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Center for Sustainable Landscapes (Pittsburgh, USA)

Credits: ©2014 Robin Rogers / Solaripedia

The Center for Sustainable Landscapes (CSL) is a veritable Phoenix of green architecture and building sustainability that rises from a restored brownfield in Pittsburgh. CSL is part of the larger 15-acre Phipps Conservatory and Botanical Gardens that were established in 1892 in Pittsburgh’s urban Oakland neighborhood. Phipps’ mission is partly fulfilled by the extraordinary building and grounds of CSL by advancing sustainability and human and environmental well-being, and inspiring and educating through plants. The CSL incorporates many passive heating, cooling and ventilation strategies found in traditional greenhouses, such as a roof-vented atrium structure, operable sidewall vent sash, and solar screening. This Net Zero Energy building uses solar photovoltaics and a wind turbine to generate all the power it consumes, and employs geothermal for heating and cooling. The building and landscape incorporate Net Zero Water strategies such as low impact development, stormwater collection, treatment and reuse, a vegetated roof, and native plantings. The 24,350 square foot building provides offices, classrooms, and research and library space for the Phipps Conservatory. The general purposes of the building and the 2.65-acre site are educational and demonstrational, as well as to provide work space for employees and volunteers. The building consists of two main regularly occupied floors with a third, non‐occupied, floor in the atrium. (Scroll down for further resources.)


CSL Roof Garden Penthouse

CSL Roof Garden Penthouse ©2014 Robin Rogers


Passive Solar Design
Designed by The Design Alliance of Pittsburgh, the architects used a passive-first strategy for the building design and orientation that helps minimize energy use for typical building operation. The CSL is designed to use 50 to 80 percent less energy than a comparable conventional office building. Located within the 15-acre Phipps Conservatory campus, the CSL is built into the north facing slope of the Phipps campus and bordered by an inaccessible steep hillside to the south. Building orientation maximizes northern and southern exposure for effective daylighting and passive solar controls. A three-story atrium is minimally conditioned and acts as a thermal buffer. Brise-soleil permanent shading devices on the exterior, light shelves, louvers and overhangs help reduce summer cooling loads and contribute to building heating during winter. No building facades or roofs are shaded by the CSL at any time of the year.

Extensive daylighting throughout the building is enhanced by light shelves and an interior daylight ceiling "cloud" to help maximize the depth of daylight penetration into the spaces. The ceiling cloud surface and interior finish color schemes also provide high reflectance values. When natural daylight is insufficient, high performance, energy efficient T-5 fluorescent lighting equipped with daylighting sensors, controls, and dimming ballasts are engaged. Occupancy sensors turn off lights in unoccupied rooms.

Natural Ventilation
Operable windows provide natural ventilation in administrative, educational, and support spaces to help reduce the HVAC system fan energy usage. To determine the optimal window locations for natural airflow, the design team performed a computational fluid dynamics study. To maximize the number of hours of natural ventilation, the thermostat setpoint was expanded up to 78°F (25.5°C) for the upper comfort temperature instead of a typical 72°F (22°C). A notification system alerts building occupants when conditions are appropriate to open the windows. In addition, the atrium is 100% passively cooled, and passive heating strategies and winter solar collection take advantage of thermal massing in walls, ceilings and floors.

Red List of Materials
The CSL also does not compromise other surrounding structures or properties from the ability to use natural ventilation. The CSL releases no noxious emissions; it is a combustion-free facility and all operational emissions are also compliant with the materials Red List. The Red List comprises materials that should be phased out of production due to health concerns and is updated as new science emerges. The list includes (as of August 2014) asbestos, cadmium, chlorinated polyethylene and chlorosulfonated polyethlene (CSPE), HDPE and LDPE, chlorofluorocarbons (CFCs), chloroprene (neoprene), formaldehyde (added), halogenated flame retardants, hydrochlorofluorocarbons (HCFCs), lead (added), mercury, petrochemical fertilizers and pesticides—for the duration of the certification period or needed for subsequent operations and maintenance, phthalates, polyvinyl chloride (PVC), and wood treatments containing creosote, arsenic or pentachlorophenol.

Building Envelope
The building is concrete and steel construction with a wood façade and metal frame windows. The robust, high performance building envelope reduces thermal heating losses and solar cooling loads, and maximizes natural daylighting. High performance wall and roof insulation reduce winter heat losses and summer heat gains. Low-e (low-emissivity) double-pane operable windows provide state-of-the-art solar and thermal control and energy efficiency, while admitting maximum daylight. An atrium is constructed mostly of glass, allowing for an interior greenhouse that can support plant life in a minimally tempered interior environment. A vegetated roof reduces heat island effect and impervious surfaces, while providing an excellent thermal barrier between conditioned and non‐conditioned spaces.

