Temperature control system for zoned space

#This invention relates generally to control systems for controlling the temperature of multiple zoned space, such as a building, and more particularly to a variable air volume digital control system having a temperature system manager device which determines an air flow setpoint in a temperature zone as a percentage of the total air volume of a terminal in the temperature zone and as a function of the deviation of a local temperature sensor temperature from a setpoint schedule in the temperature system manager device, whereby the flow adjustments made by a local terminal control unit are at a higher rate than the rate of receipt by the terminal control unit of a flow target set by the temperature system manager device.

#The utilization of variable air volume (VAV) air distribution systems to supply conditioned air from a central source thereof to offices, school rooms, and other similar spaces or areas in multi-room buildings has become increasingly more prevalent. Such VAV systems generally furnish varying volumes of air, at constant temperatures, into a space in accordance with the space or zone demands. The flow of conditioned air from outlets or terminals is generally regulated by operation of suitable damper means controlled by a thermostat sensing the temperature of the space being conditioned. Thus, as the temperature of the space deviates to a greater degree from a predetermined setpoint, the damper opens more as a direct result of the deviation and a greater quantity of conditioned air is discharged into the space. Conversely, when the temperature in the space being conditioned approaches the setpoint, the system decreases the air volume to the space depending upon the deviation of the space temperature from the setpoint. In U.S. Pat. No. 4,756,474 assigned to the same assignee as the present invention, there is described a pneumatic controller for a duct pressure powered air terminal unit having a volume controller which receives two pressure signals, whereby the controller bleeds one pressure signal so as to control the inflation of a bellows or bladder to thereby modulate the terminal unit to maintain a desired volume air flow through the unit, and bleeds the second pressure signal so as to maintain at least a minimum flow through the unit. The above-identified controller is an improvement over U.S. Pat. No. 4,120,453 which describes a three-way valve controller having two pressure regulators and a bleed type thermostat which provide four input signals to the three-way valve thereby providing a single pressure signal to the inflatable bellows.

#In these prior systems, a target flow of air discharged to the space was based on a proportional-only term described as the difference between Temperature Setpoint and Actual Temperature multiplied by an empirically-derived constant of proportionality (k). This proportional-only term is used to modify, either up or down, the flow of air into the space as required, in order to maintain Temperature setpoint in the space. The empirically derived constant of proportionality (k) is fixed in value and thus supports only the fixed load characteristics as were exercised in empirically deriving the constant of proportionality (k) in the first place. These fixed load characteristics are typically the size of the heating or cooling load relative to heating or cooling capacity of the space, and the rate of change of the gross heating or cooling load. However, any variation in these factors in the actual building or space will result in a compromise in the control's ability to maintain the temperature setpoint.

#Other objects and advantages of the present invention will be apparent from the following detailed description in conjunction with the accompanying drawings forming a part of the specification in which reference numerals shown in the drawings designate like or corresponding parts throughout the same, and in which;

#FIG. 1 is a diagrammatic representation of an air system that embodies the principles of the present invention; and

#FIG. 2 is a block diagram of flow target setpoint based control of airflow terminals by terminal control units employing the present invention.

#In FIG. 1, the numeral 10 generally designates an air source, such as an air handler which includes a fan, cooling coil(s) and an electric or hot water heater. The air handler 10 receives return air and/or outside air which it delivers to duct 14. Actuators 11 control the outside and return air dampers for controlling the amounts of return and/or outside air. The air handler control 12 controls the air handler 10 by controlling the fan speed, coil(s) and heater and bypass around the fan, as is known. Sensors 13 detect the supply air temperature, as measured for example by a thermistor, and fan speed, as measured for example by the fan motor power. The conditioned air supplied to duct 14 is, in turn, supplied to branch lines 14-n which supply terminals 15a-n, respectively. Terminals 15a-n may be the inflatable bellows damper type in which plenum air is used to inflate, and thereby close, the bellows and to deflate, and thereby open, the bellows, or of the damper blade type in which an actuator opens and closes the damper blade, or similarly controlled terminals. Actuators 16a-n control the inflation of the bellows or movement of the damper blade or the like as is well known in the art. Sensors 17a-n respectively, sense the actual space temperature in each temperature zone 20a-n which is supplied to a single terminal control units 18a-n in each temperature zone, respectively. Terminal control units 18a-n contain the logic for controlling the actuators 16a-n based upon the space temperature data supplied by the single sensors 17a-n located in each temperature zone and the space temperature setpoint, which is adjusted remotely at the terminal system manager. The temperature zone 20a-n (as shown by the dashed lines), may include a single air terminal 15a controlled by terminal control unit 18a, or may include multiple air terminals 15b, (master terminal), 15b.sub.2 (slave terminal) and 15n (master terminal), with each master terminal (15b and 15n) having a respective terminal control unit (18b and 18n), but each temperature zone having only one temperature sensor (17a-n) respectively. Space temperature control is maintained generally at the setpoint through the modulation of air flow through each air terminal. The terminal system manager 19, which may be located outside the space to be conditioned, contains occupancy schedules, set point schedules and receives, etc. and receives space temperature data from the terminal control unit. The building supervisor 30, which may also be located outside the conditioned space provides scheduling, control, and alarm functions for the air distribution system.

#Referring now specifically to FIG. 2 for details of the adjustment of air terminal 15 by terminal control unit 18, terminal system manager 60 provides a control signal to the terminal control unit at a regular predetermined interval. The temperature setpoint logic and control is included in the terminal system manager 60. The terminal system manager calculates, on a temperature zone basis, an air terminal 15 flow setpoint, i.e. the cubic feet per minute air flow through an air terminal as a percent of the total design air flow of such air terminal, based on the deviation of the temperature of the temperature zone 20 from the temperature setpoint of such temperature zone.

#The calculation of Flow Setpoint shall include a proportional term that accommodates gross temperature-setpoint errors, an integral term that provides heating or cooling load matching (air flow into the space provides a like amount of cooling for a heating load or heating for a cooling load), and a derivative term to accommodate rapid fluctuations in the cooling or heating load, as follows: