Grantee Research Project Results
2021 Progress Report: Solar Window for Water Collection and Purification
EPA Grant Number: SU840165Title: Solar Window for Water Collection and Purification
Investigators: Dyson, Anna H , Kim, Jaehong , Pretorius, Mandi , Jeon, Inhyeong , Ryberg, Eric , Novelli, Nick , Wu, Xuanhao
Current Investigators: Dyson, Anna H , Kim, Jaehong
Institution: Yale University
Current Institution: Yale University
EPA Project Officer: Spatz, Kyle
Phase: I
Project Period: December 1, 2020 through November 30, 2021 (Extended to November 30, 2022)
Project Period Covered by this Report: December 1, 2020 through November 30,2021
Project Amount: $24,851
RFA: P3 Awards: A National Student Design Competition Focusing on People, Prosperity and the Planet (2020) RFA Text | Recipients Lists
Research Category: P3 Awards , P3 Challenge Area - Safe and Sustainable Water Resources
Objective:
This project addresses strategic water and energy management techniques for the built environment through investigating the integration of novel enhanced Solar Water Disinfection (SODIS) techniques into a building envelope assembly, towards increasing the viability of on-site renewable energy-based water recuperation (Figure 1). This project incorporates ongoing multifunctional building envelope research to investigate the potential for the integration of combined solar energy collection and water disinfection into curtain wall systems and structural facades that provide architectural requirements, such as transparency to outside views, reduction of solar glare, and heat gain for modulated daylighting, and reduction in lighting loads. For this project, a novel solar-driven water disinfection process (SODIS), which has been developed by team members, is investigated for integration within an advanced window typology for solar water disinfection, daylighting, and heat remediation (Dyson et al., 2012; Novelli et al., 2021). We explored how a select optical geometry that affects solar concentration could enhance SODIS technologies, such as photocatalysis, photothermal pasteurization, and photosensitization, for distributed application within building envelopes. We hypothesize that the integration of optical components into a building envelope module could enhance the effectiveness of point-of-use water treatment strategies by both increasing solar capture with available building surface area, and by maximizing the potential for solar-driven processes through increasing flux using solar concentration. We studied how optical components in a building envelope module could enhance the effectiveness of multiple (bio)renewable-based water treatment processes, by measuring the potential impact on disinfection efficiencies of SODIS photosensitizers upon irradiation within the transparent solar concentrating window modules.
Figure 1 Building-Integrated Solar Disinfection: Incorporating renewable photochemical water treatment technologies into the Solar Enclosures for Reuse (SEWR) Framework (Dyson et al., 2012; Dyson et al., 2020; Ryberg et al., 2018; Ryberg et al., 2021).
Progress Summary:
Design Development and Modification of The Optical Component:
The solar disinfection window unit, per the Solar Enclosure for Water Reuse Framework (Dyson et al., 2012), is considered as a modular building component that integrates macro building-scale to micro material processes to receive, shape and convert solar energy for water treatment. In prior work, the team had investigated the scale-up and flow-through assessment of edible photosensitizers that enhanced SODIS within a window unit at an optimal solar tilt angle and at a 1:1 concentration (Figure 2). This served the purpose of base assessment of building-scale working conditions. We compared the photobleaching rate in batch and flow-through conditions both outdoors and at bench-scale under solar simulation. Findings showing that the photobleaching rate was linear in all cases, validated the viability for flow-through adaptation with the potential to achieve reported efficiencies measured at bench-scale. We would, therefore, within the challenges of a complex design framework incorporating optical and photochemical enhancements to water treatment, use photosensitization indicators as an indirect measure of the proposed system’s capabilities as a solar collector (collector efficiency) and as an indirect assessment of the solar concentrating component (optical efficiency).
We identified a baseline non-imaging optical component type that, as a 2D profile extrusion, could be further developed and readily fabricated for viable integration into the window design. Merging design and performance criteria required of an integrated system; we investigated the use of a non-tracking compound parabolic collector (CPC) in visually transparent dielectric media (Winston et al., 2005). By comparison to single-axis tracking collectors with up to 10-50x concentration ratios, CPC systems as low-concentration collectors of 1-5x ratios offer preferred working conditions for viable distribution in buildings: Reduced instabilities with rapid water heating; Greater optical efficiency with wider acceptance angles; The ability to accept diffuse radiation, Systems that contain no moving parts, thereby reducing maintenance costs and improving consumer payback periods.
