As We Now Think

Reflections, commentary and analysis from Consortium for Science, Policy and Outcomes at Arizona State University.

Cool It About Cooling

By Clark Miller

People are generally far more rational than our hyper-scientific culture is willing to acknowledge. Occasionally, however, faulty assumptions are so deeply built into even scientific ways of thinking that errors get perpetuated over and over without ever being examined.

So it is with the environmental costs of air conditioning. The latest analysis comes from Elisabeth Rosenthal of The New York Times, in an article titled “The Cost of Cool” (Aug. 18, 2012). “Air conditioning,” Rosenthal writes, poses “one of the world’s most vexing environmental quandaries.” But does it, really?

The argument that air conditioning is a major environmental problem stems from the belief that air conditioning consumes excessive energy. As Rosenthal observes, “Fact 2: Air conditioners draw copious energy.” (Foreshadowing: not so much.)

Underlying this belief is another one: air conditioning is sinful. Rosenthal continues, “Fact 3: Scientific studies increasingly show that health and productivity rise significantly if indoor temperature is cooled in hot weather.” Then comes the kicker: “So cooling is not just about comfort.” Notice the presumption implied in the last sentence: air conditioning has been, at least in the past, not about necessity but about feeling good. Moreover, those good feelings come with a cost—just like any good sin.

To paint air conditioning as a quandary, Rosenthal is trying to get us to see air conditioning as not just an expensive, environmentally damaging luxury available to rich people. Why? Because that’s the presumption inherent in US cultural attitudes. Leonard Jordan writes: “In the last half century, air conditioning has joined fireworks, swimming pools and charred hamburgers as a ubiquitous ingredient of an American summer.” Stan Cox has written a new book, Losing Our Cool: Uncomfortable Truths About Our Air-Conditioned World (and Finding New Ways to Get Through the Summer), in which he observes that air conditioning is not only bad for the environment but bad for our health, as well. Get outside in the summer! Everyone, it seems, would agree: air conditioning is a problem.

But are they right?

Let’s start with a new set of facts. Fact 1. In the United States, the average household uses five times as much energy for heating than for cooling, as Figure 1 attests. Let me repeat that: 5 times. And that’s just for space heating. If we add water heating, the total for heating comes to 63% of average household energy use. Space cooling use is only 9% of total. And refrigeration is only 4%. How can that be, you say? Partly, of course, these are averages. For folks in Florida and Arizona, they are unrepresentative. I can attest from my own bills that at least 50% of my energy costs, here in Phoenix, go to air conditioning. In most of the country, however, energy use for air conditioning is very low compared to energy use for heating.

Figure 1. Average US household energy use, by end use.

Fact 2: Energy use in high air conditioning states is significantly lower than in other states. Really? Yep. See Figure 2. DOE really does collect data about everything. The three lowest states in the country for average household energy consumption are CA, AZ, and FL. California is low because their state utility regulators have pushed energy efficiency for the past 40 years, reducing their consumption by enormous amounts. I can guarantee that we’ve had no such program here in Arizona. Why then are AZ and FL energy consumption so low?

Figure 2. Average household energy use in the US by state.

I think you can probably guess. In neither state do you need to heat your house in the winter. That’s right, for all of you who think—and I used to think this myself—that air conditioning is an energy hog. It’s not, at least not when you compare it to heating. My utility bills are significantly lower in AZ than they were back in Wisconsin, thanks to the fact that my energy use has declined significantly, even with Phoenix summers. Note, in Figure 2, where the greatest energy use takes place: IL, NJ, MI, IA, MN, ND, SD, CT, ME, NH, RI, VT, ID, MT, UT, WY. I’ve lived in IL, IA, MN, and WY. Talk about places that are cold! Our northern tier states, especially those at high altitudes or that get their winter weather in the form of Arctic air masses out of Canada, have the greatest energy consumption.

How can that possibly be? Well, I’ll give you a hint. Even when it’s 117 outside, I am only cooling my house about 40 degrees, to 77. In Wisconsin, when I heated my house in the winter, I often had to heat from 0 to 68 (if I was really good and didn’t turn it up to 72). And on the worst days, it was -10 outside. In other words, the temperature difference I’m trying to make up for in Arizona on the worst days (40 degrees) is only about 50% of the temperature difference I was trying to make up for in Wisconsin on their worst days (78 degrees). That’s a really big deal, since energy use and temperature difference go hand-in-hand. The greater the temperature difference, the greater the energy required to maintain it over time.

