps the water from the thermal station to each of the thermal zones and return back to the thermal station in a circulating manner. For example, when the user wants to cool down the designated thermal zone from an indoor ambient temperature to a desired temperature, the chilled water is pumped to the designated thermal zone through the duct system and the fan unit will generate the air flow to heat exchange the chilled water with the air within the designated thermal zone. 
     Conventional climate control system is able to provide thermal comfort by regulating the medium flow through control valve in response to the relationship between zone ambient temperature and the desired temperature. Generally speaking, there are two conventional configurations for the control unit. The first configuration of the control unit is an on-and-off type control unit. In this configuration, the control valve remains fully open when the indoor ambient temperature has not reached the desired temperature and is closed when the indoor ambient temperature reaches the desired temperature. The second configuration of the control unit is a flow rate regulating type control unit, which regulates the flow rate through control valve in response to a preset logic relationship between the indoor ambient temperature and the desired temperature. 
     However, the conventional climate control system has several drawbacks. One is that the system is not able to sufficiently and adequately deliver the right amount of thermal medium flow to the thermal zones in such manner that some thermal zones may receive more medium flow than it is required while others might not get enough medium flow in some situation. The other drawback is that the heat exchange efficiency occurring at the thermal zone is low because the delivery of the medium to various thermal zones is imbalanced, resulting that the system is running inefficiently but the energy consumption is relatively high. 
     SUMMARY OF THE PRESENT INVENTION 
     An object of the present invention is to provide an energy saving control system and method for climate control system for saving energy while providing a thermal comfort at each of the thermal zones. 
     Another object of the present invention is to provide an energy saving control system and method for climate control system, which ensures the heat exchange occurs at each of the end loop terminals of a duct system by selectively adjusting a flow rate of a medium towards the end loop terminal so as to provide a thermal comfort at each thermal zone while being energy efficient. 
     Another object of the present invention is to provide an energy saving control system and method for climate control system, which ensures the pressure difference between both ends of the heat exchanger located in the most adverse end loop terminal to remain constant by selectively adjusting the speed of the delivering device so as to reduce the energy use of the delivering device while providing thermal comfort at each thermal zone. 
     Another object of the present invention is to provide an energy saving control system and method for climate control system, which sends command to the thermal station control system to regulate the outlet water temperature of the thermal station in response to the degree of opening of control valves to ensure that: (i) in cooling mode, the climate control system can meet the thermal comfort need at the thermal zones with medium with the highest possible temperature; (ii) in heating mode, the climate control system can meet the thermal comfort need at the thermal zones with medium with the lowest possible temperature so as to reduce the energy use of the thermal station. 
     Another object of the present invention is to provide an energy saving control system and method for climate control system, which can also control the fan unit to selectively adjust the air flow rate of the fan unit in response to the difference between zone ambient temperature and desired zone ambient temperature T user . 
     Another object of the present invention is to provide an energy saving control system and method for climate control system, which can incorporate with any conventional climate control system without altering the original structural configuration thereof, so as to reduce the manufacturing and installing cost of the energy saving system with the climate control system. 
     Another object of the present invention is to provide an energy saving control system and method for climate control system, no expensive or complicated structure is required to employ in the present invention in order to achieve the above mentioned objects. Therefore, the present invention successfully provides an economic and efficient solution for providing a thermal comfort at each of the thermal zones and for saving energy to operate the climate control system. 
     The above and other objects of the present invention can be achieved by providing the climate control system controller with control logic, which continually polls: 
     (1) the degree of opening of all control valves from zone controller associated with a series of heat exchangers downstream of the thermal station; and/or 
     (2) the pressure difference between both ends of the heat exchanger located in each of the potential most adverse end loop terminals so as to determine which potential most adverse end loop terminal is the most adverse end loop terminal wherein its pressure difference is the smallest among the pressure differences of all of the potential most adverse end loop terminals at each moment; 
     If the pressure difference detected in every moment between both ends of the heat exchanger located in the most adverse end loop terminal is increased, the system controller will regulate the speed of the delivering device through the frequency converter to decrease the pressure difference until the pressure difference reaches the predetermined value which is the nominal pressure difference. 
     If the pressure difference detected in every moment between both ends of the heat exchanger located in the most adverse end loop terminal is decreased, the system controller will regulate the speed of the delivering device through the frequency converter to increase the pressure difference until the pressure difference reaches the predetermined value which is the nominal pressure difference. 
     If the greatest degree of opening of selected control valves is sensed to be smaller than a preset value of very close to 100%, the system controller is operative to send command to the thermal station control system to: 
     (1) in cooling mode, increase the outlet water temperature of the thermal station until the degree of opening of selected control valves reaches the preset value; 
     (2) in heating mode, decrease the outlet water temperature of the thermal station until the degree of opening of selected control valves reaches the preset value. 
     The above and other objects are also achieved by providing climate control system zone controller at each thermal zone with control logic, which is operative to configure the degree of opening of the valve to regulate the water flow in response to the inlet and outlet water temperature difference of the heat exchanger in its respective thermal zone to maintain water at the optimum flow rate to provide a thermal comfort at the thermal zone while being energy efficient. 