Geothermal Heating and Cooling
A ground-source geothermal HVAC system generates heat and cooling using 14 geothermal wells with PEX (crosslinked polyethylene) tubing loops. The system captures about 70 percent of its heating and cooling energy from the ground's consistent 55°F (13°C) temperature. The geothermal system works in conjunction with the Rooftop Energy Recovery Unit (ERU) to provide heating, cooling, ventilation, and dehumidification; in summer, heat that is removed from the heat pump refrigeration cycle is absorbed by the water circulated in the wells and the cool ground; in winter, warmth stored over the course of the summer season is recovered from the wells to heat the building spaces. The well boreholes are 510 feet deep and twenty feet on center from well to well. These wells feed water-cooled compressors for both heating and cooling loads by providing tempered water to the air handling unit (AHU) in the winter and cool water during the summer. All HVAC equipment is controlled using a direct digital control (DDC) building automation system (BAS), and all metering pertaining to HVAC work records data in conjunction with the BAS.

Rooftop Energy Recovery Unit
The rooftop Energy Recovery Unit (ERU) uses ground-source geothermal capacity. Its economizer cycle provides "free cooling" - without mechanical refrigeration - using outside air when ambient temperatures are cooler and drier than indoor temperatures. A desiccant energy recovery wheel (see below) pre-cools and dehumidifies outside air to reduce cooling loads of hot moist outside air in the summer; it also pre-heats and humidifies incoming cold outside air in winter. A high performance MERV13 air filter in conjunction with maximized outside air provide superior indoor air quality. The system includes UV lighting to reduce the potential for microbial growth. (See more on CSL energy use below.)

Desiccant Dehumidification
A desiccant energy recovery wheel (also known as a rotary enthalpy wheel) utilizes energy that would otherwise be exhausted to pre-treat temperature and moisture of incoming outside air with minimal energy use and without mechanical refrigeration. The resulting reduced moisture levels and humidity control of the air allows for a higher comfortable indoor temperature setpoint of 76°F (24.5°F), and enables an economizer feature to provide for free cooling and enhanced natural ventilation. When the economizer and desiccant wheel cannot maintain comfort conditions due to extremes in outside weather conditions, the geothermal heat pump system is energized.

Building Management System (BMS)
The Direct Digital Control (DDC) Building Management System monitors, controls, and provides feedback on various systems for optimal energy efficient operations of the CSL building. The DDC responds to current conditions, predicts daily ambient temperature and humidity swings based on time of year, and uses past historical weather patterns. A notification system alerts occupants if temperature, humidity and air quality conditions are favorable for opening windows, while also locking out mechanical systems. Meters and sensors provide building operating profiles and trend data to monitor energy efficiency on an ongoing basis. Favorable temperatures and humidity levels trigger a "night purge" to draw cool, dry outside air through building spaces to cool walls, floors, furniture, and ceilings before being occupied, saving daytime cooling energy.

Solar Photovoltaics (PV) and Solar Hot Water Collectors
The PV system produces about 135,655 kWh per year contributes to the net zero energy approach of offsetting 100% of the annual energy consumption of the CSL facility. Because available space for renewable solar photovoltaic systems was limited at the CSL itself, the design team employed an integrated design approach by utilizing space on adjacent buildings for roof-mounted arrays, as well as on-site-mounted array. The adjacent Facilities Building and the Special Events Hall roof surfaces, and the strip of site perched on the steep, inaccessible slope, provide ideal near-southern orientation for solar PV. This renewable energy system generates electricity from the sun using a 125 kW solar photovoltaic system comprising one ground- and two roof-mounted arrays. Any excess generated energy will augment the upper Phipps campus electricity needs. The DDC Building Management System meters and sensors collect and report on all energy generation from the solar PVs using an online Sunny Boy Portal system that can be accessed remotely and has applications for smart phones.

Vertical Axis Wind Turbine
The 10kW vertical axis wind turbine meets about one percent of the CSL’s annual energy demand. It is located northeast of the building and is part of the renewable energy system that generates electricity from wind, thus contributing to the net zero energy approach of offsetting 100% of the annual energy consumption of the CSL facility. The turbine is situated above the CSL site, where conditions are more favorable for wind power generation. The DDC Building Management System meters and sensors also collect and report on renewable energy generation from the wind turbine, and excess generated energy serves the upper Phipps campus electricity needs.

