Federal Technology Alert 

A New Technology Demonstration Publication 

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Summary of Results from Testing a 

30-kW-Microturbine and Combined 

Heat and Power (CHP) System 

Frank E. Pierce, Jr.


Oak Ridge National Laboratory Integrated Energy System (IES) Test Laboratory


Abstract 

A combined heat and power (CHP) system consists of a power generation system integrated with 

waste heat recovery configurations that can provide input for various thermally activated technologies 

(TATs). This publication summarizes in one document the results of a series of CHP system tests 

performed at the ORNL CHP Integration Test Facility. This document provides an energy manager 

who is considering installation of a microturbine-based CHP system a single source for performance, 

efficiency, and emissions test results for an individual microturbine or one integrated with TATs. The 

tests were performed using a 30-kW microturbine and TATs including an indirect-fired, single-effect 

absorption chiller, direct- and indirect-fired desiccant dehumidifiers, and an air-to-water heat exchanger. 

Internet: www.eere.energy.gov/femp/ 

No portion of this publication may be altered in any form without 

prior written consent from the U.S. Department of Energy, Energy 

Efficiency and Renewable Energy, and the authoring national laboratory. 

U.S. Department of Energy 

Energy Efficiency 

and Renewable Energy 
Federal Technology Alert 

LIST OF FIGURES 

Figure Page


1 Schematic of CHP Integrated Test Facility at ORNL 4


2 Schematic of direct-fired desiccant dehumidification unit 6


3 Schematic of indirect-fired desiccant dehumidification unit 6


4 Startup power output and turbine speed 8


5 Shutdown power output and turbine speed 8


6 Power dispatching response: power output and turbine speed 9


7 Microturbine power output variation for 1 h at 30 kW 9


8 Efficiency and exhaust temperature versus power output 11


9 Effect of ambient temperature on power output 11


10 Effect of ambient temperature on exhaust temperature 11


11 Experimental setup for baseline testing microturbine 12


12 Heat recovery by the HRU at a water flow rate of 4.3 m3

/h (19 gpm) 14


13 IES system and microturbine: heat recovery efficiencies 14


14 Efficiencies of microturbine (MTG) and IES 17


15 Effect of power output on latent capacity 18


16 Effect of power output on efficiency 18


17 Effect of ambient temperature on cooling capacity 19


18 Effect of ambient temperature on the COP of the absorption chiller 19


19 Effect of ambient temperature on the efficiency of IES configurations 20


20 Efficiencies of IES configurations at various dry-/wet-bulb conditions 21


21 Concentration of CO, NOx, and SO2 (ppmV15) vs microturbine power output 22


22 Concentration of CO, NOx, and SO2 (mg/m3

) vs power output 22


23 CO concentration vs air inlet temperature at 25- and 30-kW power output settings 23


LIST OF TABLES 

Table Page


1 Microturbine performance characteristics at various power settings 10


2 Capstone 30-kW microturbine with damper fully open 12


3 Capstone 30-kW microturbine with damper 3/8 open 13


4 Microturbine performance at constant speed and varying back-pressure 13


5 Comparison of manufacturer’s test data and laboratory results 15


6 Latent capacity test results (IES-based operation) 16


7 Measured performance parameters of the IES with the desiccant dehumidifier 21


ACRONYMS 

ABSC absorption chiller IES integrated energy system 

CHP combined heat and power IFDD indirect-fired desiccant dehumidifiers 

DER distributed energy resource LC latent capacity 

DFDD direct-fired desiccant dehumidifiers LCOP latent coefficient of performance 

DG distributed generation LiBr/water lithium-bromide/water 

HHV higher heating value MTG microturbine generator 

HRU heat recovery unit ORNL Oak Ridge National Laboratory 

HVAC heating, ventilating, and air-conditioning TAT thermally activated technologies 

. 

2 –– FEDERAL ENERGY MANAGEMENT PROGRAM 
Federal Technology Alert 

Contents


Page


LIST OF FIGURES 2


LIST OF TABLES
 2


ACRONYMS
 2 

1. ABOUT THE TECHNOLOGY
 4 

2. ORNL CHP INTEGRATION TEST FACILITY
 4 

2.1 TEST FACILITY CONFIGURATION 4


2.2 TEST FACILITY COMPONENTS 5


2.2.1 Microturbine 5


2.2.2 Heat Recovery Unit 5


2.2.3 Desiccant Dehumidifiers 5


2.2.4 Absorption Chiller 6


2.3 EMISSIONS MONITORING 7


3. MICROTURBINE BASELINE CHARACTERIZATION 7


3.1 STARTUP, SHUTDOWN, AND DISPATCH CHARACTERISTICS 7


3.2 POWER OUTPUT VARIATION 7


3.3 PERFORMANCE AT VARIOUS POWER SETTINGS 7


3.4 EFFECT OF AMBIENT TEMPERATURE ON ACHIEVABLE 


POWER OUTPUT AND EXHAUST TEMPERATURE 9


4. BACK-PRESSURE TESTS 10


4.1 CONSTANT POWER OUTPUT DEMAND 11


4.2 CONSTANT ENGINE SPEED 12


5. HEAT RECOVERY AND CHP EFFICIENCY 12


5.1 AIR-TO-WATER HEAT EXCHANGER (e.g., HRU) 13


5.2 DESICCANT DEHUMIDIFICATION 13


5.2.1 Direct Fired Desiccant Dehumidification 14


5.2.2 Indirect Fired Desiccant Dehumidification System 16


5.3 ABSORPTION CHILLER 17


5.3.1 Effect of Ambient Temperature on Absorption Chiller Capacity and COP 18


5.3.2 Effect of Ambient Temperature on IES Configuration Efficiency 19


5.4 ABSORPTION CHILLER AND DIRECT-FIRED 


DESICCANT DEHUMIDIFICATION
 20 

6. EMISSION TESTS
 21 

6.1 EFFECT OF MICROTURBINE POWER OUTPUT ON EMISSIONS RATE
 21 

6.2 EFFECT OF MICROTURBINE INLET AIR ON EMISSIONS RATE
 22 

7. THE TECHNOLOGY IN PERSPECTIVE
 23 

8. REFERENCES
 24 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 3 
Federal Technology Alert 

1.	 ABOUT THE 

TECHNOLOGY 

The U.S. Department of Energy’s 

Office of Electricity Delivery and Energy 

Reliability studies the integration of 

electric power generation and thermally 

activated heating, ventilating, and 

air-conditioning (HVAC) systems. This 

program has sponsored research on a 

natural-gas-fired, microturbine-based 

combined heat and power (CHP) system 

with thermally activated technologies 

(TAT) at Oak Ridge National Laboratory’s (ORNL’s) CHP Integration Test 

Facility in Oak Ridge, Tennessee. This 

report summarizes the results of 

performance and efficiency tests on a 

microturbine distributed energy resource 

(DER). The microturbine was operated 

individually as well as integrated with 

various waste heat recovery configurations 

over a range of design and off-design 

conditions in steady-state operating 

mode. More detailed descriptions of 

the tests and results can be found in 

the references cited throughout this 

summary report. 

DERs are small, modular, powergeneration systems such as gas turbines, 

microturbines, fuel cells, and advanced 

reciprocating engines that are located in 

the vicinity of the energy end user. The 

major benefits of a DER are (1) local 

control of power generation, (2) efficient 

use of waste heat, (3) increased overall 

efficiency, and (4) a reduction in 

emissions.

1,2 

In a CHP system, waste heat from the 

DER generation system, which is 

normally discharged to the environment, 

is used as input power for TATs. Overall 

efficiencies of 40 to 70% or more can be 

achieved in well-integrated CHP systems 

when the waste heat is used. Technologies that can be driven by DER system 

waste heat include (1) chillers and 

desiccant dehumidifiers for space 

cooling and dehumidification, 

(2) steam generators for space heating, 

and (3) heat exchangers for process and 

domestic hot water.

1 These CHP systems 

can maximize energy efficiency, provide 

an option to central power generation, 

and improve electric power reliability 

and quality.