     The present invention provides an energy saving system for a climate control system which comprises one or more thermal stations, a duct system for heat exchange medium to be circulated to each end loop terminal at each thermal zone, at least a delivering device for delivering the medium to circulating in the duct system, a heat exchanger located at each of the thermal zones for heat-exchanging the medium with the air at the respective thermal zone. 
     The energy saving system comprises a temperature sensor device and a zone controller at each thermal zone. 
     The temperature sensor device is arranged for detecting a temperature difference of the medium at each of the end loop terminals of the duct system for ensuring heat exchange process occurring at optimal level, that is at ΔT&gt;ΔT n , at each of the thermal zones, wherein ΔT n  is nominal temperature difference between the supply thermal medium and the return thermal medium. 
     The zone controller is operatively linking with the temperature sensor device and the flow control valve for adjustably regulating a flow rate of the medium through the control valve in response to the temperature difference at each thermal zone until the medium is maintained at the optimum flow rate to reach a desired temperature of the respective thermal zone so as to provide a thermal comfort at the thermal zone while being energy efficient. 
     The energy saving system may further comprises one or more pressure sensor devices each of which is arranged for detecting the pressure difference between both ends of the heat exchanger located in each potential most adverse end loop terminal downstream of the thermal station, wherein by polling the detected pressure differences of the potential most adverse end loop terminals, the pressure difference in every moment between both ends of the heat exchanger in the most adverse end loop terminal downstream of the thermal station can be determined and be maintained to a preset value, that is ΔP=ΔP n , wherein ΔP n  is nominal pressure difference. 
     In which, the system controller is operatively linking with the pressure sensor devices located in the potential most adverse end loop terminals for adjustably regulating the speed of delivering device in response to the pressure difference between both ends of the heat exchanger located in the most adverse end loop terminal until the pressure difference is maintained at the preset value ΔP n  from time to time so as to provide a thermal comfort at the thermal zone while being energy efficient. 
     Accordingly, the present invention also provides an energy saving method for the climate control system, which comprises the steps of: 
     (a) detecting the temperature difference of the medium at each end loop terminal of the duct system for ensuring heat exchange process occurring at each of the thermal zones; and 
     (b) adjustably regulating the flow rate of the medium through the valve device in response to the temperature difference at each thermal zone until the medium is maintained at the optimum flow rate to reach a desired temperature of the respective thermal zone so as to provide a thermal comfort at the thermal zone while being energy efficient. 
     The method may further comprise the following step(s): 
     (c) detecting the pressure difference between both ends of each of the heat exchangers located in each potential most adverse end loop terminals for ensuring adequate pressure for the duct system; and/or 
     (d) detecting the degree of opening of all control valves for ensuring heat station consume the least possible energy to condition (cool or heat) thermal medium while providing thermal comfort at each thermal zone. 
     These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a climate control system incorporating with an energy saving system according to a preferred embodiment of the present invention. 
         FIG. 2  is a schematic view of the temperature sensor device incorporating with the heat exchanger of the climate control system according to the above preferred embodiment of the present invention. 
         FIG. 3  is a graph illustrating the flow rate of the medium being regulated in different stages according to the above preferred embodiment of the present invention. 
         FIG. 4  is a flow diagram illustrating the temperature difference control of the energy saving method according to the above preferred embodiment of the present invention. 
         FIG. 5  is a schematic view of the climate control system incorporating with an energy saving system according to the above preferred embodiment of the present invention. 
         FIG. 6  is a flow diagram illustrating the pressure difference control of the energy saving system according to the above preferred embodiment of the present invention. 
         FIG. 7  is a schematic view illustrating the heat exchanging loops extended in the duct system according to the above preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1 and 5  of the drawings, a climate control system according to a preferred embodiment is illustrated for incorporating with a building having a plurality of thermal zones, wherein the climate control system comprises at least one thermal station  10 , a duct system  20 , a plurality of heat exchangers  30 , and a delivering device  50 . 
     The thermal station  10  comprises a chiller unit for cooling device and/or a heat pump for heating device. 
     The delivering device  50  comprises one or more pump units  52  for delivering heat exchange medium from the thermal station  10  to each of the heat exchangers  30  via the duct system  20 . According to the preferred embodiment, the heat exchange medium is embodied to be delivered to circulating between the thermal station  10  and the heat exchangers  30  in the duct system  20 . The delivering device  50  further comprises one or more control valves  51  operatively provided at the end loop terminals respectively to regulate the flow rate of the medium. 
     The duct system  20  comprises a plurality of delivering ducts which defines one or more end loop terminals at each of the thermal zones, wherein medium is delivered to each of the end loop terminals at the thermal zones respectively in a circulating manner. Accordingly, the duct system  20  has an outgoing duct section extending from the thermal station  10  to the thermal zones and a returning duct section extending from the thermal zones back to the thermal station  10 . 