But wait, you say: “That’s not fair. Heating is required for survival; air conditioning is not.” Now we get to the nub of it. Aside from the fact that 117 is brutal, by any definition, and can be quite deadly, think about the origins of our views about heating and cooling. Humans have heated their environments for millennia, because fire was an easily available tool. Air conditioning came along much later. Thus, we tend unconciously to take heating for granted and to think of cooling as a novelty. Worse, in the US, most of us migrated from Europe (and, even, Northern Europe), where cold temperatures predominate, as they do in much of the US. Moreover, since we view Arizona and Florida as places where rich people go to retire (this turns out to be largely a myth, too), we are culturally programmed to think of air conditioning as a luxury.

Take Andrew Ross’s new book, Bird on Fire: Lessons from the World’s Least Sustainable City. That would be Phoenix. And why, in Ross’s mind, is Phoenix unsustainable? Because it’s on fire. It’s hot, here, and that means we use a lot of air conditioning to cool our houses. Indeed, it’s fair to say Phoenix could not have reached the size and scale that it has without air conditioning. Not enough people would have been willing to move here. Now, don’t get me wrong. There are a lot of aspects of Phoenix that are highly unsustainable. But air conditioning isn’t one of them. If the 5 million people currently living in Phoenix and Tucson were, say, living in Detroit or Minneapolis, they would be consuming far more energy. (They would drive more miles on average on their daily commutes, too, according to the US Department of Transportation.) Dare we say that their lifestyles would be less sustainable, at least in terms of energy use?

Is there, in fact, any legitimate moral ground for differentiating between heating or cooling a house to a temperature that is comfortable for the people that live there? I’m afraid I can’t come up with one.

Indeed, if the subject is renewable energy, then cooling has some advantages, at least with respect to solar energy. Both heating and cooling occur on a 24-hour basis, especially in very hot and very cold environments. The greatest need for heating, however, is in the winter, often at night, when temperatures are the coldest. By contrast, the greatest need for cooling is in the summer, during the daytime, when temperatures are the hottest. Solar energy, which must ultimately provide the bulk of renewable energy, is more broadly available during summer days than during winter nights. It will be easier, therefore, to satisfy cooling needs with solar energy than it will be to satisfy heating needs. It’s not an accident that many households in Southern California and Arizona are putting solar panels on their rooftops.

One final observation: one of the sad features of the air conditioning story, at least as it is currently being told, is that it plays once again into unjust narratives about who is to blame for global warming. Rosenthal’s latest article is part of a series of articles she has written for The New York Times on the topic, all of which put the blame for global warming on rising demand for air conditioning in poor countries like India. In an article under the headline, “Chilling Effect: Relief in Every Window, but Global Worry, Too,” Rosenthal writes:

“In the ramshackle apartment blocks and sooty concrete homes that line the dusty roads of urban India, there is a new status symbol on proud display. An air-conditioner has become a sign of middle-class status in developing nations, a must-have dowry item. … But as air-conditioners sprout from windows and storefronts across the world, scientists are becoming increasingly alarmed about the impact of the gases on which they run. All are potent agents of global warming.”

It is worth remembering that, in India, per capita greenhouse gas emissions are approximately 10% of US totals, while 400 million people are completely without electricity. Over the next half century, air conditioners may, indeed, raise global greenhouse gas emissions totals—but I am willing to bet that, on a per household basis, they will never be responsible for as much of a long-term contribution to climate change as US households burning fuel oil or natural gas to heat their houses. Based on one study, space heating runs about 8000 kWh of energy use per year on average in the US. A modest-sized room air conditioner, drawing 7.5 amps, running 10 hours per day, for 100 days, would use about 800 kWh per year.

The bottom line: if you want to worry about the global warming consequences of personal comfort, worry first about heating, not cooling.

Clark Miller is the associate director for the Consortium for Science, Policy and Outcomes at Arizona State University.

5 comments on “Cool It About Cooling

  1. MarkB
    October 1, 2012

    “Solar energy, which must ultimately provide the bulk of renewable energy…”

    You were doing great until this. I’m not sure what it means. Are you talking about sun-rich Arizona? Certainly not Minnesota. If the bulk of anything is going to come from a diffuse, intermittent source, red flags should go up. I remember when we were first told that if we’d just subsidize solar power for a few years, technology would improve, factories would scale up, and we’d have virtually free energy. That was in the 1970s, and I”m not pushing my 60s. As the natural experiment in Germany has shown in bloody detail. large scale solar electricity generation is a disaster, to the point of madness.