1,2 

2.	 ORNL CHP 

INTEGRATION 

TEST FACILITY 

2.1	 TEST FACILITY 

CONFIGURATION 

The current CHP test facility configuration (Fig. 1) is flexible and contains a 

30-kW natural-gas-fired microturbine, 

which can be integrated with various 

thermally activated HVAC systems. 

TATs currently in the CHP Integration 

Test Facility are a first-generation heat 

Fig. 1. Schematic of 

CHP Integrated Test 

Facility at ORNL. 

(Source: “DER Performance 

Testing of a MicroturbineBased Combined Cooling, 

Heating, and Power (CHP) 

System PERFORMANCE,” 

Proceedings of Power 

System 2002 Conference, 

Clemson, SC, March 2002). 

. 

4 –– FEDERAL ENERGY MANAGEMENT PROGRAM 
Federal Technology Alert 

recovery unit (HRU), an indirect-fired, 

single-effect, 10-ton absorption chiller 

(ABSC), and direct-fired (DFDD) 

and indirect-fired (IFDD) desiccant 

dehumidifiers. Under normal conditions, 

the heated air or hot water input for 

these TATs is generated by natural gas 

firing. In the CHP configuration, the 

waste exhaust heat from the gas-fired 

microturbine provides the thermal 

energy input.

1,2 

The microturbine exhaust gas, at a 

temperature normally ranging from 

250 to 293°C (482 to 560°F), can be 

directed through different paths 

depending on the configuration to be 

tested. Hot water ranging in temperature 

from 85 to 95°C (185 to 203°F) can be 

generated by directing the microturbine 

exhaust gas through an exhaust-gas-toliquid heat exchanger (e.g., an HRU). 

The hot water generated in the HRU 

can be input to either an indirect-fired 

desiccant dehumidification system or 

a 10-ton, indirect-fired, single-effect 

absorption chiller. The temperature 

of the exhaust gas leaving the HRU is 

~120°C (~248°F). For testing a directfired desiccant system, the exhaust gas 

can be supplied directly to the desiccant 

system inlet plenum or passed through 

the HRU to generate hot water and then 

be directed to the direct-fired desiccant 

system inlet plenum.

1,2 

2.2	 TEST FACILITY 

COMPONENTS1,2 

2.2.1 Microturbine 

The microturbine, a three-phase 480­

VAC/30-kW-rated unit, is designed to 

operate at a maximum speed of 96,000 

rpm, generate 50 or 60 Hz power, 

produce a continuous phase current 

of 36 A at 480 VAC, and a near unity 

power factor when the unit is grid 

connected. The unit’s nominal phase-toneutral voltage is 277 VAC. The 

power-conditioning electronics of the 

turbine generator rectifies the highfrequency ac power from the generator 

to constant-voltage DC power, which is 

then inverted to 50 or 60-Hz constantfrequency ac power.

1,2 

The microturbine’s natural gas fuel is 

supplied by the gas distributor at a 

pressure of only 0.3 atm (5 psig) and 

the unit requires natural gas at a 

pressure of 3.7 atm (55 psig); therefore, 

a gas compressor is used to increase the 

pressure before it enters the microturbine combustion chamber. An exhaustgas-to-air heat exchanger/recuperator 

is used to preheat the air entering the 

combustion chamber, improving the 

electrical efficiency of the microturbine 

by ~10% from 13 to 23% based on 

the higher heating value (HHV) of the 

natural gas. 

2.2.2 Heat Recovery Unit

3–6 

The HRU, an exhaust-gas-to-liquid heat 

exchanger, is used to recover a portion 

of the waste heat in the microturbine 

exhaust gas and produce hot water for 

heating, input to the IFDD system, or 

input to the absorption chiller. Although 

the HRU nominal water flow rate is 

~4.3 m3/h (~19 gpm), CHP system 

configuration tests were performed 

with water flow rates as high as ~9 m3/h 

(~39.8 gpm). At a water flow rate of 

~5.8 m3/h (~26 gpm) the maximum 

water temperature is ~91oC (~196oF). 

Actual water temperature depends on 

several parameters, such as microturbine 

power output, ambient temperature, 

and HRU water flow rate. The exhaust 

gas leaving the HRU has sufficient waste 

heat to potentially provide the thermal 

input to additional direct-fired TATs, 

such as a direct-fired desiccant 

dehumidification unit (DFDD). 

2.2.3	 Desiccant 

Dehumidifiers1,2,4,5,7 

Desiccant dehumidifiers provide an 

alternative to mechanical refrigeration 

for removing moisture from air before 

it enters a conditioned space. The 

desiccant material attracts water from 

the air as a vapor rather than condensed 

liquid. The water vapor pressure 

difference between humid air (high 

vapor pressure) and dry desiccant (low 

vapor pressure) provides the potential 

that causes water molecule migration 

from the humid air to the desiccant. 

The desiccant dehumidifiers use a wheel 

of desiccant material mounted between 

two air streams—a process stream and a 

reactivation stream. As the wheel rotates 

between the two air streams, moisture 

is absorbed from the process stream to 

nearly saturate the desiccant, and 

the reactivation stream dries out the 

desiccant. Moisture released from the 

desiccant wheel is carried by the 

reactivation stream and discharged 

out of the building. 

Desiccant units that use heated reactivation air are called “active” to distinguish 

them from units that use dry building 

exhaust air for regeneration, which are 

called “passive.” The units in the Integrated Test Facility are active units that 

can be further classified as “direct-fired” 

or “indirect-fired,” depending on the 

method used to heat the regeneration air. 

In a direct-fired unit, natural gas combustion or other heat sources are used 

to directly heat the regeneration air as 

shown in Fig. 2. For the direct-fired 

unit tested in the Integrated Test Facility, 

hot exhaust from the microturbine 

mixed with outside air was used for 

regeneration air. 

When an indirect method, such as a hot 

water or steam-to-air heat exchanger, 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 5 
Federal Technology Alert 

is used to heat the regeneration air, the 

unit is classified as an indirect-fired 

desiccant dehumidification unit. A 

schematic of an indirect-fired unit is 

shown in Fig. 3. 

The major difference between the IFDD 

and DFDD units is in the method 

used to provide the heat necessary to 

regenerate the desiccant material. In the 

IFDD the gas burner used to provide 

heat for regeneration is replaced by a 

hot water or steam heating coil. As with 

the DFDD unit, the IFDD has two air 

streams—regeneration and process. The 

process return air enters the unit and 

passes through a desiccant material 

where heat is added, raising the air 

temperature and removing moisture1. 

After leaving the desiccant material, the 

process air flows through a heat 

recovery wheel where heat is removed 

and transferred to the regeneration air, 

decreasing the amount of thermal 

Fig. 3. Schematic of indirect-fired desiccant dehumidification unit. (Source: “CHP 

Integration (OR IES): Maximizing the Efficiency of Distributed Generation with Waste Heat 

Recovery,” Proceedings of the power Systems 2003 Conference, Clemson, SC, 

March 2003.) 

Fig. 2. Schematic of 

direct-fired desiccant 

dehumidification unit. 

(Source: “Baseline and 

IES Performance of a 

Direct-Fired Desiccant 

Dehumidification Unit 

under Various Environmental Conditions,” 

2003 ASHRAE 

Transactions of the 

Annual Meeting, 

KC-03-5-2, Kansas City, 

MI, June 2003.) 

energy required to raise it to the 

regeneration temperature. 

The regeneration air (outside air) enters 

the unit and passes through the heat 

recovery wheel, picking up heat from 

the process air. After leaving the heat 

recovery wheel, the regeneration air 

flows through the regenerative heating 

coil where it picks up additional heat 

before passing to the desiccant wheel 

to remove the absorbed moisture. The 

regeneration air is then discharged to 

the atmosphere. 

In the Integrated Test Facility, indirectfired testing configuration hot water 

generated by heat recovered through 

the HRU and a hot-water-to-air heat 

exchanger were used to heat the 

reactivation air. 

2.2.4 Absorption Chiller8 

Absorption chillers generate chilled water 

(~44°F or ~7°C) from a heat source as 

opposed to mechanical compression of 

vapor. Water-lithium-bromide 

absorption chillers using water as the 

refrigerant and lithium-bromide as the 

. 

