Methodology for the Preliminary Design of High Performance Schools in Hot and Humid Climates

This paper presents a survey of existing high performance schools in terms of energy efficiency. In general, high performance buildings are the buildings designed to maximize operational energy savings, improve comfort, health, and safety of occupants and visitors, and to limit detrimental effects on the environment. The survey provides the general literature review of the energy efficiency measures for school buildings and the case studies of several existing high performance schools. BACKGROUND Today, with the growing concerns for increasing energy costs and demand for healthy places to live and work, a high performance building (or green building) attracts attention because of its energy savings and environmentally friendly spaces. High performance buildings are buildings designed to maximize operational energy savings, improve comfort, health, and safety of occupants and visitors, and to limit detrimental effects on the environment (DDC 1999). In general, high performance building features can be categorized by several features: energy and water efficiency, indoor environmental quality (i.e., air quality, thermal comfort, and lighting), material, environmental effects (i.e., waste management and emissions), etc. When these features are successfully incorporated into the building design phase, the building can be called a high performance building. The major benefits of a high performance building can be listed below (EERE 2006a) • Energy use reduction of 50% or more. • Reduced maintenance and capital costs. • Reduced environmental impact. • Increased occupant comfort and health. • Increased employee productivity. High Performance Schools Not surprisingly, schools are one of the popular target buildings for high performance applications. Particularly, in a school, the energy efficiency and the IAQ (Indoor Air Quality) are considered as the most important aspects. According to the National Center for Education Statistics (NCES), U.S. Schools spent nearly $8 billion on energy costs in 2001, which is more than the cost of textbooks and supplies combined (Smith et al. 2003). In addition, about sixty-one percent of public school districts reported a shortfall in funding to pay their energy bills. As a result, most school districts need to reduce energy expenditures, and the application of high performance strategies to new and existing schools can be an effective solution for this need. Furthermore, the average age of America’s public school is 42 years (Rowand 1999), therefore the vast majority of existing schools could greatly benefit from energy savings improvements. Along with the energy efficiency, the IAQ issue has always been a big concern in school buildings. According to the U.S. government’s General Accounting Office (GAO), one in five schools in the United States has problems with indoor air quality (GAO 1995, 1996). Several studies have reported how IAQ affects the health and performance of students in schools. Many of them concluded that it is critical to provide the adequate amount of outdoor air and to keep proper relative humidity levels to provide a healthy and productive learning environment for students (Bayer et al. 2000). This study is a part of ongoing research to develop high performance schools in hot and humid climates. Although the IAQ issue is a significant aspect in schools, this paper only explores the high performance features in terms of energy efficiency. The ongoing research will investigate the IAQ features of the high performance schools as well. Objectives In this study, we present a survey of existing high performance schools in terms of energy efficiency. The results are divided into two sections: 1) a survey of the energy efficient building components in schools, and 2) a survey of the existing high performance schools. Although energy ESL-HH-06-07-12 Proceedings of the Fifteenth Symposium on Improving Building Systems in Hot and Humid Climates, Orlando, FL, July 24-26, 2006 efficient building components are often not considered individually in high performance building studies, the potential for energy savings is significant. Therefore, for this survey, various sources were used to find the technical reports and previous literature that covered these technologies. These include ASHRAE abstract archives, the proceedings of ACEEE, the Energy and Building Journal, the high performance buildings database of USDOE’s Energy Efficiency and Renewable Energy (EERE) program. Specifically, it is worthy to note that the buildings database of EERE (EERE 2006b) provided most of the case studies for existing high performance schools. ENERGY EFFICIENCY STUDIES IN SCHOOLS In this section, the previous general energy efficiency studies about school buildings were reviewed. As mentioned earlier, even though the schools analyzed are not defined as high performance schools, this review yielded general references about what types of energy