CA1326705C - Fan-powered mixing box assembly - Google Patents

Abstract

FAN-POWERED MIXING BOX ASSEMBLY

ABSTRACT OF THE DISCLOSURE

A fan-powered mixing box assembly through which conditioned air is supplied to a plurality of zones is controlled by a programmable fan-box monitor. The as-sembly comprises a mixing box, a multi-speed fan and a heating element having several stages. The monitor re-ceives data from and transmits data to a plurality of programmable zone thermostats each of which controls a zone via a duct damper through which air enters the zone.
The monitor receives data from duct temperature and duct air pressure sensors for use in controlling the fan and heating element. Also, the monitor is responsive to signals representative of the real time for operating the assembly in setback modes when the various zones are not occupied. The monitor modulates a master damper for control of supply air.

Description

11 ~3 ~
,,~ 1 ~ e present invention relates to apparatus and methods ~or use with heating, ventilation, and air conditioning (HVAC) units and particularly ~o the use Oe Çan-powered mixing box assemblies (also called power induction units (PIU)) in variable air volume (VAV) and variable volumehariable temperature (VVI~ systems.
Related material is disclosed in the following copending Canadian patent applications of the applicant:
Serial No. _n~ Date 569,987 June 21,1988 570,117 June æ, 1988 570,118 June æ, lg88 570,119 June 22,1988 PRIOR ART
The present invention relates to fan-powered mi~ang box assemblies and microcomputer conkols used therewith.
In many lar~e buildings, the economics of using several heating, ventilation and air conditioning ~HV~C) units becomes impractical and large single HVAC units are used.
In the usual Y~V system application, a single large HV~C unit supplies conditioned air to the various zones ~a zone dampers, such zone dampe~s controlling air flow only. As various zone dampe~s modulate closed because the zone demands have been met, as ~0 established by a Isxal thermostat, the air flow through the remaining dampers will increase.
Methods of a~ommodating the additional rnl .. ~.

7 ~ ~

.
and often excessive air flow that can result consist generally of air control systems such as discharge dampers and variable speed fans. Air flow sensors and air pressure sensors can be utilized in conjunction with the local thermostat controlling the zone damper. This capability allows the air flow to a given zone to be controlled independently of system pressure variations. The use of fan-powered mixing box assemblies in a VAV
system may provide a fan-powered source of heat in addition to the HVAC supplying heated air to the zone via its zone damper.
This type of design also can be used in the perimeter areas of a large building that might require heat on cold days independ-ently of or in addition to that supplied by the operation of the central HVAC unit providing conditioned air to other parts of the building.
The use of an air flow sensor allows for control of a damper to limit the maximum air flow to a conditioned space independently of system pressure variations which may exist in large duct systems. In smaller systems, where pressure varia-tions in the system are small, fan control can be used.
While the use of fan-powered mixing box assemblies combine the flexihility of decentralized heating with the benefits of VAV cooling systems, conventional systems have several dis-advantages. First, because each fan-powered mixing box re-guires electric power for both the fan and heater, the large number of electrical connections can be expensive and diffiault to install and maintain. Second, the high cost of using many smaller mixing bo~ assemblies often reguires the use of fewer, larger units serving larger zones resulting in a system with poor characteristics regarding the heating and cooling demands.
Finally, the distributive nature of the system requires access to tenant areas in multiple occupancy buildings which is intru-sive and can require extensive scheduling problems.
In the present invention, each of several large fan-powered mixing box assemblies can be treated as ~hough it were a separate HVAC unit operated by a microcomputer controlled monitor with zone ~3~7~

dampers controlled via W T monitor-stats as described in the related U.S. applications identifi.ed above. None of the prior art fan-powered mixing box systems provide the ease of operation and maintenance and the degree of zone aontrol as the fan-powered W T system in accord with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features which are believed to be characteristic of this invention are set forth with particularity in the ap-pended claims. The invention itself, however, both as to its organization and method of operation, together with further ob-jects and advantages thereof, may best be understood by reference to the following description tak n in connection with the accom-panying drawings in which:
FIG. 1 is a front elevational view of the fan-box monitor used in the present invention;
FIG. 2 is a pictorial diagram of the fan-powered mixing box assembly used in accord with the present invention and illus-trating its physical placement communicating with a duct system;
FIG. 3 is a pictorial diagram of the fan-powered mixing box assembly and its electronic monitor as used in a system serving five zones;
FIG. 4 is a pictorial diagram of the fan-powered mixing box assembly in accord with the present invention used with an optional bypass controller; and FIG. 5 is a pictorial diagram of the fan powered mixing box assembly in accord with the present invention used with an optional air flow sensor.

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SUMMARY OF THE lNVENTION

In accordance with the present invention, the system employs a heating, ventilating and air conditioning (}IVAC) unit for controlling the condition of air in each of a plurality of zones supplied with conditioned air via a main duct when using a fan-powered mixing box assembly in the main duct and including a fan and at least one heating element for heating air supplied to the main duct to supply conditioned air to each æone via a master damper means controlling air flow in the main duct. A zone damper means in a zone duct controls the flow of air and communicates between the main duct and each zone. A programmable fan-box monitor means controls the fan-powered mixing box assembly and the pro-grammable fan-box monitor means receives information from a controller means located in each zone interfaced wlth and controlling respective zone damper means in *he respective zone duct, and means for determining the condition of the air in each zone and supplying such information to the fan-box monitor means. The fan-box monitor means operates the fan-powered mixing box assembly in accordance with its programming, the condition of air in each zone, and in accordance with the information received from each controller means to control the fan powered mixing box in the heating or cooling mode. The con-troller means includes a zone thermostat, and the means for determining the condition of air in each zone includes a first sensor for determining the temperature of the air in its re-spective zone, with the first sensor providing electrical signals to the -thermostat indicative of the temperature of the air in the zone. The zone thermostat also includes means for establishing the desired temperature in its zone.

The programmable fan-box monitor means determines the demand for heating or cooling from all zone thermostats, de-~ermines the number of ~ones having demand for heatin~ or cooling, compares such number with a preselected number ~67~

defining the system demand number, and if the number of zones demanding heating or cooling equals or exceeds the system demand number, the fan-box monitor means selects the desired heating or cooling mode respectively of the fan-powered mixing box assembly and provides output signals to all zone thermostats for operating respective zone damper means. The fan-box monitor means operates the fan-powered mixing box assembly in the selected mode until all zone thermos-tats de-manding the selected mode have been substantially satisfied.
The fan-box monitor means has a first program means such that the fan-powered mixing box assembly is operated in a ventila-tion mode when the demand for heating or cooling from all zonss is less than the system demand number. The fan-box monitor means compares the number of zones having a demand for heating and cooling, and if the number of zones having a demand for heating is equal to the number of zones demanding cooling and such numbers equal or exceed the system demand number, the fan-box monitor means selects the zone with the greatest demand as a ref-erence zone and operates the fan-powered mixing box assembly in the mode coincident to that demanded by the reference zane until the reference zone is substantially satisfied. The fan-box mon-itor means periodically determines the demand from each zone and, if the demand in another zone, having a demand coincident with the mode in which the fan-powered mixing box is operating is greater than the reference zone, the other zone is selected as a new reference zone and the fan-powered mixing box assembly is operated until demar.d in the new reference zone is substantially satisfied. The fan-box monitor means receives data from the reference zone when the fan-powered mixing box assembly is operated in the heating mode. The fan-box monitor means pro-vides an output signal to the ~an-powered mixing box assembly for energizing the heating element in accordance with the demand of the reference zone.