6 –– FEDERAL ENERGY MANAGEMENT PROGRAM 
Federal Technology Alert 

absorbent are classified by the method of 

heat input (direct-fired or indirect-fired) 

and whether the absorption cycle is 

single or multiple effect. The direct-fired 

absorption chillers contain fossil fuel 

burners to provide the heat source. 

Indirect-fired units use hot water or 

steam from a separate heat source to 

provide the heat input. Exhaust-fired 

unites use hot exhaust gases directly as 

their heat source. 

Single-effect absorption chillers generally 

use water from 116oC to132oC (240oF 

to 270oF) with some smaller machines 

for waste heat applications using 190oF, 

or low pressure (9 to 12 psig) steam. 

Double-effect chillers provide increased 

efficiency but also need higher-pressure 

steam (i.e., 100 psig) or high-temperature water (i.e., 188oC or 370oF). The 

current CHP test facility configuration 

contains an indirect-fired, single-effect 

10-ton AC. 

2.3	 EMISSIONS MONITORING7 

The air pollutants most significant to 

gas microturbine-based CHP system 

operation are nitrogen dioxide (NO2), 

carbon monoxide (CO), and sulfur 

dioxide (SO2), all of which can have 

a significant effect on the level of environmental pollution. These pollutants 

along with, lead (Pb), ozone (O3), and 

particulates are among six criteria air 

pollutants that have had ambient air 

limits set by the U.S. Environmental 

Protection Agency. Therefore, these three 

pollutants were of most interest during 

the emissions studies performed at the 

Integrated Test Facility. 

An Enerac 3000E flue gas analyzer 

supported by Enercom 2000 software 

and electrochemical sensor was used 

for emissions monitoring of the microturbine flue gas. The concentrations of 

NOx, CO, and SO2 were measured in 

ppm by volume (i.e., volume of gaseous 

pollutant per million volumes of 

ambient air) at the test oxygen concentration, corrected to 15% O2 (typical 

requirement for comparison of various 

DG equipment) and then converted 

to mg/m3. 

3.	 MICROTURBINE 

BASELINE 

CHARACTERIZATION1,2 

The first phase of testing the 30-kW 

microturbine and CHP consisted of 

characterizing the baseline performance 

of the microturbine. The collected electrical data included the microturbine’s 

DC voltage, and single- and three-phase 

power output, voltage, and current. The 

thermal data included the microturbine’s 

input temperature, exhaust temperature, 

internal temperatures at the compressor 

and turbine, and emissions. 

The baseline characterization tests were 

performed without TATs connected to 

the microturbine exhaust. Even without the presence of any equipment for 

thermal recovery, some degree of backpressure exists (~8.0 × 10–4 atm or 0.3 

in wc), although this is quite low. The 

effect of exhaust back pressure on the 

microturbine’s power and efficiency is 

discussed in Sect. 4.0. 

3.1	 STARTUP, SHUTDOWN, 

AND DISPATCH 

CHARACTERISTICS1,2 

The startup, shutdown, and power 

dispatch characteristics (power output 

and speed) of the microturbine are 

shown in Figs. 4–6. Startup in this case 

is defined as 0 rpm and 0 power output 

to operating speed and full output power 

generation. 

As shown in Fig. 4, startup requires 

~200 s. During the initial ~40 s of 

turbine warm-up, auxiliary power 

(~2 kW) is provided by the grid, which 

is shown as negative power output in 

Fig. 4. The microturbine controls maintain the microturbine speed at ~25,000 

rpm until the microturbine begins to 

generate power and then at ~45,000 rpm 

for ~115 s during the remainder of the 

warm-up cycle. After the warm-up 

period, the microturbine controls 

increase the speed to obtain the desired 

startup output power setting. This characteristic is basically the same regardless 

of the power output setting for startup. 

Shutdown, shown in Fig. 5, requires 

520 s. Most of this time, ~475 s, is 

required to cool down the turbine. 

Although the power output dropped 

off fairly linearly, the turbine speed 

stayed at 45,000 rpm for nearly all the 

shutdown time. 

The power dispatching characteristics 

are shown in Fig. 6. It was found that 

it took ~20 s to vary the microturbine’s 

power output. Figure 6 shows the 

transition time from ~10 kW to 

~30 kW. 

3.2	 POWER OUTPUT VARIATION 

The variability of the microturbine’s 

power output at the full power setting 

(30 kW) over a one-hour period is 

shown in Fig. 7.

2 

3.3	 PERFORMANCE AT 

VARIOUS POWER 

SETTINGS2 

To characterize the microturbine’s 

performance at various power settings, 

tests were performed at power settings 

ranging from full output (30 kW) to 

one-sixth power (5 kW) in 5-kW 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 7 
Federal Technology Alert 

Fig. 4. Startup power output and turbine speed. (Source: “DER Performance Testing of a Microturbine-Based 

Combined Cooling, Heating, and Power (CHP) System,” Proceedings of Power System 2002 Conference, 

Clemson, SC, March 2002. 

Fig. 5. Shutdown power output and turbine speed. (Source: “DER Performance Testing of a MicroturbineBased Combined Cooling, Heating, and Power (CHP) System,” Proceedings of Power System 2002 

Conference, Clemson, SC, March 2002. 

increments. The results 

are presented in Table 1, 

which contains the 

microturbine’s power 

setting, measured 

power output, turbine 

speed, phase voltages 

and currents (a, b, and 

c), and rectified dc 

voltage and standard 

deviations for some of 

these values. It should 

be noted that the 

outdoor temperatures 

were below the ISO 

temperature of 15oC 

(59oF) that is the typical rating condition for 

microturbines. The 

measured emissions at 

the various power settings are also presented. 

Emission characteristics 

are discussed in Sect. 6. 

In the grid-dependent 

(grid-connected) 

mode, for a power output range of 30 to 20 

kW, the microturbine 

was found to operate 

at a power factor of 

98% with a ±0.86% 

standard deviation; 

and for power output 

range of 15 to 5 kW, 

generated at 97% 

with a standard 

deviation of ±0.80%. 

The data in Table 1 

show that the unit’s 

efficiency decreases 

with the power output 

level. At the full power 

setting of 30kW, the 

microturbine can 

produce ~28 kW at an 

. 

8–– FEDERAL ENERGY MANAGEMENT PROGRAM 
Federal Technology Alert 

efficiency of ~23%. 

At an output power 

setting of 5 kW, 

the microturbine has 

an efficiency of only 

~12%. The microturbine’s exhaust 

temperature varied 

from ~264°C (~508°F) 

at the unit’s maximum 

power demand setting 

(30 kW) to ~196°C 

(~384°F) at the 

minimum power 

setting of 5 kW. The 

energy efficiency and 

exhaust temperature 

of the microturbine as 

they vary with power 

output are shown 

in Fig. 8. 

3.4 	 EFFECT OF 

AMBIENT 

TEMPERATURE 

ON 

ACHIEVABLE 

POWER 

OUTPUT AND 

EXHAUST 

TEMPERATURE4 

One of the factors 

affecting the performance of the turbine 

is the ambient air mass 

flow. Since a turbine is 

a fixed-displacement 

machine, the air mass 

flow is a direct function 

of the ambient air density, which in turn is a 

function of the ambient air temperature and 

humidity. The tested 

microturbine generator 

(MTG) controls the 

net power output by 

Fig. 6. Power dispatching response: power output and turbine speed. (Source: “DER Performance Testing of 

a Microturbine-Based Combined Cooling, Heating, and Power (CHP) System,” Proceedings of Power System 

2002 Conference, Clemson, SC, March 2002. 

Fig. 7. Microturbine power output variation for 1 h at 30 kW. (Source: “Integration of Distributed Energy 

Resources and Thermally-Activated Technologies,” DistribuTech Conference, Miami Beach, FL, 

February 2002.) 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 9 
Federal Technology Alert 

Table 1. Microturbine performance characteristics at various power settings (Ref. 2) 

adjusting the turbine speed to achieve 

the desired power output setting at 

the given ambient temperature. The 

maximum speed allowed by the MTG 

controller is 96,000 rpm, which limits 

possible temperature compensation. 

