Scott McGavin looks at different types of control strategies for building services and the importance of having a plan for efficiency.

As we enjoy the best of the British Summer, many air conditioning systems will be cranked up to maximum to cool staff down and provide relief from the scorching sun. But how do you balance occupant comfort with the need for energy efficiency?

The answer lies in the controls on the system and the type of control strategy adopted will depend very much on the building, and how it is used.

As mentioned, one of the main challenges is to balance occupant comfort with energy efficiency - turning off the cooling will reduce energy usage, but could lead to complaints from building users if it happens in the middle of a heatwave.

You cannot measure what you cannot monitor

Scott McGavin Scott McGavin Controls & Applications Product Manager

Benefits and balance

The BS EN 15232 (2012): Energy Performance of Buildings – Impact of Building Automation, Control and Building Management Standard which I’m going to discuss more in a future article can be used at design stage, retrofit or during operation, with real benefits to all those involved.

Another important consideration is how to balance the amount of control occupants have over their space against energy efficiency. Many studies have shown that people are more productive in environments where they have a level of control over environmental factors such as temperature.

But this needs to be set against a need to optimise energy use.

Furthermore, controls must be usable - easy to understand and operate. Again, this can be challenging in certain types of building such as hotels, where guests are seldom in the building long enough to learn more than the most straightforward control functions. Or in shared spaces such as meeting rooms where one set of occupants want it warm and cosy and the next need an icy blast!

The importance of a control strategy

BS EN 15232 recommends demand control as an important strategy for managing use of building services. As the name implies, controls are set up to run building services only when occupants require it.

At the design stage of a building, simple elements can be employed such as presence detection and CO2 sensors which operate heating, cooling and ventilation, for example, when a space is occupied, or when the controls can automatically increase these elements as more people enter an area of the building.

Demand control is particularly useful for meetings rooms as these are often areas where systems operate unnecessarily, wasting energy.

Automation

Another strategy to consider is the auto-off approach. This allows occupants to turn on cooling or heating in a meeting room, but the controls will automatically revert to ‘off’ after a set amount of time, or automatically on non-occupancy. Again, this addresses a common issue of occupants turning on the building services but forgetting to switch them off after they leave a space.

Through retrofit, a well-designed, installed and commissioned BEMS (Building Energy Management System) can be invaluable to a building to ensure all building services are integrated and interlocked to operate most effectively.

It is often said you cannot measure what you cannot monitor, so adding in the ability to monitor energy, trend data or create alarms will allow maintenance managers to optimise controls and will highlight areas which need addressing.

Well-suited controls

A good example of controls that offer a strategy well-suited to the building type is Melcotel from Mitsubishi Electric. This is a system designed for hotels which will automatically switch off cooling or heating if the room windows are opened. Melcotel also offers a night set-back facility in which cooling or heating are setback in each room under non-occupancy.

This control strategy has been specifically designed to reduce energy waste whilst maintaining comfort and user control in the hotel market - reducing operational costs significantly.

The most cost-effective approach that any facilities or energy manager can take is to use their existing building controls as effectively as possible.

It is advisable to regard the controls as a tool which can be used regularly, but which also has to be maintained. Regular checking of areas such as sensors and detection devices can identify problems that can easily be rectified, saving energy immediately.

Scott McGavin is Controls & Applications Product Manager at Mitsubishi Electric