A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Development of Design 

Guidance for K-12 Schools from 

30% to 50% Energy Savings 

Preprint 

S. Pless, P. Torcellini, and N. Long 

National Renewable Energy Laboratory 

To be presented at the 2008 ACEEE Summer Study on 

Energy Efficiency in Buildings 

Pacific Grove, California 

August 17–22, 2008 

Conference Paper 

NREL/CP-550-43340 

July 2008 

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 
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Development of Design Guidance for K-12 Schools from 30% to 50% Energy 

Savings1

Shanti Pless, Paul Torcellini, and Nicholas Long, National Renewable Energy Laboratory 

ABSTRACT 

This paper describes the development of energy efficiency recommendations for 

achieving 30% whole-building energy savings in K-12 Schools over levels achieved by 

following the ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except LowRise Residential Buildings (1999 and 2004 versions). Exhaustive simulations were run to create 

packages of energy design solutions available over a wide range of K-12 schools and climates. 

These design recommendations look at building envelope, fenestration, lighting systems 

(including electrical lights and daylighting), HVAC systems, building automation and controls, 

outside air treatment, and service water heating. We document and discuss the energy modeling 

performed to demonstrate that the recommendations will result in at least 30% energy savings 

over ASHRAE 90.1-1999 and ASHRAE 90.1-2004. Recommendations are evaluated based on 

the availability of daylighting for the school and by the type of HVAC system. Compared to the 

ASHRAE 90.1-1999 baseline, the recommendations result in more than 30% savings in all 

climate zones for both daylit and nondaylit elementary, middle, and high schools with a range of 

HVAC system types. These recommendations have been included in the Advanced Energy 

Design Guide for K-12 School Buildings. Compared to the more stringent ASHRAE 90.1-2004 

baseline, the recommendations result in more than 30% savings in all climate zones, for only the 

daylit elementary, middle, and high schools, with a range of HVAC system types. To inform the 

future development of recommendations for higher level of energy savings, we analyzed a subset 

of recommendations to understand which energy efficiency technologies would be needed to 

achieve 50% energy savings. 

Introduction 

This paper describes the development of energy efficiency recommendations for 

achieving 30% whole-building energy savings in K-12 schools over levels achieved by following 

the ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise 

Residential Buildings (over both the 1999 and 2004 versions of the standard). These 

recommendations were included in the Advanced Energy Design Guide for K-12 School 

Buildings (AEDG-K-12 2008), a design guidance document intended to provide 

recommendations for achieving 30% whole-building energy savings in K-12 Schools. The K-12 

AEDG was developed in collaboration with the American Society of Heating, Refrigerating and 

Air-Conditioning Engineers (ASHRAE), the American Institute of Architects (AIA), the 

 1

 This work has been authored by employees of the Midwest Research Institute under Contract No. DE-AC36-99GO10337 with 

the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, 

acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or 

reproduce the published form of this work, or allow others to do so, for United States Government purposes. 

1
Illuminating Engineering Society of North America (IESNA), the U.S. Green Building Council 

(USGBC), and supported through the U.S. Department of Energy (DOE). 

Previous guides in this series include the Advanced Energy Design Guide for Small 

Office Buildings (AEDG-SO 2004), the Advanced Energy Design Guide for Small Retail 

Buildings (AEDG-SR 2006), and the Advanced Energy Design Guide for Small Warehouses and 

Self-Storage Buildings (AEDG-WH 2008). The guides published to date are available as free 

downloads from ASHRAE at www.ASHRAE.org/aedg 

Included in the K-12 AEDG are prescriptive recommendations by climate zone for the 

design of the building envelope, fenestration, lighting systems (including electrical lights and 

daylighting), HVAC systems, building automation and controls, outside air treatment, and 

service water heating. Additional savings recommendations for electrical distribution, plug 

loads, renewable energy systems, and using the building as a teaching tool are also included, but 

are not necessary for 30% savings. The K-12 AEDG contains recommendations only. It is not a 

code or standard. 

The K-12 AEDG was developed by a project committee (PC) that represents a diverse 

group of professionals. The formulation of the prototype, baseline, and low-energy models was 

an iterative process during the guide development; discussions about the model inputs and the 

model results were held with the PC. Results from the modeling, combined with input from the 

PC, led to the development of the final recommendations. The purpose of the recommendations 

provided in the K-12 AEDG is to help designers design energy-efficient schools. The goal of 

30% energy savings over ASHRAE 90.1-1999 was the primary focus of the Guide. The focus 

was on high performance buildings and the related energy savings, not on installations that have 

a payback of less than some given number of years. 

Our objectives, as discussed in this paper, are to: 

• Develop prototypical, baseline and low-energy EnergyPlus K-12 school models. 

• Document the EnergyPlus modeling assumptions needed to verify 30% energy savings. 

• Demonstrate that the recommendations result in 30% or greater energy savings by 

climate zone. 

Evaluation Approach 

The purpose of the building energy simulation analysis presented in this paper is to assess 

and quantify the energy savings potential of the Guide’s final recommendations. The AEDGs 

contain a set of energy efficiency recommendations for eight climate zones across the country. 

To provide prescriptive 30% recommendations, a specific quantitative energy savings goal must 

be measured against a specific version of Standard 90.1. For the K-12 AEDG, this is 90.1-1999, 

the “turn of the Millennium” standard (ASHRAE 1999). The energy savings of the prescriptive 

recommendations were also examined relative to ASHRAE 90.1-2004 (ASHRAE 2004). The 

following steps were used to determine 30% savings: 

1. Develop “typical” K-12 school prototype characteristics. 

2. Create baseline models for each climate zone from the prototypes that are minimally code 

compliant for both ASHRAE 90.1-1999 and ASHRAE 90.1-2004. 

