L ABORATORIES FOR THE 2 1 S T C ENTURY :

B EST P RACTICES

ENERGY RECOVERY FOR VENTILATION AIR IN

LABORATORIES

Introduction

Energy recovery can substantially reduce the mechanical heating and cooling requirements associated with conditioning ventilation air in most laboratories. Laboratories typically require 100% outside air at high ventilation rates—

between 6 and 15 air changes per hour—primarily for safety reasons. The heating and cooling energy needed to

condition this air, as well as the fan energy needed to move it, is 5 to 10 times greater than the amount of energy used in

most offices for those purposes. Heating and cooling systems can be downsized when energy recovery is used, because

energy recovery systems reduce peak heating and cooling requirements.

John Hopkins School of Medicine/PIX12799

U.S. Department of Energy

Energy Efficiency and Renewable Energy

Federal Energy Management Program

United States

Environmental

Protection Agency

The Bunting

Blaustein Cancer

Research Building

in Baltimore,

Maryland, is one

of several

buildings at

Johns Hopkins

that use enthalpy

wheels for energy

recovery.
There are many opportunities for energy recovery in

laboratories, and a few of them are covered here. Energy

recovery can occur between any two media or processes

that differ in energy content. The main focus of this guide

is on air-to-air energy recovery—using enthalpy wheels

(Figure 1), heat pipes, or run-around loops in new construction. Most commonly, energy is recovered from

exhaust air and used to precondition supply air. Before

deciding on an energy-recovery technology, laboratory

managers are encouraged to perform a life-cycle cost

analysis to determine the feasibility of the application in

their laboratories. As a rule, the shortest payback periods

occur when the heating and cooling load reduction provided by an energy recovery system allows the laboratory

to use smaller hot water and chilled water systems.

This guide to energy recovery is one in a series on 

best practices for laboratories. It was produced by

Laboratories for the 21st Century (“Labs 21”), a joint program of the U.S. Environmental Protection Agency and

the U.S. Department of Energy. Geared toward architects,

engineers, and facility managers, these guides provide

information about technologies and practices to use in

designing, constructing, and operating safe, sustainable,

high-performance laboratories. 

Technology Description

Air-to-air energy recovery devices exchange energy

from one stream of air to another. The air contains sensible

(heat) and latent (water vapor) energy. Both types of 

energy can be recovered; however, not all recovery devices

exchange both types of energy. The effectiveness of an

energy recovery device reflects the efficiency of the device

in recovering available energy. Most devices have a rating

for sensible effectiveness; some also have a rating for

latent effectiveness and total effectiveness. 

Energy recovery devices increase the pressure drop

across the supply and exhaust fans. Enthalpy wheels 

generally have a lower pressure drop than heat pipes and

run-around loops, although the pressure drop depends on

the design. An additional pressure drop of no more than

1 inch water gauge (1 in. w.g.) in the supply and exhaust

air streams is a reasonable design goal, and it will minimize the increase in fan energy. For example, an increase

in pressure drop of 1 in. w.g. on a 76% efficient fan and 

a 95% efficient motor assembly results in an increase in 

fan energy of 0.16 watt per cubic foot of air per minute

(W/cfm). The total increase for supply and exhaust fans

together is 0.32 W/cfm.

For laboratory applications, the design face velocity 

is typically 500 fpm or less. Lower face velocities result 

in lower pressure drops, higher effectiveness, and lower

operating costs. The trade-off is larger air handling equipment and higher first costs. An energy recovery device

will operate more efficiently with a variable-air-volume

(VAV) system than with a constant-volume system,

because VAV systems typically operate at face velocities

lower than those of design conditions. 

Enthalpy wheels. Enthalpy wheels, or rotary heat

exchangers, transfer sensible or latent energy (or both)

between the exhaust air and the incoming outside air

(Figure 1). The supply and exhaust streams must be located next to each other. Both sensible-only wheels and total

energy wheels, sometimes referred to as desiccant wheels,

are available. A 50,000 cfm total energy wheel can have a

sensible and latent effectiveness as high as 75%, which

results in a total effectiveness of 75%. Control of the wheel

2 LABS FOR THE 21ST CENTURY

Exhaust

Rotation

Supply

Purge

Section

Outside

Air

Purged

Flow

Exhaust

Air

Wheel

Supply Air 

Fan

Exhaust Air

from Lab

Purge

Section

Side Cross Section

with Purge Section

Front Cross Section

with Upstream Exhaust

034349006m

To

Labs

Exhaust

Fan

Figure 1. Cross sections (front and side) of enthalpy wheel system with purge section
at part loads is accomplished by varying the speed of the

wheel, or using a bypass duct, or both. 

