By Chad Edmondson
We know we have to balance our hydronic systems to meet the ASHRAE 90.1-2010 Standard. The next question is what balancing technology should we use. For the most part, ASHRAE leaves that up to the designer. Here are the typical options:
Calibrated Balancing Valves. These have been around for a while and are what most people commonly refer to as “circuit setters.” Calibrated balancing valves are designed for pre-set proportional system balance. This system balance method involves pre-setting the valves to achieve optimum system flow balance (at minimum horsepower) using the manufacturers performance curves. This straightforward method is based on the fact that if you know the pressure drop through the device and its Cv (the flow rate in GPM through the device that results in 1 psi pressure drop), then mathematically you can determine the flow.
Standard Ball or Butterfly Valves. These devices, along with pressure gauges or test plugs, allow the control contractor to measure a pressure drop across the coil or heat exchanger and then determine and adjust the flow based on the manufacturer’s performance data.
Automatic System-Powered Flow Limiting Valves.
Although these valves are often referred to as “automatic” flow control devices they are actually flow limiting valves. These valves can be set to reliably limit flow through a give circuit; however, if the flow drops beneath this value, there is no actual control. These valves can provide better flow control over a manual balance when a variable speed system is operating at part load.
Pressure-independent Flow Control Valves.
These valves combine all the attributes of a balancing valve, control valve, and a differential pressure regulator into one valve. An integral pressure regulator automatically compensates for fluctuations in system pressure to stabilize flow rate through the heating or cooling coil. When the actuator is installed, it will adjust flow in response to heating or cooling demands. The valves eliminate the need for any Cv calculations and maintain full authority over the entire flow range of the valve.
Ultimately, the type of pumping system you have will determine the type of control device that is best suited for your application. Stay tuned for more on that in our next blog!