Demand Controlled Ventilation (DCV)
The Demand Controlled Ventilation (DCV) system uses CO2 sensors located in the classroom, conference rooms, and office areas to match the amount of ventilation air required to the occupancy level. At less than full building occupancy, the DCV system reduces ventilation air volume, and thus reduces energy required to heat or cool and dehumidify the ventilation air.

Sustainable Materials
The main exterior siding material is crafted from wood that was salvaged from deconstructed Western Pennsylvania barns. Other materials include locally produced, low-VOC and formaldehyde-free products. Many of the sustainable and innovative materials have a high recycled content, and most are highly durable with a long service life and ease-of-maintenance. Materials were installed that are not on the Red List. Additionally, during construction, building material waste was diverted from landfills through efficient site design, recycling and reuse.

Portions of the CSL site had been characterized as brownfield due to leaking underground storage tanks owned by the site's former occupant, the City of Pittsburgh Department of Public Works. The 2.9-acre site's severely degraded soils had been almost entirely paved over but can now manage a 10-year storm event on-site (3.3 inches in 24 hours). The CSL landscapes, designed by Andropogon Associates, now use pervious paving, bioretention areas, an open water lagoon, underground storage, a vegetated roof, and rain gardens to dramatically reduce runoff, even capturing runoff from the upper campus botanical gardens that require a tremendous amount of water to function.

Gardens: As might be expected for Center for Sustainable Landscapes, the sustainable landscapes feature the reintroduction of 150 native, non-invasive plant species. Complete CSL Plant List. All around the site, plants use rainwater for their nourishment - no additional irrigation was installed. Permeable asphalt allows natural infiltration of site stormwater. A walking trail and boardwalk lead through a variety of landscape communities including wetland, rain garden, water's edge, shade garden, lowland hardwood slope, successional slope, oak woodland, and upland groves.

The many gardens restore natural landscape function to the site, provide wildlife habitat, and offer educational opportunities. Rain gardens and bioswales serve ecological and aesthetic functions, as well as capture site stormwater to allow natural infiltration. Designed with native plants for year-round garden interest, they also provide demonstration beds for residential applications.

Vegetated Roof: The fully-accessible vegetated roof is a beautifully landscaped space where events can be held. Demonstration gardens show plantings that are appropriate for residential applications, especially urban landscapes. The extensive green roof design has an eight-inch soil depth for a variety of plants, including edibles and ornamentals. The gardens help reduce the volume of stormwater runoff and pollutants in runoff, reduce heat island effect, and decrease HVAC cooling loads in summer and heating loads in winter by further insulating the building.

Rainwater Harvesting, the Lagoon and a Constructed Wetland
To achieve net-zero water use, all graywater and blackwater are treated on-site using passive systems such as a septic tank, constructed wetlands, sand filters, and a solar and UV distillation system. Water is then reused as toilet flushing water or converted to distilled water for orchid irrigation. Stormwater from the upper Phipps campus glass roofs and lower site are captured and stored in a 1,700 gallon underground cistern. The rainwater is then used for flushing ultra-low-flow, dual-flush toilets and interior irrigation and maintenance, greatly reducing the impact on municipal sewage treatment and energy-intensive potable water systems.

Lagoon: A 4,000-square-foot lagoon further captures stormwater runoff from portions of the site, the CSL roof, the maintenance building roof, and overflow from the underground cisterns. This lagoon replicates a natural water treatment process that occurs in wetlands and marshes: water flows through a seven-step process where plants and their symbiotic root microbes absorb organic and mineral nutrients; water is processed to tertiary non-potable standards, which is comparable to water exiting sewage treatment plant post-treatment; and post-treatment water that overflows the lagoon flows into 80,000 gallons of underground rain tank storage.

