Automatic temperature and humidity regulation – Ventilator type – Electrically actuated
Reexamination Certificate
2001-04-26
2003-06-24
Wayner, William (Department: 3744)
Automatic temperature and humidity regulation
Ventilator type
Electrically actuated
C236S06800R, C374S148000
Reexamination Certificate
active
06581847
ABSTRACT:
TECHNICAL FIELD
The present invention relates, in general, to heating, ventilating and air conditioning (HVAC) system and actuators therefor, and more particularly, relates to thermally-powered actuators for variable-air-volume diffusers.
BACKGROUND ART
In variable-air-volume (VAV) diffusers, room air temperature is controlled by varying the volume of supply air which is discharged into a room. The supply air will be heated when the VAV system is in a heating mode and it will be cooled when the system is in a cooling mode. The supply air is usually provided at substantially a constant temperature for each mode. A variable-air-volume diffuser, or an upstream VAV box, is used to regulate the volume of heated or cooled supply air in order to achieve and maintain the desired room air temperature. A central building controller is used to determine whether hot supply air or cool supply air flows from the HVAC air source to the VAV diffusers or box. It is possible, of course, for only cool air or only hot air to be supplied by the system. Thus, in the tropics cool supply air may always be flowing to the VAV diffusers or box.
Three types of actuators for VAV air diffusers and/or VAV duct boxes are in wide-spread use, namely, thermally-powered actuators, pneumatically-powered actuators, and electrically-powered actuators. All three types of VAV actuators are coupled through a mechanical linkage, gear assembly levers or the like to move one or more dampers, vanes, blades, etc., (hereinafter “dampers”), in the air diffuser or the control box upstream of the air diffuser. The damper position across a diffuser discharge opening, or the supply duct in the case of a VAV box, is modulated by a thermally-powered or pneumatically-powered actuator or by an electrical motor in response to sensed room air temperature. Thus, in a heating mode as the room air temperature rises toward the desired or targeted set point temperature, the damper closes down to reduce the amount of supply air being discharged into the room. Conversely, as the room air temperature drops away from the desired or targeted set point temperature, the damper is opened to allow an increase in the amount of warm supply air discharged into the room. In a cooling mode, as the room air temperature rises and moves away from the set point temperature, the actuator opens the damper to allow more cool air to enter the room. As the room air temperature drops toward the set point in the cooling mode, the damper is closed to reduce the volume of cool air discharged into the room.
Various thermal actuators, pneumatic actuators and motor assemblies have certain operating characteristics which favor their selection for particular applications. All of these prior art VAV actuators, however, have deficiencies which, if eliminated, would enhance their performance.
Thermally-powered actuator assemblies, are described in more detail in U.S. Pat. Nos. Re. 30,953; 4,491,270; 4,509,678; 4,515,069; 4,523,713; 4,537,347; and 4,821,955, which are incorporated herein by reference. Briefly, however, such assemblies will include a containment cylinder or housing filled with a thermally expandable and contractible material, such as a wax which expands or contracts during phase changes. A piston is reciprocally mounted to the containment housing so that the outwardly displaced piston, upon heating and expansion of the wax, can be used to power movement of a damper through a mechanical linkage. Cooling contracts and causes a phase change in the wax, and the piston is drawn into the housing, usually with the aid of a biasing spring.
As will be understood, the piston can be held and the housing allowed to move to drive the damper. Other forms of thermally-powered actuators can include bi-metal elements and memory metals which change shape at selected temperatures.
The response of a typical thermally-powered sensor/actuator can be seen in
FIG. 1. A
piston displacement versus temperature curve
21
is shown in which the piston is fully retracted at the bottom end of the curve and is fully extended at the top end. Since it is preferable that the piston displacement versus temperature be sensitive, the linkage assembly for most diffuser thermal actuators is constructed so as not to follow displacement curve
21
into either the extreme high or extreme low ends of the curve. Thus, a linear portion of curve
21
, namely, the portion defined by legs
23
and
25
, can be used to drive the diffuser damper by disengaging the piston from the linkage assembly at leg
22
and by providing an overtravel mechanism at leg
24
. This enables a relatively responsive or sensitive relationship to be maintained for controlling diffuser damper opening and closing. A typical actuator piston stroke used for the sensor/actuator is only about 0.1 inch, and the linkage assembly amplifies the stroke to produce longer diffuser damper displacements.
In
FIG. 1
, a typical sensor/actuator for cooling mode control is shown. Once the sensor senses that the room air temperature induced to flow through the diffuser is below 70° F., no more cool supply air will be discharged into the room because the damper will be closed. As the sensed temperature increases (when the room begins to heat up) from below 70° F., the damper does not open because the diffuser sensor/actuator is now operating on leg
22
of curve
21
. The piston displacement is shown as broken line
22
a
, and it will be disengaged from the damper-driving linkage assembly. As the sensed temperature increases between 71.5° F. to 73° F., however, the thermal sensor/actuator, through the linkage assembly, begins to open the damper until it is fully open at 73° F., which is leg
23
of curve
21
. For temperatures above 73° F., the damper will remain in the fully open position as the actuator piston continues to move outwardly against an overtravel mechanism, as indicated by broken line
24
a.
When the temperature drops to 73° F., the damper remain fully open until the temperature reaches 71.5° F. (i.e., leg
24
of the curve). As the temperature drops from 71.5° F. to 70° F., the damper begins to close, as shown by leg
25
of curve
21
. As will be seen, therefore, there is a hysteresis effect in displacement vs. temperature curve
21
of a typical thermally-powered sensor/actuator's response, which effect always opposes a reversal in motion.
In many applications the thermally-powered sensor/actuator assembly hysteresis effect can be tolerated, but in some applications it would be preferable to be able to tailor or modify displacement vs. temperature curve
21
in order to optimize actuator performance. For example, the hysteresis effect could be substantially eliminated by shortening or eliminating legs
22
and
24
of curve
21
. Moreover, the sensitivity of the thermal actuator also could be advantageously changed. Curve legs
23
and
25
, for example, might be made to be near vertical, so that full displacement of the actuator piston would occur over a very small room temperature, or process variable, change, for example, 0.2 degrees, rather than 1.5 degrees. It is desirable in many applications, for example, to be able to control room temperature to within about 0.5° F. or less.
Still further, the temperature at which the diffuser actuator opens or closes the damper could advantageously be modified or controlled without changing the actuator wax or adjusting the mechanical linkage between the actuator and the displaceable diffuser damper.
Another source of hysteresis in thermally-powered, VAV, diffuser assemblies is the mechanical linkage between the thermal actuator and the movable damper. When a reversal of the direction of displacement of the damper occurs, for example, the cumulative tolerance and friction effects in the diffuser linkage assembly can produce a lag before diffuser damper displacement occurs.
Still another source of performance affecting factors in thermally-powered diffusers is the positioning or location in the diffuser of the sensor/actuator element. In most thermally-powered, VAV diffusers, the t
Costick Matthew L.
Hunka Robert S.
Kline James R.
Acutherm L.P.
Chickering Robert B.
Dorsey & Whitney LLP
Wayner William
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