University of British Columbia building aims for LEED Platinum
By Alex Chou, P.E., LEED AP BD+C, The AME Consulting Group Ltd.
Last month marked the beginning of a new school year. Students at one of the world’s leading universities are now enjoying use of their new Student Union Building (SUB), home to the Alma Mater Society (AMS). Having just held its opening ceremony on September 9, the new building is situated in the core of the University of British Columbia’s (UBC) Point Grey Campus and has a floor area of over 250,000 square feet, a 50 percent increase in area over the existing Student Union Building built in the 1960s. The building will be the home to over 50,000 students and the local community in the surrounding Point Grey campus area.
The modern, 5-story SUB, also known as the “Nest,” is aiming to achieve LEED Platinum Certification, the highest level of sustainable building design. This new “heart” of student life on campus is designed to promote sustainability and energy efficiency. Notable sustainable elements in the building’s systems are the Rainwater Harvesting System and Solar Thermal Heating and Cooling System.
Water is a precious resource that is too often wasted or taken for granted. With the high volume of people expected to be using the Nest, the annual potable water usage for toilet flushing is expected to be just over 2.6 million gallons by using low flow fixtures.
To help further reduce consumption of potable water, the building has incorporated a Rainwater Harvesting System into the building for toilet flushing and for irrigating a small, landscaped area and the crop garden on one of the building patio roofs. Rainwater is collected from roof surfaces and gets redirected to the rainwater storage tank. Crops harvested on site will be used by the AMS food services in specialty dishes served in the building and on campus.
The crop garden roof drainage does not divert to the rainwater storage. Collection of rainwater from the crop roofs, or any green roofs with a growth medium, will introduce suspended solids, which is not desirable. These solids will result in high maintenance for the rainwater harvesting system. Therefore, it is generally not recommended to collect rainwater from these roof areas.
Upstream of the rainwater storage tank is a pre-filter unit that is designed to provide a high level of filtration at the front end of the system by removing over 90 percent of the suspended solids prior to the storage cistern. The Nest’s cistern sizing was determined based upon the following criteria:
- Roof collection area
- Toilet flushing demand
- Irrigation demand during period of low rainfall
- Rainfall intensity for the site
With the above criteria, the Nest’s rainwater cistern was designed to have a storage volume of 105,700 gallons. The expected annual volume of rainwater that can be collected for use is 760,000 gallons.
There was a concern of stagnant water in the cistern due to the requirement of storing the required volume of water to meet irrigation demand for LEED and the amount of water that may be in the cistern. Stagnant water provides a breeding ground for insects and algae growth in the enclosed tank area.
To limit these risks, a pipe ring for compressed air was installed near the bottom of the cistern and connected to a compressor located in the mechanical room. The compressor is on a pre-programmed timer that enables it to automatically operate and aerate the stored water.
From the cistern, duplex submersible pumps are used to convey the stored water into a 300 gallon day tank. The duplex submersible pumps pump the rainwater through a particulate filter and a UV filter unit before it enters the day tank. At the designed flow rate, the particulate filters will remove sediments down to 5 microns before the water is treated by the UV lamps, which will ensure an exposure dosage of at least 40,000 micro watt-sec/sq.cm.
A two-pump booster package draws the water from the day tank and delivers it to a separate non-potable water pipe distribution system. This system delivers water to the toilets and urinals in the building and to the irrigation systems. The Nest, using low flow fixtures along with the Rainwater Harvesting System, has successfully reduced its water consumption by 64 percent to that of a standard building of this type and size.
Typically, a Solar Thermal Heating System is used for domestic hot water heating. The system installed in the Nest is also utilized for chilled water production for the cooling system through a unique chiller arrangement. The Solar Thermal Heating System in the Nest consists of 84 glazed flat-plate panels mounted on the saw-tooth roof of the building to blend in with the architectural appearance, facing south to optimize the exposure to the sun. The size of this system will provide a maximum annual energy savings of 52,300 kWh for the building. The heating water produced by the 84 solar panels is used to heat the domestic water in four 750-gallon storage tanks separated by a double-walled heat exchanger.
Once the domestic water demand is satisfied, any excess heat from the solar thermal panels is typically rejected to the atmosphere to protect the system from overheating. Should a cooling demand exist in the building, instead of wasting the heat, the Nest Solar Thermal Heating System is used to provide heating water for the Adsorption Chiller. Adsorption Chiller is a piece of innovative technology that makes use of heat (in our case waste heat) to drive the chiller media phase change that produces chilled water. The waste heat is used to provide the same operation as a traditional electrical operated compressor. The Adsorption Chiller is using water as a refrigerant to produce chilled water by using evaporative latent heat.
A nominal 30 ton Adsorption Chiller was installed to match the size of the Solar Thermal Heating System. The chiller was designed to operate with 170°F heating water temperature to produce 45°F chilled water. Under the design conditions, the Adsorption Chiller will provide 22 tons of cooling for the building cooling usage.
Even though the Adsorption Chiller will accept the waste heat from the Solar Thermal Heating System, the system is still provided with a dry cooler that will protect the Solar Thermal Heating System from overheating when there is neither demand for domestic hot water heating nor demand for cooling in the building. This contributes to the expected annual energy performance of the building which is a 50 percent energy saving below ASHRAE 90.1.
Through the incorporation of the Rainwater Harvesting System and the Solar Thermal Heating System, the Nest, representing the heart of campus furthermore demonstrates UBC's dedication to promoting sustainability – a value that adds to the countless merits that the university embodies.