Seminar 14 – Desiccant Enhanced Air Conditioning
Desiccant Enhanced Evaporative Air Conditioning
Eric Kozubal, Sr. Mechanical EngineerNational Renewable Energy Laboratory
[email protected]‐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 [email protected]