2
3. Create the low-energy models based on the recommended energy efficiency technologies 

in the Guide. 

4. Verify 30% energy savings across the various school types, HVAC system types, and 

daylighting options over the 15 climate zones and sub-zones. 

Evaluation Metrics 

The 30% energy savings goal of the AEDG series is based on site energy savings 

between a minimally code compliant school and a low-energy school that uses the 

recommendations in the Guide. Other metrics, such as energy cost savings, source energy 

savings, and carbon savings, could be used to determine energy savings. Each metric has 

advantages and disadvantages from an implementation and a calculation perspective, and each 

can favor different technologies and fuel types. The K-12 AEDG uses “whole-building” site 

energy savings to retain consistency from the previous AEDGs. The “whole-building” energy 

savings indicate the savings when all the loads (regulated and unregulated) are included in the 

energy savings calculations. 

The K-12 AEDG was written to help owners and designers of elementary, middle, and 

high schools achieve energy savings of at least 30% compared to the minimum requirements of 

ANSI/ASHRAE/ IESNA Standard 90.1-1999, which is consistent with other AEDGs in the 

series. It is also the most recent code for which DOE had issued a formal determination of 

energy savings at the time the first AEDG was written. 

Climate Zones 

The AEDGs contain a unique set of energy efficiency recommendations for a range of 

climate zones. The four AEDGs developed to date have standardized climate zones that the 

International Energy Conservation Code and ASHRAE have adopted for residential and 

commercial applications (Briggs et al. 2003). It includes eight zones covering the entire United 

States (see Figure 1). Climate zones are categorized by heating degree days and cooling degree 

days, and range from the very hot zone 1 to the very cold zone 8. Some are divided into subzones based on humidity levels. Humid sub-zones are A zones, dry sub-zones are B zones, and 

marine sub-zones are C zones. Figure 1 also shows the cities that were used in the modeling 

analysis to represent the 15 climate zones (and sub-zones). 

Prototype Model Development and Assumptions 

For school characteristics that are not specified by ASHRAE 90.1-1999, ASHRAE 90.1-

2004, or ASHRAE 62.1-2001 (ASHRAE 2001), but are needed to develop code compliant 

baseline and low-energy models, we attempted to document “typical” K-12 practices, 

characteristics, and features. Typical school characteristics helped to inform our development of 

realistic models for the 30% AEDG analysis. Data sets evaluated include: 

• The 2003 Commercial Building Energy Consumption Survey (CBECS) (EIA 2005). 

• The School Planning and Management (SPM 2007) and American School and University 

(ASU 2006) annual construction survey and report. 

3
• Additional data sets from the PC, including plug load surveys, actual floor plates, and 

space programming requirements. 

Figure 1. DOE Climate Zones and Representative Cities 

From the survey of “typical” school characteristics, we developed prototype elementary, 

middle, and high school models (see Table 1). 

Table 1. K-12 AEDG Prototype Characteristics and Data Sources 

School Characteristic K-12 AEDG Prototype Source 

Size 73,930 ft2 elementary, 116,080 ft2 middle, 210,810 ft2 high ASU, SPM, CBECS 2003, 

AEDG PC 

Number of floors 1 for elementary, 1 for middle, 2 for high schools CBECS 2003 

Constructions Mass walls, insulation entirely above deck CBECS 2003, AEDG PC 

Floor plan North- and south-facing classrooms similar to example 

floor plans AEDG PC 

Window area 35% fenestration to gross wall area CBECS 2003, AEDG PC 

Occupancy Fully occupied during school hours, partially occupied 

year round and into the evening CBECS 2003, AEDG PC 

Peak plug loads 1.1 W/ft2 for elementary, 1.0 W/ft2 for middle and high AEDG PC 

Percent conditioned Fully heated and cooled CBECS 2003 

HVAC system types Baseline: PSZ 

Low-energy: PSZ, PVAV, and VAV 

2003 CBECS 

AEDG PC 

4
Space Type Sizes and Layout 

The space types and layouts of the prototype models were developed based on the 

average sizes of elementary, middle, and high schools, the “typical” space types included in 

elementary, middle, and high schools (SPM 2007), the North Carolina Schools standard area 

profiles (North Carolina 2007), and the sample floor plans provided by the PC. In general, 30 ft 

× 32 ft double loaded classrooms, 10 ft wide corridors in the elementary schools and 15 ft wide 

corridors and lockers in the middle and high schools were used to construct the prototype 

classroom wings. Classrooms at the end of a wing are modeled as individual thermal zones, and 

classrooms with similar configurations are modeled as a lumped thermal zone. Classrooms that 

are expected to have significantly different use or internal gain schedules, such as the computer 

classrooms or extended use/community use classrooms, are modeled as separate zones. The 

classrooms were configured in “wings” that face north and south. A main corridor and lobby 

separate the classroom wings from the support spaces on the east side of the prototype model 

configurations. Table 2 shows the space types and sizes included in each prototype. 

