Download 3Office building in Agoura Hills

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2014 ¥ 1   ∂Green
Office building in Agoura Hills
Form follows (air)flow
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Agoura Hills is a prosperous town with around 20,000 inhabitants approximately 45 km northwest of downtown Los Angeles.
The main arterial road linking the town to Los Angeles is lined
with gas stations, fast food restaurants and shopping malls.
A short distance further west, however, the landscape changes
dramatically: the buildings dissipate and the topography rises in
the direction of the Santa Monica Mountains, which separate the
valley of Agoura Hills from the Pacific Ocean.
The Conrad N. Hilton Foundation has chosen to build their new
headquarters at the foot of this mountain range. It was the
founder of the homonymous hotel chain, Conrad Hilton, who,
70 years ago, started the foundation that bears his name. Since
then, the charity has donated nearly a billion US dollars to eleven causes including: substance abuse prevention for teens, disaster relief, as well as aid for the homeless and AIDS orphans.
The Hilton Foundation plans further expansion in the future: the
masterplan by ZGF Architects comprises a total of four office
buildings with more than 8,000 square metres of total surface
­area on the 18-hectare site. With the completion of the first new
building in 2013, the architects have set a high standard in design, as well as in sustainability for the foundation’s future building projects.
A showpiece for sustainable design
The foundation headquarters accommodates a workforce of just
over 50 people. Most of the staff work in private offices along the
north and south facades; administrative support staff are arranged in cubicles at either end of the central circulation zone.
Additionally, there are two conference rooms on the ground level, as well as a third one on the upper level. In the entrance lobby and at the northwest end of the building, stairs and lofty double height spaces connect the two office levels with one another.
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Client:
Conrad N. Hilton Foundation, Agoura Hills
Architects:
ZGF Architects LLP, Los Angeles
Construction management:
Bigelow Development Associates, Malibu
Structural engineering:
KPFF Consulting Engineers, Los Angeles
MEP engineering, energy consultant:
WSP/Built Ecology, San Francisco
Landscape architect:
Van Atta Associates, Santa Barbara
Phase 3
Phase 1
Phase 4
1Eastern elevation
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Site plan Scale 1:5000
3Northern facade with recreation courtyard (looking east)
4Ground floor plan Scale 1:750
5Upper floor plan Scale 1:750
Phase 2
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Office building in Agoura Hills
2014 ¥ 1   ∂Green
Energy balance and water use
• Projected water use (base building)
• of which recycled water
• Projected energy demand
• Projected electricity yield of PV array
• resulting energy surplus
217 m3/a
79,5 %
147 MWh
(= 71,3 kWh/m2a)
76,0 kWh/m2a
4,7 kWh/m2a
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Due to the culture and mission of the foundation, the client felt
obliged to create more than just a comfortable workplace for the
employees, but also to build a prototypical project for sustainability. Guests and new employees are regularly shown around
the new building to provide an impression of how energy efficiency in a subtropical climate functions. The architects focused
on passive methods of air-conditioning and strategies for the
use of daylight in their design. These priorities give the building
its distinctive form.
By US American standards, the new-build is fairly narrow, a feature more typically seen in Europe. Daylight enters all the office
spaces through large windows along the northern and southern
facades. The central circulation area of the office wing is supplied with daylight through additional clerestory windows. Seventeen ventilation chimneys (referred to henceforth as downdraft
shafts) give the facades their distinctive rhythm, which are part
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ofSHADES
a carefully
balanced
ventilation
and
SHADES
OPENsystem to provide natural
SHADES CLOSED
OPEN
SHADES
CLOSED
passive heating and cooling. The central, slightly elevated section of the flat roof is covered by 100 m² of evacuated-tube solar
collectors, which provide hot water, whilst a 115-kilowatt photovoltaic system installed as a shading element of the neighbouring parking lot will provide electricity. With these resources,
the goal of the Foundation is to achieve a zero-energy building.
Thanks to its credentials, the building has already been awarded
LEED Platinum sustainability certification.
