When the Texas heat and humidity gets so awful that even the sun starts looking for some shade, you know your air conditioner is going to eat lots of electricity. What’s worse is that for each degree of extra cooling you set below 78°F your energy usage — and your bill —increases by 6-8%.
Another factor of high energy bills in summer is rising electricity rates. Energy rates increase when the margin between the demand for power and the available supply decreases. As temperatures rise, your AC needs more energy to cool your home, so electricity demand increases and causes prices to increase. If you are on a variable-rate plan or have recently switched your electric plan, this price increase might affect your bills.
You can combat those higher energy bills by raising the thermostat settings on your air conditioner. By raising the thermostat up 10° to 15° for 8 hours every day when you’re at work or inactive, you can save 5% to 15% on your energy usage. The savings get even better if you have a programmable thermostat, which can lead to a savings of as much as 1% for each degree if the setback period is eight hours long.
Even still, some folks refuse to believe that raising their thermostat will save them money or keep them comfortable based on a few myths. The problem is that these notions are based on shaky assumptions and not facts.
Addressing Three Big Air Conditioner Myths
Myth 1: Keeping the air conditioner set to the same temperature saves money because keeping your home at a steady temperature uses less energy.
This argument is fallacious because it assumes that heat acts like Wile E. Coyote charging off a cliff chasing the Roadrunner — plunging straight down with a sudden, messy stop at the bottom. Heat doesn’t end abruptly or fade quickly. Instead, Newton’s Law of Cooling shows that it tapers very gradually, and it works like this: the rate of change of the temperature of an object is proportional to the difference between its own temperature and the ambient (or surrounding) temperature.
Basically, heat energy moves towards cold. During the winter, heat moves from inside your home to the outside. In summer, heat moves from outside to inside. As inside and outside temperatures approach equilibrium, the rate of heat conduction slows. Say for example, your thermostat is set to 74°F when you are home and the outside temperature is 90°F. That’s a 16° difference. But if you raise your thermostat to 80°F before leaving for the day, then it’s only a 10° difference.
True, if raise your settings during the day and then lower them upon your return your AC system will run for a long time bringing the temperatures to your at-home setting. BUT it won’t use as much energy during that relative brief time compared to the amount of energy it requires to maintain temperatures 6° cooler for an 8-hour period or longer. That 6° extra cooling can add 36% more to your energy usage (6% more for every extra 1 degree of cooling). Setting the temperature lower in the winter or higher in summer by 5 degrees or more while you are away or sleeping reduces your energy use and lowers your costs.
Myth 2: Raising the temperature when I’m away and then lowering it will make my air conditioner work harder
The things that makes your AC system work harder are dirt-clogged air filters, kinked or leaky air ducts, and poor maintenance because these prevent the unit from working properly or efficiently. These things are all preventable and fixable. If your HVAC system is cleaned, oiled, and spinning like a top, then it’s doing exactly what’s designed to do without breaking a sweat.
Not having enough insulation, poor air sealing, plus using appliances that add more heat to your home (its cooling load), all these things make your air conditioner run longer and use more energy. They are also preventable and fixable.
Myth 3: Air conditioners just cool the air, so by cranking the temperature lower, it will cool my home faster.
Relative humidity (RH) is the amount of water vapor present in air at a particular temperature. The warmer the ambient temperature, the more water the the air can hold. That’s why 50% RH at 74°F feels comfortable while 50% RH at 85°F or 95°F feel sticky. Water vapor also holds heat energy.
An air conditioner’s cooling coil works by pulling heat out of the air it contacts. That heat is then moved and shed in the the outside system. When an air conditioner starts up, most initial cooling goes to reducing the humidity in your home. That’s because, when humid air hits the cooling coils, the water condenses and gives up its heat energy to the cooling coil. The higher the humidity in your home, the longer it will take for the system to reduce the air temperature because all that heat energy must be released from the humid air first.
Cranking your thermostat lower to cool your house faster doesn’t work that way. Thermostats are not like volume knobs or gas pedals. For all the new bells and whistles and programmability, thermostats are just on-off switches. They monitor the ambient temperature until it reaches a certain point and either turns the cooling system on or off. That’s it. You can actually see the electricity connect/disconnect spark in older mercury bulb thermostats where the mercury that moves with the increase/decrease in temperature is used make the electrical contact that turns on air conditioning system.
How to Combat the Summer Heat
Summer heat doesn’t begin building from the overnight low until 7 am. Between 10 AM and noon, heating accelerates, usually approaching day time peak at 3 pm. Your home, meanwhile, depending on how well air-sealed and insulated it is, will absorb and retain heat through heat transfer, conduction, and radiant heating. Consequently, your home will retain heat and gradually release it through the night.
The most cost-effective cooling strategies for cooling you home are those that prevent heat building up in your home. Reducing your home’s heat gain reduces your air conditioner system’s cooling load:
- Close curtains and drape on south- and west-facing windows. This reduces the amount of sunlight and heat that comes into you home.
- Make sure your attic is adequately ventilated. Keeping your attic cooler reduces heat radiation and transfers into your living space.
- Avoid using appliances that use lots of heat during the hottest part of the day (usually 3 pm to 7 pm). Ovens, clothes dryers, dishwashers, and clothes washers (all that hot water), stove tops — all these things add heat to cooling load.
- Use a microwave to prepare meals. They use much less energy and create less waste heat.
- Use ventilation fans when you shower or bathe to blow moist, humid air outdoors. Don’t leave them running for too long. Most residential vent fans can clear a bathroom of steam in ten minutes.
- Turn on ceiling fans to keep the air circulating. Their breezes make it feel 4 to 6 degrees cooler. Turn them off when you leave the room.
Hopefully. you can use this information to combat high Texas Summer temperatures and home energy bills by knowing when and how to raise the settings of your air conditioner.