Increasing Efficiency of Building Systems and Technologies, Lecture notes of Technology

Download Increasing Efficiency of Building Systems and Technologies and more Lecture notes Technology in PDF only on Docsity! QUADRENNIAL TECHNOLOGY REVIEW AN ASSESSMENT OF ENERGY TECHNOLOGIES AND RESEARCH OPPORTUNITIES Chapter 5: Increasing Efficiency of Building Systems and Technologies September 2015 Quadrennial Technology Review 5 Increasing Efficiency of Building Systems and Technologies Issues and RDD&D Opportunities The buildings sector accounts for about 76% of electricity use and 40% of all U. S. primary energy use and associated greenhouse gas (GHG) emissions, making it essential to reduce energy consumption in buildings in order to meet national energy and environmental challenges (Chapter 1) and to reduce costs to building owners and tenants. Opportunities for improved efficiency are enormous. By 2030, building energy use could be cut more than 20% using technologies known to be cost effective today and by more than 35% if research goals are met. Much higher savings are technically possible. Building efficiency must be considered as improving the performance of a complex system designed to provide occupants with a comfortable, safe, and attractive living and work environment. This requires superior architecture and engineering designs, quality construction practices, and intelligent operation of the structures. Increasingly, operations will include integration with sophisticated electric utility grids. The major areas of energy consumption in buildings are heating, ventilation, and air conditioning—35% of total building energy; lighting—11%; major appliances (water heating, refrigerators and freezers, dryers)—18% with the remaining 36% in miscellaneous areas including electronics. In each case there are opportunities both for improving the performance of system components (e.g., improving the efficiency of lighting devices) and improving the way they are controlled as a part of integrated building systems (e.g., sensors that adjust light levels to occupancy and daylight). Key research opportunities include the following:  High-efficiency heat pumps that reduce or eliminate the use of refrigerants that can lead to GHG emissions  Thin insulating materials  Windows and building surfaces with tunable optical properties  High efficiency lighting devices including improved green light-emitting diodes, phosphors, and quantum dots  Improved software for optimizing building design and operation  Low cost, easy to install, energy harvesting sensors and controls  Interoperable building communication systems and optimized control strategies  Decision science issues affecting purchasing and operating choices 147 5 Table 5.1 Sample ET Program 2020 Goals Current 2020 goal Insulation R-6/in and $1.1/ft2 R-8/in and $0.35/ft2 Windows (residential) R-5.9/in and $63/ft2 R-10/in and $10/ft2 Vapor-compression heating, ventilation, and air conditioning (HVAC) 1.84 COP and 68.5 $/ kBtu/hr cost premium 2.0 Primary COP and $23/kBtu/hr cost premium Non-vapor compression HVAC Not on market 2.3 Primary COP and $20/kBtu/hr cost premium LEDs (cool white) 166 lm/W and $4/klm 231 lm/W and $0.7/klm Daylighting and controls 16% reduction in lighting for $4/ft2 35% reduction in lighting for $13/ft2 Heat pump clothes dryers Not on market 50% savings and $570 cost premium commercial investment in the technology is driving change so fast that federal applied research will have limited value. Rapidly increasing demand for fast information processing, for example, is facing energy- use limits, which are driving an enormous amount of private research investment. It is important to determine where and how to productively invest in RDD&D that could improve the efficiency of an electronic component used by these products, and depending on research results, private research efforts and competing priorities within budget limitations, the mix of appropriate investments is likely to change over time. As an example, the development and application of wide band gap semiconductors could reduce energy use in a number of miscellaneous devices but currently has insufficient RDD&D investment to drive this forward in a timely manner. Excluding this “other” category, Figures 5.2 and 5.3 show that building energy use can be reduced by about half. Buildings last for decades (consider that more than half of all commercial buildings in operation today were built before 1970),5 so it’s important to consider technologies that can be used to retrofit existing buildings as well as new buildings. Many of the technologies assumed in Figure 5.2 and Figure 5.3 can be used in both new and existing structures (e.g., light-emitting diodes [LEDs]). Retrofits present unique challenges, and technologies focused on retrofits merit attention because of the large, existing stock and its generally lower efficiency. These include low-cost solutions such as thin, easily-installed insulation, leak detectors, devices to detect equipment and systems problems (e.g., air conditioners low on refrigerants), and better ways to collect and disseminate best practices. Energy use in buildings depends on a combination of good architecture and energy systems design and on effective operations and maintenance once the building is occupied. Buildings should be treated as sophisticated, integrated, interrelated systems. It should also be understood that different climates probably require different designs and equipment, and that the performance and value of any component technology depends on the system in which it is embedded. Attractive lighting depends on the performance of the devices that convert electricity to visible light, as well as on window design, window and window covering controls, occupancy detectors, and other lighting controls. As the light fixture efficiency is greatly increased, lighting controls will have a reduced net impact on energy use. In addition, the thermal energy released into the room by lighting would decrease, which then affects building heating and cooling loads. Since buildings consume a large fraction of the output of electric utilities, they can greatly impact utility operations. Specifically, buildings’ ability to shift energy demand away from peak periods, such as on hot summer afternoons, can greatly reduce both cost and GHG emissions by allowing utilities to reduce the need for their least efficient and most polluting power plants. Coordinating building energy systems, on-site Quadrennial Technology Review148 5 Increasing Efficiency of Building Systems and Technologies generation, and energy storage with other buildings and the utility can lower overall costs, decrease GHG emissions, and increase system-wide reliability. The following discussion describes the next generation of research opportunities and priorities using three filters:  If the research is successful, would it result in a significant increase in building energy performance?  Is the research likely to lead to a commercially successful product in five to ten years?  Is there evidence that private research in the field is inadequate? 5.2 Thermal Comfort and Air Quality Providing a comfortable and healthy interior environment is one of the core functions of building energy systems and accounts for about a third of total building energy use. New technologies for heating, cooling, and ventilation not only can achieve large gains in efficiency, but they can improve the way building systems meet occupant needs and preferences by providing greater control, reducing unwanted temperature variations, and improving indoor air quality. Opportunities for improvements fall into the following basic categories:  Good building design, including passive systems and landscaping  Improved building envelope, including roofs, walls, and windows  Improved equipment for heating and cooling air and removing humidity  Thermal energy storage that can be a part of the building structure or separate equipment  Improved sensors, control systems, and control algorithms for optimizing system performance Both building designs and the selection of equipment depend on the climate where the building operates. 