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THERMAL PERFORMANCE COMPARISON OF ALTERNATIVE BUILDING ENVELOPE SYSTEMS:
An Analysis of Five Residences in the Community of CIVANO.
Nader V. Chalfoun, Ph.D. and Richard J. Michal P.E.
University of Arizona College of Architecture, Planning, and Landscape Architecture firstname.lastname@example.org and email@example.com
Abstract This paper describes the impact of alternative building material envelope systems on the overall thermal performance of five selected residences in Civano; a residential development in Tucson, Arizona. These systems included adobe, Integra block, strawbale, metal stud framing with rigid insulation (Heydon system) and structurally insulated panels (SIPs). After thorough on-site investigation and data collection by the House Energy Doctor (HED) team, the information, along with regional weather data, were input into the CalPas3 energy simulation software for thermal performance evaluation. While all of the five homes studied outperformed the average for Tucson home heating and cooling energy use and were within compliance with the 1995 Model Energy Code (MEC), three of the homes were found to exceed the energy cost per square foot source consumption guidelines required under the 1997 sustainable energy standards (SES). It was also determined that at least in the cases studied, the performance of each of the alternative building material envelope systems exhibited common design deficiencies while attempting to address issues not necessarily focused on energy conservation and solar technology. These deficiencies, related to orientation, placement of windows, insulation and shading, are also discussed in this paper. Introduction Energy consumption in the United States costs $450 billion each year. The growing awareness of the importance of energy conservation has resulted in savings in the United States of $160 billion annually since 1973 . One of the areas related to energy conservation and of particular interest within the field of architecture is the development of non-traditional or alternative building materials. The purpose of this paper is to demonstrate the thermal performance, as measured by the students and faculty of the House Energy Doctor Program (HED), of five single family residences each utilizing alternative building materials. The five residences chosen for analysis by the HED program each represents a unique alternative building envelope system. Each of these systems is intended to improve the overall thermal performance and therefore reduce energy consumption. The authors assume that this paper will serve as a basis to begin to compare the effectiveness of each of these unique systems and to discuss additional factors that may have affected their performance. The House Energy Doctor The House Energy Doctor is a program at the University of Arizonas College of Architecture that provides education and research experiences for students as well as no cost energy consultation and design prescription services for home owners. The advanced methods taught to students provide them with the necessary skills to conduct residential energy analysis and performance predictions utilizing computer simulation. Among others, the CalPas3 computer energy simulation software was used in this
analysis . The House Energy Doctor residential analysis is performed through a ten step procedure starting from the site survey and ending with conclusions and recommendations for improving energy consumption of buildings .
Figure 1: House Energy Doctor Students conducting site surveys (Photos by Dr. Chalfoun)
Project Description and Background During the spring semester of 2002, students and faculty in the HED program selected CIVANO as the site for investigation of the thermal performance of alternative construction materials. CIVANO is a residential development located in Tucson, Arizona intended in part to showcase passive solar and energy conservation designs in
Figure 2: CIVANO Community, looking north (Photo by Dr. Chalfoun, 2001)
residential housing. While CIVANO was originally envisioned to be the Solar Village, the project was subsequently modified to incorporate Neo-Traditional or New Urbanism design characteristics such as increased landscaping areas, narrower curvilinear streets, wider pedestrian pathways and sidewalks with landscaping buffers and the use of front porches to connect with the streetscapes and pedestrian pathways. It is the authors view that while these added design criteria provided some benefits for the community as a whole, they also may have resulted in some compromises in the thermal performance of some of the homes within the community. The five residences selected for the study, each utilizes a unique alternative building material envelope system. These systems included adobe, Integra block, strawbale, metal stud framing with rigid insulation (Heydon system) and structurally insulated panels (SIPs).
