Heat exchange – With timer – programmer – time delay – or condition responsive... – Temperature responsive or control
Reexamination Certificate
2000-05-04
2002-03-05
Wayner, William (Department: 3744)
Heat exchange
With timer, programmer, time delay, or condition responsive...
Temperature responsive or control
C062S201000, C236S07800D, C237S00800C
Reexamination Certificate
active
06352106
ABSTRACT:
TECHNICAL FIELD
This invention pertains to the field of heating, ventilation, and air conditioning and, more specifically, to an improved type of control valve and method of actuation for improved efficiency of operation and longer valve and actuator operating life in a variable-flow fluid distribution system.
BACKGROUND OF THE INVENTION
This invention pertains to systems in which a fluid, such as hot or chilled water, is pumped into a header or main distribution network with the intention of distributing it into a series of outlets or devices wherein the quantity of such fluid through each outlet into each device is intended to be regulated so as to meet a particular condition such as a variable thermal load or other variable condition that requires a continuously regulated, variable flow through such outlet into such device. Fluid distribution systems are regularly employed in buildings and industrial facilities for heating, air conditioning, and many processes in which continuously regulated flow through multiple outlets and into multiple devices is required to meet constantly changing load requirements. Typical applications of such systems include heated or chilled water distribution systems that serve multiple thermal loads, each with the capacity to continuously adjust the flow through a thermal device (air coil, radiant panel, or other heat transfer device).
Such a system is shown in FIG.
1
. In
FIG. 1
, a fluid distribution system serves a number of loads, A through N, each of which employs a modulating valve
111
A through
111
N and a modulating valve actuator
116
A through
116
N operated by a control device
120
A through
120
N that is capable of sending a control signal
117
A through
117
N, the purpose of which is to adjust the fluid flow through the load to meet the current load requirements. A load can be any end device or equipment that is served by the fluid distribution system.
The flow of fluid, in this case water, through each outlet is regulated to control the flow of chilled or heated water through a coil
114
A through
114
N, which conditions air that is being circulated from the space and through the coil by a fan
118
A through
118
N. The valve can be installed on the inlet to the load, or the outlet from the load, but is usually installed on the outlet as shown in
FIG. 1
to reduce noise of the water in the coil, which would be transferred to the air. Positioning of the valve on the load outlet is also preferred to reduce the temperature extremes to which the valve is exposed. The opening of each water control valve is modulated to maintain a specific temperature of air being supplied to the space as measured by a supply air temperature sensor
122
A through
122
N or to maintain some other parameter that requires continuously adjustable flow through the load. The temperature of the space is often regulated by another temperature sensor
124
A through
124
N, which is located in an enclosed area or space
128
A through
128
N, or as required to sense the temperature, and therefore load condition, of the space. When employed to modulate heating or cooling water for commercial or industrial processes, the configuration in
FIG. 1
may vary slightly. The method of obtaining an error signal to control a load valve for space or process thermal control is well known and not a subject of this invention.
Such a hydronic thermal distribution system may be quite extensive, serving an entire building, or sometimes multiple buildings. To ensure adequate fluid is supplied at all times to all the loads, the prime mover, in this instance one or more electrically driven centrifugal pumps
150
, which circulate water through a closed circuit that is heated or cooled by a heat exchanger
158
or some other means, is often operated by a variable speed drive
154
. Pump motor speed is adjusted by a digital or other type controller
156
to maintain a differential pressure between a water supply header
162
and water return header
166
, using a differential pressure sensor
168
. The differential pressure sensor is typically installed at, or very near, the end of the distribution system to ensure the design fluid pressure is maintained at a minimum setpoint throughout the distribution circuit.
FIG. 1
is typical of the type of hydronic pumping systems that are employed to distribute heated or chilled water to systems within buildings, or to multiple buildings in a campus type arrangement. The distribution system in
FIG. 1
serves a total of “N” loads, but only the first (A) and last (N) are shown. Flow to each device is regulated by some thermal sensing means linked to a controller that operates a modulating valve. The pump(s) is (are) controlled by one or more differential pressure sensor(s) at or near the end of the distribution piping main(s). This method of regulating pump operation is also well known and not a subject of this invention.
In such systems, each valve is modulated from full closed to full open to meet the flow or capacity requirements of the device to which it is connected. For example, if, as in
FIG. 1
, the device is a heating or cooling coil in an air supply system for comfort conditioning, the valve may be modulated to maintain a specific air temperature into the space served by the device. As the load in the space changes due to loads external or internal to the space, the space temperature sensor senses the change in space temperature and control logic is employed to adjust the valve in order to change the temperature of the air supply to the space. In other applications, the control valve may be modulated to maintain parameters other than air discharge or space temperature. In present art, each modulating control valve is carefully selected to ensure when full open the valve will permit the correct flow to meet the maximum design load at the design distribution pressure conditions.
Distribution systems of the type shown in
FIG. 1
are very commonly employed in comfort and process control systems, but they do have several important limitations that reduce their effectiveness and efficiency. Furthermore, such conventional systems require very frequent valve repositioning and thus do not work effectively with newer electronically operated “ball” style valves for which frequent repositioning reduces their life. In addition, conventional design practice encourages designers to size valves with substantial pressure drops across each valve to obtain stable operation. This design practice adds to pumping energy requirements for the system pump or pumps. Finally, although valve sizing is based on a single design pressure across the valve and coil that is used to operate the pump, loads not located near the pressure sensor are often subject to a wide range of pressures that are generally much larger than the design pressure. This causes control instability and also leads to a system problem called “low Delta T” wherein a much larger quantity of fluid must be pumped through the system than designed because the temperature difference between supply and return is lower than the design value.
Consider that in the
FIG. 1
configuration the presence of the valve
111
A very close to the pump makes it very important the valve be carefully sized such that a fall open condition does not result in excessive flow that would limit the flow available to valves farther from the pump. This consideration makes it imperative that the control valves be sized small in comparison to the system piping so that no such “full open” valve will affect the capacity of other valves to serve their loads. Designers accomplish this valve sizing by calculating and specifying a specific “flow coefficient,” which is called the “C
v
” for each valve. The C
v
for a valve is the number of U.S. gallons of water per minute (GPM) that will flow through the valve in a wide open position with a pressure drop of 1 psi. It is determined by flow testing.
Because each valve is sized with a valve C
v
specifically selected for the load it serves, there may be as many different valve siz
Stoel Rives LLP
Wayner William
LandOfFree
High-efficiency pumping and distribution system... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High-efficiency pumping and distribution system..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High-efficiency pumping and distribution system... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2851914