The type of desiccant used in a total energy wheel

must be designed to transfer only moisture and not airborne contaminants. To further reduce potential contamination of the supply air stream, the wheel is flushed with

supply air that is deflected by a damper in the purging

section of the rotor. The damper redirects supply air leaving the wheel to the inlet side of the wheel exhaust. The

purge section utilizes the pressure difference between the

supply air and exhaust air streams (see Figure 1). Purge

volumes for laboratory applications are typically between

5% and 10%, so additional fan energy is required to move

this air.

The Whitehead Biomedical Research Building at

Emory University in Atlanta, Georgia, uses enthalpy

wheels for energy recovery between the supply and

exhaust air streams. The installation cost for the wheels

was reported at $425,000, and anticipated energy savings

are $125,000 per year. The simple payback is less than four

years.

Heat pipes. Heat pipes transfer only sensible energy. 

If air is cooled to below its dew point, however, condensation occurs on the heat pipe and results in some latent heat

transfer. In heat pipe applications, the supply and exhaust

air streams are next to one another, although some modified or “split” heat pipes allow the air streams to be 

separated. 

The sensible effectiveness of heat pipes is between

45% and 65%. Cross-contamination is not an issue. Heat

pipes have no moving parts, and failure of the entire unit

is rare. A tube may malfunction, but other tubes continue

to transfer energy. Heat pipes can be controlled for partload operation with a bypass duct or by tilting the unit.

Heat pipes can be used as indirect evaporative 

coolers, in which water is sprayed on the exhaust side of

the pipe to precool the supply air (Figure 2). This application has been successful at the Fox Chase Cancer Center 

in Philadelphia, Pennsylvania, and in the Process and

Environmental Technology Laboratory at Sandia National

Laboratories in Albuquerque, New Mexico. 

Run-around loops. Run-around loops circulate a 

fluid between two air streams. This technology may seem

familiar to most designers because it usually just involves

additional coils and pumps. The air streams do not need 

to be next to one another, and there are no cross-contamination issues. Run-around loops have a sensible effectiveness between 55% and 65%. In the U.S. Department of

Agriculture’s new laboratory in Ames, Iowa, the preheat

coil and run-around loop coil are combined, so the added

pressure drop in the supply system is lower than that of a

system with separate energy recovery and preheat coils.

Run-around loops are well-suited for transferring

energy between process loads and ventilation air. 

Fred Hutchinson Cancer Research Center in Seattle,

Washington, uses a run-around loop to take heat rejected

from the process cooling water system to preheat outside

air, thus providing free cooling of the process cooling

water.

Run-around loops and heat pipes can also be used 

to reduce reheat energy by transferring heat from the 

outdoor air to a reheat device located next to the 

LABS FOR THE 21ST CENTURY 3

Conditioned

Exhaust

Air

Cool

Supply

Air

Cool

& Wet

Air

03434902m

Warm

Exhaust

Air

Hot

Outside

Air

Heat Pipes

Evaporative

Pads

Figure 2. Heat pipe system
dehumidification cooling coil in warm, humid climates.

The energy recovery device precools the outside air before

the air enters the main dehumidification cooling coil, and

the dehumidification reheat device reheats the air leaving

the main cooling coil. This precooling and reheating can

be accomplished with a device that wraps around the

cooling coil, often called a “wrap-around loop.” It can also

be accomplished with two energy recovery stages between

the supply and exhaust air streams on either side of the

cooling coil. A wrap-around loop can be added to a runaround energy recovery loop by adding a coil on the 

leaving side of the cooling coil (Figure 3). The Viral

Immunology Center at Georgia State in Atlanta, Georgia,

uses a packaged rooftop ventilation dehumidification 

unit with two heat pipes. In the summer, one heat pipe

precools the outside air by transferring heat to the exhaust

air, the mechanical system DX coil subcools the air, and the

other heat pipe reheats the air with heat recovered from

the exhaust air. In the winter, both heat pipes are used to

heat the air.

Design Considerations 

The following are some considerations that can help

you determine whether air-to-air energy recovery is 

feasible for your project.