Table 2. Total Space Sizes Included in the AEDG Prototypes 

Elementary School Middle School High School 

Space Type 

Total Size 

(ft2) 

% of 

total Total Size (ft2

) % of 

total 

Total Size 

(ft2

) 

% of 

total 

Classrooms (all types except 

computer classrooms) 35,443 47.9% 47,161 40.6% 64,108 30.4%

Offices 4,745 6.4% 8,586 7.4% 11,449 5.4%

Multipurpose room/gym 3,841 5.2% 12,008 10.3% 34,690 16.5%

Computer classrooms 1,743 2.4% 2,227 1.9% 10,265 4.9%

Kitchen 1,808 2.4% 2,324 2.0% 2,324 1.1%

Cafeteria 3,389 4.6% 5,229 4.5% 6,714 3.2%

Media center 4,293 5.8% 5,810 5.0% 9,038 4.3%

Corridors/lobby 13,913 18.8% 25,351 21.8% 49,711 23.6%

Mechanical/restrooms 4,756 6.4% 7,381 6.4% 11,879 5.6%

Auditorium 0 0.0% 0 0.0% 10,631 5.0%

Total 73,932 116,079 210,810 

Baseline Model Development and Assumptions 

The baseline models for the elementary, middle, and high schools were developed by 

applying the criteria in ASHRAE 90.1 and ASHRAE 62 to the prototype characteristics. We 

used the criteria in ASHRAE 90.1-1999 and ASHRAE 62-2001 as the baselines to calculate 

energy savings for the K-12 AEDG recommendations. For the baselines needed to verify 30% 

savings over ASHRAE 90.1-2004, we updated the K-12 AEDG baselines to be minimally code 

compliant with ASHRAE 90.1-2004. 

5
Form and Floor Plate 

The prototype characteristics as documented in the previous section, combined with 

modeling assumptions, were used to generate the baseline models form and floor plate. The 

baseline fenestration to gross wall area and skylight area in the gym were determined based on 

the expected window and skylight area needed to provide full daylighting to the classrooms and 

gym. The fenestration was equally applied over all of the exterior walls. Per ASHRAE 90.1, 

Appendix G modeling rules, the baseline fenestration and skylight area should be the same as the 

low-energy model. No overhangs were included. No plenums were modeled. 

Envelope 

The PC assumed, based on experience of those in the K-12 school construction industry, 

that schools are typically constructed with mass exterior walls, built-up roofs, and slab-on-grade 

floors. These envelope constructions represent common construction practices for K-12 schools. 

There is some regional variation in construction techniques, but the PC felt that mass walls and 

built-up roofs were the most common due to their durability. This assumption is confirmed by 

the CBECS analysis of construction types. The baseline school envelope characteristics were 

developed to meet the prescriptive design option requirements in accordance with ASHRAE 

90.1-1999, Section 5.3. For the ASHRAE 90.1-2004 baselines, we used the prescriptive building 

envelope option in Section 5.5 of the standard. 

The baseline schools are modeled with mass wall constructions. The layers consisted of 

stucco, concrete block, rigid insulation, and gypsum board. The U-values of the insulation 

varied based on the respective standard and were adjusted to account for the standard film 

coefficients. R-values for most of the layers were derived from Appendix A of ASHRAE 90.1-

1999. Insulation R-values for continuous insulations were selected to meet the insulation 

minimum R-values required in Appendix B (Building Envelope Requirements) of ASHRAE 

90.1-1999, as defined by climate range. Similar wall insulation values were modeled in the 

ASHRAE 90.1-2004 baselines, as the mass wall requirements did not change significantly from 

ASHRAE 90.1-1999 to ASHRAE 90.1-2004.

Built-up, rigid insulation above a structural metal deck roof was used in the baseline 

models. The layers consisted of the roof membrane, roof insulations, and metal decking. The Uvalues varied based on the respective standard and were adjusted to account for the standard film 

coefficients. Added insulation is continuous and uninterrupted by framing. Roof insulation Rvalues were also set to match the minimum roof insulation requirements in Appendix B 

(Building Envelope Requirements) in ASHRAE 90.1-1999, by climate. Similar roof insulation 

values were modeled in the ASHRAE 90.1-2004 baselines, as the insulation above deck roof 

requirements did not change significantly from ASHRAE 90.1-1999 to ASHRAE 90.1-2004. 

The baseline buildings were modeled with slab-on-grade floors. The layers consist of 

carpet pad over 8 in. of heavyweight concrete. For this analysis, the average monthly 

temperatures were used as the input for the ground temperatures under the floor slab in the 

EnergyPlus input files. 

Fenestration systems in the baseline schools were modeled as single banded windows 

with one band per floor per façade, at 35% fenestration to gross wall area. Windows are 

collected into a single object and frames are neglected to reduce complexity in the EnergyPlus 

6
models and make the simulations run faster. The window performance is modeled as for the 

entire glazed area. U-factor and solar heat gain coefficient (SHGC) values were treated as whole 

assembly. Window U-factor and SHGC were set to match the fenestration performance criteria 

outlined in Appendix B of ASHRAE 90.1-1999, by climate zone. If the SHGC had no 

recommendation in ASHRAE 90.1 (1999 or 2004), the SHGC was set to the previous table’s 

value of SHGC. Similar window U-factors and SHGCs were modeled in the ASHRAE 90.1-

2004 baselines, as the window requirements did not change significantly from ASHRAE 90.1-

1999 to ASHRAE 90.1-2004. The multipliers from the visible light transmittance (VLT) tables 

in ASHRAE 90.1-2004 Appendix C, Table C3.5 (ASHRAE 2004) were used to calculate 

baseline VLT values for the windows. 

The K-12 AEDG recommends daylighting in the gyms. One of the gym daylighting 

options includes skylights with an area of 4% of the floor area. The baseline models also include 

the skylights, but without daylighting controls, as recommended in Appendix G of ASHRAE 

90.1-2004. The skylights are 4 ft × 4 ft (1.22 m × 1.22 m) and spaced equally throughout the 

gym and multipurpose spaces. Window U-factor and SHGCs are set to match the fenestration 

performance criteria outlined in Appendix B of ASHRAE 90.1-1999, by climate zone. 