5.2.1 The Building Envelope The walls, foundation, roof, and windows of a building couple the exterior environment with the interior environment in complex ways (see Table 5.2).6 The insulating properties of the building envelope and construction quality together control the way heat and moisture flows into or out of the building. The color of the building envelope and other optical properties govern how solar energy is reflected and how thermal energy (heat) is radiated from the building. Windows bring sunlight and the sun’s energy into the building. About 50% of the heating load in residential buildings and 60% in commercial buildings results from flows through walls, foundations, and the roof (see Table 5.2).7 Virtually the entire commercial cooling load comes from energy Table 5.2 Energy Flows in Building Shells (Quads) Residential Commercial Building component Heating Cooling Heating Cooling Roofs 1.00 0.49 0.88 0.05 Walls 1.54 0.34 1.48 -0.03 Foundation 1.17 -0.22 0.79 -0.21 Infiltration 2.26 0.59 1.29 -0.15 Windows (conduction) 2.06 0.03 1.60 -0.30 Windows (solar heat gain) -0.66 1.14 -0.97 1.38 149 5 entering through the windows (i.e., solar heat gain). The bulk of residential cooling results from window heat gains although infiltration also has a significant role. Future cooling may be a larger share of total demand since U.S. regions with high population growth are largely in warmer climates. Windows and Skylights The quality of a window is measured by its insulating value8 and its transparency to the sun’s visible and infrared light9 recognizing that an ideal system would allow these parameters to be controlled independently. An ideal window would provide attractive lighting levels without glare, high levels of thermal insulation, and allow infrared light to enter when it is useful for heating but block it when it would add to cooling loads (see Figure 5.4).10 It would also block ultraviolet light that can damage skin and materials. Windows should also be effective parts of building climate control and lighting systems. Without active control of optical properties, static window requirements will depend on the climate, orientation, and interior space use. If cooling loads dominate, windows that block the invisible (i.e., infrared) part of the solar spectrum are desirable. Significant progress has been made in window technology over the past three decades. Thanks in large part to DOE’s research investment, sealed windows (multiple panes sealed in a factory) now comprise about 95% of windows sold for residential installation and 89% of windows sold for nonresidential installation.11 Low- emissivity ENERGY STAR® windows make up more than 80% of the market12 and are twice as insulating as the single-glazing windows that were the default option for generations. Innovations include glass coatings that reduce absorption and re-emission of infrared light, thermal conductivity improvements (e.g., multiple panes of glass, filling gaps between glass panes using argon, krypton, or xenon,13 and improved frame design), and the use of low-iron glass to improve visible clarity. Commercial products are now available that provide seven times the insulation provided by single-glazing windows without compromising optical properties. A typical single-glazed window has an R value of one, but R-11 glazing materials and combined frame/glazing units with R-8.1 are commercially available.14 The “solar heat gain coefficient” is a measure of the fraction of total sunlight energy that can pass through the window while the “visual transmittance” measures the fraction of visible sunlight that gets through. A typical single-glazed window has a solar heat gain coefficient and visual transmittance of about 0.7. Commercially available windows can come close to this with a transmittance of 0.71 and a solar heat gain coefficient that can be selected in the range 0.29–0.62.15 Window frames transmit unwanted heat directly through rigid materials. While progress has been made both in insulating framing materials and in frame design to reduce conduction, challenges still remain. Durable edge seals remain a challenge, and stress under large temperature differences remains problematic. Figure 5.4 Only 44% of the energy in sunlight is visible light. Credit: PPG Industries, Inc. TOTAL SOLAR ENERGY INFRARED 53% UV 3% VISIBLE 44% Quadrennial Technology Review152 5 Increasing Efficiency of Building Systems and Technologies  Use efficient, variable speed motors: Most ventilation systems adjust flow rates only by turning motors off and on or by using dampers. Significant energy savings can be achieved using efficient, variable air volume systems with variable-speed fans along with properly designed and sealed ducts.35 There are also major opportunities for improving the efficiency and lowering the cost of variable speed motors and motor controls.36 Innovations that improve the performance and lower the cost of wide bandgap semiconductors are an important part of this work (see Chapter 6).  Use heat and moisture exchange devices: Even greater energy savings can be achieved by using heat exchangers that allow incoming cool air to be heated by warm building air being exhausted (or the reverse if the building is cooled). Advanced systems can also exchange moisture (i.e., enthalpy exchangers). These systems are discussed in the section on heat pumps. It has been particularly difficult to get advanced systems into smaller buildings. More than half of buildings larger than 10,000 square feet use economizers and variable air volume systems, but less than 10% of buildings smaller than 10,000 square feet use them.37 Technologies that are inexpensive and easy to use in smaller buildings would be particularly useful. 5.2.3 Space Conditioning Equipment Although well-designed building envelopes can dramatically reduce heating and cooling loads, there will always be a need for mechanical systems to condition air. Fresh outdoor air will need to be brought into the building and conditioned to replace exhaust air and the heat and moisture generated by occupants and building equipment will need to be removed. Space conditioning involves two distinct operations: 1) increasing or decreasing air temperature (i.e., adding or removing “sensible heat”), and 2) humidifying or dehumidifying air (i.e., adding or removing “latent heat”). Figure 5.5 Types of Building Heating Equipment 153 5 Because warmer air can also contain more moisture (water vapor), heating usually needs to be coupled with humidification and cooling with dehumidification. Traditional air-heating equipment includes furnaces and heat pumps (see Figure 5.5).38 About half of the floor space is heated with systems that burn fuels and produce CO2 that cannot practically be captured or sequestered with conventional technology. In large commercial buildings, space heating typically uses boilers to heat water, piping the hot water to spaces (i.e., offices and other rooms), and then blowing air over compact hot water coils or running the coils through the floor or wall and radiating heat into the space. These systems require a separate, dedicated outdoor air system to bring in fresh air. The combination of water pipes/pumps and small air ducts/efficient fans not only requires less energy than large air ducts, it also needs less space between floors. Air