Abstract:
The present invention relates to a system and method of HVAC (Heating, Ventilating, Air Conditioning) energy management system. More specially, the present invention provides a system and method that can provide automatic optimized control mechanism for HVAC system to save energy.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of and incorporate in full the provisional application entitled “Smart Building HVAC Energy Management System” with Application No. 62/231,058 filed on Jun. 23, 2015. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a system and method of HVAC (Heating, Ventilating, Air Conditioning) energy management system. More specially, the present invention provides a system and method that can provide automatic optimized control mechanism for HVAC system to save energy. 
       BACKGROUND OF THE INVENTION 
       [0003]    Energy consumptions of HVAC systems for buildings are significant portions of overall energy consumptions. Therefore, energy management systems for HVAC systems that could significantly reduce energy consumption will be very useful. However, most of the energy management systems are basically monitoring systems, rely heavily on human interventions for actual management and controls. There are few optimized energy control systems based on automatic control sequence to specifically control system operating conditions. 
         [0004]    For example, U.S. Pat. No. 9,026,261, “Methods and systems for managing energy usage in buildings” mostly disclosed energy usage monitoring and data recording systems. U.S. Pat. No. 8,235,776, “Fully articulated and comprehensive air and fluid distribution, metering, and control method and apparatus for primary movers, heat exchangers, and terminal flow devices” and U.S. Pat. No. 7,216,698, “Air-conditioning system” failed to provide comprehensive automatic control logic to achieve automatic control. U.S. Pat. No. 7,216,021, “Method, system and computer program for managing energy consumption” mostly provide operation data analysis but failed to provide actual workable operation logic for daily operations. 
       SUMMARY OF THE INVENTION 
       [0005]    An exemplary building HVAC system to be controlled by the present invention includes a hot water distribution system  10 , a hot water generating system  11 , a chilled water distribution system  12 , a chilled water generating system  13 , and a plurality of air distribution systems  14 . 
         [0006]    A system and method for a complete HVAC system control and management comprises a data intake module 800, a data storage module 810, a process module 820 and a control module 830. The data intake module 800 taking information from data input by manual inputs, and by receiving signals from sensors placed in the HVAC system. The data storage module 810 stores operation data and related data in a HVAC operation database. The process module 820 processes data from intake module 800 and data storage module 810 and sending output information to the control module 830. The control module 230 controls equipment in the HVAC system such as fans, pumps, dampers and valves. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The above and further features and advantages of the present invention may be appreciated from the detailed description of preferred embodiments with reference to the accompanying drawings, in which: 
           [0008]      FIG. 1  is a schematic illustration of one exemplary air distribution system of the building air conditioning system; 
           [0009]      FIG. 2  is a schematic illustration of one exemplary hot water distribution system of the building air conditioning system; 
           [0010]      FIG. 3  is a schematic illustration of one exemplary chilled water distribution system of the building air conditioning system; 
           [0011]      FIG. 4  is a schematic illustration of one exemplary chilled water ancillary system of the building air conditioning system; 
           [0012]      FIG. 5  is a schematic illustration of one preferred embodiment of the computer hardware implication of the system of the present invention; 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    The detailed description set forth below in connection with the appended drawings is intended as a description of presently-preferred embodiments of the invention and is not intended to represent the only forms in which the present invention may be constructed and/or utilized. The description sets forth the functions and the sequence of steps for constructing and operating the invention in connection with the illustrated embodiments. However, it is to be understood that the same or equivalent functions and sequences may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention. 
         [0014]    An embodiment of the present invention is now described with reference to the accompanying drawings. 
         [0015]    An exemplary building HVAC system related to the present invention includes a hot water system  10 , a chilled water system  12 , a chilled water ancillary system  13 , and a plurality of air distribution systems  14 . 
         [0016]    As illustrated in  FIG. 1 , each air distribution system  14  includes an air conditioning unit  20 , more than one VAV (Variable Air Volume) boxes  22 , supply air distribution ducts, return air ducts (not shown completely), control dampers  24  (not shown, can be used as alternative to VAV boxes), and air distribution terminal devices such as supply air grills and return air grills (not shown). Each of the air conditioning unit  20  is connected to air distribution terminal devices through supply air ducts, and return air ducts. The air distribution systems  14  are also equipped with thermostats with temperature sensors  26  for sensing actual room temperatures and meanings to adjust set point (Tr) for room temperatures. Alternatively, the air distribution system  14  can be equipped with temperature sensors  26  only, and set point (Tr) for room temperatures can only be controlled at the central control station (set at fixed point, or can be a part of data input of the system). The thermostats or temperature sensors generally are corresponding with VAV boxes  22  or control dampers  24 , meaning one thermostat or temperature sensor for each VAV boxes or control damper. 
