SAGE (Sound Advice for a Green Earth) is a project by advanced students in Earth Systems and other programs to answer sustainability questions. Submit questions at stanfordmag.org.
Q: What is the energy cost/carbon footprint of drinks served with ice cubes compared with that of room-temperature drinks?
The Essential Answer
It’s a sweltering summer day, the kind when buzzing cicadas and the relentless sun inundate your senses. You take a sip of ice water or iced tea and relish the sound of ice cubes clinking in your glass. It’s almost as refreshing as the drink itself.
But what environmental impact does this indulgence have? At home, you likely make ice with a built-in dispenser in your fridge-freezer or in an old-school ice tray. So let’s examine how much energy your trusty refrigerator uses. After all, the easiest place to make changes is at home.
I compared energy consumption figures for 15 Energy Star fridges with volumes between 15 and 23 cubic feet (a common size range for domestic use) and found that on average, a new, efficient fridge emits about 0.357 tons of CO2 per year — approximately the same as driving a gas car from Stanford to Seattle. I say new fridge because older fridges are far less efficient than current models. With 170 million fridges in the United States, 60 million of which are over 10 years old, we’re looking at annual emissions of more than 60 million tons of CO2!
So if you want to reduce the carbon emissions of your cold beverage at home, your first step is to make sure you have an efficient fridge. It’ll save you money too — older, inefficient fridges cost consumers $4.4 billion a year! So if yours is past its 10- to 15-year expected life, consider recycling and replacing it. A fridge with the Energy Star label is the best choice; these are guaranteed to be at least 9 percent better than the federal minimum efficiency standard. And you’ll likely save more energy than that, since that figure is compared to other new fridges. The result: savings on your electricity bill, a nice rebate, and a smaller carbon footprint.
Your own kitchen is a great starting point, but unless you own the store, you probably can’t buy your local Starbucks a new freezer (though you could opt for hot drinks instead of iced). But not all hope is lost. Check out the Nitty-Gritty, below, for more tips on how to run your fridge-freezer efficiently and to read about a cool new technology for commercial enterprises that could revolutionize how we chill our beverages.
The Nitty Gritty
In my answer above, I did a back-of-the-envelope calculation to estimate the energy consumption of household fridge-freezers in the United States as a proxy for the energy footprint of the ice we put in drinks. I also recommended replacing your old fridge with a new, more efficient one to reduce the environmental cost of chilling your beverages. Of course, buying a new fridge is not an option for everyone. Luckily, there are other ways to minimize the footprint of that frosty mug of your lab mate’s home-brewed lager.
If you can’t buy a new fridge, there are several things you can do to make sure the fridge you have is running as efficiently as possible.
1. Set your fridge temperature between 36º F and 38º F. That’s plenty cold for anything that doesn’t go in the freezer, which should be set between 0º F and 5º F.
2. Check the door seals by shutting a dollar bill in the door. It should stay put — otherwise, the seals are letting in warm air and need replacing.
3. Keep your fridge and freezer full. This may seem counterintuitive, but Stanford physics major Hart Goldman explained why it works: Adding a given amount of heat results in a smaller temperature change for a large mass than it does for a small mass. This is because the heat has to spread through the whole object to change its temperature. Goldman provided an intuitive example: “It will take more energy to melt lots of ice than it will to melt less ice.” So when you open the door of your freezer and let in a blast of warm air, if your freezer is fuller, that warm air won’t have as much of an effect, and your freezer won’t have to work as hard to cool everything down again.
4. Defrost regularly if you don’t have an automatically defrosting machine. Built-up frost makes your freezer work harder to maintain its temperature. Check your user manual for instructions on how to do this.
5. Turn off your built-in icemaker and use ice trays instead. Icemakers are huge energy suckers, especially the type with a built-in door dispenser. It’s not because they’re freezing ice — the freezer is already cold — but because the motor in the dispenser needs to be warm to function, so the icemaker, confusingly, has a heating element in it. You can always turn the icemaker on again if you need lots of ice for a party or a picnic cooler.
“But I hardly ever drink iced beverages at home!” you say. It’s true that most ice is produced for commercial enterprises, like restaurants, bars, hotels and gas stations. So when you order a drink, opt for something not on the rocks. If enough people did this, the demand for ice would decrease enough that establishments could run their icemakers less, and save energy.
The biggest energy footprint from chilled drinks in the commercial sector isn’t ice cubes, though. It’s the open-front display fridges common in supermarkets. These waste a huge amount of energy, since warm air from the rest of the room is free to circulate around the beverages. Essentially, these display cases are locked in a futile battle with the store’s heating system as they try to cool down the entire room. Like a regular fridge, they benefit from being fully stocked, so if you don’t need your drink cold when you buy it, opt for something that’s stored at room temperature.
Even when they’re full, those display fridges are huge energy suckers. Fortunately, there’s a new wave of cold-beverage technology on the horizon. Some stores, like Whole Foods Market in Mountain View, Calif., have reduced their need to stock drinks in fridges by providing a water-bath chilling station for customers who want their chardonnay or cola to be cold right away. Submerging a drink in circulating cold water chills it much more quickly than sticking it in a fridge or freezer — consider the difference between standing around in 55 F weather and jumping into a 55 F lake! The energy required to keep one of these small units cool is far less than what’s needed for an open-front refrigerator. The V-Tex, a water-bath device from Enviro-Cool, based in the United Kingdom, uses up to 90 percent less energy than an open-front fridge. By eliminating the need to keep a big stock of drinks cold all the time and allowing customers to chill what they want on demand, stores can save money on utilities and slash their energy footprints.
Iced drinks may not be the greenest way to cool off in the summer heat, but if you follow the tips here to maximize your fridge-freezer’s efficiency at home and to buy smart when you’re out, you can rest easy while you and your ice water defy the sweltering sun.
Sophia Christel, ’15, received her MS in Earth Systems in 2017. Edited by Virginia Fay, who received her MA in Journalism in 2017.