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Are We Over-Air Conditioned?

Air conditioning  made lots of headlines this summer. In newspaper accounts, internet memes, and office gripe sessions, there was much commiseration about the over-air conditioning of the American workplace….


Someecard Source

It seems no one is spared from these polar working conditions – not even energy efficiency advocates!  Colleagues of mine recently attended an energy efficiency conference in the midst of a summer heat wave. Organizers courteously (but ironically) distributed blankets to help shivering attendees keep warm in heavily air conditioned meetings (about energy efficiency!). This is like handing out jelly doughnuts at a weight watchers meeting.

On the face of it, widespread accounts of frigid summer working conditions seem to point to an absurd waste of energy.  But thermal comfort is highly subjective. If complaints are all coming from the easily-chilled tail of the thermal preference distribution, is it possible that office temperatures are about right on average?

The Goldilocks question

In theory, indoor office temperatures should be about right. Temperature control standards for most office building are calibrated to optimize something called the “Predicted Mean Vote”. This is a formula that predicts how a large group of people would vote (too cold registers as a negative number; too hot registers as positive; zero = just right) as a function of indoor temperatures, metabolism rate, clothing, etc.

But a provocative study released last month suggests this PMV formula needs updating. These authors claim that one of the primary inputs to current standards – the metabolic rate- is calibrated to the average male. When the researchers measure the average metabolic rate for a small group of young adult females performing light office work, they find significantly lower metabolic rates.

The media spin on this paper played up the irresistible battle of the sexes dimension. This set off a heated/amusing debate between freezing women who decry “sexist thermostats!” and sweaty men who point to the first fundamental law of clothing (you can always put more on -but there is a limit to how much you can appropriately remove!).

The industry response to the study looks quite different. The engineers at the Association of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE)– who know a thing or two about temperature control standards in buildings- say that the authors have misinterpreted how the standards are actually set. They assert that thermal comfort criteria are based on extensive laboratory studies of both men and women. These studies find that when men and women do the same kind of sedentary work in the same type of clothing, there are no relevant differences in preferred temperatures across sexes.

To make sense of all of this, I went to find my Berkeley colleague Stefano Schiavon who studies indoor work environments and building energy consumption. Ask Stefano whether commercial office buildings in the US are kept too cold in the summer and you get an impassioned (he is Italian after all) Yes!!

By 3 degrees Celsius at least, he says. But, he argues, factors such as oversized HVAC systems – not sexist thermostats – are to  blame. For example, a temperature check across a sample of U.S. office buildings finds average summer temperatures in US office buildings are not only below the recommended ASHRAE standards, but colder in summer than in winter!

How much energy wasted?

Whereas office buildings are often cooled to around 72°F  in the summer, experts suggest  something in the range of 77°F can be maintained (assuming good air circulation) with no loss of worker satisfaction.  Lose the necktie, put on some linen shorts, and you have Japan’s “Cool Biz” campaign which recommends an 84°F set point for office air conditioners.


Super Cool Biz : Looking super cool in 28°C!

How much energy could be saved if we increased the average cooling set point in office buildings?  A team of Berkeley researchers recently looked at increasing cooling set points in office buildings from 72°F  to 77°F.  Across climate zones and office buildings types, they estimate a reduction in cooling energy consumption of 29 percent on average.

By my very crude calculations, if we apply this reduction across all air conditioned office space in the United States (estimated at 14,095 million square feet in 2012), this amounts to a reduction in electricity consumption of 11,300 GWh/year.[1]

Compared to total annual electricity consumption, this does not amount to much ( less than half a percent).  But the impact would be comparable with other climate change mitigation measures we get excited about. For example, the EIA estimates nationwide solar PV production in 2014 at  15,874 GWh (utility scale).  In other words, keeping indoor air temperatures too cool in the summer is working to offset hard won emissions reductions achieved elsewhere.

Too much of a good thing

Air conditioning at the office – when used in moderation – is a very good thing.  There is plenty of research demonstrating that air conditioning reduces mortality, boosts productivity, and makes us happier, more agreeable people.  However, in many American workplaces, it seems this good thing is being taken to a wasteful extreme.

We should be paying more attention to how we (over-) cool our commercial buildings. But it can be very hard to get people excited about energy efficiency and/or conservation.  Several new technologies (such as apps that help individuals control their cubicle climate) on the market make energy conservation more accessible and more fun. Between the stereotypical shivering female office worker and her gadget-loving male counterpart, this could lead to smarter cooling – and some energy savings- in our office buildings next summer.

[1] EIA estimates the average cooling energy intensity for office buildings is 8,900 btu/square foot – or 2.764 kWh/square foot accounting for line losses.  2.764 * 14 095 million * 29 percent ~= 11,300 GWh per year.