     Accordingly, each of the end loop terminals is defined at the respective thermal zone. Therefore, between the outgoing duct section and the returning duct section of the duct system  20 , the medium is pumped to each of the end loop terminals through the outgoing duct section of the duct system  20  and is returned from each end loop terminal back to the thermal station  10  through the returning duct section. In other words, the medium is guided to enter into and exit from the end loop terminal at each of the thermal zones. 
     The heat exchanger  30 , such as a fan coil unit or an air handling unit, is located at each of the thermal zones for generating an air flow to enhance the heat-exchange between the medium and the air within the respective thermal zone. According to the preferred embodiment, the heat exchanger  30  may comprise a fan unit  31  for generating the air flow and a heat exchanging unit  32 , which is located at the respective end loop terminal of the duct system  20  and arranged in such a manner that when the medium is guided to pass through the heat exchanging unit  32 , the air flow is guided to blow towards the heat exchanging unit  32  for proceeding the heat exchange process. It is worth mentioning that the air temperature of the incoming air flow is the ambient temperature of the respective thermal zone. 
     According to the preferred embodiment of the present invention, the energy saving system for the climate control system, which comprises a temperature sensor device  41  and a zone controller  42 , is operatively linked to the thermal station  10 , the delivering device  50  and the heat exchangers  30  in order to control the operation of the thermal station  10 , the delivering device  50  and the heat exchangers  30  in an energy saving manner. 
     As shown in  FIG. 4 , by means of the energy saving device, the climate control system can substantially execute an energy saving method comprising the following steps: 
     (1) Detect the temperature difference ΔT of the medium at each end loop terminal of the duct system  20  by the temperature sensor device  41  for ensuring efficient heat exchange process occurring at each of the thermal zones. 
     (2) Adjustably regulate the flow rate of the medium through the control valve in responsive to the temperature difference ΔT at each thermal zone, via the zone controller  42 , until the medium is maintained at the optimum flow rate to reach a desired temperature of the respective thermal zone, so as to provide a thermal comfort at the thermal zone while being energy efficient. 
     According to the preferred embodiment, the temperature sensor device  41 , which is linked and equipped with the zone controller  42 , comprises a temperature inlet sensor  411  and a temperature outlet sensor  412 , wherein the temperature inlet sensor  411  and the temperature outlet sensor  412  are arranged to determine the temperature difference ΔT of the medium at each of the end loop terminals of the duct system  20 , as shown in  FIG. 2 . 
     The temperature inlet sensor  411  is located at an inlet of the end loop terminal at each of the thermal zones for detecting an inlet temperature of the medium. In other words, the temperature inlet sensor  411  is installed at the outgoing duct section of the duct system  20  to directly detect the temperature of the medium before entering into the thermal zone. Particularly, the temperature inlet sensor  411  is positioned at the inlet of the heat exchanging unit  32  of the heat exchanger  30  to detect the temperature of the medium before the heat exchange process. 
     The temperature outlet sensor  412  is located at an outlet of the respective end loop terminal of the thermal zone for detecting an outlet temperature of the medium. In other words, the temperature outlet sensor  412  is installed at the returning duct section of the duct system  20  to detect the temperature of the medium after exiting out of the thermal zone. Particularly, the temperature outlet sensor  412  is positioned at the outlet of the heat exchanging unit  32  of the heat exchanger  30  to detect the temperature of the medium after the heat exchange process. According to the preferred embodiment, the temperature difference ΔT is determined between the inlet temperature and the outlet temperature for ensuring efficient heat exchange process occurring at each of the thermal zones. 
       Practically,  ΔT=|T   in   −T   out |  (1)
 
     In the equation (1), T in  is the inlet temperature detected by the temperature inlet sensor  411  and T out  is the outlet temperature detected by the temperature outlet sensor  412 . 
     According to the preferred embodiment, the inlet temperature and the outlet temperature can be obtained by two different configurations. The temperature inlet sensor  411  and the temperature outlet sensor  412  are installed within the duct system  20  to directly detect the temperature of the medium before entering into the thermal zone and after exiting out the thermal zone respectively. In other words, when the medium flows within the duct system  20 , the temperature inlet sensor  411  and the temperature outlet sensor  412  will directly contact with the flow of the medium to detect the inlet temperature and the outlet temperature respectively. 
     Alternatively, the temperature inlet sensor  411  and the temperature outlet sensor  412  are installed at the duct system  20  to detect the temperature of the duct system while the medium flowing through at a position before entering into the thermal zone and after exiting out the thermal zone respectively. Particularly, the temperature inlet sensor  411  and the temperature outlet sensor  412  can be installed at the duct surface of the duct system  20  such that when the medium passes through the duct system  20 , the temperature inlet sensor  411  and the temperature outlet sensor  412  can detect the duct surface temperature in response to the temperature of the medium. 
     Accordingly, the temperature sensor device  41  not only ensures heat exchange process occurring at each of the thermal zones but also provides a precise measurement of how much heat exchange is done by the heat exchanger  30  by determining the temperature difference ΔT between the inlet temperature and the outlet temperature. 
