"So, what does SEER mean?"
SEER Quick Brief
|SEER||Seasonal Energy Efficiency Ratio||Air Conditioners / Heat Pumps||Cooling||Energy Efficiency|
So, what is SEER?
The Seasonal Energy Efficiency Ratio (SEER) is an efficiency rating required by the federal trade commission to be labeled on air conditioning and heat pump equipment. It was developed in 1979 with the help of the DOE (Department of Energy) and the ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) and is used to express an air conditioner's (or heat pump's) energy consumption during an average period of cooling.
The higher an air conditioner's SEER, the less energy it consumes during a cooling season.
Technically, a SEER is a ratio composed of the cooling output of an air conditioner (or heat pump) measured in BTUs, divided by the energy input of the air conditioner consumed in Watt-Hours, as the air conditioner is operated over a period of time in a controlled environment which simulates the average outdoor cooling conditions experienced across the United States.
It is important to note that the SEER label on AC equipment is essentially the result of tests performed in a laboratory setting that serves to simulate an averaged seasonal "cooling" environment which includes testing AC equipment at a constant indoor temperature of 80°F at 50% relative humidity, and at an outdoor temperature of 82°F at 39% relative humidity, over a period of time. These exact testing procedures are formed by the AHRI (Air Conditioning, Heating, and Refrigeration Institute) and are documented in an articled called: The ANSI/AHRI Standard 210/240-2008.
And, although the testing procedures performed in the lab are very accurate, the controlled laboratory testing environment is very different from any real environment found at a home. Which means a SEER rating may or may not reflect the actual energy consumption of your home.
Today, modern air conditioners have a minimum SEER rating of 13 to 14 SEER depending on the location and type of equipment installed, and a somewhere around a maximum of 25 SEER as of 2017 based on modern technological limitations.
It is also important to note that SEER evaluations are performed across an entire package of components, and tested as a single set supplied by the manufacturer. Meaning, manufacturers that are having their equipment's SEER evaluated supply 3 pieces of equipment that are all used during a SEER evaluation, including: An Outdoor Condensing Unit, a Furnace, and an Indoor Evaporator Coil, all 3 of which are all tested at once and used to calculate SEER - Simply purchasing a new 20 SEER condenser and plugging it into your existing furnace and evaporator coil does not upgrade the entire system to 20 SEER.
Interestingly enough, several tests are performed during a SEER evaluation, however, only 1 test is required to be published as public SEER reference data, the rest is kept confidential by the AHRI. These testing procedures are however outlined by the AHRI:
How SEER Testing Takes Place (In a nutshell).
"Yeah? Well, that's a pretty thick document, and I really don't have the time to read all 136 pages of that.. Is there anyway you can just quickly sum things up?"
Sure thing! So, if you don't wish to read the AHRI's 136 page document on exactly how SEER testing takes place, allow me to sum it up real quick:
AC equipment for which a SEER rating is going to be determined is set up inside a laboratory setting consisting of 2 side by side rooms. Since air conditioning equipment transfers heat from an indoor environment, to an outdoor environment, one of the rooms in the laboratory simulates an indoor environment, and the other room simulates an outdoor environment. For the most common types of AC systems, including AC systems that use a single speed compressor and a furnace that delivers a constant volume of air, the indoor and outdoor testing environment is as follows:
The simulated outdoor environment, which contains the outdoor condensing unit, is maintained at 82°F with a relative humidity of 39% by an electric heater that matches the capacity of the cooling equipment.
Yes, you read that correctly. A SEER evaluation is based off a small 2 degree difference maintained between the simulated indoor and outdoor environments, which is not exactly realistic by any means, especially in Houston, however, that is how the test is performed. It's important to note this because the difference in temperature between the outdoor and indoor environments for which an air conditioning system transfers heat between has a big impact on the air conditioning systems energy consumption and performance - The greater the difference of temperature between the environments where the heat is being transfered to and from, the more work the system has to do to in order transfer the heat from one area to the next, and therefore the greater the energy consumption.
