About the Solar Decathlon

Transcription

1 About the Solar Decathlon Photos of 2007 solar decathlon winning entry from Technische Universitat Darmstadt in Germany. The Solar Decathlon is a competition in which 20 teams of college and university students compete to design, build, and operate the most attractive, effective, and energy-efficient, solar-powered house. The Solar Decathlon is also an event to which the public is invited to observe the powerful combination of solar energy, energy efficiency, and the best in home design. Teams of college students design a solar house, knowing from the outset that it must be powered entirely by the sun. In a quest to stretch every last watt of electricity that's generated by the solar panels on their roofs, the students absorb the lesson that energy is a precious commodity. They strive to innovate, using high-tech materials and design elements in ingenious ways. Along the way, the students learn how to raise funds and communicate about team activities. They collect supplies and talk to contractors. They build their solar houses, learning as they go. The 20 teams transport their solar houses to the competition site on the National Mall and virtually rebuild them in the solar village. Teams assemble their houses, and then the active phase of the Solar Decathlon begins with an opening ceremony for students, media, and invited guests. The teams compete in contests, and even though this part of the Solar Decathlon gets the most attention, the students really win the competition through the many months of fund raising, planning, designing, analyzing, redesigning, and finally building and improving their homes. The public is invited to tour the solar homes and event exhibits during much of the competition.

2 UC Boulder identifies the above condition as the urban desert. Architectural Concept The Solar Decathlon competition challenges each team to design, build, and operate their small, solar-powered home on the National Mall in Washington, D.C. Yet, the event is not really about college kids building houses on the Mall. Rather, the Solar Decathlon seeks to provide real-world training for the next generation of engineers and architects, to promote the development of innovative solutions for sustainable building design, to transfer these solutions to a diverse building industry, and to educate the public about the energy solutions available in today's market. However, some of the constraints of the Solar Decathlon competition pose a challenge for meeting these underlying objectives. Specifically, competition rules and practical logistics dictate that these homes are small, lightweight, easy to transport, all-electric, off-grid, and completely covered with solar energy systems. Few of these competition artifacts dominate the real world. While competition rules limit the floor area to about 700 ft 2 (70 m 2 ), very few of us live in such small houses - the average new home in the US has a floor area of about 2100 ft 2. While it might be easier to design, build, and transport a 700 ft 2 home for the competition, how do you make the design relevant to students, homeowners, the building industry, and the public? How do you rationalize a 7 kw photovoltaic system on a 700 ft 2 home? How much bigger would the system have to be if it were in my house? How do you explain a construction cost of over $300 per square foot? How do you design appropriate thermal mass for effective passive solar heating while minimizing transportation weight? How do you develop solutions for the two million new housing units built every year by focusing on mobile homes? from

3 Three dimensional model and constructed entry on the national mall in Washington, D.C. Architectural Concept The University of Colorado design seeks to address these questions to provide real-world solutions for the real energy challenges we all face while honoring the constraints of the Solar Decathlon competition. Although the competition limits each team s home size to about 700 ft 2, the Colorado team took a bold approach by building a 2100 ft 2 full-size home and delivering a smaller competition module to Washington, D.C. The competition module or more simply the module represented the full house in the Solar Decathlon events. The module conforms to the constraints of the competition and included only the kitchen, part of the living room, guest bedroom, bathroom, and an integrated hallway and mechanical room. The full-size house or more simply the house has 2100 ft 2 of floor area, and includes three bedrooms, three bathrooms, a larger living room and a small family/ office area. All building systems, including mechanical, electrical, and solar energy systems, are designed and sized for the house, rather than the module. All heating, cooling, and indoor air quality control systems were sized for the full house, yet allowed modularity for the competition module. The PV system used for the competition provided the full house with an appropriately-sized array to make it a net zero energy home. from

