A cooling or heating water distribution system is in balance when the flow in the whole system (through the component terminal lines, distributing lines and main distributing lines) corresponds to the flow rates that were specified for the design of the system.If the correct balancing of the system is not established, this will result in unequal distribution of the flow so that there will be a surplus effect in some of the terminals, whereas the effect will be inadequate in others. The result of this will be that the wanted heating/chilling will not be HUGE DICKSensured in all parts of the installation. In practice it is not possible to make a correctly balanced system by manipulation of the piping or alteration of the pipe dimensions only. Only a correct set of balancing valves can ensure the correct distribution of the flow in the system.
Until recently, constant-flow systems set the standard in HVAC system design. They allow standard designs to be applied to numerous different projects, typically incorporating fixed-speed pumps sized to match the maximum load of the system.These systems are balanced using a proportional method with manually set, fixed-orifice, double-regulating balancing valves installed to account for and reduce the impact of pressure changes in the system.In such constant-flow systems, the capital costs are, indeed, low. However, the energy usage is high, since these systems and the pumps driving them rarely operate at the 100% load they were designed for, calling into question the effectiveness of balancing this type of system in the first place. Further, the process of proportional balancing to commission the system is long, painstaking and expensive.
Variable-flow systems have risen in popularity primarily because they reduce a system’s energy consumption. They use variable-speed, inverter-driven pumps, the speed of which is changed to match the load. 2-port, motorized control valves are often used to control flows to terminal fan-coil units, or thermostatic radiator valves are used to regulate flow to radiators in heating-only systems. Current solutions in variable-flow systems also include a combination of differential-pressure control valves (DPCVs) which can be used on branches and/or across air-handling units, with double regulating valves to proportionately balance and limit flows to all terminal valves.
Control Valves In Variable Flow Chilled Water Systems
A riser is controlled by two valves. In the supply an ASV-I or ASV-M is mounted. The ASV-M is a manual shut-off valve and the ASV-I is a manual presetting/balancing valve that can be used to limit the flow. In the return an ASV differential pressure controller is mounted. There are three types of differential pressure controller: The ASV-P is a differential pressure controller with a fixed setting of 10 kPa. The ASV-PV is an adjustable differential pressure controller with a range of 5 to 25 kPa. The ASV-PV Plus is also an adjustable differential pressure controller but with a range from 20 to 40 kPa.