This means, at 82°F outside, and 80°F inside, the SEER evaluation doesn't test equipment at peak demand times, and therefore does not accurately show peak demand time savings - SEER is an evaluation tests air conditioning equipment during a period of moderate to low demand - At a 2 degree difference it could be argued that you might as well just open the windows of your home. This is also important to note, because an equipment's ability to transfer heat better in an environment of low to moderate demand, does not necessarily mean the equipment will perform the same way when operated within an environment of high demand.
On the bright side, the SEER evaluation does test equipment over time with an electric heater that generates a heat load that is equivalent to the equipment's total cooling capacity, which is a scenario a home rarely encounters - A 5 ton air conditioning system that can transfer 60,000 BTUs per hour is tested with an electric heater that delivers 60,000 BTUs of heat per hour.
Anyway, the equipment is then operated within these simulated indoor and outdoor conditions as described above, and over the course of time the energy consumption and cooling capacity of the equipment is gathered through testing equipment and logged as a series of recorded EER (Energy Efficiency Ratio) values. In the end, the results that were collected throughout the testing procedure are averaged as a single EER (Energy Efficiency Ratio) which is then multiplied by a PLF (Partial-Load Factor), and a SEER is born. The actual equation listed by the AHRI is as follows:
So this equation may seem kind of confusing, but that's because the AHRI defines each of the variables within the above equation separately throughout the ANSI/AHRI Standard 210/240-2008. Basically what this equation is stating is: SEER is equal to the average of the EERs collected during test B, multiplied by the Part Load Factor. Let's talk about these variables very quickly:
"What is EER?"
EER stands for Energy Efficiency Ratio, and an EER is just like a SEER (Seasonal Energy Efficiency Ratio), except where a SEER measures energy efficiency over a period of time where conditions vary, an EER only measures energy efficiency for a single set of conditions, and it essentially tells us how many BTUs of cooling output we can get out of a piece of equipment at a specific energy input, for a single set of conditions. EER is also used as an efficiency rating on it's own, however, we will explain the EER efficiency labeling requirements later. For now, simply consider EER as a variable used to calculate SEER, and consider SEER nothing more than a season composed of averaged of EERs.
So, during the SEER testing procedure out lined above, several EERs or "snapshots" of energy efficiency are captured and recorded as separate EER values, which are then plugged into the "SEER = Part Load Factor X Averaged EER Test Data" formula listed above.
PLF & Other Assumptions
"And, What's PLF again?"
PLF stands for Partial-Load Factor. The Partial-Load Factor is a factor that takes into account the fact that AC equipment isn't always operating at 100% capacity when it's consuming energy, such as when it is cycling on and off during a cooling period, as well as the fact that the heat load in the occupied space doesn't always match the total capacity of the HVAC equipment. Therefore, the PLF is a variable that defines the AC equipments cycling efficiency. Generally, residential AC equipment handles the heat load of an occupied space by cycling on and off as the heat load within the occupied space rises and falls. Therefore, the part-load factor is used to predict this "on and off" behavior and adjusts the energy efficiency ratio accordingly.
- AC equipment isn't always operating at 100% capacity when it's consuming energy, such as when it is cycling on and off during a cooling period.
- The available heat load within the occupied space varies, and doesn't always match the available capacity of the HVAC equipment, therefore the AC equipment is not always operating 24/7 under 100% load.
- AC equipment consumes energy in order to start components such as compressors and fan motors without transferring any heat in or out of the occupied space, and during AC equipment start-up the majority of AC equipment energy consumption is used to "Kick-Over" these components into the proper directional rotation, as well as separate the refrigerant within the system into 2 separate states of matter (High pressure liquid, low pressure vapor), and it is only after these acts of energy consumption have occurred, does the equipment begin to transfer heat in or out of the occupied space.
- AC equipment also consumes electrical energy from various sources when it's not operating, including: Crank-Case Heaters (Compressor Heaters), as well as Control Components (Thermostats, Control Transformers, Circuit Boards).
