Sunday, December 21, 2008

Thermal comfort in China

Walk into almost any building in Beijing and you will notice that thermal comfort standards are not as high as they are in the West. While wearing a jacket inside in the winter (or short sleeves in the winter) is not necessarily comfortable, it is energy efficient. And it also raises a key issue of whether growth of America's LEED green building standard in China is a good thing or a bad thing.

What are thermal comfort standards like in America?
Thermal comfort standards are designed to ensure that buildings occupants are comfortable while indoors, which is important since Americans spend 90% of their time indoors. Thermal comfort standards in America are set largely by ASHRAE Standard 55-2004. According to ASHRAE,
the standard specifies the combinations of indoor thermal environmental factors and personal factors that will produce thermal environmental conditions acceptable to a majority of the occupants within the space. Environmental factors include temperature, thermal radiation, humidity and air speed, while personal factors are activity and clothing.
According to Stephen Turner, PE, of CTG Energetics and a key contributor to ASHRAE Standard 55-2004:
[ASHRAE 55-2004] is based on chamber studies and results in a range of temperatures over which conditions are predicted to result in an acceptably low percent [generally 20%] of people who would express dissatisfaction with thermal conditions in the space.
So using the ASHRAE standard, you will arrive with a range of acceptable temperatures that looks like this:
This is a pretty tightly controlled range, and generally ensures you won't have to wear your Christmas sweater indoors. Increased occupant comfort also generally increases productivity. So this is a good thing. But unfortunately, there is also an energy cost associated with keeping the temperature in such a tight set range. This is why Jimmy Carter suggested that we turn down our thermostats and wear sweaters to save energy.

But as Carter's failed attempt to get people to turn down the thermostat showed, Americans are unwilling to give up their thermal comfort. So in America, the goal has shifted from expanding the range of acceptable occupancy temperatures. As codified in the LEED rating system (which has 3 ASHRAE Standard 55-2004 related credits), the new goal is to maintain the same thermal comfort standards but keep the associated energy cost as low as possible.

But as Carter's failed attempt to get people to turn down the thermostat showed, Americans are unwilling to give up their high thermal comfort standards. Rather, the new goal is to maintain the same thermal comfort standards but keep the associated energy cost as low as possible. In fact, even the LEED green building rating system codifies this high thermal comfort standard by including 3 credits related to ASHRAE Standard 55-2004.

And China?
Ostensibly, thermal comfort in Chinese buildings conforms to ASHRAE 55 or other international standards. But as with most standards in China, few buildings actually meet these standards. For example, a recent study of buildings in central southern China found that during the summer 52% of buildings had temperatures outside of the acceptable ASHRAE 55 range. But surprisingly, most building occupants still reported satisfaction with thermal comfort, with fully 87% reporting that the thermal comfort conditions were acceptable! This suggests that Chinese people are comfortable, or at least okay with, occupying buildings with temperature ranges well outside of what the ASHRAE 55 standard would require.

Thermal comfort expert Professor Zhu Yingxin of Tsinghua University fully agrees with this finding. Her research has shown that Chinese people can be comfortable at temperatures significantly warmer than ASHRAE 55 would allow, even up to 30* C (86* F). The upshot of this is that Chinese may be willing to accept a higher variation in indoor temperature, which would require less cooling and heating energy.

This suggests that applying both ASHRAE 55, and by extension, LEED, standards to China could result in unnecessarily high uses of energy for heating and cooling spaces to such tight temperature ranges. Professor Zhu agrees, and thinks it’s critical for China to create their own thermal comfort standards that effectively reflect the uniqueness of Chinese characteristics.

What about productivity?
By extension then, the widespread adoption of LEED (which again, gives 3 credits for buildings that comply with ASHRAE 55) in China may have the perverse affect of driving China to use more energy than it otherwise would have.

But on the other hand, much research related to green buildings in America has shown that green buildings can increase occupant productivity. For example, a 2005 LBNL-University of Helsinki study (PDF) suggested that the performance of office workers is best between 21-22* C and declines as temperatures rise. This temperature is within the ASHRAE 55 temperature range and suggests that adopting the ASHRAE standard could boost productivity.

So by not adopting these standards, are workers in Chinese buildings less productive? Maybe. The LBNL study concluded that at 30* C, productivity declines by 9%. But again, these results were based on American office workers. More study is needed on how Chinese worker productivity responds to temperatures.

The inevitable climb
In my view, although Professor Zhu’s research shows that the Chinese can accept warm temperatures, they don’t necessarily prefer them. For example, a Beijinger could theoretically accept public transportation, but in practice, many buy Audis. So are we to expect that as Chinese building occupants continue to increase their standards of living, they won’t aspire to the American level of thermal comfort standards? Let’s just hope that the Chinese do it in the most energy-efficient way possible.

In fact, Professor Zhu’s research will hopefully help do just that: she has found that proper natural ventilation in building spaces can make Chinese people feel much more comfortable at relatively higher temperatures. And Stephen Turner hinted that ASHRAE would think incorporating this type of research into the next Standard 55.

3 comments:

Héctor Z said...

Never thought about this standards. Nice post.

SteveInChina said...

As a British guy living in China I can confirm that Chinese people seem comfortable in a much wider range of temperatures than many other folks. A good post, which I found by randomly surfing, and also related to an entry I just made on my own blog - I've linked and commented here ^_^

jon SA said...

hi Geoff, you have a very interesting blog! I'm working in EE in South Africa, but spent a year in Shanghai and it's great to see what you're doing. At the moment I'm working on a paper to investigate thermal comfort standards or building codes for low-cost housing here in SA. It seems like that would be a good place to start considering the apparent savings that would be possible. At the moment there are some voluntary energy efficiency guidelines, but nothing mandatory at this stage. Will be checking on your blog to see what else you've found out. great job!