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One of the most common energy efficiency measures we recommend to our clients is to either retrofit existing or install new HVAC systems with variable speed fans.  In short, a variable speed fan allows the airflow through a unit to slow down.  This allows a building to save money on energy usage and even increase occupant comfort.

HVAC systems are sized based on the worst case scenario.  Engineers use computer programs to predict what the maximum cooling and heating needs will be in a building.  As you may have guessed, the building spends most of it’s time outside of these maximums.  That is when a variable speed fan can really be helpful since it allows your system to pretend its much smaller.

A variable speed drive primarily saves energy be slowing the fan down.  As you can see in the graph below for a typical fan, slowing it down to 80% of its maximum output can save around 50% of the energy.  Additionally, all electric motors require an extra boost of energy when they start up called Locked Rotor Amperage (LRA).  This can be up to 5 times the amount the motor will require to simple stay running (which is called the Full Load Amperage or FLA).   By keeping the motor on longer but at a slower speed, the motor won’t short cycle (turning off and then quickly turning back on) near as much as it would when running at full speed.

Slowing down the airflow through a unit can also increase the comfort in the room.  Say you would like to have a room at 75 °F in the summer.  With a constant speed fan, the unit would turn on and cool the room down to 73 °F then wait for it to warm up to 77°F before turning on again (traditional systems use this strategy, called a deadband, to reduce short cycling).  Under this arrangement the room temperature is constantly fluctuating between 73 °F and 77 °F.  With a variable speed fan, the thermostat can respond to temperature increases with gradual fan speed changes in an effort to keep the room the same temperature.  Additionally, a variable speed fan can be programmed to change its speed based on the amount of humidity that needs to be removed from the air.  The slower the air speed, the more dehumidification that will occur.  This can be very useful in areas with high summer humidity.

Variable speed fans are also great candidates for utility rebates and tax incentives, further increasing their value.  Variable Frequency Drives (what controls a variable speed fan) can also be used to slow down compressors on an air conditioning unit for increased efficiency.  However, the most common usage is on the fan side of the equipment.  If you think that your building or project may be a good candidate for variable speed fans, please contact us today and we can work with you to determine if it is a good fit.

Now that you know a little more about the history and general types of refrigerants (I recommend you read Part 1 if you haven’t already) it’s time to get to the really interesting part, refrigerant nomenclature or naming convention.  To develop the nomenclature for common refrigerants, ASHRAE developed Standard 34, Designation and Safety Classification of Refrigerants.  This standard also provides safety classifications for flammability and toxicity of refrigerants, but this article will concentrate on the naming only.

Refrigerants are named using an “R” (as in Refrigerant) following by a dash and a two to four digit number.  Some refrigerants will also have a letter prefix or suffix that further specifies the chemical makeup.  Refrigerants are classified into 10 groups called series.  These are shown in the table below:

For the first four series (000, 100, 200, 300), the refrigerants are generally a combination of Carbon (C), Hydrogen (H) and Florine (F) with some other elements mixed in here and there.  For these series, a very handy trick called the “Rule of 90” applies.  With the Rule of 90, you simple take the refrigerant number and add 90 to come up with the number of Carbon, Hydrogen and Florine atoms in each molecule.  Here’s an example to demonstrate:

Using this method, we can see that R-22 (CHClF₂) has a single Carbon, one Hydrogen and 2 Florine atoms.  It also has a Chlorine, but that isn’t included in the Rule of 90.

Series 400 and 500 are refrigerant blends (mixtures or two or more pure refrigerants).  This allows engineers to tweak the refrigerant properties and to make the suitable direct replacements for outlawed refrigerants.  These blends are categorized into two blend types, zeotropic (Series 400) and azeotropic (Series 500).  An azeotropic blend behaves much as a pure refrigerant would with the entire substance boiling and condensing at the same temperature. In a zeotropic blend, the various refrigerants in the mixtures would boil or condense at difference temperatures giving the substance what engineer’s call “glide.”  A more in depth look at glide may be a future column, but is beyond the scope of this article.

The Organic Compounds go in series 600.  These are or hydrocarbons and oxygen compounds.  Refrigerant numbers are based on the number of Carbon atoms in each molecule.  In general, the name is derived from adding the number of carbon atoms to 600 and then subtracting 4.

Series 700 is reserved for the inorganic compounds.  Usually a single atom or diatomic molecule (H₂, N₂, etc).  These are numbers according to their molecular mass.  If the molecular mass is less than 100, you just add the mass to 700 and you have the refrigerant number.  For larger masses, you add the mass to 7000 for a 4 digit number.

Lastly, you have a small group of unsaturated organic compounds (Series 1000).  An unsaturated (or olefin) compound is similar to the Series 600 organic compounds but has one or more double bonds between the carbon atoms.

As you can see, refrigerant classification and nomenclature is based heavily in the chemistry of the refrigerant, and this article only scratched the surface of all the rules and tricks that go into the names of refrigerants.  ASHRAE Standard 34 is the authority on all naming rules and has more information about each series if you are looking to continue reading.

At Forward Engineers, we seek to not only be a design and consulting firm but to also educate our clients about engineering technology.  While doing so, we inevitably refresh our own knowledge and sometimes even learn something ourselves.  If you are seeking to work with an engineering firm that is client-centered and strives to provides services that are on time, on budget and exceed expectations, please contact us.  We would love to work with you on your next project!