     In addition, once the temperature inlet sensor  411  and the temperature outlet sensor  412  read the inlet temperature and the outlet temperature, the temperature sensor device  41  will send the temperature difference information to the zone controller  42  by wire or wirelessly. Accordingly, the zone controller  42  will control the control valve  51  to adjust the flow rate of the medium at the respective thermal zone with respect to the temperature difference information sent to the zone controller  42 . 
     Accordingly, the signal of the temperature difference information can be sent by wiring the temperature inlet sensor  411  and the temperature outlet sensor  412  to the zone controller  42  or by wirelessly linking the temperature inlet sensor  411  and the temperature outlet sensor  412  with the zone controller  42 . 
     It is worth mentioning that when two or more end loop terminals are used at one thermal zone, one temperature inlet sensor  411  can be used to detect the inlet temperature of the group of the end loop terminals and one temperature outlet sensor  412  can be used to detect the outlet temperature of the group of the end loop terminals. Or, alternatively, two or more temperature outlet sensors  412  can be used to detect the outlet temperature of the medium of the two or more end loop terminals respectively. 
     Also, when two or more neighboring thermal zones are grouped to form a thermal group, one temperature inlet sensor  411  can be used to detect the inlet temperature of the thermal group while two or more temperature outlet sensors  412  can be used to detect the outlet temperature of the neighboring thermal zone respectively. In other words, the temperature difference ΔT can be determined by the difference between the inlet temperature of the temperature inlet sensor  411  and outlet temperature of each of the temperature outlet sensor  412 . 
     According to the preferred embodiment, water, especially pure water, can be used as the medium to flow along the duct system  20  by the delivering device  50  of the thermal station  10 . As the cooling device, the chiller unit of the thermal station  10  will chill the medium at a predetermined temperature lower than the ambient temperature of the thermal zones and the delivering device  50  will deliver the chilled water to each of end loop terminals at the thermal zones for heat exchange. As the heating device, the heat pump of the thermal station  10  will heat the medium at a predetermined temperature higher than the ambient temperature of the thermal zones and the delivering device  50  will deliver the heated water to the end loop terminals at the thermal zones. 
     Generally speaking, water has larger specific heat compared with any gas such that the heat exchange is much better than any other gas. On the other hand, water has higher stability such that is much safer for use. Moreover, the demand of the thermal medium is usually huge especially in the building. Water is easy to get in our lives and is also inexpensive. Therefore, water can be a better choose as the medium. 
     When water is used as the medium, the temperature inlet sensor  411  and the temperature outlet sensor  412  can read the inlet water temperature and the outlet water temperature. 
     It is appreciated that other medium, such as gas, air or other liquids, can be used as the medium too. Since the temperature difference ΔT can be precisely detected by the temperature inlet sensor  411  and the temperature outlet sensor  412 , the temperature inlet sensor  411  and the temperature outlet sensor  412  can also read the inlet temperature and outlet temperature of other thermal medium in order to determined the temperature difference ΔT. 
     It is worth mentioning that other sensor device can be used as well in responsive to the physical properties of the medium for heat exchange. Accordingly, the temperature of water is changed before and after the heat exchange. Therefore, temperature sensor is preferably used to detect the water temperature when water is used as the medium. However, other physical properties of the medium, such as pressure, can be used as a parameter to measure the energy consumption of the heat exchange. In other words, other thermal medium, which is able to change a physical property in response to heat exchange, can be used as the medium in the climate control system. 
     According to the preferred embodiment, each of the zone controllers  42  polls the inlet and outlet temperatures of its respective heat exchanger  30  downstream of the thermal station  10 , wherein the zone controller  42  is operatively linked with the control valve  51  to control and actuate the control valves  51 . In particularly, each zone controller  42  is operative to configure the degree of opening of the control valve  51  to regulate the medium flow in responsive to the inlet and outlet temperature difference ΔT of the heat exchanger  30  in its respective thermal zone to maintain the medium at the necessary flow rate to provide a thermal comfort at the thermal zone while being energy efficient. 
     According to the preferred embodiment, a nominal temperature difference ΔT n  is preset in the zone controller  42 , as a set-point value, to control the temperature difference ΔT not smaller than the nominal temperature difference ΔT n  in order to adjustably regulate the flow rate of the medium. 
       ΔT&gt;ΔT n   (2)
 
     In the above equation (2), the nominal temperature difference ΔT n  can be preset according to the design of the climate control system. As shown in  FIG. 3 , the nominal temperature difference ΔT n  is preset as a non-zero constant that heat exchange is directly proportion to the flow rate of the medium. 
         E=C*ΔT*F   (3)
 
     In the above equation (3), E is the heat exchange quantity (joule/time), C is a constant (joule/(volume*Temperature)), ΔT is the temperature difference (° C. or ° F.), and F is the flow rate (volume/time). 
