SmartScreen: Controlling Solar Heat Gain with Shape-Memory Systems (Patent-Pending) Martina Decker and Peter Yeadon, Decker Yeadon LLC New York City

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1 SmartScreen: Controlling Solar Heat Gain with Shape-Memory Systems (Patent-Pending) Martina Decker and Peter Yeadon, Decker Yeadon LLC New York City Abstract It is widely understood that motorized window treatments, such as shades and blinds, can assist in the reduction of solar heat gain in buildings; these electrically-driven systems can help conserve energy that is expended on cooling. Herein, we describe and demonstrate how a novel material device might be engineered to open/close apertures in a surface when solar heat gain is advantageous/disadvantageous. As this device includes a smart material that is only activated by changes in interior ambient air temperature, the system can directly influence a building s climate without expending any fuel or electricity for its own operation. In our SmartScreen system, the R-Phase SMA smart material is both a sensor and a motor.

2 SmartScreen: Controlling Solar Heat Gain with Shape-Memory Systems (Patent-Pending) Martina Decker and Peter Yeadon, Decker Yeadon LLC New York City Introduction It is widely understood that window treatments, such as shades and blinds, can assist in the reduction of solar heat gain in buildings. There are many products on the market that use sensors, processors, controls, and motors to automatically close/open blinds when a room becomes too warm/cool. One of the advantages of these automatic systems is that they can help conserve energy that is expended on cooling. However, motorized shades consume electricity in order to operate, and no zero-power system exists on the market. Our team investigated how a particular set of smart materials, thermo-responsive shape-memory alloys (SMAs), can regulate solar heat gain through glazed building envelopes, to conserve energy expended on cooling. Our main objective was to demonstrate how a new class of material devices might be engineered to open/close apertures in a surface when solar heat gain is advantageous/disadvantageous, simply by changing their shape when the interior ambient air temperature falls/rises. As these smart materials are only activated by temperature changes, our ambition was to create a system that can directly influence a building s climate without expending any fuel or electricity for its own operation. We call this system SmartScreen. Research Method

3 The research consisted of three stages: Design, Fabricate, and Confirm. These three stages were preceded by a discovery stage, wherein we were able to identify a particular type of smart material that could drive the SmartScreen system with changes in ambient room temperature. This material is known as an R-Phase Shape-Memory Alloy and it differs significantly from standard SMAs. Applications with conventional SMAs commonly need electricity to drastically change the alloy s temperature (see Supplementary Information: R-Phase SMA Actuators). Design The original design (see Figure 1), with its integrated actuators, was not going to work with R-Phase SMAs because of their allowable strain of less than 1%. We pursued four additional SmartScreen designs, and reduced the number of actuators that would be needed to open/close the apertures. This reduced costs and embodied energy in the entire system. We decided to develop a design that could perform with just one R-Phase SMA actuator. We reasoned that if one actuator could move the entire screen to open/close the apertures, then two or more actuators could apply even more force to move the screen if necessary. If a user needed to override the system, to manually open/close or entirely roll up the screen, a single actuator would also be less problematic to disengage (see Supplementary Information: SmartScreen Design). Fabricate

4 A few prototypes of the SmartScreen were made for testing. Various sheet materials were lasercut and printed for use as screens, however all of the prototypes included the same actuator design. The R-Phase SMA actuator housing assemblies were ABS plastic, which has a reasonable strength-to-weight ratio. Acetal/nylon/glass bearings were used to mount the rods to the actuator assembly (see Supplementary Information: SmartScreen Prototypes). Confirm Four test environment boxes, including a control environment box, were constructed and installed at the Rhode Island School of Design. The location offered large windows and uninterrupted southern exposure; we could also control the HVAC system in this space. Temperature sensors were added to each box, and SmartScreens were installed in all but the control box. As the ambient temperature in the test boxes rose/fell, we found that a single R- Phase SMA actuator could close/open apertures in response to solar heat gain. We made improvements to the screens and ran tests again at our office in New York (see Figures 2 and 3). Key Findings and Conclusion The tests served as an excellent proof-of-concept. The R-Phase SMA actuators were positively capable of moving the screens in response to solar heat gain in the test environments, to open and

5 close the apertures. However a number of problems emerged, and the following improvements could be made to the system: Instead of ABS actuator housings, precision-milled aluminum could reduce friction that resists the movement of the R-Phase SMA. A clutch assembly would be advantageous for disengaging the smart materials, so that one might manually open/close or entirely roll up the screen. Adjustable restrictors could be used to set, or modify, the range of activation temperatures for the actuator. Better woven and non-woven sheeting materials need to be acquired, that reduce friction between layers and do not deform when stressed. SmartScreen: Controlling Solar Heat Gain with Shape-Memory Systems (Patent-Pending) Martina Decker and Peter Yeadon, Decker Yeadon LLC New York City Figures Figure 1: The original SmartScreen design included numerous integrated SMAs that were woven into the sheeting; it would have required the attainment of significant deformation in the SMA actuators.