conditioning involves both cooling the air and removing moisture. The traditional approach does both using vapor-compression heat pumps. Smaller systems, including most residential systems, move conditioned air while most large commercial buildings use central chillers to cool water and transfer heat from water to air closer to the occupied spaces. Dehumidification is the process of taking water out of air, and it accounts for nearly 3% of all U.S. energy use. It is typically achieved by inefficiently cooling moist air until the water vapor condenses out and then re-heating the air to a comfortable temperature, which is an inefficient process. Efficiency improvements in heating, ventilation, and air conditioning (HVAC) systems will involve efforts to improve the efficiency of heating or cooling air and technology that can efficiently remove moisture from air. Heat pump systems are often used for heating in regions where natural gas39 is not available. Next-generation cold weather heat pumps can be cost effective in a wide range of climates. Current heat pumps lose 60% of their capacity and operate at half the efficiency when operating at -13oF. Work is underway to develop a heat pump capable of achieving a Coefficient of Performance (COP)40 of 3.0 for residential applications at that temperature (compared with a COP of 3.6 for an ENERGY STAR® heat pump operating with no more than a 25% reduction in capacity).41 Work is also underway to improve the performance of cold-weather gas furnaces.42 Heat pumps have the advantage of providing both heating and cooling with a single unit offering an opportunity to lower initial costs. Vapor-compression heat pumps and air conditioners rely on refrigerants (working fluids) such as hydrofluorocarbons that have a significantly higher global warming potential (GWP) than CO2 when they are released to the atmosphere. The search for substitutes has proven difficult since alternatives present challenges in toxicity, flammability, lower efficiency, and/or increased equipment cost. It is an area of active, ongoing research by the National Institute of Standards and Technology (NIST) and others.43 See Table 5.3 for more information.44 There is a number of promising heat-pump technologies that have the potential to increase system efficiency and eliminate refrigerants with high GWP.45 Some use vapor- compression with CO2, ionic Table 5.3 Non-Vapor Compression Heat Pump Technologies Magnetocaloric: Certain paramagnetic materials undergo temperature changes when placed in magnetic fields. Specifically, they undergo heating when a magnetic field aligns the magnetic dipoles of their atoms and cooling when the field is removed and dipole directions randomize. Thermoelectric: Current flowing through two different semiconductors can either add or remove heat at the junction. Thermoelastic: Shape-memory alloys heat up when physically stressed and cool down when stress is removed. Electrochemical: This device uses a membrane that allows protons but not electrons to pass through. When a voltage is applied across the membrane, protons (hydrogen nuclei) accumulate at pressure on one side of the membrane. This leads to compressed hydrogen on one side of the membrane which can create cooling when expanded. Electrocaloric: This device uses a dielectric that is heated when exposed to an electric field and gives off heat when the field is removed. Quadrennial Technology Review154 5 Increasing Efficiency of Building Systems and Technologies liquids, water, and various combinations as working fluids. Heat pumps can also be built that do not require vapor compression (see Table 5.3). There are also opportunities to improve thermally driven technologies using adsorption and absorption devices and duplex-Stirling heat pumps. While a key interest in developing these new approaches is to reduce GHG emissions, some can exceed the efficiency of current vapor-compression units. 5.2.4 Moisture Removal Well-designed building shells and foundations can greatly reduce moisture infiltration, but residual moisture transfer coupled with moisture generated by people and building operations will continue to make moisture removal a priority in building energy systems. A number of new approaches do not require heat pumps and could lead to major gains in efficiency. Membrane technologies allow water vapor to pass but block the passage of dry air or can be used to separate moisture from air using only the difference in vapor pressure, passing thermal energy from outgoing to incoming air. Alternatively, these systems may develop a vacuum on one side of the membrane and then compress and exhaust the water vapor removed. These systems can be combined with evaporative cooling stages to provide both dehumidification and chilling.46 5.2.5 Heat Exchangers Heating and cooling systems depend on devices called “heat exchangers” that transfer heat from the surfaces of the equipment, usually metal surfaces, to air. Efficient heat exchangers are typically large and expensive. It may be possible to greatly improve heat exchange efficiency through improved designs such as microchannel devices47 or the rotating heat exchanger.48 New manufacturing methods as discussed in Chapter 6, including additive manufacturing, may allow production of heat exchange designs not possible with traditional approaches, which could increase the efficiency of commercial air conditioners by as much as 20%.49 5.2.6 Thermal Storage The performance of building heating and cooling systems and the electric grid system serving the building can be enhanced by systems that store thermal energy, particularly cooling capacity. Thermal storage can be provided with a number of different technologies and a number of commercial products are available.50 Approaches include the following:  Designing buildings to store and remove thermal energy in the mass of the building itself (i.e., floors, support columns, etc.)  Using ice and other phase change materials Since chillers are more efficient when outdoor air is coolest, systems that pre-cool buildings in the early morning can result in energy savings. Chillers can also store cooling capacity by pre-cooling chilled water or ice during night hours and then shutting off the vapor compression systems during peak cooling demand periods in the afternoon. This can yield small site energy savings through chiller efficiency improvements during the cooler nighttime hours, but the largest site benefit of thermal energy storage lies in reducing the site peak demand and peak energy usage. Shifting energy demand away from peak periods could improve electric utility operations by requiring fewer generation plants to be brought on line and reducing the need to build new plants and distribution systems.51 Thermal storage could also be a dispatchable asset, mitigating problems associated with the intermittent output of wind and solar energy systems. Such systems must be operated as part of an integrated building control system (this is discussed in a subsequent section of this report). 