For example: Most AC equipment is sized to handle a heat load that is based off of a worst case scenario that rarely occurs within the occupied space, that is to say, your home may have a 5 ton air conditioning system which can transfer a heat load of 60,000 BTUs per hour, however, there are few times when a heat load of 60,000 BTUs is present in your home all at once, which then has to be removed by your 5-ton air conditioning system (which would require the system to operate for a full hour). Instead, your air conditioning system periodically cycles on and off and handles the heat load through periods of cycling. This behavior, of cycling on and off, plays a big role in determining the total energy consumption over an entire season, which is what SEER attempts to predict and the PLF attempts to account for.
"Interesting. Well, how on Earth is a PLF determined?"
Manufacturers actually have the option to run a separate test to determine the equipment's PLF when they are having their equipment's SEER evaluated, or they can opt out, and simply use a default PLF of 0.875. Equipment PLF is not something that is published by the AHRI after it is determined, but a study (link below) has been done that essentially works backwards in order solve what this default PLF variable represents, which concluded the default PLF factor represents a start-up time of 76 seconds, and a maximum equipment cycling time of 3.125 cycles per hour (which is considered very poor).
So a default PLF resembling poor performance is obviously a good thing for consumers. If manufacturers could simply opt out and receive a default value that resembled an AC system that performed better, which resulted in a better efficiency rating, then they most likely would, as we are constantly reminded by various sources to spend more money initially on purchase equipment at a higher SEER.
PLF Curve Study
So, in most cases the manufacturer most likely does choose to have their PLF evaluated. Modern equipment includes various features that allow cyclic performance to score much better than calculations made using the default PLF, including features such as: Time Delays, Variable Speed Compressors, Variable Speed Fans, and Electronic Expansion Valves, all of which are components that would contribute to a lower PLF than what this default value represents.
In the end the SEER calculation of the equipment is obviously going to be conducted with a PLF of which ever is lowest, either the tested PLF or the default PLF - Because the lower a PLF, the more efficient the AC system is on paper (and within the lab), and in turn the more money a manufacturer could charge for a product by claiming it has a higher performance value.
This value is again however, just another variable which will change between every single residence - A partial-load factor obviously depends on, among other things: The Available Heat Load, The Length of the Refrigerant Line-set, and the Duct System Design within a home, all of which are factors that are going to vary between every single home and equipment installation.
PLF, as well as the entire SEER evaluation, also makes the assumption that installed AC equipment has been properly sized to the home and calculated by a professional contractor who understands how to perform a proper residential heat load calculation according to the ASHRAE's (American Society of Heating, Refrigeration and Air Conditioning Engineers) head load calculation guidelines listed a document called the Manual J.
Unfortunately, we often find this is not the case, as the majority of the time AC equipment is very undersized or oversized within the homes we visit, especially when AC systems are installed by home builders.
Home construction companies typically have absolutely no idea how to properly size HVAC equipment to a residence, and, throughout the cookie-cutter home construction process, many homes are built with HVAC issues stemming back to design and installation failure. There is no law which requires a heat load calculation when a home is constructed, yet there is a law that requires a minimum SEER efficiency for AC equipment, which assumes a home's heat load has been properly addressed by properly sized equipment.
The home inspection process, which all homes must endure and successfully pass in order to be bought or sold, simply addresses code violations and safety concerns - A home may look very nice on the inside, and pass a safety and code inspection, but behind the illusive curtain of beautiful interior design that most home builders expect shopping consumers to never see beyond exists a very different story of undersized or oversized AC equipment and very poor duct systems, which isn't detected until the home is inhabited by the buyer for a full season of AC run time. If you are one of those people who constantly complains of a room or two within your home that constantly remains too hot or too cold, then unless your HVAC system is having a mechanical issue, or duct work has simply fallen apart, then you're most likely experiencing a issue that stems back to poor practice.
SEER Testing Summary (The Technical Version)
So if you like math, and want to see the actual calculations involved in the SEER testing process, the procedure is outlined below:
SEER ratings require up to 4 laboratory tests - Test A, Test B, Test C, and Tess D. (Shown in table below)
Only two of these tests are required in order to calculate SEER - Test A and Test B.