The optical design development iteratively incorporated functional criteria required for the water treatment process, non-imaging optics for concentrating solar, as well as needs of performative building glazing and for near-term manufacturability. As optimization parameters, the primary factors that could enable a balance of year-round solar capture efficiency with identified goals for enhanced photochemical processes included 1.) Optimizing the solar window orientation with respect to the designed-for acceptance angle of the building-integrated optics, 2.) Finding an optimal mediation of the desired concentration ratio with realistic optical efficiency, and therefore 3.) Accounting for cost-benefit factors for viable building-scale integration of custom shaped glass optical components. We iteratively developed the optical design in relation to increasingly impactful contextual and material parameters. The ideal geometry of the selected optical component needed to be minimally adapted to meet basic building integration and fabrication criteria. As opposed to standalone systems or those modeled on peak performance conditions, the design and development of affordable and readily manufacturable geometries for building envelopes imposed additional design criteria on the concentrating solar lens units, such as sizing tolerances related to the integration with standardized parts, building systems, and means of fabrication.
Simulated optical performance:
Adapting an ideal optical geometry for design application within building constraints realistically reduces the estimated optical efficiency and solar concentration. The baseline optical design was selected based on a reported 8x concentration ratio, and an average optical efficiency of 49% (peak; 72.7%) within a 22.19° half acceptance angle (Winston, 2005), and that could adopt various receiver geometries at the focal point. As a 2D solar collector type with a single axis bias, simulation of the baseline and modified optical components were plotted as optical efficiency by incident angle of irradiance source. Approximate simulation of iterative design modifications was investigated as a preliminary evaluation of the design approach by assessing the feasibility of augmenting building system criteria within an optical design process. The simulated optical efficiency resulting from two stages of design modifications to the receiver geometry, simulated within the acceptance angle range 0°- 30°, suggested potential for greater average optical efficiencies than the baseline optical profile with increases of up to 25%, albeit at a lower effective concentration ratio.
Physical Testing of Optical Component’s Impact on Photosensitization:
We ultimately gained inconclusive results with bench-scale testing: Based on the photosensitizer response measured with FFA degradation, all instance of the optical component performed poorly relative to the expectations with the simulated performance. We saw no significant impact on the rate of 1O2 production albeit tested in various configurations that attempted to overcome potential energy losses at each surface interface. Several factors that contributed to ineffective solar concentration was observed, including the impact of material properties, surface finishes, surface interfaces between the optical component and fluid passageway, and internal losses due to refraction within surface solids.
Several configurations of the modified optical component’s receiver assembly were assessed as an attempt to overcome the poor or incongruent physical testing results in comparison with the simulated performance. Control testing compared the receiver with and without adjacent reflective surfaces. The fabricated optical component was tested with various fluid passageway assemblies: a tube inserted into the receiver notch, a hemicylindrical tube that completed the lower half of the fluid passageway, a tubeless configuration where half the water volume is enclosed by a flat plate in clear acrylic and with the clear acrylic back-surfaced with reflective aluminum foil.
Table 1: Photosensitization 1O2 production in flow-through and batch configurations by residence time
Table 1Flow-through (sec) | Batch (sec) | ||||
Pitch (degree) | 20 | 20 | 40 | 60 | Decay over time |
0 | 1.57 | 1.6 | 1.2 | 1.16 | 73% |
15 | 1.44 | 1.46 | 1.31 | 1.13 | 77% |
30 | 1.75 | 1.46 | 1.18 | 1.04 | 71% |
45 | 1.51 | 1.41 | 1.31 | 1.23 | 87% |
Degree | Pitch | [relative] | Yaw | [relative] |
0 | 1.57 | 1.00 | 1.51 | 1.00 |
15 | 1.44 | 0.92 | 1.89 | 1.25 |
30 | 1.75 | 1.11 | 1.74 | 1.15 |
45 | 1.51 | 0.96 | error | error |
Tabled results for batch and flow-through samples validated batch-testing for the purpose of indoor laboratory work, prior to incorporating flow-through testing with field studies (Table 1). Furthermore, batch samples taken at 20, 40 and 60sec timestamps underwent similar decay rates at the 0°, 15°, and 30° incident angles. When comparing measured 1O2 concentration of pitch and yaw-axis orientations observing relative changes from direct normal (Table 2), pitch-axis angles show a deviation of ~11% compared to a yaw-axis deviation of 25% (flow-through, 20 sec residence). This finding contradicts the simulated expectation for the yaw-axis to have negligible effects on optical efficiency by changing incident angle.
Supplemental Keywords:
Solar concentration, solar collectors, photoreactor design, building facade design
Relevant Websites:
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.