Method and apparatus for multi-zone air distribution system

A zoned HVAC system for a building is provided with three control zones: an internal zone (14), a perimeter zone (16) and a skin zone (18). The internal zone (14) provides cooling of internal heating loads from equipment and personnel as determined from internal zone (14) thermostats (43, 46, 48). Perimeter zone (16) provides cooling against interior and solar heating loads, with thermostats (51, 52, 53, 54) controlling associated sectors dampers (56, 57, 58, 59). The skin zone (18) provides both heating and cooling against thermal transmissions through the building exterior (10). Each skin zone sector (30, 31) is assigned to a plurality of perimeter zones (24, 25, 26, 27). Operation of a skin zone sector (e.g. 30) is effected by a control box (e.g. 64) receiving inputs from perimeter zone thermostats (e.g. 51, 52) with a control output functionally related to the perimeter zone sector with the lowest cooling demand.

TECHNICAL FIELD 
This invention relates generally to heating, ventilating, and air 
conditioning (HVAC) systems and, more particularly, to methods and 
apparatus for controlling and sequencing the distribution of conditioned 
air in a multi-zone HVAC control system. 
BACKGROUND OF THE INVENTION 
HVAC systems have improved considerably in efficiency and utility from the 
early on-off systems where an entire volume was being conditioned as a 
function of a single thermostat. Building designs using skin facade 
structures and windows rather than more substantial exteriors tend to 
exaggerate thermal transmissions across the building exterior. Electrical 
office equipment and lighting can exhaust substantial heat, generally in 
the central area of a work space. Thus, heating and cooling requirements 
for an HVAC system tend to be a function of location within the volume 
served by the system. 
With the advent of flexible control systems and the impetus of improved 
efficiency, zoned HVAC systems began to develop. Controlled zones can be 
arranged to provide for exterior spaces having a variety of solar heating 
loads and building thermal transmission loads and for interior spaces 
having a relatively constant and uniform cooling requirement from heat 
generated by the people, lighting and equipment in the interior space. 
A typical early HVAC zoned system simply had two systems responding 
independently to the demands of the interior and exterior zones. One 
improvement was to space several exterior zones about the periphery to 
accommodate substantial changes in solar heat loads as a function of 
building exposure, seasonal changes and hourly variations in sun location. 
Typically, an interior zone has only cooling requirements and the air flow 
is controlled by dampers in air distribution ducts connected with a 
central air shaft. The exterior zone typically has a number of 
controllable sectors, with each sector having a thermostatic sensor, 
cooling air flow damper controls and an air heating system. The heating or 
cooling of each sector is controlled by the thermostatic sensor in that 
sector. 
Applicant is also aware of a three zone HVAC distribution system. An 
interior zone is provided as described above. A first exterior zone is 
then provided around the interior zone to generally accommodate solar 
heating loads and a second exterior zone is provided about the first 
exterior zone to generally accommodate thermal transmissions through the 
building exterior facade. Each zone may include a plurality of sectors 
where each zone sector has a dedicated associated thermostatic control 
system. Further, each sector of each second exterior zone includes a 
heating system. 
The three zone system generally described above offers some operational and 
efficiency improvements. However, a substantial amount of heating 
equipment is required to complete each second exterior zone sector. 
Further, adjacent sectors in a second exterior zone can become unstable 
where one sector is heating and the adjacent sector is cooling responsive 
to the heat input, and vice versa. A second exterior zone sector may even 
be trying to heat cooled air from the central air shaft. 
These and other disadvantages of the prior art are overcome by the present 
invention, and an improved HVAC air transmission distribution and control 
system is provided. 
SUMMARY OF THE INVENTION 
A zoned HVAC system is provided for a building having an improved air 
distribution system. A perimeter duct zone is provided with a cooling 
capacity suitable for expected thermal radiative heating loads. Around the 
perimeter zone is a skin duct zone having both cooling and heating 
capacities sized for expected thermal transmissions through the building 
exterior facade. 
Control inputs for the perimeter and skin duct zones are provided by a 
plurality of thermostats operatively located to control a corresponding 
plurality of perimeter zone sectors. The outputs of the thermostats are 
combined to obtain a single control signal for the entirety of a 
designated skin zone operatively assigned to a number of perimeter zone 
sectors. 
It is a feature of the air distribution system according to one embodiment 
of the present invention that a designated skin zone has a single fan and 
heater unit serving a plurality of skin zone sectors. 
It is another feature that the perimeter zone sector thermostatic output 
indicative of the greatest need for heating is selected to control the 
designated skin zone assigned to the perimeter zone sector. 
