Definitions of Commonly Used HVAC Efficiency Terms

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Definitions of Commonly Used HVAC Efficiency Terms

Postby AC480 » Mon Oct 06, 2014 6:40 am



When considering the purchase of a new vehicle, we often look at the economy rating sticker in the window that states miles per gallon.

When considering the purchase of air conditioning and heating equipment, we see terms such as SEER, EER, COP, HSPF, and AFUE.
Have you ever wondered, what is SEER? What is EER? What is COP? What is HSPF? What is AFUE? What is KW?
How do these terms relate to cost of operation? Don't feel bad if you are confused, because most people don't understand them either. It is not uncommon for a salesperson or field technician to stumble with the definitions and explanations as well. Actually, they are relatively simply. Someone just needs to cut through the double talk and explain the terms.
We pay for electricity by the Kilowatt unit, often listed on your electric bill as "KW". A KW is 1000 watts. The "K" stands for 1000.
It would be much easier to understand if the sticker would just tell you how many BTU's a unit will remove (in cooling) or create (in heating) from the conditioned space and how many watts or KW it will use.

The efficiency ratings that you see affixed to a piece of equipment do tell you this, but it's almost like a code that has to be deciphered. You have to know how these ratings were derived to convert it to dollars and cents.

There are two ways to heat your home. I like to explain it this way: You can either make heat, by burning fossil fuels, wood, electricity, or you can move heat. Air Conditioners and heat pumps move heat. Furnaces and boilers make heat. Whether it is electric, gas or oil, they make heat from a fuel source. You need to determine what will be the most economical for your application. The type of home you have, your climate, and the energy sources available to you play into making this determination. This information can also be used to determine what type of water heater to use. Water heaters are often the second largest users of energy in the home.



Here is a list of commonly used terms, the definitions, and explanation of how it applies.

KW- Kilowatt. 1000 watts. The unit of electricity that is used for billing purposes. Typically, in the United States, that cost varies between $0.07 and $0.15, 7 cents and 15 cents. Your cost is dependent on the cost of generating and distributing the electricity to your home, which varies upon geographical location.

ARI- This is the American Refrigeration Institute- This is an independent 3rd party organization that tests various types of heating and cooling equipment. After testing the equipment in controlled environmental conditions and to an exhaustive list of requirements and specifications comparable to the Code of Federal Regulations, efficiency ratings are assigned. The ARI is the official HVAC testing agency in the United States. Their ratings are placed on all new equipment. You should use these ratings to compare different manufacturer’s equipment. The manufacturers pay a lot of money to get their equipment tested and rated. These cost are eventually passed on to the consumer when new equipment is purchased. You just as well take advantage of these numbers since the cost of deriving them are passed on to the consumer in the cost of the equipment.

All of the heat pumps and air conditioners that we shall discuss here will be mechanical electrically driven units. That means they run on electricity and it has a compressor in it. Furnaces shall be natural gas, LP, or Fuel Oil.

AIR Source- refers to a type of Air Conditioner, which uses outside air as its method of heat rejection or absorption. A standard air conditioner would absorb heat from the air inside the home and reject it into the outside air.

Water Source or Geothermal: This is a unit that utilizes well water or water in a closed loop as a source of disposing of heat adsorbed in your home during the cooling season, or absorbing heat from outside and moving it inside during heating season. They are available in package units, which means all components are in a single enclosure, or split system, which places the outdoor unit consisting of a water to refrigerant heat exchanger and compressor in an outdoor unit and an indoor air moving unit that is located in a closet or attic.


SEER- Seasonal Energy Efficiency Ratio
This is the energy efficiency rating given by the (ARI)
It applies to Air source type Air Conditioners, or Heat Pumps operating in the "cool" mode.
The ARI test A/C and Heat Pump units based on an outside air temperature that is representative of the average air temperature encountered during the cooling season to compare efficiency among the different brands of Air Conditioners. This is sort of like the EPA fuel usage stickers on cars. Actual results may vary, but it is valuable for comparison purposes among other units. If an A/C unit has a SEER of 12, that means that it will move 12 BTU's of heat for each watt of electricity that it uses. A SEER of 10 means that it will move 10 BTU's of heat for each watt of electricity it uses at the representative temperature. Sometimes it will be more, and sometimes it will be less in actual operating conditions.

EER- Energy Efficiency Ratio
Previously applying only to water source heat pump systems, it is being used to rate equipment at a specific water loop temperature. Since the ground is being used to dissipate the heat that was absorbed from inside the home instead of outside air, and the ground below a certain depth depending on location has a constant temperature regardless of the outside air temperature, it is simply an EER, instead of an SEER, because its efficiency is not dependent on outside air temperature. More recently, ARI began testing air source units at specific outdoor temperatures, usually 2. The unit or matched system will be tested and the EER determined at specific outdoor air temperature. There is still a SEER rating which is explained above.

COP- Co-Efficient of Performance- This is a term that is used to measure heating performance in heat systems that use electricity for a power source. A COP of 1 (as in electric heat) means that for every unit of electricity used one unit of heat is produced. A COP of 3 (as in a heat pump) means 3 units of heat are delivered to the conditioned space for every unit of electricity used. Once again, a water source heat pump that has a constant water temperature is rated with a COP. In air cooled equipment if you see COP it will be at a specific outdoor temperature. Like the EER for cooling, the COP for heating rating applies to a outdoor or geothermal, or ground, temperature.

HSPF- This is a new rating that is similar to a SEER, except for heat pumps in Heat Mode. The SEER applies to cooling; the HSPF is the average number of BTU's per watt of electricity that you can expect your unit to produce during a full heating season. It is based on a temperature that ARI endeavors to be representative of the average outside air temperature that is encountered during the heating season. This also takes into consideration the amount of time that a unit will need back up electric heat to maintain the comfort zone during the defrost cycle and extremely cold temperatues.

AFUE- Annual Fuel Utilization Efficiency
This applies to gas and oil fired furnaces and boilers. It is the average amount of heat that is actually used to heat your home during the entire heating season. Since the efficiency varies dependent upon conditions such as make up air temperature and humidity, the term "Annual" is added to represent the average.
Some of the heat made goes up the flue (vent) and is wasted.

BTU- British Thermal Unit
This is currently the most common term that is used to measure capacity. This term is currently transitioning to Kilowatt, or KW. Some manufacturers have already started using the term KW in the rating of their equipment. This is based on the metric system. Technically, 1 BTU is the amount of heat required to raise the temperature of 1 pound of water 1 F in 1 hour. One ton is 12,000 BTU's. Ton's are most often used to describe cooling capacity, while heat is most often described in BTU's. No matter what term is used, it is still a measure of the capacity to make or move heat. Also know as a BTUH, the amount of BTU's produced in an hour. Most of the time when you see BTU, it means BTUH.

Electric Heat- This applies to a plain old resistance electric heat. There are coils in the air stream and electricity is applied directly to them. As a result, they get very hot. When air is passed over them, it is heated.

***This will be an evolving topic. My next post in this series will move into comparing and calculating the cost of different fuel types and efficiency ratings so you can make an informed decision by calculating the increased cost of higher efficiency equipment vs. the amount of time it will take to payback the energy savings spent on investing in higher efficiency equipment.***

"We do these things not because they are easy, but because they are hard"
-John F. Kennedy, Rice University, Sept. 12, 1962

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