ASHRAE Rocky Mountain Chapter
Evaporative Cooling
Rick Phillips, P.E., LEED AP
Senior Mechanical Engineer
The RMH Group, Inc.
May 2, 2014
1
Fundamentals
Dry Bulb
Temperature
Wet Bulb
Temperature
Evaporation
Wet Bulb Depression = DB – WB
Design Day in Denver 93° DB, 59° WB
2
Direct Evaporative Cooler
3
Media
4
Performance
Cooling
EDB – LDB
Effectiveness =
EDB – EWB
(%)
5
Indirect Evaporative Cooling
6
Hybrid Indirect Evaporative Cooler with
Energy Recovery
(Could be DEC)
(Used as IEC)
7
Psychrometrics
DIRECT
INDIRECT
INDIRECT / DIRECT
8
Direct Evaporative Cooling Pad Performance
OA DB
RANGE
95-99
90-94
85-89
80-84
75-79
70-74
65-69
60-64
55-59
MCWB
60
59
58
57
55
54
52
50
47
HOURS/
YEAR
3
118
235
348
390
472
697
699
762
4" PAD
8" PAD
12" PAD FINAL RM COND (74 DB)
LAT (DB)
LAT (DB)
LAT (DB)
(WB)
(%RH)
77.4
67.6
64.1
63.05
57.3
74.5
65.8
62.6
62.65
55.9
71.6
63.9
61.2
62.13
54.1
68.8
62.1
59.8
61.59
52.3
65.3
59.5
57.4
60.64
49.2
62.5
57.7
56.0
60.09
47.4
59.1
55.1
53.7
59.1
44.2
55.6
52.5
51.3
58.23
41.5
51.7
49.1
48.1
56.75
36.9
 Bin weather data, Denver, CO
 Doesn’t include fan temperature rise
9
Indirect/Direct Evaporative Cooling
System Performance
OA DB
RANGE
95-99
90-94
85-89
80-84
75-79
70-74
65-69
60-64
55-59
MCWB
60
59
58
57
55
54
52
50
47
HOURS/ INDIRECT
YEAR
LAT (DB)
3
74.4
118
71.9
235
69.3
348
66.8
390
63.6
472
61.0
697
57.9
699
54.7
762
50.9
INDIRECT
4" PAD
LAT (WB)
LAT (DB)
52.13
62.6
51.86
61.3
51.71
60.0
51.43
58.6
50.01
56.4
49.85
55.1
48.43
52.9
47.11
50.7
44.35
47.4
8" PAD
LAT (DB)
56.7
56.0
55.3
54.6
52.8
52.1
50.4
48.7
45.7
12" PAD FINAL RM COND (74 DB)
LAT (DB)
(WB)
(%RH)
54.6
58.96
43.7
54.1
58.96
43.7
53.6
58.96
43.7
53.1
58.81
43.3
51.5
58.23
41.5
51.1
58.23
41.5
49.5
57.50
39.2
47.9
56.90
37.4
45.1
55.68
33.7
 Bin weather data, Denver, CO
 Doesn’t include fan temperature rise
10
Typical Meteorological Weather Data (TMY2)
 Hourly weather data for a typical
year (not averaged)
– Includes typical extreme weather
conditions
 Database includes conditions like
this:
– 78°F DB, 66°F WB
•
Under these conditions, direct
evaporative cooling does not
perform well.
12” PAD (LAT)
67°F DB
Final Room Conditions
74°F DB, 76% RH
11
Typical Meteorological Weather Data (TMY2)
 Number of hours/year with high
WB
– > 60°F – 378 hours
– > 63°F – 146 hours
– > 65°F – 33 hours
 Using a 63°F DAT requires 67%
more airflow than using 55°F DAT.
12
Systems that Can Use Higher SAT
Displacement Ventilation
63F - 68F
UFAD
60F - 64F
Data Centers
(hot aisle/cold aisle)
64F - 80F
13
For Conventional VAV Applications
 Combine chilled water with direct evaporative cooling
 Advantages
–Can reduce chiller ton-hours/year by 2/3 ($$).
–Can deliver 55°F DAT at any time.
• Don’t have to oversize fans and ducts.
–Can limit humidity levels in the building.
Note: still requires a full-sized chiller
14
CHW/DEC Component Arrangement for
Optimal Performance
* Fan Upstream – 35% less CC energy
:
(compared to CC upstream of DEC)
:
(compared to DEC upstream of of CC)
15
For which types of buildings does
evaporative cooling work?
Direct evaporative cooling alone
 Warehouses
 Vehicle repair facilities
 Any type of building with low internal cooling loads
 Makeup air for commercial kitchens
 Gymnasiums
 Spaces that are open to the outdoors
16
For which types of buildings does
evaporative cooling work?
Indirect evaporative cooling combined with direct
evaporative cooling
 Commercial office buildings
 Retail spaces
 Recreation center
 Any type of building with moderate to low internal cooling
loads
Direct and/or indirect evaporative cooling
combined with CHW or DX cooling
 Any type of building
17
Pros
 Saves energy
 Works well in the Denver climate
 Low tech and easy to maintain with unskilled labor
 Lower cost than a chilled water cooling plant
 Can also be used to cheaply humidify air
 Direct evaporative cooling is inexpensive
18
Cons
 If not maintained properly, can produce odors
 If wrong materials are used, can have corrosion
problems
 Poor construction can result in leaks and water
carryover, resulting in flooding of the space below
the unit
 People don’t understand how to maintain it or fix
problems
19
Maintenance and Operation
 Dry the pad out daily.
 Drain the sump weekly.
 Run the pad wild.
 Don’t recirculate air.
 Pads last approx. 8-12 years.
 Pipe for maintenance (strainers,
PRV, flowmeters, etc.).
20
Direct Evaporative Cooler Piping
21
Water Treatment
 Scale buildup prevention
 Continuous bleed or
automatic control
 Biocides
22
Control Sequence
 Economizer (OA)
 Direct evap first
 Indirect/direct (if used)
 Direct with chilled water
 High humidity lockout
 100% outside air whenever
direct evap is active
23
Myths
 Legionella disease
 Over humidification
 Smell
 High maintenance
 High water usage
24
Typical HVAC Systems
Estimated Total Water Consumption
Air Cooled Chiller
2.8
COP
=
10
Lb.
H2O
Ton-Hr
DX Air Conditioner
2.8
COP
=
10
Lb.
H2O
Ton-Hr
Water Cooled Chiller
5.55
COP
=
25
Lb.
Ton-Hr
(150 ton – 300 ton)
Evaporative Cooler
H2O
80oF
(Direct/Indirect)
O.A.
=
21
Lb.
H2O
Ton-Hr
Assumptions
•Power plant overall efficiency of 35%
•Average O.A. temperature of 80oF
•Cooling tower bleed rates of 20% to 33%
25
Case Study − Golden Hill Office Center
 212,000 sf office building
constructed in 1983
 Designed in conjunction with
SERI (NREL)
 Model project for energyconscious design
 National ASHRAE First Place
Energy Award for New
Construction, 1988
26
Case Study − Golden Hill Office Center
 Features
–
–
–
–
–
–
–
–
–
100% indirect/direct evaporative cooling system
Solar hot water heating
Three 10 kW roof-mounted photovoltaic arrays
Passive solar design with east-west axis
Six high-efficiency, condensing boilers
Natural ventilation for parking garage
Heat and light reclaimed from atriums to offices
South side window overhangs
38 kBtu/sk/year measured without atrium; DOE
1995 energy evaluation of comparative buildings is
90 kBtu/sf/year
– 43 kBtu/sf/year measured with atrium
– 28 kBtu/sf/year with light shelves (not installed)
27
Case Study − Golden Hill Office Center
 Indirect/direct evaporative cooling process
28
Case Study − CU-Boulder ATLAS Center
 66,000 sf of classroom,