Building air infiltration is addressed indirectly in the Standard through the requirements 

in building envelope sealing, fenestration and door air leakage, etc. ASHRAE 90.1 does not 

specify the air infiltration rate. For this analysis, the infiltration rate was assumed to be a peak of 

0.5 air changes per hour (ACH). The infiltration schedule was also incorporated into the 

modeling by assuming 0.25 ACH of infiltration when the HVAC system is enabled and the 

building is pressurized and 0.5 ACH of infiltration when it is disabled at night and on weekends. 

The ACH assumption was based on Chan’s (2006) work on determining typical infiltration in 

commercial buildings. Chan’s results show an ACH range from 0.1 to 1.0 for a typical range of 

temperature and wind conditions, with a medium near 0.5 ACH. 

Internal Loads 

Internal loads include heat generated from occupants, lights, and appliances (plug loads 

such as computers, printers, and small beverage machines). For the occupancy loads, the load 

intensity refers to the maximum occupancy at the peak time of a typical day. Lighting and plug 

loads are represented by peak power density in watts per square foot. The equipment load 

intensities for the classrooms are assumed based on the results of the plug load audits performed 

by members of the PC. Elementary schools have a higher plug load than middle and high 

schools due to the amount of equipment elementary school teachers bring in from home and plug 

in their classrooms, such as fish tanks, refrigerators, and microwaves. 

The equipment loads include all loads not associated with HVAC, service water heating, 

and lighting. In addition to all loads that are plugged in, equipment loads include items such as 

elevators, distribution transformer losses, cooking appliances, and kitchen walk-in refrigerators. 

The occupancy loads are based on typical occupant density for schools. The baseline 

interior lighting power density (LPD) for each specific area is derived using the space-by-space 

method described in ASHRAE Standard 90.1-1999. The baseline ASHRAE 90.1-1999 and 

ASHRAE 90.1-2004 LPDs, peak occupancy, and peak plug loads are shown in Table 3. Plug 

load schedules, occupancy schedules, and lighting schedules were developed by modifying the 

standard educational building schedule sets available in ASHRAE 90.1-1989 (ASHRAE 1989), 

7
based on input from each PC member and from the typical operating characteristics from 

CBECS. 

Table 3. Elementary, Middle, and High School Baseline Internal Loads by Space Type 

Space Type 

ASHRAE 

90.1-1999 LPD 

(W/ft2

) 

ASHRAE 

90.1-2004 LPD 

(W/ft2

) 

Peak Equipment 

Load (W/ft2

) 

Maximum 

Occupants 

(#/1000 ft2

) 

Classrooms (Elementary) 1.6 1.4 1.4 25 

Classrooms (Middle and High) 1.6 1.4 0.9 25 

Offices 1.5 1.1 1.0 5 

Multipurpose room (Elementary) 1.9 1.4 0.5 30 

Gym (Middle and High) 1.9 1.4 0.5 100 

Auxiliary gym (High) 1.9 1.4 0.5 30 

Computer classrooms 1.6 1.4 1.9 30 

Kitchen 2.2 1.2 1.9 15 

Cafeteria 1.4 0.9 1.0 100 

Media center 1.8 1.2 1.4 25 

Lobby 1.8 1.3 0.4 10 

Corridors 0.7 0.5 0.4 1 

Restrooms 1.0 0.9 0.4 10 

Mechanical 1.3 1.5 0.9 1 

Auditorium (High) 1.6 1.4 0.5 100 

Elementary weighted average 1.53 1.25 1.10 20 

Middle weighted average 1.52 1.22 0.82 27 

High weighted average 1.57 1.25 0.74 30 

HVAC Systems and Components 

The scope of this Guide covers all sizes of K-12 schools that use multiple HVAC system 

types. To meet the minimum energy efficiency requirements of ASHRAE 90.1-1999 and 

ASHRAE 90.1-2004 for the baseline models, the PC agreed to use packaged single-zone (PSZ) 

unitary heating and cooling equipment. The types of HVAC systems in K-12 schools are highly 

variable. The PC felt that package rooftops were an acceptable baseline system based on 

industry experience and on the CBECS analysis, which showed that package rooftop units are 

common. The code minimum EER of these system types are also the highest as compared to 

larger PSZs, PVAV, and VAV with air-cooled chiller systems. This ensured the best case 

baseline cooling efficiency, and ensured the low-energy recommendations would result in at 

least 30% savings. To model this baseline system type, we modeled each thermal zone with an 

autosized package single-zone (PSZ) system with a constant volume fan, direct expansion (DX) 

cooling, and gas-fired furnace. To apply ASHRAE 90.1-1999 and ASHRAE 90.1-2004, we 

8
assumed the baseline rooftop units would be on individual classroom rooftops in the range of 5 

tons and 2,000 cfm (0.94 m3/s). For larger spaces, multiple 5-ton units would be used. A 1.2 

sizing factor was applied to all autosized heating and cooling capacities and air flow rates. 

Ventilation rates by space type were determined based on ASHRAE 62-2001 (ASHRAE 

2001). Demand-controlled ventilation is required by ASHRAE 90.1-1999 in densely occupied 

spaces such as auditoriums and cafeterias. The ASHRAE 90.1-2004 baselines used these same 

outdoor air (OA) rates. To model demand-controlled ventilation in these spaces, we modified 

the OA rates to match the baseline occupancy schedules. 