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The fan-box monitor means includes a first program means such that when the number of zones demanding heat exceeds a predetermined number defining the heating demand qualifier number, and the fan includes a multi-speed motor, the fan-box monitor means provides an output signal to the fan-powered mixing box assembly for increasing the speed of the fan motor. In other aspects the fan-box monitor means also includes a first sensor for determining the temperature of air adjacent the heating elements and de-energizes the heating elements of the fan-powered mixing box assembly if the air temperature exceeds predetermined setpoints established by the fan-box monitor means. The fan-box monitor means in-cludes indicating means for providing data indicative of the information associated with the operation of the fan-powered mixing box assembly. ~he fan-box monitor means also includes a first sensor for determining the temperature of outside air.
In this aspect of the invention, the fan-box monitor means in-cludes a first program means such that when the fan-box monitor means receives a signal from the first sensor i.ndicating out-side air temperature is greater than a predetermined value, the fan-box monitor means maintains the heating elements in off condition even if demand therefor is called for by any zone. Each zone may have a heating source independently con-trolled by the zone thermostat and the fan-box monitor means includes a first program means such that when the fan-box monitor means receives a signal from the first sensor in-dicating outside air temperature is greater than a predeter-mined value~ the operation of the heating source by the zone thermostat is disabled by a signal from the fan-box monitor means to the zone thermostat.
Further aspects are seen wherein the fan-box monitor means includes a second sensor for determining the temperature of air in the main duct supplying air to the zone ducts. The fan-box monitor means further includes a ~econd program means 132~70~

such that when the fan-powered mixing box assembly is operated in the ventilation mode, the fan-box monitor means will operate the master damper and the fan motor to main-tain main duct temp-erature within predetermined setpoints as established by the fan-box monitor means. The fan-box monitor means also includes a sensor for determining the air pressure in the main duct and a first program means such that the fan-box monitor means op-erates -the master damper to maintain duct air pressure within predetermined setpoints as established by the fan-box monltor means. The fan-box monitor means includes a program means such that when the heating mode has been selected by the fan-box monitor means, the fan motor is energized and the heating element is not energized unless the heating demand exceeds a predetermined level established by the fan-box monitor means.
If the motor of the fan has been energized in low speed, the fan-box monitor means will compare the number of zones demanding heat with a predetermined number defining the heating demand qualifier number established by the fan-box monitor means and the number of zones equals or exceeds the heating demand quali-fier number the motor will be operated in high speed. The fan-box monitor includes a sensor for determining the air pres-sure in the main duct, the fan-box monitor means further in-cludes program means such that when the fan-box monitor means is operating the motor in high speed, the motor will remain operating in high speed until the number of zones demanding heat is less than the heating demand qualifier number and the air pressure in the main duct is greater than a maximum predetermined setpoint as established by the fan-box monitor means.
Additional aspects relate to the fan-box monitor means as including a program means such that when the fan-box monitor means is actuated in the heating mode, the zone having the greatest demand for heating is chosen as a reference zone, She fan-box monitar means providing output signals to the fan-powered mixing box assembly for energizing the heating element in accord-ance with She demand of the reference zone. When heating demand ll32~70~

in the reference zone exceeds a first predetermined value the fan-box monitor rneans will provide an output signal to the fan-powered mixing box assembly for increasing the heating supplied to the reference zone by the fan-powered mixing box assembly. The fan-box monitor means includes a means for monitoring the temperature trend in the reference zone such that the fan-box monitor means will not provide an output signal to the fan-powered mixing box assembly for in-creasing the heating supplied to the reference zone when the temperature trend in the reference zone indicates that the heat demands of the reference zone are being substantially satisfied. In the heating zone the fan-box monitor means selectively controls the heating element in response to the temperature trend.
Basically, the method according to the invention con-trols the operation of a plurality of zone duct damper means located in respective zone ducts and a fan-powered mixing box assembly controlled by a means supp~ying heated or cooled conditioned air into a main duct having ai~ flow control means in the main duct which communicates with zone ducts associated with respective zones and comprises (A) determining the demand for heating or cooling in all zones and the heating or cooling mode for the fan-powered mixing box; (B) controlling the fan-powered mixing box in the heating or cooling mode selected;
(C) operating one duct dampers to close all not desiring con-ditioned air from the fan-powered mixing box in the mode selected and to open all desiring conditioned air in the mode s01ected; and (D) operating the air flow control means and the fan-powered mixing box to control air supplied to the ~ones until all zones demanding the selected mode have been substantially satisfied. The method Eurther comprises (E) de-tarmining the zone which has the greatest demand after step ~A);
and (F) operating the air flow control means and the fan-powered mixing box to control air supplied to the zones until the reference ~one has been substantially satisfied. Also, the method may 132670~
I
include (G) measuring the temperature trend in the reference zone when the fan-powered mixing box is in the heating mode;
and (H) operating the fan-powered mixing box to supply heating to the reference zone in response to the temperature trend.
In accord with the present invention, a method is pro-vided for controlling the operation of a plurality of æone duct damper means located in respective zone ducts and a fan-powered mixing box assembly controlled by a programmable fan-box monitor that supplies heated or cooled conditioned air into a main duct having a master damper means in the main duct which communicates with zone ducts associated with respective æones and each having a æone thermostat associated with the respective zone and con-trolling its zone damper means comprising the steps of (A) determining the demand for heating or cooling from all the zone thermostats; (~1 determining the number of the zones having a demand for heating or cooling from all the zone thermostats;
(C) selectively preselecting the number of the zones having demand for heating or cooling that is necessary to select a heating or cooling zone; ~D) comparing the numbers obtained from steps (B) and (C) and selecting the heating or cooling mode when the number of the zones having a demand for heating or cooling respectively is e~ual or greater than the number sel-ected in step (C~; (E) operating the appropriate zone damper means to closed position if the zone thermostat controlling the appropriate dampers have no demand or demand a mode different than the mode selected in step (D), and positioning open the other zone dampers; (F) actuating the fan-powered mixing box assembly in the selected mode and operating the master damper until all zone thermostats demanding the selected mode have been sati~fied; (G) deactivating the fan-powered mixing box assembly;
and (~) repeating steps (A)-(G) for the other mode when demand for the other mode has been selected in accord with ~teps (A) (D).
~he method may include in step (E) the ~tep of (I) actuating some of the-zone dampers to a partially open position depending upon g_ ~32~70~ `

the amount of demand by their respective thermostats and modulating such dampers between open and closed until the demand is satisfied. The method ~urther comprises the steps of (J) comparing the number of demands after steps (A)-(D) and if the demands for heating and cooling are equal, the zone with the greatest demand is chosen as the reference zone and the fan-powered mixing box assembly is activated in step (F) in the mode coincident with the demand of the zone with the greatest demand; and (K) increasing or decreasing the heating output of the fan-powered mixing box assembly by the fan-box monitor in accordance with the demand of the reference zone.
The method may also comprise the steps of ~L) deter-mining the temperature in the heating compartment of the fan-powered mixing box assemblys and (M) deactivating the heating output of the fan-powered mixing box assembly by the fan-box monitor if the heating compartment temperature exceeds predetermined setpoints established by the fan-box monitor.
The method also comprises the steps of tN) determining the number of zones demanding heating; and (O) increasing the speed of the fan in the fan-powered mixing box assembly when the number of zones demanding heating exceeds a predetermined number as established by said fan-box monitor and may include the step of (P) activating the fan-powered mixing box assembly by the fan-box monitor in the ventilation mode when the number of zones demanding heating and cooling is less than a predetermined number as eqtablished by the fan-box monitor. Further aspects of the method include the steps of (Q) determining the outside air temperature outside the zones and (~) deactivating the fan-powered mixing box assembly by the fan-box monitor when the outside air temperature is greater than a predetermined value as established by said fan-box monitor as well as the steps of (S) determining the air pressure in the main duct; and (T) oper-ating the master damper means by the fan-box monitor to maintain air pressure within setpoi~ts as established by the fan-box monitor.