5.2.7 Integrated System Analysis Taken together, the technologies described above can achieve major improvements in efficiency. Figure 5.6 through Figure 5.9 summarize some of the cost and performance goals for key technologies and estimate the 157 5 A detailed discussion of research opportunities for windows and wall materials can be found in a DOE report on windows and buildings envelope RDD&D,53 and a detailed discussion of advanced non-vapor compression heat pumps can be found in a report on that topic.54 In brief, areas where fundamental research problems remain unresolved include the following:  Glazing materials with tunable optical properties (transmissivity and emissivity adjustable by wavelength) including materials that could be applied to existing windows  Materials that are thin and provide tunable insulating and vapor permeability and materials that could be used in next-generation enthalpy exchange devices  Technologies that could lower the cost of producing noble gases and identifying transparent, low- conductivity gases that could substitute for noble gases  Strategies for using vacuum as a window insulation  Innovative heat exchanger designs for heat pumps and other uses (variety of scales) that reduce the volume and weight of heat exchangers  New ways to enhance ventilation and health that are cost-effective, energy-efficient, and practical to implement  Improved ways to control moisture transfer into and out of buildings  Components for non-GHG heat pumps including magnetocaloric, thermoelastic, thermoelectric, electrochemical, and electrocaloric systems In a number of cases, the technology for achieving needed system performance is known but products are too expensive. In most cases, costs will decline as production volumes increase. Emphasis should also be placed on lowering manufacturing costs. In some cases, finding inexpensive materials is also important. Areas with opportunities include electrochromic windows, variable speed motors, vacuum insulation/advanced insulation (e.g., aerogel), sensors, and controls. Continuing research brings the goal of creating a “net-zero energy façade or envelope” within reach. A window could reduce a building’s need for external energy sources more than a highly-insulated opaque wall. While the specifics vary with location and orientation, the opportunities to do this include: 1) reduce thermal losses by a factor of two to three below current code requirements; 2) provide active control of solar gain and daylight over a wide range; 3) introduce sufficient daylight to adequately light the outer thirty-foot depth of floor space; and 4) use natural ventilation when it can offset HVAC use. These systems require careful integration with other building systems to be effective and to provide the required levels of thermal and visual comfort. 5.3 Lighting Lighting quality plays an essential role in the appeal and safety of interior and exterior spaces. Well-designed lighting systems can enhance productivity while glare and other harsh lighting features can decrease it.55 Light quality also affects sleep patterns and health56 and can shape the mood of any space. About 18% of U.S. electricity consumption and 6% of all U.S. energy consumption is used to provide indoor and outdoor lighting. The goal of the DOE lighting research is to give designers the strategies and the devices that can provide optimal lighting performance while minimizing energy use. The new technologies can do much more than match existing lighting system performance with far less energy use. They can improve the quality of lighting by allowing greater user control including an ability to select color as well as intensity. The new lighting systems may be able to operate for decades without replacement or maintenance. Quadrennial Technology Review158 5 Increasing Efficiency of Building Systems and Technologies The key strategies for improving the efficiency and quality of lighting are good building and lighting design, window and window covering technologies (such as blinds and diffusers), lighting sensors and controls (including occupancy sensors and light sensors), and lighting devices (LEDs and others). Good lighting design can ensure that light levels are adjusted to user requirements. Intense task lighting may be needed for detailed work while much lower levels are needed in hallways. Since each of these elements is influenced by the others, it is important to evaluate each as a part of an integrated system. It must also be recognized that lighting, whether provided by daylight or by artificial light, can have a significant impact on heating and cooling loads. The energy and environmental impacts of lighting systems must always be considered as a part of integrated building performance. While 71% of all lamps in the United States are installed in residential units (Figure 5.10), commercial building lighting is by far the largest consumer of energy and lumens (lm).58 Although only 29% of lamps are installed in commercial buildings, these buildings make significantly heavier use of fluorescent lighting fixtures—which on average use four times less electricity to produce a lumen than a typical residential incandescent lighting fixture. The market for efficient lamps, driven in part by regulations, is rapidly changing the lighting market. Electricity used for lighting fell 9% between 2001 and 2010 even though the number of installed lamps increased by 18%.59 The efficiency of a lighting unit is best measured by the lumens produced for each unit of electricity consumed, lumens per watt (lm/W). Lumens are a measure of light the human eye actually perceives. A candle produces about 12.6 lm and a traditional 100W incandescent light bulb produces about 1700 lm. The human eye is much more efficient at processing green light than it is processing deep reds or blues, and we are completely blind to infrared and ultraviolet (see Figure 5.11). The efficiency of incandescent bulbs is about 17 lm/W while a good fluorescent bulb can achieve 92 lm/W.60 Figure 5.10 Most light fixtures are in residences, but the bulk of lighting energy is in commercial buildings. The average commercial device is 3.6 times as efficient but is in use more than six times (in hours) as much per day.57 Credit: Navigant Consulting Number of Lamps Residential 71% 25% 8% 25% 50% 60% 2% 8% 11% 2% 17% 21% Commercial Industrial Outdoor Energy Use Lumen Production 159 5 Figure 5.11 The efficiency of the human eye is highest for green light at 683 lumens per watt. Credit: E. Fred Schubert, Light Emitting Diodes. Second Edition. Cambridge University Press (2006). Figure 5.11 shows that one watt of energy in the form of green light results in 683 lm. This means that the absolute limit of a light device’s efficiency is 683 lm/W. White, of course, is a mixture of many different colors and therefore seeing it requires eye receptors that are much less efficient than the green peak (Figure 5.11). There has been extensive analysis of what qualifies as an acceptable “white light.”61 The “white” that is acceptable depends on what is being illuminated (i.e., food, living areas, or streets), and there may be cultural differences.62 Preferences for “warm” colors with more red or preferences for “cool” colors, which more closely match sunlight on a clear day, depend on a range of individual tastes.63 New lighting technology, which allows a range of color and even an ability to adjust light color, will allow this diversity to be expressed in the marketplace.64 Taken together, the potential of daylighting, controls, and more efficient devices can be enormous. And the impact could be rapid if lighting devices, lighting sensors, and lighting controls were easily retrofit without major renovations. 