As part of its grid-interactive efficient buildings (GEB) vision, BTO directs breakthrough research that will make building technologies smarter, more connected, and more efficient. When these technologies can more flexibly react to changing conditions, new opportunities will emerge for both building occupants and the electric grid. The grid can benefit from reduced power generation and delivery costs. Building occupants can gain greater control over and value out of their building assets, while also benefiting from a cleaner, less expensive, and more resilient electrical system.

But the full potential of this GEB vision has yet to be realized, and questions remain. What benefits can grid-interactive efficient buildings offer to the grid? How can building technologies like HVAC, water heating, and lighting provide those benefits? How flexible are our current technologies? And what are our outstanding research needs?

To answer these questions, let’s begin by exploring the two general types of benefits, or simply “services,” that flexible building loads can offer. Avoided generation costs are actions that reduce peak demand, shift generation to less-expensive sources, offset the need to build more power plants, and maintain the grid’s frequency. Avoided delivery costs are actions that reduce a utility’s need to invest in new wires and substations (i.e. non-wires alternatives) and help with voltage regulation.

Each of these actions has different characteristics. Some actions last for seconds, while others last for hours. Some are requested far in advance, while others are requested on very short notice. To better understand which building technologies are capable of delivering which services, let’s examine these technologies one at a time.

Heating, Ventilation, and Air Conditioning (HVAC) and Water Heating

For years, many utilities have utilized simple on/off switches to control building HVAC systems. While this can reduce peak demand, it is not always ideal for building occupants. As Technology Manager Tony Bouza discussed in a previous article, it is more efficient to operate HVAC equipment with variable power levels, similar to how a car operates with multiple transmission speeds.

Grid-interactive water heaters can quickly change their power draw without impacting occupant comfort. This speed can help the grid maintain a safe frequency and voltage. Water heaters can also be used to store thermal energy. By heating water only when electricity is inexpensive, occupants and grid operators can both save money.

Thermal Storage

Energy resources like solar and wind yield variable amounts of power throughout the day. This production does not always coincide with when it’s needed. In these cases, some of that energy can be stored for later. Pumped hydroelectric is the most common grid-scale storage solution, while electrochemical batteries are becoming an increasingly popular resource.

Buildings offer an additional way to store energy – thermally. For example, during the middle of the day when lots of solar energy is being generated, a residential building can pre-heat or pre-cool itself. If the building is constructed with advanced thermal materials, it can act much like a thermos – keeping the temperature constant for a longer period of time without consuming electricity at the most expensive time of the day. This strategy can also help customers reduce costly demand charges.

Some of the most promising advanced thermal materials are phase-change materials (PCMs). Because these materials do not change temperature when their phases change, lots of thermal energy can be comfortably stored in PCMs. Developing new PCMs with advanced chemistries is an active area of research for BTO. Researchers are working to improve the rates at which these “thermal batteries” can charge and discharge. They are also looking to increase their heat storage capacities, reduce the rate at which they leak energy, and develop smart controls to optimize their usage.

Envelope and Windows

Buildings could more flexibly utilize thermal storage if their walls’ insulation levels could be tuned dynamically. For example, by temporarily lowering your walls’ insulation level on a cool summer night, your home could reject unwanted heat without the need for air conditioning. This approach not only reduces electricity generation costs, but it allows the customer to gain additional value from a historically passive building asset.

Researchers are also investigating whether dynamic windows can be generators of solar energy. Today’s efficient solar windows tint darker when collecting energy. This means there is work to be done to develop these as revenue-generating assets that also meet occupants’ aesthetic and comfort requirements.

Advanced sensing could also enable windows to automatically alter their function depending on whether the building is occupied or not. For instance, if sensors notice that a room is unoccupied, the windows could function as efficient solar panels and/or thermal insulators, then transition back to conventional windows when occupants return.


Until recently, lighting had been unable to offer grid services without undermining occupant satisfaction. But now, new white- and color-tunable LED technologies allow their power-draw to be modulated by deep dimming and spectrum variation. Lights can also respond extremely quickly, allowing them to provide grid services within timeframes that range from sub-seconds (for frequency regulation) to hours (for energy services).

Connected lighting with embedded sensors will also have the capability to self-monitor and report their consumption. This not only provides valuable data that helps optimize lighting with other building equipment, but also allows utilities to quantitatively characterize demand flexibility and confirm delivery of service.


We’re still in the early years of grid-interactive building technologies, and we have much to learn. Without optimizing building technologies for the grid services they are able to provide, future buildings are unlikely to reach their full potential. Developing quantifiable metrics will provide the research community with clear technical targets. GEB technologies will interact with each other, other buildings, and across the meter in complex ways. Modeling this complexity will be key to optimizing outcomes for building occupants, managers, and utilities alike.

At the direction of BTO, several national labs are investigating these dynamics. Lawrence Livermore National Laboratory (LLNL) will analyze data from 80 different buildings to determine the parameters that most greatly influence a building’s peak shaving potential. The National Renewable Energy Laboratory (NREL) is developing metrics to quantify a building’s flexibility to respond to demand response events. Lawrence Berkeley National Laboratory (LBNL) is constructing a framework that will not only map the landscape of potential flexible loads, but also identify – in real time – grid-interactive efficient buildings that would be most disrupted by and least able to respond to a demand response event. Oak Ridge National Laboratory (ORNL) is pursuing the development of a transactional control mechanism that could automatically modulate building loads in response to a utility-provided price signal.

As energy efficiency and demand response become more integrated into building components, BTO will continue to work to co-optimize them, including an LBNL project to assess their relationship. Through this and other system-level studies, we will continue to improve our grid while maximizing comfort and minimizing costs for consumers.

Robert Fares
Robert Fares worked as an AAAS Science and Technology Policy Fellow at the U.S. Department of Energy’s Building Technologies Office in the Emerging Technologies (ET) program.Robert Fares worked as an AAAS Science and Technology Policy Fellow at the U.S. Department of Energy’s Building Technologies Office in the Emerging Technologies (ET) program.
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