Measuring ultra-low flows for commissioning

Published:  02 February, 2012

SAV Systems, commissioning, flow measurement

As buildings have become better insulated, with lower space-heating demands, variable-volume hydronic heating systems have become much more common. As a consequence, commissioning engineers often find themselves dealing with ultra-low flows (<0.015 l/s) which are too low to measure accurately and consistently with standard flow-measurement devices.

This makes it difficult to comply with CIBSE Code W (CIBSE Commissioning Code W: Water distribution systems 2010 and BSRIA Guide BG2/2010: Commissioning Water Systems).

To address this issue, SAV Systems has introduced ultra-low-flow commissioning modules to its FloCon range. These modules connect groups of terminal units to a single, compact manifold that includes a different-pressure control valve (DPCV). The module then acts as a ‘control centre’ for commissioning, enabling flow measurement by subtraction — one of the methods recommended in the latest revisions to CIBSE Code W.

For example, if six terminal units are connected to a single manifold the total flow rate for all six units is easily measurable. If one terminal unit is then isolated, the total flow rate for the remaining five units will be reduced but is still high enough to measure. The difference, gives the flow rate through the isolated terminal unit. The procedure is repeated for each terminal unit.

As well as enabling accurate measurement of ultra-low flows, this approach also saves time as each group of terminal units can be commissioned from a single point, rather than needing to visit each terminal unit separately. Experience on a number of projects shows that installation and commissioning time can be reduced by as much as 60% using FloCon manifolds.

FloCon ultra-low-flow modules are suitable for use with fan-coil units, chilled beams, radiant heating and radiator systems. A patented bypass configuration maintains a permanent path for flow when all 2-port control valves are closed, enabling the system to respond more quickly to change and ensuring that variable-speed pumping systems never run dry. In addition, the risk of air and dirt ingress is minimised, and water treatment chemicals are circulated to all parts of the system.

For more information on this story, click here: February 2012, 115

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