A steel frame behind solid walls
With regards to the construction, the building is a hybrid. The
exterior walls on the western and eastern facades, the walls in
the entrance area and the downdraft shafts are all constructed
with in-situ concrete. A rear-ventilated facade construction was
applied on the exterior of these walls, which is clad with thin tiles
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Site area: 17,8 ha � Gross floor area:
2066 m2 � Percentage of open spaces versus
site area: 61,5 % � Total number of building
­users: 56
6Light deflection and glare protection when the shades are open (left)
or closed
7Entrance area with staircase to the upper floor
8Reception area; looking northwards across the building
9Ventilation and cooling concept
10 Southern facade; viewed from the west
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of mottled ochre meta-quartzite veneer. These solid walls provide the lateral bracing for the building structure; additionally the
thermal mass of the concrete downdraft shafts helps passively
cool the supply air.
In contrast, the interior of the office building is supported by a
steel frame which, with its riveted connections and visible crossbracing, appears delicate and is faintly reminiscent of historic
steel constructions. In the event of demolition, this steel frame
will be easier to disassemble than a welded construction. However, according to Ted Hyman, a partner at ZGF Architects, this
only played a minor role due to the planned lifespan of the building of 80 to 100 years. The deciding factor was rather the fact
that a riveted construction is simpler to erect on site.
The floor slabs and flat roofs of the office building consist of
steel trapezoid sheets onto which in-situ concrete was poured.
White acoustic ceiling panels were suspended from the under-
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side of the slab. Floors of finely patterned white marble and dark
metal window frames complete the palette of materials.
As with many LEED certified buildings, the new building in
­Agoura Hills gained credits by using a minimum percentage of
recycled and regional construction materials. The quartz sandstone, which so distinctively anchors the building to its location,
was quarried and fabricated in a site near Las Vegas. Along with
the concrete and the gypsum fibreboard, the carpets and the
ceramic tiles, these materials were all sourced from within the
‘regional’ area considered by LEED: i.e. a 500-mile radius.
The steel structural frame, the metal cladding of the facades,
floor finishes, acoustic ceilings, WC partition walls and gypsum
fibreboards all consist of a high percentage of recycled materials. The in-situ concrete substituted a portion of Portland cement
with fly ash, which is a waste product from heating power stations and waste incineration facilities.
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Office building in Agoura Hills
11LEED certification results
12Main entrance on the south side
13Conference room on the ground floor
14Energy concept
a Solar collectors
b Buffer stores
c Electric water heater
d Cooling tower
e Compression chiller
f Downdraft shaft with cooling coil
15 Water usage concept
g Potable water
h Grey water
i Future well
j Tap
k Sensor
l Vent controls
mCistern
16 Eastern elevation showing solar collectors and downdraft shafts
2014 ¥ 1   ∂Green
LEED certification results (Version: LEED for New Construction 2009)
Category
Points
achieved max. possible
Sustainable Sites
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Water Efficiency
8
10
Energy & Atmosphere
33
35
Materials & Resources
5
14
Indoor Environmental Quality
13
15
Innovation in Design
6
6
Regional Priority
4
4
Total
81
110
Result
LEED Platinum
(Certified: 40 – 49 points, Silver: 50 – 59, Gold: 60 – 79, Platinum: 80 – 110)
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Double shading and passive cooling
The interior organisation of the office wing is clearly expressed
by its facades: the unitised aluminium curtain walls of the offices
and the sandstone cladding of the downdraft shafts alternate
in a regular rhythm. Since the passive cooling of the rooms is
negatively affected by direct sunshine, the offices are equipped
with motorised exterior roller shades with stainless steel microblades. Exposures that did not require the exterior shades on
the north were outfitted with fabric roller shades in the interior.
The exterior shades are designed to deflect the rays of the high
summer sun whilst also allowing a relatively clear view of the
outside. The blinds are automatically regulated to deploy according to the sun’s angle of incidence; the employees can also
manually override the controls at any time.
Overall, only the lower three quarters of each office window is
equipped with sun shading and glare protection. Above this a
horizontal ‘lightshelf’ is situated the upper surface of which reflects daylight further into the room. Daylight sensors near the
­facade automatically turn off the artificial lighting if the office has
enough natural illumination.
