Grantee Research Project Results
Final Report: Harvesting the Otherwise Wasted Heat of LED Lights in Green Buildings
EPA Grant Number: SU836134Title: Harvesting the Otherwise Wasted Heat of LED Lights in Green Buildings
Investigators: Cai, Hongyi
Institution: University of Kansas
EPA Project Officer: Page, Angela
Phase: I
Project Period: September 1, 2015 through August 31, 2016
Project Amount: $14,949
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities , P3 Challenge Area - Sustainable and Healthy Communities
Objective:
Most of the electricity (70-80%) consumed by light-emitting diodes (LED) is converted to heat rather than light. We are developing new LED luminaires to harvest both the light and the heat generated by the same LEDs for effective lighting and heating uses in the conditioned interior spaces. To that end, we have developed an integrative Illumination, Heating, Ventilation, and Air Conditioning (iHVAC) system to displace the current separative illumination and HVAC systems in residential and commercial buildings. In the iHVAC system, the new LED luminaires are integrated with the existing building HVAC systems, whose operations are tuned for optimal interactions between lighting heat gain and space heating and cooling to reduce overall building energy uses for space heating, cooling, and lighting. Our goal is to increase the LED luminaire system efficiency (i.e., the ratio of [(the output light energy (in watt) + the harvested LED heat (in watt)]/the total electricity wattage of the LED luminaire)) to at least 75% in the end of the proposed project period. With the aid of the new LED luminaires, we expect that the iHVAC system can help green buildings reduce their annual overall building Energy Use Intensity (EUI) for space heating, cooling, and lighting by 6-15% in retrofit projects and new constructions. At Phase I (2015-2016), two innovative LED technologies of “Heated Lens Lighting Arrangement” and “Heated Air Diffusers with LEDs” are developed for use in the design and development of next-generation LED luminaires. At Phase II (2017-2018), we will conduct laboratory mock-up tests to validate the two aforementioned innovations and develop a third new innovation of “Heat Arrangement of LED Arrays in Low Profile”. These new LED luminaire system architectures and form factors are used to develop the novel LED luminaires deployed in the iHVAC system. The new LED luminaires and the iHVAC system, once validated in both laboratory and field mock-up tests for implementation, will transform the current separative lighting and HVAC industries towards unity at a higher level of sustainability. The iHVAC system will also transfer the concept of separative building lighting and HVAC systems design and engineering to an integrative system design.
Description: The design and engineering of current luminaires installed in the existing buildings and available in the market focus on their light output, not heat. However, most of the electricity used by artificial light sources is converted to heat (e.g., 92% of the electricity for incandescent lamps, 79% for fluorescent lamps, 54% for metal halide (MH) lamps, 70-80% for LED lights) rather than light. The heat generated by artificial light sources is often trapped
inside the luminaire housing or ceiling cavity and not efficiently used for heating the interior spaces in winter to reduce the space heating load, or cannot be quickly dissipated away in summer that increases the space cooling load. As a result, the great deal of waste heat of artificial light sources and its interactions on space heating and cooling energy uses prevent an overall energy savings in green buildings at a higher level towards sustainability. The proposed new LED luminaires and iHVAC system are aimed to solve this problem. Tiny LEDs can easily fit in small spaces to enable novel luminaire system architectures and form factors in low profile. The heat generated by an LED, which remains on its back, can also be effectively harvested without interruption of the light output in the forward direction. Thus, the proposed new LED technologies enable a unique solution to harvesting a great deal of LED heat (>70%) and light (>90%). The new LED luminaires are designed and engineered to quickly dissipate the harvested LED heat into the conditioned interior spaces. In a heating season (winter), such supplemental LED heat entered into the conditioned space will reduce the building heating loads. In a cooling season (summer), a central air conditioning system will first cool the air to a low temperature (50° F - 55° F) to condense and remove moisture for humidity control. Such air is too cold for interior occupants and thus need to be re-heated using the reheat coils of the HVAC system to, e.g., 67° F. With the aid of the new LED luminaires, the reheat coils only need to heat the cold supply air to, e.g., 65° F. The 65° F air is further heated to 67° F by the harvested LED heat entering into the interior space. Consequently, the new LED luminaires whose operation is tuned with the existing HVAC system may reduce heating energy uses in winter and cooling energy uses in summer, in addition to lighting energy savings via increased luminous efficacy (≥ 150 lm/W). This has been validated at Phase I of the project. At Phase I (2015-2016), we have validated via laboratory tests and computer simulations the concept of iHVAC system for reduction of the annual building Energy Use Intensity (EUI) by 6%-15% for space heating, cooling and lighting in retrofit projects and new constructions. First, the technical feasibility of the new LED luminaire system architectures is tested to harvest both the light and the heat generated by the same LEDs. Prototypes are tested in the laboratory under room temperature, then in a cold room at an ambient temperature just above freezing, and then
inside a chest freezer to simulate harsh environments. The lens surface temperature is measured in different ambient temperature 3.6° F - 84.4° F (-15.8° C to 29.1° C), relative humidity (32.0% - 68.8%), and air velocity (0 – 0.012 m/s). Second, we have validated the feasibility of the iHVAC system for overall building energy savings in spacing heating, cooling, and lighting via computer simulations in software programs of FloVent and ENERGY Plus. In this computer simulation study, the new LED luminaires are tuned with the existing building HVAC system of a test space in a typical classroom setting located in Topeka, KS. A total of 84 test scenarios cover two heating and cooling seasons year around, four types of ceiling mounted luminaires, four types of supply air diffusers, and three air flow speeds of the discharge air. Moreover, at Phase I, we have conducted cost-effectiveness analysis on implementation of the iHVAC system in all U.S. residential and commercial buildings. We have also calculated the simple payback period in 2020 for an assumed project size of 1000 square foot.
