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The comfort factor, myths and myth busters

air conditioning

FROM THE TREASURE CHEST (2013) My name is L30NW-007. Sounds like a secret agent. But I am not – I am a thermostat. I am mounted at 1.7 metres on a column, in the north west corner of this prestigious building in Sydney on level 30.

What I am about to share with you involves information that could demystify the phenomenon of comfort.


Comfort is a complex issue and very personal. I see that every day. Very highly paid workers surround me and you can be rest assured that, being a thermostat, I am blamed every day by a select few for not looking after their comfort needs.

I certainly try because my sole aim in life is to control the airconditioning system serving this corner of the building – during the normal occupied times. Most weekends I am off – though that is changing as the lifestyle of the office worker changes. I am starting to see more workers coming in on weekends.  No rest for the wicked as they say – I mean the workers of course!

How does a humble thermostat fit into the operations of a commercial workplace?

The simple answer is that the thermostat is the most visible part of the airconditioning system. I maintain pre-set indoor conditions. Obviously, this is subject to whether the cooling and heating systems are designed and installed properly.

So do you want to know how I work?

In this case, my job is to control the relevant components of the airconditioning system. So when it’s warm in the summer I tell the system to provide some cooling.

Similarly, during the cooler conditions, I initiate heating. I make it all happen automatically, so those important office workers have nothing to complain about.

So I hope you can now appreciate that I, and my thermostatic colleagues, play pivotal roles in the lives of so many, bearing in mind that a majority of people in the western world spend more than half their lives in artificial environments.  In my (rare) idle moment I wonder whether human beings were ever designed to spend so much time indoors with artificial lighting and controlled thermal environment…but it’s not for me to judge…just to do my duty.

Warren S Johnson

Let us take a walk back in history. My ancestor used to be a simple device invented in 1883 by Warren S Johnson – bless his soul. It was an electric device which included a mercury thermometer with electrodes inserted directly through the glass so that when a certain fixed temperature was reached, the contacts would be closed by the mercury. That would start or stop a fan or a heating unit. These types of devices were accurate to within a degree of temperature. Not bad for the period, you’d have to agree.

But the basic concept behind airconditioning goes back a lot further. In ancient Egypt, reeds were hung in windows, with water trickling down them. The evaporation of water cooled the air blowing through the window, though this process also made the air more humid.

Ancient Romans went a little further and used water from aqueducts circulated through the walls of houses and temples to cool them down.

Similarly the old Indian and Chinese palaces adopted evaporation and air breeze techniques to keep occupants cool. Other inventions included use of cisterns and wind towers in medieval Persia to cool buildings during the hot season.

Modern airconditioning emerged from advances in refrigerant chemistry during the 19th century, and the first large-scale electrical airconditioning was invented and used in 1911 by Willis Haviland Carrier.

Thermostats, in all forms, have become integral parts of the heating, ventilation and airconditioning systems. Some of my cousins have time clocks so that multiple functions can be carried out.

However, things have come a long way since then. I am now part of a very sophisticated next generation computer based building management and control system.

I am actually a sensor as my “intelligence” is based in the electronic panel, which essentially is a computer that directs the signals from and to the various input and output devices.

I am pre-set to maintain 22.5 degrees in the zone and when the condition in the space gets outside this by half a degree in either direction that’s when I kick in with some heating or cooling.

The BMCS is often judged by how well it can control the pre-set zone conditions. Most of the sophisticated systems are able to control within a quarter of a degree, as opposed to the good old pneumatic systems of the 70s that generally controlled within two degrees.

I wonder what the level of complaints were during that era.

The BMCS computer also has the ability to carry out various other functions such as set the times of operation of the airconditioning system, record the temperatures, humidity, energy consumptions and other valuable data.

Knowledgeable engineering consultants and facility managers use this data to optimise the operation of the airconditioning system to achieve minimum energy consumption values so that the building can be rated and given environmental and energy ratings.

Our building has recently been awarded five stars through the National Australian Building Environmental Rating System. While that is good news for the building owner, not all the occupants are necessarily happy. The diversity in opinions about the indoor conditions is very evident, especially where I am located. The north west zone gets the sun every afternoon every day and also during the winter months.

Mike, who sits in the workstation closest to me, seems to be happy. He also dresses sensibly – summer clothing in summer and often a sleeveless sweater during the cooler months. Rhonda, on the other, who sits at the next workstation, always complains. She looks at me all the time as if it is my fault. She does not dress according to the seasonal changes. Her complaints range from conditions being too hot or too cold or airflow too drafty.

The most interesting observation was when we had the hottest day in Sydney; she actually put on a cardigan because she reckoned that it was too cold inside.