     It is worth mentioning that the nominal temperature difference ΔT n  is set to form a nominal temperature difference line which is a straight line, as shown in  FIG. 3 , by plugging into ΔT n =ΔT. In addition, the nominal temperature difference line further defines two areas in  FIG. 3 . The efficient area is defined at the area on or above the nominal temperature difference line, wherein the heat exchange process can efficiently proceed in response to higher heat exchange quantity and lower flow rate of medium, i.e., at the efficient area, ΔT&gt;=ΔT n . Another area is the inefficient area defined below the nominal temperature difference line, wherein the heat exchange process inefficiently proceeds in response to lower heat exchange quantity and higher flow rate of medium, i.e. at the inefficient area, ΔT&lt;ΔT n . 
       FIG. 3  further illustrates the heat exchange characteristics curves of heat exchange unit at different ambient temperatures, wherein the uppermost heat exchange characteristics curve shows the characteristics of the ambient temperature, for example 28° C., and the lowermost heat exchange characteristics curve shows the characteristics at the user desired temperature T user . It is worth mentioning that for cooling mode, as shown in  FIG. 3 , the ambient temperature T ambient  is greater than the user desired temperature T user . For heating mode, the ambient temperature T ambient  is smaller than the user desired temperature T user . 
     Each of the heat exchange characteristics curves shows two different phases. The first phase of the heat exchange characteristics curve is that when the flow rate of medium is substantially increased from zero, the heat exchange is dramatically increased. The second phase of the heat exchange characteristics curve is that when the flow rate of medium is kept increasing, the increase of heat exchange is zero or tends to be zero. 
     According to the preferred embodiment, the zone controller  42  controls the flow rate of the medium at each end loop terminal at the respective thermal zone in responsive to the nominal temperature difference ΔT n  from a first stage to a second stage. Accordingly, a maximum flow rate F max  is set when the control valve  51  is fully opened. 
     At the first stage, the flow rate of the medium is set at its maximum F max , i.e. the control valve  51  is fully opened, until the temperature difference ΔT reaches the nominal temperature difference ΔT n . As shown in  FIG. 3 , when the maximum flow rate F max  is maintained for a predetermined time period, the heat exchange quantity E will dramatically drop from point A at the higher zone ambient temperature heat exchange characteristics curve to point B at the lower zone ambient temperature heat exchange characteristics curve, wherein at point B, ΔT=ΔT n . In other words, at the first stage, the heat exchange quantity E will drop from point A to point B at the maximum flow rate F max  of the medium. 
     At the second stage, the flow rate of the medium is gradually reduced in condition that the temperature difference ΔT is detected not smaller than the nominal temperature difference ΔT n  according to the equation (2). Accordingly, the heat exchange quantity E will drop until it reaches the nominal temperature difference line at point C. The heat exchange quantity E will gradually reduce along the nominal temperature difference line until reaching point C wherein the zone ambient temperature reaches the desired temperature T user . In other words, points B and C lie on the nominal temperature difference line. 
     At the second stage, the zone controller  42  controls the flow rate of the medium in a linear manner in response to the nominal temperature difference ΔT n . Accordingly, when the value of the temperature difference ΔT is detected equal to or smaller than the nominal temperature difference ΔT n , the zone controller  42  will adjustably decrease the flow rate of the medium. When the value of the temperature difference ΔT is detected larger than the nominal temperature difference ΔT n , the zone controller  42  will maintain the flow rate of the medium. Depending on the temperature difference ΔT, the zone controller  42  will gradually reduce the flow rate of the medium preferably in a linear manner. 
     As shown in  FIG. 3 , the zone controller  42  will reduce the flow rate of the medium in response to the nominal temperature difference ΔT n  until the desired zone ambient temperature T user  is reached, i.e. point C. It is worth mentioning that when the flow rate of medium is gradually reduced, the power usage of the delivering device  50  will correspondingly be reduced thus saving energy. 
     At the third stage, the zone controller  42  further controls the flow rate of the medium in response to the desire zone temperature T user  that the flow rate of the medium is kept reducing and maintaining the desire zone ambient temperature T user  at the respective thermal zone. According to the third stage, the flow rate of the medium is reduced from point C to point D along the heat exchange characteristics curve in response to the desired ambient temperature T user . Accordingly, the zone controller  42  will control the flow rate of the medium at its minimum flow rate F min  such that point D is the minimum flow rate F min  of the medium. In other words, by using the system of the present invention, the flow rate of medium at each thermal zone can be efficiently controlled between the minimum flow rate F min  and the maximum flow rate F max . 
     It is worth mentioning that when the flow rate of the medium is reduced at the third stage, the ambient temperature of the thermal zone is remained at the desired temperature T user  for providing a thermal comfort at the thermal zone according to the desired temperature heat exchange characteristics curve. 
     It is worth mentioning that at the third stage, the temperature difference ΔT is greater than the nominal temperature difference ΔT n . Therefore, the main focus of the zone controller is to monitor the ambient temperature to ensure the zone ambient temperature staying at the desired ambient temperature T user  while gradually reducing the flow rate of the medium until the flow rate can no longer be reduced, i.e. the point D. 