Test C and Test D are optional, and serve to determine the systems Cycling Degradation Coefficient, also known as (Cd), which is a variable used to calculate the Partial Load Factor (PLF) which is used to account for a system's cycling efficiency and offset the total energy efficiency calculation to compensate for the ON/OFF cycling behavior of an air conditioning system.
If the optional Tests C & D, which are used to determine Cd, are not conducted, then a default value for Cd is assigned at 0.25, which results in a PLF of 0.825.
The table below summarizes the 4 tests and their simulated indoor and outdoor environments:
SEER Testing Guidelines and Conditions
|Test #||Rating Determined||Requirement||Mode of Operation||Outdoor Dry Bulb||Outdoor Wet Bulb||Indoor Dry Bulb||Indoor Wet Bulb|
|Test A||EER||Required||Steady State||95°F||75°F||80°F||67°F|
|Test B||SEER||Required||Steady State||82°F||65°F||80°F||67°F|
|Test C||Cd||Optional||Steady State||82°F||65°F||80°F||57°F|
|Test D||Cd||Optional||Cyclic (6 Minutes OFF / 24 Minutes ON)||82°F||65°F||80°F||57°F|
EER (which is a separate efficiency rating on it's own that we will get to later), is determined from the equation below with results measured during the required steady state Test A:
SEER is determined from the equation below with results measured from required steady state Test B and/or Optional Cyclic Tests C & D:
Again, if the optional Test C and optional Test D are not performed, the variable (Cd) is given a default value of 0.25.
Tests C & D are based off of the EER values gathered from starting and stopping the equipment, and are used in the above calculation to determine the variable Cd. The calculations are evaluated as follows:
And, that is how it is done.
It's important to note that these test procedures vary depending on the type of equipment installed, more tests are required for equipment that doesn't fit within the guidelines of a system that contains a single speed compressor and indoor fan that delivers a constant volume of air. If your AC system is variable speed, and essentially changes capacity based on a demand, then there are additional tests conducted to measure the efficiency of the variable speed equipment at various demands within these simulated indoor and outdoor environments, which we have not listed on this page.
Thoughts on SEER
So, as we can see, much of calculating SEER involves a unique environment that most of us don't see within our outside of our homes. The SEER evaluation also makes a many assumptions, and contains many variables that differ between residences and locations where AC equipment is installed.
The bottom line is many of the factors involved in the laboratory scenario where the SEER evaluation is performed simply don't resemble a real life scenario, and one of the main concerns about the SEER rating being so different from a real life scenario is: Are manufacturers simply making equipment that performs well in a laboratory setting within these artificial testing procedures, and not in a home or regions where large differences in temperature exist between the indoor and outdoor environment?
The 2 studies listed below show us that equipment with a high SEER often scores very low against other efficiency ratings, such as EER, which unlike SEER, an EER is an efficiency rating used to evaluate a systems performance that better resembles a Peak Demand environment. Some of the results of these studies show us that manufacturers have produced equipment that simply scores high in a laboratory setting and receives a high SEER, but performs at an average to low EER rating that compares to much more inexpensive equipment with a lower SEER.
So, with so many variables involved, and evidence of high SEER performance at low EER performance in the studies outlined below, it's important to note that we shouldn't simply depend on any single efficiency label as an absolute value or absolute factor in our equipment selection process or comparisons. It's important to instead include multiple views of energy consumption, from multiple perspectives and through multiple efficiency ratings - So we can see the whole picture.
Studies comparing SEER vs EER
Using a SEER rating to calculate energy cost.
"So, how can I actually use a SEER to calculate the cost of energy?"
Alright so now that we know all about SEER, how about we put SEER to use and calculate some energy costs?
Let's step through a quick example of how a SEER can actually be used to determine the amount of energy and the cost of that energy, which an air conditioner might consume over the course of 180 days.