At a given ambient temperature when 

the maximum turbine speed limit is 

reached for a specific power output 

setting, it is not possible to compensate 

for any further increases in ambient 

temperature. Therefore the net power 

output of the MTG decreases as the 

ambient temperature increases, and the 

desired power output setting cannot 

be achieved. 

For the tested microturbine, the 

maximum speed limit was found to 

affect only the 30-kW and 25-kW 

power settings. As can be seen in 

Fig. 9, at the 30-kW and 25-kW 

output settings the critical ambient 

temperature is ~13oC (~56oF) and 

~21oC (~70oF), respectively. 

The effect of ambient air temperature 

on exhaust gas temperature is shown 

in Fig. 10: exhaust gas temperature 

increases with the rise in ambient 

air temperature. After the critical 

temperature is reached, the exhaust 

gas temperature continues to increase 

with increased ambient temperature, 

but at a lower rate.6 

4.	 BACK-PRESSURE 

TESTS1–3 

For a turbine-only configuration, the 

back-pressure (i.e., pressure at the 

turbines exhaust outlet) consists of the 

pressure drop through the exhaust stack 

and silencers. Heat recovery equipment 

interfaced with a turbine increases the 

back-pressure and reduces the power 

output. The objective of this test was 

to investigate the dependence of the 

microturbine’s power and efficiency 

on the exhaust back-pressure. 

Two series of back-pressure tests were 

performed; one at constant output 

power demand and another at constant 

engine speed. In each series of tests, 

the total power output demand of the 

microturbine was varied in increments 

of 5 kW from 10 kW to 30 kW. The 

back-pressure on the unit was adjusted 

by a slide damper in the exhaust duct, 

as shown in Fig. 11. Constant output 

power demand tests were performed 

with the damper in three different 

. 

10 –– FEDERAL ENERGY MANAGEMENT PROGRAM 
Federal Technology Alert 

Fig. 8. Efficiency and exhaust temperature versus power output. (Source: “Integration of Distributed Energy 


Resources and Thermally-Activated Technologies,” DistribuTech Conference, Miami Beach, FL, 


February 2002.)


Fig. 9. Effect of ambient temperature on power output. (Source: 

“CHP Integration (OR IES): Maximizing the Efficiency of Distributed 

Generation with Waste Heat Recovery,” Proceedings of the Power 

Systems 2003 Conference, Clemson, SC, March 2003.) 

Fig. 10. Effect of ambient temperature on exhaust temperature. 

(Source: “CHP Integration (OR IES): Maximizing the Efficiency of 

Distributed Generation with Waste Heat Recovery,” Proceedings of 

the Power Systems 2003 Conference, Clemson, SC, March, 2003.) 

positions—fully open, 1/4 closed, and 

3/8 closed—and for the constant engine 

speed tests, the slide damper was varied 

over five settings. In both tests, the 

back-pressure was monitored by a 

pressure transducer also located in 

the exhaust duct. 

Because the microturbine was located 

outdoors, the microturbine’s air inlet 

temperature was dictated by outdoor 

conditions. 

4.1 	 CONSTANT POWER 

OUTPUT DEMAND 

Tests were conducted at various power 

output demands and microturbine 

back-pressures (damper at three different 

positions of fully open, 1/4 closed, and 

3/8 closed). At full power demand, the 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 11 
Federal Technology Alert 

Fig. 11. Experimental setup for baseline 

testing microturbine. 

(Source: “Experimental and Theoretical 

Study of Gas Micro-turbine-Based BCHP 

System,” Proceedings of the 2001 ASME 

International Mechanical Engineering 

Congress and Exposition, AES-23622, 

New York, NY, November 2001.) 

back pressure varied from 8.34 × 10–4 

atm to 1.8 × 10–2 atm (0.34 to 7.34 in. 

water column). During these tests, the 

microturbine’s controller adjusted the 

engine speed to match the power 

demand setting as closely as possible 

with or without the back-pressure. The 

results for damper at the full open and 

3/8 closed positions are presented in 

Tables 2 and 3, respectively. 

The turbine inlet air temperature is not 

controlled but dictated by ambient 

temperature and, as noted in Sect. 3.4, 

the turbine speed is increased to 

compensate for increases in ambient 

temperature. Therefore, the rpm increase 

observed between Tables 2 and 3 is 

dependent on both increased ambient 

temperature and increased backpressure. Since the engine speed could 

adjust and compensate for the back 

pressure and ambient temperature 

increases, the power output and 

efficiency at corresponding output power 

demands were not significantly affected. 

In order to show the reproducibility of 

the measured data, the tests with the 

damper fully open were repeated for the 

power demand setting of 20 kW. The 

observed relative power output and 

efficiency percentage differences were 

less than 0.3%. 

4.2 	 CONSTANT ENGINE SPEED 

Another series of tests were conducted 

while the microturbine was maintained 

at approximately constant engine speed 

and the back-pressure was varied for 

each nominal power output. Table 4 

shows the results at full power 

demand of 30 kW only. At the full 

power demand and approximately 

constant engine speed, as the back-pressure was increased from approximately 

8.00 × 10–4 to 1.72 × 10–2 atm (0.33 to 

6.99 in. water column), the average 

turbine efficiency dropped by less than 

2%, and the average turbine power 

output decreased by less than 6% of 

the values with damper fully open. 

5.	 HEAT RECOVERY 

AND 

CHP EFFICIENCY 

On-site distributed generation (DG), 

as part of an integrated energy system 

(IES), allows the waste heat from fuelfired DG sources to be used to meet 

the end user’s thermal loads and substantially improve overall system energy 

efficiency and fuel economy. As discussed 

in Sect. 1, the IES Test Laboratory at 

ORNL allows configuration of DG with 

various heat recovery units (presently an 

air-to-water HRU, direct- and indirectfired desiccant dehumidification systems, 

and an indirect-fired, single-effect 

absorption chiller) in order to test the 

Table 2. Capstone 30-kW microturbine with damper fully open (Ref. 3) 

. 

12–– FEDERAL ENERGY MANAGEMENT PROGRAM 
Federal Technology Alert 

Table 3. Capstone 30-kW microturbine with damper 3/8 open (Ref. 3) 

Table 4. Microturbine performance at constant speed and varying back-pressure (Ref. 3) 

component and overall IES performance. 

The following sections discuss results of 

tests performed at the ORNL IES 

Laboratory for configurations of a 

30-kW microturbine DG source, an 

HRU, and various thermally activated 

technologies. 

5.1	 AIR-TO-WATER HEAT 

EXCHANGER (e.g., HRU)

1,2 

Since all of the thermally activated 

technologies were tested with the HRU 

as a part of the IES, the first tests to be 

discussed are for the MTG and exhaustgas-driven, air-to-water heat exchanger 

HRU. These tests were performed to 

determine the quantity of MTG waste 

heat that could be recovered to generate hot water for space heating or use 

with other thermally activated technologies and to determine the IES (MTG + 

HRU) efficiency, both as a function of 

microturbine output power. The HRU 

water flow rate for this series of tests was 

4.3 m3/h (19 gpm), and the power 

output of the turbine was varied from 

10 to 30 kW in increments of 5 kW. 

The resulting recoverable waste heat was 

found to be ~23 kW (~75,000 Btu/h) 

with the microturbine at one-third 

power up to ~ 44 kW (or~150,000 

Btu/h) with the unit at full power as 

shown in Fig. 12. The measured exhaust 

flue gas temperature rejected to the 

atmosphere (leaving the heat exchanger) 

was ~127oC (260oF) at full power; 

however, at one-third power the exhaust 

temperature was ~93oC (200oF). 

Figure 13 shows a relatively constant 

measured IES system (measured CHP) 

efficiency of ~55% based on a higher 

heating value (HHV) for the natural gas 

over the microturbine’s power output 

range. For comparison purposes, the 

microturbine efficiency without heat 

recovery (microturbine), which ranges 

from approximately 18 to 24%, and the 

manufacturer’s data are also shown in 

Fig. 13. The test efficiency agreed well 

with the published performance data. 