Schematic Design

• Identify energy recovery opportunities. Manifold

exhaust systems are ideally suited to energy recovery

because all the potentially available energy can be 

captured by one energy recovery system. 

• Consider the location of the supply and exhaust. If they

can be located next to one other, enthalpy wheels and

heat pipes can be used. Otherwise, modified heat pipes

and run-around loops are best suited for separate 

supply and exhaust. 

• Consider a wrap-around loop, if enthalpy wheels are

not an option in warm, humid climates where dehumidification is necessary.

• Assess the risk associated with cross-contamination 

of the air streams. Purge sections on enthalpy wheels

reduce cross-contamination to below 0.1%, according to

ASHRAE. There are no cross-contamination issues with

heat pipes and run-around loops. 

• Address the potential for fouling and corrosion of the

devices. Routine maintenance and controls may be sufficient, although the most suitable equipment depends

on the chemicals being released into the air stream.

Select air filters with a low pressure drop.

• Determine the space requirement for additional equipment needed and its impact on design and costs. 

• Estimate operation and maintenance costs for the

device, as well as replacement costs. 

• Calculate the impact of energy recovery on energy

costs.

• Include the cost benefit of being able to downsize the

heating and cooling systems.

4 LABS FOR THE 21ST CENTURY

Optional

Dehumidification

Reheat

Coil

Energy

Recovery

Coil

Cooling

and

Dehumidification

Coil

To

Labs

Exhaust

Air

Coil

Exhaust

Air

Heat

Optional Preheat 

Heat Exchanger

From

Labs

034349004m

Outside

Air

Supply

Air Fan

Exhaust

Fan

Energy recovery from exhaust air loop

Energy recovery from dehumidification cooling coil loop ("wrap-around loop")

Figure 3. Run-around energy recovery loop with dehumidification
Design Development and Construction

Documents

• Identify appropriate control strategies for part-load

operation and for preventing condensation and potential freezing. Using bypass ducts reduces the increase in

fan energy.

• Clearly define the commissioning of the energy 

recovery device.

Codes and Standards 

As with all building components, various codes and

standards apply to energy recovery. There are standards

for testing the performance of the equipment and standards that specify when energy recovery must or must 

not be applied. American Industrial Hygiene Association

codes and standards affecting laboratories can be found

on the Web (see www2.umdnj.edu/eohssweb/aiha/

technical/codes.htm#Energy, accessed in 2003). Here is 

a brief overview of codes and standards pertaining to

energy recovery:

• Air-Conditioning and Refrigeration Institute (ARI)

Standard 1060-2000 for Air-to-Air Energy Recovery

Ventilation Equipment rates the sensible, latent, and

total effectiveness of equipment, excluding run-around

loops. The ratings are performed by an independent

laboratory per ASHRAE 84 (see below), except as

amended by ARI 1060. The ARI-certified product directory (2001) is a useful resource for identifying various

manufacturers and their products and for comparing

effectiveness ratings.

• American National Standards Institute (ANSI)/

ASHRAE Standard 84-1991, Method of Testing Air-toAir Heat Exchangers, specifies the data, equipment,

and reporting procedures for testing the sensible,

latent, and total effectiveness of air-to-air heat exchangers. There are similar Canadian and European

standards.

• In the most recently adopted version of the

International Mechanical Code (2003), section 514 has

been added to cover the installation of energy recovery

ventilation. This section prohibits the use of all types of

energy recovery ventilation, including heat pipes and

run-around loops, with hazardous exhaust systems, as

defined in section 510.This is a significant change to the

2000 version of the code.

• National Fire Protection Association (NFPA) 45 (2001)

states that, if there is a chance of cross-contamination

between air streams, air-to-air energy recovery can be

used only on general exhaust. The code has not been

LABS FOR THE 21ST CENTURY 5

Key Issues Concerning Energy

Recovery in Laboratories

Integration of energy recovery into a laboratory ventilation

system requires careful consideration of some key issues.

Design teams have taken different approaches to handling

these issues, which demonstrates the importance of

considering all options.

Contamination. If cross-contamination from fume hood

exhaust is an issue, consider heat pipes or run-around loops.

Another approach is isolating the fume hood exhaust and

recovering energy from the general exhaust only. Note that 

the chemicals in the fume hood exhaust may become too

concentrated and require additional treatment.

Space requirements and duct adjacencies. Enthalpy wheels

and most types of heat pipes require the main supply and

exhaust ducts to be located next to each other; run-around

loops do not. Additional space is required for the energy

recovery device, typically in the makeup air unit and main

exhaust duct. Run-around loops also require space for a pump.

