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3 2014 ¥ 1 ∂Green Office building in Agoura Hills Form follows (air)flow 1 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. ∂Green 2014 ¥ 1 3 Sustainable architecture 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 2 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 2 3 4 5 21 22 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 6 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 7 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 8 ∂Green 2014 ¥ 1 3 Sustainable architecture 23 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 9 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- 10 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. 24 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 12 26 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) 11 12 13 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 % ∂Green 2014 ¥ 1 3 Sustainable architecture 25 f a b c g d 16 h i e j k l m 14 15 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. 26 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 a b c d e f g h 17 18 ∂Green 2014 ¥ 1 3 Sustainable architecture a i g 19 h 20 21 27