5.3.1 Windows, Daylighting, and Lighting Controls Daylight provided by windows can make a major contribution not only to the ambiance of indoor environments but to reducing a building’s demand for artificial light. Windows account for about four quads of energy in terms of their thermal impacts and can influence another one quad. This complex connection to other building energy systems means that windows and daylighting sensors and controls can only be understood as a part of an integrated building system analysis. This integrated design impact will be considered later in this report. Quadrennial Technology Review162 5 Increasing Efficiency of Building Systems and Technologies Figure 5.13 The price and performance of LEDs have steadily improved since 2009. Credit: Navigant Consulting One of the challenges in using multiple LEDs has been the low efficiency of green LEDs. Table 5.4 shows the performance challenges facing LEDs that use phosphors to convert blue LED output into other colors.75 Significant improvements are needed in both green and red phosphors.76 Quantum dots, which are nanoscale semiconductor structures, can substitute for phosphors, but challenges remain in achieving high efficiency without use of cadmium.77 Innovations are also needed to improve the fraction of light that actually leaves the device (as opposed to being absorbed internally) and the electronic subsystems that provide dimming and convert alternating current (AC) plug power into the direct current (DC) required by the lights. Color reliability and guaranteed lifetimes are also a challenge. Research teams have been attempting to achieve efficiency, reliability, and other targets that would make them convincing competitors to other LEDs. While progress has been steady, major challenges remain. Table 5.4 LED Efficiencies LED efficiency in percent (Light energy out/electric energy in) Effective phosphor conversion efficiency in percent Blue Green Amber Red Green phosphor Red phosphor Current efficiency 55 22 8 44 Current efficiency 44 37 2025 goal 80 35 20 55 2025 goal 67 56 163 5 Other Advanced Technologies A variety of innovative strategies have been proposed for bringing natural light into interior spaces. They include the following:  Internally reflective light conduits that bring light from roof collectors into interior spaces  PV devices that are transparent to visible light but convert infrared and other portions of the sunlight into electricity (these devices may cut installation costs for self-powered window and window shading devices)  Combined systems that generate electricity in rooftop PV units and transmit visible light through fiber optic systems to interior spaces 5.3.3 Integrated System Analysis Taken together, use of efficient lighting devices, daylighting, sensors and controls, and good design can reduce the energy used for lighting by an order of magnitude. Potential savings from integrated systems is shown in Figure 5.14 and Figure 5.15. The order in which measures are considered shapes the magnitude of savings for subsequent measures. Least expensive measures were considered first, therefore sensors and controls were considered first. Figure 5.14 A combination of improved lighting devices and controls meeting 2020 program goals (ET) can reduce residential lighting energy 93% of the theoretical limit. Figure 5.15 A combination of improved lighting devices and controls meeting 2020 program goals (ET) can reduce commercial lighting energy 81% of the theoretical limit. 5.3.4 Research Opportunities Innovators ranging from large global glass companies to small venture-supported firms are making significant investments in new window and window control systems. Federal research investment focused on devices should be limited to high-risk innovations such as novel optical materials and new manufacturing methods. There is a clear and continuing need for federal support of testing protocols for advanced glazing and fenestration systems, and the development of voluntary interoperability specifications for building controls that integrate and optimize dynamic envelope components, lighting, and HVAC. There is also a continuing role for the development of performance databases and simulation tools with open and validated algorithms and models. Detailed research priorities are laid out in recent roadmaps.78 Quadrennial Technology Review164 5 Increasing Efficiency of Building Systems and Technologies One fundamental need is the development of test procedures for reliably determining the expected lifetime of commercial products. LEDs can last for decades but there are no data on long-lifetime units. A standard method for accelerated lifetime testing is essential. Opportunities for fundamental research also include the following:  Understanding why LED efficiency decreases at high power densities  High-efficiency green LEDs  Efficient quantum dot materials  Glazing with tunable optical properties (also needed for thermal load management)  Efficient, durable, low-cost OLEDs Opportunities for reducing costs through improved design and manufacturing and other mechanisms include the following:  Sensors and controls  Lowering retrofit costs of new light fixtures 5.4 Major Energy Consuming Appliances: Hot Water Heaters, Refrigerators, and Clothes Dryers Water heaters, refrigerators, and clothes dryers are major energy consumers and are responsible for about 18% of all building energy use. Many of the technologies designed to improve whole building energy performance discussed earlier can also be used to increase the efficiency of these appliances. For example, water heating efficiency can be improved using advanced heat pumps, low-cost variable-speed motors, thin insulation, and other improved designs. Improved insulation and other strategies can reduce the losses from lengthy hot water distribution systems in commercial buildings and large homes. Water heaters with storage tanks are good candidates for load shifting and providing other services important for optimizing electric utility performance with the help of improved controls and communications technologies. Work is often needed to ensure that these approaches are designed for the size ranges needed for appliances. Significant gains have been made in refrigerator performance over the past decades but these gains have been partially offset by the increasing number of refrigerators and freezers used per household.79 Improvement in heat pumps, advanced thermal cycles, heat exchangers, and thin, highly-insulating materials (e.g., vacuum insulation) can lead to major performance gains. Further gains are possible by using separate compressors optimized for freezers and refrigerator compartments and using variable speed drives and new sensors and controls to reflect ambient temperatures and react to signals from utilities. Until recently, clothes dryers were untouched by the technical advances transforming markets for other building equipment, but this is changing rapidly. New clothes dryers now on the market use heat pumps to circulate heated air over clothing in a drum, pass the air over a heat exchanger cooled by the heat pump, condense the water out of the air, and then reheat and recycle the air. Since air is recycled, there is no need for an air vent. These appliances operate at lower temperatures (thus are gentler to clothes) and reduce utility peaks since their peak electric demands are one-fifth of conventional dryers’. The technology is attractive for designs that provide washing and drying in the same front-loading unit.80 U.S. sales have been limited because of their comparatively high cost and longer cycle times (typically double current times). American consumers, used to doing multiple loads of laundry, demand dryers that have roughly the same cycle time as washing machines. However, improved heat pumps, insulation, heat exchange, variable speed motors, and other innovations promise further gains in performance and lowered costs.81 There are also 167 5 Figure 5.16 The “other” category of demand in buildings is created by a huge variety of devices—many of which are miscellaneous electric loads. Total “Other” primary energy use in residential buildings = 5.1 Quads Cooking 0.57 Other Appliances 0.71 Other (Electric) 2.50 Spas 0.11 Pool Heat/Pumps 0.25 Ceiling Fans 0.27 Furnace Fans/Pumps 0.36 Dishwashers 0.30 2014 Residential Building "Other" Primary Energy Use (Quads) Total “Other” primary energy use in commercial buildings = 6.5 Quads 2014 Commercial Building "Other" Primary Energy Use (Quads) Street Lights 2.31 Other (All Fuels) 2.28 Lab/Medical Equip. 