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- 1. SinBerBEST Singapore-Berkeley Building Efficiency and Sustainability in the Tropics Simulations of Innovative Solutions for Energy Efficient Building Façades Aashish Ahuja PhD candidate Mechanical Engineering UC Berkeley
- 2. 2 Outline • Introduction • Proposed Technology • Methods and Simulation Results • Future Work
- 4. 4 Introduction 1. Working on a multi-disciplinary project called SinBerBEST. 2. Seeks cooperative interaction between the grid, building and occupants. 3. Optimizing energy consumption, productivity, emissions, comfort, productivity and the entire building lifecycle. 4. My work: Analyze new energy efficient building material for façades.
- 7. 7 Energy Usage a) Sources of energy use b) Energy consumption in commercial buildings Images Source: DOE 2011
- 9. 9 Proposed building material The proposed building element is referred to as ‘Translucent Concrete Panel’
- 10. 10 Features of TC panels • Structural panels that can support buildings. • Fibers channel diffused daylight into the room. • Sunlight into room can be controlled by varying volumetric ratio of fibers. • The panels can be coupled with other technologies [Mosalam13].
- 11. 11 Construction Procedure: Part A a) Preparing the acrylic formwork b) Greasing the formwork c) Roughening fibers for Better bonding
- 12. 12 Construction Procedure: Part A d) Inserting fibers and clamping them e) Casting concrete f) Cutting concrete blocks into panels
- 13. 13 Translucent Concrete Sample of TC panel held against Sun
- 14. 14 Methods and Results: Optical and Thermal Behavior
- 15. 15 Optical behavior: Ray tracing • Ray tracing tracks light rays across different media. • Trajectory followed by rays is continuous. Expressed in form of differential equation. , n(x, y, z) : Refractive Index at (x, y, z) dR ds =[cosa, cosb, cosg]= Awhere: Eikonal equation
- 16. 16 Marching rays • For each ray, the equation is discretized spatially. • Algorithm developed in Fortran and Python. • At each time step, the location and velocity of ray is updated. Forward ray marching in TC panel
- 17. 17 Light interaction with fibers Reflection and Refraction Fresnel’s Laws Total Internal Reflection Other losses: 1) Light scattering 2) Absorption 3) Surface roughness of fibers Section of optical fiber
- 18. 18 Light interaction with concrete Reflection and Absorption Concrete part of TC
- 19. 19 Sunlight distribution model Perez Sky Distribution Model [Perez87] Diffused Radiation
- 20. 20 Sky cover for Berkeley Variation of the solar flux with sun’s position. {1: least clear; 8: most clear}
- 21. 21 Illumination Calculations Ray Tracing Database
- 23. 23 Illumination Calculations 1) Optical fibers are modeled as light emitting luminaires [Ahuja14, Ahuja151]. 2) Illumination can be calculated at any point inside the room.
- 24. 24 Energy calculations • Illumination calculations are further extended to include occupant behavior. • The occupant behavior decides light switching activity. • For the times light is switched off, electrical energy is conserved.
- 25. 25 Algorithm for Energy Calculations Start Ray Trace through Translucent Concrete
- 26. 26 Algorithm for Energy Calculations Start Ray Trace through Translucent Concrete N
- 27. 27 Algorithm for Energy Calculations Start Ray Trace through Translucent Concrete N Markov chain Occupancy Profile Monday occupancy profile between 8am and 6pm
- 28. 28 Algorithm for Energy Calculations Start Ray Trace through Translucent Concrete N Markov chain Occupancy ProfileLight Switch-on at arrival Light Switching Events
- 29. 29 Algorithm for Energy Calculations Start Ray Trace through Translucent Concrete N Markov chain Occupancy ProfileLight Switch-on at arrival Light off; Energy saved Light on; Energy spent
- 30. 30 Results • For fiber density of 5.59%, lighting energy saved is about 50% compared to constant use of T8-tubes. • The energy saved increases to 65% for a fiber density of 10.6%.
- 31. 31 Results • For fiber density of 5.59%, lighting energy saved is about 50% compared to constant use of T8-tubes. • The energy saved increases to 65% for a fiber density of 10.6%. Energy savings with fiber density Gradual slopeSteep slope
- 32. 32 Results • For a fiber density of 5.59%, the lighting energy saved is about 50%. • The energy saved increases to 65% for a fiber density of 10.6%. 1) Occupancy schedules for NREL, DOE-2 gives lower energy savings 2) Does not account properly for occupancy during weekends.