For the spaces without demand-controlled ventilation, OA was scheduled based on the 

HVAC system availability schedule. Code allows OA to be controlled with a gravity damper, 

which opens whenever the fans operate. However, we modeled an OA motorized damper based 

on HVAC system availability schedules in the baseline models. The motorized damper is closed 

during unoccupied hours, resulting in no OA when the system night cycles. Using gravity 

dampers in colder climates that have significant night cycling can result in significant heating, 

which would inflate the baseline energy use in these climates. Therefore, all the baseline models 

include motorized OA dampers. The PC also felt that gravity dampers were not a common 

configuration for OA control. In accordance with ASHRAE 90.1-1999 and ASHRAE 90.1-

2004, an economizer is not required if the system is smaller than 65,000 Btu/h in cooling 

capacity, regardless of climate location. Therefore, the 5-ton rooftops do not include 

economizers in the baseline models. 

The constant volume fan energy use is determined from two primary input parameters: 

total supply fan static pressure drops and fan/motor efficiency. We have assumed that the 

package rooftop system contains only a supply fan, and there is no return fan or central exhaust 

fan in the system. The total supply fan static pressure drops were based on PC members’ input 

on standard HVAC ductwork design for representative duct runs served by the packaged unitary 

equipment. A total fan static pressure of 2.50 in. water column (w.c.) (625 Pa) was used for the 

5-ton unit. The total fan efficiency is a combination of the supply fan, motor, and drive 

efficiency. To calculate the total fan efficiency, the power delivered to the airflow by the fan is 

divided by the maximum allowable motor power, which equates to a 33% efficient 

fan/motor/drive combination. This efficiency was used as the baseline model input for the 

EnergyPlus package rooftop total fan efficiency. 

The code minimum efficiency for cooling equipment is determined based on cooling 

system type and size. To apply ASHRAE 90.1-1999 and ASHRAE 90.1-2004, we assume the 

baseline rooftop units would be individual classroom rooftop units in the range of 5 tons and 

2,000 cfm. ASHRAE 90.1-1999 and ASHRAE 90.1-2004 require that the energy efficiency of 

single packaged unitary air conditioners at this level (less than 65,000 Btu/h) should be rated by 

the seasonal energy efficiency ratio (SEER). Therefore, for the elementary, middle, and high 

school ASHRAE 90.1-1999 baseline models, the minimum efficiency of 9.7 SEER was used for 

each rooftop. For the ASHRAE 90.1-2004 baseline models, the minimum efficiency 

requirements were increased to a 12 SEER for this sized package rooftop unit. The gas-fired 

furnace efficiency levels were incorporated as 80% efficient gas furnaces in the package 

rooftops, to match the minimum efficiency requirements for both ASHRAE 90.1-1999 and 

ASHRAE 90.1-2004. 

9
Service Water Heating 

The PC defined the baseline service hot water system for the K-12 schools as a gas-fired 

storage water heater that meets the minimum Standards requirement for medium-sized water 

heaters under Standard 90.1-1999. Gas water heaters were chosen for the baseline to be 

consistent with the use of gas for heating in the baseline prototype schools. The thermal 

efficiency of the baseline water heaters is 80% for ASHRAE 90.1-1999 and ASHRAE 90.1-

2004. 

Low-Energy Model Development and Assumptions 

The final recommendations included in the Guide were determined based on an iterative 

process that uses the PC’s expertise and results from modeling the recommendations. To 

quantify the potential energy savings from the final recommended energy efficiency measures in 

the Guide, we implemented the following energy efficiency technologies to simulate the lowenergy building models. The energy efficiency measures included in the 30% saving calculation 

are: 

• Enhanced building envelope, including additional insulation and high-performance 

window glazing with overhangs 

• Reduced LPD and occupancy controls, combined with classroom and gym daylighting 

• Higher efficiency HVAC equipment, combined with demand-controlled ventilation, 

energy recovery ventilator (ERV), economizers, and lower pressure ductwork design and 

higher efficiency fans 

• High-efficiency service water heating 

 The following guiding principles were used to develop the final recommendation for the 

K-12 AEDG: 

• Provide recommendations that represent responsible, but not necessarily the best, K-12 

school design practices. If a recommendation generally represents good design practice, 

it is recommended for all climate zones, even if the resulting savings exceed 30%. 

• Use off-the shelf technologies that are available from multiple sources. The PC did not 

recommend technologies or techniques that are unique or available from a single 

manufacturer. 

• Provide recommendations that are at least as stringent as those in the forthcoming 

ASHRAE 90.1-2007, including Addenda AS and AT (ASHRAE 2007). We did not want 

our recommendations to be less stringent than the most recent version of ASHRAE 90.1. 

• Use the recommendations from the previous AEDGs as a starting point for fine tuning the 

K-12 AEDG recommendations. Develop recommendations to address concerns on 

usability, operations and maintenance, simplicity, and flexibility. 

• Verify 30% energy savings for the recommendations that represent the most typical K-12 

school components, or for the components that are the least likely to result in 30% 

savings. 

10
Lighting and Daylighting Recommendations 

The PC considered daylighting to be the most important recommendation in the K-12 

AEDG because daylighting has many benefits, both real and perceived, in the K-12 school 

industry. One measurable benefit is energy savings because electrical lighting is one of the 

largest energy users in schools. Depending on climate, lighting energy use can be as high as 

about 35% of the total energy use of a basic energy code-compliant school. Because lightingrelated improvements can be inexpensive and offer rapid payback, these are at the top of the list 

of recommendations for meeting an overall target of 30% energy savings or greater. There are 

two distinctly different approaches to reducing electrical lighting power: through daylighting or 

with high-efficiency electrical lighting systems. Either can be used to meet the recommendations 

in this Guide. 

