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TRANSCRIPT
ANNUAL
AIRAH
AWARDSSPECIAL
SUMMER 2020 · VOLUME 19.8
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ANNUAL
AIRAH
AWARDSSPECIAL
The University of Queensland (UQ) Gatton campus is located 90km west of Brisbane. The site has a long and storied history – first established as the Queensland Agricultural College (QAC) in 1897 before being requisitioned (on one day’s notice) as the site of a US Army hospital during The Second World War.
In 1990, QAC amalgamated with the University of Queensland, and UQ Gatton was formed.
Today’s campus features buildings of varying age, with a gross floor area of about 115,000m² and an internal usable floor area (UFA) of 69,600m². A development plan will see an additional 14,500m² UFA created in new buildings and facilities to cater for student demand by 2025.
But with a large percentage of the site’s mechanical services plant ageing – and excess energy generated from its large-scale solar farm spilling into the grid – UQ Gatton made a decision to explore a campus solution to suit its long-term requirements.
“The university’s aim was to find the lowest net present value (NPV) operating condition, reduce reliance on carbon energy and reduce its greenhouse gas emissions,” says Craig McClintock, M.AIRAH, director of McClintockEngineering Group.
Following a detailed feasibility study completed in 2015, McClintock Engineering Group was engaged by UQ.
With more than a decade’s experience in stratified chilled water storage and district cooling systems, the Group was called on to master plan the campus over a 10-year development. Other tasks were to manage end-of-life mechanical assets, optimise the site’s chilled water architecture, and reduce the operating cost position.
“All our recommendations were adopted by the university,” says McClintock. “By 2018 the project was fully documented, and construction had begun.”
The outcome is described as a next-generation, interactive microgrid district cooling system (DCS) chilled water plant.
It incorporates a 3ML stratified chilled water thermal energy storage (TES) tank, a 3km underground chilled water ring main, and microgrid “interaction”, which utilises the site’s excess solar PV energy production.
“For more than a decade, we’ve designed, monitored and studied numerous stratified chilled water storage systems and district cooling systems,” says McClintock.
26 SUMMER 2020 • ECOL IBR IUM
For more than a decade,
we’ve designed,
monitored and studied
numerous stratified chilled
water storage systems and
district cooling systems
F E AT U R EF E AT U R E
Big tank on campusUniversity of Queensland Gatton has installed a district cooling system and thermal energy
storage tank to take advantage of excess solar energy generated by its large‑scale solar PV farm. Sean McGowan explores the clever design that will deliver significant energy and expenditure
savings for this AIRAH‑Award‑winning project.
Images courtesy McClintock Engineering Group.
“This in-depth knowledge of how systems actually perform allowed us to apply the learnings of previous projects into the design at UQ Gatton.”
These include a pumping design devised for low-load and peak-load, low-return water temperature mitigation, chemical mixing in the ring main pipework at low load, central plant piping design for load management of chillers, and the ability to change chiller locations in the network.
The Group was able to implement control strategies for stability and energy efficiency. These strategies have been refined over many years. It also introduced a TES tank design that incorporates specific material selections, insulation detailing and safety factors.
THREE STAGESThe UQ Gatton project is being approached in three stages, with 20 buildings identified for the system. These account for 35 per cent of the site’s UFA and about 80 per cent of the site’s energy consumption.
The first stage connected seven buildings to the district cooling system. This formed the initial baseline of the investment, capturing all the existing “chilled water” buildings and critical 24/7 buildings.
The subsequent stages allow for building conversion from DX systems to chilled water and future building developments on the campus. The overall design solution is master planned for all 20 buildings.
“Stage 1 diversified maximum chilled water demand is approximately 2,500kWr, aligning with the system’s N+1 chilled water architecture,” says Matthew McDonald, senior mechanical engineer at McClintock Engineering Group, and one of the lead engineers on the project.
“The current installed field chilled water plant is 4,500kWr, with a final future capacity of 8,400kWr. The TES charge chillers total 2,000kWr.”