         [0017]    The each of air distribution system  14  can also be equipped with a flow measuring device  23  such as flow meter or as part of the VAV box near (or in) each of the VAV box  22 , or near each of the control damper  24 . 
         [0018]    The air distribution system may further include an outside air intake control damper  25 , humidity sensors  27 , and Co2 sensors  28 . 
         [0019]    Each air conditioning unit  20  also includes a heating coil  31  and a cooling coil  41 , and at least one fan  21  for moving air in the distribution system  14 . The air conditioning unit  20  can also be equipped with an economizer  29 . 
         [0020]    As illustrated in  FIG. 2 , the hot water system  10  includes one or more pumps  30 , one or more boilers  36 , connected with pipe lines, to heating coils  31  of air handling units  20 . The hot water system  10  also includes control valves  32  located near each heating coil  31  of each air handling unit  20 . The hot water system  10  is equipped with temperature sensing devices (such as temperature sensors)  34  and  35  for sensing supply and return water temperature for each heating coil  31  for each air handling unit  20 . The hot water system  10  can also be equipped with a flow measuring device  33  such as flow meter for each of the heating coil  31 . 
         [0021]    As illustrated in  FIG. 3 , the chilled water system  12  includes one or more pumps  40 , one or more chillers  46 , connected with pipe lines, to cooling coils  41  of air handling units  20 . The chilled water system  12  also includes control valves  42  located near each cooling coil  41  of each air handling unit  20 . The chilled water system  12  is equipped with temperature sensors  44  and  45  for sensing supply and return water temperature for each cooling coil  41  of each air handling unit  20 . The chilled water distribution system  12  can also be equipped with a flow measuring device  43  such as flow meter for each of the heating coil  41 . 
         [0022]    A pair of temperature sensing devices  50  and  51 (such as temperature sensor) and a flow measuring device  52  such as flow meter can be provided for each chiller. A control valve  53  can be provided for each chiller corresponding to the temperature sensing device  50  and  51  and flow measuring device  54 . 
         [0023]    As illustrated in  FIG. 4 , a chilled water ancillary system  13  includes one or more pumps  47 , one or more chillers  46 , one or more cooling towers  48 , that are connected to pumps  47  with pipe lines. 
         [0024]    A pair of temperature sensing device  55  and  56  (such as temperature sensor) and a flow measuring device  57  such as flow meter can also be provided for each chiller  47  and cooling tower  48  in the chiller-cooling tower loop. A control valve  57  and control valve  58  can be provided for each chiller  47  and cooling tower  48  corresponding to the temperature sensing device  55  and  56 , and flow measuring device  57 . 
         [0025]      FIG. 5  is a schematic diagram illustrating an exemplary hardware structure of a preferred embodiment of present invention for building HVAC Energy Management System. In facility with one or more buildings, an Energy Management System (EMS) center server  101  in charge of conducting energy management is electrically connected to one or more controllers  110  through a building communication line  120 . 
         [0026]    The EMS center server  101  can include devices for connecting to and receiving information from data inputting devices (such as keyboard) and controllers  110 , devices for connecting to (and receiving information from) and sending information to data displaying devices (such as monitors), devices for connecting to and sending information to) data outputting devices and controllers  110 , data storage devices and data exchange devices, and data processing devices. 
         [0027]    The EMS center server  101  can gathers information on operation of the HVAC system in the facility and control the operation of the through controllers  110 . The controllers  110  can be connected to EMS center server  101  through building automation communication line  120 . In one preferred embodiment of the present invention, a switch  130  is provided for each controllers  110  connecting to the building communication line  120 . Alternatively, one type of controllers can perform information gathering function, while another type of controllers can perform control function of the system. In one preferred embodiment of the present invention, the building communication line  120  can be part of the Ethernet network. 
         [0028]    The EMS center server  101  also serves as a gateway between the internet  130  and the building communication line  120 . 
         [0029]    The Energy Management System for HVAC system may be part of overall building energy management system include other types of controllers or control mechanism that can be connected to a general power supply system, or a system for appliances, a lighting system, a disaster prevention system, a security system, an elevator system and an environment monitoring system, etc. 