Designing a daylit school. For the daylighting options, recommendations are given for 

classrooms and gyms/multipurpose rooms. There are three classroom daylighting patterns: a 

toplit pattern, a sidelit pattern, and a combined toplit and sidelit pattern. For the 

gym/multipurpose rooms, there are two toplit daylighting patterns: a roof monitor pattern and a 

skylight pattern. Recommendations for north- and south-facing versions for each pattern are 

provided in the Guide. East- and west-facing daylighting systems are not recommended. 

Recommended patterns are also provided by climate zone. The gym daylighting and classroom 

sidelighting recommendations were included in the low-energy models, as this was considered 

the daylighting design that would provide the least amount of daylighting. 

Using efficient and state-of-the-art products and techniques to design electric lighting. Site 

constraints or program requirements may preclude daylighting solutions. Therefore, a nondaylit 

path is provided to meet the recommendations in this Guide. These recommendations include 

lighting systems that use the most current, energy-efficient lamps, ballasts, and integrated 

controls. The nondaylit low energy models used the reduced LPDs as recommended in the 

Guide. 

HVAC Recommendations 

Recommendations were developed based on the availability of daylighting for the school 

and by the type of HVAC system. The types of HVAC systems in K-12 schools are highly 

variable. Therefore, recommendations for multiple HVAC types are provided. To verify savings 

over this range of design options, we modeled low-energy versions of the elementary, middle, 

and high schools, each with the daylit option and the nondaylit option. For each daylit and 

nondaylit option, we modeled three HVAC types. The low-energy HVAC system types included 

a constant volume package rooftop DX system (PSZ), a package variable air volume (VAV) DX 

system with a central boiler (PVAV), and a VAV air-cooled chiller and central boiler (VAV). 

These system types were chosen based on the PC input as to the systems that were the least 

stringent as well as the most common. 

Because conditioning OA for ventilation is such a big contributor to the energy use in a 

K-12 school building, either exhaust-air energy recovery or demand-controlled ventilation is 

recommended. The K-12 AEDG provides multiple options beyond code minimum for reducing 

11
OA loads, including scheduled OA control for all zones, carbon dioxide (CO2) demandcontrolled ventilation in all zones, and energy recovery from exhaust air. The PC felt that the 

use of CO2 demand-controlled ventilation and ERVs was not a practical technology combination 

and unneeded for 30% savings. Either demand-controlled ventilation or ERVs can significantly 

reduce OA loads. However, when one is applied, the energy savings potential for the other is 

limited. Therefore, for the PSZ, PVAV, and VAV HVAC system types, either CO2 demandcontrolled ventilation or an ERV is recommended. For all HVAC types, recommendations are 

provided for controlling the OA based on a schedule of the expected occupancy. 

To model these recommendations, we modeled the CO2 demand-controlled ventilation in 

the low-energy PSZ system and ERVs in the low-energy PVAV and VAV systems. The PC felt 

that the application of CO2 demand-control ventilation matched the PSZ configuration better 

because CO2 sensors in each zone could control OA for each zone. Likewise, the application of 

ERVs matched the single OA intake configuration of the PVAV and VAV systems. The HVAC 

baseline and low-energy modeling inputs are summarized in Table 4. 

Table 4. Baseline and Low-Energy HVAC Models Summary 

HVAC Input Baseline PSZ Low-Energy PSZ Low-Energy PVAV Low-Energy VAV 

COP of compressor/ 

condenser 

3.5 COP 

ASHRAE 90.1-1999 

(SEER 9.7) 

4.5 COP 

(SEER 13) 

CZ 1-4: 4.7 COP 

CZ 5-8: 4.3 COP 

CZ 1-4: 2.93 COP 

CZ 5-8: 2.80 COP 

COP of compressor/ 

condenser 

4.4 COP 

ASHRAE 90.1-2004 

(SEER 12) 

4.5 COP 

(SEER 13) 

CZ 1-4: 4.7 COP 

CZ 5-8: 4.3 COP 

CZ 1-4: 2.93 COP 

CZ 5-8: 2.80 COP 

Heating efficiency 80% 80% CZ 1-2: 80% 

CZ 3-8: 85% 

CZ 1-2: 80% 

CZ 3-8: 85% 

Fan efficiency 33% 36% 44% 44% 

Fan power 

limitation 1.2 hp/1000 cfm 1 hp/1000 cfm 1.3 hp/1000 cfm 1.3 HP/1000 cfm 

Total fan static 

pressure 

2.5 in. w.c. 2.3 in. w.c. 

A and B zones: 3.6 in. 

w.c. 

C zones: 3.1 in. w.c. 

A and B zones: 3.6 in. 

w.c. 

C zones: 3.1 in. w.c. 