It is yet another feature that the cooling output of the perimeter zone 
sectors will be damped closed before the skin zone heater is activated. 
One other feature is deriving a control signal for the skin zone from a 
plurality of thermostats, each thermostat operatively located for 
controlling a perimeter zone sector. 
These and other features and advantages of the present invention will 
become apparent from the following detailed description of the preferred 
embodiment, wherein reference is made to the figures in the accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, there is shown a mechanical schematic of a 
heating-ventilating-air conditioning (HVAC) system embodying the present 
invention. Building exterior 10 is provided with an HVAC system having 
three heat load zones defined therein. An internal zone 14 is provided for 
handling heat loads such as equipment, lighting, occupants, etc. typically 
generated at locations remote from building exterior 10. Perimeter zone 16 
is provided to accommodate some mechanical heat loads and, additionally, 
solar heat loads from the radiative heating of the sun. Finally, skin zone 
18 is provided to accommodate thermal loads from heat transmission through 
building exterior 10. 
In a conventional HVAC system, mechanical shaft 11 operates as a downcomer 
for cooled air. The cooled air is moved by common fans located adjacent 
the cooling system (not shown). The cooled air is then provided to primary 
distribution ducts 12 and the distribution is thereafter controlled by 
dampers in control zones 14, 16 and 18. The operation and interaction of 
control zones 14, 16 and 18 according to the present invention afford 
increased efficiencies and economies. 
Internal zone 14 primarily furnishes cooling in response to various 
internal mechanical heat loads, discussed above. Internal zone ducts 20, 
21 and 22 are schematically shown for distributing conditioned air within 
internal zone 14. Actual air outlet registers and connecting flexible duct 
work to the outlet registers are not shown, and the actual location may be 
selected based on the architectural configuration and placement of heat 
generating equipment. Thermostats 43, 46 and 48 may be placed within 
selected locations of internal zone 14 for determining the zone cooling 
requirements. The thermostats may conveniently be pneumatic reverse-acting 
thermostats, as described below for other zones, to control damper 
actuators 44, 47 and 49 in ducts 20, 21 and 22, respectively. 
Thus, internal zone 14 furnishes only cooled air in a quantity sufficient 
to maintain the output of thermostats 43, 46 and 48 within a preselected 
band about a desired temperature. As the heat load of internal zone 14 
decreases, damper actuators 44, 47 and 49 act to close their respective 
dampers and reduce the cooled air volume being provided to internal zone 
14. As shown herein, internal zone 14 is independent of zones 16 and 18 
since it is not expected that internal zone 14 will require direct heating 
inputs to raise the zone temperature. 
Perimeter zone 16 is the next control zone outward of internal zone 14. 
Perimeter zone 16 is also provided with cooled air flow from mechanical 
shaft 11 through primary distribution ducts 12. A plurality of sector 
distribution ducts 24, 25, 26 and 27 are provided for distributing cooled 
air within zone 16. Associated with sector ducts 24, 25, 26 and 27 are an 
additional plurality of outlet air registers and connecting flexible duct 
work. These items are omitted for clarity, but are also generally located 
in accordance with architectural considerations within the zone and the 
solar exposure of the adjacent building exterior. 
Thermostats 51, 52, 53 and 54 are depicted within zone 16 for detecting 
temperatures within perimeter zone 16. As shown, thermostats 51, 52, 53 
and 54 are operatively associated with perimeter zone sector duct systems 
24, 25, 26 and 27, respectively. The output from sector thermostats 51, 
52, 53 and 54 are provided to control boxes 64 and 65 with associated 
control system outputs for sector damper actuators 56, 57, 58 and 59, 
respectively. Thus, each perimeter zone sector thermostat will actuate a 
damper control in the perimeter zone sector duct system adjacent the 
thermostat to control the zone sector input air volume adjacent the input 
thermostat. 
About the periphery of building exterior 10 is provided skin zone 18. Skin 
zone 18 is provided with cooling air from primary distribution ducts 12, 
as are perimeter zone 16 and internal zone 14. However, skin zone 18 
further provides for distribution of heated air as necessary to control 
heat losses from the interior of the building through building exterior 
10. 
Skin zone duct systems 30 and 31 are provided with damper actuators 61 and 
62 for controlling the cooling air flow. Again, a plurality of outlet air 
registers and associated flexible ducts are provided, although not shown 
in FIG. 1. However, skin zone duct systems 30 and 31 are further provided 
with air mixing boxes 32 and 33 and with skin zone heaters 35 and 36 for 
providing a heating air flow in addition to a cooling air flow. Air mixing 
boxes 32 and 33 are preferably similar to the apparatus disclosed in U.S. 
