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A S H R A E J O U R N A L a s h r a e . o r g A U G U S T 2 0 183 4
ASHRAE TECHNOLOGY AWARD CASE STUDIES 20
18
The San Francisco Museum of Modern Art (SFMOMA) consists of a 10-story addition and a renovated existing five-story building. Pictured is the view from the Yerba Buena Gardens.
PHOTO CREDIT JON MCNEAL, ©SNØHETTA.JPG
BY STEVEN T. TAYLOR, P.E. FELLOW ASHRAE; DAVID HEINZERLING, P.E. MEMBER ASHRAE
A New Approach to Museum HVAC Design
This article was published in ASHRAE Journal, August 2018. Copyright 2018 ASHRAE. Posted at www.ashrae.org. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE. For more information about ASHRAE Journal, visit www.ashrae.org.
This�file�is�licensed�to�Steven�Taylor�(staylor@taylor-engineering.com).�Copyright�ASHRAE�2018.
A U G U S T 2 0 18 a s h r a e . o r g A S H R A E J O U R N A L 3 5
FIRST PLACE | 2018 ASHRAE TECHNOLOGY AWARD CASE STUDIES
Steven T. Taylor, P.E. and David Heinzerling, P.E., are principals at Taylor Engineering in Alameda, Calif. Taylor is a member of SSPC 90.1 and GPC 36. Heinzerling is a member of SSPC 55.
Building at a Glance San Francisco Museum of Modern Art (SFMOMA) Location: San Francisco
Owner: San Francisco Museum of Modern Art
Principal Use: Museum
Includes: Art galleries, theater, administrative offices, library, café, event space, retail shop, wood shop, art conservation studios, cafeteria, and cold and cool storage rooms.
Employees/Occupants: 470 staff and 1.2 million visitors in first year
Gross Square Footage: 486,000
Conditioned Space Square Footage: 350,000
Substantial Completion/Occupancy: June 2016
Occupancy: 100%
The San Francisco Museum of Modern Art (SFMOMA) consists of a 10-story new addition to a fully renovated existing five-story museum. Program elements for the 486,000 ft2 (45 000 m2) project include art galleries, theater, administrative offices, library, café, event space, retail shop, wood shop, art conservation studios, cafete- ria, and cold and cool storage rooms. The entire project is served by an innovative HVAC system that could become a new standard for museums and similar applications.
Museum Environmental Criteria
Museums are traditionally large
energy users because of the need to
provide tight humidity control. The
design team worked closely with
SFMOMA conservationists to study
various published environmental
criteria for museums as well as those
from major museums across the
country. Through this roundtable
process, the team concluded that a
seasonally adjusted relative humidity
setpoint (Figure 1) could be used while
still maintaining acceptable condi-
tions for artwork and still maintain-
ing a Class A rating.1 Concurrent
temperature control was specified to
be 72.5°F ± 2.5°F (22.5°C ± 1.4°C).
This relaxation in humidity con-
trol allowed the design team to con-
sider centralized, rather than zonal,
humidification systems. Zonal
humidity controls can handle wide
variations in humidity loads from
people and infiltration, but they
cost more, have higher maintenance
costs, and are less energy efficient.
Centralized humidity control, on
the other hand, relies on low zone
humidity loads from infiltration,
but the relaxed humidity setpoints
in Figure 1, along with a tight enve-
lope, allows it to provide acceptable
control because the infiltration
loads tend to vary in the same way as
the humidity setpoints.
The concept behind central
humidification is to maintain a
nearly constant supply air condi-
tion: saturated air with a dew-
point temperature just above that
at the lowest acceptable space
temperature and lowest accept-
able relatively humidity, in our
case 70°F (21.1°C) and 45% relative
This�file�is�licensed�to�Steven�Taylor�(staylor@taylor-engineering.com).�Copyright�ASHRAE�2018.