4 CORE Concept Drawings of first floor plan with programmatic CORE highlighted on right. The is based on a prefabricated and customizable central core that includes kitchen, bath and mechanical equipment. In fact, there is no piping, ductwork, plumbing, or other mechanical equipment outside the core. The uses the shipping container spine to modulate the spatial experience of the home. The containers central position allows them to function as transition zones between the public and private areas of the home. The leverages the efficiencies of factory-built, modular construction for those parts of a dwelling that best lend themselves to industrial prefabrication and the economies of scale. Yet, it allows a limitless number of user options in customizing the core components and encourages individual, sustainable, home plans and construction techniques outside the core. In addition, the sophisticated mechanical, electrical, and plumbing systems are fully fabricated, installed, and calibrated in a factory environment, are protected during transport by the container, and require no additional on-site construction or adjustment. The CORE strategy encourages freedom of aesthetics, construction methods, and material selection. In a production home environment, modular construction can be employed without every house looking the same. The system also allows users to create connection and response to local conditions. By combining a prefabricated core and high performance energy technologies with vernacular architecture and local materials and methods, housing can be created with better local economic regeneration, lower material costs, and less overall embodied energy. Countless other variations are possible. The core s flexible, transportable, and modular nature allows it to be used in diverse applications, from off-grid vacation cabins to high-density in-fill housing. Cores can be stacked in multi-story designs. They can be combined with local materials and methods. Over time, the footprint size can change as the lifestyle of the owner evolves, adding rooms for a larger family or removing rooms as the nest empties. from

5 Clockwise from left: longitudinal section, cross section through clerestory, west kitchen elevation drawing, east kitchen elevation drawing, cross section through mechanical + storage attic.

6 Engineering a New Paradigm The University of Colorado house design is based on a modular and prefabricated engineering spine. The spine, formed by conventional shipping containers, provides structure and life support. Programmatically, it comprises the kitchen, laundry, bathrooms, and equipment spaces, and includes the building electrical service and all plumbing and HVAC systems. In their specific design, there are two shipping containers the competition module including a container for the kitchen, bathroom, and systems area, while the second container houses the laundry, master bathroom, and guest bathroom. The engineering spine offers the opportunity for modular mass production. UC Boulder chose to use surplus shipping containers, although conventional construction methods could also be used. In any case, the spine elements include standard configurations of high-value kitchen and bath spaces while allowing a selection of custom cabinetry and fixtures by the owner. Prefabricated, wired, and plumbed, these containers can be shipped directly to the construction site where they are connected to the home s electrical service, water main, and sewer. from Top left: north elevation of module with CORE illustrated in yellow. Bottom left: south elevation of module with CORE illustrated in yellow.

7 Engineering a New Paradigm While conventional homes typically have HVAC registers or baseboard heaters along the outside walls, a wellinsulated house with high-performance windows does not require heating and cooling at the perimeter. By centralizing the HVAC system within the spine, heating and cooling loads can be met with smaller pressure losses, less air leakage, and lower material costs. By locating all equipment in the spine, the system can be prefabricated, minimizing or eliminating the need for mechanical contractors at the construction site. While the University of Colorado design takes advantage of modularity and factory methods for the high-value portions of the building, their design does not seek to prefabricate the entire house. Rather, their approach provides architectural flexibility in the design of the building exterior shape and envelope system, avoiding the cookie-cutter sameness of conventional modular housing. In UC Boulder s design, the walls and roof of the house can take any form and use any appropriate construction material. With proper engineering, it is also possible for the spine to be used for structural support. from Top left: east elevation of module with CORE illustrated in yellow. Bottom left: west elevation of module with CORE illustrated in yellow.

8 Building Integrated Photovoltaic/Thermal System While there is ample evidence that zero energy homes can be built today with off-the-shelf technologies, not all necessary technologies are economically competitive. In particular, additional development is required to improve the competitiveness of PV technology. One opportunity for reduced PV cost is better integration within the building envelope, specifically, the roof. Most current systems are installed over the roof, with additional cost for the PV support system and framing. Integration would eliminate redundant construction elements and improve overall cost effectiveness. Working with industry manufacturers, our design showcases a prototypical BIPV system in which the PV system is the weatherproof membrane of the roof. The European system, manufactured by Ernst Schweizer Company, allows full-size PV modules from a variety of manufacturers to be coated and mounted without additional shingles underneath. In our case, we are using 8.8 kw of SunPower modules with one of the highest efficiencies on the market. The system provides a single, uniform, weather-proof plane for the competition module roof. This same system will also produce more energy over a year than is required by the full house, thus making it a zero-energy home. The PV roof will be further integrated with the building mechanical system with a network of water tubing, manufactured by Thermo Dynamics Ltd., between the PV modules and the roof insulation. The water flowing behind the PV modules will cool the PV modules, increasing PV efficiency and providing hot water for the house when needed. The roof will also be used as a sky radiator in the summer, cooling water at night for use in air conditioning Axonometric of competition module showing PV/T cells on roof. during the day.