5.2	 DESICCANT 

DEHUMIDIFICATION4,5 

Tests were conducted at the ORNL IES 

Laboratory Facility for IES configurations employing a commercially available 

direct-fired desiccant dehumidification 

FEDERAL ENERGY MANAGEMENT PROGRAM ––13 
Federal Technology Alert 

Fig. 12. Heat recovery by the HRU at a water flow rate of 4.3 m3/h (19 gpm). 

(Source: “Integration of Distributed Energy Resources and Thermally-Activated 

Technologies,” DistribuTech Conference, Miami Beach, FL, February 2002.) 

Fig. 13. IES system and microturbine: heat recovery efficiencies. (Source: “Integration of 

Distributed Energy Resources and Thermally-Activated Technologies,” DistribuTech 

Conference, Miami Beach, FL, February 2002.) 

unit and an indirect-fired (hot water) 

desiccant unit. Both configurations 

used the 30-kW microturbine as the 

DG source. These tests investigated the 

performance of the desiccant dehumidification units as one of the components 

of an IES. The desiccant unit performance parameters of most interest were 

the latent capacity (LC) and the latent 

coefficient of performance (LCOP). 

The LCOP is a measure of the desiccant 

dehumidification unit’s efficiency and is 

calculated as the ratio of the LC to the 

total energy input (thermal + electrical), 

including the gas input, which is based 

on HHV of the gas and electrical 

parasitics (desiccant wheel motor, fans, 

electronics, etc.). Both configurations 

are discussed in the following sections. 

5.2.1	 Direct-Fired Desiccant 

Dehumidification4,5 

A commercially available direct-fired 

desiccant dehumidification unit was 

used in this series of tests. Test conditions for the process and regenerative inlet dry bulb temperatures were 

maintained by 10- and 30-kW heaters, 

and the dew-point temperatures were 

maintained by injecting steam into the 

inlet sections of the process and 

regenerative air streams. 

Tests were performed for the baseline 

configuration, with regeneration air 

heated by direct burning of natural gas, 

and an IES configuration, where the 

exhaust gas from the microturbine was 

used as the regeneration energy source. 

In the IES configuration, the gas burner 

was deactivated. The exhaust gas was 

passed through the HRU to produce 

hot water prior to entering the desiccant 

unit regeneration inlet plenum. 

. 

14 –– FEDERAL ENERGY MANAGEMENT PROGRAM 
Federal Technology Alert 

Table 5. Comparison of manufacturer’s test data and laboratory results (Ref. 5) 

5.2.1.1 Baseline Configuration4,5 

In an attempt to verify that the laboratory-installed desiccant system’s performance was comparable with the manufacturer-supplied performance data, 

baseline configuration testing was performed prior to IES testing. The baseline 

desiccant unit airflow rates were found 

to be within the range of 76.5 m3/min 

to 80.7 m3/min (2,700 to 2,850 scfm) 

with a face velocity of 262.9 to 277.7 

m/min (862.6 to 911.2 ft/min) for the 

process side and 21.2 to 24.1 m3/min 

(750 to 850 scfm) for the regeneration 

side. Process air flow reported by the 

manufacturer was 68.0 to 70.8 m3/min 

(2,400 to 2,500 scfm)—slightly lower 

than the values observed during the 

tests. The electrical parasitic loads were 

measured to be between 5.6 and 5.8 kW. 

A comparison of the Integrated Test 

Facility test data with the manufacturer’s 

test data for the process air circuit is 

presented in Table 5. There was relatively 

good agreement between the laboratory 

baseline configuration and the manufacturer’s data for LC. The laboratory 

results for LC are within +1–5% and 

+13%, respectively, for the three 

test conditions. 

5.2.1.2 IES Configuration4,5 

The IES configuration consisted of a 

MTG with an HRU and DFDD in a 

series arrangement with respect to the 

MTG exhaust gas. As previously stated, 

the microturbine exhaust gas flowed 

through the HRU, where hot water was 

produced, then to the regeneration inlet 

plenum of the DFDD. 

The DFDD requires a regenerative air 

flow of 25.5 m3/min (900 scfm), and the 

microturbine’s exhaust flow rate of 14.2 

m3/min (500 scfm) was not adequate for 

this direct-fired desiccant unit. In order 

to provide the required regenerative air 

flow, the exhaust gas was mixed with 

outside air at the same conditions as the 

process inlet air. During these tests, the 

temperature of the turbine exhaust gas 

at the HRU outlet ranged from 122.8 to 

136.7oC (253 to 278oF). 

Because of ambient air temperatures 

and the microturbine being located 

outdoors, the turbine maximum power 

output was limited to 25 kW during the 

tests. Tabulated DFDD latent capacity 

results for two different microturbine 

outputs (20 kW and 25 kW) and the 

direct-fired baseline configuration at 

three different process/outside air inlet 

conditions are shown in Table 6. 

Increasing the power output by 25% 

from 20 to 25 kW results in an LC 

increase of 18 to 45%, depending on the 

process/outside air inlet conditions. The 

IES maximum LC was observed at the 

dry-/wet-bulb conditions of 29.4/24.3°C 

(85.0/75.8°F) and the minimum at 

26.7/19.7°C (80.0/67.4°F). The DFDD 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 15 
Federal Technology Alert 

unit LC at the maximum and minimum 

conditions with a microturbine power 

output of 25 kW is only 58 and 35% 

of the baseline direct-fired capacity. A 

microturbine with a minimum exhaust 

flow rate of at least 25.5 m3/min (900 

scfm) would not require mixing of 

exhaust gas with outside air and should 

yield better results from the desiccant 

dehumidification unit. 

To show the improvement in IES 

efficiency with utilization of the waste 

heat, the efficiencies of the MTG only, 

the MTG and HRU, and the total IES 

(MTG, HRU, and DFDD) at various 

power levels are shown in Fig. 14. The 

efficiencies for each configuration were 

determined by the ratio of the total 

energy output to the total energy input. 

For the IES configuration, the total 

energy output consisted of the electric 

power output generated by the MTG, 

the heat recovered by the HRU, and 

the LC of the desiccant dehumidification unit. 

The energy input included the gas input 

(based on the HHV of the gas) to the 

MTG and the electrical parasitics (all 

the power used by the fans, pumps, and 

electronics of the MTG, desiccant, and 

HRU units). 

Addition of the DFDD to the MTG 

and HRU configuration resulted in 

increased overall IES efficiency at all 

power levels with higher IES efficiencies 

and efficiency increments at higher kW 

output. Specifically, the IES efficiency 

increased by 7% from approximately 

53% to 60% with addition of the 

DFDD (based on the HHV of the 

natural gas) at 25 kW (85,361 Btu/h) 

MTG power output.5 

5.2.2	 Indirect-Fired Desiccant 

Dehumidification System4 

An IES configuration consisting of the 

MTG, HRU, and the IFDD was tested 

at the IES laboratory facility to determine the effects of power output of the 

MTG on the LC and latent LCOP of 

the IFDD, as well as on the overall IES 

efficiency. In this configuration, the 

regeneration heat source was a hot water 

loop interfacing with a heating coil in 

the IFDD. Heat is transferred to the 

water loop from the MTG exhaust 

through the HRU. 

The maximum water loop flow rate 

through the HRU was ~5.8 m3/h 

(~26 gpm) with a maximum hot water 

temperature of ~91oC (~196oF). The 

actual temperature depends on several 

parameters such as MTG output, 

Table 6. 

Latent capacity test 


results (IES-based 


operation) (Ref. 5)


. 

16 –– FEDERAL ENERGY MANAGEMENT PROGRAM 
Federal Technology Alert 

ambient temperature, and HRU water 

flow rate. The turbine exhaust gas was 

at a temperature of ~275oC (~527oF) 

entering the HRU and ~124oC 

(~255oF) leaving the HRU. 

The ratio of the IFDD LC to the total 

energy input is the LCOP. The total 

energy input to the IFDD includes the 

HRU input on the regeneration heating 

coil side and electrical parasitics, such 

as the energy use of the desiccant wheel 

motor, fans, and electronics. The overall 

IES efficiency is defined as the ratio of 

the sum of the net electric power output 

of the MTG and the LC of the IFDD to 

the total energy input. The net electrical 

power output of the MTG consists of 

the total power generated by the MTG 

minus the auxiliary power consumed by 

the IES. The total energy input to the 

IES includes the gas input to the MTG 

(based on the higher heating value or 

HHV of natural gas) and the electrical 

parasitics (all the power used by the fans, 

pumps, and electronics of the MTG, 

HRU, and IFDD). 

