Do you remember mom cooking corn in a huge pressure cooker and hearing that “whoosh” of steam when the steam release valve was opened.
Little did I know, but I was witnessing an example of superheating, the process where water and water vapor under pressure can reach temperatures above boiling.
When that pressure is released, pent-up energy emerges as steam while the liquid boils away until the temperature drops. Another phenomenon is called subcooling, defined as when a liquid is cooled to below the temperature at which it turns liquid. In the case of water at atmospheric pressure, that temperature is 212°F meaning that all the oceans and lakes on earth plus that can of beer in your refrigerator are technically subcooled. This should not be confused with condensation, those droplets of water that magically appear on that beer can and drives your spouse crazy if you don’t use a coaster. Except for corn, superheating and subcooling of water are unimportant in our everyday lives, but another liquid circulating in our home’s HVAC system depends on these phenomena. R410A refrigerant boils at -55°F and to keep it in liquid form requires a pressurized system just like mom’s corn-cooker. R410A expands into a gas as it travels through the HVAC cooling tubes and is compressed back into a liquid to repeat the process. Its superheated state in the evaporator, prevents liquid refrigerant from entering the compressor. Subcooled R410A in the condenser will stop any vapors from entering the expansion device. Both of these conditions are needed to prevent damage to your HVAC system. Old-time HVAC technicians will reminisce about the suction line being “beer can cold”. That means everything is working well and you can sip on that beer and enjoy pressure-cooked corn to your heart’s desire.