It is evident that the level of complaints of the zones being too hot or too cold have increased in the last few years, probably since the commencement of the “green” movement in the 90s. There is no doubt that the focus on minimisation of energy use, and hence reduction of greenhouse gas emissions, has been beneficial – taking into account that airconditioning, as an entity, contributes significantly to generation of greenhouse gases.

But has this been at the expense of compromising occupant comfort conditions?

So the obvious question is: What is indoor thermal comfort? Various scholars have researched this important topic and have come up with the following factors that contribute to indoor thermal comfort:

  • Firstly – activity – such as walking in shopping mall, sitting in the office, exercising at a gym. The human metabolic rate depends on the activity. Hence the term is called “met” value when assessing an activity. Intensive activity would attract a higher “met” value.
  • Secondly, clothing – this is interesting: each item of clothing is given a value. For example, a sweater would have a much higher value compared to say a swimming costume. Thus when assessing the overall “clothing” or “clo” value the individual clothing indices have to be taken into account.

Already one can see that if the activity is high, like working out in a gym, then the clothing has to be light for comfort. It also makes perfect sense why people have to dress according to the season.

For given activity and clothing the other environmental parameters that influence human comfort are:

Temperature – this is the one that most people relate to. In fact every morning most people look outside or check the weather forecast to see what the temperatures are going to be so that they can dress accordingly.

There are two components of temperature that one needs to understand – the air temperature and the radiant temperature.

The radiant temperature is as a result of heat source like the sun’s rays on your body.  An example is when you are in a car – the air temperature within the car maybe suitable (if say the air conditioning is working) but you may still feel “uncomfortable” if the sun rays are directly on the your skin.

It is possible to measure the air and radiant temperatures using special instruments. However, for most applications air temperature is more commonly measured and referred to. It is a vital part of the thermostat. Since it is an important measure, every thermostat, including myself, requires frequent recalibration to make sure that it is sensing the correct temperature.

Humidity – It appears that not as many people seem to be affected by variations in humidity as they are by temperature. Most commercial airconditioned spaces try to maintain between 40 per cent and 60 per cent relative humidity.

Generally there are no humidistats installed in normal offices. My girlfriend is a humidistat located in the computer room. It is interesting that humidity variations have more of an impact on electronic equipment so she certainly plays an important role in maintaining close humidity conditions.

Air flow – this certainly has an impact on comfort, including air circulation and air movement. If the air velocity is high one may feel “cooler”, mainly due to evaporation of sweat from the skin.  However, high velocities could lead to drafts.

The most common complaint is the “cold” draft on one’s neck. Not enough air flow, on the other hand, could lead to “stuffiness”.

No wonder there were “pankavallas” in the olden days, who provided air movement, using manual fans, for the “Maharajas”. Modern day version of this phenomenon is the ceiling and other ventilation fans that are capable of providing some relief from hot conditions. Almost at the cost of putting myself and the airconditioning industry out of business, I have to agree that there is nothing like a cool breeze – especially a cool change after some of the scorchers that prevailed during the summer months

Comfort “gurus” have combined these three measureable parameters and developed a single “thermal comfort” unit called predicted mean vote.

This has been documented in an International Standard ISO 7730, if one wants to know some of the intricacies associated with comfort. One important correlation is that PMV has a relationship with percentage of people dissatisfied. What this means in simple language is that if the PMV is at its extreme value (plus or minus three) when either temperature, humidity or air flow are very high or very low, then 100 per cent of a group will be dissatisfied. As the PMV approaches zero the PPD levels improve.

When the temperature, humidity and airflow are “ideal” for a given activity and clothing value, there will still be around 5 per cent of any group dissatisfied. This is human nature. You may have noticed this in your own experiences. Some estimate the percentage of people dissatisfied to be greater than 5 per cent during those ideal conditions.

The office space, where I am located, has a PMV range of 0.5 to 0.75 – which is very good – bearing in mind PMV closer to zero is ideal. However, as outlined earlier, the level of occupant complaints is still high and hence one wonders whether PMV is more theoretical rather than practical. The more one researches in this area of comfort complexities the more one realises that only the surface has been scratched.

To add to this intrigue is the whole question of human productivity with respect to indoor thermal comfort. The question being – does human productivity increase with better indoor thermal comfort?

There are various assertions made on numerous case studies but there are no conclusive results. If the correlation was simple it would have been documented by now and we would not be talking about it.  It is the “holy grail”!

Ashak Nathwani

Maybe one day I will be replaced with a sophisticated PMV capable device, appropriately called “Comfortstat” that will be able to assess what the indoor comfort levels are and the more intelligent ones may even be able to “calculate” the productivity levels. Until then I believe the humble thermostat will continue to play the key role in peoples live.

Make sure you pay due respect when you see the next thermostat. Until next time, try and be comfortable with whatever suits you!

Ashak Nathwani is Adjunct Senior Lecturer, Faculty of Architecture, Design & Planning, at the University of Sydney.

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