Control for all seasons

A BEMS must be given attention throughout the year in order to maximise its potential. Casey Wells explains why a 24/7/365 approach to BEMS optimisation is essential.

The run up to spring this year was an interesting one, with unseasonably warm, sunny weather at the end of February, followed by howling winds and colder temperatures in March! Such dramatic fluctuations mean that a BEMS must be agile, flexible and responsive as extreme temperatures can be problematic for a wide variety of reasons that need to be addressed throughout the year.

We’ve all experienced the effects of poor comfort conditions and the negative effect they can have on productivity and our sense of wellbeing. While energy management is important in buildings, the focus should also be on the people that occupy them and BEMS technology can be used to improve their engagement.

Modern airtight buildings can suffer from poor quality air. Ensuring they operate in ways that ensure optimum comfort conditions as soon as heating, ventilation and air conditioning (HVAC) is switched on, will be time well spent.

It should also be remembered that increased productivity offers a significant return on investment (ROI). This was highlighted by research from the UK Green Building Council (UKGBC), which found that temperature can negatively affect productivity by 2 percent for each 1°C above the ideal temperature and 4.7 percent for each 1°C below. Furthermore, good air quality can improve productivity by up to 11 per cent.

A BEMS should automatically control to pre-defined setpoints – constantly tracking changes in both external and internal temperatures and light quality, and adjusting the HVAC and lighting before any occupants even notice. Furthermore, the data it produces allow building and facilities managers to better analyse, understand, reconfigure and improve a building’s internal environment.

A BEMS is ideal for carrying out energy monitoring, as it will often possess unused capacity, have an existing service arrangement and generally be better supported than a stand-alone energy logging application. The equipment itself may also be more robust and modular and, in the case of a modern BEMS, have the capability to carry out virtual energy measurements from plant run times. So, it makes sense to determine whether changing monitoring requirements can be met by an existing BEMS system and, if not, investigate whether some simple upgrades or reprogramming is required.

When employees begin to embark on their summer holidays, most companies experience periods of reduced occupancy. This is an ideal situation for a programme of BEMS optimisation, for instance using a plant on a demand-led basis at this time of year is the ideal strategy for reducing wear and tear, and making use of resources such as free cooling. With a demand-led strategy, when specific areas need different levels of HVAC, this can be achieved using as little energy as possible.

For example, many buildings have a central air handling unit (AHU) to supply air at a constant temperature to fan coil units (FCU) that carry out the local temperature control. Chillers are activated whenever the AHU return air temperature is above a setpoint, resulting in all the cooling being handled by the chillers, which are energy intensive and costly. Furthermore, whenever outside air is below the required supply temperature, an AHU has to heat it up but, sometimes, due to internal heat gains, this air then has to be mechanically cooled – wasting both gas on heating and electricity on cooling. Finally, ineffective use of an optimiser results in an increase in the air conditioning time zones during hot weather, so that during warmer months plant is set permanently to run for longer hours than normal.

In this situation the answer is to initiate a strategy where, if cooling demand is between 0-50 percent, fresh air dampers modulate to meet this requirement by using fresh air only, without the need to initiate chillers. If this free cooling is not sufficient and the cooling demand continues to rise above 50 per cent, only then can chillers be activated. To make this more effective, the supply air setpoint can also be reduced to make maximum use of the fresh air cooling effect.

During the colder months, before things get too chilly and energy demand increases, it’s a good idea to implement an optimum start/stop (OSS) strategy.

OSS offers an efficient and automatic way of maintaining space temperatures, while controlling the amount of energy used to achieve them. By using a rolling profile of when a setpoint was achieved the previous day and by monitoring outside temperatures, an OSS calculates a start time for the heating system, so that a building is warmed up when the occupation period begins. Conversely, OSS can work well in the summer months to ensure that a building is cool enough during periods of occupancy.

While the ability of a BEMS to reduce energy use and save money is without question, organisations should remember that an improved working environment that has the health, happiness and wellbeing of occupants at its core offers a significant ROI through improved productivity, less absence as a result of illness and highly motivated personnel.

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