Hazardous chemicals. If isolating the fume hood exhaust 

or condensate from a heat recovery device results in too high a

concentration of volatile organic compounds, disposal could

become a problem. Potential hazardous waste issues need to

be addressed early on.

Humidity. If humidity is being controlled, energy used for

space heating will increase by an estimated 25%. The potential

energy savings with energy recovery increases and so do the

possible alternatives. Desiccant wheels can be used for

dehumidification, wrap-around coils can be used for reducing

reheat energy, and evaporative cooling can be used for

humidification. Avoid over-specifying control of humidity; the

wider the control range, the less energy used.

Maintenance. Maintenance differs according to the type of

energy recovery and the application. Heat pipes appear to have

the lowest maintenance requirements, followed by run-around

loops. Periodic cleaning needs depend on the fouling and

corrosion potential of the exhaust air, but cleaning is critically

important to maintaining the performance of the equipment.

Part-load operation. Outside-air bypass dampers can be 

used for part-load operation to minimize overheating,

overcooling, and fan energy use. They can also serve to prevent

condensation and frosting. Alternatively, you can vary the wheel

speed on enthalpy wheels, change the tilt on heat pipes, or vary

the flow on run-around loops. 

Redundancy. Laboratories usually have redundant chillers and

boilers to ensure control over a room’s climate conditions at all

times. If the capacity provided by energy recovery is not

accounted for in sizing the chilled water and hot water systems,

then the systems should at least be optimized to operate with

the lower loads resulting from the use of energy recovery.

Otherwise, the chillers and boilers may operate very

inefficiently at low part loads.
adopted by all states, although it raises liability concerns for design teams. At the National Institutes of

Health (NIH) Louis Stokes Laboratory and the Nidus

Center in St. Louis, the general exhaust system is 

separate from the fume hood exhaust, and there is an

enthalpy wheel on the general exhaust. NIH had to use

stainless steel ductwork for the fume hood exhaust,

because the exhaust was no longer being diluted

enough to allow for galvanized ducts.

• The ASHRAE 90.1-2001 energy efficiency standard for

nonresidential buildings requires energy recovery on

fans of 15,000 cfm or greater in buildings with fume

hoods. Laboratories with VAV fume-hood exhaust or

direct make-up air for the hoods are exempt. The 

standard states that the recovery method must have a

minimum total effectiveness of 0.5. This is not always

achievable, although this caveat is often ignored if a

device proves to be cost-effective. Note that the calculation of fan power limitations in the standard includes

an adjustment for energy recovery. 

Performance Examples 

Air-to-air energy recovery reduces energy use and 

can significantly reduce heating and cooling system sizes.

A large installation of enthalpy wheels done in 1991 at the

Johns Hopkins Ross Research Building has resulted in 

millions of dollars in energy savings. All exhaust, including fume-hood and biological safety cabinet exhaust, is

passed through the enthalpy wheels. The equipment paid

for itself in first-cost savings because the hot water and

chilled water systems could be downsized (see Engineered

Systems, September 1995). The enthalpy wheels have performed so well that Johns Hopkins is installing enthalpy

wheels in its new lab buildings, including the Cancer

Research Building shown on the cover of this guide and

the Broadway Research Building, scheduled to be completed in early 2004.

In 2002, an energy analysis of enthalpy wheels, 

heat pipes, and run-around loops was performed for

Laboratories for the 21st Century. It analyzed a typical

100,000-square-foot (sf) laboratory in four locations:

Minneapolis, Denver, Seattle, and Atlanta. The simulation

model assumes a constant-air-volume system (unless 

otherwise noted in the study). Electricity rates include an

energy charge of $0.03/kilowatt-hour (kWh), an on-peak

demand charge of $7/kW, and an off-peak demand charge

of $4/kW. On-peak hours are 8 a.m. to 10 p.m., Monday

through Friday. For natural gas, a rate of $0.60/therm is

assumed. (All studies need to use actual utility rates.) The

most significant findings include the following:

• Air-to-air energy recovery reduces gas usage for space

heating and reheat for dehumidification by more than

35% in all climates (see Table 1). 

• Savings in peak electricity demand associated with an

enthalpy wheel depend on climate (see Table 2). No

savings are predicted for heat pipes and run-around

loops, because the increase in the fan energy demand

offsets the decrease in the cooling energy demand associated with these technologies. 

