FMJ Facilities Management magazine providing industry-specific intelligence to FM and property professionals
Andy Sparrow, Head of Energy and Sustainability at Platinum Facilities explains the energy and cost saving benefits of turning your building BMS into a BEMS
Converting your Building Management System (BMS) into a Building Energy Management System (BEMS) is very cheap to do and can provide massive energy savings, combined with very good paybacks. Working through the various control functions systematically, ensures that energy use is optimised, and the maximum savings realised.
TIME CONTROL
This ensures that plant only operates when it is needed. A seven-day programme allows individual days to be programmed, as weekends may be different to weekdays, and allows Bank Holidays to be taken into account.
An air conditioning system needs to switch on an hour or two before people arrive, to get the building up to its normal occupancy temperature. This is known as the warm-up period and its length depends on the outside temperature. An optimum start control system monitors the outside temperature and ensures that the warm-up period is the minimum length of time, which minimises energy wastage. Similarly, the system can switch off plant before the end of the occupancy period, so that the building can run on residual heat left within the heating system, thereby reducing run times.
‘ON-DEMAND’ HEATING AND COOLING
Plant should only operate when required. On-demand control ensures that heating and cooling only operates when an area calls for it. If the whole building is at or above the set point temperature, then the heating will not be operational. Similarly, the cooling will not operate when the building is cool enough. It is important to avoid simultaneous heating and cooling.
Plant should be sized so that units can come on incrementally. We do not want the total heating/ cooling capacity to operate in one hit, when only a proportion would suffice. For instance, when cooling is called for, the first stage will operate for a set period. If this can maintain the set point temperature, then the second stage is not required. However, if the temperature is still too high the second stage will be brought in, followed by the third, fourth etc, as required.
UTILISING THE EXTERNAL CONDITIONS
The difference between the heating and cooling set points is known as the dead-band, which is the temperature range where the system remains idle. Only when the heating or cooling set points are exceeded will the system reactivate. For instance, if the heating set point is 19°C and the cooling set point 23°C, then heating will only operate below 19°C and cooling above 23°C. The system will not operate between 19°C to 23°C.
The heating set point is normally fixed, but the higher the external ambient temperature, the higher the cooling set point can be, and hence the wider the dead-band. For instance, if the external ambient temperature is 30 °C then the cooling set point can be increased to 24 °C (and the dead-band increases from 4 to 5 °C).
When the external ambient temperature exceeds 16°C, buildings generally do not require any heating. Hence, the heating system should be locked out, providing it doesn’t also heat the hot water.
When the external ambient temperature drops below 13°C, office buildings will generally not require any mechanical cooling. Free cooling should suffice, and the mechanical cooling system should be locked out, providing local hot spots are still cooled.