- 34. 34 Composition of wall Model a room Different layers of the wall, R-value of opaque wall = 16
- 35. 35 Representative Vol. Elem. (RVE) • Thermal behavior of opaque walls is easy and can be solved as a 1D problem. • Thermal behavior of TC panel requires a 3D algorithm as the fibers passes through all layers. • But 3D simulations are slow…divide the TC panel into repeating blocks or RVE. TC panel Front view Repeating block or RVE
- 36. 36 Heat Contribution • Three sources of heat are considered in the room: – Heat Conduction through walls – Solar radiation through optical fibers – Heat dissipation by Fluorescent tubes
- 37. 37 Radiation and Lighting loads • Radiation loads depends on the fiber density ratio of the TC panels. • Lower density of fibers is bad and so is higher density. Optimal density required. • When solar radiation contribution is large, less artificial lighting is needed. Radiation and heat dissipation loads for TC panels with 1.4% fiber density ratio. Heatenergy(kWh)
- 38. 38 Loads on HVAC 1) Heat added into room by conduction was small. 2) Cooling loads were majorly from solar radiation. 3) Heating loads due to conduction were substantial. 4) Heat dissipation from artificial lighting decreased as the fiber density increased. Parameters for simulation: R-value of wall = 16; R-value of fibers = 5.7; Dissipation factor for tubes = 0.77; HVAC operation time: 8am-6pm Inside Temp. = 22°C
- 39. 39 Heating loads %age of heat removed at beginning of the day 1) Heat removal due to conduction was large. 2) Most of the heat from room was removed during start of HVAC operation schedule (8 am-6 pm). 3) The initial temperature at start of simulations (i.e. 8 am) were set to temperature at 7 am 4) Temperature at 7 am << 22°C
- 40. 40 Results: Net savings Parameters: Heater COP: 3.5; Air-conditioner COP: 4.0 Utilities prices for SF Bay Area Electricity: 23.3 ¢/kWh; Natural gas: 5.4 ¢/kWh 1) Combining the loads on HVAC with lighting requirements. 2) A fiber density ratio of 5.6% performs best in saving about 26% costs [Ahuja152] . 3) Small fiber density makes TC fabrication process easier. 4) High fiber density leads to monetary loss as solar radiation loads are high.
- 41. 41 Results: Net savings 1) Lighweight composites used as building material. 2) Uses cenospheres which are hollow glass spheres and are produced as byproducts of coal combustion. 3) Cenospheres also enhance the thermal conductivity. 4) Expenditure reduces by 4% for fiber density of 5.6%. Parameters for TC w/cenospheres: Thermal conductivity: 0.4 W/mK Density: 1303 kg/m3 Specific heat: 788 J/kgK
- 42. 42 Conclusions • Developed algorithms to analyze the thermal and optical behavior of translucent concrete. • Translucent concrete shows promising results in saving energy. • A fiber density of 5% can save ~50% on lighting energy. • A fiber density of 5% can save ~24% total energy. • Interfacing the algorithms with EnergyPlus to model complex situations.
- 43. 43 Future Work
- 44. 44 Tilted Panels Avg. sunlight influx for whole year A TC wall with a tilt of 30° with horizontal transmitted maximum sunlight.
- 45. 45 Capturing more daylight Modifying fiber shape Using sun-tracking beams
- 46. 46 Coating optical fibers 1) Potential in reducing energy usage by coating fibers to eliminate UV and infrared transmission. 2) Cuts down on solar radiation and increases savings to almost 40%.
- 47. 47 References • [Ahuja14] Ahuja, A., Mosalam, K.M., and Zohdi, T.I. (2014). "Computational Modeling of Translucent Concrete Panels." Journal of Architectural Engineering. • [Ahuja151] Ahuja, A., Mosalam, K.M, and Zohdi, T.I. (2015). "An Illumination Model For Translucent Concrete Using RADIANCE", 14th International Conference of the International Building Performance Simulation Association (IBPSA). (accepted) • [Ahuja2] Ahuja, A., Casquero-Modrego, N. and Mosalam, K.M. “Evaluation of Translucent Concrete using ETTV-based approach”, International Conference on Building Energy Efficiency and Sustainable Technologies (ICBEST), 31st Aug – 1st Sep 2015, Singapore • [Ahuja152] Ahuja, A., Zohdi, T.I., and Mosalam, K.M. "Heat transmission in innovative façades". (Manuscript in preparation) • [Mosalam13] Mosalam, K., Casquero-Modrego, N., Armengou, J., Ahuja, A., Zohdi, T., and Huang, B. (2013). "Anidolic Day-Light Concentrator in Structural Building Envelope." In "First Annual International Conference on Architecture and Civil Engineering (ACE 2013)," Singapore.