Constructed Wetland: A subsurface-flow constructed wetland system treats all sanitary water from the CSL and an adjacent maintenance building. The system uses a two-stage wetland treatment cell configuration. Sand filtration provides additional treatment of the wetland effluent, and an ultraviolet process disinfects water to graywater standards.

by International Living Futures Institute

A concept design energy model for the CSL showed an Energy Use Intensity (EUI) of 19 kbtu/sf‐year with an energy usage for the building at 117,623 kwh per year. During the 2013 calendar year, the CSL was net positive on energy by 3,425 kWh, with an actual EUI of 20 kbtu/sf‐year, as shown below:

Annual Energy Use

Actual: 129,876 kWh

Simulated/Designed: 117,623 kWh

Annual Energy Generation
Energy Generated: 133,301 kWh

Energy Use Intensity: 20 kbtu/sf

End Use Breakdown

  • 1st Floor Plug Loads: 18,749 kWh/yr
  • 2nd Floor Plug Loads: 9,152 kWh/yr
  • Exterior Site Power: 2,720 kWh/yr
  • Site Lights: 3,537 kWh/yr
  • Geothermal Pumps: 7,607 kWh/yr
  • Elevator: 1,943 kWh/yr
  • Interior Lighting: 10,179 kWh/yr
  • Berner Unit - HVAC RTU: 73,246 kWh/yr


Mechanically, the building is primarily served by an efficient, low-energy-consuming Under Floor Air Distribution (UFAD) system. The heart of the building's HVAC operation is the Tricoil energy-recovery system by Sensible Equipment. The 12,000-cfm Tricoil supplies both enthalpy-wheel dehumidification and mechanical dehumidification via a patented recuperative loop that pre-cools and reheats outside air requirements. The system, which is supplemented by the building's natural ventilation and under-floor ductwork air-displacement strategy, also provides air-conditioning and heating with help from energy recovery. Its water-source heat pump is supplied by a 14-well vertical geothermal field. A building automation system monitors and controls all building environmental conditions.

The two-inch-thick doors and panels of the Tricoil unit have a solar-reflective paint and maintain a positive-pressure and near-zero air leakage due to tight-fitting gaskets and door latches. Like the project's other construction materials, the HVAC enclosure's insulation, gaskets and other materials use no CFCs, VOCs and other environmental contaminants.

The UFAD provides optimum comfort control while preventing over-ventilation by reducing ventilation to unoccupied air volumes. The UFAD system introduces ventilation air directly into the breathing zone and allows heat from internal loads to stratify above the occupants. When outside air conditions permit, the building is cooled by natural ventilation through motorized operable windows and full economizing cycle on the rooftop unit. The atrium is not mechanically conditioned. HEPEX Tubing for a future radiant hydronic heating system is installed to temper the space in the heating season (if necessary), and no cooling is provided to the atrium in the cooling season. Instead, the atrium relies totally on natural ventilation.

The entire system is served by a roof top air handling unit (AHU‐1). One dedicated rooftop unit serves the under floor system for the entire building. The unit consists of a filter module (MERV 9 pre‐filters and MERV 13 final filters), recirculating/mixing box module, exhaust fan with VFD, enthalpy wheel module, tricoil module, supply fan with VFD and water cooled compressors. The unit provides approximately 12,000 cfm supply air with the ability to go to a full economizer cycle when outdoor air conditions allow. The unit responds to CO2 demand control ventilation. The tri‐coil design includes a DX coil sandwiched in between a glycol run-around loop. The run-around loop and associated fractional horsepower pump provide pre‐cooling and reheating to increase dehumidification capacity. The desiccant-coated total enthalpy recovery wheel provides free heating, cooling, dehumidification and/or humidification depending on the season. The system capacity is based on loads and ventilation requirements as calculated using Trane Trace 700 software program. All occupied spaces are ventilated with outdoor air (OA) in accordance with ASHRAE 62.1‐2004, and thermal comfort conditions comply with ASHRAE Standard 55‐2004 within all mechanically ventilated spaces.

Tours of the CSL
Phipps offers docent-led tours of the Center for Sustainable Landscapes (CSL) daily Thursdays through Sundays at 1 pm and lasting approximately 60 to 90 minutes. No pre-registration is required; spots are offered on a first-come, first-served basis and limited to 20 people per day. Tours begin in the CSL and are free with Phipps admission.

View map


  CSL Technical Report 1 by Daniel Zartman (7,277 kb)

  CSL Architectural Engineering Thesis by Josh Wentz 2012 (5,815 kb)

  CSL Technical Report 2 by Daniel Zartman (11,656 kb)

  CSL Technical Report 3 by Daniel Zartman (976 kb)

  Living Building 2.0 (3,569 kb)


Andropogon Associates (Philadelphia, USA)

Phipps Conservatory and Botanical Gardens (Pittsburgh, USA)

Center for Sustainable Landscapes at Phipps Conservatory

The Design Alliance (Pittsburgh, Pennsylvania, USA)

International Living Future Institute