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In another aspect of the invention, the method com-prises the steps of ~U) programming the setpoints of the :
zone thermcstats during a pl~rality of distinct time periods;
(V) determining the real time; and operating the system as hereinbefore described.

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DET~ILED DESCRIPTION OF THE PR~FERRED EMBODIMENT
OF THE INVENTION

I~eEerring now to the drawings, the fan-powered mixing box assembly in accord with the present invention is depicted by the numeral 10 in FIG. 2 illustrating its relative placement in a duct wherein air flow is controlled by a damper 11. The electronic controls for the damper 11 and mixing box 19 are comprised of a microcomputer-controlled fan-box monitor 12. The fan-box monitor 12 shown in FIG. 1, has a removable front cover 12a, a liquid crystal display 13, a real time clock 14 ~nd four resilient portions 15-18 for operating switches Sl - S~ respec-tively which are located below the cover 12a. The electronic circuitry in the fan-box monitor 12 is substantially identical in all respects to the electronic circuitry employed in the monitor thermostats disclosed in our first tllree copending applications identified above. The fan-box monitor 12 employs a convent;onal microcomputer with internal memory supplemented by progra~mable logic consisting of an electronically erasable Prom (EEPROM)and a ROM which contains instruction codes and fi~ed data.S7, S8, and S9, each of which are 0tandard 2-position awitches, ~nable their functions ~a lnd~ cated.
Air flow through the main or master damper 11 is mixedin box 19 with air supplied by fan 20 through heating element 21. As a matter of electrical design, the control signals from fan-box manitor 12 are wired to damper control board 22 from which relay control signals are derived for operation of the damper motor 22a, the fan 20, and the heating element 21. The damper control board 22 that is used in the present invention is preferably identical to that used with the monitor thermo-stats in the "thermostat control system" and W T system appli-cations referenced above.
Referring now to FIG. 3, an overview of the fan-powered mixing box assembly 10 as used in a system of five zones will be of assistance in understanding the details hereinafter qet forth. Zones 23, 24, 25, 26 and 27 are supplied air which i5 .~
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regulated by dampers 28, 29, 30, 31 and 32 and thermostats 33, 34, 35, 36 and 37 via ducts 3~, 39, 40, 41 allcl 42 respec-tively. Each of the thermostats 33-37 is preferably identical to the sl~ve thermostats described in the copending application "Thermost~t" referenced above. Depending upon the system design, however, ane thermostat may be a monitor-stat that controls the system HVAC unit. A trunk duct 43 is supplied air Erom the HVAC unit via damper 11. Ai_ from the return air plenum located in the ceiling of the building is supplied to return duct 50 which is also in communication via the plenum with zone return ducts 51. AS illustrated in FIG. 3 the fan-box monitor 12 is in electro~ic co~nunication with all thermostats 33-37 via bus 44. The monitor 12 controls damper 11, the activation of fan 20 and heater 21 depending upon the demand for cooling and heating in the zones 23-27. The fan-powered mixing box assembly 10 is in essence designed to be an auxiliary HVAC unit so far as the programs and logic of the system design is concerlled. ~ descrip-tion of progral~ming and operation of the fan-box monitor 12 will illustrate the unique features of the invention.
As illustrated in FIG. 4 of the application "Thermostat Control Sy~tem", Ser. No. 570,119l June 22, 19~8, swi~ches 91-S4; S5, and S6 are used to provide digital input signals to the electrQnic controls of the thermostat described therein.
In the fan-box monitor 12, switch Sl is located beneath resilient portion 15 ("Outside Temperature"); switch S2 is located beneath resilient portion 16 ("Damper Position"); switch S3 is located beneath resilient portion 17 ("Pressure Counts"); and S4 is located beneath re~ilient portion 18 ("Duct Temp."). Switches Sl-S4 provide input signals to general purpose interface circuit U4 which is electrically interfaced to microprocessor Ul. S5 a rotary BCD switch,supplies data to U4 and S6 supplies as input signal to Ul. S5 and program switch S6 are accessible only by removing cover 12a. During programming of the fan-~ox monitor 12 cover 12a is removed and switches Sl-S6 are operated directly by the installer, during normal operation of the fan-box monitor 12 ~3~7~

switches Sl-S4 are operated by depressing a resilient portion 15-18 respectively to display the associated data on display 13.
Damper board 22 is illustrated in FIG. 7 oE the "Thermostat Control System" reference above~ Fan 20 and heating element 21 are controlled via U7 which supplies output signals to TS4 (identified on FIG. 7 as "To HVAC Unit Control"). Analog sensors such as outside air temperature sensor 52 and air pressure sensor 49 are enabled by U7 via TSl. Controls for duct temperature sensor 53 and motor 72a are the same as that described in the "Thermostat Control System" application.

PROGRAMMING THE MONITOR

CONFIGURATION DISPLAY
Switches S1-S4, 16-position rotary BCD ~witch S5 and display 13 are used for the general programing of the functions of the monitor 12. The display 13 is a conventional LCD display and is divided into four sections for purposes of describing the proyL ; ng of the monitor 12.

1. Configuration Display dl In Configuration Display ~1, a 2-digit number is displayed in the upper left hand portion of the display 13. Sl (raise) and S2 (lower) are used to adjust the displayed 0 number to the desired value. A 2-digit number is also displayed in the lower right-hand portion of the display 13 and this value is established by S3 (raise) and S4 (lower).

2. Configuration Display ~2 In "Config. ~2", one number i9 displayed on the display 13. The number may contain from 2 to 4 digits with the most significant digits in the upper left-hand corner. Switches Sl and S2 are used to raise or lower the value of the first two digits; S3 and S~ are used to raise or lower the last two digits (which are displayed in the lower right-hand portion of display 13).

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3. Configuration Display #3 In ''Config. #3", one 2-digit number is displayed in the upper left-hand corner of display 13. Any switch Sl-S4 can be used to raise or lower the value as desired.

4. Configuration Display #4 In "Config. #4", a 2-digit number is displayed in the upper left-hand corner of display 13. A function ON/OFF is displayed in the upper right-hand corner of display 13. Switches ~l and S2 are used to raise or lower the value of the number.
Switches S3 and S4 are used to alternately toggle the display ON or OFF for control of a given function as described herein below. S5 is placed in position "F" for all Config. #4 programing.