Economizers None 

CZ 1, 2A: None 

CZ 2B, 3-8: 

Yes 

CZ 1, 2A: none 

CZ 2B, 3-8: yes 

CZ 1, 2A: none 

CZ 2B, 3-8: yes 

ERV None None 

A zones: 50% total 

effectiveness 

B zones: 50% sensible 

effectiveness 

C zones: none 

A zones: 50% total 

effectiveness 

B zones: 50% sensible 

effectiveness 

C zones: none 

OA control 

HVAC operational 

schedule, CO2

demand controlled in 

cafeteria, gym, 

auditorium 

CO2 demand 

controlled in all 

zones 

Expected occupancy 

schedule, CO2 demand 

controlled in cafeteria, 

gym, auditorium 

Expected occupancy 

schedule, CO2

demand controlled in 

cafeteria, gym, 

auditorium 

12
Evaluation Results 

This section documents the energy savings from the recommendations for 30% savings 

over ASHRAE 90.1-1999 and ASHRAE 90.1-2004. Recommendations are provided based on 

the availability of daylighting for the school and by the type of HVAC system. To verify savings 

over this range of design options, we modeled low-energy versions of the elementary, middle, 

and high schools, each with the daylit option and the nondaylit option. For each daylit and 

nondaylit option, we modeled three HVAC types. The low-energy HVAC system types included 

a constant volume package rooftop DX system, a package VAV DX system with a central boiler, 

and a VAV air-cooled chiller and central boiler. The recommendations in the K-12 AEDG result 

in more than 30% savings in all climate zones, for each daylit and nondaylit elementary, middle, 

and high school, with a range of HVAC system types. For 30% savings over ASHRAE 90.1-

2004, the recommendations are almost the same as those that are in the K-12 AEDG. The 

nondaylit option presented in the K-12 AEDG is not available for 30% savings over ASHRAE 

90.1-2004, as 30% savings were not possible over all climate zones for the nondaylit 

recommendations. 

The whole building energy savings results for the recommendations in the K-12 AEDG 

are shown in Figure 2 and Figure 3. Energy savings are relative to the ASHRAE 90.1-1999 

baseline energy use, and include plug loads in the energy use of the baseline and low-energy 

models. The analysis shows that the recommendations in the K-12 AEDG succeeded in meeting 

the goal of 30% or greater energy savings and that this goal can be met for daylit and nondaylit 

options with a range of HVAC system types. Energy savings are also shown for each 

elementary, middle, and high school prototype. In general, all the nondaylit models had less 

energy savings than the daylit equivalent. The daylit models do not have a reduced LPD, but 

used less lighting energy than the nondaylit models. The nondaylit low-energy PSZ models were 

just above 30% savings, and the PVAV daylit low-energy models were significantly above 30% 

energy savings. The PVAV system types performed the best, because of a combination of the 

higher VAV fan efficiency, higher compressor COP, and higher boiler efficiency. Energy 

savings by school type did not vary significantly for a given climate zone. Further end use 

breakdowns are available in Pless et al. (2007). 

The energy savings results for the recommendations in the K-12 AEDG, relative to 

ASHRAE 90.1-2004 are shown in Figure 4. The recommendations in the K-12 AEDG result in 

30% or greater energy savings over ASHRAE 90.1-2004 for just the daylit options with a range 

of HVAC system types. Energy savings are also shown for each elementary, middle, and high 

school prototype. For many climate zones and school types, energy savings exceeded 30% 

savings. However, for the most temperate climate zones (such as 4C), combined with the least 

effective recommendations, energy savings are just above 30%. The project committee felt that 

if the recommendations in these climate zones are considered good design practices, then they 

should also be included in the other climate zones. This was the case for recommendations such 

as air conditioner efficiency, demand controlled ventilation, and energy recovery ventilators. We 

did allow insulation and lighting power densities recommendations to vary based on climate 

zone. 

13
Figure 2. Energy Savings over ASHRAE 90.1-1999 for Non-daylit Schools 

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7A 8A

Climate Zone

Energy Savings

No Daylight PSZ

No Daylight VAV

No Daylight PVAV

Figure 3. Energy Savings over ASHRAE 90.1-1999 for Daylit Schools 

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

Elem

Middle

High

1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7A 8A

Climate Zone

Energy Savings

Daylit PSZ

Daylit VAV

Daylit PVAV

14
Figure 4. Energy Savings over ASHRAE 90.1-2004 for Daylit Schools 

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

Elem

Middle

High 

Elem

Middle

High 

Elem

Middle

High 

Elem

Middle 

High 

Elem

Middle 

High 

Elem

Middle 

High 

Elem

Middle 

High 

Elem

Middle 

High 

Elem

Middle 

High 

Elem

Middle 

High 

Elem

Middle 

High 

Elem

Middle 

High 

Elem

Middle 

High 

Elem

Middle 

High 

Elem

Middle 

High 

1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7A 8A

Climate Zone

Energy Savings

30% - Daylit PSZ

30% - Daylit VAV

30% - Daylit PVAV

Beyond 30% Energy Savings 

To inform the future development of more stringent K-12 AEDGs, we performed a 

scoping study to understand which energy efficiency technologies would be needed to achieve 

50% energy savings. Recommendations included in the 50% scoping analysis include the most 

stringent of each recommendation in the 30% guide, combined with plug load reductions 

resulting from high-efficiency distribution transformers and Energy Star® equipment, 

daylighting in all zones, infiltration reduction, and water-cooled chillers. We modeled these 

recommendations in a daylit middle school to determine energy savings over ASHRAE 90.1-

2004 in each of the 15 climate zones and sub-zones. Based on this initial scoping study, 50% 

savings should be possible in all climates. For the most temperate climates such as 3C and 4C, 

energy savings are just above 50%. The study also suggests that 50% savings are possible, but 

that efficiency measures of unregulated loads, such as plug loads and infiltration, are required. 

Additional focus on “typical” plug load schedules in K-12 schools and the expected energy 

savings from ENERGY STAR equipment will be needed to accurately predict the plug load 

savings. Baseline infiltration inputs will also need to be further researched. 