         [0030]    Information of the operation of HVAC system provided by sensing devices such as sensors and metering devices that are placed in the HVAC system and the building environment is in the form of electronic signals, either analog or digital, while controllers  110  can convert analog signals to digital signals. The controllers  110  send all signals received from sensing devices to the EMS center server  101  via the BA communication line  120 . 
         [0031]    Control signals are sent by the EMS center server  101  to each of the controllers  110  via the building communication line  120 , to control movable devices in HVAC system, such as fans, pumps, control dampers, and control valves. 
         [0032]    A remote control server  150 , which is also electrically connected to the internet  140 , is able to communicate with the EMS center server  101 . 
         [0033]    The EMS center server  101  includes a HVAC operation database, which can include all the information related to the operation of the HVAC system. 
         [0034]    The HVAC operation database can include information related to facility structure which includes data associated with the buildings to be controlled, such as building IDs, types for the buildings, names for peculiar buildings, and zones within the buildings. The HVAC operation database can further include information related to HVAC systems within each building, such as HVAC system IDs, types of HVAC systems, HVAC equipment and device IDs, types of the HVAC equipment and devices, etc. Preferably, these information can be received from inputting devices in system initial setup process, can be revised through inputting devices. 
         [0035]    Preferably, the HVAC operation database can be organized based on building information, HVAC system information, HVAC equipment and device information, and operation time or real time. 
         [0036]    The HVAC operation database can include other information for the equipment and devices, for example, information for year-month-date of installation, a control method, a rated capacity, characteristics, a manufacturer, attachments, special notes, a covering area. 
         [0037]    The HVAC operation database can also include design condition information for various measuring points, which can be correlated with sensing device information. For example, for each flow measuring device such as flow meter, the reading of the flow meter when the HVAC system is operating at design condition can be inputted as initial system setup information. 
         [0038]    The HVAC operation database can also include operation information received from the controllers  110 , including an ID of received information, a name (or type) of received information (such as temperature, flow rate, etc.) and the received information corresponding to operation time or real time. The received information can be related to and organized based on building information, HVAC system information, HVAC equipment and device information, based on the controller and sensor information, and initial system set up. 
         [0039]    The HVAC operation database can also include information related to control data sent to the controllers  110  from the EMS center server  101 , including an ID for the control information, a name for control information sending to controllers  110 , and the control information corresponding to operation time or real time. The control information can be related to and organized based on building information, HVAC system information, HVAC equipment and device information, based on the controller information, and initial system set up. 
         [0040]    Meteorological information can also be included in the HVAC operation database, inputted manually, or downloaded from weather information source. Meteorological information is organized according to time, and can be corresponding to operation data accordingly. For example, control data corresponding to certain meteorological information at certain time can be used when later meteorological information resemble the certain meteorological information. 
         [0041]    The HVAC operation database can also provide HVAC system operation conditions by providing direct correlations between temperatures, flow rates, dampers and valves positions, and fan and pump speeds, etc. by reading and storing all operating related data at particular time (and/or per system requests), and corresponding to time. 
         [0042]    The EMS center server  101  can provide an inputting means in a user interface device for inputting system setup information. The data input can be in fill out form format, or in document format. The inputted information will be saved into the HVAC operation database. 
         [0043]    Detailed steps carried out by a HVAC EMS system  100  for managing HVAC system operation according to the present invention is described below. 
       Initial System Calibration 
       [0044]    In one preferred embodiment of the present invention, the HVAC EMS system  100  perform the task of “Initial System Calibration”, to adjust the speed of fans  21  (or pumps  36  or  40 ) in air distribution system  14  (or hot water distribution system  10  or chilled water distribution system  12 ) to be within the margin of “design condition”. 
         [0045]    HVAC system operation is guided by design documents requiring the system capable of meeting the design conditions. However, this design condition usually is not automatically achievable at initial system setup during to various reasons such as excess capacity of the fans or pumps, variations of the air ducts (or water pipes) and fittings with the design values, etc. Therefore, it is possible that the fans or pumps can run at less than full capacities to meet the design condition. 
         [0046]    In one preferred embodiment of the present invention, an process for controlling a chilled water distribution system  12  is provided as following: 
         [0047]    In step  200 , the EMS center server  101  sends control signals to set all control valves  42  to “wide open” or indexed to maximum positions with no unintended obstruction, and starting all pumps operating in maximum capacity. 
         [0048]    In step  201 , the EMS center server  101  reads all inputting information received from flow meters  43 , and comparing the information with design conditions. All readings of inputting information received from flow meters  43  are saved in the HVAC operation database. 
