One Person's Opinion: Balancing Act (December 2000)
Labor Saving Combination ValvesBalance valves include ball valves, manual balancing valves, and automatic flow limit controls. Temperature controls include globe valves and actuated ball valves. Piping components from 0.5- to 2-in. for terminal units include isolation ball valves, bushings, y-strainers, and unions. In the past, each of these had to be considered, installed, and paid for separately.
Today, products combine up to seven functions into one valve body. The return-side valve may feature an isolation ball valve, automatic flow limit control, actuated ball valve temperature control, union, air vent, PTs, and end connections or hoses. The supply side valve may include isolation ball valve, y-strainer, blow-down drain valve, union, PTs, and end connections or hoses. Manufacturers now assemble, package, and specifically label these combination valves into sets for on-site delivery to contractors.
Innovative combination products also add performance by applying the parabolic curve to limit flow in automatic flow controls, to quickly set venturi balance ball valves, and to achieve a near equal percentage characteristic in actuated ball valve modulating temperature controls. A parabolic flow orifice, commonly called a "characterizer" or "optimizer," allows a greater range of Cv's for more accurate selections, delivers a near equal percentage characteristic, and enhances design accuracy. In addition, the installed footprint is smaller, the products are lighter in weight, and product/installation/balance costs are lowered.
Accuracy & Energy EfficiencyMechanical product designs for boilers, chillers, and pumps are reaching their maximum cost-effective efficiency. Balancing valves are a next-generation opportunity for reducing energy consumption and operating costs of building mechanical systems. Accuracy can be misunderstood in manufacturers' literature unless design engineers put valve selection into the context of the complete system installation and balance method used for building commissioning. It is easy to incorrectly equate the most accurate product feature (1%, 3%, 5%) with the accuracy of the entire system's performance (5%, 10%, 20%).
As you read literature and listen to presentations, ask questions about the several product types and manufacturers' offerings. Range and accuracy are dominant characteristics of manual balance valves, but they are inherently dependent on the proportional balance method, which is static - not dynamic - in nature.
If you want to optimize the system balance dynamically, the automatic flow control is the preferred choice - particularly in today's pumping systems with variable-frequency drives. A simple pressure differential check on a selected sample of automatic flow limit controls can achieve dynamic balancing of the building system. The penalty of increased pressure in the index circuit is small compared to the benefit of pressure absorption that dynamically and automatically redistributes flow to demand. It is the dynamic accuracy (after the balance contractor leaves the job) that defines the impact of balancing valves on reducing the operating cost of the building hvac system.
Flow Limit Plus Temperature ControlFlow limit and actuated ball valve temperature controls can be integrated into the same valve body because they perform sequentially. Temperature controls are selected by Cv's to achieve a specific upward limit gpm flow. While actuated ball valves now provide more Cv selection than traditional globe valves, there can still be overflow conditions at a specific coil location.
This is when the automatic flow limit control does its job. It only limits flow to the specific gpm selected for a specific coil and thereby permits the unwanted water to be diverted (to less resistant circuits) and flow through the system to meet demand from other locations. The temperature control has complete authority throughout its design flow; the automatic flow control has authority only when the temperature control is fully open and flow would normally exceed the specific gpm selected by the design engineer.
Ball valves, balancing valves, temperature controls, and new balance/temperature control products are available from engineered products manufacturer reps, controls manufacturer reps, traditional controls distributors, e-commerce catalog distributors, pipe and fitting distributors, and manufacturers' direct-ship.
As design engineers, maintenance engineers, and distribution channels learn about combination balance/temperature control valves and packages through business commerce, they will cross over traditional specification boundaries to offer owners greater energy efficiency and increased productivity from the design, distribution, and maintenance chain. ES