As governments introduce environmental legislation that will expose and inflict the full cost of power, building owners, operators and occupier’s costs will escalate. Bob Lawrence reports on a system which can help mitigate rising energy costs.
There have been primitive attempts at cogeneration for decades, with boiler room heat used for secondary purposes. Modern day cogeneration has built on these methods and is reliant on the natural gas that has fuelled Australian capitals for the past 30 years.
Simon Bennallach, national manager of Urban Energy Australia, says cogeneration (or combined heat and power) is the simultaneous production of electricity and heat using natural gas. “Modern cogeneration harnesses the waste heat via a jacket surrounding the block or internal coils within that allow a fluid running through to take the heat away for reuse elsewhere in the building,” he says.
“Add to this an absorption chiller using latent heat to transfer energy, and provide cooling liquids to assist in air-conditioning, and you have trigeneration. It is a sophisticated form of the old kerosene refrigerator where a transfer fluid absorbs large amounts of heat as the latent energy needed in transformation between liquid and gas. Obviously, the great advantage is cuts in power costs and greenhouse gases.”
Bennallach says cogeneration and trigeneration systems can work in any premises with a high and consistent consumption of electricity. However, there must be a continuing capability of using the waste heat, due to a constant demand for heating and cooling. He says hospitals are a classic example, with high energy requirements 24/7.
“Waste heat from one demand is the energy supplier for another demand,” he says, with large factories, residential communities, hotels and sporting complexes, particularly aquatic centres, also greatly benefiting from energy savings.
Urban Energy Australia import TEDOM cogeneration and trigeneration systems from the Czech Republic and has installed two systems for NSW Housing in residential blocks in Chatswood and Rouse Hill. “Cogenerations units are sized to the individual clients needs. Typically they have been designed with the figures provided by an electrical engineer engaged to assess the building's requirements,” Bennallach says.
He believes some of the main issues to be thought about when considering a trigeneration plant is the base load of the building, the operation hours and the footprint of the building. “We then work out the unit size and the operating hours in a fully detailed business case study of the project that determines its financial feasibility.”
As the basic T25 kilowatt unit weighs 1 tonne, installation in an existing building can pose problems. So far, most installations in existing buildings have been on the roof, which can be straight forward. “There needs to be more government action and consistency in promoting energy savings. Governments brag about being green, but it is much harder to get money from them,” Bennallach says.
Adrian Michaels from Mirvac participated in the installation of a trigeneration system in the upgrade of 101 Miller Street in North Sydney, the former home of Optus Communications. Co-owners Mirvac Property Trust and Eureka Funds Management targeted a 5 star ABGR rating in the refurbishment of the 15 year-old building. “They could have achieved a 4.5 star rating without much difficulty, but they wanted a premium graded building, so opted for a Cogent trigeneration plant to ensure that rating with a reasonable degree of comfort,” Michaels says.
“There was room to install a trigeneration system to integrate with the existing electrical systems. We installed two natural gas generators, two absorption chillers to provide chilled water in the building via a methyl bromide based operation, and heat exchanges to boost the heating system,” he says.
The trigeneration plant at 101 Miller Street can provide up to 2.4 MW of electrical power and 1.5 MW of air-conditioning cooling capacity. The generators were designed by Cogent to operate in tandem with power, which means in the event of the trigeneration plant failing, grid electricity will continue to power the building.
The waste heat from the generator is used to provide thermal cooling through the use of an absorption chiller. Absorption chillers use waste heat to provide the energy to drive the cooling process, rather than an electrically-powered compressor in conventional chiller systems and accounts for around 60 per cent of total cooling capacity.
Philip Mitchell, project manager for Canberra-based Rudds Consulting Engineers, managed the installation of a trigeneration system at Majura Office Park, a greenfields development at Canberra Airport which has a 5 star NABERS energy rating. The four-building complex has a central energy plant servicing 37,000 sqm of office space.
“It comprises conventional heating and air-conditioning equipment, plus a one megawatt trigeneration system, conventional boilers and electric chillers along with the necessary pumps, main electrical switchboards and equipment to provide base load energy for heating, cooling and electricity,” Mitchell says.
The trigeneration system works in tandem with the conventional heating, ventilation and air- conditioning plant. During normal operation, heating or cooling can be obtained virtually cost free while the electricity generated on-site has 50 per cent less carbon dioxide emissions than grid power. “At peak times the buildings also draw grid electricity, but otherwise the trigeneration system provides the load,” Mitchell says.
Mitchell also managed design and the installation of a trigeneration system in the new Santos House in Brisbane. Rudds was called upon to integrate trigeneration into the building’s design when construction of the 37-storey building had already reached 15 floors. “A one megawatt trigeneration system was installed in the existing level 37 plant room. This system, as with Majura, used a German made MTU engine and a Chinese broad absorption chiller, all powered by natural gas.
“The Brisbane installation, however, also required a selective catalytic reduction system from Exhaust Control Industries, Melbourne to cut nitrous oxide.”