PROGRAWING IN CONFIG. #l 1. System Mode Demand Switch S5 is placed in position "2" and the system mode demand number is displayed in the upper left-hand corner of display 13. This number represents the number o~ Zones 23-27 that must call for heating or cooling for the heating or cooling mode of operation to be selected. This number can be adjusted to between l and 4 zones using switches Sl and S2.
2. Heatin~ Demand Qualifier If the number of zones demanding heat is greater than the heating demand qualifier, the monitor 12 will operate the fan 20 from FAN-LO to FAN-HI as will be further discussed below.
`Switches S3 and S4 can be used to raise or lower the heating demand qualifier from 1 to 4 zones. The number is displayed in the lower right-hand corner of display 13 while S5 is in position "2".
3. High Temperature Trip Points The fan-powered mixing box assembly 10 according to the present invqntion has three stages of heat represented by heating element 21: Heat-l; Heat-2; and Heat-3. There are two tempera-ture trips, one for Heat-l and another for Heat-2, and Heat-3.

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132~7~5 soth limits can be set within the range 105-180F and utilize heater temperature sensor 54. With S5 in position "3", Sl and S2 are used to set the Heat-l trip point which is displayed on the upper left-hand corner of display 13. The Heat-2 trip point is displayed in the lower right-hand corner of display 13 and is adjusted using switches S3 and S4. The most significant digit "1" is not displayed on the display 13 because all possible setpoints are above 100F.
4. Heating Mode Lockout Temperature The Heat mode of the fan-box 19 can be locked out when outside air temperature exceeds a certain limit. With S5 in position "4", this setpoint will be displayed in the upper left-hand corner of display 13 and can be adjusted using switches Sl and S2 to between 10-80F in 5 degree increments. If it is desired to completely disable the Heat mode irrespective of outside air temperature, the display is ad~usted using switch S2 to lower the setpoint to 0F.

5. Supplemental Heat Lockout Temperature IP any of the zones 23-27 are equipped with a supplemental heat option, such as baseboard heaters, this heat option can be locked out when outside temperature exceeds a certain limit.
With S5 in position "4", the supplemental heat option setpoint is displayed in the lower right-hand corner of display 13 and can be set using switches S3 and S4 to any setting between 10-~0F
iQ 5 degree increments. 54 ~an be used to lower the setpoint to 0F i~ the heat option is to be disabled. This feature is controlled by a signal from monitor 12 to the respective zone thermostat having supplemental heat.

6. Maximum Ventilation ~ erature The monitor 12 can be operated in the ventilation mode when neither the heating or cooling mode is required. The maximum temperature setpoint, as measured by duct temperature sensor S3, during the ventilation mode is established by using switches Sl and S2 to set the reading in the upper left-hand :

``:
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corner of display 13 with S5 in position "5". The range of this setting is 65-80F in 1 degree increments.

7. Minimum Ventilation Temperature With S5 in position "5", the minimum temperature in the duct 43 during the ventilation mode is set using switches S3 and S4 with the setpoint displayed in the lower right-hand corner of display 13. Range of this setpoint is 40-60F in 5 degree increments. The minimum ventilation temperature set-point can be disabled by using S4 to lower the setpoint to 0F.
This option will allow the fan 20 to remain in FAN-LO regard-less of minimum ventilation temperature as will be discussed below.
PROGRAMING IN CONFIG. #2 8. Duct Temperature Sensor Calibratlon Duct temperature sensor 53 can be calibrated by comparing the reading indicated on display 13 with that of a reference thermometer placed near the sensor 53. The temperature reading on the display 13 consists of two digits in the upper left-hand corner which are adjusted using switches Sl and S2 and a single number, representing tenths of a degree, in the lower xight-hand corner which is adjusted using switches S3 and S~. The tempera-ture is adjusted to match that of the reference thermometer.
The A/D circuitry in U~ in the monitor 12 supplies a 10-bit word representative of the temperature consisting of 2-bits for the most significant digit ~MSD~ and 8-bits for the least signifi-cant digit (LSD). A 2-bit calibration word, 1 bit for MSD, l-bit for LSD, is entered into the memory of the U-2 E PROM
for use in modifying the 10-bit word sent to the microcomputer Ul. The 2~bit calibration word is created using switches Sl-S4 by setting the reading on display 13 to be the same as that of the reference thermometer.

9. Pressure Sensor Calibration With switch S5 in position "7", switches Sl-S4 can be used to calibrate a pressure/airflow sensor 49 provided the sensor is of a given type. The calibration procedure is similar - 132~7~

to that used with the duct temperature sensor calibration discussed above. The use of a pressure/airflow sensor option will be discussed in more detail below.

10. Maximum/Minlmum Duct Pressure Limit With switch S5 in position '18'7 the display 13 will show the setpoint for maximum duct pressure (Hi Limit). The readout will be from 0 to 2,047 counts in 1 count increments, 1 count =
.001 inch water column. The digits in the upper left-hand corner are the most significant; the digits in the lower right-hand corner are the least si~nificant. Switches Sl-S4 are used to set the desired limits.
Switch S5 is placed in position "9" for setting the minimum pressure limit (Lo Limit) in the same manner as for the Hi Limit.
PROGR~MING IN CONFIG. #3:

11. Set Device Address Switch S5 is placed in positian "1", and a 2-digit number from 01 to 64 is displayed in the uppsr left-hand corner of display 13. ~ny switch Sl-g4 can be used to set the address of fan-box monitor 12 for purposes of communication. All devices on the communications bus 44 have an address. The monitor 12 is g~ven the highest number.
PROGRAMING IN CONFIG. #4:

12. Local Setback Control The monitor 12 can ba programed to follow its own setback program or follow that of another communication device such as a computer with switch S5 in position "F", switches Sl and S2 are used to enter the number "1" onto the upper left-hand corner of display 13. Switch S5 is now in the "Fl" position function. Switches S3 and S4 can be used to toggle ON or OFF
(annunciators displayed in upper right) the function whereby the monitor 12 will follow (1) "Setback" and "Comfort" programs in memory - O~ displayed - or (2) will follow the Setback~Comfort programs of another device on the communication bus 44 (OFF
displayed) .

~2~71~5 13. Setback Programing Lock With S5 in position "F" and "02" entered via Sl and S2 on display 13, function "F2" is created. Monitor 12 can be locally programmed to set the time periods associated with comfort and setback modes of operation. When the setback programing lock is togg].ed ON via S3 and S4, the local time period programing of monitor 12 is diabled and the time periods are established via communication bus 44. When the lock is OFF, the time periods can be established locally or via communi~ation bus 44.

14. Ventilation Mode _ In addition to the heating and cooling mode, the fan-box monitor 12 can be operated in the ventilation mode when any of the associated slave thermostats 34-37 is in the comfort - as opposed to setback - mode. This featured is toggled ON with S5 in "F" and "03" entered on the display 13. When S3 and S4 are used to toggle the mode OFF, the fan-box monitor 12 cannot select the vetilation mode.

15. Celsius Temperature Display With S5 in "F" and "04" entered on display 13, 53 and S4 can toggle ON or OFF the readout of the display 13 in C (ON) or in E' ~OFF).