efficiency measures have been applied in school buildings. Many papers on energy efficiency in school buildings have been written over the years. For this research, over fifty papers were reviewed. Of these, sixteen studies were selected for a closer review. Table 1 shows a summary of the selected papers. This table presents the author of paper, the classification of energy efficiency measures, the application of energy efficiency measures, the climate zones where the schools are located, the number of schools analyzed in each study, the total floor area of the school, the method of energy use analysis if any, and finally, the energy savings compared to other conventional schools. Figure 1: Climate Zones for Energy Design Guidelines In general, the energy efficiency measures analyzed in the previous studies can be classified into 1 References in this paper show the list of the studies 2 For this study, the climate zones defined in the Design Guideline for High Performance Schools (USDOE 2002). See Figure 1. two types: building envelope and building systems. Of the sixteen papers, three papers showed the energy savings from the use of an energy efficient building envelope such as tight windows, high insulation levels, shading devices, etc. Eleven papers presented energy efficient HVAC systems for schools such as ground source heat pumps, ice thermal storage system, dual path air distribution system, etc. The annual energy savings from these studies varies from 1% to 49%. However, most of the annual energy savings are in the range of 20 through 40%. The energy savings were most often calculated by measured energy use. In general, the baseline energy use was measured from the typical existing school buildings nearby. Some of the papers used building energy simulation programs such as DOE-2.1 to calculate the savings. In the following section, a detailed review is provided for studies that covered energy efficient envelope and HVAC systems. Energy Efficient Envelope Akbari et al. (1997) reported on the energy savings effects of high-albedo roofs. They monitored peak power and cooling energy savings from highalbedo coatings from one house and two school buildings in Sacramento, California. The measured and simulated cooling energy saving in the two schools was 3.1 kWh/day (35% of base-case use), and the peak demand reduction was 0.6 kW(41% of base case-use). Hunn et al. (1993) presents the results of a study of the effect of shading devices on annual heating, cooling, and total energy use, peak electric demand, and energy cost savings in a school as well as residences, a small office, and a high-rise office in Minneapolis, Minnesota. To estimate energy savings, the DOE-2 building energy simulation program was used. The results show that the annual energy savings for schools were less than 1%. This value is much less than the annual savings for residence (4%), small office (5%), and high-rise office (5%). Even though the annual energy savings for the school was marginal, the savings can be significantly increased in cooling-dominated climates. For example, another study (Pletzer et al. 1988) shows that the proper application of shading devices on residential buildings in Austin, Texas reduced annual energy use by 14%. Energy Efficient HVAC System In school buildings, ground source heat pumps have been one of the most popular choices for energy saving strategies particularly given the large land area that surrounds the schools. Five papers (Cane et al. 1995, Dinse 1998, Goss 1992, Rafferty 1996, and Shonder et al. 2000) present results of analysis of ESL-HH-06-07-12 Proceedings of the Fifteenth Symposium on Improving Building Systems in Hot and Humid Climates, Orlando, FL, July 24-26, 2006 ground source heat pumps in schools. Dinse (1998) described the energy and cost effectiveness of the geothermal systems installed in an existing school. In the study, the original school system, located in Washington County, Tennessee, which was a twopipe chilled water system for cooling and electric resistance heating, was replaced with the geothermal heat pump (i.e., a water loop heat pump with a closed loop geothermal heat exchanger). The measured energy consumption indicated that the annual energy consumption was reduced from 3,481 MWh to 2,298 MWh (i.e., 34% savings), which corresponds to a six year simple payback time. This study is particularly noteworthy because it provided results from measured data from a retrofit to an existing school. Another detailed study about geothermal heat pumps (GHP) in schools was conducted by the Oak Ridge National Laboratory (Shonder et al. 2000). This study verified the energy efficiency and lifecycle cost savings of the GHP systems installed in four identical schools in Lincoln, Nebraska. According the measured data and utility bills, on average, the GHP schools used 26% less source energy per square foot per year than the non-GHP new schools nearby. Furthermore, the GHP schools had 100% of their floor area cooled and met the ASHRAE 62-89