10 thoughts on “Are We Over-Air Conditioned? Leave a comment

  1. I’ve been victimized by overly cooled buildings. One of the coldest work environments I ever experienced was a two week stint in the same building occupied by the Public Utility Commission…in August. We had to go outside every few hours to thaw out.

    Indoor temperature is one source of energy inefficiency. Ancient, low tech cooling systems are another. Variable speed chillers coupled with variable air volume air distribution, all driven by a properly tuned control system can make a significant dent in cooling energy use.

  2. Okay,

    Among the solutions described in the new technologies link, Honeywell indicates that it has an app that will allow control of the thermostat via voting. But what sort of method? Plurality? Hare? Borda?

    Someone call Ken Arrow, , , ,

  3. ” ….. Stefano Schiavon …… he argues, factors such as oversized HVAC systems – not sexist thermostats – are to blame.”

    Total rubbish.

    HVAC systems are sized to cope with ‘the worst’ expected conditions; so for cooling, any day other than the hottest ‘design’ day, means the system is ‘oversized’.

    What causes perceived human discomfort, (assuming adequate fresh-air ventilation rate and acceptable humidity) is poor control, and, poor air distribution.

    Perhaps he confuses system efficiency with system effectiveness? It’s entirely possible to have a highly efficient system which is ineffective; and conversely, a highly effective system which has low efficiency.

    I’ve experienced open-plan areas which have had heaters operating in one area, with cooling operating simultaneously in a different area. Simply because solar gain was affecting the south side of the building.

  4. Meredith
    You are just tip-toeing around an issue. One of the major problems is an unrealistic design Outside Air Temperature {OAT}. For example, on the East Coast, the design OAT is 95dF DBT / 76dF WBT.

    Global warming notwithstanding, that condition only exists a very brief time. Moreover the daily excursion of temperatures can take one of three tracks from morning to mid day; 1) constant wet bulb; 2) wet bulb depression during fair weather, & 3) increased wet bulb.

    After mid day the temperatures regress back to the due point.

    Demonstrate this for yourself by down-loading the hourly weather data for a sample of days and plot the data on a psychrometric chart.

    By basing the cooling coil design on an unrealistic criteria, the coils are difficult to control (too often operate at minimum capacity or sub-cooling).

    The use of so called DEDICATED OUTSIDE AIR SYSTEMS [DOAS], especially those using enthalpy heal wheels, only increases the cost and complexity of HVAC systems but does little to solve the problem of sub-cooling occupied space.

    USGBC -LEED is also counterproductive to good space conditioning. The LEED point approach to design is like a paint-by-number Mona Lisa (artless).


  5. In Davis I have noticed that the outside temp. has an effect on how warm I feel even though the inside air temp is set the same, say 75. My office has an outside wall with considerable glass.
    Can it be the radiation to and from this wall that makes me feel warmer when it is 95 outside compared to when it is 65? I have the same amount of clothing on.

  6. Be interesting to study gender segregated workplaces (somewhere in the Middle East perhaps?) to see whether their thermostat set-points end up different.
    The campaign to make workplace dress less formal, and therefore buildings warmer in summer, has been around for a while, and based on my experience seems to have been pretty much a failure. Never overlook the importance of culture in energy use patterns.

    • There are no truly gender segregated spaces since the AC systems are common. While teaching at a university overseas I was always cold in the spring/ summers [outside temps in the 100-125degF range] and too hot in the winters [outsides at 35-50degF]. The retort from facilities was that they keep the setting at 60degF in summers and 78degF in winters. The NATURAL response of about half the professors was to keep the screened windows open to ‘leak out’ the over chilled/heated air.

      The solution really is to get better circulation of the conditioned air. Because of poor circulation parts of the offices and the classrooms were too hot/ too cold – so you had to chill/ heat the whole so that the worst areas of the environment were comfortable.

      There are simple steps to fix the circulation problem both in retro-fit and a new building stages. Probably the most efficient energy savings technique.

  7. I question whether this is an actual gender-based difference, or simply multicollinearity between gender and physical size.

    Smaller people have a higher surface-to-weight ratio. Regardless of gender. These folks are more likely to be cold. Most women (but not all) and some men (but not most) are smaller than average.

    Those of us (in every gender) who are well-insulated (i.e., cuddly) feel the world differently.

    I’d be interested in seeing a controlled test among people with the same height and weight as to whether there are truly gender differences in preferred indoor temperature.

    I have no doubt that a building conditioned for the comfort of older men wearing neckties will be too cold for younger people wearing more sensible clothing. But I question whether it’s a gender-driven difference.

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