0.15 Cooking 0.26 Dry Transformers 0.41 Kitchen Ventilation 0.44 Water Distribution 0.67 5.5.3 Research Opportunities The diversity in these electronic and other building energy loads is so great that it has proven difficult to devise research strategies for addressing them; yet, the large amounts of energy they use becomes increasingly significant as other end uses become more energy efficient. An important part of the strategy will involve finding technologies that could address efficiency issues across a wide range of these miscellaneous end uses. Such technologies include more efficient circuitry, more flexible power management (though hardware and software solutions), and standardized communications protocols. Wide bandgap semiconductors (discussed in Chapter 6) can improve controls, and highly efficient motors, next-generation heat exchangers, and thin- insulation can improve the performance of a wide range of devices. In the case of computers, basic research in materials, algorithms, and other work funded by the National Science Foundation, DOE’s Office of Science, and other federal agencies has been the foundation of this rapid growth. Building on this basic research foundation, the pace of change in the “computer and electronic products” industries has been extremely rapid because of high levels of commercial investment in innovation. This sector invested nearly 10% of their sales to research and development in 2007 in comparison to the national average of 3.8%.94 While energy use has become a priority in areas like large server systems, where energy dissipation is becoming a barrier to progress, energy efficiency in a diverse set of other products is often neglected in the race to bring innovations to the market. 5.6 Systems-Level Opportunities 5.6.1 Sensors, Controls, and Networks Lighting, windows, HVAC equipment, water heaters, and other building equipment are starting to be equipped with smart controllers and often wireless communications capabilities. These systems open many opportunities for improving building efficiency, managing peak loads, and providing services valuable to controlling the cost of large utility systems. They also offer many non-energy benefits that may be of greater interest to building owners and occupants than just energy usage. These include improved security, access control, fire and other emergency detection and management, and identification of maintenance issues before they lead to serious Quadrennial Technology Review168 5 Increasing Efficiency of Building Systems and Technologies problems. Low-cost sensors and controls also expand opportunities for individuals to have greater control of the thermal and lighting conditions, and if they power themselves using available light, vibrations, or fields generated by AC lines, it simplifies installation. More than 40% of all commercial buildings more than 100,000 square feet had some kind of “energy management control” system but less than 7% of buildings smaller than 10,000 square feet used them in 2003.95 Data on the type of controls and the way they are used (or misused) are very poor. A recent study of controls for packaged air units in California showed that 4.75% used manual controls while 35.7% employed a programmable thermostat.96 Only 4% were part of an energy management system. Innovations that greatly lower the cost and simplify the installation and operation of control systems will be particularly valuable for expanding markets for advanced control systems in smaller commercial buildings and residences. While individual subsystems such as lighting require their own control, the building as a whole will perform most efficiently if all the building systems are controlled as a part of an integrated system. Well-designed control systems can increase building efficiency up to 30% without the need to upgrade existing appliances.97 Figure 5.17 demonstrates the wide range of actors and interactions that characterizes the integrated building and grid system. Additional needs of the integrated electric grid are discussed in Chapter 3. Systems should be able to do the following:  Control room temperatures, humidity, ventilation rates, tunable windows, variable louvers, and dimmable lights  Control major appliances—most devices are controlled by turning them off or on, but the new generation of appliances allows more sophisticated adjustment of operation  Use weather forecasts to develop optimum strategies for preheating or cooling the structure  Detect and identify component failures and look for signs that equipment is about to fail  Adapt performance in response to communications from utilities using new rate structures to minimize overall system costs  Learn and anticipate user behaviors including adjusting for holidays and integrate user preferences dynamically Cost has been a major barrier to the use of self-powered sensors and controls connected by wireless communication systems. Advances in designs and production technologies can cut the cost of lighting, temperature, occupancy, current, and other sensors from the $150–$300 per node to $1–$10 per node using printed electronic substrates for circuits, sensors, antennas, PVs, and batteries.98 Since buildings are responsible for more than 76% of all electric demand, control systems in buildings can also play a major role in optimizing the performance of the next-generation electric grid. Advanced building controls and control strategies can provide a portfolio of services ranging from helping maintain utility sixty- cycle frequency over periods of seconds, to short-term load shedding by controlling water heaters and other appliances, to longer-term load shifting using the thermal mass of the building or storage systems. PVs are rapidly entering the market in some regions, and the inverters that connect them to building loads and the electric grid can also provide services to the building and the electric grid.99 Control strategies can be designed for small grids internal to a building, micro-grids serving clusters of buildings, and large utility-scale “smart” grids. Benefits to the grid include improved frequency control, reduced spinning reserve, deferred expansion of transmission and distribution systems, and smoother reaction to unplanned outages. Early estimates suggest that intelligent building controls could potentially be worth $59 billion (in 2009 dollars) annually in the United States by 2019.100 These savings require major innovations in the financial incentives provided to customers for these services. Capturing these benefits requires building 169 5 Figure 5.17 Future grid systems and smart building controls can communicate in ways that improve overall system efficiency and reliability. Credit: National Institute of Standards and Technology communications networks allowing the components to interoperate and respond to facility-wide control systems for both functionality and power distribution. Inverters connecting distributed PV systems can create problems if not effectively managed as a part of a grid system, but if properly managed, they, like other building control systems, can make significant contributions in the form of frequency regulation and in other areas. Today, there is a lack of agreement on comprehensive communications and data standards. Competing, proprietary systems inhibit the widespread adoption of technologies and control strategies and drive up the cost of deployment. The absence of dynamic price incentives for customer grid services in most areas is a major barrier to development and commercialization of sophisticated systems. Two major challenges in developing widely affordable building sensor and control systems