SHARED EXPERIENCEHaving previously designed the two largest stratified chilled water TES district cooling systems (12ML and 9ML) in Australia, Craig McClintock, M.AIRAH, says this prior experience was integral to the success of the UQ Gatton project.
“Our learnings from previous projects over the past 10 years and implementation of these into this design has been a real success and something our engineering team is proud of,” he says.
“UQ also has an experienced and knowledgeable team that knew what they wanted to achieve. They gave us the trust and flexibility to work within a framework to deliver the project and build on our previous experiences.”
WINNER
The rooftop view, with cooling towers
and solar panels visible.
28 SUMMER 2020 • ECOL IBR IUM
DEEP ANALYSISAs with any project requiring major infrastructure changes to be made to existing conditions, deep analysis was required of UQ Gatton’s system architecture.
McClintock says the existing buildings had a mix of design principles, technologies, coil temperature splits, air handling unit types, water chemistry and valve types. All needed to be adapted to the new system.
“Each building needed its own detailed assessment,” he says. “Component upgrades were made to ensure compatibility with the district cooling system. For example, three-way valves were replaced with two-way valves. And once these works were completed, a hydronic balance was carried out.”
Primary-secondary-tertiary pumping configurations allowed for direct control management of production, ring main and building systems to satisfy the cooling demand without over-pumping or diminishing the network chilled water temperature splits.
“To optimise the tertiary pump selections,” McClintock says, “each connected building flow rate and system operating pressure was measured and fine-tuned.”
A ring main chilled water network was also included to provide a low loss secondary pumping loop and security of supply with valve-out stations.
McClintock says the size of the campus was not a challenge, and in fact, assisted the project’s financial viability.
“Once our project-specific design principles were developed,” he says, “the actuality was, the larger the system, the better the return on investment – and the more simplistic solution can be with larger chillers.”
CENTRAL ENERGYThe central energy plant comprises two 1,950MWr high-efficiency water-cooled variable-speed screw chillers with provision for another future duplication.
The plant also features two 1,000kWr re-purposed (relocated) air-cooled screw chillers, and three plate heat exchangers, separating field production from the TES tank production and export.
Chilled water is delivered to tertiary pumps in each connected building
via 3km of underground chilled water MDPE (medium-density polyethylene) ring main pipework, or at valve pits ready for future connections.
Two ring main booster pumps and two cleaning systems were installed to mix the chemicals during winter low-load and low-velocity periods where chemical separation results. Each building connection features multiple tertiary pumps for varying load conditions and air dirt separators.
The 3ML stratified chilled water TES tank and a variable primary/variable secondary pumping network complete the plant.
The TES is a glass-fused steel tank with a geomembrane liner that is lighter, stronger and cheaper for the material thickness than alternatives.
The TES at UQ Gatton is designed to act as a battery. It enables the excess solar PV energy generated from the campus solar farm to be used to run chillers. It stores the chilled water in the tank for use at another time.
F E A T U R E
MANAGING ENERGY PRICEFour levels of control for the TES tank are provided, with interaction to the electricity grid (demand and market pricing), the onsite solar PV system, SCADA (supervisory control and data acquisition), and chiller optimisation control and BMS (building management system).
UQ Gatton can create parameters on spot pricing within the control system, in turn enabling the SCADA/BMS to control the plant to actively charge or discharge the TES and take advantage of electricity price and demand events.
The SCADA system passes information to the BMS for action on market events and actions, as determined by the university.
“The BMS makes the process logic decisions on normal operation and when a SCADA pass-through event is enabled,” designer Craig McClintock, M.AIRAH says. “In addition, the BMSalso controls the system for a monthlysite maximum demand threshold.”
The size of the campus
was not a challenge,
and in fact, assisted the
project’s financial viability
Excess solar PV energy generated from the campus solar farm is used to run chillers.
RING MAINThe ring main has been designed using a hydronic model to balance the building entering pressures, and only serves nominated buildings.
