Vav diffuser controls

Abstract

A method of controlling an HVAC system comprising an air handling unit having at least one supply air fan or motorised supply air damper, the system comprising a plurality of VAV diffuser units, each VAV diffuser unit comprising a diffuser, a motorised variable damper to alter a diffuser airflow rate of a diffuser airflow delivered by the corresponding diffuser unit into the corresponding zone, and a diffuser pressure sensor for determining a pressure of the diffuser airflow; the system further comprising a plurality of zone temperature sensors; the method comprising determining a target thermal capacity for a selected diffuser unit with reference to a target diffuser airflow rate and a target diffuser temperature differential and controlling the motorised variable damper of the selected diffuser unit with reference to the determined target thermal capacity for the selected diffuser unit.

1 . A method of controlling an HVAC system, the HVAC system comprising an air handling unit to produce a supply airflow, the air handling unit being connected via a ducting system to a plurality of VAV diffuser units, each VAV diffuser unit influencing air temperature in a corresponding zone by delivering supply air to the zone, wherein
 the air handling unit comprises at least one supply air fan or motorised supply air damper; and   each diffuser unit comprises a diffuser, a motorised variable damper to alter a diffuser airflow rate of a diffuser airflow delivered by the corresponding diffuser unit into the corresponding zone, and a diffuser pressure sensor for determining a pressure of the diffuser airflow; wherein   the HVAC system further comprises a plurality of zone temperature sensors;   the HVAC system further comprising at least one control unit connected to the supply air fan or motorised supply air damper, each diffuser unit motorised variable damper, each zone temperature sensor and each diffuser pressure sensor;   the method comprising determining a target thermal capacity for a selected diffuser unit with reference to a target diffuser airflow rate and a target diffuser temperature differential and controlling the motorised variable damper of the selected diffuser unit with reference to the determined target thermal capacity for the selected diffuser unit.   
     
     
         2 . The method of  claim 1  wherein the control unit further comprises a plurality of micro-controllers that communicate with one another. 
     
     
         3 . The method of  claim 2  wherein the plurality of micro-controllers comprise micro-controllers provided on each of the diffuser units. 
     
     
         4 . The method of  claim 1  in which the air handling unit further comprises at least one heat exchanger, and the at least one control unit is connected to the at least one heat exchanger. 
     
     
         5 . The method of  claim 1  comprising, for the selected diffuser unit:
 determining a zone temperature setpoint; 
 determining a zone air temperature with a corresponding zone temperature sensor; 
 determining a diffuser unit control output in dependence on the zone temperature setpoint and the determined zone air temperature; 
 determining the target diffuser airflow rate in dependence on a diffuser design airflow rate and the diffuser unit control output for the selected diffuser unit; 
 determining a diffuser design temperature differential; 
 determining the target diffuser air temperature differential in dependence on the diffuser design temperature differential and the diffuser unit control output for the selected diffuser unit; and 
 determining the diffuser target diffuser airflow rate in dependence on the diffuser target temperature differential, or determining the diffuser target temperature differential in dependence on the diffuser target diffuser airflow rate. 
 
     
     
         6 . The method according to  claim 5  wherein the design temperature differential is determined in relation to a diffuser supply air temperature. 
     
     
         7 . The method according to  claim 6  wherein the diffuser supply air temperature is determined by a sensor incorporated into the selected diffuser unit or by a sensor located remote from the selected diffuser unit. 
     
     
         8 . (canceled) 
     
     
         9 . The method according to  claim 6  wherein the target thermal capacity is calculated according to the following formula: 
       
         
           
             
               
                 C 
                 ⁢ 
                     
                 % 
                 ⁢ 
                     
                 D 
               
               = 
               
                 
                   D 
                   ⁢ 
                       
                   % 
                   ⁢ 
                       
                   SdTR 
                 
                 ⋆ 
                 
                   D 
                   ⁢ 
                       
                   % 
                   ⁢ 
                       
                   AR 
                 
               
             
           
         
         where C % D is the target thermal capacity expressed as a percentage of maximum diffuser unit control output, D % SdTR is the target diffuser air temperature differential expressed as a percentage of the diffuser design temperature differential, and D % AR is the target diffuser airflow rate expressed as a percentage of the diffuser design airflow rate. 
       