         [0049]    If all readings are higher than design conditions (exceeding the preset margin), then continue to step  202 . 
         [0050]    If there are readings that are lower than design condition (exceeding the preset margin), then continue to step  206 . 
         [0051]    In step  202 , the EMS center server  101  sends signal to VFD drive (or similar control devices to control operation of the pumps) to reduce speeds of pumps with a preset margin. 
         [0052]    In step  204 , the EMS center server  101  reads all inputting information received from flow meters  43 , and comparing the information with previous readings to determine if the system is stabilized after the adjustment of speeds of fans and pumps. All readings of inputting information received from flow meters are saved in the HVAC operation database. 
         [0053]    This step can be performed in a preset time margin repeatedly, until it is determined that the system is stabilized. For example, the EMS center server  101  can performed step  204  every 5 minutes, and determine the system is stabilized if all the subsequent readings are within 5% margin of difference with the prior readings. All the time margins and differential margins can be inputted in the EMS system setup stage, correlated to HVAC system information. 
         [0054]    Once it is determined that the system is stabilized, the EMS center server  101  repeats the steps of  201  to  204 , until one of readings in the chilled water distribution system  12  are within the acceptable margin of the design condition. For example, if the design condition correlating to a flow meter is 10 GPM, and the acceptable margin for this calibration process is 5%, then when a reading from a flow meter is 10.5 GPM, the calibration process is completed. 
         [0055]    However, if a reading from the chilled water distribution system  12  is that are lower than design condition (exceeding the preset margin), step  206  will be activated. 
         [0056]    In step  206 , the EMS center server  101  sends signal to VFD drive (Variable Frequency Drive, or similar control devices to control operation of the fans and motors) to increase speeds of pumps with a preset margin. Then proceed to step  204 . 
         [0057]    Steps  200  to  206  can be identified as the initial system calibration process, as it adjusts the pump speeds to a value necessary to assure all design conditions are met. The same process can be performed by EMS center server  101  to control hot water distribution system  10 , and air distribution system  14 . 
       Initial System Balancing 
       [0058]    In another preferred embodiment of the present invention, the HVAC EMS system  100  perform the task of “Initial System Balancing”, to adjust the control valves (for hot water distribution system  10  or chilled water distribution system  12 ) or dampers (for air distribution system  14 ) for maintaining the flow rate at each flow meter reading within the margin of “design condition”. This margin can also be inputted as part of the EMS initial system setup. 
         [0059]    In air distribution system and water distribution systems with various branches, the variations between readings with design conditions in various branches after the calibration process of step  200  to  206  can be greater than acceptable. “Initial System Balancing” steps for a chilled water distribution system  12  are as following: 
         [0060]    In step  300 , the EMS center server  101  reads and compares all inputting information received from flow meters  43  with the correlating design conditions. 
         [0061]    If there are reading that are lower than design condition (exceeding the preset margin), then continue to step  306 . 
         [0062]    If all readings are higher than design conditions (exceeding the preset margin), then finds the “worst case scenario” in the chilled water distribution system  12  and continue to step  302 . All readings of inputting information received from flow meters  43  are saved in the HVAC operation database. 
         [0063]    In one preferred embodiment of the present invention, a formula for obtaining the “worst case scenario” in the system is provided: Max [(Vr−Vd)/Vd], where Vr is the actual flow rate reading from a flow meter, and Vd is the design condition correlating to the flow meter. 
         [0064]    In step  302 , the EMS center server  101  sends signal to control valve  42  (or similar control devices to control the flow in the system) correlating to the flow meter  43  of the “worst case scenario” to close the control valve  42  at certain set margin. This set margin can also be preset at EMS system initial setup. 
         [0065]    In step  304 , the EMS center server  101  reads all inputting information received from flow meters  43 , and comparing the information with previous readings to determine if the system is stabilized after the adjustment of control valves  42 . All readings of inputting information received from flow meters  43  are saved in the HVAC operation database. 
         [0066]    Once it is determined that the system is stabilized, the EMS center server  101  repeats the steps of  300  to  304 , until all of the flow meter readings are within the acceptable margin of the design condition. 
         [0067]    At the completion of these processes, the chilled water distribution system  12  is calibrated and balanced to operate at design condition (or near design condition, as it will be difficult to operate completely at the design condition, some variations and imbalances will still exist, depending on the set margins). The same process can be performed by EMS center server  101  to control hot water distribution system  10 , and air distribution system  14 . 