9 High Performance Envelope Systems Smart Glass High performance windows can substantially reduce heat from the sun and greatly increase window insulation. External radiated heat is reflected. Direct heat from the sun is reduced. Internal radiated heat is reflected. UC Boulder design uses Heat Mirror - low-emissivity, coated films suspended inside an insulating glass unit - to achieve exceptional thermal and optical properties. The airspaces created by the suspended the film, filled with a noble gas, further increase the window s thermal performance. The glazings have a thermal resistance of R-12.5, a solar heat gain coefficient of 0.4, and a visible transmittance of High resistance fiberglass frames complete the package. Passive Solar With appropriately selected glazing and dimensionally correct shade devices and louvers, passive solar design techniques are applied to both the south and north wings of the full house. In the summer, the awning and shades are designed to block direct exposure to the living room and sunspace. The sunspace is ventilated or opened up to the courtyard. In the winter, full solar gains help heat the mass within the home during the day and reduce heating loads through the night. Building Integrated Overhangs Passive design strategies seek to design overhangs or louvers that admit solar energy in the winter and shade the solar energy in the summer. By placing the window pane inboard of the custom jamb-sill assembly, the window header acts as the shade, without the use of an overhang or awning. The optimal depth is dictated by the location latitude. Architecturally Integrated Louvers Tall windows require greater depth of overhang to shade the windows in summer months. Site specific angles designed into artful, exterior louver retain visibility from the interior and block the summer sun from the entire vertical height of the wall

10 Materials Location Marine plywood MDF Gypsum board Bamboo Linoleum Paper composite HDPE HDPE Porcelain tile Carpet Paint VOC sealer Watersealer Backer board Shipping container flooring + subflooring Cabinetry All interior wall + ceiling surfaces Kitchen + bathroom cabinetry Living room + bedroom flooring (snap in place) Kitchen + bathroom counter surfaces Kitchen backsplash + mechanical closet door Bathroom door + shower door Bathroom + entry floor surfaces Living room + bedroom floor surfaces (snap in place) All interior surfaces Shipping container flooring + subflooring Bathroom floor surface bathroom Interior photo of the competition module bedroom during public tour. Manufacturer photos of some of the interior materials.

11 Appliances In keeping with the Solar Decathlon requirements of zero-energy design, the appliances incorporated in the University of Colorado design are highly energy efficient. Unlike some of the other entries prefabricated kitchen modules, the UC Boulder scheme uses an assembly of off the shelf products from many of the nation s leading appliance manufacturers. Selections were made based on energy efficiency, space efficiency, and cost. The combination of appliances functioned successfully in accordance with the overall competition parameters. Clockwise from top left: refrigerator dimensions, Trivection oven installation, Trivection oven control panel, combination washer/dryer, burnproof stovetop, and under counter dishwasher dimensions.

12 Left: interior rendering of space above the bedroom as it might appear on a late summer afternoon. Right: lighted rendering of kitchen with ambient and task lighting. Lighting analysis Initially, the lighting scheme (i.e. indirect, direct, and/or semi-direct lighting) was decided for each room of the house. Preliminary lighting analyses for each space were conducted using a Lumen Method spreadsheet, in order to determine an approximate number of required lumens, based upon the type of lighting. Next, appropriate light fixtures were selected to achieve the desired illuminance values. After each option of lighting type and placement was developed, AGI 32 was used to determine illuminance levels provided by the lighting fixtures at specific points within the 3D model of the house. Several different iterations were then run to help determine the correct quantity and placement of fixtures to meet the foot-candle requirements of the competition and to achieve desired aesthetics for the particular spaces. Additionally, daylighting calculations were performed with AGI32 as well. Key locations within the space were monitored at different times of day and times of year, to minimize glare problems and ensure adequate daylight delivery during important hours of the day. from