Pat. No. 3,951,205 to Zilbermann and U.S. Pat. No. 4,203,485 to Zilbermann 
and Aronoff. Heaters 35 and 36 may likewise be similar to the duct heaters 
described in these U.S. patents. 
However, any suitable mixing box and duct heater may be used in accordance 
with the following functions. Mixing boxes 32 and 33 act to enable air 
from a return plenum to be recirculated back through skin zone ducts 30 
and 31 to recover heat which would otherwise be exhausted from a return 
plenum. Typically, an air volume is located above a floor ceiling 
structure and serves as the return air plenum. Heated cooling air tends to 
naturally rise into the volume for removal or recirculation. As 
hereinafter explained, heaters 35 and 36 provide all the heating for the 
three zones 14, 16 and 18 and are energized when the heat available from 
the return air plenum (not shown) is less than the heat lost through the 
building exterior 10 and the temperature within perimeter zone 16 drops to 
actuate at least one sector thermostat 51, 52, 53 or 54, as shown in FIG. 
1. 
In a preferred operational sequence, the heating and cooling portions are 
cooperatively staged so that the system does not attempt to heat air which 
has first been cooled. Thus, as the temperatures begin to decrease in 
perimeter zone 16, the outputs from thermostats 51, 52, 53 and 54 act to 
close air flow dampers 56, 57, 58 and 59, respectively, to decrease the 
cooling air flow from perimeter zone sector ducts 24, 25, 26 and 27. The 
control systems and control boxes 64 and 65, hereinafter explained, select 
the lowest cooling demand from the perimeter zone sector duct systems to 
control air flow in the associated skin zone duct system. In a preferred 
embodiment, and to provide operational stability, the perimeter zone 
sector thermostat indicating the greatest demand for heating, or having 
the lowest temperature, controls the air flow and temperature from the 
skin zone duct system 30 and 31 assigned to the particular perimeter zone 
sector. 
As hereinafter explained, as the thermostat outputs 51 and 52, for example, 
begin to indicate reduced sector temperatures, perimeter zone dampers 56 
and 57 will begin to move toward a closed position. When one of perimeter 
zone damper 56 or 57 is fully closed, skin zone air flow damper 61 will 
begin to close. Where thermostats 51 and 52 indicate the need for 
additional heat input, the blower in air mixing box 32 cycles on, causing 
the mixing box back flow air damper to open to the return air plenum and 
circulate return air, which has been heated during circulation through the 
zones, through skin zone duct system 30. When skin zone damper 61 is fully 
closed, i.e., only return air is being circulated, and thermostat 51 or 52 
shows a need for additional heat input, duct heater 35 will be activated 
to further heat the circulating air from air mixing box 32 for outlet 
through skin zone duct system 30. 
Referring now to FIG. 2, there is shown in schematic form a control system 
for carrying out the above operational sequence. Perimeter zone control 
system 70 includes sector thermostats 72, damper actuators 76 and relays 
78, as hereinafter explained. Skin zone control system 80 includes a 
system of relays and switches for actuating the damper of the associated 
skin zone duct system, for activating the return air circulating fan and 
for energizing the skin zone duct heaters in a staged manner. 
Perimeter zone control system 70 is depicted as having three thermostatic 
sector inputs 72. It will be appreciated that one thermostatic sector 
input 72 exists for each perimeter zone sector duct system (e.g., ducts 
24, 25, 26 and 27 in FIG. 1). In a preferred embodiment, thermostat 72 is 
a reverse acting pneumatic thermostat (i.e., the control pressure 
appearing at the output of the thermostat decreases as the temperature 
increases). The input pressure is provided by main pneumatic line 74, 
which may conventionally be a pressure of 20 psi. The outputs from 
thermostat 72 are provided to damper actuators 76. Damper actuators 76 are 
preferably connected with normally open dampers so that an increasing 
pressure applied to damper actuators 76 will act to close the associated 
damper. Thus, a decreasing temperature will cause an increasing pressure 
output from thermostats 72 tending to move damper actuators 76 in a 
direction closing the associated damper. 
As shown in FIG. 2, greater pressure relays 78 and 79 are provided. Greater 
pressure relays 78 and 79 take inputs at ports (5) and (3) and provide the 
greatest input pressure as the output pressure at port (2). Thus, with 
reverse acting thermostat 72, the greatest pressure is indicative of the 
lowest temperature and will appear at an output port (2). Greater pressure 
relay 78 is shown with two thermostatic sector inputs 72 which provide an 
input to greater pressure relay 79 at input port (5) in addition to a 
third thermostatic sector input 72 at port (3). The resulting output 
pressure at port (2) forms a single input signal 82 to skin zone control 
80 having a pressure indicative of the lowest perimeter zone sector 
temperature. 