- 48. 48 References • [Witkowski08] Witkowski, J. S., and Grobelny, A. (2008). "Ray tracing method in a 3D analysis of fiber-optic elements." Optica Applicata, 38(2), 281-294. • [Perez87] Perez, R. , Seals, R., Ineichen, P., Stewart, R., and Menicucci, D. (1987). "A new simplified version of the Perez diffuse irradiance model for tilted surfaces." Sol. Energy , 39 (3), 221-231. • [Hunt79] Hunt, D. (1979). "The Use of Artificial Lighting in Relation to Daylight Levels and Occupancy." Building and Environment, 14(1), 21-33. • [Page08] Page, J., Robinson, D., Morel, N., and Scartezzini, J. L. (2008). ”A generalised stochastic model for the simulation of occupant presence." Energy and buildings, 40(2), 83-98.
Editor's Notes
- Introduce the title
- The project was started as a collaboration between Berkeley and Singapore to research on buildings. Trying to find the cooperative interaction between the grid, buildings and occupants inside the building. The final outcomes should be able to optimize the energy consumption, increase productivity of people, lower emissions, improve comfort and extend the building lifecycle. Design algorithms to analyze new building materials using simulations so that the behavior of these new materials can be quantified. This would ensure that lesser number of iterations are required to get the final product
- The first thrust models and forecasts energy consumption in the indoor environment by deploying sensing technologies and performing data analysis. In the second thrust optimization of resources using modeling and controlling of air conditioning systems is undertaken. The third thrust plans to develop an intelligent system for consumption of energy and generation within the building. The fourth thrust is interested in maintaining an improved indoor environment quality for high productivity. I work in the fifth thrust and as a team, we look at development of new building materials that are energy efficient and sustainable. The last thrust provides a common platform for testing and understanding the interplay between ideas across thrusts.
- Building sector utilizes almost 41% of total energy in US and specifically the commercial sector share is 19% In terms of energy utilization in commercial buildings, lighting, heating and air conditioning combined contribute to over 50% of total energy consumption.
- It will really beneficial if we could substitute use of artificial lighting with natural daylight. Not just from the perspective of saving energy but also daylight provides health benefits to the occupants.
- My team mates and I came up with the idea of developing a façade material that can transmit light and optical fibers is one solution that can channel light through them. So we started researching on it and we called this as Translucent concrete, for obvious reasons.
- The translucent concrete is an element that has structural integrity to support a building. The fibers in concrete can channel diffused daylight into the room, so glare is avoided. Unlike windows, the amount and distribution of sunlight in the room can be controlled by varying the geometrical properties like density of fibers, pattern of fibers, etc. The TC panels are developed to be modular to be coupled to other passive and active daylighting systems which is part of the future extension to this work.
- We had to go through a completely new procedure to produce the panels. And I remember clearly, it was very tedious too. So we prepared an acrylic formwork which had two faces that was predrilled with holes to accommodate optical fibers. Next we greased the formwork and roughened the fibers with sand paper to ensure good bonding between fibers and concrete
- Then the fibers were inserted and clamped on both ends to restrict their movement. The concrete was placed into the formwork and allowed to cure. Finally after the concrete hardened, the formwork was removed and the blocks were cut into several panels.
- And you can see me holding the TC panel against sun as it emits diffused light.
- I developed algorithms to tackle the issues related to optical analysis and thermal analysis. Both these methods are aimed to find the TC panel design that will be optimal in saving energy costs.
- The first analysis was conducted on the optical behavior of TC panels I used ray tracing to track the behavior of light as it passes through different media including fibers Since the trajectory of rays was continuous, it was expressesd as a differential equation. This equation comes from the general second order wave eqaution.
