SPONSOR CPD PROGRAMME Continuing professional development (CPD) is the regular maintenance, improvement and broadening of your knowledge and skills, to maintain professional competence. It is a requirement of CIBSE and other professional bodies. This Journal CPD programme can be used to meet your CPD requirements. Study the module and answer the questions on completed module is equivalent to 1.5 hours of CPD. Modules are also available at Proportional balancing for circulating water systems This module explores proportional balancing methods for setting heating or cooling water systems for effective operation Despite the increasing application of variable volume systems and pressure independent control valves (PICVs), there are still many systems old and new that require balancing to ensure proper performance and efficiency. No matter the skill of the designer, a commercial buildings circulating heating or cooling water system, particularly if it includes constant-volume elements, is unlikely to be self-balancing. This CPD will explore the proportional balancing method as a means of setting such systems for effective operation. Pipework systems, such as those used in cooling and heating systems in buildings, will not operate as intended without proper commissioning. Inadequate balancing of constant-volume systems will lead to poor control of terminals such as fan coils, heating and cooling coils, radiators, convectors and panels. It is likely that in variable flow systems and, increasingly, systems that employ PICVs, there is limited need for balancing devices. However, for many legacy systems that have been modified or simply need recommissioning, larger systems, and constant volume systems, it is important that appropriate devices are included for regulating and measuring the flowrates in the piping circuits to allow onsite balancing. For all systems, the decisions on commissioning need to be taken at the design stage and well before work commences on site. Although many contemporary commercial installations are designed as variable volume systems, potentially they still include sub-systems that have constant-volume requirements. Also, where PICVs control a sub-network that serves more than one terminal unit (for example, multiple fan coils), there may be the need to balance these terminal units against each other. For those terminals (hydraulically) furthest from the pump, lack of balance could mean an inadequate flow of water, and those closer to the pump may suffer from poor control as their control valve struggles to overcome a high-pressure differential (which results in a low valve authority). Poorly performing terminals can encourage users and building occupants to tweak the system, which, in turn, is likely to exacerbate poor environmental control, increase unnecessary energy use and lead to poor occupant comfort and productivity. As discussed by Roger Legg1 and as recommended by BSRIA2 and CIBSE3 a standard, methodical way to balance pipework systems is known as proportional balancing. This employs the simplified relationship for fully developed turbulent fluid flow, p = RQ2, where p = pressure drop, kPa, in a particular pipework section, Q = volume flowrate, L.s-1, and R is a constant of proportionality that reflects the resistance to flow in the particular pipe network from pipe friction, turbulence www.cibsejournal.com August 2021 57 CIBSE Aug 21 pp57-60 CPD 183.indd 57 23/07/2021 12:19