The efficiency of the system is determined by its SEER, EER, HSPF, and AFUE ratings and those are affected by the components and design of the system. The efficiency of the system is important because it determines how much energy or fuel it can convert into actually cooling or heating your home.
SEER: Seasonal Energy Efficiency Ratio measures heat pump and air conditioning cooling efficiency. It’s a ratio of how much electricity the system uses to reject BTU’s from your home over a range of temperatures in a season. The higher the SEER rating the more efficient the system will be at cooling your home in the summer time.
EER: Energy Efficiency Ratio is determined by the BTU’s removed divided by the electrical power input. EER is typically determined by a set outside air temperature, a set inside air temperature and a 50% relative humidity. It’s like a standardized efficiency rating because the conditions are the same to get the ratio number.
HSPF: Heating Seasonal Performance Factor is used to measure the heating efficiency of heat pumps. The higher the number the more efficient it is, it’s a ratio of BTU’s to electrical usage in a given heating season. It’s how efficient your unit is in the winter time.
AFUE: Annual Fuel Utilitzation Efficiency is a measure of how much fuel a gas furnace can convert into heat energy. Like the other ratings the higher the rating the more efficient.
High Efficiency Systems
Basically the more efficient your system is, the better it is at taking the energy it draws and then cooling or heating your home. These units give you the most long term value for your investment. In the long run you will make your money back on the unit with reduced utility cost. The most efficient systems have variable speed technology and can communicate with the thermostat, motor speeds, and the compressor speed and they can be zoned. Those systems use the least amount of energy necessary to satisfy your thermostats temperature.
ECM and Variable Speed Motors
More efficient systems use ECM and variable speed motors. The ECM motors have constant torque technology that allows the fan to blow at a constant speed and allows for better airflow, they can have 2 or 3 different speeds. In a variable speed system the torque will vary depending on what is needed from the thermostat and how the rest of the system is performing. Imagine its speed being able to operate on scale anywhere between 0 to 100%.
2 Stage and Variable Speed Compressors
Just like the motors the compressors for theses systems can also operate in different stages and can be variable speed. When they operate in stages they are typically 2 stage compressors. They have a high stage for the summer time and a lower stage for the cooler times of the year. The variable speed also can operate on scale anywhere between 0 to 100%.
Read more about variable speed versus regular air conditioners.
Low Efficiency Systems
Systems that aren’t as efficient require more energy to satisfy your thermostat because they waste more energy that is wasted and not converted into cooling or heating. The motors and compressors for these systems will just turn on and off and only operate at one speed. They aren’t as good as the more efficient systems but if there is ever a breakdown not covered under warranty the parts are cheaper and makes maintenance easier in the long run. If your unit is over 10 years old chances are it isn’t that efficient anyway so if you upgrade to the government required minimum of 14 SEER you will still save money on utilities in the summer time, however you might not make money back on your investment.
The less efficient motor used in lower SEER systems operates without constant torque. These fans are less reliable and are simple for manufacturers to make, which is why they are used in cheaper systems. They don’t distribute air efficiently and will eventually wear down because they only work in one speed that is inconsistent due to the design of it.
Single Stage Compressors
The cheaper systems also use cheaper compressors. They only operate at one speed. When your thermostats calls for cooling or heating then the compressor will kick on till satisfied then turn off. They aren’t as efficient because they turn on at full strength no matter what time of year it is. This can make a huge difference in electrical cost because of how hot it gets in Arizona, so even when its 80 to 90 degrees outside it will still operate like its 115 outside!