• Annual energy cost savings are $0.27 to $1.95/cfm 

of fan air flow (see Table 3). Enthalpy wheels, with 

sensible and latent heat recovery, appear to be costeffective in all climates. The cost savings obtained with

heat pipes and run-around loops are relatively small in

warm, humid climates; however, using these devices as

wrap-around loops for dehumidification may be costeffective. 

• Only in the hot, humid climate of Atlanta did annual

electricity savings occur with the enthalpy wheel; in the

other climates, the increase in annual fan energy offset

the annual electricity savings.

6 LABS FOR THE 21ST CENTURY

Table 1. Percent Gas Savings (%)

Minneapolis Denver Seattle Atlanta 

Enthalpy Wheel 65% 58% 49% 48%

Enthalpy Wheel 75% 64% 62% 68%

w/VAV

Heat Pipe 41% 36% 41% 36%

Run-Around Loop 44% 36% 42% 38%

Table 2. Peak Electricity Demand

Savings with Enthalpy Wheel (W/sf)

Minneapolis Denver Seattle Atlanta 

Enthalpy Wheel 3 W/sf 1 W/sf 0 3 W/sf

Enthalpy Wheel 3 W/sf 1 W/sf 0 4 W/sf

w/VAV

Table 3. Annual Energy Cost

Savings ($/cfm/yr)

Minneapolis Denver Seattle Atlanta 

Enthalpy Wheel $1.59 $0.96 $0.55 $0.59 

Enthalpy Wheel $1.95 $1.19 $0.82 $1.00 

w/VAV

Heat Pipe $0.86 $0.56 $0.41 $0.27 

Run-Around Loop $0.91 $0.52 $0.41 $0.32 
• The greatest reduction (approximately 20%) in chiller

size occurs with enthalpy wheels in humid climates;

the savings are approximately half this amount with

sensible-only recovery devices. In the dry Denver 

climate, the potential reduction is 10% with all three

devices.

• The minimum reduction in boiler size is 15% with any

of the devices. If the building is also being humidified

in the winter, the additional latent energy recovery with

enthalpy wheels results in up to a 50% reduction in

heating and humidification requirements. 

At the 120,000-sf Fox Chase Cancer Center in

Philadelphia, heat pipes with bypass sections were

installed in two 30,000-cfm air handling units. The incremental cost for heat pipes with the indirect evaporative

cooling option on the exhaust was $300,000. Anticipated

energy cost savings were $72,510, resulting in a simple

payback of 4 years.

Conslusion

Installing energy recovery systems can substantially

reduce the cost and use of energy in laboratories. Selecting

an appropriate energy recovery technology, properly

designing the system, meeting the applicable codes, and

commissioning the system are all important. When an

energy recovery system is design, installed and operated

correctly it will provide significant energy and environmental benefits.

Acknowledgements

We wish to thank the primary author of this guide,

Sue Reilly of Enermodal Engineering, Inc. This guide

would not have been possible without the additional 

contributions of Mike Walsh of Vanderweil Engineers,

Inc.; Michael Dausch of Johns Hopkins; and John Fisher of

SEMCO. Nancy Carlisle, Otto Van Geet, Paula Pitchford,

editor, and Susan Sczepanski, graphic designer, all of

NREL, also contributed to this best practices guide. 

For More Information

The different types of air-to-air energy recovery

devices are discussed in numerous sources. For example,

the American Society of Heating, Refrigerating, and AirConditioning Engineers (ASHRAE) Handbook of Heating,

Ventilating, and Air-Conditioning Systems and

Equipment covers a wide range of devices, compares their

performance, and identifies appropriate applications. 

The ASHRAE Laboratory Design Guide by McIntosh 

et al. includes a chapter on energy recovery and discusses 

laboratory-specific concerns. Also, A Design Guide for

Energy-Efficient Research Laboratories is available in 

electronic format from Lawrence Berkeley National

Laboratory. This searchable document includes a discussion of different types of energy recovery as well as case

studies. 

Also, the U.S. Environmental Protection Agency and

the U.S. Department of Energy have prepared several

Laboratories for the 21st Century case studies (http://

labs21.lbl.gov/cs.html). Several case studies feature 

energy recovery; for an example of enthalpy wheels, see

the studies on Pharmacia Building Q, the Nidus Center,

and Building 50 at the National Institutes of Health ; for 

an example of heat pipes, see the study on the PETL at

Sandia National Laboratories, Albuquerque. Several other

good sources of information are listed below.