The test results reported were for MTG 

net power output varying from 10 to 25 

kW. The upper limit was again constrained by ambient conditions. Other 

test parameters included HRU flow rate 

of ~5.8 m3/h (~26 gpm), IFDD dry-/ 

wet-bulb temperature at process and regeneration inlet of 35oC/24oC (95oF/ 

75oF), process/regeneration air flow rate 

of 76.5 m3/min (2,700 scfm) and IFDD 

desiccant wheel speed of 58 rph.

6 

The LC and LCOP as a function of 

the MTG power output is shown in 

Fig. 15.

6 

The results indicate that the LC of the 

IFDD increases with an increase in the 

MTG output. An increase in MTG 

output from 10 to 25 kW resulted in an 

increase in the observed LC from 

~11.1 kW to ~18.8 kW (~38,000 Btu/h 

to ~64,000 Btu/h). 

The LCOP was observed to increase 

from a minimum of ~46% at a power 

output of 10 kW to a maximum of 

~54% at a power outputs of 15 and 20 

kW and decreased to ~51% at a power 

output of 25 kW. The decrease in LCOP 

at 25 kW is attributed to the impact of 

ambient temperature on the operating 

parameters of the MTG and the heat 

recovery equipment, as discussed in Sect. 

3.4. These test runs were performed 

at ambient temperatures ranging from 

25oC to 30oC (77oF to 86oF). 

The effect of the MTG output on the 

overall IES efficiency is shown in Fig. 

16. For comparison, Fig. 16 also shows 

the effect of the MTG output on the 

individual unit’s efficiency and the 

combined MTG and HRU efficiency. 

The combined MTG and HRU 

efficiency is the efficiency of the IES 

without the IFDD.

6 

Regarding the efficiencies, the effect of 

power output is much less pronounced 

than with the LCOP. After an MTG 

output of 20 kW, the IES efficiencies 

start to fall. 

Analysis of Fig. 16 shows that the 

addition of the IFDD to the IES 

system does not increase its overall 

efficiency: it drops from 53% (MTG + 

HRU system) to 34% (MTG + HRU + 

IFDD system). The drop in efficiency is 

believed to be due to the parasitic losses 

in the IFDD. 

5.3 ABSORPTION CHILLER6 

A series of tests were performed on 

an IES configuration consisting of an 

MTG, an air-to-water HRU, and a 

single-effect lithium-bromide/water 

(LiBr/water) absorption chiller (ABSC). 

In this arrangement, the MTG’s 

exhaust gas passes through the HRU, 

generating hot water that is directed to 

the AC’s generator. When the MTG 

is located outdoors, as in this case, 

Fig. 14. Efficiencies of microturbine (MTG) and IES. (Source: “CHP Integration (OR IES): 

Maximizing the Efficiency of Distributed Generation with Waste Heat Recovery,” 

Proceedings of the Power Systems 2003 Conference, Clemson, SC, March 2003.) 

FEDERAL ENERGY MANAGEMENT PROGRAM –– 17 
Federal Technology Alert 

ambient temperature can be a major 

factor in the performance when no 

attempt is made to adjust the inlet air 

temperature (i.e., air cooling to maintain 

a constant or lowered inlet air temperature during extremely hot weather). 

Higher ambient turbine inlet air 

temperatures result in lower MTG 

efficiency, higher exhaust temperatures, 

higher exhaust heat available for 

recovery, and higher heat input to 

the ABSC unit, resulting in better 

ABSC unit and IES performance. The 

following sections present the results 

from tests performed to quantify the 

effect of ambient air temperature on 

ABSC unit capacity, COP, and IES 

efficiency. 

An MTG power output setting of 

20 kW was selected for this series of 

tests. This power setting was achievable 

over the entire wide range of ambient 

temperatures experienced during the 

tests, 17.2 to 30oC (63 to 86oF). The 

hot water flow rate from the HRU and 

cooling water flow rate from the cooling 

tower were 0.15 m3/min (39.8 gpm) 

and 0.28 m3/min (74 gpm), respectively. 

Results will be presented for evaporator 

chilled water flow rates of 0.07 and 

0.13 m3/min (19 and 34 gpm). 

5.3.1	 Effect of Ambient 

Temperature on 

Absorption Chiller 

Capacity and COP6 

The heat input required to drive the 

ABSC at the full rated load of 35 kW 

(120,000 Btu/h) of cooling is ~50 kW 

(172,000 Btu/h). During testing, the 

maximum heating capacity produced 

by the MTG + HRU, due to the design 

features of the HRU and MTG output 

power setting of 20 kW, was only ~37.9 

Fig. 15. Effect of power output on latent capacity. (Source: “CHP Integration (OR IES): 

Maximizing the Efficiency of Distributed Generation with Waste Heat Recovery,” 

Proceedings of the Power Systems 2003 Conference, Clemson, SC, March 2003.) 

Fig. 16. Effect of power output on efficiency. (Source: “CHP Integration (OR IES): 

Maximizing the Efficiency of Distributed Generation with Waste Heat Recovery,” 

Proceedings of the Power Systems 2003 Conference, Clemson, SC, March 2003.) 

to 40.8 kW (130,000 to 140,000 The effect of ambient temperature on 

Btu/h). Therefore, at a constant MTG the ABSC cooling capacity (Qchw) is 

power output setting of 20 kW, the shown in Fig. 17 for the two chilledABSC unit could only be driven to water flow rates (Gchw) that were tested. 

~82% of its full rated load. 

. 

18–– FEDERAL ENERGY MANAGEMENT PROGRAM 
Federal Technology Alert 

Based on the increased heat available for 

input to the ABSC unit with increased 

ambient temperature, the ABSC unit 

cooling capacity (Qchw) increase was 

observed to be nearly linear with 

ambient temperature from ~19 kW 

(65,000 Btu/h) at 17.2oC (63oF) to 

over 26 kW (90,000 Btu/h) at 30oC 

(86oF) for a Gchw of 19 gpm. At a 

Gchw of 34 gpm the cooling capacity (Qchw) increase was from ~21 kW 

(71,000 Btu/h) at 17.2oC (63oF) to 

~27 kW (92,000 Btu/h) at 30oC (86oF). 

General observations that can be drawn 

from the test results are that cooling 

capacity increases with ambient temperature at rates of 1.24% per degree F at a 

chilled water flow rate of 0.07 m3/min 

(19 gpm) and 1.6% per degree F at a 

chilled water flow rate of 0.13 m3/min 

(34 gpm), and cooling capacity increase 

ranges from 0.77 %/gpm to 2.11%/ 

gpm when the Gchw increases from 

19 gpm to 34 gpm. 

The COP of the ABSC was defined 

as the ratio of ABSC cooling capacity, 

Qchw, to QHRU (AC), the heat 

supplied by the HRU at the ABSC 

inlet. Use of the heat supplied at the 

ABSC inlet takes into account the losses 

in the hot water loop from the HRU to 

the AC. 

The effect of ambient temperature on 

the coefficient of performance (COP) 

of the ABSC is shown in Fig. 18. 

The COP increased with ambient temperature from ~57 to ~72% (~0.65% 

per degree F) at the chilled water flow 

rate of 0.07 m3/min (19 gpm) and from 

~62 to ~75% (~0.57% per degree F) 

at the chilled water flow rate of 0.13 

m3/min (34 gpm). Increasing the chilled 

Fig. 17. Effect of ambient 

temperature on cooling 

capacity. (Source: “Laboratory R&D on Integrated 

Energy Systems 

(IES),” Proceedings of 

the 2003 International 

Congress of Refrigeration, 

ICR2003,Washington, DC, 

August 2003.) 

water flow rate from 0.07 to 0.13 m3/ 

min (19 to 34 gpm) resulted in COP 

increases ranging from 2 to 5% (0.133 

to 0.33% per gpm). The increased COP 

with increased chilled water flow rate 

was calculated without consideration 

of the increased parasitics required to 

achieve the higher water flow rate. 