       Partial Load 
       [0068]    In another preferred embodiment of the present invention, the HVAC EMS system  100  perform the control in “Partial Load” condition, to adjust the pumps (for hot water distribution system  10  or chilled water distribution system  12 ) or fans (for air distribution system  14 ) for maintaining the temperature at temperature sensor reading within the margin of “design condition”. This margin can also be inputted as part of the EMS initial system setup. 
         [0069]    Almost no HVAC system operates at design condition. Or, we can say HVAC systems operate at “Partial Load” most of the time. So, control the system at “partial load” is very important for saving energy. 
         [0070]    This type of control process can be applied to VAV system for air distribution, and water distribution system, including hot water distribution system and chilled water distribution system. 
         [0071]    Traditionally, VAV system is controlled by temperature sensor at each zone served by the VAV box. When a sensor sensed the room temperature is lower than set point, a control signal will be sent to the VAV box close down the damper in the VAV box, so that the air flow supplied by the VAV box will be reduced. The fan controls of Air Handling Units for VAV systems mostly focus on maintaining certain constant static pressure at some arbitrarily selected point in the distribution system, commonly by a single static sensor placed approximately ⅔ into the system. 
         [0072]    But closing down the dampers in VAV boxes mostly will increase the system overall resistance, and maintaining constant system static pressure at set point also mean fan speeds required for the operation will not be greatly reduced, thus less energy saving. In addition, this control method provides no assurance that desired air distributions can be achieved. 
         [0073]    The water distribution systems (hot water and chilled water) are facing the same problem. Traditionally, air handling units for VAV systems are paired with control valves in water distribution systems, hot water system and chilled water system. The control valves are controlled by temperature sensors sensing the return air of the Air Handling Units. The pumps for the water distribution systems are generally controlled by maintaining certain pressure drops in the supply and return pipes at certain set point of the system. Again, closing control valves mostly will increase the overall system pressure requirement, and there is not clear assurance that maintaining certain pressure drops in the supply and return pipes at certain set point of the system will provide adequate water supply to each Air Handling Unit. 
         [0074]    In a preferred embodiment of the present invention, VAV systems are controlled mostly by controlling the fan speed directly responding to temperature readings. The same mechanism is used in water distribution systems, wherein temperature readings of the return water lines of the Air Handling Units will be used to control pump speeds. This control process may provide the best performance after the HAVC system are adjusted by the “Initial Calibration” and “Initial Balance”. “Partial Load” steps for controlling a chilled water distribution system  12  are as following: 
         [0075]    In step  400 , for VAV (Variable Air Volume) system controls, the EMS center server  101  reads all inputting information received from room temperature sensors of all zones and compares the information with various set points of each zones. All readings of inputting information received from temperature sensors are saved in the HVAC operation database. 
         [0076]    Generally speaking, as the system rarely operate exceeding design condition (meaning design conditions are meant to be “worst case scenario”), the room temperatures when the system is running at design flow condition should be lower than desired room temperatures when the system is in cooling mode (when the system is in heating mode, the room temperatures should be higher than desired room temperatures). If this is the case, then continue to step  402 . 
         [0077]    If the room temperatures when the system is running at design flow condition is higher than desired room temperatures when the system is in cooling mode (When the system is in heating mode, the room temperatures are lower than desired room temperatures), then continue to step  406 . 
         [0078]    For water distribution system controls, the EMS center server  101  reads all inputting information received from temperature sensors at return water lines for heating coils or cooling coils of the air handling units and comparing the return water temperature with the set points. (For example, the return water temperature for hot water distribution system could be 90 degree Fahrenheit, and return water temperature for chilled water distribution system could be 48 degree Fahrenheit.) These set points can also be inputted into HVAC operation database in EMS system initial setup. All readings of inputting information received from temperature sensors can be saved in the HVAC operation database. 
         [0079]    Generally speaking, as the system rarely operate exceeding design condition (meaning design conditions are meant to be “worst case scenario”), the return water temperature when the system is running at design flow condition should be lower than the set point when the system is in cooling mode (When the system is in heating mode, the return water temperatures should be higher than the set point). If this is the reading, then continue to step  402 . 
         [0080]    If the return water temperature when the system is running at design flow condition is higher than set point when the system is in cooling mode (When the system is in heating mode, the return water temperature are lower than set point), then continue to step  406 . 
