Recently we came across a vav installation with no flushing loops on the vav boxes. This is an extract from the BSRIA Guide high lighting the importance.
The flushing by-pass should be line size and must be located upstream of control valves and regulating valves, but as close as possible to the terminal unit. It is particularly important to avoid the need to flush through high resistance â€˜low flowâ€™ regulating valves since these may prevent the achievement of acceptable flushing velocities. Materials downstream from the flushing by-pass will be excluded from the chemical clean, and should therefore, ideally, be constructed from non â€“ ferrous materials, e.g. copper or from plastic.