A comfortable office temperature doesn’t depend just on the temperature, there are other factors that come into play. These include the relative humidity, the temperature of surrounding surfaces and the speed of any air movements.

Craig Ryan of Johnson Controls has prompted this second posting with some good observations about humidity and comfort on my first posting on a comfortable office temperature.

The more humid it is, the higher the temperature feels. This is shown in the thermal comfort chart below.

In climates which are always hot, or climates that are mostly cold, our bodies acclimatise somewhat to these conditions. The chart above is most appropriate for cooler rather than hot climates.

Moving air makes it feel colder. When its hot creating air movement (eg through fans) can mean that air conditioning systems can be set to provide higher temperatures than would otherwise be the case.

Radiant temperatures of nearby surfaces also make us feel warmer or colder. Because of this sitting next to a large window in winter may still feel cold even though the inside air temperature is 22 degrees Celcius.

By operating heating and cooling systems out to the limits of what is perceived to be a comfortable temperature significant energy and greenhouse gas savings can be achieved. Attention also needs to be paid to air movement and surface radiant temperatures.

Changes to temperature settings are a little known but easy way of getting significant carbon savings in offices.

In office buildings the single largest energy user is the heating, cooling and ventilation system. This system will typically account for 40% to 60% of the buildings energy cost and greenhouse gas emissions. A major determinant of how much energy your system uses is the temperature at which it is set to operate. Depending on climate, most offices are set to maintain a year round temperature of either 22OC or 24OC.

Hobsons Bay City Council in Melbourne had temperature settings at the Hobsons Bay Civic Centre adjusted by CarbonetiX engineer Linton Hartfield to allow the temperature to vary between 20 and 25 degrees Celcius. Electricity metering of the air conditioning system showed a 25% energy saving on the packaged heat pump units supplying the building. The air conditioning temperature changes occurred a couple of months after a building extension – which had increased electricity consumption by 10%. According to Environment Officer Rowena Joske, “After the temperature adjustments the electricity bills dropped back to what they were before the extension.” In other words simply adjusting the temperature settings has cut carbon emission by 10%.

Temperature complaints are, however, a major bane to facility managers who can’t seem to keep everyone happy. Do adjustments to temperature settings increase the number of complaints? In the case above more complaints did occur about it getting above 25 degrees in some parts of the building. So the system has been adjusted back in those parts of the building to limit the maximum temperature to no more than 25 degrees.

Comcare, a federal government organisation for public sector employees, has produced guidelines as to what a comfortable office temperature is. According to Comcare the acceptable range of office temperatures is 20 to 26 degrees Celcius, with 20 to 24 degrees recommended in winter and 22 to 26 degrees recommended in summer.

In temperate and cold climates in Australia allowing the temperature in the office to float between 20 to 24 or 25 degrees will significantly cut energy use and carbon emissions as compared to setting the system to maintain exactly 22 degrees. In hotter climates allowing the temperature to go up to 26 degrees instead of making it stay at 24 degrees will similarly save energy and carbon emissions.

For offices in terms of carbon reduction per dollar spent it doesn’t get much better than changing building temperature settings.