Seminar 14 – Desiccant Enhanced Air Conditioning

Desiccant Enhanced Evaporative Air Conditioning

Eric Kozubal, Sr. Mechanical EngineerNational Renewable Energy Laboratory

Eric.Kozubal@nrel.gov303‐384‐6155NREL/PR‐5500‐57624

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Learning Objectives

• Explains how liquid desiccant based coupled with an indirect evaporative cooler can efficiently produce cool, dry air.

• Explains how a liquid desiccant membrane air conditioner can efficiently provide cooling and dehumidification without the carryover problems of previous generations of liquid desiccant systems.

• Provides an overview to a liquid desiccant DX air conditioner that can efficiently provide cooling and dehumidification to high latent loads without the need for reheat.

• Explains how liquid desiccant cooling and dehumidification systems can outperform vapor compression based air conditioning systems in hot and humid climates

• Explains how liquid desiccant cooling and dehumidification systems work. • Describes a refrigerant free liquid desiccant based cooling system.

ASHRAE is a Registered Provider with The American Institute of Architects Continuing Education Systems.  Credit earned on completion of this program will be reported to ASHRAE Records for AIA members.  Certificates of Completion for non‐AIA 

members are available on request.

This program is registered with the AIA/ASHRAE for continuing professional education.  As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.  Questions related to specific 

materials, methods, and services will be addressed at the conclusion of this presentation.

Agenda for Session

Technical description

Benefits

Laboratory testing

“Desiccant Enhanced Evaporative” (DEVAP) Air Conditioning

Desiccants:WARM / DRY air

Indirect evaporative cooling:

COOL / Dry air

What Problems Does DEVAP Air Conditioning Address?

Vapor compression: Uses a lot of energy

In the US, ~15% of annual electric generation 1

Major contributor to peak power up to 50% in western states 2

Often inefficient at humidity control

Uses environmentally harmful refrigerants

1. DOE Buildings Energy Data Book ‐ http://buildingsdatabook.eren.doe.gov/2. Western Cooling Efficiency Center – http://wcec.ucdavis.edu3. http://en.wikipedia.org/wiki/File:Big_Bend_Power_Station.jpg

Credit: Wikipedia user Wknight94 3

Sensible and Humidity Control with Vapor Compression

Reheat required for lower SHRs

Apparatus dew point

0.000

0.005

0.010

0.015

0.020

0.025

30 40 50 60 70 80 90 100 110 120

(lb

/lb)

Dry Bulb Temperature (F)

Psychrometric Chart at 0 ft Elevation (14.7 psia)

Comfort Zone (Summer)

Room or Return Air

DEVAP Cooling Process (Using Liquid Desiccants)

DEVAP Heat and Mass Exchangers

Outdoor Air

Return AirSupply Air

Exhaust Air Exhaust Air

Membrane Contained Liquid Desiccant

dry airmoist air

plastic sheetdesiccant filmdesiccant film

Membrane(>70% open area)

absorption

SEM photograph of a micro porous membrane (Photo used with permission from Celgard, LLC) 

Dehumidifier Fluid Flows (In one channel pair)

return + outdoor air

warm, dry air

humid exhaust air

desiccant

wateroutdoor air

absorption

evaporation

1

34

1.5

heat flow

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

50 55 60 65 70 75 80 85 90 95 100

Hum

idity

ratio

(lb/

lb)

Dry Bulb Temperature (oF)

Psychrometric Chart at 12 psia

1

2

3

1.5

4

5

RA

DEVAP Cooling Process

21

3

4 5

1.5

OA

Heat and Mass Exchangers for Desiccant Regeneration

outdoor air

Credit: Andrew LowensteinCredit: Andrew Lowenstein

DEVAP System Diagram

DEVAP conditioner

Heat

Liquid desiccant storage Regenerator

Electricity (fans and small liquid pumps) < 0.2 kW/ton

Thermal Energy (natural gas, waste, or solar heat)depends on latent load

Annual / Hourly Commercial Building Energy Simulation - Phoenix, AZ

(Using a 2-stage regenerator & natural gas as thermal source)

EnergyPlus used to generate loads with a small office benchmark building model (10,000 sqft)

DEVAP simulation follows hourly sensible and latent loads

Model Estimate:40%-80% Source Energy Savings

Note: DEVAP a/c model matches hourly sensible and latent cooling from E-Plus “small office benchmark” simulation. Results for different building types will vary.

(hot/humid climate) (hot/dry climate)

Electric

Nat. gas

ElectricNat. gas

Model Estimate:80% Peak Electric Demand Savings

Note: DEVAP a/c model matches hourly sensible and latent cooling from E-Plus “small office benchmark” simulation. Results for different building types will vary.

(hot/humid climate) (hot/dry climate)

Laboratory Testing (Fall 2011)

Credit:  Warren Gretz

Prototype Unit #1

First Stage

Second Stage

Credit: Andrew Lowenstein

Credit: Andrew Lowenstein

Prototype Unit #2

First Stage

Second Stage

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

40 50 60 70 80 90 100 110

(lb

/lb)

Dry Bulb Temperature (F)

Psychrometric Chart at 82 kPa

AHRI conditions (1st Stage Only)

13

4

1.5

liquid desiccant equilibriumliquid desiccant equilibrium

Psychrometric chart at 12 psia

Unit #1Unit #2

Lab test Model

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

40 50 60 70 80 90 100 110

(lb

/lb)

Dry Bulb Temperature (F)

Psychrometric Chart at 82 kPa

AHRI conditions (2nd Stage Only)

1.52

5

Psychrometric chart at 12 psia

Unit #1Lab test Model

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

40 50 60 70 80 90 100 110

(lb

/lb)

Dry Bulb Temperature (F)

Psychrometric Chart at 82 kPa

AHRI conditions

1

2

5

3

4

Psychrometric chart at 12 psia

Unit #1Lab test Model

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

40 50 60 70 80 90 100 110

(lb

/lb)

Dry Bulb Temperature (F)

Psychrometric Chart at 82 kPa

Rainy Day:High Latent, Low Sensible

1

2

5

3

4

Psychrometric chart at 12 psia

Unit #1Lab test Model

SHR = 0.25

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

40 50 60 70 80 90 100 110

(lb

/lb)

Dry Bulb Temperature (F)

Psychrometric Chart at 82 kPa

Hot-dryHigh Sensible, Low Latent

1.5

2

5

Psychrometric chart at 12 psia

Unit #1Lab test Model

Wet Bulb Effectiveness = 128%

Benefits: Desiccant Enhanced Evaporative Air Conditioning

• Estimated savings (commercial buildings):– 40%-80% energy– 80% peak power

• Controls temperature and humidity separately

• No harmful refrigerants• Natural gas or waste heat

Bibliography

• Information at: www.nrel.gov/publications

Search keyword: Desiccant Enhanced Evaporative

Acknowledgements

• Department of Energy: – Tony Bouza, Alexis Abramson, Colin McCormick

• AIL Research: – Andy Lowenstein

• Synapse Product Development: – Dylan Garrett, Ian Graves, and Redwood Stephens

• University of Colorado: – John Pellegrino and Michael Brandemuehl

• NREL– Jason Woods, Ron Judkoff, Michael Deru, Jay Burch, Paul

Torcellini, Ren Anderson

Unless otherwise indicated, all photos and figures were created by NREL staff: Eric Kozubal, Jason Woods, NREL photographers or NREL graphic artists

Questions?

Eric KozubalEric.Kozubal@nrel.gov