16. outslde Air Temperature Sensor With 55 in "F" and "05" entered on display 13, an outside air temperature sensor ~2 can be used when this function is ON.
When this function has been toggled OFF via switches S3 and S4, fan-box monitor 12 is programed to receiva data indicating out-side -temperature from another device on the communicatlon bus 44.

17. Fan Only First 5tage Heat The monitor 12 can be programed to provide that only the fan 20 will be enargized when first stage heat is otherwise selected (as will be discussed below). With 55 in "F and "06"
entered via Sl and S2, this option can be toggled ON or OFF as desired.

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18. Supplemental ~eat Callers:
The fan-box monitor 12 allows slave thermostats 33-37 to be considered as "Zone Heating Callers" when their respective supplemental heat source is energized. This option can be toggled ON via Function "F7" by placing S5 in "F" and entering "07" on display 13. S3 and S4 are used to toggle this option ON or OFF.

19. High To_que Actuator/Damper Rotation Direction Different types of actuators may be used in the present invention for operation of the damper 11. If a high torque actuator is used, 95 is placed in "F" and "08" is entered on the display 13. This feature is toggled ON via S3 and S~.
The damper 11 can be operated in either a clockwise or counterclockwise manner to open it. In function "F9", ON is clockwise rotation, OFF is countercloc~wise.

20. 2400 Baud Rate Data transmission over Bus 44 can be at 2400 Baud ON
or 4800 OFF and is set in Function "F10".

21. SUPPLEWENTA~ ~EAT FAN RE~
When the system is not in either the heating or cooling mode, the fan 20 is energized in FAN-LO anytime a slave thermo-stat 33-37 energizes its associated supplemental heat when this option is ON (Function "Fll"~.

22. TEMPE~TURE TREND
As will be explained in more detail below, the fan-box monitor 12 not only receives data from the slave thermostat 33-37 as to zone demand but also monitors the "Temperature Trend" in the various ~ones 23-27 calling for the heating mode. With S5 in "F"
and "12" entered on the display 13, "Temperature Trend Staging"
can be toggled ON to energize sacond stage heating when the "Reference Zone Temparature Trend" is positive or zero for six minutes continuously~ When this feature is OFF, second stage heating is ~nPrgized when the reference zone has a heating demand of 2.0F or greater.

--~0--` 13267~ -;

OTHER PROGRAMMED FEATURES

23. SYSTEM MODE RESELECT
,~ If the fan-box monitor 12 has activated the system in ; either the heating or cooling mode and zones 23-27 have zone thermostats 33-37 simultaneously calling for heating and cool-ing for a given length of time - the mode reselect time - the ,` system must reselect the mode of operation and can change mode. The mode reselect time can be set for 0-2550 minutes in 10-minute increments with S5 in positon "~". The setpoint is adjusted via communication 8us 44 from another device (such as a central computer). If the setting is at 0 minutes, the mode reselect is disabled.

24. COMM~NICATION C~ECK
With S5 in position "E", the monitor 12 will perform a communications check with each device on Bus 44. The following information is provided for each device:
Device address; whether it is a heating caller or cooling caller; indication if the device is a reference zone and if so, whether demand in that zone is less than 1.5F; and, operating error signals. For example, display 13 may have "04" in the upper left and "on" in upper right indicating that the device at address 04 is under a communication check. "04" is selected via Sl and S2; the check is toggled ON via any switch Sl-S4.
COMFQ~ CO~lU~L
The monitor 12 can be programmed to operate the associated ystem in the normal or "comfort" mode for those days and times when the various zones 23-27 are occupied and operate in the "setback" mode for non occupied days and times such as the weeXends and nights. When the monitor 12 is in the setback mode the display 13 will display the word SETBAC~ in the upper right-hand corner. There is no annunciator for the comfort mode.
To program the comfort/setback modes, the monitor cover 12a is removed exposing switches Sl-S4, S5 and S6. For purposes of this programming step the following switch designations ars used: switch Sl is ~DVANCE TIME: S2 is COPY; S3 is ON/OFF;

.

132~7~

S4 is DAY SELECT; and S6 i9 PROGRAM BUTTON~ S5 is in normal (position "0").
Depress the PROGRAM BUTTON to activate the "Program Mode". Press the DAY SELECT button to enter the correct day which are designated as follows: Monday = 1 to Sunday = 7.
Press the ON/OFF button to display ON. Press ADVANCE TIME
until the time for the beginning of the comfort mode is displayed. Press the ON/OFF button to OFF. Now depress the ADVANCE TIME button until the time for the beginning of the . _ _ setback mode is displayed on display 13. The beginning of the setback mode is set as the end of the comfort mode.
At this point the comfort and setback periods for the day selected are entered in the monitor 12. A second set of comfort and setback periods for any day can also be programmed by repeating the above steps.
To exit the program mode press the PROGRAM BUTTON. If no further adjustments are made for 30 seconds, the above programs are entered in memory for monitor 12 operation.
To erase the daily program periods simply select the day to be erased and simultaneously press either the ADVANCE
TIME and COPY buttons or the ON/OFF and DAY SELECT button~.
To copy a program from one day to another day, press the ~OPY button after selecting the day to receive the new program periods. The program periods from the day previous to that currently displayed will be read into the memory for the current selected day.
Setback and comfort modes work in conjunction with time data from real time clock 1~ or received time from other device via communication Bus 44.

; MODES OF OPERATION
The fan-box monitor 12 periodically receives data from the zone thermostats 33-37 via communication Bus 44. If any thermostat has zone temperature more than 1.5F from its associated set point it becomes either a `'Heating Caller" or "Cooling Caller". The fan-box monitor selects the coolinq mode i32~7~
. .

if the number of cooling callers equals or exceeds the system mode demand number as programmed and selects the heating mode if the number of heating callers equals or exceeds the system mode demand number. If the number of zone callers for heating and cooling are equal and they both equal or exceed the system mode demand number, the monitor 12 selects the mode matching the zone caller which as the greatest demand (measured in F).
If the number of heating and cooling callers each equal or exceed the system mode demand number but are not equal to each other, the majority rules.
once a mode has been selected, the zone 23-27 that has the greatest demand will be selected as the "Reference Zone".
The system will be operated by the monitor 12 until either (1) the referenca zone has a demand less than .5F or (2) system mode re-select selects the opposite system mode. The reference ~one can change when the system is in a given mode so that it is always the zone with tha greatest demand.
COOLING MODE OPERATION
once the fan-box monitor 12 selects the cooling mode, it will modulate the damper 11 until system static pressure equals the minimum pressure setpoint or until the full open position is reached. If the cooling mode is ~Releasedll due to the reference zone having demand of .5F or less, the damper 11 is fully closed until the same or another mode is selected.
If during system operation, the static pressure reaches the maximum pressure setpoint, the damper 11 is modulated closed.
The fan-powered mixing box does not have its own source of cooling and thus the system herein described must be supplied cool air from an HVAC Unit. The fan-box monitor 12 will not select the cooling mode u~less the central unit is in the cooling mode when a particular system configuration is used that need not be further discussed in this application.
HEATING MODE OPERATION
As discussed above, the monitor 12 will select the heating mode when a su~ficient number of heating callers exist for opera-tion in this mode.
-23_ 13267~ ~