- Each individual ray follows Eikonal equation To track the ray numerically, the equation is discretized spatially. The algorithm was then coded in fortran and python, to march the rays forward in time and space.
- The light interact with TC components namely optical fibers and concrete mix. The rays interact with three media, namely air, core and cladding as they travel through the optical fibers in Translucent concrete. At the boundary of each separating media, ray is split into a reflected and refracted ray and the energy split is given by Fresnel’s laws. Inside the light travels using total internal reflection that depends on the angle subtended by ray with the interface between core and cladding. Apart from losses due to reflection on the top surface and during total internal reflection, light is also lost due to scattering of light inside the fiber, the absorption of light energy by the fiber material and due to roughness of the fiber surface.
- Light interaction with the concrete leads to reflection of a fraction of light energy while the rest is absorbed. The absorbed light appears as heat which leads to heating of TC panels and will form a part of thermal analysis.
- The next step is to associate the amount of radiation with these rays. The sunlight distribution model proposed by Perez divides the solar radiation incident on earth into Direct radiation, uniformly distributed isotrpic radiation and anisotropic radiation. The last two components together collectively form diffused radiation.
- By knowing the contribution of direct radiation to the total solar radiation incident on surface, we can divide the skies in Berkeley for the year into 8 different kinds given by 8 epsilons. From the \epsilon number, what is the contribution of isotropic and anisotropic to the final diffused radiation. The overcast skies have the lowest solar flux and are almost independent to the position of sun in sky On the other hand, clear skies as given by \epsilon = 6 and 7 show strong dependence with the altitude of sun in sky. Berkeley very rarely experiences \epsilon = 8 which is shown only by 1 point
- The light that is transmitted through the TC panel and which is entering into the room is calculated using ray tracing algorithm The results file containing light transmission values is stored in a database.
- 1) To see the benefits of using TC, a room is modeled in Radiance for Berkeley with the south wall composed of TC panels.
- In the room, the optical fibers are modeled as point luminaires The optical fibers disperse light in an anisotropic way as given in the figure. It can be seen that maximum light is directed at an incidence angle of 13 degress with respect to normal We load this information while declaring optical fiber as a luminaire Using Radiance, we can calculate what is the light that is received by a point in the room for certain sunlight flux being transmitted by the fibers.
- Energy calculations are performed to quantify the benefit of daylight distributed in the room by optical fibers in TC panels. The occupant behavior decides whether they will switch off the light in case there is enough illumination on the workspace. By recording the time duration when the light is switched off can give an estimate of how much energy can be saved annually The algorithm to do this can be clearly defined by the following flowchart.
- 1) Go back to ray tracing through the TC panels to find the light transmitted
- Define a room in Radiance with a wall composed of TC panels Define three positions, identified as A, B and C here, which will be occupied by people and calculate illuminance at these points
- We should find out at what times during the year is the occupant present. To do this I collect occupancy data for three people, 2 students 1 lab staff member for three months. From this data, I can generate their average occupancy profile for each day of week and how mobile they are in their lab. The Markov chain method introduces randomness to the average occupancy profiles which follows the randomness of the occupant’s behavior and can generate a random presence profile for each occupant during the entire year.
- The occupant may switch on or switch off the light, in case it was on before, depending on the illumination on his workspace. A lot of work has been done in the past to calculate this, and previous researchers have been able to develop probability curves for the light switching events
- So if the light is switched on, then it can be recorded by the computer that the energy was not saved during that time instant And it will run this algorithm again to see if the occupant will turn off the light in the next time instant. For all the instants the occupant turn off their lights, the computer records savings in energy and that gives me an estimate of how much electrical energy can be saved in the entire year.
- It is observed that with a fiber density of about 5%, there is a potential to save about 50% of lighting energy consumed by occupants. Well, if I increase the density to 10%, the energy increases by 15% so the relation is not linearly proportional.
- 1) In fact the rate of savings is steep up to a fiber density of 7.5% and then becomes more gradual for the rest of the fiber density ratios.
- 1) A Thesis committee member asked to calculate the energy savings using NREL, DOE-2 occupancy profile. In both cases, energy savings was a litlle lower since they are based on schedules observed in offices and not labs. In university labs, people also tend to work during weekends which causes the gap.
