Conquering comfort myths: Game, setpoint, match
How can a perception of comfort be ensured? And, how can the best balance between comfort and energy savings be achieved? Total Facilities 2013 speaker, JAMES HENRY of Logical Group Companies has the answers.
When I was asked to be a speaker at Total Facilities 2013, the topic I decided to speak on was indoor comfort as I felt it would be an interesting subject for both facilities managers and owners. In addition, Logical Group had contributed to the building of an indoor environmental quality (IEQ) laboratory at the University of Sydney a few years ago, so I had access to Dr Richard De Dear from the university’s faculty of architecture. The lab was the brainchild of De Dear, who I had met in September 2012 when the laboratory was opened by Minister Greg Combet.
So, I contacted De Dear about doing a presentation on the new IEQ laboratory and its findings so far. He was cooperative, but not very engaging when he learned I had never heard of the Adaptive Comfort Model or several other terms that he used. It wasn’t until later that I realised that he had tried to discuss comfort with me, but that I was completely ignorant of developments in our field for the past 20 years.
WHAT IS COMFORT?
I had always accepted the basic premise that we control buildings to 23 degrees Celsius and that the closer we stay to this number the happier our tenants will be. But, come to think of it, I couldn’t answer the simple question: what is comfort?
Richard politely suggested that I read Chapter 8 of ASHRAE Handbook—Fundamentals for starters. From Chapter 8 we learn that there are six physiological factors that affect our perception of comfort. They are:
- Air temperature
- Radiant temperature
- Air speed (how fast air is passing over you)
- CLO (your clothing)
- MET (your metabolic rate, or how much activity you are doing)
In addition, people vary individually based on their weight and personal preferences. Further, the colour and feel of the space will affect your perception of comfort.
I made sure I read some additional articles as well so that the next time I talked to De Dear I had a better of idea of the subject of comfort.
ADAPTIVE COMFORT MODEL
Still, though I understood that comfort was more complicated, I still believed that 23 degrees Celsius was the target temperature. Graph 1 displays how with the traditional graph of perceived comfort, we target slightly cooler buildings in winter and slightly warmer ones in summer, with an overlap at 23 degrees Celsius. So, most tenancy agreements are written around that one setpoint.
Next De Dear had me read his 1997 report on comfort that he wrote for the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). This is now ASHRAE Standard 55.
When I read about the Adaptive Comfort Model I was amazed. It turns out that large-scale studies of people’s perceptions of comfort give the correlation shown of the graph of outdoor temperature versus indoor temperature (Graph 2).
This means that we should change the setpoint as the outdoor air temperature changes. When this is done, as you can see from the graph, people are far less concerned with maintaining an exact temperature than having the right general temperature setpoint.
The next thing De Dear had me review was his more recent study of perceptions of comfort with varying setpoint accuracies. Basically, as this fairly large study indicates (Table 1), people don’t perceive that they are any more comfortable when the temperature is kept close to a specific setpoint.
SAVINGS TO BE GAINED
What have I learned from all this? Basically, I have learned that we are setting buildings to the wrong temperature setpoints. A lot of energy can be saved by lowering the setpoint in cooler outdoor temperatures and raising the setpoint in warm weather.
Further, it costs a lot of money for control systems to maintain buildings at and exact setpoint, when it turns out that tenants don’t perceive themselves to be any more comfortable when the setpoint accuracy is relaxed from 5 degrees Celsius to 2.2 degrees Celsius.
James Henry is the managing director of Logical Group.