COMMISSIONING | HEAT-RECOVERY VENTILATION Getting heat-recovery ventilation right at commissioning stage Ashley Phillips and A s an industry, we seldom have the opportunity to learn from feedback or digest lessons learned. However, over the past 18 months, we have had the benefit of direct liaison with our in-house commissioning and project management team. Being able to use this commissioning first-hand knowledge at the early stage of the design process has enabled a true commisionability review to be incorporated into our design process long before the start of any first-fix installations, thereby avoiding abortive site works or costly investigations and potential changes. In this article, we share a selection of items that our building services consultancy has encountered and resolved when it comes to the commissioning of heat-recovery ventilation systems. The commissioning of air systems can be a particularly thorny process; if the pre-planning is not right from the outset, problems can be extremely difficult to diagnose and resolve. Issues such as limited access, poor as-built information, and limited measurement points for testing and readings are often overlooked. In general, the lack of commisionability at preconstruction design stage can result in future fault-finding being intrusive and costly, and remedial actions resulting in repairs that can be aesthetically unpleasing. One of the primary considerations when commissioning equipment or plant is location, ease of access and adequate clearances; this includes the routing of services that may restrict access or installation height for example, any component, fitting, equipment or plant around the air handling unit. This may be an obvious point, but it is easily overlooked. Easier access will result in easier commissioning, fault finding and future maintenance for replacement of filters, fans, and other components. The successful commissioning of ventilation systems is subject to the particular parameters of the installed and operated system. For example, the pressure drop of the installed system may not be as calculated; additional ventilation air supply may be used to compensate for duct and component leakage; ventilation requirements may have increased because of more occupants or additional rooms; fittings, particularly those that are bespoke, may add unexpected resistances; or the routes of installed ducts may impact originally expected resistances. These can all affect the performance of the ventilation unit and the system balancing. With regards to application of heat exchangers, there are different types and materials that have limitations and need to be considered with the application. In light of the emergence of Covid-19, use and application of heat exchangers is under greater scrutiny to avoid the recirculation of air particles and contaminants. Heat-recovery systems will, typically, have a summer bypass function to prevent overheating by diverting the fresh air from passing through the heat exchanger. Not all bypasses are capable of diverting 100% of the airflow and there are no specifically required compliance checks. Employing appropriately approved heat-recovery systems would be most effective for compliance and function. For commissioning of heat-recovery systems, we have found that, generally, only boost ventilation rates are provided in the operational specification; it is important, however, that trickle ventilation rates are also given in order to set the low background ventilation speed of the heat-recovery mechanical ventilation unit. The use of MVHR is often applied as a ventilation strategy that aims to maintain occupants comfort by providing good indoor air quality. It can also have a beneficial effect on energy use and carbon-emission reduction. With regulatory improvements in building fabric performance, the ventilation system has become a more significant element of the total building heat load. As a rule of thumb, efficient ventilation heat-recovery ASHLEY PHILLIPS is technical director and LAFIA TOUR is an energy consultant at John Francis www.cibsejournal.com May 2021 71 CIBSE May 21 pp71-72 Heat Recovery.indd 71 23/04/2021 16:15