The ultimate adaptive building with features like a moveable skin or a sweat response in high humidity is still a way off, though it appears from our portfolio wide trials that using more dynamic temperature setpoints in existing buildings is a good early step to more responsive building management.

Office buildings, like shopping centres and hotels, generally provide internal environment conditions which are consistent day after day, regardless of the weather outside. Yet the result of two years of trials in 29 existing buildings suggest that those more in tune with outside conditions can improve occupant comfort and reduce their air conditioning energy costs.

Investa Property Group has been taking small steps towards adaptive comfort in their office buildings during the last two summers for two important reasons:

• Comfort: air conditioning in a typical Australian office building is generally set to target 22.5°C in summer, yet this temperature setpoint is well below ASHRAE’s comfort standard which recommends a range from 23 to 26°C for lightly active occupants wearing typical summertime office attire. From our previous research we know that roughly one third of summertime air conditioning complaints are because it’s too cold inside the building!

• Energy: CSIRO carried out a ‘Smart Thermostat’ trial in one of Investa’s Melbourne buildings over the 2006/07 summer, which raised the internal temperature setpoint by 1°C. The results concluded that over the whole summer period heating, ventilation and air conditioning (HVAC) savings of 5 – 10% are possible with every 1°C the setpoint is raised.

Investa’s first trial was a simple 1°C setpoint raise across 33 buildings during the 2009/10 summer, which resulted in HVAC savings of approximately 6% [1] from the sample of analysed buildings and a reduction in cooling complaints by 3% compared to 2008/09. After this trial we did a detailed analysis of building energy, weather and air conditioning complaint data from the previous year, and developed and selected new strategies for the following summer than we considered most likely to enhance occupant comfort and reduce HVAC energy demand in each building. The strategies we specified included:

1. Floating Setpoints (varying internal temperature setpoints throughout the day in response to external temperature): During the previous summer, some buildings automatically switched on their heating during cool summer mornings to try meet the higher summer temperature setpoint. Varying the setpoint in response to external temperature avoids the possibility of the building switching its heating on during those cooler summer mornings. In addition, more actively responding to changing external conditions better aligns the expectations of occupants as they enter the building; who wants to enter a 22.5°C building when its 40°C outside? Floating setpoints were implemented in 11 buildings.

2. Time-of-day based setpoints (a step-up in the temperature setpoint at a certain time during the day): In one building a high proportion of ‘too hot’ complaints were measured in the morning during the previous summer. The solution was to provide cooler internal conditions during the morning to improve comfort and then to step the setpoint up in the afternoon to save energy when minimal complaints were measured.

3. Simple setpoint raise: A simple setpoint raise provides internal conditions which are more in line with ASHRAE’s temperature recommendations for summer, suggesting that comfort will be improved. If the simple setpoint raise was successful last year, or if the buildings couldn’t implement another strategy, they employed a simple setpoint strategy. This was implemented in 12 buildings.

4. In addition to these three strategies, we looked at implementing complimentary strategies such as air conditioning optimum start and modifying plant operation times in some buildings.

To work out how successful the various strategies were, we used simple weather adjusted energy models for each building, as seen in Figure 1 for one Brisbane building. Overall, for the most recent summer (2010/11), savings of 4.1% were measured compared to 2009/10 and 8% compared to the 2008/09 summer, based on an analysis of a sample of 15 buildings. For the studies we collected air conditioning complaint data from a tenant ‘help desk’. Air conditioning complaints fell by 13% in 2010/11 compared to 2009/10, indicating that occupants inside were generally more comfortable.

Figure 1. Energy versus temperature scatter plot for a building in Brisbane

This summer’s strategy is more simple, “if it worked last year, [optimise it and] do it again. If it didn’t work, optimise the strategy or try a new one. Apply a strategy if the building didn’t have one last year”. With new in-house technologies developed to track building performance on a daily basis, we can continuously use ‘trial and error’ to optimise the strategies throughout the summer, and look forward to reporting the results next year.

The strategies in place are an encouraging early step towards an ultimate goal of creating “adaptive” buildings that can respond to the weather for the benefit of the people inside, and the energy bill. We encourage other buildings to get involved with these simple trials.

This blog summarises a paper presented to the Australian New Zealand Architectural Science Association Conference in Sydney on 18th November, 2011.

[1] Roussac, C., J. Steinfeld, R. De Dear, (2011). A preliminary evaluation of two strategies for raising indoor air temperature setpoints in office buildings, Architectural Science Review, doi:10.1080/00038628.2011.582390

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