5.3.2	 Effect of Ambient 

Temperature on IES 

Configuration Efficiency6 

The effect of ambient temperature on 

the efficiency of IES MTG + HRU + 

ABSC configuration is shown in 

Fig. 19. Also shown in Fig. 19, for 

comparison, are the efficiencies of 

various combinations of the MTG, 

HRU, and ABSC components. The 

combinations include MTG (producing 

electric power only), MTG + HRU 

Fig. 18. Effect of 

ambient temperature 

on the COP of the 

absorption chiller. 

(Source: “Laboratory 

R&D on Integrated 

Energy Systems 

(IES),” Proceedings 

of the 2003 International Congress 

of Refrigeration, 

ICR2003,Washington, 

DC, August 2003.) 

(producing electric power and heating), 

and MTG + HRU + ABSC (producing 

electric power and cooling). 

All of the efficiencies, defined as the 

ratio of the energy output to the energy 

input, presented in Fig. 19 are based 

on the HHV of natural gas. When 

calculating the MTG efficiency, the 

energy output consisted of the net 

electric power generated by the MTG, 

and the energy input was the natural 

gas input. The energy input and output 

for the IES configuration of the MTG 

and HRU were the net electric power 

generated by the MTG plus the heat 

recovered by the HRU and natural gas 

input plus the electric power consumed 

by the HRU including the booster 

pump. For the overall IES configuration 

of the MTG, HRU, and AC, the energy 

output consisted of the net electric 

FEDERAL ENERGY MANAGEMENT PROGRAM ––19 
Federal Technology Alert 

power generated by the MTG plus the 

ABSC cooling capacity, and the energy 

input consisted of the natural gas input 

plus the total electric power consumed 

by the HRU, AC, CT, and pumps. 

Tests were performed for chilled water 

flow rates of 0.07 and 0.13 m3/min 

(19 and 34 gpm). The variation in the 

chilled water flow rate had practically 

no effect (only a 0.5 to 0.8% average 

increase) on the overall IES efficiency. 

Therefore, the efficiency versus ambient 

temperature for only one flow rate is 

presented in Fig. 19. 

In spite of a decrease in MTG efficiency 

(20–18%) with ambient temperature, 

the two IES configuration overall 

efficiencies increased with ambient 

temperature. The MTG + HRU 

configuration showed an efficiency 

range of 53 to 55% over the ambient 

temperatures experienced during the 

test while the MTG + HRU + ABSC 

configuration yielded an efficiency range 

of 37 to 42%. 

Addition of the ABSC to the MTG 

+ HRU configuration resulted in a 

decrease in IES efficiency ranging from 

16 to 13%, indicating, as expected, that 

using the waste heat to generate hot 

water for end use is more efficient than 

generating hot water for use to drive a 

single-effect absorption ABSC unit with 

a nominal COP of 0.7. 

5.4	 ABSORPTION CHILLER AND 

DIRECT-FIRED DESICCANT 

DEHUMIDIFICATION6 

In the previous IES configuration 

(MTG + HRU + AC) the temperature 

of the exhaust gas leaving the HRU and 

discharging to the environment is in 

many cases sufficient for use in 

regenerating the desiccant in a DFDD. 

Addition of a DFDD to this configuration will increase the utilization of the 

MTG waste heat and the efficiency of 

the IES. A series of tests were performed 

to compare a MTG + HRU + ABSC + 

DFDD configuration with the 

previously tested configurations. 

The LC and LCOP of the DFDD 

increase with an increase in process air 

dew-point or humidity ratio. Therefore, 

the series of tests were performed at the 

two DFDD process inlet dry-/wet-bulb 

temperature conditions of 29.4/24.3oC 

(85/75.8oF) and 35.0/23.9oC 

(95/75oF). The corresponding dewpoint conditions were 22.4oC (72.4oF) 

and 19.2oC (66.5oF), respectively. At 

both inlet process air conditions, MTG 

power output, hot water, cooling water, 

and chilled water flow rates were held 

approximately constant at the measured 

conditions listed in Table 7. 

Also listed in Table 7 are the major 

performance parameters (i.e., HRU heat 

capacity, ABSC cooling capacity, and 

DFDD latent capacity) measured at the 

two process air conditions. As seen in 

Table 7, the LC of the DFDD for the 

22.4oC dew-point condition was much 

higher than that for the 19.2oC 

dew-point inlet air. 

Fig. 19. Effect of 

ambient temperature 

on the efficiency of 

IES configurations. 

(Source: “Laboratory 

R&D on Integrated 

Energy Systems (IES),” 

Proceedings of the 

2003 International 

Congress of 

Refrigeration, 

ICR2003, Washington, 

DC, August 2003.) 

The MTG exhaust flow rate, ranging 

from 11.33 to 4.16 m3/min (400 to 

500 scfm), passed through the HRU and 

entered the regeneration inlet plenum 

of the DFDD. In the regenerative inlet 

plenum, in order to achieve a required 

regenerative stream air flow of 

25.5 m3/min (~900 scfm), the MTG 

exhaust flow was mixed with outside air. 

The DFDD’s air flow rates, measured 

during the tests, were found to be within 

the range of 92.60 to 94.58 m3/min 

(3,270 to 3,340 scfm) with a face 

velocity of 318.4–325.3 m/min 

(1,044.7–1,067.1 ft/min) for the 

process side and 25.63–25.77 m3/min 

(905–910 scfm) with a face velocity of 

88.1–88.6 m/min (289.1–290.7 ft/min) 

for the regeneration side. 

The overall IES efficiency with the 

addition of the DFDD calculated as 

the ratio of the energy output and the 

energy input was determined for the two 

process-air inlet conditions. The energy 

output consisted of net electric power 

generated, the ABSC cooling capacity, 

and the DFDD latent capacity; the 

energy input included the natural gas 

input and the total electric power consumed by the HRU, AC, DFDD, CT, 

and pumps. The efficiencies of 

the MTG, MTG + HRU, and MTG + 

. 

20–– FEDERAL ENERGY MANAGEMENT PROGRAM 
Federal Technology Alert 

Table 7. Measured performance parameters of the IES with the desiccant dehumidifier 

HRU + ABSC IES configurations were 

calculated as described in Sect. 5.3.2. 

Figure 20 shows the different IES 

configuration efficiencies for the two 

dry-/wet-bulb conditions. The addition 

of the DFDD to the MTG + HRU + 

ABSC configuration increases the overall 

IES efficiency by 5–7%. The IES 

efficiency with the DFDD decreases 

with a decrease in dry-/wet-bulb temperatures (dew-point and humidity ratio), 

with all other parameters constant. The 

(MTG + HRU + ABSC + DFDD) 

configuration’s overall efficiency is still 

less than the MT + HRU configuration. 

6.	 EMISSION TESTS7 

The objective of the series of emission 

tests was to study the emissions levels 

under varying electric loads and microturbine inlet air conditions. The CHP 

system configuration used for the emissions tests consisted of the 30-kW-rated 

natural-gas-fired microturbine and the 

air-to-water HRU. The emissions data 

was obtained with the microturbine 

operating over a wide range of power 

outputs at different ambient temperatures. The basic results are shown in 

Figs. 21–23 and are discussed in the 

following sections. 

Fig. 20. Efficiencies of IES configurations at various dry-/wet-bulb conditions. 

(Source: “Laboratory R&D on Integrated Energy Systems (IES),” Proceedings of the 

2003 International Congress of Refrigeration, ICR2003, Washington, DC, August 2003.) 

6.1	 EFFECT OF MICROTURBINE 

POWER OUTPUT ON 

EMISSIONS RATE7 

During the steady-state emissions tests, 

microturbine power outputs ranged 

from one-third to full power (10–28 kW) 

in 1-kW increments. The full-power 

output of the microturbine is 30 kW; 

however, approximately 2 kW is 

auxiliary power consumed by the 

microturbine. 

Figures 21 and 22 present the CO, 

NOx, and SO2 emissions at the 

various power outputs in parts per 

million volume (ppmV) corrected to 

15% O2 (ppmV15) and converted to 

mg/m3. Concentrations of ~36 ppmV15 

(41 mg/m3) CO, ~4 ppmV15 (8 mg/m3) 

NOx, and ~0.6 ppmV15 (1.5 mg/m3) 

SO2 were observed at full power output 

(28 kW). 