6 Figure 2: The SmartScreen prototype with a single R-Phase SMA actuator shown at the left of the rotating top rod. This version of the screen sheeting is 50% open when cool and 100% closed when warm.

7 Figure 3: The R-Phase SMA actuator includes a bias spring and center piston that turns the top rod. When warmed, the R-Phase SMA pushes the piston down; when cooled, the bias spring overcomes the R-Phase SMA to push the piston back up and open the screen.

8 SmartScreen: Controlling Solar Heat Gain with Shape-Memory Systems (Patent-Pending) Martina Decker and Peter Yeadon, Decker Yeadon LLC New York City Supplementary Information R-Phase SMA Actuators At the heart of the SmartScreen system, is a shape-memory alloy (SMA) actuator. This material is both the sensor and the motor of the system. Some designers have experimented with standard NiTi-based SMA products that are readily available, such as Flexinol actuator wire by Dynalloy. But because the hysteresis of these long-established alloys is large (e.g., the hysteresis between the heating and cooling cycles of Flexinol is approximately 30K) electricity is used to induce these SMAs to transform, due to heat that builds in the material as it resists electric current. It is not a challenge to use electricity to raise the temperature of an SMA from 60ºC to 90ºC, to produce a transformation in the material. However, as our SmartScreen is to consume no power whatsoever, and because standard SMAs do not operate within the range of ambient room temperatures that we require for the system, we had to locate an alternative to conventional SMAs. Recently, materials scientists have shown much interest in a different type of shape-memory material, known as R-Phase SMAs, whereby the polycrystalline lattice structure of R-Phase SMAs will undergo an intermediate phase of rhombohedral distortion that

9 develops from austenite prior to martensite. One advantageous property of R-Phase SMAs is their low hysteresis, which is less than 3K; additionally, SMAs can be designed to work at ambient room temperatures. After many months of working with Sumitomo Metals, Japan, they were able to formulate and produce an R-Phase SMA coil springs that might serve as an actuator in our SmartScreen system. However, unlike conventional SMAs that allow for a restorable deformation strain of about 7%, R-Phase SMAs only allow about 1% strain or less (see data in Supplemental 1 and Supplemental 2). This meant that we had to design a system that could make use of very little movement in the R-Phase SMA springs, which has far less movement than a standard, electrically driven SMA. SmartScreen Design The original SmartScreen design included numerous SMA actuators that were integrated into the fabric of the screen, whereby each actuator would enable a single aperture to independently open and close (see Supplemental 3). Having recognized that R-Phase SMAs could not undergo such a large deformation, and eager to reduce the number of actuators in the entire system, we conceived two more designs that used fewer actuators with less movement to open/close rows of apertures (see example in Supplemental 4).

10 In an effort to further reduce the number of R-Phase SMA actuators, we modeled two more actuators. Each of these final actuator designs makes use of just a single R-Phase SMA spring, however one version has a concealed R-Phase SMA spring, whereas the other enables one to easily witness how the R-Phase SMA spring is responding to changes in temperature. We decided to develop the design of a SmartScreen that could perform with just one exposed R-Phase SMA actuator. The actuator included restrictors that limited the movement of the R-Phase SMAs, between 21ºC and 26ºC; any ambient temperatures above or below this range would not cause the actuator to move, due to the restrictors. At the low ambient room temperature (21ºC), the screen would be fully open to absorb solar heat gain; at the high ambient room temperature (26ºC), the screen would be fully closed to deny solar heat gain (see Supplemental 5). Hence, the system takes advantage of higher temperature fluctuations at the window, caused by solar heat gain and heat loss. In resolving to run the entire system with just one actuator, we reasoned that if one actuator could move the entire screen to open/close the apertures, then two or more actuators could apply even more force to move the screen if necessary. Furthermore, if one needs to override the system, it is advantageous to have just one actuator automatically driving the entire screen. With a single actuator, it would be less problematic to disengage the smart

11 materials so that one might manually open/close or entirely roll up the screen. We focused on designing the actuator assembly so that it would turn a single rod to move the entire screen. In order to reduce the moment force needed to turn the rod and eliminate any eccentric dead load that the sheet material might impart on the rod we draped the fabric over the rod and let it hang as a wide band, so that it could serve as its own counterweight (see Supplemental 6). SmartScreen Prototypes The R-Phase SMA actuators were secured in white rapidprototyped ABS housing assemblies, which have a reasonable strength-to-weight ratio. The actuator assemblies, rods, bearings, and various types of shade sheeting were installed in test box environments, along with temperature sensors (see Supplemental 7). Because the shade sheeting is draped over the rod, to serve as its own counterweight, this arrangement enabled us to entirely rethink the configuration of the shading surface. We created a novel multi-layer shade with each layer positioned very close to the next. Unlike conventional blinds, which have some depth that can still block direct sunlight when the slats are fully open, our multi-layer shade fell in a narrow plane so that more sunlight could pass through the aperture openings (see Supplemental 8). The tests served as an excellent proof-of-concept. The R-Phase SMA actuators were positively capable of moving the screens in