performance, and study space
Opened for classes in August
2006
Features direct evap + CHW
cooling, carbon dioxide
monitoring, and VAV systems
Certified LEED-NC Gold
4 points for optimizing energy
performance – 30% reduction
29
Case Study − CU-Boulder Wolf Law Building
 Five-story, 184,000 sf
 Opened for classes in
August 2006
 Features direct/indirect
evap + CHW cooling, carbon
dioxide monitoring for
demand ventilation, and
VAV systems
 Certified LEED-NC Gold
30
Case Study − CSM Student Recreation Center
 110,000 sf facility
 Direct/indirect evaporative
cooling only
– $500,000 deferred cost for
chiller plant
 Natatorium
– IEC
– Outside air for humidity
control
 Competition gymnasium
– DEC/IEC
31
Case Study − Colorado Springs Utilities Laboratory
 Project Description
– 45,000 sf (2/3 laboratory space,
1/3 office space)
– Direct evaporative cooling with
chilled water, energy recovery
– Designed with the Labs-21/LEED
Guidelines
– Certified LEED-NC Silver
– 50% energy savings compared to
base case
– USGBC-CO Bldg. of the Year Award
32
Case Study − Colorado Springs Utilities Laboratory
 2 AHUs – 62,000 cfm for labs,
25,000 cfm for offices
 Annual chiller operating costs
with chilled water cooling only $17,900
 Annual chiller operating costs
with combined chilled water/
evaporative cooling - $5,900
33
Case Study − Colorado Springs Utilities Laboratory

Cost of adding direct evaporative
cooling modules
Equip. Cost
Hookup/Controls
Lab AHU
$9,500
$2,500
Office AHU
$6,000
$2,000
Total
$12,000
$8,000

Payback with addition of
evaporative cooling
= First Cost/
Yearly Savings
= $20,000/
$12,000
= 1.67 years (20 months)
34