1. FAN ONLY 1st STAGE HEAT IS ON
If the "Fan Only" is used for the first stage of heating, fan 20 will be operated in FAN-LO. ~EAT-2 will be energized when the reference zones demand reaches 2.0F or greater if "Temperature Trend Staging" is OFF. If HEAT-2 is operating and the reference zone heating demand is 2.5F or greater the HEAT-3 stage will be energized.
2. FAN ONLY 1st STAGE HEAT IS OFF
If the "Fan Only" option was set to OFF, the monitor 12 will energize the fan 20 in FAN-LO and energize the HEAT-l stage of heating element 21. If the reference zone has a demand of 2.0F or greater, HEAT-2 stage will be energized if "Temperature Trend Staging" is OFF. If HEAT-2 is energized and the reference zone has a demand of 2.5F or greater, HEAT-3 will be energized.
3. FAN OPERATION DURING THE HEATING MODE
When the heating mode is initially selected, fan 20 will be operated in FAN-LO f~r one minute. After the one minute waiting period during which the system is stabilized, the monitor 12 will compare the number of heating callers to a minimum demand number as the "Heating Demand Qualifier". The fan 20 will remain in FAN LO if the number of zones 23-27 calling for heat is less than the heat demand qualifier. If the number of heating callers is greater than the heat demand qualifier, the fan 20 will be operated in FAN-~I and will remain in this speed until both of the following conditions exist: (1) the number of heating callers is less than the heat demand qualifier and (2) system static pressure is greater than the maximum pressure setpoint.
4. TEMPERATURE TREND STAGING
When the heating mode is initially selected it may occur that the temperature condition in the selected reference zone is improvLng. The ~EAT-2 stages need not be energized in this situation if the situation is improving quic~ly enough. Tempera-ture trend staging provides a means to prevent unnecessary energization of HEAT-2 and thus allows for more economiGal D ~

operation of the mixing-box assembly 10 without sacrificing comfort in any zone 23-27. Equally important, temperature trend staging allows for a determination of whether zone conditions are getting worse.
When ON temperature trend staging works as follows:
When the reference zone has a demand of 2.0F or greater, the initial value of the temperature trend (TT) is set to zero.
Approximately every 12 seconds, the monitor 12 performs a temperature trend calculation to determine a new temperature trend value. This value is arrived at by determining the difference between current demand (Cmd) and previous demand ~Pmd) = Cmd-Pmd. This difference is added to the TT(OLD) to get TT(NEW). If TT(NEW) is negative, zone conditions are improving~ If TT(NEW) is zero, zone conditions are not improving.
If TT(NEW) is positive, zone conditions are worsening. The fan-box monitor 12 will energize HEAT-2 if the reference zone's TT(NEW) is continuously positive or zero for six minutes.
Assume that initial zone demand in the reference zone was 3.0F (TT=0). If zone demand decreases to 2.5F, TT(NEW) is negative. Now assume that zone demand increases to 2.7F.
TT(NEW) will stlll be negative even though the zone condition i3 worsening. In this special case, programming will replace the negative TT(NEW) with only the difference between Cmd and Pmd, which in this case will be positive (+.2). Operation of the monitor 12 will then proceed as described above.
VENTILATION MODE OPERATION
If neither the heating or cooling mode is selected, the fan-box monitor 12 can operate the damper 11 in the ventilation mode. In this mode, the fan 20 is operated in FAN-LO and damper 11 is modulated open to keep duct temperature below the maximum ventilation temperature setpoint.

3L32~7~:~
.
~ .
1. DAMPER MODULAT _ hen the ven-tilation mode is selected, monitor 12 will initially close damper 11 and energize fan 20 in FAN-LO for one minute. After one minute, if duct temperature is 1.5F greater than the maximum ventilation temperature setpoint, the damper 11 will be opened. The damper 11 will continue to open the damper 11 until duct temperature is reduced to within 1.5F of the maximum temperature setpoint.
When the duct temperature drops to less than 1.5F above the maximum setpoint, the damper 11 is closed.
To maintain air pressure within the operating limits, the moitor 12 will modulate damper 11 closed if static system pressure is greater than the maximum pressure setpoint.
During operation of the damper 11, the monitor 12 will not exceed the maximum pressure setpoint to maintain the maximum ventilation temperature setpoint.
During the ventilation mode, if duct temperature is below the minimum ventilation temperature setpoint the fan ,.
20 is deenergized. If, after one minute, duct temperature exceeds the minimum ventilation setpoint, the fan 2Q will be ~, energized in FAN-LO.
i' ~ FIG. 2 illustrates the basi~ configuration of the ~t~ fan-powered mixing box assembly 10 without an air pressure sensor used. FIG. 5 illustrates the placement of air pressuxe sensor 49 in series with air flow through txunk duct 43.
~j ~ FIG. 4 illustrates the use of the fan-powered mixing !`~,` box assembly 10 providing air to a duct 43 controlled by a VVT
bypass controller such as that described in our copending , application entitled "Bypass Controller And Bypasg System".
'5 ~! In this application, the bypass controller utilizes its own air flow/pressure sensor 46 with its associated damper 47 and damper board 48. Bypass controller 45 is also on communication bus 44 for connection to monitor 12.
As understood in the art, the particular configura-'~ tion used in a system depends upon the number and size of 20nes ~ -26-~`

1~2~7~f 23-27 which are to be supplied by a given fan-powered mixing box assembly lOo Real time data from clock 14 or received via communica-tion bus 44 is utilized by the monitor 12 for comfort and set-back modes of operation. In addition, monitor 12 will broad-cast time data to zone thermostats 33-37 for use system operation. (For example, the thermostats 33-37 follow their own setback programs or can be programmed to follow monitor 12, as described in the "Method And System For Controlling A
Single 20ne ~VAC Supplying Multiple Zones" application referenced above.) As discussed above in the section entitled "Programming The Monitor", each zone thermostat 32-37 may employ supplemental zone heating sources. Two features of the monitor 12 can be made operative if supplemental heat is used with a given thermo-stat 33-37. When the monitor 12 is not in the heating, cooling, or ventilation mode, fan 20 can be energized in FAN-LO when any thermostat 33-37 energizes its supplemental heat sources. In addition, when any zone thermostat 33-37 energizes its supple-mental heat, the thermostat 33-37 may be considered a heating caller regardless of zone demand.

DIAGNOSTICS
Finally, the fan-box monitor 12 employs programming diagnostics to display error data on display 13. Such error data includes system errors such as temperature or pressure sensors out of the operating range and errors regarding the movement of damper 11. Also included in diagnostics is informa-tion indicating whether supply air temperature to the fan-powered mixing box assembly 10 is out of the range required for proper overall system operation.

., ~ -27-.

1 3 ~

While the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention.
It is intended, therefore, by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.