include the high labor cost for retrofitting new lighting and lighting control systems and for getting complex control systems to work correctly. It takes many hours of expensive, highly-skilled system designer/operators to adjust schedules and ensure that building lighting and comfort levels actually reflect user needs. There is growing concern that building communications systems need cybersecurity and privacy protection as an integral part of their design. Security concerns are particularly important in hospitals and other sites where life and safety are at risk.101 Finding ways to update the software embedded in low cost devices is a new challenge. Quadrennial Technology Review172 5 Increasing Efficiency of Building Systems and Technologies 5.6.4 Embodied Energy There is great variation in the energy needed to produce construction materials and build a structure (embodied energy). Analysis shows that this “embodied energy” is 5% of total building energy use for single- family residential building113 and 16%–45% for office buildings.114 NIST has recently introduced a powerful set of tools for evaluating the embodied energy of buildings.115 The greatest potential for reducing the embodied energy of building materials involves strategies such as increasing recycling and the use of recycled materials, reducing process yield losses, substituting with less energy-intensive materials, and optimizing product design for minimal material use. 5.6.5 DC Systems LED lights, computers, TVs and computer monitors, and many other modern devices operating in buildings now use relatively low-voltage DC instead of the AC available at wall plugs. The ubiquitous Universal Serial Bus connectors operate at five volts DC. PV devices and associated battery systems, as well as electric vehicles, operate on DC. Recent analysis suggests that a typical house using a PV system could reduce its electric demand by 14% if it was equipped with energy storage and 5% if there was no storage.116 While AC to DC and DC to AC converters are becoming very efficient (typically greater than 90%) and are designed to go into hibernation modes when not in use, the large number of conversions leads to significant losses. There may also be a growing market for distributed electrical storage to provide a variety of grid support services in future electric grid and microgrid systems. The best location and size of electric storage systems in any region will require a careful analysis of the value of increased reliability, economies of scale, diversity, and many other factors (see Chapter 3). 5.6.6 Thermal Energy Distribution and Reuse Refrigeration equipment, clothes dryers, washing machines, and many other building energy systems generate heat that is typically dumped into the ambient air. It is clearly possible, however, to capture and circulate this heat so that it can be reused (possibly after its temperature is increased). Waste heat from refrigeration could be used to help heat hot water. Waste heat may also be available from combined heat and power systems and possibly from rooftop solar devices. In high-density areas, it might even be reasonable to share heat or cooling between buildings. The core of large buildings in most climates require air conditioning even in cold weather and improved strategies for moving heat from the core could contribute to system efficiency. Very little work has been done to explore low cost approaches to such energy sharing systems. 5.6.7 Research Opportunities Many research topics exist covering a wide variety of areas. Among the priority areas are the following:  Reducing the cost of sensors and controls for electrical current, temperature, CO2 emissions and other airborne chemicals and materials, occupancy, and many others  Developing energy harvesting systems to provide power for wireless sensors and controls  Improving the design of sensor and control systems including cybersecurity and improved methods for installing and commissioning these systems  Developing easy-to-use, fast, accurate software tools to design highly-efficient buildings and to assist operations  Improving support for co-simulation with other modeling engines using a widely used interface standard  Developing algorithms that allow building sensor and control systems to automatically optimize system performance without large inputs from skilled designers 173 5  Developing open-source software modules that can be combined to form sophisticated commercial control systems to enable flexible and dynamic buildings that provide value on both sides of the utility meter (DOE is encouraging the use of interoperable communications protocols for all building control and sensor systems and open-source system integration tools that will encourage creative commercial algorithms using both open-source and proprietary components.)  Developing accurate, reliable sensors with low-installed costs, including occupancy sensors that can provide real-time occupancy counts  Incorporating more decision science research while protecting the privacy of individuals and businesses  Developing components and system designs that allow building devices to share waste heat 5.7 The Potential for Building Efficiency Taken together, the technologies that can result from successful completion of the research topics discussed in this chapter have the potential to make significant reductions in building energy use at costs lower than forecast energy prices (Figure 5.18).117 For reference, Figure 5.18 also shows energy prices that include the cost of GHG emissions now used to establish federal appliance standards; it is not intended to reflect a new analysis of the actual cost of these emissions. In Figure 5.18, the red “Current Tech” curve shows the costs of efficiency measures now on the market. All the measures below the “2030 cost of energy” line—roughly nine quads—could be saved if all cost effective measures were purchased.118 This would reduce building consumption by about 23%. If the 2020 goals described Figure 5.18 More than seven quads of energy could be saved in buildings by cost effective technologies by 2030. Meeting program goals would increase this by 3.9 quads. A carbon price would increase savings further. Quadrennial Technology Review174 5 Increasing Efficiency of Building Systems and Technologies earlier in this chapter for major technology categories are met, the cost-effective savings potential increases to nearly thirteen quads or about 34% of all building energy use. The additional four quads of energy savings represent an associated CO2 emissions reduction of 203 million metric tons.119 This estimate is conservative for several reasons. For example, it does not address opportunities for reductions in miscellaneous electric loads that contribute significantly to building energy consumption. The analysis also doesn’t place a value on increased amenities associated with an efficiency measure (such as increased comfort and safety), or on the ability of these measures to provide valuable services to electric grids (such as frequency regulation and load shifting). It is also highly likely that currently unknown innovations will lead to further cost reductions and performance improvements. 