A S H R A E J O U R N A L a s h r a e . o r g A U G U S T 2 0 183 6
20 18 ASHRAE TECHNOLOGY AWARD CASE STUDIES
humidity, where RH is adjusted based on time of year
as discussed above. For zones that are unoccupied with
low cooling loads, the resulting space condition is the
“Unoccupied” point in Figure 2. For spaces that are fully
occupied, the room temperature is allowed to rise to
75°F (23.9°C) and, with the moisture added by people,
the resulting condition is the “Fully Occupied” point.
Thus, with a single supply air condition, all spaces can
be maintained in the required humidity range pro-
vided humidity loads from infiltration, especially of
cold, dry air, are small. Where they are not expected
to be small, e.g., at entries, local humidifiers can be
added to augment the centralized system.
Existing System Upgrades The two air handlers serving the existing museum
were single-fan/dual duct (SFDD) systems with return
fans and steam humidifiers in the cold duct mains
on each floor. Operational problems with the systems
included:
• The economizer on the SFDD significantly increases heating energy use on the hot deck because the hot wa-
ter coil entering air temperature is the same as the cold
deck supply air temperature. The added outdoor air to
the hot deck also increases the humidification load. The
economizer had to be disabled even at mild outdoor air
conditions, causing the chiller plant to run most of the
time.
• The blow-through arrangement of the SFDD system results in nearly saturated cold duct supply air when
mechanical cooling is active. This resulted in over-satu-
ration and condensation on the supply air ducts leaving
the cold deck discharge plenum due to the pressure
drop as air accelerated into the supply air mains. This
65
60
55
50
45
40
35
Re lat
ive H
um idi
ty (%
)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Dehumidification Setpoint (Highest Allowable RH Level)
Humidification Setpoint (Lowest Allowable RH Level)
FIGURE 1 Relative humidity seasonal setpoints.
FIGURE 2 Psychrometric process of centralized humidity control.
resulted in microbial growth and all cold duct acoustical
lining had to be removed.
• Access to the coils, filters, and fans of the field-built air handlers was very poor, requiring the building en-
gineer to climb over obstructions with ladders to reach
this equipment. Replacing the 100 hp (75 kW) supply fan
motors and 40 hp (30 kW) return fan motors bordered
on impossible.
• The variable pitch vane-axial fans required annual tear-down and rebuild, made more difficult and expen-
sive by the poor access.
• The humidifiers were located in ceiling plenums that were difficult to access for maintenance. They also
caused condensation in ductwork due to the nearly satu-
rated supply air when the chillers and cooling coils were
active, which was most of the time. Some were relocated
to the hot decks to avoid this problem. Humidity control
was accordingly very poor.
These two air-handling systems were gutted and
replaced with dual-fan/dual-duct (DFDD) systems with
relief fans and central humidification shown schemati-
cally in Figure 3. A third DFDD system was installed in
the expansion building. Together the systems totaled
350,000 cooling cfm (165 000 L/s) and 123,000 heating
cfm (58 000 L/s).
The revised design resolves all the operational prob-
lems of the existing system and included additional
features to further improve energy efficiency and tem-
perature and humidity control:
This�file�is�licensed�to�Steven�Taylor�(staylor@taylor-engineering.com).�Copyright�ASHRAE�2018.
A S H R A E J O U R N A L a s h r a e . o r g A U G U S T 2 0 183 8
20 18 ASHRAE TECHNOLOGY AWARD CASE STUDIES
• The use of a DFDD design instead of SFDD resolved the first two issues listed above. DFDD also has lower
fan energy because with SFDD systems, duct pressure
is always higher than it needs to be in one of the two
supply air ducts. DFDD systems can maintain hot and
cold duct pressure independently with independent
pressure setpoint reset based on VAV box damper posi-
tion.
• Centralized humidity control with direct evapora- tive (adiabatic) humidifiers reduces energy use, first
costs, and maintenance costs (see next section for
details).
• The use of relief fans instead of return fans allowed the layout of the mechanical rooms to be improved,
resolving the maintenance access issues. Relief fans are
more flexible because, unlike return fans, they need
not be in series with the supply fans and can be located
anywhere in the common return air path. Relief fans in
this application are also more eff
