As Australia accelerates commitments to net zero emissions, there are some steps owners and operators of large commercial buildings can take to improve environmental impact, reduce carbon emissions and reduce energy costs.
With inflation putting many businesses under increasing cost pressure and having flow on effects to consumers, building optimisation and efficiency is a key measure to reduce operational expenditure while boosting the sustainability performance of built assets.
David Walsh, founder and CEO of CIM, says improving the energy efficiency of buildings has two possible approaches: capital expenditure and operational improvement.
“While both have value, you should always prioritise the smarter use of existing equipment over capital outlays on new equipment. The cheapest energy is always the energy you don’t use.”
He says enhancing the performance of equipment via control systems can provide immediate cuts in power use and therefore reduce energy costs.
“The ROI can often be measured in weeks and months, not years. Most improvements that impact operational efficiency have to do with HVAC systems, which consume most of a building’s energy. Optimising HVAC systems alone can yield a 10-15 per cent energy reduction.”
Below are six practical ways that Australian building owners and operators can take now that will have immediate big impacts.
- Run a BMS control strategy
Start by running a building management system (BMS) control strategy to review, identify and resolve operational inefficiencies. These optimisation initiatives have the potential to yield distinct efficiency gains when supported by robust building analytics data:
- Outside air temperature lockouts
- Cooling tower temperature control
- Chiller cooling & boiler heating calls
- Zone temperature setpoints
- Night purge operation
- CHW temperature setpoint
- Outside air temperature lockouts
Cooling towers reduce the temperature of water used by chillers, by extracting heat from the chillers’ condenser. While chiller manufacturers specify the maximum water temperature the chillers can operate with to deliver the cooling requirements there are more efficient approaches that take into account the amount of moisture available in the air, or wet-bulb temperature. Ideally, you want all cooling towers to track the outside air wet-bulb temperature and control to it with an offset of between 4 and 5 ̊C.
Optimisation tip:
- The condenser water temperature should be reset based on the buildings’ outside air temperature wet-bulb + 5 ̊C (adjustable) with a minimum temperature of 20 ̊C (adjustable) and maximum temperature of 29.5 ̊C (adjustable).
- Chiller cooling and boiler heating
For central cooling systems, you want to ensure the chillers kick on at the right time to address the cooling requirements of the building. Engaging the chillers early increases the risk of energy over-consumption and may reduce the life of your equipment over time.
Similarly, boilers should be enabled when needed, not before. Operating boilers earlier than required increases consumption without achieving the desired outcomes and may lead to equipment malfunctions caused by short cycling (frequently turning on and off). Therefore, it’s important to set the correct setpoint and time interval for both the chilled and hot water valves.
Optimisation tips
Chiller
- If the maximum chilled water valve position is 90% for 10 minutes, the cooling call is to be generated
- If the maximum chilled water valve position drops below 20% for 10 minutes, the cooling call is to be disabled
Boiler
- If the maximum hot water valve position is 90% for 10 minutes, the heating call is to be generated
- If the maximum hot water valve position drops below 20% for 10 minutes, the heating call is to be disabled
- Zone temperature setpoints
Zone temperature setpoints are constantly adjusted by Facilities Managers and contractors to address tenant complaints. But it’s important to keep the big picture in mind, aligning all setpoints so nearby systems aren’t fighting each other.
Optimisation tips
- Install more efficient light fixtures – cool light is best to reduce the chance that lighting is warming the thermostat controls and throwing off the temperature
- Clean out the ducts, vents and filters – which can become clogged with grime, dust and debris
- Update outdated components or systems within your HVAC
- Modify ductwork – new office and cubicle layouts can sometimes require changes to the positioning of your ductwork
- Install new window shades – energy-efficient window coverings can help reduce energy costs and improve comfort levels
- Add window film – these can improve thermal properties by providing sun control and UV protection, while reducing hot spots
- Night purge operation
In warmer climates, buildings require additional cooling during the evening period, when ambient light and temperature conditions are more favourable. In commercial offices that are unoccupied over the weekend, buildings act as thermal storage, and temperatures may soar. This places a massive load on building air conditioning. To minimise this load, a night purge is recommended to ventilate the building during early morning hours and remove the excess cooling load.
Optimisation tips
- Night purge usually operates when ambient conditions are at their lowest, generally between 2am and 4am. It’s purpose is to exhaust the warm air has built up in the building when the internal temperatures are high (> than 25 ̊C). This usually occurs in warmer climates and is apparent in office buildings when HVAC isn’t operated for an extended period (i.e. over the weekend).
- We recommend operating the supply fan with the economy dampers 100% open to introduce cooler air into the building whilst exhausting the warm air out of the building without operating the central chilled water system. It’s important that the fans don’t operate for extended periods beyond 1 hour. If operated for more than one hour, an assessment needs to be done on the thermal benefit over the energy consumption.
- Chilled water temperature setpoint
The building management system is capable of adjusting the chiller’s chilled water temperature setpoint based on the building load requirements. Buildings are typically designed with the chilled water set to 6 ̊ C to maintain internal thermal comfort conditions during the warmest months. Knowing when to raise the temperature setpoint of the chiller is critical, as resetting down too early may impact energy and operation of the chillers, while resetting up might impact thermal comfort for occupants.
Optimisation tips
- The chilled water temperature setpoint shall reset up if the average chilled water valve position is less than 60%
- The chilled water temperature setpoint shall reset down if the average chilled water valve position is greater than 70%
- The chilled water temperature setpoint will reset at a rate of 0.5 ̊C every 5 minutes
- The minimum chilled water temperature setpoint = 6 ̊C
- The maximum chilled water temperature setpoint = 9 ̊C