As the power output decreases, the 

concentration of these pollutants 

changes significantly. The trends of 

the CO and SO concentrations were 2

similar—both containing two peaks 

occurring at ~16 kW and 20 kW, while 

the minimum concentrations were 

observed to occur at full power output 

(28 kW). At a power output of ~15 kW, 

the maximum NO concentration x

FEDERAL ENERGY MANAGEMENT PROGRAM –– 21 
Federal Technology Alert 

occurred. In order to minimize 6.2 EFFECT OF MICROTURBINE 

emissions, a microturbine-based INLET AIR ON EMISSIONS 

CHPsystem should be sized for and RATE7 

operated as close to full power output 

as possible. Special tests were performed at MTG 

power output settings of 25 and 30 kW 

to study the effect of microturbine air 

Fig. 21. Concentration of CO, 

NOx, and SO2 (ppmV15) vs 

microturbine power output. 

(Source: “Environmental 

Aspects of Operation of a 

Gas-Fired MicroturbineBased CHP System,” 

Proceedings of the 19th 

Annual International 

Pittsburgh Coal Conference, 

Pittsburgh, PA, 

September 2002.) 

Fig. 22. Concentration of 

CO, NOx, and SO2 (mg/m3) 

vs power output. (Source: 

“Environmental Aspects of 

Operation of a Gas-Fired 

Microturbine-Based CHP 

System,” Proceedings of the 

19th Annual International 

Pittsburgh Coal Conference, 

Pittsburgh, PA, 

September 2002.) 

inlet temperature on the emissions rate 

of the microturbine-based CHP system. 

In this test, the air inlet temperature and 

ambient temperature varied throughout 

the day and from day to day and season 

to season, depending on weather conditions. The other parameters remained 

. 

22 –– FEDERAL ENERGY MANAGEMENT PROGRAM 
Federal Technology Alert 

Fig. 23. CO concentration vs air inlet 

temperature at 25- and 30-kW power 

output settings. 

(Source: “Environmental Aspects 

of Operation of a Gas-Fired 

Microturbine-Based CHP System,” 

Proceedings of the 19th Annual 

International Pittsburgh Coal 

Conference, Pittsburgh, PA, 

September 2002.) 

constant during the tests. The only 

flue gas pollutant significantly affected by a change in microturbine 

air inlet temperature was CO. As 

shown in Fig. 23, at both 25- and 

30-kW power output, the CO 

concentration levels decreased with 

higher air inlet temperatures. 

7.	 THE TECHNOLOGY 

IN PERSPECTIVE 

The major benefits of a DER/CHP are 

(1) local control of power generation, 

(2) efficient use of waste heat, 

(3) increased overall efficiency, and 

(4) a reduction in emissions. 

Local power generation applications 

include continuous power generation, 

remote power generation for facilities 

isolated from the grid, cogeneration, 

provision of a peaking operation to 

reduce purchase of electricity during 

high-price periods, and provision of 

electrical service at a high level of 

reliability and quality. 

Technologies that can be driven by the 

DER waste heat in a CHP system 

include (1) chillers and desiccant 

dehumidifiers for space cooling and 

dehumidification, (2) steam generators 

for space heating, and (3) heat exchangers for process and domestic hot water. 

These CHP systems can maximize 

energy efficiency, provide an option for 

central power generation, and improve 

electric power reliability and quality. 

FEDERAL ENERGY MANAGEMENT PROGRAM ––23 
92

William Lintner

New Technology Demonstration

 Program Manager

Federal Energy Management 

 Program

U,S. Department of Energy

1000 Independence Ave, SW, EEWashington, DC 20585

Phone: (202) 586-3120

Fax: (202) 586-3000

william.lintner@ee.doe.gov

Steven A. Parker

Pacific Northwest National

 Laboratory

P.O. Box 999, MSIN: K5-08

Richland, WA 99352

Phone: (509) 375-6366

Fax: (509) 375-3614

steven.parker@pnl.gov

Technical Contact

Michael Kintner-Meyer

Pacific Northwest National

Laboratory

P.O. Box 999, MSIN: K5-08

Richland, WA 99352

Phone: (509) 375-4306

Fax: (509) 375-3614

Michael.Kintner Meyer@pnl.gov

Produced for the U.S. Department

of Energy, Energy Efficiency and

Renewable Energy, by the Pacific

Northwest National Laboratory

DOE/EE-0000

xxxx 2006 

General Contacts

8. REFERENCES 

1.	 “DER Performance Testing of a Microturbine-Based Combined Cooling, Heating, 

and Power (CHP) System,” Proceedings of Power System 2002 Conference, 

Clemson, SC, March 2002. 

2.	 “Integration of Distributed Energy Resources and Thermally-Activated 

Technologies,” DistribuTech Conference, Miami Beach, FL, February 2002. 

3.	 “Experimental and Theoretical Study of Gas Micro-turbine-Based BCHP System,” 

Proceedings of the 2001 ASME International Mechanical Engineering Congress 

and Exposition, AES-23622, New York, NY, November 2001. 

4.	 “CHP Integration (OR IES): Maximizing the Efficiency of Distributed 

Generation with Waste Heat Recovery,” Proceedings of the Power Systems 2003 

Conference, Clemson, SC, March 2003. 

5.	 “Baseline and IES Performance of a Direct-Fired Desiccant Dehumidification Unit 

under Various Environmental Conditions,” 2003 ASHRAE Transactions of the 

Annual Meeting, KC-03-5-2, Kansas City, MI, June 2003. 

6.	 “Laboratory R&D on Integrated Energy Systems (IES),” Proceedings of the 

2003 International Congress of Refrigeration, ICR2003, Washington, DC, 

August 2003. 

7.	 “Environmental Aspects of Operation of a Gas-Fired Microturbine-Based CHP 

System,” Proceedings of the 19th Annual International Pittsburgh Coal Conference, 

Pittsburgh, PA, September 2002. 

8.	 ASHRAE Handbook, Refrigeration 2002, Chapter 41, “Absorption Cooling, 

Heating, and Refrigeration Equipment. 

Log on to FEMP’s Web site for information about New Technology Demonstrations 

www.eere.energy.gov/femp/ 

You will find links to 

• A New Technology Demonstration Overview 

• Information on technology demonstrations 

• Downloadable versions of publications in Adobe Portable Document Format (pdf) 

• A list of new technology projects under way 

• Electronic access to a regular mailing list for new products when they become available 

• How Federal agencies may submit requests to us to assess new and emerging technologies 

DISCLAIMER 

This report was sponsored by the United States Department of Energy, Energy Efficiency and Renewable Energy, 

Federal Energy Management Program. Neither the United States Government nor any agency or contractor 

thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or 

responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process 

disclosed, or representsthat its use would not infringe privately owned rights. Reference herein to any specific 

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A Strong Energy Portfolio 

for a Strong America 

Energy efficiency and clean, renewable 

energy will mean a stronger economy, 

cleaner environment, and greater 

energy independence for America. 

Working with a wide array of state, 

community, industry, and university 

partners, the U.S. Department of 

Energy’s Office of Energy Efficiency 

and Renewable Energy invests in a 

diverse portfolio of energy technologies. 

For More Information 

EERE Information Center 

1-877-EERE-INF 

1-877-337-3464 

www.eere.energy.gov/femp 

General Contacts 

Will Lintner 

Team Lead, RSTT 

Federal Energy 

Management Program 

U.S. Department of Energy 

1000 Independence Ave, SW 

EE-92 

Washington, DC 20585 

Phone: (202) 586-3120 

Fax: (202) 586-3000 

william.lintner@ee.doe.gov 

Technical Author 

Ed Pierce 

Oak Ridge National Laboratory 

(865) 574-6369 

piercefejr@ornl.gov 

-

DOE/EE-0316 

May 2007 

U.S. Department of Energy 

No portion of this publication may be altered in any form without Energy Efficiency prior written consent from the U.S. Department of Energy, Energy and Renewable Energy Efficiency and Renewable Energy, and the authoring national laboratory.