     Accordingly, when the ambient temperature increases, i.e. above the desired zone temperature T user , the zone controller  42  will controllably increase the flow rate of the medium from point D towards the point C along the desired temperature heat exchange characteristics curve. When the zone ambient temperature keeps increasing, zone controller  42  will controllably increase the flow rate of the medium from point C towards the point B along the nominal temperature difference line. In other words, the flow path from point A, point B, point C, to point D is reversible that the zone controller  42  can efficiently regulate the flow rate of the medium. It is worth mentioning that the path from point A, point B, point C, to point D is set within the efficient area. 
     The present invention is able to particularly save the energy consumption of the circulating delivering device  50  by controlling the flow rate of the medium. In other words, when the flow rate of the medium is reduced, the delivering device  50  requires less energy to pump the medium to the thermal zone through the duct system  20 . The following is to illustrate how to determine the thermal transporting efficiency of the delivering device  50 . 
         ER=E/P   (4)
 
     In equation (4), ER is the thermal transporting efficient rate of the delivering device  50 , E is the medium heat exchange quantity (joule/time), and P is the power consumption of the circulating delivering device  50  (joule/time). 
     In addition, the power consumption of the circulating delivering device  50  is that: 
         P=F*g*H/η   (5)
 
     In equation (5), F is the flow rate of the medium, g is the gravity, H is the elevation distance of the medium being delivered from the delivering device  50  (water-head), and η is the efficiency of the delivering device  50 . 
     By combining the equations (3), (4), and (5), the thermal transporting efficiency of the delivering device  50  is that: 
         ER =( C*ΔT*F )/( F*g*H /η)=( C*ΔT *η))/( g*H )
 
     For water as the medium, C is 4.18, therefore: 
         ER= 427* ΔTη/H   (6)
 
     When ΔT=ΔT n , ER n =427*ΔT n *η/H 
     According to the equation (2), when ΔT≧ΔT n , then: 
       ER≧ER n  
 
     In other words, the thermal transporting efficiency of the delivering device  50  (ER) at any operating condition is equal to or larger than the nominal transporting efficiency of the delivering device  50  (ER n ) at the nominal temperature difference ΔT n , i.e. ΔT≧ΔT n . Therefore, the delivering device  50  also works within the efficient area according to the preferred embodiment. 
     As mentioned above, energy saving can be achieved by providing the zone controller  42  at each thermal zone with control logic to operatively configure the degree of opening of the control valve  51  to regulate the medium flow in response to the inlet and outlet temperature difference of the heat exchanger  30  in its respective thermal zone to maintain medium at the minimum flow rate to provide a thermal comfort at the thermal zone while reducing the energy consumption of the delivering device  50 . 
     It is worth mentioning that when the degree of opening of the control valve  51  is reduced, the flow of medium through the duct system  20  will be correspondingly reduced. Then, the water-head (evaluation distance) H of the delivering device  50  will be increased. As a result, the pressure difference ΔP at the most adverse end loop terminal will be increased. Therefore, the system controller  43  will regulate the pressure difference ΔP at the most adverse end loop terminal until the pressure difference ΔP at the most adverse end loop terminal reaches the nominal pressure difference ΔP n . Specifically, the system controller  43  will decrease the speed of the delivering device  50  in response to the pressure different ΔP between both ends of the heat exchanger  30  located in the most adverse end loop terminal downstream of the thermal station  10  to ensure that ΔP=ΔP n . As the speed of delivering device  50  is reduced, further energy saving is achieved because the delivering device  50  with lower speed will require less energy to operate. 
     According to the preferred embodiment, the energy saving system  40  further comprises a pressure sensor device  44  at each of the selected thermal zones, as shown in  FIG. 2  and  FIG. 7 . The pressure sensor device  44  is arranged for detecting a pressure difference ΔP of medium between inlet and outlet of the heat exchanger  30  at the respective thermal zone. Accordingly, the pressure sensor device  44  ensures the pressure difference ΔP between both ends of the heat exchanger  30  located in the most adverse end loop terminal to remain constant by lowering or increasing the speed of the delivering device  50  so as to minimize the energy use of the delivering device  50  while providing a thermal comfort at the thermal zone. 
     According to the preferred embodiment, the pressure sensor device  44 , which is linked to the system controller  43  comprises a pressure inlet sensor  441  and a pressure outlet sensor  442 , wherein the pressure inlet sensor  441  and the pressure outlet sensor  442  are adapted to determine the pressure difference ΔP of the medium at the potential most adverse end loop terminals of the duct system  20 , as shown in  FIGS. 2 and 7 . 
     The pressure inlet sensor  441  is located at an inlet of the end loop terminal at each of the thermal zones for detecting an inlet pressure of the medium. Particularly, the pressure inlet sensor  441  is located at the inlet of the heat exchanging unit  32  of the heat exchanger  30  to detect the pressure of the medium before the heat exchange process. 
     The pressure outlet sensor  442  is located at an outlet of the respective end loop terminal of the thermal zone for detecting an outlet pressure of the medium. Particularly, the pressure outlet sensor  442  is located at the outlet of the heat exchanging unit  32  of the heat exchanger  30  to detect the pressure of the medium after the heat exchange process. According to the preferred embodiment, the pressure difference ΔP is determined between the inlet pressure and the outlet pressure of the medium. 