Table 1: Selected Residences Residence Lot# Envelope System Mechanical System 1. Strawbale 4 2-string straw bale 14x18x40 SEER12, HSPF7 Elec. heat pump 2. Adobe 123 14 Adobe + exterior insulation SEER18 AC & radiant floor heat 3. SIPs 46 4 SIPs + 1 foam SEER12 AC & hydroponic heat 4. Heydon 6 Steel Frame w/ rigid insul. SEER12, HSPF 7 Elec.heat pump 5. Integra Blockr 96 8 integra block SEER12 AC & gas furnace Figure 3: Map of Neighborhood 1 of the Community of CIVANO
Strawbale Residence The strawbale residence is a 1386 square foot single story post and beam straw bale home. The home includes two bedrooms, two baths a kitchen and family/living/dining room with concrete floors throughout. The roof system is galvanized corrugated steel on roof trusses with 10 blown-in cellulose insulation. The home has a two car detached garage. The mechanical system is a SEER12 electric heat pump for heating and cooling. Figure 4: Strawbale house
The envelope system incorporates 14x18x40 tied bales of straw infill within a post and timber structural frame to form 18 thick walls with an additional 2 of cement plaster on each side. The effective overall R value of this envelope system is approximately R-16. Figure 5: Detail of Bales Heydon System Residence Figure 6: The Heydon Envelop System
The Heydon System residence is a 1,842 square foot single family dwelling. The home consists of three bedrooms, two bathrooms, a kitchen, a living room and a dining room with 10 foot ceilings throughout. The wall construction is the Heydon System discussed below. The exterior of the home is made up of cement plaster walls and clay tile roofing. The mechanical system is an electric heat pump with SEER12, HSPF 7 efficiency. The Heydon System consists of steel stud framing with 4 rigid polystyrene foam insulation panels incorporated both between and on to the exterior face of the steel framing members. The overall insulating value of this wall system is R-25. Integra Block Residence
Figure 8: The Integra Block Residence The Integra Block house is a 1,680 square foot single family dwelling built with Integra Block. The home is currently detached but is intended to share common walls with future homes on both its east and west elevations. The home is two stories at the south end and slopes down to a single story at the north end forming a large vaulted ceiling sloping down to the north over the family room in the center. The home consists of two bedrooms, two and a half baths, a kitchen, large central family/living/dining room and a study. . The mechanical systems include an 80% efficient 3.5 ton gas furnace and a SEER 12 air conditioning unit. Integra block is a concrete masonry unit system designed to minimize thermal bridging by filling the masonry cells with urethane foam insulation and reducing the webbing between the two faces of the block. The stated R value of a properly installed 8 Integra block system is between R-16 and R-20. The advantage of the Integra block system is its duel role of providing both high R value and thermal mass within the envelope system.
Figure 10: The Adobe Residence The adobe residence consists of two dwelling units, a primary residence as well as a guest house above the garage. Both units are oriented eight degrees east of south and share a radiant floor heating system. The primary residence (which is the focus of this paper) is 1,600 square feet, with 10-0 ceilings, three bedrooms and two full baths. Floor construction is concrete slab on grade with radiant floor heating.. Exterior wall construction is 14 adobe with 1 paper based exterior plaster. Two natural gas water heaters and a solar pre-heater are used for domestic water heating as well as the radiant floor heating system. The roofing is 26 gauges galvanized corrugated steel on roof trusses with 10 blown-in cellulose insulation. The primary residence is cooled by a SEER18 air conditioning unit. The type of adobe blocks used in the Calhoun residence measure 10x4x14, weigh approximately 40 pounds each and have an R-4.5 insulation value. The overall envelope system is approximately 15 thick with exposed adobe to the interior and a 1 paper based exterior plaster applied to the exterior (R-3). Adobe represents a high thermal mass material but the effective R value of the envelope system including air films, was only approximated to be R-8. SIPs Panel Residence The SIPs Panel Residence is a 1,280 square foot single family residence consisting of two bedrooms, two bathrooms, and a family/kitchen/dining