Alison Ledwith

sustainable design

Thermal Mass Performance in Residential Construction: An Energy Analysis Using a Cube Model

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Abstract

Given the pervasiveness of energy efficiency concerns in the built environment, this research aims to answer key questions regarding the performance of thermal mass construction. The work presents the Cube Model, a simplified model of the single-family home. The model combines simplified geometry and equivalent envelope parameters with accurate climate data and internal loading assumptions. The model first addresses the notion as to whether building simplification is a valid means of analysis through a calibration and validation study. Then, the model is used to address three research areas on passive thermal mass: (1) the quantification of thermal mass performance with respect to material thermal properties; (2) the optimization of thermal mass performance for given material parameters; and (3) the sensitivity of thermal mass performance to infiltration and geometry effects. The experiments for wall and slab constructions, to address the first research area, demonstrate that the energy savings from thermal mass are both climate and season dependent. Results provide the magnitude of energy savings in fifty climates across the United States. Optimization experiments on the material thickness and conductivity, to address the second research area, show that constructions do not reach peak thermal mass performance at the same thermal properties in all climates. Sensitivity analyses, to address the third research area, indicate that passive thermal mass and tight construction practices can be mutually optimized without a trade-off of energy performance. Geometry effects demonstrate that modifications in building design can either benefit or hinder the performance of passive thermal mass. The combination of the results suggests that optimum design for thermal mass performance and the resulting energy consumption are climate-dependent and sensitive to many factors aside from material thermal properties.

Documentation

The thesis is available for download in full through DSpace at MIT. A summary report is available for download through the MIT Concrete Sustainability Hub.

LCRA Environmental Learning Center, Matagorda Nature Park, Matagorda, TX

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The Lower Colorado River Authority maintains a series of nature centers, including a small center in Matagorda, TX. A second, larger building is desired in the area to include conference space, exhibits, and offices for the nearby region. This 12,000 square foot nature center can function either as an enclosed center or as an open pavilion. Since the river is a fundamental portion of the mission, this building has been sited half upon land and half in water. The lower level includes decks, docks, and expendable program elements to accommodate the fifteen foot storm surge in the area. The upper level features the main spaces. All of these components are beneath a curved photovoltaic roof with integral gutters, which provides a substantial percentage of the electricity and rainwater needs of the building.

Program Description

One can explore the docks on the lower level or proceed upstairs to the exhibit and conference spaces. The longest bar, spanning both over land and water, is the main exhibit space of the building. To accomodate the flexible needs of the center, sliding walls form both the exterior perimeter and interior subspaces for classroom needs. The bar along the entry includes the conference space and support facilities, while the terminal angled bar houses an observation deck for bird watching. This center is part of a larger development plan including the parking area and a nature trail for incorporating exhibits within the lagoons.

Form and Structure

The building uses a 20’x20′ modular grid in all bars of the program. The three programmatic bars form an outdoor courtyard space, which can also be used for conference proceedings. Roof level on the second floor is dictated by program and creates an overall umbrella-like canopy over the space. Construction details of this system continue the umbrella metaphor in creating a structural grid with separate components resisting gravity and uplift. The roof bends into two cores used to house rainwater collection and native aquatic life; in addition to their programmatic purpose, these cores are reinforced for shear to guard against hurricane force winds. The remaining structural elements of the building include a glulam frame and concrete pile foundation, whose continuous load path is indicated in the large-scale construction details.

 Environmental Learning Center

The architecture of the building seeks not just to house conferences on environmental learning but to use the building itself as an instructional tool. To that end, all services are integrated and exposed, such as the use of the roof to channel rainwater into collection tanks. Walls in the building completely open up for natural ventilation, allowing the conditioning to occur without the use of electricity during the better weather seasons in the region. Integrated cool beams provide additional climate control when natural efforts are insufficient. Photovoltaic panels, LED lighting, and the use of stable ground and water temperatures in system design minimize the energy use of the building.

Documentation

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Oasis@6th Mixed Use Development, 6th and Colorado, Austin, TX

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Oasis@6th is a proposed mixed use development located in the heart of downtown Austin. An iconic midcentury modern building, used originally as a banking headquarters and now known as the Starr Building, forms the core of the project. An urban wellness center develops through a collaborative venture between the academic concentrations of historic preservation (Reed), interior design (Bodet), and architecture (myself).

A Mixed Use Development

Character defining features such as the 10′ x 30′ mural in the main banking space are preserved in the Starr Building while other spaces are adaptively reused. Adjacent sites to the east and south are included in the complex; an 8-story office and retail structure and a 15-story boutique hotel and modernized parking facility are proposed in their place. Finally, a two-story amenity deck is included in the footprint of the original mid-century pilotis-supported awning. The deck serves the office park and hotel with its fitness and spa facilities.

Wellness and Sustainability

Wellness-themed tenants have inspired the many sustainability features of the building. Such features include the green roof on the amenity and office buildings, the natural materials in cladding and interiors, and the new daylighting features in preserved buildings. Light wells in the historic building preserve the original intent of the facades and add daylighting. The hotel lobby engages the Austin street life, while a bamboo cladding system conceals the parking structure above. Light and views are present in the hotel guest and lobby levels. Water flows through channel glass to form the exterior threshold of the lobby, and landscaping completes the urban oasis.

Detailing brings sustainability into the user experience. Rich interior materials, such as the cork flooring in the spa, provide a similar experience of wellness inside the complex. Natural stones and wood provide a similar experience in the hotel rooms. Translucent plastic panels finished in wood veneer allow light into the hotel spaces. The slanted north wall and stepped south wall of the hotel create the angled effect of the tower and interact with the structure, building services, and guest amenities as shown in the detail drawing set.

Documentation

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