Thus, while each thermostat 72 and perimeter zone control system 70 acts to 
operate its associated sector damper actuator 76 so that decreasing 
temperatures close the normally open dampers, a single output signal 82 is 
provided for an entire skin zone control 80. Input pneumatic signal 82 is 
directed to port (3) of sequencing pneumatic relay 84. The main pneumatic 
line pressure 74 is connected with input port (1) of relay 84. Sequencing 
relay 84 provides an output at port (2) such that for input pressure 
P.sub.1, there is an output pressure P.sub.2, where P.sub.2 is greater 
than P.sub.1. 
In a typical embodiment, the main pressure is 20 pounds at port (1) and is 
regulated by the pressure appearing at port (3) to obtain the output 
pressure at port (2). A typical input signal 82 is in the range of 7-12 
psi with an output pressure at port (2) regulated to be greater than input 
signal 82 but within the range of approximately 8-13 psi. 
The output signal from sequencing relay 84 is provided as output pneumatic 
signal 98 to regulate skin zone damper actuator 102 and to provide control 
signal 104 to a pneumatic-electric relay energizing a series of duct 
heaters (heater 35 in FIG. 1). The signal at output port (2) of relay 84 
is also provided to pneumatic-electric switch 86 to actuate electrical 
devices. Input power is provided at terminals 88. One terminal line is 
provided to a network of fuses and safety relays 90 to terminal "C" of 
switch 86. The electrical power connection to the duct heaters 92 and fan 
94 is provided through switch 86 at the "NO" contact where the connection 
between the "C" and the "NO" contacts is provided by pneumatic actuation 
of switch 86. 
Thus, through reverse acting thermostat 72, the pneumatic pressure applied 
to switch 86 increases as the temperature decreases. When a selected 
pressure is obtained, switch 86 closes the contact between terminals "C" 
and "NO" to provide power to a duct heater interlock at terminals 92 and 
to energize fan 94 through starting capacitor 96. 
As hereinabove explained, fan 94 is energized, causing heated return air to 
be recirculated through skin zone ducts 30. The pressure relationships for 
actuating damper controller 102, fan 94 and the heaters through signal 104 
are such that damper actuator 102 is about 50% closed before fan 94 is 
actuated through switch 86. Pneumatic signal 104 is provided to a 
plurality of pneumatic-electric switches, similar to switch 86, which 
energize heater elements in stages as the temperature decreases. The first 
heating stage is sequenced to actuate after damper actuator 102 has fully 
closed, fan 94 has attempted to recirculate return air and the temperature 
sensed by thermostats 72 has continued to decrease. 
It is apparent from the above description that a stable HVAC distribution 
system is obtained in the above arrangement. Skin control system 80 begins 
to provide heated input only after the cooling damper is closed in the 
associated skin zone and after return air flow has been established to use 
floor exhaust heat carried by the circulating air. Thus, thermostats in 
perimeter zone 16 (FIG. 1) are not trying to furnish cooling air at the 
same time the heating system in skin zone 18 is trying to heat skin zone 
18. It is also generally preferred to locate a skin zone 18 duct (e.g., 
duct 30) adjacent the same portion of building exterior 10 as the 
associated perimeter zone 16 duct sectors (e.g., ducts 24 and 25) to 
further coordinate thermal load requirements and stabilize operations of 
the adjacent zones. 
Further, the zoned system depicted in FIG. 1 permits a minimum of heating 
equipment to be utilized. The only heating equipment is provided in a skin 
zone 18 and only one air mixing box and one heating section (for example, 
air mixing box 32 and heating element 35) are provided for a skin zone 
associated with a plurality of perimeter zone sectors. Internal zone 14 is 
a substantially independent zone having thermostats generally removed from 
the heating and cooling associated with perimeter zone 16 and skin zone 
18. Each internal zone 14 duct system simply has a thermostat, which may 
conveniently be a reverse acting pneumatic thermostat, acting on a damper 
actuator to close the damper as the temperature decreases, indicating a 
reduction in the need for cooling air flow; see, for example, internal 
zone duct 22 with thermostat 48 and associated damper control 49. 
As many possible embodiments may be made of this invention without 
departing from the spirit or scope thereof, it is to be understood that 
all matters herein set forth and depicted in the accompanying drawings are 
to be interpreted as illustrative and not in any limiting sense.