         [0081]    In step  402 , the EMS center server  101  sends signal to VFD drive (or similar control devices to control operation of the fans and motors) to reduce speeds of fans or pumps 
         [0082]    In one preferred embodiment of the present invention, when reducing fan speed in VAV system, outside air damper should be adjusted (opening up) (and/or damper in return air duct to close up in certain margin) to maintain minimum fresh air intake. 
         [0083]    In step  404 , the EMS center server  101  reads all inputting information received from temperature sensors, and comparing the information with previous readings to determine if the system is stabilized after the adjustment of speeds of fans or pumps. All readings of inputting information received from temperature sensors can be saved in the HVAC operation database. 
         [0084]    Once it is determined that the system is stabilized, the EMS center server  101  compares the reading with the set point, and repeating the steps of  400  to  404  ( 406 ), until the temperature sensor readings are within the acceptable margin of the set point. 
         [0085]    In step  406 , the EMS center server  101  sends signal to VFD drive (Variable Frequency Drive, or similar control devices to control operation of the fans or pumps) to increase speeds of fans or pumps at set margin. Then goes back to step  404 . 
         [0086]    In one embodiment of the present invention, the temperature readings in the air distribution systems and water distribution systems will only be used to control fan speeds, and the EMS system will not rebalance the air distribution system or water distribution system responding to return air or return water temperature changes. 
         [0087]    In another embodiment of the present invention, the temperature readings in the air distribution systems and water distribution systems will not only be used to control fan speeds. The EMS system will rebalance the systems responding to return air or water temperature changes. The following steps are continuation of the process of step  400  to  406 : 
         [0088]    In step  500 , the EMS center server  101  reads all inputting information received from temperature sensors, and compares with the design conditions to find the “worst case scenario” in the system. All readings of inputting information received from temperature sensors can be saved in the HVAC operation database. 
         [0089]    In one preferred embodiment of the present invention, a formula for obtaining the “worst case scenario” in the system is provided: Max [(Tr−Ts)/Ts], where Tr is the actual temperature of the system, and Ts is the system set point for return temperature. 
         [0090]    In step  502 , the EMS center server  101  sends signal to control dampers or control valves (or similar control devices to control the flow in the system) to close the control dampers or control valves as certain set margin. 
         [0091]    In step  504 , the EMS center server  101  reads all inputting information received from temperature sensors, and comparing the information with previous readings to determine if the system is stabilized after the adjustment of control dampers or control valves. 
         [0092]    Once it is determined that the system is stabilized, the EMS center server  101  compare the reading with the design condition, and repeating the steps of  500  to  504 , until all of the system readings are within the acceptable reign of the design condition. 
         [0093]    Depending on the system layout and the range of the fan speed and pump speed, it might be possible that as the result of the adjustment process from steps  500  to  504 , there are readings from the temperature sensors that are below the design condition, then in step  506 , the EMS center server  101  can send signal to control dampers or control valves (or similar control devices to control the flow in the system) to open the control dampers or control valves as certain set margin and continue with step  504  and so forth. Details of this process are similar to steps  300 - 306 , and with steps  500 - 506 . 
         [0094]    The control process of “partial load” can also be conducted based on readings from humidity sensors, Co2 sensors, or sensors measuring other conditions, and compares with design conditions in the same manner. 
         [0095]    There are other factors that could affect the HVAC system operation, that could set restrictions on the control process. For example, the boilers and chillers could require minimum flow rate to maintain operation condition, or maintain certain efficiency requirement. Thus the control process may include a set point for minimum flow rate that prevent the pumps from running below the set point conditions. 
         [0096]    There are many variations of HVAC systems. There are primary-secondary systems that basically separate hot or chilled water distribution systems from hot or chilled water generation system. And, there are package air handling units that do not require hot water or chilled water supply. However, the control process of the present invention can be used for these system as well that the basic principles for these systems are the same or similar to the systems in the present invention. For example, for the VAV system with package air handling units, all control processes illustrated here can used. For water distribution systems that have primary-secondary configuration, the control processes illustrated here can used for primary system, and the minimum flow rate in the primary system may be further reduced. 
         [0097]    Chilled water ancillary system can also be controlled with the same principle as the present invention. 
         [0098]    For VAV air distribution system with multiple air terminal devices for each VAV box, each air terminal device is provided with a volume air damper (not shown in  FIG. 1 ), and air balancing of each air terminal device is done manually prior to the process as illustrated in the present invention. 
         [0099]    The method and system of present invention can be used to control other system than have similar configuration.