Energy Conservation – Electrical Autotransformers

by / Monday, 22 February 2016 / Published in Energy Auditing

Many of Efficiency Engineering’s clients contact us from time-to-time to comment on the validity of claims from product vendors.  It is our experience that vendors of products with questionable energy conservation claims tend to approach building owners/managers directly instead of approaching engineering firms.

Some products that we review very quickly fall into the “not a chance that their claims are legitimate” category.  An example of this is magnets strapped onto water and fuel lines.  They are sold to building owners, car owners, etc.  No valid scientific theory predicts that they would work.  No peer reviewed studies have ever shown them to make sense.  Automotive manufacturers spend billions of dollars trying to improve the efficiency of their vehicles.  You’d think that a simple magnet on the fuel line would be in every car if it actually worked.  But these companies continue to sell their products through anecdotal evidence, bad science and gullible purchasers.

Other products fall into the category of “has some legitimacy, but claims are likely way overstated”.  A client recently asked me to review a product that falls into this category.  The product promises “up to 10% savings” for an electrical device that essentially is an autotransformer, adjusting the voltage to the building by up to 8%.  The claim is that a building that is supplied with too high of a voltage will use more electricity.

The first red flag for me is that the autotransformer can reduce the building voltage by up to 8%, yet the manufacturer claims up to 10% savings.  So let’s dig into this claim by looking at typical building loads.  The two main types of loads are linear and non-linear.

Linear Loads

Linear loads consist of Linear Loadsany electrical load where the draw (amperage) is linear or proportional to the voltage.  This can be further subdivided into purely resistive loads and resistive loads with an inductive or capacitive load to it.  Purely resistive loads would include incandescent (and halogen) lights, electric resistance heat (baseboards, duct heaters, stoves, etc.).  Resistive loads with an inductive component include fixed speed motors, lighting with magnetic ballasts.  There really aren’t any capacitive loads in buildings save for capacitor banks installed to offset inductive loads to improve power factors.

For purely resistive loads, reducing the voltage by 8% would result in a corresponding energy reduction of 8%.  (One could argue that the energy reduction would result in a reduction of cooling load on the building, which is perhaps where the vendor feels that a 10% savings claim is justifiable.)  Resistive loads that are regulated by a thermostat, however, such as baseboard heaters, duct heaters, water heaters and stoves, would simply turn off more quickly, resulting in no electrical savings (but possibly some demand savings depending on the length of cycle time).

Incandescent lights and lamps that have magnetic ballasts would definitely see an 8% savings for an 8% reduction in voltage.  These types of lights, however, are going the way of the dodo bird.  It would likely be better to manage these loads instead of installing an autotransformer.

Non-Linear LoadsNon-Linear Loads

Non-Linear loads consist of electrical loads that have a non-sinusoidal amperage for a given sinusoidal voltage.  This includes any electronics such as Variable Frequency Drives, most lighting, computers, etc.

As time goes on, more and more loads are shifting from linear to non-linear.  Incandescent lights are being switched to LED, magnetic ballasts are mostly all replaced with their electronic equivalent.  Since non-linear loads are usually electronic in nature, they can be designed to be independent of voltage over a given range; a properly designed product would draw the same amount of power regardless of voltage.

Simple Savings from an Auto Transformer

Lets assume a building with natural gas heating and some electric baseboards has the following breakout of loads:

Load Percent Load Type Savings from an 8% Voltage Reduction
Plug Load – Electronic 15% Non-Linear 0%
Plug Load – Linear 5% Linear – Varies with voltage 8%
Air Conditioning 10% Linear – Thermostat 0% – AC would cycle more often
Lighting – Electronic 40% Non-Linear 0%
Lighting – Incandescent 10% Linear – Varies with voltage 10% – includes some AC
HVAC 10% Linear – Induction Motors 2.3% – From reduced slip of 0.75%
Heating – Electric 10% Linear – Thermostat 0% – Heaters would cycle more often
Total 100%   1.63%

Therefore, there would be a 1.63% savings in the total electrical energy consumption.  (The demand savings could be higher, but for simplicity sake, we’ll focus on energy.)  Since the Autotransformer itself has a loss of 0.27%, the net savings would be 1.36%.  This may not be insignificant, but it is nowhere near the 10% savings claim.  If incandescent lamps were replaced with LED or Compact Fluorescent, and Variable Frequency Drives were installed on all HVAC pumps and fans, the savings would be reduced to almost zero.

The lesson from this is that manufacturers’ claims tend to be a best case scenario.  They are in the business of selling product.  We are in the business of helping building owners make the best decisions with their money, and under most circumstances it would not include the purchase of autotransformers to reduce building voltage.

Scott Martin, P.Eng., CMVP

Scott is President and Owner at Efficiency Engineering. He has more than 25 years in the energy efficiency field and has been with EE since 1994.

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