Thermal Comfort or Temperature Control?

You can’t please all of the people all of the time.

We want it not too cold in winter, not too hot in summer. But when people are unable to work, or just want to be somewhere else, because of the thermal environment then something’s gone wrong somewhere. Getting thermal comfort right isn’t just about the temperature; it’s about the people.

Unsurprisingly people who are under physiological stress don’t function very well. Thermal comfort is achieved when there is a heat balance between the body and the environment, and we are very good at acting when things get out of kilter. We’ve all reached for a jumper, or a fan, or changed our posture instinctively and we’ve all had reason to wonder if there is a better way.

Science has made many attempts over the years to describe the conditions that will best work for most of us.

Typically temperature is used as the starting point and specifications often set the air temperature that is expected to be provided within our buildings. 22+/-2°C became a standard point for design purposes but actually it’s a control standard, not one that delivers thermal comfort.

The most complex systems for the prediction of thermal comfort combine physical measures for the air temperature, humidity, the radiant environment and air motion together with personal values describing metabolism and the effect of clothing and other insulation. Whilst this system works in highly controlled situations such as laboratory experiments, or buildings that operate in a similar way, it can put us very wide of the mark in others.

Using our typical control air temperature of 22°C, in combination with a radiant environment of a similar temperature and typical office data for the remainder of the parameters, shows that in New Zealand we may well be designing to miss the comfort standards set out in EN-15251 and ASHRAE 55-2013.

Watching people leave their air conditioned buildings for their lunch break in Summer, stripping off clothing as they go, shows how they have had to adapt to the conditions they have. Watching them prepare to return, by putting on layers of knitted clothing, jackets, and scarves, clearly indicates there is an issue with thermal comfort.

And we are paying for all this discomfort by using energy to deliver it. Energy at additional operational cost; energy meaning additional capital spent on plant; energy with resource and generation implications; energy which affects our future. People can dress for success, but at what cost.

It’s expensive and often difficult to make a physical difference once the building is complete and running. In effect we hardwire in the building materials choices, the HVAC, the façade, the control mechanisms. We hope we have designed away the effects of location and sun and wind and rain.

In fact we don’t always know whether we have created buildings which work well in their locations and for their function but often rely on people to manage, or adapt or take measures to overcome the indoor environment when it has a direct impact on their productivity.

And that productivity is a huge reason to get thermal comfort right in the first place, to know what your specification should be, and to know you are designing for it.

Studies have suggested that the cost of workers is somewhere around 90% of a business’ operating outlay and this means the productivity of those people is pretty important. Even if they don’t work harder or better due to an improved thermal environment perhaps they will work longer. If every employee saved just ten minutes per day by not having their thermal comfort needs uppermost in their mind or having to respond to deficiencies then this translates to a 2% increase in available time. If they are also relieved of thermal stress think how much more they will be able to achieve.