Heating loads, or the amounts of heating that buildings need, are major consumers of energy in buildings across the nation. Fuel-fired appliances, including stoves, water heaters, and furnaces, account for more than 25% of the primary energy consumed within residential and commercial buildings … currently, most widely used fuel sources¹ for building heating loads. As part of EERE’s comprehensive energy strategy, efforts are needed to reduce the energy consumption of natural gas and other thermally driven appliances for a more secure, reliable, and affordable energy future. In support of this, multiple BTO programs, including the HVAC, Water Heating, and Appliance subprogram, have directed multiple R&D efforts toward the next generation of thermally driven appliances.

Natural gas furnaces can be found in millions of homes and businesses across the country. Unfortunately, compared to standard furnaces, high-efficiency condensing devices typically come at a price premium. One reason for this is the need to use corrosion-resistant alloys in the condensing furnace’s construction, which supports reliable operation by resisting any acidic content that may form after combustion, thereby improving product reliability. To help reduce these cost disparities, BTO has invested in advanced adsorption technologies for gas furnaces. By using an acid gas trap, this technology could potentially reduce the risk of corrosion and allow for the use of less-expensive metal alloys in the manufacture of condensing furnaces, ultimately making the efficient technology affordable for consumers.

Most furnaces and water heaters are thermodynamically constrained; for every 1 unit of heat that is released from a fuel, up to only 1 unit of heat can be delivered to the building. In order to make the fuel more productive, a heat pumping cycle must be employed. These cycles absorb heat from a lower temperature (typically ambient air) and boost it to a higher temperature to service a load. Thermally driven heat pumps in the form of absorption cycles have been explored for decades, but their complexity and expense have remained high, limiting market penetration.

To address these challenges, BTO has funded research at multiple stages of development. A prototypical absorption heat pumping concept, as well as this early-stage triple-state sorption heat pump, both hold the potential to make thermally driven heat pumps more ubiquitous throughout the built environment. It is estimated that for every 1 unit of heat released to fuel these concepts, as much as 1.4 units of heating energy could be delivered to the building. 

Although space and water heating take up the most energy among thermally driven devices in buildings, BTO has also explored performance improvements for other end-uses. Work has been done to develop a natural-gas-driven thermo-vacuum clothes dryer, which has the potential to consume half the energy of conventional commercial dryers while drying clothing 5-10 times faster. In the kitchen, natural gas stoves can be a significant source of pollution if not properly vented. The BTO-funded smart range hood concept can sense and safely remove these pollutants with minimal noise and increased efficiency.

Typically, thermally driven devices, such as natural gas appliances, are solely associated with heating applications. While it is true that heating is a primary role of many thermally driven devices, by incorporating additional services through multifunctional designs, the services derived from a single fuel source can be increased. BTO has funded the development of such devices like the Combined Air Conditioner and Power System that provide heating, electrical power generation, cooling, and dehumidification from a single device.

In addition to energy savings, thermally driven devices of the future also have the ability to provide resiliency benefits and grid services. As energy transmission and distribution networks face increasing demands, technologies to alleviate stresses on these systems and allow for operation independent of these systems will become increasingly important. By capitalizing on these added-value streams, higher efficiency products can see greater deployment.

Although natural gas and other thermal inputs are the primary driver of many heating appliances, most equipment uses electricity to drive controls and other auxiliary functions. This means that if an electrical outage occurs, even though a furnace is mainly gas powered, it will not be able to function and provide heating to a home or business. BTO has invested in the further development of self-powered furnaces to boost system performance and provide additional resilience. Because these self-powered devices can operate independently of electrical connections, heating loads can continue to be met as long as the gas supply is operational.

BTO, in conjunction with EERE's Strategic Priorities and Impact Analysis program, is also exploring the technical potential and impacts of natural gas demand response. Natural gas is widely used in power generation as well as direct end-uses in buildings for applications that include heating, water heating, and cooking. Prolonged cold temperatures can place high demands on natural gas infrastructure, leading to supply shortages. In order to ensure adequate natural gas is available for both power generation and building heating, consumer demand response programs could potentially offset the need to expand expensive natural gas infrastructure.

While demand response programs, like Consolidated Edison’s natural gas demand response pilot program, have long been used in the power sector, there has been little assessment of its potential for natural gas. SPIA and BTO, with the assistance of NREL, are investigating the ability of buildings to provide demand flexibility through natural gas-driven devices. The results of this analysis can inform utilities and other market actors of the benefits of more intelligent and flexible grid-connected natural gas devices.

As the energy landscape continually evolves, BTO strives to ensure that all energy sources consumed within the built environment are utilized as efficiently as possible – and thermally driven devices, which play a significant role in many residential and commercial buildings, are no different. With continued investment and innovation, the economic and environmental impacts of driving these devices can be reduced through increased energy efficiency and system performance.

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¹ Energy Information Administration, U.S. Department of Energy, Annual Energy Outlook 2019, https://www.eia.gov/outlooks/aeo/