     
     
         10 . The method according to  claim 1  further comprising determining a plurality of sets of control variables, each set comprising a target factored diffuser airflow rate and a target factored diffuser temperature differential, in which each set satisfies the predetermined target thermal capacity for the selected diffuser unit. 
     
     
         11 . The method according to  claim 10  wherein the HVAC system further comprises an economiser damper system for selectively mixing an air supply from outside the HVAC system with the supply air when the HVAC system is in an economiser mode, the method further comprising, when the HVAC system is in an economiser mode:
 each set of control variables satisfies the predetermined target thermal capacity for the selected diffuser unit additionally comprises a target factored economiser deadband; 
 determining the target factored economiser deadband; and 
 controlling the economiser damper system with reference to said target factored economiser deadband. 
 
     
     
         12 . The method according to  claim 10  further comprising selecting one of said plurality of sets of control variables according to one or more criteria. 
     
     
         13 . The method according to  claim 12  wherein the criteria include one or more of humidity, over-cooling, over-heating, outdoor air temperature, energy conservation, indoor air quality, noise, excess pressure. 
     
     
         14 . The method of  claim 1  wherein the control unit further controls one or more of: a supply air temperature, supply air pressure, and supply air fan speed or damper position of the motorised supply air damper; to alter or maintain a temperature of at least one zone. 
     
     
         15 . The method according to  claim 14  wherein;
 the control unit controls the supply air pressure to alter or maintain a temperature of at least one zone when the motorised variable damper of the diffuser unit serving the at least one zone is fully open and/or 
 the control unit controls the supply air temperature to alter or maintain a temperature of at least one zone when the motorised variable damper of the diffuser unit serving the at least one zone is fully open. 
 
     
     
         16 . (canceled) 
     
     
         17 . The method of  claim 1  further comprising, for the selected diffuser unit, adjusting the motorised variable damper to deliver an adjusted target factored damper airflow rate. 
     
     
         18 . The method of  claim 17 , further comprising determining a plurality of sets of control variables, each set comprising a target factored diffuser airflow rate and a target factored diffuser temperature differential, in which each set satisfies the predetermined target thermal capacity for the selected diffuser unit; wherein the adjusted target factored damper airflow rate is determined with reference to an actual temperature differential relative to a target factored diffuser air temperature differential for the diffuser unit, and an actual pressure at the diffuser unit relative to a target factored diffuser pressure. 
     
     
         19 . The method of  claim 18  further comprising, for a selected diffuser unit with fully open motorised variable damper, adjusting the target factored diffuser pressure as a function of the target factored diffuser airflow rate. 
     
     
         20 . The method according to  claim 1  further comprising, for each diffuser unit, determining a diffuser temperature offset request and a diffuser pressure offset request. 
     
     
         21 . The method according to  claim 20 , wherein, for each diffuser unit, the diffuser temperature offset request is determined by subtracting the actual temperature differential from the target factored diffuser temperature differential, or if the actual pressure is greater than the target factored diffuser pressure then from the target factored diffuser temperature differential multiplied by the square root of the target factored diffuser pressure divided by the square root of the actual pressure. 
     
     
         22 . The method according to  claim 21 , wherein the diffuser pressure offset request is determined by subtracting the actual pressure from the target factored diffuser pressure, or if the actual temperature differential is greater than the target factored diffuser temperature differential then from the target factored diffuser pressure multiplied by the square of the target factored diffuser temperature differential divided by the square of the actual temperature differential. 
     
     
         23 . The method according to  claim 21  further comprising realising, for each diffuser unit, a diffuser pressure offset request of zero when the target factored diffuser pressure is equal to the actual pressure and the target factored diffuser temperature differential is greater than or equal to the actual temperature differential; or
 realising a diffuser temperature offset request of zero when the target factored diffuser temperature differential is equal to the actual temperature differential and the target factored diffuser pressure is greater than or equal to the actual pressure. 
 
