Basics of Home Efficiency and Your HVAC System
It's easy to take home heating and cooling for granted. In the summer, we expect our air conditioning units to keep us cool, and in the winter we depend on our heating systems to keep us warm. Our body processes work in much the same way, and in understanding those principles we can learn some basics about home efficiency.
The 3 Principles of Heat Transfer
Heat is transferred between objects via convection, conduction, and radiation. Your body cools itself down through similar processes: convection, perspiration, and radiation. Ventilation improves these processes.
Hot air naturally rises, which conveys the heat away from your floors and walls, and it circulates throughout your house. An HVAC system harnesses this process of convection by using water, steam, refrigerants, and forced air in the ductwork to bring the heat to parts of your home. When this warmer air circulates past you, it warms you by absorption through your skin and lungs. Convection is heating through the air. Remember how hot air rises? This explains why attics are often a target in home efficiency complaints. If there are large gaps or poor insulation fill, hot air can also pass through to upper floors via convection. That hot air on the ground floor then uses conduction through your ceilings to 2nd floors or attic spaces. When your A/C unit is operating properly, convection will carry heat away from your body by moving the air. If the surrounding air is colder than your skin, the air itself will absorb this warmth. The warm air naturally rises away from you, and cooler air is pushed in.
Conduction is the process of heat traveling to a solid object. Have you ever put your hand on a frosted windowpane in the winter and watched your handprint form on the glass? That's a perfect example of heat transfer by conduction. Conduction is heating through touch. But heat does not conduct at the same rate with different objects or materials - copper conducts at a different rate than iron, for example. On hot or very sunny days, the atmospheric heat outside is conducted into your home through the windows, roof, and walls (proper insulation and energy efficient windows can help with increasing your home's efficiency). On cold days, a heat exchanger in an HVAC system uses conduction to transfer heat inside your home.
Radiation is heat transferred through space without super-heating that space. This radiant heat is absorbed by the first solid object it encounters but does not transfer the original temperature. Sunlight is the perfect example of radiant heat. The sun heats the home and the ground, but not the air around the home (and it definitely doesn't heat your home to the sun's 10 million degrees!).
Additionally, infrared radiation can direct infrared heat straight into a room or space to create heat on the object it reaches. Most older windows will let in infrared radiation - shades, blinds, or other window coverings can help tamp this problem down in the summer. Newer energy efficient windows come with coatings that block infrared radiation. Transferring heat through ventilation (such as a ceiling fan) can also help decrease the temperature of your ceilings, walls, and floors.
It helps to remember that both air conditioning and heating work on the same principle: heat moves from a warm object to a cooler object. A/C units remove heat from your home, and furnaces put heat into the air.
If you are having efficiency issues with your HVAC system, we can help! Consult us at Outstanding Heating and Cooling and we will be happy to advise you. You can contact us here for a call or email on how you can address comfort and home efficiency.