Buildings were selected on locality, size and capital cost of infrastructure delivery versus return on investment. Given the sprawling site, the final building mix was tailored to the core of the campus and larger buildings only.
“We knew from prior learnings that the ring main offers significant benefits, with the ability to move load (chilled water) easily in two directions as development plans change,” says McClintock.
He says the ring main also provides a level of security in the event the chilled water pipe is cut, as sections can be valved out without loss of supply.
WINNER
The TES at UQ Gatton is designed to act as a battery.
30 SUMMER 2020 • ECOL IBR IUM
Commissioned in 2015, the 3.275MW (peak capacity) solar farm uses fixed, single-axis tracking and dual-axis tracking arrays to produce about 6,000,000kWh per annum.
“The TES enables manipulation of power profiles and creates a dynamic large-scale battery for energy market trading and support,” McClintock says.
“When the energy network has a high price peak event, all chillers and production plant can be turned off – depending on tank inventory – and excess solar energy exported.”
During low-price events, all chillers can operate to “charge” the TES tank.
“The TES can successfully be used in all climates and can be a smart addition to a network, but it does add a level of complexity,” explains McClintock.
“A TES is most effective with large heating or cooling loads that have a large demand difference between daytime and night-time periods.”
VALIDATIONUQ Gatton’s next-generation, interactive microgrid district cooling system (DCS) chilled water plant was completed in January 2020.
It has been modelled to deliver a demand saving of 1.17KVA (a reduction of 35 per cent over business as usual) and provide site-wide savings of 2.17MWH, or 14 per cent.
Operational expenditure savings of 18 per cent, or about $384,000 per annum, are expected – with a net positive value (NPV) saving over business-as-usual of $6 million.
The project has an 18-month validation process, which will be extended post-COVID-19 when the campus returns to normality.
A monthly maximum power demand target is set for the site, which is monitored and reported on. The upper limit threshold is used by the BMS for control. The monthly energy target is also monitored, but is heavily impacted by the large-scale solar PV farm.
There are several key performance indicators (KPIs) that are monitored to ensure the system delivers the expected outcomes. These include total system COP (coefficient of performance), chiller COPs, water quality, TES tank inventory, the chilled water supply, and return temperatures to the site.
“Due to COVID-19, the reporting period is not comparable to the baseline years (2015 and 2018),” says McClintock.
“But using total system COP as a guide, the system is outperforming the business case energy model.” ❚
F E A T U R E
PROJECT AT A GLANCE
The personnel
▲ Architect: Wilson Architects
▲ BMS contractor: JCI Australia
▲ Building contractor:McNab Construction
▲ Client:The University of Queensland
▲ Electrical, hydraulics, structuralconsultants: Aurecon
▲ Mechanical engineers (DCS, TES,BMS): McClintock EngineeringGroup
▲ Mechanical services contractor:A.G. Coombs
▲ Principal consultant: Aurecon
▲ Superintendents representation:Turner & Townsend
The equipment
▲ AHUs: PAC AIR –Pacific Ventilation
▲ Air separators: Masterflow
▲ BMS: JCI
▲ Buffer tank: Masterflow
▲ Chillers: Carrier
▲ Controls:JCI & Carrier Plant Manager
▲ Fans: Fantech
▲ FCUs: Pacific HVAC
▲ Pumps: Xylem
▲ Tanks: Tasman Tanks
▲ VSDs: ABB
(Source: McClintock Engineering Group)
OPA Eco UltraAIR COOLED PACKAGE UNIT
W I N N E R
P R O D U C T O F T H E Y E A R
Using total system COP as a guide, the system is outperforming the
business case energy mode
AIRAH AWARDS 2020 WINNERThe design for the next-generation, interactive microgrid district cooling system (DCS) chilled water plant earned McClintock Engineering Group the 2020 AIRAH Award for Excellence in Innovation.
WINNER
The TES stores the chilled water in the tank for use at another time.