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The need for dynamic, flexible HVAC systems in a changing workplace

Frank Taaning Grundholm, Vice President – Global HVACR Sales – Drives, ABB Motion, elaborates on the winds of change blowing through the commercial buildings sector and the unique challenges they are posing in terms of climate control

| | Jun 23, 2020 | 4:44 pm
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Serviced office spaces, also known as shared offices, are no longer the exclusive domain of small, independent start-ups. Larger and well-established businesses are also taking note of this revolutionary concept to create an innovative space outside of the core workplace. Such multi-occupancy workspaces, as well as large open-office spaces, present unique challenges in terms of climate control.

Indeed, where it was once possible to create a pleasant working environment within a limited, closely controlled area, heating, ventilation and air-conditioning (HVAC) systems now have the challenge of serving large open spaces. Traditional control systems, using fans that are either fully ‘on’ or ‘off’, together with dampers that have a significant lag in their response, are no longer sufficient.

Flexible, shared offices can benefit from smart technologies in several ways – from access control to improved temperature and lighting control. The challenge to attaining this, however, is human: Unlike corporate offices, shared office spaces are occupied by multiple ‘owner’ tenants with varying needs.

Temperature preferences vary greatly among individuals, and no one temperature can satisfy everyone. For instance, for every person that finds the temperature is just right for them, some co-workers are too hot, too cold, or are troubled by draughts. An office that is too warm makes its occupants feel tired, while one that is too cold causes the occupants’ attention to drift, making them restless and easily distracted.

When you have different temperature zones within the same room, the air is forced to move around – hot air rises and cold air fills the bottom. The result is a draught. People sitting near an air inlet in the ceiling, for instance, might be exposed to a draught permanently. For the majority of office workers, sitting in a draught is even more unpleasant than being too hot or too cold.

Other factors impacting the balance include low ceiling height, room size, lack of central control and the movement of people. As a result, managing and maintaining thermal comfort conditions in an open-plan space becomes one of the most challenging of environments to get right.

To address this issue, it is essential to have a detailed understanding of the load profile of the building, both in terms of temperature requirements and varying occupancy levels. This type of profiling generally reveals that a full load rarely occurs; many buildings of this kind operate at 80% load or less, for 99% of the time.

Dealing with unoccupied buildings

Unoccupied buildings present a specific challenge. If a building is unused for a long period of time, it will most likely open with a different load than what it was set for before the shutdown, so the systems need to be able to dynamically adapt to this.

Furthermore, in some buildings, the HVAC systems may have been turned off. Firstly, it is important that the systems are turned on before any cleaning is done in the building, as there will be a potential build-up of dust and bacteria in the ducts, which will potentially contaminate the cleaned surfaces. The ducts should also be cleaned properly before start-up, if the system had been completely shut down.

The best practice is to keep the ventilation running at low volumes, even in empty buildings, since this avoids both the build-up and the ‘blow out’, when you start the system. If the systems are started on the morning of opening a building, there is a high risk of spreading diseases to the occupants, due to particulates from the ductwork.

Centralised control with automated systems and drives

Rather than seeking the most energy-efficient and cost-effective HVAC solution for a full load that may never occur, it makes sense for designers to specify for an optimised system that offers the best performance under the most common part-load situations. Of course, the system will still need to have the capacity to support a full load on the rare occasions it occurs.

The best way to ensure a comfortable environment is to use variable speed drives (VSDs), as they provide precise, dynamic control of fan speed to allow airflows to meet constantly varying demands. VSDs integrate seamlessly into building management and automation systems and are highly adaptable.

As an example of the need for adaptability, there are often cases where the final construction of a building has varied from the plan – there might be a roof support column, where an air duct was meant to go. This forces the air duct to be displaced, with a resulting drop in pressure. This throws out the entire climatic planning, as more capacity is required from the HVAC system to push air through the building.

If the system does not have sufficient capacity and the fan motors have only direct online controls, it might be necessary to replace the whole unit. However, if VSDs have been installed, then it will have the flexibility to adapt. A 50 hertz (Hz) system might be pushed up, so the fan runs at 55Hz or even 60Hz, which would then provide an extra 10-13% capacity.

Optimising for peak efficiency

Today’s VSDs offer a wealth of features and smart functions that enable building operators to optimise the efficiency of motor-driven applications. It is feasible to optimise the systems for performance at or below 80% load to increase energy efficiency and reduce operating costs. This is possible by selecting the pump, fan and cooling units, and the motors operating the application, so that they achieve their best efficiency at the normal load point for pressure and flow.

A major advantage of the optimisation process can be the specification of a smaller fan, which, thanks to the VSD, can be operated at a higher than nominal speed for the few occasions during the year when peak load is experienced. Smaller units take up less space in the building, making more room available for tenants and, therefore, potentially increasing revenue. There is also a knock-on effect throughout the system, as smaller fan units can save costs by reducing the size of ducting, dampers and other equipment.

An added factor to consider in a shared office space is that of overutilisation. For example, a meeting room might have been designed for six people, but with extra seating, it is possible to squeeze in 10 people. Therefore, if the space gets filled, CO2 levels will spike and compromise air quality, which in turn, can cause people to feel drowsy.

In HVAC, the key to success is for building operators to start by focusing on the needs of people, rather than on the technical solutions. What seems like cutting-edge technology today may soon be out of date, while multi-occupancy workspaces need to provide a pleasant environment well into the future, even as their usage patterns change. This requires constant, active dialogue between owners, operators and occupants.

Frank Taaning Grundholm

Frank Taaning Grundholm is Vice President, Global HVACR Sales – Drives, ABB Motion. The writer may be contacted at frank.grundholm@dk.abb.com

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