How to save energy without capex
Energy savings and NABERS rating maintenance without dipping into capital expenditure is possible when you use your Building Management System (BMS) to its full potential, writes DAVID ODD, National Sustainability Engineer, AE Smith.
Imagine you’re sitting in a racing car. You’re in the driver’s seat on the starting grid. You feel the engine throbbing. It’s hot and it’s noisy. The start flag goes down and your pit crew’s screaming at you over the radio, “Go, go, go!” It’s then you realise you’re blindfolded! You take off down the straight. You hit the wall on the right, so you turn left. You hit the wall on the left, so you turn right. It’s scary how little control you actually have.
Now, replace the car with the Building Management System (BMS) in your facility. This is exactly how it’s ‘driving’ right now. It can’t see the corners in the road ahead, such as changes to the weather throughout the day. In effect, your BMS is blindfolded as well, bouncing from one set point to another.
With HVAC systems typically accounting for 60 to 70 percent of Base Building Energy consumption, arguably your BMS poses the single greatest risk to controlling energy in existing facilities. The value of removing the blindfold is undeniable, particularly when it promises energy savings and maintenance of a building’s hard-earned NABERS rating. All without spending any of your capex (capital expenditure) budget.
Understand what puts your energy targets at risk
The first step to reduce risk is to understand the difference between expectation and reality.
Expectation is based on an understanding of how a building HVAC system operates using historical data, energy consumption models and future vacancy rates, whereas reality is driven by other, less predictable factors such as the weather, the behaviour of occupants, the placement of the thermostat, the efficiency of equipment.
To align expectation and reality, a formal risk assessment is undertaken to identify all the variables that place your energy targets at risk. The outcome of which is an accurate baseline to predict, track and optimise energy performance for the life of the building.
Simulate building energy performance
Returning to the racing car analogy, every driver would benefit from a course simulation to know what’s coming before the real race begins. A tool that allows you to do just that for a building, and thereby accurately assess risk, is Dynamic Thermal Modelling.
A 3D model of the facility is built and meta-data is loaded such as the thermal properties of every element and every room, internal heat loads such as occupants and lighting, load reactions of HVAC equipment and any known equipment inefficiencies. The model is then subjected to a year’s worth of dynamic weather data including ambient temperatures, cloud cover and wind speed.
This technology is often used for new construction projects to predict energy performance, but has only recently been applied by AE Smith to building retrofits and refurbishments, using existing performance data.
Done correctly, this delivers a very accurate energy profile for the life of the building for each piece of HVAC equipment, creating a baseline for any HVAC upgrade you can imagine. It also allows a NABERS rating to be predicted far more accurately.
Turn your BMS into an HVAC watchdog
Once there is a reliable baseline, alarms can be added into a BMS to alert a facility manager to energy wastage. Typically, though, a BMS only provides alarms for system faults – for example, when a piece of equipment fails to start when scheduled.
However, it won’t set off an alarm if that same piece of equipment is running when it shouldn’t be. While the existing sensors in the building are already connected, the energy- based alarms that use these sensors are, surprisingly, not programmed as standard practice.
There are myriad energy focused alarms that can be added in to any BMS. These provide alerts long before energy reports reveal a problem. Consider installing alarms to check for leaking valves, correct economy cycle operation and equipment running out of schedule.
In one building in Sydney, AE Smith identified 1200 individual alarms that could be added to the BMS with no additional sensors.
Once energy wastage is under control, you can look at ways to optimise your systems to reduce energy use.
Measuring the temperature of comfort
Thermal comfort is complex because it’s related to air temperature, humidity, air movement, radiant heat sources, clothing levels and the metabolism of every individual occupying the space. But for the facility manager, only one of these variables is controllable – air temperature.
Research shows that the ideal temperature for the majority of occupants will still cause discomfort to five percent of building occupants. Any adjustment to the ‘ideal’ temperature to appease the unhappy occupant is likely to cause even more people to be dissatisfied. So, how can you keep the most people comfortable, whatever the weather, and still save energy?
Using a change of season as an example, research tells us the majority of people will be more comfortable with a higher space temperature in summer than in winter. As many buildings have a constant annual set point of 22.5 degrees Celsius, this in fact means more energy is used for cooling throughout summer than is required to keep occupants happy.
A simplistic solution would be to manually adjust the set point based on the current ambient temperature. However, this doesn’t take into account the fact that people take time to acclimatise to changes in the weather.
If you have a string of cool days and then a much hotter day, people will likely still be wearing warmer clothing. But if you have four warmer days in a row, by then people will have changed their dress and will accept a gradual change in set point.
A more intuitive solution would be to build in Adaptive Temperature Control algorithms into your BMS. These gradually adjust set points, (possibly just 0.1 degree per day) based on a weighted rolling mean of previous ambient temperatures.
Both of these methods will improve occupant comfort levels and save energy. Neither method will truly remove ‘the blindfold’ because they’re based on the previous days’ and weeks’ weather. To remove the blindfold entirely, you need a system that can look into the future.
Smart enough to predict the future
Australia’s CSIRO developed a system called BuildingIQ, which optimises energy consumption, energy costs and occupant comfort utilising 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 set points to achieve 10 to 25 percent energy savings on the HVAC system overall, while maintaining high levels of occupant comfort.
For commercial buildings, these energy savings can result in a NABERS improvement of 0.5 to 1 Star, with little or no capital investment – and no disruption to building operation and occupants.
Changed HVAC maintenance practice
Back in the pits your crew is collecting and analysing all sorts of information to inform your next lap, with the aim of taking your blindfold off. Once you start collecting and trending data on your building’s system performance, you can identify energy wastage, faults or imminent failures. With enough data, the way you maintain your facility can be changed for a better outcome. Routine preventative maintenance has been around since the start of the Industrial Revolution. When you monitor and report on the performance of a system remotely and in real time, you can start to employ condition-based maintenance, a much more effective modern practice.