Conclusions 

To inform the development of the 30% K-12 Advanced Energy Design Guide, we 

performed exhaustive simulations to evaluate packages of energy design recommendations 

available over a wide range of K-12 schools and climates. These design recommendations look 

at building envelope, fenestration, lighting systems (including electrical lights and daylighting), 

HVAC systems, building automation and controls, outside air treatment, and service water 

15
heating. Compared to the ASHRAE 90.1-1999 baseline, the recommendations result in more 

than 30% savings in all climate zones for both daylit and nondaylit elementary, middle, and high 

schools with a range of HVAC system types. These recommendations have been included in the

Advanced Energy Design Guide for K-12 School Buildings. Compared to the more stringent 

ASHRAE 90.1-2004 baseline, the recommendations result in more than 30% savings in all 

climate zones, for only the daylit elementary, middle, and high schools, with a range of HVAC 

system types. 

References 

AEDG-K-12. 2008. Advanced Energy Design Guide for K-12 School Buildings: Achieving 

30% Energy Savings Over ANSI/ASHRAE/IESNA Standard 90.1-1999, American 

Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, Georgia, 

2008. 

AEDG-SO. 2004. Advanced Energy Design Guide for Small Office Buildings: Achieving 30% 

Energy Savings Over ANSI/ASHRAE/IESNA Standard 90.1-1999, American Society of 

Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, Georgia, 2004. 

AEDG-SR. 2006. Advanced Energy Design Guide for Small Retail Buildings: Achieving 30% 

Energy Savings Over ANSI/ASHRAE/IESNA Standard 90.1-1999, American Society of 

Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, Georgia, 2006. 

AEDG-WH. 2008. Advanced Energy Design Guide for Small Warehouses and Self-Storage 

Buildings : Achieving 30% Energy Savings Over ANSI/ASHRAE/IESNA Standard 90.1-

1999, American Society of Heating, Refrigerating and Air-Conditioning Engineers, 

Atlanta, Georgia, 2008. 

ASHRAE. 1989. ANSI/ASHRAE/IESNA Standard 90.1-1989 Energy Efficient Design of New 

Buildings Except Low-Rise Residential Buildings. American Society of Heating, 

Refrigerating and Air-Conditioning Engineers, Inc. Atlanta, Georgia, 1989. 

ASHRAE. 1999. ANSI/ASHRAE/IESNA Standard 90.1-1999 Energy Standard for Buildings 

except Low-Rise Residential Buildings. American Society of Heating, Refrigerating and 

Air-Conditioning Engineers, Inc. Atlanta, Georgia, 1999. 

ASHRAE. 2001. ASHRAE Standard 62-2001 Ventilation for Acceptable Indoor Air Quality. 

American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 

Atlanta, Georgia, 2001. 

ASHRAE. 2004. ANSI/ASHRAE/IESNA Standard 90.1-2004 Energy Standard for Buildings 

except Low-Rise Residential Buildings. American Society of Heating, Refrigerating and 

Air-Conditioning Engineers, Inc. Atlanta, Georgia, 2004. 

ASHRAE. 2007. ANSI/ASHRAE/IESNA Standard 90.1-2007. Energy Standard for Buildings 

except Low-Rise Residential Buildings. American Society of Heating, Refrigerating and 

Air-Conditioning Engineers, Inc. Atlanta, Georgia, 2007. 

ASU. 2006. American School and University 32nd Annual Official Education Construction 

Report. May, 2006. http://asumag.com/ar/605asu21.pdf. 

16
Briggs, R.S., R.G. Lucas, and Z.T. Taylor. 2003. Climate Classification for Building Energy 

Codes and Standards: Part 2—Zone Definitions, Maps, and Comparisons. ASHRAE 

Transactions 109(2). 

Chan, W.R.. 2006. “Assessing the Effectiveness of Shelter in Place as an Emergency Response 

to Large Scale Outdoor Chemical Releases.” Ph.D. dissertation, Department of Civil and 

Environmental Engineering, University of California, Berkeley. 

EIA. 2005. 2003 Commercial Buildings Energy Consumption Survey. Washington, DC: EIA. 

Available from www.eia.doe.gov/emeu/cbecs/cbecs2003/introduction.html. 

North Carolina. 2007. North Carolina State Suggested K-12 School Space Profiles, 

www.schoolclearinghouse.org/. Last Accessed May 2007. 

Pless, S.; Torcellini, P.; Long, N.. 2007. Technical Support Document: Development of the 

Advanced Energy Design Guide for K-12 Schools--30% Energy Savings. 178 pp.; NREL 

Report No. TP-550-42114. Golden, CO. 

SPM. 2007. School Planning and Management 2007 Construction Report. 

www.peterli.com/global/pdfs/SPMConstruction2007.pdf Last Accessed May 2007. 

17
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Development of Design Guidance for K-12 Schools from 30% to 

50% Energy Savings: Preprint 

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14. ABSTRACT (Maximum 200 Words)

This paper describes the development of energy efficiency recommendations for achieving 30% whole-building 

energy savings in K-12 schools over levels achieved by following the ANSI/ASHRAE/IESNA Standard 90.1, Energy 

Standard for Buildings Except Low-Rise Residential Buildings (1999 and 2004 versions). Exhaustive simulations 

were run to create packages of energy design solutions available over a wide range of K-12 schools and climates. 

These design recommendations look at building envelope, fenestration, lighting systems (including electrical lights 

and daylighting), HVAC systems, building automation and controls, outside air treatment, and service water heating. 

15. SUBJECT TERMS

energy efficiency; schools; energy design; daylighting; building envelope 

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