13 Chart showing different fixtures and their uses included in the competition module.

14 Comfort Zone The Solar Decathlon teams design their houses to remain a steady, uniform, comfortable temperature and humidity throughout. Full points for this contest are awarded for maintaining narrow temperature (72 F/22.2 C - 76 F/24.4 C) and relative humidity (40% - 55%) ranges inside the houses. from High Efficiency Water to Water Heat Pump Left: diagrammatic drawing showing operation of water to water heat pump unit used in competition entry. Right: graph of heat pump performance. Using the EnergyPlus whole house energy model, the water to water heat pump was sized based on the peak heating and cooling loads. A water to water heat pump was chosen because it is compatible with the system with two thermal storage tanks and is inherently more efficient than air to air or air to water systems. In addition, it is possible to use refrigerant R410A instead of R22 with this system, which has zero ozone depleting potential and will lessen the house s environmental impact. from

15 Architecturally Integrated Heat Exchangers The design of low energy building HVAC systems requires a balance between energy efficiency methods and providing a suitable indoor environment for occupants. The University of Colorado house uses architecturally integrated (hybrid forced air / radiant) heat exchangers to condition the space. The heat exchangers consist of 2m tall bundles of copper pipes in a 2-row staggered arrangement. Values for approximate heat transfer characteristics were determined analytically based on calculations for tube bundles. The heat exchangers utilize heating hot water and chilled water from a heat pump/thermal storage system to supply heating and cooling to the space. The system utilizes both the radiant effect of the heat exchangers, forced convection, and buoyancy driven flow along the tubes for heat transfer. Computational fluid dynamics (CFD) analysis was used to predict the comfort parameters for determining the predicted mean vote (PMV), mean age of air, and draught in the room. from Top: diagram of free-convection driven airflow during cooling mode. Bottom: temperatures for natural convection (top), forced convection (second to top), heat recovery (third from top), and contour of absorber plate (bottom).

16 Case 1: BABM Benchmark house simulation results show a maximum energy use in January of 8,382MJ, a minimum of 4,017MJ in September and annual energy use of 70,632MJ. High energy use in winter months can be attributed to the heating dominated climate of Denver, CO and the relative inefficiency of an air-to-air heat-pump with low source-side temperatures. Note that cooling energy is required in June per the modification to the benchmark assumption discussed previously. Also note that water heating loads vary as expected due to the variation in mains temperature throughout the seasons. Chart showing the average energy consumption per year for a residence in Denver, CO.

17 Case 2 : Denver, CO The prototype results show the drastic impact of energy efficiency measures and site generation on overall energy use and annual energy balance. Peak loads still appear in the winter months, but the curve is flattened with additional peaks occurring in the summer cooling season. Peak electricity use occurs in January at 2,814MJ nearly 34% the peak load of the benchmark. October is the month with the lowest electricity use at 2,087MJ. Annual energy use is 28,985MJ, or 41% of the benchmark energy usage. Note the relatively low heating and cooling energy required for space conditioning, due to the higher efficiency of the water-to-water heatpump and coupled thermal storage. Note also the decrease in lighting loads as function of an increased percentage of fluorescent lighting. Left: monthly energy consumption for prototype in Denver, CO. Right: total solar energy production and outdoor heat exchanger energy capture for Denver, CO.

18 Case 3 : Phoenix, AZ Results from the Phoenix simulation can be seen in the figure below. Total energy peaks during summer months as expected due to the cooling dominated climate; heat-pump cooling energy is approximately 2.4 times that of Denver. Energy requirements in July total 5,234MJ and total 37,531MJ annually. Net electricity production reaches 44,417MJ annually, resulting in net electricity production Chart showing the monthly energy consumption/production for the prototype in Phoenix, AZ.