     Particularly, each of the pressure sensor devices  44  is arranged for detecting the pressure difference between both ends of the heat exchanger  30  located in each potential most adverse end loop terminal downstream of the thermal station  10 , wherein by polling the detected pressure differences of the potential most adverse end loop terminals, the pressure difference in every moment between both ends of the heat exchanger  30  in the most adverse end loop terminal downstream of the thermal station  10  can be determined and be maintained to a preset value, that is ΔP=ΔP n , wherein ΔP n  is nominal pressure difference. 
     According to the preferred embodiment, as shown in  FIG. 7 , depending on the actual arrangement or layout of the environment, the duct system  20  may extend to have more than one heat exchanging loops  21 , each grouping a plurality of the heat exchangers  30 , wherein one of the grouped heat exchangers  30  of each the heat exchanging loop  21  is predetermined as the potential most adverse end loop terminal thereof and the respective pressure sensor device  44  is located at each the potential most adverse end loop terminal to detect the pressure difference thereof. It is worth mentioning that which heat exchanger  30  within each of the heat exchanging loops  21  should be designated as the potential adverse end loop terminal could be determined by the experienced designer of the climate control system, for example the most distal heat exchanger  30  of each heating exchanging loop  21  would be the one having the least pressure of that heating exchanging loop  21 . 
     As shown in  FIG. 7 , the pressure sensor device  44  is located at each the potential most adverse end loop terminal to detect the pressure difference thereof, wherein under different operating conditions, the potential most adverse end loop terminal will be changed correspondingly. For example, the duct system  20  may have a plurality of heat exchanging loops  21 A to  21 M, wherein the medium is arranged to flow to all heat exchanging loops  21 A to  21 M that all control valves  51  thereof are fully opened. The system controller  43  will determine the pressure differences ΔP A1  . . . ΔP An  . . . , ΔP M1  . . . ΔP Mn  of the potential most adverse end loop terminals of the heat exchanging loops  21 A to  21 M. Then, the system controller  43  will determine the most adverse end loop terminal with the least value of ΔP, such that the ΔP min  is the pressure difference of the most adverse end loop terminal. For example, if ΔP An  is the ΔP min , the heat exchanger  30 (A n ) at the heat exchanging loop  21 A will be designated as the most adverse end loop terminal. 
     Another example illustrates that when the control valve  51  at the heat exchanging loop  21 A is closed, the potential most adverse end loop terminal will be located at the heat exchanging loop  21 M. According to the heat exchanging loop  21 A, the pressure differences of all the end loop terminals at the heat exchanging loop  21 A at point P A  and P B  are the same, i.e. ΔP A-B , wherein AP A-B  is larger than the pressure difference at all the end loop terminals at the heat exchanging loop  21 M. When ΔP Mn  is the ΔP min , the heat exchanger  30 (M n ) at the heat exchanging loop  21 M will be designated as the most adverse end loop terminal. 
     Another example illustrates that when the control valve  51  at the heat exchanging loop  21 M is closed, the potential most adverse end loop terminal will be located at the heat exchanging loop  21 A. When ΔP An  is the ΔP min , the heat exchanger  30 (A n ) at the heat exchanging loop  21 A will be designated as the most adverse end loop terminal. 
     Therefore, under different operating conditions, the potential most adverse end loop terminal will be altered correspondingly. When the pressure sensor device  44  is located at each the potential most adverse end loop terminal to detect the pressure difference thereof, the system controller  43  can poll the pressure difference ΔP between both ends of the heat exchangers located in each the potential most adverse end loop terminal downstream of the thermal station  10  every moment so as to determine which potential most adverse end loop terminal is the most adverse end loop terminal. When ΔP min  is found within the pressure differences ΔP of all heat exchangers  30 , the system controller  43  will regulate the delivering device  50  through the frequency converter until ΔP=ΔP n . 
     Another example illustrates that when only one control valve  51  at the heat exchangers  30 A 0  of the first level of the end loop terminal of the heat exchanging loop  21 A is opened while the rest of the control valves  51  at the end loop terminal of the heat exchanging loop  21 A are off, the pressure sensor device  44  at the heat exchanger  30 A 1  will obtain the pressure differences ΔP thereat which is the same as the pressure differences ΔP at the heat exchanger  30 A 1 . Therefore, the system controller will regulate the delivering device  50  until ΔP A0 =ΔP n . 
     The system controller  43  polls the pressure difference ΔP between both ends of the heat exchangers located in each the potential most adverse end loop terminal downstream of the thermal station  10  every moment so as to determine which potential most adverse end loop terminal is the most adverse end loop terminal wherein its pressure difference is the smallest among the pressure differences of all of the potential most adverse end loop terminals at each moment. 
     Accordingly, the system controller  43  is operatively linking with the pressure sensor devices  44  located in the potential most adverse end loop terminals for adjustably regulating the speed of delivering device  50  in response to the pressure difference until the pressure difference ΔP in the most adverse end loop terminal is maintained at the preset value ΔP n  so as to provide a thermal comfort at the thermal zone while being energy efficient. 