Air Conditioning and Refrigeration Institute (ARI).

2001. Air-to-Air Energy Recovery Ventilation Equipment

Certified Product Directory. ARI, Arlington, VA

(www.ARI.org).

ARI Standard 1060. 2001. Rating Air-to-Air Energy

Recovery Ventilation Equipment. ARI, Arlington, VA.

ANSI/ASHRAE Standard 84-1991 (ARI 1060). 1991.

Method of Testing Air-to-Air Heat Exchangers. American

Society of Heating, Refrigerating and Air-Conditioning

Engineers, Inc., Atlanta, GA (www.ashrae.org).

Cockerham, K. 2000 (July). “A Tale of Two Systems.”

Consulting Specifying Engineer.

DiBlasio, R. 1995 (September). “Conditioning a

Research Facility.” Engineered Systems.

LABS FOR THE 21ST CENTURY 7

Key Terms

Effectiveness: The ratio of actual energy recovered to

theoretical energy that could be recovered.

Latent energy: The energy contained in moisture.

Latent effectiveness: Proportional to the ratio of the difference

between the humidity ratio of the outside air and the supply air,

and the difference between the humidity ratio of the exhaust air

and the outside air.

Sensible energy: The energy associated with a temperature

difference.

Sensible effectiveness: Proportional to the ratio of the

difference between the dry-bulb temperature of the outside air

and supply air, and the difference between the dry-bulb

temperature of the exhaust air and the outside air. 

Total effectiveness: Proportional to the ratio of the difference

between the enthalpy of the outside air and the supply air, and

the difference between the enthalpy of the exhaust air and the

outside air.
8

Gibson, Tom, 1999. “Special Ventilation System

Helps Prevent Release of Dangerous Agents at

Georgia State,” The News: Air Conditioning,

Heating and Refrigeration.

International Code Council, 2003. International

Mechanical Code. ICC, Falls Church, VA.

McIntosh, I.; Dorgan, C.B.; and Dorgan, C.E.,

2001. ASHRAE Laboratory Design Guide. American

Society of Heating, Refrigerating and AirConditioning Engineers, Inc., Atlanta, GA.

National Fire Protection Association 45, 2001.

Standard on Fire Protection for Laboratories Using

Chemicals. NFPA, Quincy, MA.

National Wildlife Federation, 2002. Emory

University Campus Ecology Yearbook 2001-2002.

NWF, Reston, VA.

Paarporn, S., P.E., 1999. “Run-around Loop

Heat Recovery with Dehumidification System.”

ASHRAE Journal, June.

Reilly, S., and Van Geet, O., 2003. Laboratories

for the 21st Century Energy Analysis. U.S.

Environmental Protection Agency and U.S.

Department of Energy Federal Energy

Management Program, Publication No. DOE/

GO-102003-1694. Prepared by the National

Renewable Energy Laboratory, Golden, CO,

http://labs21.lbl.gov/docs/labs21energyanal_

33410.pdf. 

On Laboratories for the 21st Century:

Phil Wirdzek

U.S. Environmental Protection Agency

1200 Pennsylvania Ave., N.W.

Washington, DC 20460

202-564-2094

wirdzek.phil@epamail.epa.gov

Will Lintner, P.E.

U.S. Department of Energy

Federal Energy Management Program

1000 Independence Ave., S.W. 

Washington, DC 20585

202-586-3120

william.lintner@ee.doe.gov

On Energy Recovery:

Otto Van Geet, P.E.

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401

303-384-7369

otto_vangeet@nrel.gov

Sue Reilly, P.E.

Enermodal Engineering, Inc.

1554 Emerson Street

Denver, CO 80218

303-861-2070

eeinc7@qwest.net

DOE/GO-102003-1774

October 2003

Printed with a renewable-source ink on paper containing at least 

50% wastepaper, including 20% postconsumer waste

Laboratories for the 21st Century

U.S. Environmental Protection Agency

Office of Administration and Resources Management

www.epa.gov/labs21century/

In partnership with the 

U.S. Department of Energy

Energy Efficiency and Renewable Energy

Bringing you a prosperous future where energy 

is clean, abundant, reliable, and affordable

www.eere.energy.gov/

Prepared at the 

National Renewable Energy Laboratory

A DOE national laboratory