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Clients with limited budgets tend to neglect benefits of VFDs

Martin Williamson, Head of Commissioning (Middle East), AESG, gives a consultant’s perspective on whether a critical mass has been reached with regard to the uptake of variable frequency drives (VFDs). Excerpts from the interview he gave to Surendar Balakrishnan…

| | Aug 4, 2021 | 3:17 pm
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Given that VFDs have been around for quite a while now, have we seen sufficient acceptance in the GCC region to confidently say we have reached a certain critical mass of their use in projects across the region, or even as a default solution?

In my opinion and experience, the use of VFDs in the region could be considered as the default option for ventilation and hydronic systems in new construction projects. It could even be argued the use of VFDs has become so widely accepted as the ‘go to’ option that even constant speed ventilation systems, such as fresh air handling units (FAHUs), designed for constant fresh air volume, are also fitted with VFDs where, with minor exceptions, modulating the air volume during operation will not be needed. On hydronic systems, such as chilled water systems, I don’t believe I’ve seen a system where VFDs are not utilised to modulate pump speed, even seeing the use of ‘Triple Duty Valves’, in addition to VFDs, on a few occasions. The Middle East building services sector has evolved in the past decade in terms of awareness regarding balanced energy consumption and utilisation. This includes use of VFDs for almost all rotary equipment as an overall control and protection device.

Martin Williamson

To what extent are VFDs being used in retrofit projects? Is there a greater uptake, on the basis that they can lower the total cost of ownership (TCO) of buildings across the region?

It is essential to make evident to the client the multiple long-term operational benefits of using such devices. A certain segment of decision-making teams that are purely cost-based, tend to neglect the long-term perspective. At AESG, for the retrofit projects we have handled, we have proposed VFDs and other sensory devices as alternatives to traditional manually operated systems, projecting the reduction in operating costs in the long run.



How much is cost an impediment, despite the ability to prove their positive impact on TCO?

Base product cost of any equipment is a vital factor, which directly contributes to the initial BOQ, built essentially considering the construction phase and incorporating minimal operational requirements. Clients with limited base-build budgets and, in some cases, clients that are not end-users, tend to neglect these benefits.

Typically, what are the challenges in properly installing VFDs in retrofit projects? Are there constraints in the forms of space, access, etc.?

Most buildings have plantrooms that could accommodate retrofitting VFDs within MCC panels, with smaller wall-mounted VFD options available, where space may be a constraint. One area of consideration would be the electrical demand of a VFD when added to a system within an existing building. Incorporating VFDs on an existing system can be less challenging than presumed if certain fundamental parameters are considered. The basics being motor running current, distance from the control panel for cable sizing, and secondary protection for the VFD, such as overload and earth fault protection.

Does the deployment of VFDs in buildings connected to district cooling schemes have any impact on the contractual obligations between the district cooling provider and the building owner?

Generally, VFDs are connected to pumps that are in-feeding the building from the primary DCP system, with the secondary building[1]side, more often than not, also utilising VFDs. These are a collateral matter of concern for the district cooling provider, as these devices, in conjunction with actuator-controlled valves, will eventually affect the Differential Temperature (ΔT). With VFDs on the building system, these are likely to assist with control of the system, and should the system be set correctly with pressure set points, this should be of overall benefit with respect to the required ‘Delta T’. However, we do not believe the contractual obligations would be void even though there would be a perceived benefit.

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