12 response to solar heat gain in the test environments, to open and close the apertures. However a number of problems emerged, all of which are not utterly insurmountable, during the fabrication of the prototypes and the tests that were performed. Although they are lightweight, the ABS components produced a lot of friction, which the actuators had to overcome in addition to moving the rod and screen. Often the actuator would not fully close the screen until it had reached 28ºC, a couple of degrees above the target design temperature. This problem with friction resulted in the screens jumping swiftly from open to close, as the springs warmed and finally built up enough force to overcome the friction. The ABS components were redesigned and smoothed, however they continue to present some challenges in terms of both friction and striking a balance between weight and strength. Precision-milled aluminum housings might be better for reducing friction; we do not suspect the acetal/nylon/glass bearings that were used to mount the rods. Many textiles that are used in conventional window treatments, such as shades and blinds, have already shown that they can reduce solar heat gain. What was initially thought to be one of the least difficult aspects of the SmartScreen the selection of appropriate fabrics for the sheeting was soon recognized to be a challenging aspect of the project. Existing fabrics that would fit our requirements for aperture locations, configurations, and sizes do not exist in the marketplace. We custom designed a fabric and

13 commissioned a sample to be woven on a loom, however the fabric was not stable (i.e., it could stretch) and the apertures lacked precision. Additionally, as was the case with many of the fabrics we tested, the surface of the fabric created friction in the multilayer system. We chose to laser-cut apertures in six different types of fabrics that were deemed promising. These fabrics were thinner and more flexible, but we continued to have problems with: friction between the fabric sheets, stretching, and deformation both during and after cutting. We attempted printing on sheer fabrics but, in the end, found printing and masking polymer sheeting to be superior for the test. The sheer sheet layers tended to reflect a high percentage of sunlight, even when the screen was in its open state and should have been permitting more solar heat gain to pass through. The sheer sheets also stretched and produced some minor friction; the polymer film, however, reduced friction between the sheet layers and remained stable. We continue to seek a selection of appropriate sheet materials for the SmartScreen. Finally, the screens exhibited more movement than expected, as the ambient temperature in the test boxes rose, and sometimes overshot their target movement (i.e., the apertures continued to move from open, through fully closed, to open again). However this excessive movement can be adjusted with restrictors, as long as the R-Phase SMA is not allowed to exceed its permissible strain. An improvement of the actuator housing might include set screws that

14 could be used to adjust the position and length of the restrictors, by simply turning the screws from outside an aluminum actuator housing.

15 Temp. deg. Cooling C SMA coil Length LSMA mm Bias coil Length Lbi mm Supplemental 1: Design data for the cooling phase of the R-Phase SMA spring and Bias spring. Restrictors were used to prevent the R-Phase SMA from being compressed when temperatures dropped below 21ºC. Temp. deg. C SMA coil Length LSMA mm Bias coil Length Lbi mm Heating Supplemental 2: Design data for the warming phase of the R-Phase SMA spring and Bias spring. Restrictors were used to prevent the R-Phase SMA from continuing to deform the Bias spring when temperatures rose above 26ºC.

16 Supplemental 3: The original SmartScreen design included numerous SMA actuators that were woven into the fabric of the screen, whereby each actuator would enable a single aperture to independently open and close. Supplemental 4: One of two SmartScreen designs that uses fewer actuators, with less movement, to open/close rows of apertures.

17 Supplemental 5: Quicktime movie (top) records the movement of a single R-Phase SMA actuator (double-click to play movie). The actuator included restrictors to limit the movement of the R-Phase SMAs, between 21ºC and 26ºC; temperatures above/below this range

18 would not move the actuator. Bottom image sequence shows quick check for movement, with a low-precision temperature sensor, before installation in test environments. Supplemental 6: A single actuator turns a top rod to move the entire screen. To reduce the moment force needed to turn the rod, the screen sheeting (orange) was draped over the rod to serve as its own counterweight. This created a multi-layer screen, from which various shapes and sizes of apertures could be fashioned. The center layer (grey) is fixed and static.

19 Supplemental 7: R-Phase SMA and Bias springs in ABS housing assemblies, rods, bearings, and shade sheeting were installed in test box environments, along with temperature sensors.

20 Supplemental 8: Unlike conventional blinds, which have some depth that can still block direct sunlight when the slats are fully open, our novel multi-layer shade falls in a narrow plane so that more sunlight can pass through the aperture openings. When open, a

21 two-layer system (bottom) provides 50% opening, a three-layer system (top) provides 66% opening, and a four-layer system would provide 75% opening.