Summary/Accomplishments (Outputs/Outcomes):
In the laboratory tests, the lens’ surface temperature of the new LED luminaires would be lower if the LED consumes less power, vice versa. We have looked into the increase of the lens’ average surface temperature above the ambient temperature versus the LED power at all tests. The temperature difference is almost linearly proportional to the power consumption with a slope of 1.2342 °F/W. It is thus estimated that for the new LED luminaires installed in building conditioned interior spaces that consume power of approximately 5-100 W, the lens’ surface temperature may be 6.2° F – 123.4° F above the room temperature. The actual temperature increase varies with many other factors, such as room temperature, humidity, indoor air velocity, efficacy of the LEDs, lens gap, lens materials, construction of the LED luminaires, etc. For the 84 different test scenarios in the computer simulations, the corresponding annual building Energy Use Intensity (EUI) for space heating, cooling, and lighting in this classroom is in a range of 52.10 – 66.31 kBTU/ft2. When the new LED luminaires are used to displace the existing fluorescent luminaires, the proposed iHVAC system could reduce annual building EUI 6.7%-20.5% (or approximately 4.23 – 13.43 kBTU/ft2) for space heating, cooling, and lighting in total. When the new LED luminaires are used to displace the existing LED luminaires in legacy form factors, the iHVAC system could reduce annual building EUI 3.8%-16.8% (or approximately 2.37 – 10.52 kBTU/ft2) for space heating, cooling, and lighting in total. Additionally, we have calculated the simple payback period in 2020 for an assumed project size of 1000 square foot. The calculated simple payback period for residential buildings is 1.53-3.83 years and 0.73-1.81 years for commercial buildings.
Conclusions:
The new LED luminaires and the iHVAC system can promote sustainability of green buildings, where the new LED luminaires displace all existing luminaires in legacy form factors and are tuned to the existing HVAC systems. First, implementation of the proposed new LED technologies using off-the-shelf LEDs can reduce annual building energy uses by 503.4 – 1258.5 TBTU or Energy Use Intensity (EUI) at least 6%-15% as the targeted level (3.8%-20.5% revealed in the computer simulations) for space heating, cooling and lighting energy in existing buildings, which can help DOE achieve its
energy saving goals of 2020 and 2030. The LED luminaires cooled and cleaned by the supply air have longer life and more efficient performance, resulting in long-term savings in operating and maintenance costs. Future design of the iHVAC system can reduce its initial heating and cooling loads, leading to lowered initial and maintenance costs over the product lifetime.
Second, the integration of LEDs with the HVAC system can minimize environmental impacts. The new LED luminaires can reduce greenhouse gas emissions by 246 million metric tons of carbon (MMT CO2) over two decades. Harvesting the otherwise wasted LED heat for reducing spacing heating and cooling loads can further reduce carbon dioxide emissions by 28.32 – 70.82 MMT CO2 per year when massive implementation of iHVAC system in all buildings is expected (e.g., in 2030). Also, replacing those fluorescent and HID lamps with LEDs (no mercury) can eliminate the mercury pollution inside most green buildings. The iHVAC system can also reduce solid waste of ceiling mounted fixtures (luminaires and air diffusers).
Third, the new LED luminaires and their integration with the building HVAC system will improve the indoor lighting quality and thermal comfort that benefit the building occupants. Airflow passing through the luminaires can clean the light-emitting surface and cool down the LED junction temperature for elongated life and better lighting performance. In return, the airflow is heated by the harvested LED heat entered into the conditioned space for better thermal comfort of the room occupants.
Fourth, the estimated short payback period (1.53-3.83 years for residential buildings and 0.73-1.81 years for commercial buildings) of the new LED luminaires and the iHVAC system will enable their wide implemented in practice by 2030. The new LED luminaires and the iHVAC system will see a great market adoption in green buildings across the states and worldwide. Fifth, this proposed research project is an endeavor to expand the University of Kansas
lighting program to green building sector for energy saving and sustainability. The proposed new LED technologies will be used as case studies taught in seven courses in architecture and Architectural Engineering to augment class learning of green buildings with integrated solidstate lighting and HVAC systems. This research project will be in line with the education of graduate students as part of their thesis studies.
Supplemental Keywords:
Sustainability, integration, energy conservation, computer simulation, laboratory testsRelevant Websites:
http://people.ku.edu/~h717c996/research.html Exit
The 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.