    If solar is to provide the bulk of ‘renewable’ power, renewable will never be more than a vanity project. Simple fact.

    • clarkamiller
      October 1, 2012

      MarkB — Thanks for your comment. Solar obviously wasn’t the point of the essay, but I can tell you what I know.

      If you look at the total available resource from different renewable resources, what you see is that the available solar resource is not only significantly greater than any other single source of renewable energy (e.g., wind, waves, geothermal) but it is also larger than the rest combined. To be sure, other renewable resources are not small, and combined add up to a significant fraction of current total global energy use. So, all of them will be significant during an energy transition. But solar is the only renewable resource that could theoretically provide energy on scales significantly larger than is currently consumed around the planet.

      I spent this summer in Germany talking to energy engineers working with their utilities. Far from a disaster, Germany has demonstrated that large-scale renewable energy use is viable. They have had days for which renewable energy provided greater than 50% of the country’s total energy needs. Key individuals indicated to me that, based on their success to date, they felt that 100% renewable generation was possible for Europe as a whole in the coming decades. It will be a substantial engineering and socio-political project, but they are convinced it can be done.

      It’s also important to look at energy storage. Various groups around the US are working on technologies that would directly convert solar energy into transportation fuels (i.e., not biofuels but chemical conversion processes) that are carbon neutral. There are other storage options available as well. The German’s are envisioning hot water, for example, for district heating, as a key storage technology. With significant storage, the problems of diffuseness, intermittency, and geographic variation become significantly less relevant. Electric vehicle batteries, for example, could be charged during the daytime using solar energy transmitted around the country on the electricity grid, while people are at work.

      • MarkB
        October 2, 2012

        Your take on Germany is remarkable. I would suggest that you’ve been talking to the true believers. German heavy industry is being forced to build its own backup generation due to fluctuations coming from your ‘renewables.’ Some industries can suffer serious damage to their facilities when voltage/current swing too far, and it is already happening.

        Solar subsidies cost German users billions each year already. The production you cite is built on those subsidies entirely. From Spiegel Online:

        ” Photovoltaics are threatening to become the costliest mistake in the history of German energy policy. Photovoltaic power plant operators and homeowners with solar panels on their rooftops are expected to pocket around €9 billion ($11.3 billion) this year, yet they contribute barely 4 percent of the country’s power supply, and only erratically at that.

        When night falls, all solar modules go offline in one fell swoop; in the winter, they barely generate power during the daytime. During the summer, meanwhile, they sometimes generate too much power around midday, without enough storage capacity to capture it all. The distribution network is also not laid out in a way that would allow the country’s thousands of owners of photovoltaic arrays — a term used to denote an installation of several panels working together — to feed into the grid as well as draw power from it.”

        The build-out of solar photovoltaic in Germany makes about as much sense as hydro in the desert. Berlin is as far north as Quebec City. The wrong-headedness of the thing is mind-boggling. The modern industrial civilization is built on reliable electrical power. If you think solar is a good idea, I invite you to tie in to solar yourself – with no backup. When the sun goes down, your lights go out. See how this – ” They have had days for which renewable energy provided greater than 50% of the country’s total energy needs.” – works for you then. A day is 24 hours the last time I looked.

  2. Clark, thanks for the provocative piece. It seems particularly counter intuitive, as I would have imagined cooling to be a less efficient process than heating (since other technologies we use anyways contribute to heat, and inefficient heating byproducts at least are beneficial). I’m curious to know a bit more…

    Is the national average energy consumption figure adjusted for population distribution? We’d expect heating numbers to be higher if more people are heating in the average. I assume it’s reflective of an entire year too, not a smaller sample?

    How is the figure for space heating/cooling energy use calculated? How do they, for instance, determine whether the A/C is being used to heat or cool at a given time?

    What I think would be more telling would be a per capita energy use related to energy for heating/cooling. I wonder how the “household” measure adds variability (i.e., if the average household has more or fewer people in the SW), and the state-by-state diagram doesn’t parse out temperature-related energy use.

    Again, thanks for the interesting piece!


  3. Nichol Brummer (@Twundit)
    February 25, 2013

    Isn’t the real big picture that both cooling and heating can be reduced by large factors, or even made unnecessary .. by the right architecture? Insulate. Catch the heat when you want it, keep it out when you don’t want it in. Store the warmth of day for the cool night, or the coolth of night for the scorching day. It isn’t rocket science.

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This entry was posted on September 13, 2012 by in Energy and tagged , , .
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