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May 9, 2011

Time to Fight the Rising Plug Load Monster

 

Maybe you just got your coffee, checked your emails and then started reading this blog. Your printer is sitting on your desk innocuously, but it actually keeps feeding an insatiable monster. It and its neighbors—lamps, the computer, the scanner—all typically draw electricity around the clock. This drain, called plug load, which accounts for about a third of commercial building energy use, might be why your electricity use has increased over the last few years. As electricity demand increases, new power plants are constructed around the country. Rocky Mountain Institute has historically looked at this issue from the other side: Rather than focusing first on energy production, have we utilized all possible ways to lower demand?

While every energy sector is faced with this issue, efforts in the built environment are particularly significant because our buildings are responsible for 41 percent of U.S. primary energy use. Improving building energy efficiency is vital to the cleaner energy future that RMI envisions in Reinventing Fire. Reducing energy demand in our buildings can also help to create job opportunities and free up financing for renewable energy sources.

The revolution toward energy-efficient buildings is well under way. Increasing energy prices and demand for healthier buildings put pressure on the construction industry to build greener buildings. The market is being transformed by many efforts, including retrofitting lighting and HVAC systems; increasing popularity of high-performance window and envelope systems; more stringent energy codes; and the influence of recent green building rating systems and efficiency programs such as LEED and Energy Star. However, considering the urgency of carbon emissions reduction, we must ramp up our efficiency efforts to reduce the amount of CO2 in the atmosphere to safer levels.

Any effort targeted at realizing the full efficiency potential of the existing building stock must address end uses that have historically been overlooked, including plug loads. Plug load is a term for the energy consumed by devices plugged into electric outlets, such as computers, TVs, refrigerators, kitchen appliances, phone chargers, servers, and task lights. Almost any device in our buildings consumes electricity while on standby or even when switched off—known as phantom (or ghost or vampire) load.

Plug loads are a major contributor to building energy consumption, especially in offices. In commercial buildings, plug loads are one of the fastest-growing end uses in terms of energy consumption and typically account for 30-35 percent of the total electricity used.

Plug loads are becoming more and more important in efficiency efforts. Because lighting retrofits are the most common energy-efficiency measure, lighting loads have remained stable as commercial floor space has increased. HVAC loads have grown proportionally to the 0.9-1.2 percent average annual growth in floor space. But even though efficiency of electronic devices has constantly improved, proliferation and increased use of office equipment continues to elevate plug loads as a percentage of the total building energy use. Since 1995, plug load energy consumption increased about 235 percent. Since the building shell and major building systems are becoming more efficient and the solutions for reducing plug loads are challenging to implement, plug loads become a larger and larger piece of a shrinking pie.

As plug load energy consumption continues to grow, building codes are still not addressing the issue. Moreover, project teams rarely focus on it in the early stages of design and typically make final decisions about equipment procurement after construction completion. Each plug load device contributes to internal heat gains and therefore increases ventilation requirements and cooling loads. Poorly specified plug loads might cause HVAC systems to be over or undersized and perform below their optimum, contributing to higher operating costs.

So the plug load threat is emerging like a monster against building energy efficiency efforts. However, there are easy-to-implement, cost-effective ways to tame and control plug loads that offer high potential for substantial energy and cost savings. It is important to implement strategies to reduce peak energy use both for in-use and off-hour (standby) modes for as many types of plug loads as possible. Let’s consider workstation setups in typical office buildings. First of all, proper space planning (such as cubicles with low-rise panels) can promote daylighting penetration and minimize the need for under-cabinet task lights and desk lamps. An LED (light-emitting-diode) desk lamp that consumes 10 watts or less can keep the task lighting power density at a minimum and also provide flexibility for employees. Moreover, flat screen monitors, especially LED monitors, provide better energy savings than typical bulky CRT (cathode ray tube) monitors and save valuable desk space. Using proper screen size, adjusting monitor display settings and limiting use of multiple screens can further lower energy use. Using a laptop and a monitor allows employees to still benefit from two screens, promotes remote working and provides up to 85 percent energy savings compared to a setup with two regular monitors and a desktop.

When it is not possible to use laptops due to security requirements or any other reasons, choosing mini-desktops or nettops can still provide substantial energy savings over desktops. A nettop might consume as little as 38 kilowatt hours per year, whereas typical desktops consume about 185 kWh/year. Phones are also responsible for significant energy use in offices since they are plugged in 24/7. Replacing analog phones with VoIP Phones (a phone model that allow calls over an IP network such as the Internet instead of an ordinary telephone network) would provide significant energy savings.

Typical Workstation Setup

Energy-Efficient Workstation Setup

 

Many similar, easy-to-implement and cost-effective strategies are also applicable to other plug load equipment. Choosing Energy Star-rated products can be an effective way to lower energy use when proper equipment category is selected according to the user needs. (For example, while plasma TVs can be Energy Star-rated, they consume far more energy than a non-Energy Star-rated LCD TV of similar screen size.) Independent international programs such as Topten can help to select a comparable, best-in-class alternative in the market. Using easy-to-use power meters such as Kill A Watt or Watts up? can help identify energy hogs in buildings through simple audits. To control idle power draw (phantom loads), it is wise to use smart power strips, which are low-cost, practical devices that help to cut the idle power draw when devices are not in use. National Renewable Energy Laboratory’s How to Brochures can also help assess and reduce plug loads. NREL achieved about 50 percent plug-load reduction in its new Research Support Facility in Golden, Colorado. Raising building owner and tenant awareness can save large amount of energy due to behavioral shifts.

Since efficiency is far cheaper than adding power plants, we can no longer ignore plug loads. While finding reliable and efficient energy sources is inevitable for the path to sustainable future, let’s not forget the insatiable monster.

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