- The walls of a building experiences convection of heat due to outside wind and the movement of air inside the room. Solar radiation is incident on the concrete surface while in case of TC panels, some of the solar radiation is transmitted by the optical fibers, Also during hot weather, heat is conducted from outside to inside while in cold weather, the heat conduction direction is reverse.
- To conduct thermal analysis, I model a room which has 1 south facing wall made up of TC panels and the remaining 3 walls are opaque. Each wall is multilayered and consists of a layer of concrete, insulation XPS and dry wall. The fibers run through the length of the wall for a TC panel.
- The heat transfer by opaque walls can be easily solved as a 1D problem with different material properties representing different layers. But in a TC panel, the materials properties of each layer also differs as optical fibers passes through the layer This leads to solving 3D models but since their simulation is slow, we have to divide the TC panel into repeating blocks or rep. vol. elem. The simulations are performed for RVE and the results are then used for the entire TC panel.
- Three sources of heat contribute to thermal exchange in room First is the heat conduction through different layers of walls in the room. The algorithm for this problem was again developed in Fortran and Python Second source is the solar radiation transfer through the fibers which was calculated using ray tracing Last is the heat dissipated by fluorescent or T8 tubes which will depend on illuminance of workspace and occupant behavior during light switching action. So it’s was treated as a random event.
- Solar radiation loads depends on the fiber density ratio of the TC panels. Lower density of fibers brings in less light but also decreases cooling loads. Higher density reduces lighting usage but also increases heat input which affects the cooling loads. So we should search for an optimal density to maintain a balance in heat input From the figure, when solar radiation input is higher, less artificial lighting is required in the day to illuminate the space. On weekends, instead the majority heat is always due to solar radiation because of low occupancy.
- Combining the contribution from all the sources, it was observed that the cooling loads due to conduction were small. Cooling loads were majorly generated from solar radiation and increased with the fiber ratio. This trend was similar to what is obserevd for windows The biggest surprise was from the heating loads which was large for a room inspite of high R-value. The heat removed due to conduction increased with the fiber density which showed that greater optical fiber density allowed more heat to escape through the fibers which offers lower resistance More dependence on optical fibers reduces the use of artificial lighting which is also reflected in the figure.
- Now I would like to talk about why the value of heating loads was substantial. Most of the heat is added by the HVAC during its start of operations for the day which was set as 8am to 6pm The initial temperature of the wall interior at the start of simulations was set to be the temperature at 7am And this intial temperature was always about 10-15 degrees lower than the indoor air temperature, which caused a lot of heat to be removed. As the day progressed, the heat removal became smaller and sometimes during day it let to heat addition as well.
- To look at the utility of TC panel, it is necessary to quantify its benefits in terms of cost offsets or reduction in bills. So by combining the heating and cooling load requirements of HVAC with the benefits that are achieved due to reduction in lighting requirements, it was observed that a TC panel with about 5.6% reduces about 25% of expenditure in bills. This also consistent with the construction procedure, which as shown before, was tricky and required a lot of manual interventions. Having high fibers as shown in figure is a bad choice since it also raises bill expenditures among other problems like structural stress concentration, material costs, etc.
- Also been experimenting with light weight concrete composites for buildings They primarily reduce the dead weight of building, while maintaining structural integrity and also use byproducts from powerplants called cenospheres, thereby reducing material usage. The cenospheres are hollow structure and their addition increases the resistivity of the concrete composite. So using this new mix, it was found that there can be further reduction in bills by about 4%.
- One of the analysis considered was also to find out the maximum light that can be transmitted. Among multiple tilt angles, TC panels that subtend an angle of 30 degrees with the horizontal transmit the maximum amount of light.
- So as future work, my team has started exploring possibility of coupling TC panels with other daylighting systems. The normal fibers only allow very limited amount of light (movie 1) So improvements are made to the design by modifying the top and bottom (movie2). The light is more uniformly distributed and more light is transmitted. Sun tracking beams which can follow the light source and capture maximum number of rays. Whole new range of problems like fatigue, cost effectiveness, type of material
- There is also a potential in saving a lot of energy by coating the tips of fibers This will reduce the transmission of non-visible wavelength UV and infrared and reduce the cooling loads of room. From a simple simulation, it was observed that the savings in expenditure could be as high as 40% Thus it seems that are implementing some or all of these technologies, we can improve the functioning of the TC panels and move couple of steps closer to developing a sustainable building material.