-~8-

Claims (47)

1. In a system employing a unit for controlling the condition of air supplied to a plurality of zones via a main duct when using a fan-powered mixing box assembly in said main duct and having a fan and at least one heating element for heating air supplied to said main duct to supply conditioned air to each said zone via a master damper means controlling air flow in said main duct and a zone damper means in a zone duct communicating between said main duct and each said zone, a programmable fan-box monitor means controlling said fan-powered mixing box assembly, said programmable fan-box monitor means receiving information from a controller means located in each zone interfaced with and controlling respective said zone damper means in respective said zone duct, means for determining the condition of the air in each said zone and supplying such information to said fan-box monitor means, said fan-box monitor means operating said fan-powered mixing box assembly in accord-ance with its programming, the condition of air in each zone, and in accordance with the information received from each said controller means to control said fan-powered mixing box in the heating or cooling mode.

2. In the system as defined in Claim 1 wherein said controller means includes a zone thermostat, said means for determining the condition of air in each said zone including a first sensor for determining the temperature of the air in its respective said zone, said first sensor providing electri-cal signals to said thermostat indicative of the temperature of the air in respective said zone.

3. In the system as defined in Claim 2 wherein said zone thermostat includes means for establishing the desired termpera-ture in respective said zone.

4. In the system as defined in Claim 3 wherein said programmable fan-box monitor means determines the demand for heating or cooling from all said zone thermostats, determines the number of zone having demand for heating or cooling, compares such number with a preselected number defining the system demand number, and if the number of zones demanding heating or cooling equals or exceeds said system demand number, said fan-box monitor means selects the desired heating or cooling mode respectively of said fan-powered mixing box assembly and provides output signals to all said zone thermo-stats for operating respective said zone damper means, said fan-box monitor means operates said fan-powered mixing box assembly in the selected mode until all said zone thermostats demanding the selected mode have been substantially satisfied.

5. In the system as defined in Claim 4 wherein said fan-box monitor means has a first program means such that said fan-powered mixing box assembly is operated in a ventilation mode when the demand for heating or cooling from all zones is less than said system demand number.

6. In the system as defined in Claim 4 wherein said fan-box monitor means compares the number of zones having a demand for heating and cooling and if the number of zones having a demand for heating is equal to the number of zones demanding cooling and the numbers equal or exceed the system demand number, said fan-box monitor means selects the zone with the greatest demand as a reference zone and operates said fan-powered mixing box assembly in the mode coincident to that demanded by said reference zone until said reference zone is substantially satisfied.

7. In the system as defined in Claim 6 wherein said fan-box monitor means periodically determines the demand from each zone and, if the demand in another said zone, having a demand coincident with the mode in which said fan-powered mixing box is operating is greater than said reference zone, said other zone is selected as a new reference zone and said fan-powered mixing box assembly is operated until demand in said new reference zone is substantially satisfied.

8. In the system as defined in Claim 7 wherein said fan-box monitor means receives data from said reference zone when said fan-powered mixing box assembly is operated in the heating mode, said fan-box monitor means provides an output signal to said fan-powered mixing box assembly for energizing said heating element in accordance with the demand of said reference zone.

9. In the system as defined in Claim 8 wherein said fan-box monitor means includes a first program means such that when the number of zones demanding heat exceeds a predetermined number defining the heating demand qualifier number, said fan includes a multi-speed motor, said fan-box monitor means provides an output signal to said fan-powered mixing box assembly for increasing the speed of said fan motor.

10. In the system as defined in Claim 1 wherein said fan-box monitor means includes a first sensor for determining the temperature of air adjacent said heating elements and de-ener-gizes said heating elements of said fan-powered mixing box assembly if said air temperature exceeds predetermined setpoints established by said fan-box monitor means.

11. In the system as defined in Claim 1 wherein said fan-box monitor means includes indicating means for providing data indicative of the information associated with the opera-tion of said fan-powered mixing box assembly.

12. In the system as defined in Claim 1 wherein said fan-box monitor means includes a first sensor for determining the temperature of outside air.

13. In the system as defined in Claim 12 wherein said fan-box monitor means includes a first program means such that when said fan-box monitor means receives a signal from said first sensor indicating outside air temperature is greater than a predetermined value, said fan-box monitor means maintains said heating elements in off condition even if demand therefor is called for by any said zones.

14. In the system as defined in Claim 12 wherein at least one said zone has a heating source independently controlled by said zone thermostat, said fan-box monitor means includes a first program means such that when said fan-box monitor means receives a signal from said first sensor indicating outside air temperature is greater than a predetermined value, the operation of said heating source by said zone thermostat is disabled by a signal from said fan-box monitor means to said zone thermostat.

15. In the system as defined in Claim S wherein said fan-box monitor means includes a second sensor for determining the temperature of air in said main duct supplying air to respective said zone ducts said fan-box monitor means further including a second program means such that when said fan-powered mixing box assembly is operated in the ventilation mode, said fan-box monitor means will operate said master damper and said fan motor to maintain main duct temperature within predetermined setpoints as established by said fan-box monitor means.

16. In the system as defined in Claim 4 wherein said fan-box monitor means includes a second sensor for determining the air pressure in said main duct.

17. In the system as defined in Claim 16 wherein said fan-box monitor means includes first program means such that said fan-box monitor means operates said master damper to maintain duct air pressure within predetermined setpoints as established by said fan-box monitor means.

18. In the system as defined in Claim 4 wherein said fan-box monitor means includes a first program means such that when the heating mode has been selected by said fan-box monitor means, said fan motor is energized and said at least one heating element is not energized unless the heating demand exceeds a predetermined level established by said fan-box monitor means.

19. In the system as defined in Claim 18 wherein said fan includes a multi-speed motor, said fan-box monitor means operating said fan motor in accordance with the programming of said fan-box monitor means.

20. In the system as defined in Claim 19 wherein said fan-box monitor means includes a second program such that if said motor of said fan has been energized in low speed, said fan-box monitor means will compare the number of zones demanding heat with a predetermined number defining the heating demand qualifier number established by said fan-box monitor means and if said number of zones equals or exceeds the heating demand qualifier number said motor will be operated in high speed.

21. In the system as defined in Claim 20 wherein said fan-box monitor includes a second sensor for determining the air pressure in said main duct, said fan-box monitor means further including third program means such that when said fan-box monitor means is operating said motor in high speed, said motor will remain operating in high speed until the number of zones demanding heat is less than the heating demand qualifier number and the air pressure in said main duct is greater than a maximum predetermined setpoint as established by said fan-box monitor means.

22. In the system as defined in Claim 4 wherein said fan-box monitor means includes a first program means such that when said fan-box monitor means is actuated in the heating mode, the zone having the greatest demand for heating is chosen as a reference zone, said fan-box monitor means providing out-put signals to said fan-powered mixing box assembly for energiz-ing said heating element in accordance with the demand of said reference zone.

23. In the system as defined in Claim 22 wherein said fan-box monitor means includes a second program means such that when heating demand in the reference zone exceeds a first predetermined value, said fan-box monitor means will provide an output signal to said fan-powered mixing box assembly for increasing the heating supplied to said reference zone by said fan-powered mixing box assembly.

24. In the system as defined in Claim 23 wherein said fan-box monitor means includes a third program means for monitoring the temperature trend in said reference zone such that said fan-box monitor means will not provide an output signal to said fan-powered mixing box assembly for increasing the heating supplied to said reference zone when the tempera-ture trend in said reference zone indicates that the heat demands of said reference zone are being substantially satisfied.

25. In the system as defined in Claim 5 wherein said fan-box monitor means has a second program means for monitoring the temperature trend in said reference zone when said fan-powered mixing box is being operated in the heating zone, said fan-box monitor means selectively controlling said heating element in response to said temperature trend.