     
     
         24 . (canceled) 
     
     
         25 . The method according to  claim 21 , further comprising realising, for each diffuser unit, a diffuser pressure offset request of zero when the target factored diffuser pressure is greater than the actual pressure and when the target factored diffuser pressure divided by the actual pressure is equal to the square of the actual temperature differential divided by the square of the target factored temperature differential. 
     
     
         26 . The method according to  claim 21 , further comprising realising a diffuser temperature offset request of zero when the target factored diffuser temperature differential is greater than the actual temperature differential and the target factored diffuser temperature differential divided by the actual temperature differential is equal to the square root of the actual pressure divided by the square root of the target factored diffuser pressure. 
     
     
         27 . The method according to  claim 21  further comprising ranking each diffuser temperature offset request in a temperature rank and ranking each diffuser pressure offset request in a pressure rank. 
     
     
         28 . The method according to  claim 27  wherein the HVAC system further comprises an air supply controller with proportional-integral (PI), proportional-integral-derivative (PID) or nudge-and-wait control, and with the setpoint set to zero, and with the process value designated as the highest diffuser pressure offset request from the pressure rank. 
     
     
         29 . The method according to  claim 27  wherein the HVAC system further comprises a thermal capacity controller with proportional-integral (PI), proportional-integral-derivative (PID) or nudge-and-wait control, and with the setpoint set to zero, and where the direction of the thermal capacity control is set by a requirement for system cooling or system heating, with the former designating the process value to be the lowest diffuser temperature offset request from the temperature rank and the latter designating the process value to be the highest diffuser temperature offset request from the temperature rank. 
     
     
         30 . The method according to  claim 29  wherein the requirement for system cooling or system heating is determined by a vote of the diffuser units. 
     
     
         31 . The method according to  claim 27  wherein the HVAC system further comprises an air supply target from the air supply controller, wherein the air supply target determines a supply air pressure setpoint for the air handling unit in relation to an air handling unit supply air pressures sensor, or directly determines the fan speed of the at least one supply air fan. 
     
     
         32 . The method according to  claim 30  wherein the HVAC system further comprises a cooling or heating capacity target from the thermal capacity controller, wherein the cooling or heating capacity target determines a supply air temperature setpoint for the air handling unit in relation to an air handling unit supply air temperature sensor, or directly determines the cooling or heating output of the at least one heat exchanger. 
     
     
         33 . The method according to  claim 12 , wherein the HVAC system further comprises an economiser damper system for selectively mixing an air supply from outside the HVAC system with the supply air when the HVAC system is in an economiser mode, and the method further comprises, when the HVAC system is in an economiser mode:
 each set of control variables satisfies the predetermined target thermal capacity for the selected diffuser unit additionally comprises   a target factored economiser deadband;   
       determining the target factored economiser deadband; and controlling the economiser damper system with reference to said target factored economiser deadband; and
 determining an economiser damper temperature setpoint with reference to a target economiser deadband for each diffuser unit. 
 
     
     
         34 . The method according to  claim 7  further comprising, for each diffuser unit, subtracting the actual temperature from the economiser damper temperature setpoint to determine an economiser offset request. 
     
     
         35 . The method according to  claim 34 , further comprising ranking each diffuser unit economiser offset request in an economiser rank. 
     
     
         36 . The method according to  claim 35  wherein the HVAC system further comprises an economiser controller with proportional-integral (PI), proportional-integral-derivative (PID) or nudge-and-wait control, and with the setpoint set to zero, and with the process value designated as the lowest economiser offset request from the economiser rank. 
     
     
         37 . The method according to  claim 36  further comprising an economiser target from the economiser controller, wherein the economiser target determines an economiser supply air temperature setpoint for the economiser damper system in relation to the air handling unit supply air temperature sensor, or directly determines an economiser damper system output to directly modulate the economiser damper system.