If we recall with the SEER formula mentioned earlier, SEER is equal to the output cooling energy measured in BTUs over the course of time divided by the input of electrical energy in Watt-Hours during that same period of time, or:
Since the formula above requires BTUs worth of heat energy measured over a period of time, let us set up an air conditioning scenario and begin to define our variables that we are going to use in our calculation:
First, lets consider our air conditioner to be a 5 ton air conditioner. At 5-Tons of cooling power, our air conditioner is capable of transferring a maximum of 60,000 BTUs of heat energy per hour, however, air conditioners don't always run for an hour at a time, they also don't transfer 60,000 BTUs worth of energy every single hour. With that in mind, our scenario is assumed as follows:
Assume the cooling season for which we will be calculating the energy cost of running our air conditioner within is exactly 180 days long.
Assume our air conditioner being operated through this cooling season is a 5 Ton air conditioner (60,000 BTU/H of Total Cooling Capacity).
Assume the 5 ton air conditioner runs at an average of 8 hours per day during our cooling season.
Assume the 5 ton air conditioner runs at an average of two thirds it's total BTU cooling capacity.
Assume the 5 ton air conditioner is rated at 14 SEER.
Assume the price of energy from the electric company is $0.08 cents per Kilowatt Hour worth of energy consumed.
Alright so our scenario is set up and all the variables we need to make a cost calculation are defined above.
Now, the first thing we need to do is determine what two thirds of 5 tons is, because if we recall from our scenario above, our air conditioner is running at an average of 2/3 it's total cooling output capacity.
If a ton of air conditioning power is equal to 12,000 BTUs per Hour, and we have a 5 ton air conditioner, then 5 tons is equal to 60,000 BTUs per hour. So what is two thirds of 60,000? We can find out simply by multiplying our available capacity of 60,000 BTU/H by two thirds:
With our actual and modified cooling output capacity of 40,000 BTUs per hour, we now need to figure out how many BTUs we use over the course of 8 hours, because in our scenario we are running our air conditioner for a total of 8 hours per day. This can be achieved by multiplying our actual BTUs per hour, by 8 Hours, as follows:
Our calculation shows us that our air conditioner is transferring 320,000 BTUs worth of heat energy per day. We now need to find out how many BTUs our air conditioner will transfer over the course of our 180 day cooling season, which we can calculate by multiplying our daily transfer rate of 320,000 BTUs per day by 180 days, as shown below:
Awesome! So, we now have calculated how many BTUs worth of heat our air conditioner will transfer over the course of 180 days and we have officially calculated half of our equation! Yay! It's almost over!
Now we need to figure out how much electrical energy in Watt-Hours this entire load will consume. This can be calculated by simply dividing our the 180 day season's BTUs by our air conditioner's SEER of 14, like so:
Wow. So in order to transfer 57,600,000 BTUs worth of heat with our 14 SEER air conditioner, it will require around 4.11 Mega Watt-Hours worth of electrical energy consumption! Sounds expensive! Let's find out:
The next step is to figure out how much the electric company is going to charge us to consume all this electrical energy over the course of our 180 day cooling season, but right off the bat we have a problem - Electric companies don't bill us based on Watt-Hours worth of energy consumption, they bill us based on Kilowatt Hours worth of energy consumption. So, let's go ahead and convert our very large and ugly number of 4,114,285.714285714 Watt-Hours into Kilowatt Hours.
Since Kilowatts are simply units consisting of 1000 watts, in order to convert Watt-Hours to Kilowatt Hours all we have to do is divide our rough number of Watt-Hours by 1000, as shown below:
Alright! So we now have our Watt-Hours worth of energy used converted into Kilowatt Hours worth of energy used. How about now we convert all of this electrical energy usage directly into a total cost? This can easily be achieved by multiplying our total Kilowatt Hours worth of energy consumed for this cooling season, by the cost the electric company charges us for each Kilowatt Hour worth of energy we use. As mentioned earlier, in this scenario the electric company charges us $0.08 cents per Kilowatt Hour worth of energy we use, which makes our total come out to:
Nice! So at $0.08 cents per Kilowatt Hour of energy consumption, we only end up paying $329.12 dollars for all that energy consumption! Not bad..
This is exactly how a SEER is supposed to be used to calculate energy consumption over time. It's important to remember that we assumed so much in our calculations, and so does the SEER evaluation at the lab, that this most likely isn't going to be what we end up paying after 180 days of operation with a 5 Ton 14 SEER air conditioner, even if we operate this air conditioner the same way that we defined in our scenario.
