How many times have you gotten up, opened your fridge, looked in for a minute for something to eat, then closed it again without taking anything out today? If we discount the fact that leaving the fridge door open wastes up to 7 percent of the appliance’s energy use when was the last time you thought about your fridge or your air conditioner and how they work to keep your home and snack food cool? How did the milk in your fridge make it from the cow that created it to your home without spoiling? Let’s take a closer look at the cool (pun intended) science behind refrigeration that we so often take for granted.
Why is Refrigeration Important?
We all know that we keep our milk in the fridge to keep it from spoiling, but how does keeping it cold make sure that you’ve got a fresh dairy topper for your morning Frosted Flakes?
We’ve been keeping food cold since prehistoric times. Even cave dwellers realized that if they kept their food in a cool cave or packed it in the snow, it would last longer. Thankfully, we don’t have to wait for a snow day to keep our food cold these days — most homes in developed countries have at least one refrigerator, with 23 percent having two or more.
Refrigeration keeps temperatures below 40 degrees F or below 32 F for frozen foods. This low temperature prevents bacteria from growing, which means the food doesn’t spoil as quickly and is safer to eat for more extended periods. How does it work?
The Science of Refrigeration
The science of refrigeration relies on the Second Law of Thermodynamics — everything tries to maintain the same temperature over time. Heat naturally moves from high-temperature areas to low-temperature ones. That’s why cold air sinks and hot air rises, and why ceiling fans can keep your home more comfortable — because the air wants to stay the same temperature, but the hot air is rising to the ceiling while the cold air sinks to the floor. Ceiling fans keep everything moving, mixing the two temperature substrates.
Refrigeration uses the same principle, whether it’s your homes HVAC unit or the fridge in your kitchen. Refrigerant circulates through pipes in the system. When it leaves the compressor, the gas is hot, so it naturally wants to move into cool areas. It is converted into a liquid as it cools, then into a cool gas that travels back to the compressor.
In your fridge, this is contained within the appliances. In your home, it’s split between the compressor which is usually outside the house and the air handler within. The refrigerant gas expands as it travels through the system, absorbing heat that can then be released outside the appliance. This is why the air from your home’s exterior HVAC unit is hot, and the exterior of your fridge is warm to the touch. The heat is pulled out of the interior, keeping your home or your snack food cold.
Taking it Up a Notch
This system might work well for a single appliance or keep the interior of your house temperate, but it isn’t enough to cool the massive warehouses that hold your milk at a low temperature while you wait for it to reach the grocery store. Industrial chillers use the same principles as your home fridge, but the equipment is scaled up.
Industrial chillers have many different applications in everything from food storage to plastic manufacturing and metal plating. They can even cool industrial equipment to ensure that the interior temperature of a facility is moderate. As industrial automation in climate controlled warehouses becomes more prevalent, this will become essential to prevent damage.
The next time you head to the fridge, consider deciding what you want to eat before you open the door, so your appliance’s compressor doesn’t have to work so hard. Now that you have a better idea of how your fridge works, what do you think about the science of refrigeration?