HVAC&R management
Know your buildings to make huge energy savings David Odd asks you to imagine how much easier your life would be if you woke up tomorrow and your facility was consuming less energy and you still had your capex budget intact.
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here are many ways to save energy even if you’ve already completed an upgrade and your building management system (BMS) is optimised. You can use adaptive temperature control, add energy-based alarms to your BMS, install predictive energy optimisation and switch to conditionbased maintenance with remote monitoring. Technology and data are the key to saving energy in heating, ventilation and air conditioning (HVAC), and will become even more so in the years to come. Two primary methods, that we examine here, include energy efficiency modeling and monitoring. You can also use technology and data to change the way you do maintenance and studies have shown that if you fail to manage your energy efficiency following an upgrade, you can lose most of those savings in just a few years.
Modelling existing buildings AE Smith were among the first to use Dynamic Thermal Modelling on existing facilities when designing an energy efficiency upgrade. Using this method you start by creating a 3D model of the building, including the thermal properties of every element of every room. You include internal heat loads and a model of all energy using systems,
including HVAC and BMS operation. You then run a simulation for a year using actual weather data and calibrate this against the actual energy consumption data for the building. This process provides an accurate baseline of energy consumption for every major system and item of equipment. Once you have this baseline, you can simulate any changes you’re proposing, and measure the outcome, to within a few percentage points. That could be changes to the façade or changes to the HVAC system. From a major upgrade right down to a simple set point change in the controls.
Monitoring and optimisation Once you have a reliable baseline from your modelling, you can start building in alarms to your energy management package. If a sub-meter strays outside of its expected profile, an alarm is raised. At that point, you would normally need to analyse the data to identify the cause before it can be rectified. In short, the current process represents an opportunity to improve performance. While the energy management system will provide energy-based alarms, your typical BMS only provides alarms for system faults. For example when a piece of equipment fails to start when directed.
FACT FILE
Predictive energy optimisation: what have you got to lose? Australia’s CSIRO developed a system called BuildingIQ which optimises energy consumption, energy costs and occupant comfort using predictive energy optimisation. This technology continuously monitors inputs including hourly weather forecasts, occupancy, demand response events and real time energy prices. The system begins with a ‘watch and learn’ phase as it builds a thermal dynamic model of the facility and learns how the building reacts to changes in load such as occupancy and weather. When the system is fully deployed, usually only two to three months after installation, it makes hourly adjustments to setpoints to achieve 10-25% energy savings on the HVAC system overall while maintaining high levels of occupant comfort.
WME magazine DECEMBER 2014/JANUARY 2015
David Odd: accurate baseline is important.
But it won’t give you an alarm if that same piece of equipment is running when it shouldn’t. So wouldn’t it be great if your BMS was always on the lookout for energy wastage? Well 9 times out 10 you will already have sufficient sensors installed to achieve this, and it seems obvious, but it’s just not done as standard practice in our industry. There are many ways that you can optimise the control of HVAC systems, but one area often overlooked is thermal comfort. Even if you use data to identify an ideal temperature, typically 5% of people are still uncomfortable. The other problem is, that ideal temperature changes throughout the year as people acclimatise to the different seasons. However, by using the International Comfort Standard, based on over 100 years of research, for every one degree set point change you can expect 5 to 12% energy savings on cooling and heating. The operating expenditure that is required to implement any of the methods discussed here will be more than offset by the savings generated. So what have you got to lose? David Odd is national sustainability engineer at AE Smith: davidodd@aesmith.com.au
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