26. A method of controlling the operation of a plurality of zone duct damper means located in respective zone ducts and a fan-powered mixing box assembly controlled by a controller means that supplies conditioned air into a main duct having a master damper means in the main duct which communicates with zone ducts associated with respective zones each having a zone damper means and a means of determining the desired zone setpoint and the zone temperature comprising the steps of:
A. determining the demand for heating or cooling from all the zones;
B. determining the number of the zones having a demand for heating or cooling;
C. selecting a heating, cooling, or ventilating mode based upon mode demand;
D. operating the appropriate zone damper means to closed position if the means controlling the appropriate dampers have no demand or demand a mode different than the mode selected in step C, and positioning open the other zone dampers;

E. actuating the fan-powered mixing box assembly in the selected mode and operating the master damper until all zones demanding the selected mode have been satisfied;
F. deactivating the fan-powered mixing box assembly; and G. repeating steps A - F for the other mode when demand for the other mode has been selected in accord with steps A - C.

27. The method of Claim 26 wherein step B includes the steps of:
H. selectively preselecting the number of the zones having demand for heating or cooling that is necessary to select a heating or cooling zone;
I. comparing the numbers obtained in steps B and H
and selecting the heating or cooling mode when the number of the zones having a demand for heating or cooling respectively is equal or greater than the number selected in step H.

28. The method of Claim 26 wherein step D includes the step of:
H. actuating some of the zone dampers to a partially open position depending upon the amount of demand by their respective thermostats and modulating such dampers between open and closed until the demand is satisfied.

29. The method of Claim 26 further comprising the step of:
H. comparing the number of demands after steps A - B
and if the demands for heating and cooling are equal, the zone with the greatest demand is chosen as the reference zone and the fan-powered mixing box assembly is activated in step E in the mode coincident with the demand of the zone with the greatest demand.

30. The method of Claim 29 further comprising the step of:

I. increasing or decreasing the heating output of the fan-powered mixing box assembly by the fan-box monitor in accordance with the demand of the reference zone.

31. The method of Claim 29 further comprising the steps of:
I. determining the temperature in the heating compart-ment of the fan-powered mixing box assembly; and J. deactivating the heating output of the fan-powered mixing box assembly by the controller if the heating compartment temperature exceeds predetermined setpoints established by the controller.

32. The method of Claim 29 further comprising the steps of:
I. determining the number of zones demanding heating;
and J. increasing the speed of the fan in the fan-powered mixing box assembly when the number of zones demanding heating exceeds a predetermined number as established by the controller.

33. The method of Claim 29 further comprising the step of:
I. activating the fan-powered mixing box assembly by the fan-box monitor in the ventilation mode when the number of zones demanding heating and cooling is less than a predetermined number as establsihed by the fan-box monitor.

34. The method of Claim 29 further comprising the steps of:
I. determining the outside air temperature outside the zones; and J. deactivating the fan-powered mixing box assembly by the fan-box monitor when the outside air temperature is greater than a predetermined value as established by said fan-box monitor.

35. The method of Claim 29 further comprising the steps of:
I. determining the air pressure in the main duct; and J. operating the master damper means by the fan-box monitor to maintain air pressure within setpoints as established by the fan-box monitor.

36. A method of monitoring and controlling the condition of air within each of a plurality of zones being supplied with conditioned air through zone dampers and zone ducts from a fan-powered mixing box assembly via a main duct communicating with the zone ducts and a master damper means in the main duct, a programmable fan-box monitor controls the master damper means and the fan-powered mixing box assembly, and programmable zone thermostats in respective zones control respective zone dampers comprising the steps of:
A. programming the setpoints of the zone thermostats during a plurality of distinct time periods;
B. activating the mixing box assembly by the fan-box monitor in the selected mode until all the zone thermostats demanding the selected mode have been satisfied;
C. positioning the zone duct damper means open if the zone thermostats are demanding the selected mode and closed for the other zone damper means; and D. deactivating the mixing box assembly by the fan-box monitor.

37. The method of Claim 36 further comprising the steps of:
E. determining the real time;
F. monitoring the demand for heating or cooling from all zone thermostats by the programmable fan-box monitor which selects either of the heating or cooling mode of the mixing box assembly during a distinct time period.

38. The method of Claim 37 further comprising the step of:
G. selecting the mode of operation of the mixing box assembly in step F in accordance with the programming of the fan-box monitor such that when an equal number of zones demand heating and demand cooling during a distinct time period and the number of such zones is greater than a preselected number programmed in the fan-box monitor the zone with the greatest demand is chosen as the reference zone and the mixing box assembly is operated in a mode coincident with the mode demanded by the zone with the greatest demand.

39. The method of Claim 38 further comprising the step of:
H. increasing or decreasing the heating output of the mixing box assembly by the fan-box monitor in accordance with the demand of said reference zone.

40. The method of Claim 38 further comprising the steps of:
H. determining the temperature in the heating compart-ment of the mixing box assembly; and I. deactivating the heating output of the mixing box assembly by the fan-box monitor if the heating compartment temperature exceeds predetermined setpoints established by the fan-box monitor.

41. The method of Claim 38 further comprising the steps of:
H. determining the number of zones demanding heating;
and I. increasing the speed of the fan in the fan-powered mixing box assembly when the number of zones demanding heating exceeds a predetermined number as established by said fan-box monitor.

42. The method of Claim 38 further comprising the step of:
H. activating the mixing box assembly by the fan-box monitor in the ventilation mode when the number of zones demanding heating and cooling is less than a predetermined number as established by said fan-box monitor.

43. The method of Claim 38 further comprising the steps of:
H. determining the outside air temperature outside the zones; and I. deactivating the mixing box assembly by the fan-box monitor when the outside air temperature is greater than a predetermined value as established by said fan-box monitor.

44. The method of Claim 38 further comprising the steps of:
H. determining the air pressure in the main duct; and I. operating the master damper means by the fan-box monitor to maintain air pressure within setpoints as established by said fan box monitor.

45. A method of controlling the operation of a plurality of zone duct damper means located in respective zone ducts and a fan-powered mixing box assembly controlled by a means supplying conditioned air into a main duct having air flow control means in the main duct which communicates with zone ducts associated with respective zones comprising the steps of:
A. determining the demand for heating or cooling in all zones and the heating or cooling mode for the fan-powered mixing box;
B. controlling the fan-powered mixing box in the heating or cooling mode selected;

C. operating zone duct dampers to close all not desiring conditioned air from the fan-powered mixing box in the mode selected and to open all desiring conditioned air in the mode selected; and D. operating the air flow control means and the fan-powered mixing box to control air supplied to the zones until all zones demanding the selected mode have been substan-tially satisfied.

46. The method of Claim 45 further comprising the steps of:
E. determining the zone which has the greatest demand after step A; and F. operating the air flow control means and the fan-powered mixing box to control air supplied to the zones until the reference zone has been substantially satisfied.

47. The method of Claim 46 further comprising the steps of:
G. measuring the temperature trend in the reference zone when the fan-powered mixing box is in the heating mode; and H. operating the fan-powered mixing box to supply heating to the reference zone in response to the temperature trend.