The Forgotten Key Component
Achieving Zero Net Energy Buildings in the 21st Century
When a zero net energy building is achieved, its plug load system will be projected to use 50 percent of electrical energy and the Low Voltage Distribution Transformer that is installed will be key.
By Maj. Lorenz Schoff, P.E., M.SAME, USAF (Ret.)
Turning on the nightly news in October 1973, the headline was: “OPEC imposing an oil embargo on the U.S. and other western countries,” for supporting Israel in its war with neighboring countries. The conflict lasted for 20 days, but its impact and a second embargo in 1979 lasted for a couple of decades. This began the era of energy conservation, which led to today’s emphasis on energy efficiency and sustainability.
The 1990s emphasized improving the energy efficiency of buildings, and improving its environment. This resulted in new design standards, including Leadership in Energy & Environmental Design (LEED). Today, high performance (HP) design—improving building and systems energy efficiency for new construction and renovations—is the rule rather the exception, with energy system’s equipment and components concurrently evolving.
The evolution of LEED/HP buildings continued as the 21st century began, with the goal of achieving maximum energy efficiency. This evolution resulted in the next step, zero net energy (ZNE).
Many LEED/HP buildings reduced energy use to very low levels—kBtu/ft²—influencing this next step and achieving sustainability in every aspect of building operations. A ZNEB is a building with zero net energy consumption annually equals the energy produced by renewables on the building/site or credits. This is the core definition. If more energy is produced on site than used, this results in a surplus of energy or a positive net energy building.
Minimizing energy use through efficient building design is fundamental to the development and design of a ZNEB. Energy efficient design is the lowest cost strategy with the highest rate of return on investment before consideration of renewable energy sources. Its lifecycle cost is pennies to save a kilowatt-hour of electricity, while it takes dollars to save the same using renewables.
IMPORTANCE OF PLUG LOADS
One major element in building operations and electrical energy use that has been overlooked is plug loads, including its components. Currently, in most building types, plug loads can be up to 25 percent of electricity used. But when ZNE is achieved, this is projected to be 50 percent. Improving the efficiency of system components has been key to lighting systems (LED lamps, sensors), and HVAC systems (motors, boilers, compressors, sensors). But it has been overlooked for the plug load system.
The overlooked component in the plug load systems is the Low Voltage Distribution Transformers (LVDT), which provides the energy to the plug load. This component steps down incoming voltage to 120/208-V. This component is not seen; it resides behind a closed/locked doors, requires no maintenance, and consumes energy all day every day whether items are plugged in or not. It may appear to be “Out of Sight and Out of Mind,” yet when opening the door to where it resides, you are often met with heat—a clear sign of energy waste and inefficiency.
A study of transformer efficiency conducted by Oak Ridge National Laboratory in 1995 found transformers used by utilities (high & medium voltage) increased in efficiency between 1950 and 1995. Why? It was less expensive to improve efficiency of substation transformer than to build power plants. The study found that the efficiency of LVDT decreased, from 1970 to 1995, when low electricity rates took the focus off efficiency, and the units were designed to achieve lowest manufacturing cost.
About the same time period, another study measured the loads on LVDT in five building types: Office, Manufacturing, Retail, Education and Healthcare. All these categories can be identified on military installations in one form or another. The results emphasized the inefficiency of LVDT.
The electrical energy used just to energize the unit and not to provide any energy to the outlet is known as No Load Losses (NLL). For example, an existing LVDT 75-kVA (which is a common size) had NLL of more over 800-W.
Since the 1970s, electrical profile of the plug loads has changing from linear to non-linear (electronic loads). This change can be illustrated by comparing tube televisions to integrated circuit LED televisions; or moving from overhead/opaque projectors to LCD projectors. These changes have resulted in changing the load profile on LVDT, but the design criteria has not changed in response to this loading change. Linear loads are still assumed to be predominate. That is wrong.
REDUCING ENERGY USAGE
The Department of Energy conducted a study to help improve the efficiency of all transformers, with an emphasis on LVDT. The preliminary findings were published in 2004 in the Federal Register. This resulted in the establishment of a transformer known as TP-1, which was included in Energy Policy Act of 2005 as the minimum efficiency LVDT to be manufactured after July 2007. The LCC unit with the highest efficiency was classified as CSL-3. It was estimated over 40 million LVDT existed in the nation’s building and if all could be replaced overnight, it would reduce electrical energy use by 2.6 percent annually, or 60- to 80-billion-kWh.
Manufacturers began to produce minimally compliant efficient TP-1, or slightly more efficient NEMA Premium units. These units only addressed linear loads and to accommodate the non-linear loads by down-rated larger transformers to a lower level and give them a K rating. A couple of manufacturers recognized the change in profile—linear to non-linear—and produced units matching the efficiency of CSL-3 and capable of 100 percent non-linear loads. These units had lower NLL and achieved higher efficiencies at today’s loads.
A study of transformer efficiency conducted by Oak Ridge National Laboratory in 1995 found transformers used by utilities (high & medium voltage) increased in efficiency between 1950 and 1995. Why? It was less expensive to improve efficiency of substation transformer than to build power plants.
The final ruling on LVDT was published in 2013 with an effective date of Jan. 1, 2016 (DOE 2016 LVDT). On that date, TP-1 could not be manufactured and the efficiency of the minimum unit increased. The lowest LCC design was designated EL-6; but the minimum unit that could be manufactured was EL-1 with a slightly higher overall efficiency compared to the TP-1, but still only addressing linear loads. Additional lower NLL were achieved when compared to the TP-1. Most manufacturers are complying with the minimum unit but still ignoring the real world of non-linear plug loads.
Those who manufactured the CSL-3 again took the step to provide customers with units providing the highest efficiency and further reduce NLL with the manufacturing of units complying with EL-4 and EL-5 requirements since the quality and grade of steel for the EL-6 core is not available at this time.
An example of potential energy savings is illustrated at an Army installation where several existing transformers were measured and projected to be replaced with EL-4. A 75-kVA had 10.75 percent loading and losses of 0.543-kW. It was projected to reduce losses to 0.149-kW with a 2016 EL-4. A 225-kVA had 11.18 percent loading and losses of 2.01-kW and projected to reduce losses to 0.382-kW, or a saving of 81 percent. Remember, these devices run constantly.
THE TIME IS NOW
With HP design and achievement of ZNE requirements a target of new buildings and many retrofits, consideration should be given for specifying LVDT capable of achieving efficiencies with non-linear loads. Specifications should require documented measured performance of LVDT installed complying with specifications.
The same DOE 2016 LVDT should be a required Energy Conservation Measure for all future Energy Saving Performance Contracts (ESPC), since the LVDT is about the only Energy Conservation Measures with a service life longer than the typical 25-year ESPC. DOE estimates the service life of a LVDT is over 30 years. The time is now for specifying DOE 2016 LVDT, both for today’s energy needs and the achievement of ZNE.