The sandstone-clad downdraft shafts are internally divided into
two rows. One of the rows supplies the ground level rooms
through raised access floors, whilst the second row supplies the
upper level of the building with fresh air. The exhaust air from
the office spaces flows through openings at the top of the office
partition walls into the circulation area at the centre of the building. From there it escapes to the outside through digitally controlled clerestory windows directly below the flat roof. According
to calculations by the engineers of WSP Built Ecology, the ventilation system should be able to function by means of the stack
effect without the need to use fans. According to the architects,
a further advantage of the system is that there will be no
draughts, which are one of the disadvantages of conventional
air-conditioning systems.
Zero energy with solar power
The supply ventilation is also the means used to cool the offices.
Water-filled cooling coils were installed near the top of each
downdraft shaft, which are supplied with cold water by a series
of electric compression coolers. These are, in turn, cooled by a
cooling tower on site. As long as outside temperatures are moderate, the cooling tower supplies the coils directly with cold water without needing to loop back to the coolers. This ‘economizer
loop’ leads to significant electricity savings in the system.
The solar collectors on the roof provide around 70 % of the heating and hot water needs of the building; the remaining 30 % is
supplied by a back-up electric boiler. An 11,300-litre hot water
tank serves as buffer storage for overcast days.
With all of these efficient technologies, the energy demand for
heating, cooling and ventilation for the building is about 61 %
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lower than that of the reference building according to ASHRAE
90.1-2007, which also serves as reference for the LEED certification. The total energy demand, including electricity, for the
new-build is 46 % lower than that of the reference building.
If one factors in the electric yield of the photovoltaic system
(167,000 kWh/year), the new-build will have produced slightly
more energy than it consumes.
In order to ensure that these benchmarks are not only met in
theory, the building’s energy consumption is continuously monitored and the systems are adjusted based on need. In the first
few months, this applied to the heating system in particular. After
some initial issues, the engineers reprogrammed the heating
controls and since then the system performs as initially planned.
Ted Hyman from ZGF Architects is confident that a zero-energy
balance will be achieved in the second year of operation.
Automated rainwater storage
In a place like California, where potable water is often transported over long distances, any sustainable building would be incomplete without a water conservation concept. Rainfall runoff
from the driveways, sidewalks and parking spaces can drain
naturally on the grounds. The rainfall that flows off from the
planted roof areas is collected in a 75-m3-large subterranean
cistern and is used for flushing the toilets and for watering the
on-site vegetation. When there is insufficient rainfall, the cistern
is supplied by a combination of potable water, grey water and,
in future, also by water from a well that is still to be drilled onsite. An automated water blending system with sensors in the
cistern will monitor the water quality, ensuring that neither too
much potable water is used, nor that the water is too polluted to
use for irrigating the site.
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Office building in Agoura Hills
2014 ¥ 1   ∂Green
17Northern side of the building with the covered
courtyard
18Sectional detail of the office facade Scale 1:50
aVentilation grille, aluminium, 50 mm; on
­aluminium support frame
bRoof:
Green roof tray system, 108 mm; single-ply
PVC waterproofing membrane, 1,4 mm; roof
board, 6,3 mm; PIR rigid insulation laid to falls;
in-situ concrete roof slab, 158 mm, on trapezoid
sheet metal 1,3 mm; void/insulation,
330 mm; suspended acoustical panel ceiling,
27 mm
cFacade:
Unitized aluminium curtain-wall facade with
double glazing
dExterior roller shade with stainless steel micro
blades
eReveal, aluminium plate
fUnderfloor radiator
gFloor slab of upper floor:
Carpet tile, 7 mm; access floor system,
457 mm; in-situ concrete slab, 158 mm,
on trapezoid sheet metal 1,3 mm; air void/insulation, 330 mm; suspended acoustical panel
ceiling, 27 mm
hGround floor slab:
Carpet tile, 7 mm; access floor system,
457 mm; reinforced concrete slab, 152 mm;
vapour barrier, 1 mm; sand bed, 100 mm;
gravel fill, 180 mm
19Steel frame in the central circulation area.
The clerestory windows also provide exhaust
­ventilation for the building.
20View of a typical office
21Sectional detail of a downdraft shaft Scale 1:50
iVentilation chimney:
Adhered quartz stone veneer, 25 mm; epoxy
mortar; cement board, 25 mm; stainless steel
framing, 64 mm; spray-applied waterproofing
membrane, 1 mm; reinforced concrete wall,
305 mm; installation shaft, 762 mm; stainless
steel framing, 64 mm; painted gypsum board,
13 mm
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