     As shown in  FIG. 6 , if the pressure difference ΔP is increased, the system controller  43  will decrease the speed of the delivering device  50  through the frequency converter to decrease the pressure difference ΔP until the pressure difference ΔP reaches predetermined value which is the nominal pressure difference ΔP n . If the pressure difference ΔP is decrease, the system controller  43  will increase the speed of the delivering device  50  through the frequency converter to increase the pressure difference ΔP until the pressure difference reaches the nominal pressure difference ΔP n . 
     As shown in  FIGS. 1 and 5 , the system controller  43  polls the degree of opening of all control valves  51  from the zone controllers  42  associated with a series of heat exchangers  30  downstream of the thermal station  10 . In particular, the system controller  43  is operative to send command to the thermal station control system to regulate the outlet medium temperature of the thermal station  10  in response to the degree of opening of control valves  51  to ensure the thermal station  10  consuming the least amount energy to provide the conditioned (heated or cooled) medium to each thermal zone to meet the thermal comfort need at the thermal zones. Accordingly, the system controller  43  will regulate the medium at the highest possible temperature outputting from the thermal station  10  in a cooling mode such that the thermal station  10  will save energy to chill the medium for delivering to each thermal zone. Likewise, the system controller  43  will regulate the medium at the lowest possible temperature outputting from the thermal station  10  in a heating mode such that the thermal station  10  will save energy to heat the medium for delivering to each thermal zone. 
     In other words, the system controller  43  will send command to the thermal station  10  to regulate the outlet water temperature of the thermal station in response to the degree of opening of control valves to ensure that: (1) in cooling mode, the climate control system can meet the thermal comfort need at the thermal zones with medium with the highest possible temperature; (2) in heating mode, the climate control system can meet the thermal comfort need at the thermal zones with medium with the lowest possible temperature so as to reduce the energy use of the thermal station  10 . 
     If the greatest degree of opening of the selected control valves  51 , which are the control values located at the thermal zones where the zone ambient temperature has reached the user desired temperature T user  steadily, is sensed to be smaller than a preset value of very close to 100%, the system controller  43  is operative to send command to the thermal station  10  to: (1) in cooling mode, increase the outlet temperature of the thermal station until the greatest degree of opening of selected control valves  51  reach the preset value; (2) in heat mode, decrease the outlet temperature of the thermal station  10  until the greatest degree of opening of selected control valves  51  reach the preset value. 
     Therefore, the system controller  43  of the present invention will (1) polls the pressure difference ΔP between both ends of the heat exchanger located in each the potential most adverse end loop terminal downstream of the thermal station, and/or (2) poll the degree of opening of all control valves  51  from zone controllers associated with a series of heat exchangers  30  downstream of the thermal station  10 . 
     Accordingly, the energy saving method for the climate control system further comprises the following step. 
     (3) Detect the pressure difference between both ends of the heat exchanger located in each the potential most adverse end loop terminal for ensuring adequate pressure for the duct system  20 . 
     The energy saving method for the climate control system according to the preferred embodiment may further comprise the following step. 
     (4) Detect the degree of opening of all control valves  51  for ensuring heat station  10  consuming the least possible energy to condition (cool or heat) medium while providing thermal comfort at each thermal zone. 
     According to the preferred embodiment, the zone controller  42  further operatively controls the heat exchanger  30  to adjustably regulate an air flow thereof in response to the difference between zone ambient temperature and desired ambient zone temperature T user , i.e. zone ambient temperature−desired zone ambient temperature T user =ΔT ambient . Accordingly, the zone controller  42  operatively controls the operation of the fan unit  31  to regulate the air flow towards the heat exchanging unit  32 . When the air flow rate of the fan unit  31  is increased, the heat exchange process at the heat exchanging unit  32  is correspondingly speeded up. Likewise, when the air flow rate of the fan unit  31  is reduced, the heat exchange process at the heat exchanging unit  32  is correspondingly slowed down. 
     Preferably, the fan unit  31  is set to provide three different rate settings, i.e. high rate, medium rate, and low rate. When ΔT ambient  is equal to or greater than a preset value V 1 , the high rate of fan unit  31  is selected to enhance the heat exchange process such that the ambient temperature will dramatically drop. When ΔT ambient  is equal to or greater than a preset value V 2  but smaller than V 1 , the medium of fan unit  31  is selected. When ΔT ambient  is smaller than a preset value V 2 , the low rate of fan unit  31  is selected. 
     It is worth mentioning that the preferred embodiment of the present invention not adopts the energy saving mode through the circulating delivering device  50  efficiency improvement, but better utilize controlling the temperature difference at the heat exchange end. In other words, the preferred embodiment of the present invention is not aimed at improving the equipment efficiency, but aim at improving the thermal transporting efficiency of the climate control system. Therefore, every circulation of the thermal medium is capable of take advantage of good heat exchange efficiency thus saving energy of the delivering device  50 . 
     One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting. 
     It will thus be seen that the objects of the present invention have been fully and effectively accomplished. The embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.