19 Case 4 : Sterling, VA The energy use profile for the prototype house in Virginia shows similar trends when compared to Denver. Both locations show nearly equal heating and cooling peaks with the lowest energy use occurring during the swing seasons. Peak electricity use occurs in July at 3,774MJ, while October is the month with the lowest electricity use at 2,044MJ. Annual energy use for Sterling is 33,269MJ and total electrical production is 33,857MJ. The same house in Virginia is still a net energy producer albeit at a much smaller margin than either Denver or Phoenix. This can be attributed to the relatively high HVAC and pump energy use and lower overall electricity production from PV due to a higher incidence of cloud cover. Chart showing monthly total energy use for the prototype in Sterling, VA.

20 Conclusions The CU prototype home shows significant energy savings when compared to the Building America Benchmark home. Energy efficiency measures implemented in the prototype home result in a reduction in electricity use by 59% over the benchmark. The PV/T system is more than capable of providing enough electrical and thermal energy to satisfy all energy requirements, resulting in a home that is a net energy producer in all three test climates. Optimization of system controls will likely have a significant impact on total energy use as indicated by the adverse effects of an increased setpoint temperature. The modest impact of the PV/T system over a standard BIPV installation on total energy use must be considered as an alternative to additional PV, but must be carefully evaluated for each climate. Chart showing total monthly electricity use for prototype without PV/T system in Denver, CO.

21 Communications The Communications contest challenges teams to communicate about the technical aspects of their homes as well as their experiences to a wide audience through Web sites and public tours. Points are awarded based on success in delivering clear and consistent messages and images that represent the vision, process, and results of each team's project. To judge this contest, a jury of Web site development and public relations experts evaluate the team Web sites and experience student-led tours of each home. The jurors evaluate how informative and engaging the Web site content is, as well as how easy it is to find that information. The sites must also adhere to technical standards. Jurors also evaluate the house tour content and presentation by tour guides. from Top and middle left: images of the UC Boulder winning competition entry from Bottom left: UC Boulder winning entry from Bottom right: a UC Boulder team member leads the Solar Decathlon judges through the team s 2007 competition entry.

22 Pre Fab Meets Mass Customization Transportation of the competition module. The University of Colorado offers a prototype geared for mass production of zero-energy homes that meet the strict demands of a competitive market and offers the same or a better level of comfort as any production home. Code named the REAL (Renewable Energy Accessed at Low-cost) System, it presents a methodology for the mass production and distribution of a mechanical core designed to be the heart of any solar powered home. It also outlines a procedure for mass customization that enables consumers not only to specify appliances and finishes, but to determine entire floor plans and wall constructions appropriate for any geographic location, building site, and living situation. In this study, we sought to first understand the general housing market and key trends within that market. They then sought to define and estimate the size of a consumer segment within the housing market that would be most likely to buy a zero-energy home. Next, they developed a series of key market differentiators that would propel the market viability of the REAL Houses among consumers and industry even during a sluggish home market. These drivers became the team s design goals and acted to shape the REAL House System and the marketable prototype presented on the National Mall. The contest criteria of livability, buildability, and flexibility have been at the heart of the design approach to the UC Boulder prototype from the inception. Their prototype is ultimately the size of an average home, takes advantage of the benefits offered by a modular, prefabricated mechanical core, and allows for customization of the larger envelope. These traits, combined with an array of efficiency components including innovative use of a building integrated PV system and heat exchangers, creates clear benefits outlined in the competition criteria. from

23 Contemporary western American suburb. Pre Fab Meets Mass Customization The U.S. housing market has been in decline since 2005 and the future housing forecast index indicates the national housing market will continue to struggle in the near future. The University of Colorado system however, has been designed to respond to 3 key market trends (shown below) which will allow it to remain competitive throughout the housing market decline. According to their research, the University of Colorado has created an industrial system for production of zeroenergy houses that have a strong likelihood of garnering consumer acceptance in western U.S. housing markets. Market size estimates indicate the potential for over 7.5 million possible customers and REAL Houses are conceived to appeal to buyers, builders, communities, policymakers, and financiers equally. Trend/Need Demand for environmentally friendly housing. Opportunity Response/ Energy efficiency and renewable energy infrastructure. Demand for uniquely suited homes. Rising costs of labor, materials and land. Mass customization. Mass production of modular mechanical core. from