Remember, just about every little thing that goes on inside of (and outside of) your home contributes to it's heat load, which contributes to your air conditioners energy consumption. There are literally so many factors involved with heat that we just don't have the time to sit down and calculate them all right now, including factors such as: Every home is different, every duct system is different, climates are different and so is weather, insulation is different between homes, the number of people living in a home varies and so do their indoor activities - How often do those people shower? How often they cook? How many televisions and light bulbs and computers do they have? How often do they operate their electronics? Do they leave the window blinds opened or closed during the day? What cardinal direction does their home face? What type of air filters are they using and when is the last time they were changed? - The list of factors that affect AC energy consumption goes on and on and on! But this brings up an important point to remember about SEER:
SEER is just a Tool
A SEER is a tool. It's simply an attempt to show consumers how much energy can be saved between pieces of cooling equipment, and is really just nothing more than a tool for consumers to use when they are comparing the energy consumption of cooling equipment before making an equipment purchase.
For example: When you are shopping for a new vehicle, and that shiny new Toyota Prius catches your attention and you notice on the window there is a sticker, and on that sticker it claims that the vehicle gets 60 MPG in the city, 51 MPG on the highway, and 55 MPG combined. Do you consider these numbers to be absolute fact?
If so, within a month of owning the new Prius you've probably noticed that the sticker MPG ratings were way off, "Someone must have switched the stickers on this car and fooled me, it's those darn salesmen up to no good!" you tell yourself, as you drive it back to the car lot and attempt returning it to the car dealer.. "Sorry!", they say.. the manager then begins to explain: "You actually drive with the air conditioner turned on, and you actually drive your vehicle when the outdoor temperature is above 75°F, and you actually drive above an average speed of 48 miles per hour, oh, and you're front left tire happened to actually be a little low on air pressure.. What? You didn't know that all of these factors exceed the limitations defined in the MPG testing procedure?" - They laugh and murmur: "Of course your going to use more fuel with the typical, down-to-earth, practical and super realistic way your driving that thing!"
The tests that determine these efficiency ratings don't actually resemble real life, do they?
They don't resemble real life, because they are designed to be as accurate as possible in an artificial setting in order to allow people to compare products on an equal playing field, although not a real one - Actual real life mileage may vary.
So, when we look at SEER, we should look at it the same way. We can compare products using their SEER, and we can compare cost savings through SEER calculations, but we shouldn't assume that our calculations which determined that we are going to save $100.00 a month on energy consumption is actually going to apply to real life, because it most likely isn't.
SEER labels exist for comparison purposes only, and are regulated by law so consumers can compare products on an equal playing field. Manufacturers don't let you take their AC equipment home, install it in your home, run it for a year, and then return it just because your calculation was off and the equipment actually consumes more energy than you assumed it would, which is why these labels exist and are regulated by law. So, when doing these calculations, it's important to remember:
- SEER is evaluated in a laboratory setting, within an artificial and simulated indoor and outdoor environment, not within your actual home's indoor and outdoor environment - The SEER testing procedure includes testing AC equipment where the indoor and outdoor environments only differ in temperature by 2 degrees!
- The factors that affect actual AC energy consumption are: Everything!
- Manufacturers that are having their equipment's SEER ratio evaluated supply 3 pieces of equipment that are all used to calculate the SEER rating as a collective package, including: an Outdoor Condensing Unit, a Furnace, and an Indoor Evaporator Coil, all 3 of which are all tested at once and used to calculate a SEER. This means: If you purchase a new 20 SEER outdoor condensing unit, and plug it into your existing furnace or evaporator coil that you purchased 10 years ago, you no longer have a 20 SEER condensing unit - It's a packaged deal!
- A SEER is a tool, and only a single perspective which we can use to view energy consumption across multiple products. It's important to compare products using many different efficiency ratings, and thus view energy consumption from many different perspectives, as test procedures can vary greatly from a real life scenario - Actual MPG may vary!