5.8 Conclusion While there has been spectacular progress in building energy efficiency over the past few decades, it is clear that major opportunities remain. In many areas there are still large gaps separating the performance of commercial equipment and theoretical limits. In some cases our understanding of the nature of theoretical limits has changed because some novel mechanism has been discovered, such as membranes used to separate water from air or use of ultrasound to dry clothes. The limits have also changed because of better understanding of the way building technologies can take advantage of the external environment (e.g., daylighting and use of natural ventilation), and they should reflect the opportunity to reuse waste heat generated by building equipment. Reaching the potential will require ingenious product designs, advanced manufacturing methods that can lower costs and improve product quality, and advances in basic science—particularly in areas of materials science where novel approaches are needed on optical and thermal properties, magnetic materials, and on heat exchange and enthalpy exchange. The problems lead to a number of fundamental research challenges (see Table 5.7). It is DOE’s hope that this discussion effectively outlines the breadth, complexity, and importance of building energy technologies and help the nation’s innovators understand where they can make critical contributions; those RDD&D opportunities presented in this chapter are summarized in Table 5.8. Table 5.7 Fundamental Research Challenges  Materials with tunable optical properties (adjust transmissivity and absorptivity by wavelength)  Materials for efficient LEDs  Materials for efficient motors and controls (magnets and wide bandgap semiconductors)  Enthalpy exchange materials  Materials for low-cost krypton/xenon replacement  Materials for non-vapor compression heat pumps (e.g., thermoelectric, magnetocaloric, and electrocaloric)  Big-data management for large networks of building controls and next-generation grid systems  Ultra-efficient computation (neural networks)  Decision science research 177 5 19 Aspen Aerogel. “Highly Insulating Windows.” Northborough, MA: Aspen Aerogel, not date. Available at: http://sites.energetics.com/ buildingenvelope/pdfs/Aspen.pdf. 20 Carver, R. “High Performance Insulation in Existing Multifamily Buildings: A Demonstration Project Using Aerogel Materials.” Albany, NY: New York State Energy Research and Development Authority, 2013. 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I.; Payne, W. “Sensitivity Analysis of Installation Faults on Heat Pump Performance.” Washington, DC: NIST, Department of Commerce, 2014. Available at: http://nvlpubs.nist.gov/nistpubs/TechnicalNotes/NIST.TN.1848.pdf. 36 Department of Energy. “Energy Savings Potential and Opportunities for High-Efficiency Electric Motors in Residential and Commercial Equipment.” Washington, DC: U.S. Department of Energy, 2013. Available at: http://energy.gov/sites/prod/files/2014/02/f8/Motor%20 Energy%20Savings%20Potential%20Report%202013-12-4.pdf. • Dols, J.; Fortenbery, B.; Sweeney, M.; Sharp, F. “Efficient Motor-Driven Appliances Using Embedded Adjustable Speed Drives. ACEEE Summer Study on Energy Efficiency in Buildings.” Washington, DC: ACEEE, 2014. Available at: http://aceee.org/files/proceedings/2014/ data/papers/9-886.pdf. 37 Energy Information Administration, DOE. “2003 Commercial Buildings Energy Consumption Survey 2003.” Washington, DC: DOE, 2006. 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Available in: http://energy.gov/sites/prod/files/2014/06/f16/A2%20Poster-Altex%20AMO%20RD%20Project%20Peer%20 Review%202014.pdf. • “HEATING UP.” Oak Ridge National Laboratory. Accessed March 15, 2015: http://www.ornl.gov/ornl/news/features/2015/heating-up. 48 EERE/DOE. “Energy Department Invests $14 Million in Innovative Building Efficiency Technologies.” 2014. Available at: http://energy.gov/ eere/articles/energy-department-invests-14-million-innovative-building-efficiency-technologies. 49 Sandia National Laboratories. “RVCC Technology: A Pathway to Ultra-Efficient Air Conditioning, Heating, and Refrigeration.” Albuquerque, NM: Sandia National Laboratories, 2014. Available at: http://energy.gov/eere/buildings/downloads/rotary-vapor-compression-cycle- technology-pathway-ultra-efficient-air. 50 Zhou, D.; Zhao, C.; Tian, Y. (2012). “Review on Thermal Energy Storage with Phase Change Materials.” Applied Energy, 2012; pp. 593-605. 51 Pacific Northwest National Laboratory. “The Role of Energy Storage in Commercial Buildings: A Preliminary Report.” Richland, WA: Pacific Northwest National Laboratory, 2010. Available at: http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-19853.pdf. 52 Abdelaziz, O.; Farese, P.; Abramson, A.; Phelan, P. “Technology Prioritization: Transforming the U.S. Building Stock to Embrace Energy Efficiency.” NSTI-Nanotech, 2013. Available at: http://www1.eere.energy.gov/buildings/pdfs/technology-prioritization.pdf. • Each measure in the analysis is added to the baseline building, but energy savings depend on whether other measures are installed first. The analysis accounts for using the measures in different building types and climates as well as the fact that some measures do not work well as retrofits. 53 EERE/Department of Energy. Windows and Buildings Envelope Research and Development. Washington, DC: DOE, 2014. 54 Department of Energy. Energy Savings Potential and RD&D Opportunities for Non-Vapor-Compression HVAC Technologies. Washington, DC, 2014. 55 Boyce, P.; Hunte, C.; Howlett, O. “The Benefits of Daylight Through Windows. Washington, DC: U.S. DOE, 2003. Available at: http://www.lrc. rpi.edu/programs/daylighting/pdf/DaylightBenefits.pdf. 56 Stevens, R. G.; Brainard, G. C.; Blask, D. E.; Lockley, S. W.; Motta, M. E. “Adverse Effects of Nighttime Lighting: Comments on American Medical Association Policy Statement.” American Journal of Preventive Medicine, 2013; pp. 343-346. Available at: http://dx.doi.org/10.1016/j. amepre.2013.04.011. • Brainarda, G. C.; Coylea, W.; Ayersa, M.; Kempa, J.; Warfielda, B.; Maidab, J.; et al. “Solid State Lighting for the International Space Station: Tests of Visual Performance and Melatonin Regulation.” Acta Astronautica, 2013; pp. 21-28. 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Available at: http://www.lrc.rpi.edu/education/outreachEducation/pdf/CLE6/3-Rea.pdf. 63 Dikel, E. E.; Burns, G. J.; Veich, J.; Mancini, S.; Newsham, G. R. “Preferred Chromaticity of Color-Tunable LED Lighting.” LEUKOS: The Journal of the Illuminating Engineering Society of North America, 2014; pp. 101-115. Available at: http://ies.tandfonline.com/doi/pdf/10.1080/15502724.2 013.855614. • A commonly used index of color is the temperature of a glowing incandescent material in degrees Kelvin. This can range from 800 degrees (very red like glowing embers) to 12,000 degrees or more (very blue like skylight). Artificial devices that do not produce light like a glowing, heated object are matched to this scale by using a visual best-match called the “correlated color temperature” (CCT). 64 Cunningham, K.; Herbert, T. “Consumer Preference Survey on Directional LED Replacement Lamps for Retail Applications.” San Francisco, CA: Pacific Gas and Electric Co, 2012. Available at: http://cltc.ucdavis.edu/sites/default/files/files/publication/2012_ET11PGE2201_LED_ Showcase_Report.pdf. 65 Chen, C.-C.; Dou, L.; Zuh, R.; Chung, C.-H.; Song, T.-B.; Bing, Z. Y. (2012). “Visibly Transparent Polymer Solar.” ASC Nano (6:8), 2012. 66 GSA Public Building Service. “Thermochromic and Electrochromic windows.” Washington, DC: GSA, 2014. Available at: http://www.gsa.gov/ portal/mediaId/188003/fileName/Smart-Windows-Findings-508.action. 67 Arasteh, D.; Selkowitz, S.; Apte, J. “Zero Energy Windows. 2006 ACEEE Summer Study on Energy Efficiency.” Pacific Grove, CA, 2006. Available at: http://aceee.org/files/proceedings/2006/data/papers/SS06_Panel3_Paper01.pdf. • Klammt, S.; Neyer, A.; Muller, H. “Redirection of Sunlight by Microstructured Components—Simulation, Fabrication and Experimental Results.” Solar Energy, 2012; pp. 1660-1666. Available at: http://dx.doi.org/10.1016/j.solener.2012.02.034. 68 Building Technologies Office, U.S. Department of Energy. 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