To achieve its target of achieving Net Zero Emissions by 2030, Monash University utilised the latest in solar technology to provide preheating to a low load boiler serving a campus-wide high temperature hot water system.
Like many other university campuses in the southern states of Australia, Monash University’s Clayton campus relies heavily on natural gas to meet the demand for high temperature hot water (HTHW).
As one of Australia’s largest, the Clayton campus features 100 buildings, accommodates eight faculties and educates over 30,000 students annually.
The university’s campus-wide HTHW system consists of a gas-fired boiler plant connected to a network of pipes that deliver high temperature hot water around the campus for process (absorption cooling) as well as heating hot water applications.
Such is the system’s size, that gas represents approximately half of the campus’ total energy consumption. And although the university was seeking to transition its campuses to 100 per cent renewable energy, it could find few viable alternatives to eliminate its reliance on natural gas to meet its HTHW demands.
This led to discussions between Monash University’s engineering and sustainability manager Dr Rob Brimblecombe and LCI Consultant’s principal engineer, Simon Witts about alternative energy solutions that may work in a suburban environment like that at Clayton.
Among these solutions was the incorporation of a solar evacuated tube field – the technology of which had matured considerably in recent years to enable high temperatures to be achieved.
Soon after, the concept of a solar farm to supplement the university’s HTHW system was born.
LCI saw an opportunity to integrate the latest series of evacuate tubes, which have a higher collection efficiency and higher operating temperatures than previous versions, into a high temperature hot water environment.
Despite the promise of the system, funding constraints saw the project put on hold.
In 2016, as funding became available for a new boiler, LCI Consultants were asked by Monash University to review and update the preliminary study that was completed in 2013, with a view to progressing to a full project.
Prior to the project, the boiler house contained three large HTHW boilers, each approximately 8MW. Although adequate at the time, the campus load profile had changed during the life of these boilers.
As a result, LCI Consultants needed to establish a load profile for the campus, to determine the size of the solar field and low load boiler required.
The university was able to provide LCI with detailed gas consumption records that produced detailed yearly, monthly and daily load profiles. These profiles aided in the assessment of the boiler capacity, and identifying both the size of the proposed replacement boilers, and a matching solar field.
The daily boiler profile (Diagram 1) revealed significant variations in the boiler load across the year, as well as during the day. And tellingly, the study revealed that the primary boilers on site were operating at less than 20 per cent load for significant periods of time during the summer months.
Diagram 1 – Daily Boiler Profile
The concept was then developed to incorporate a low load boiler, with a solar field acting as a preheat/low demand system. Following discussion with the university, a 4MW low load fluid heater was selected and matched to a 400kW solar field.
The Monash University Solar Farm project was designed in two stages.
Stage 1, completed in June 2017, comprised of the 400kW solar field (split into two) installed on the roof of Building 37, which accommodates the Faculty of Engineering.
A further two fields on the same building will form Stage 2 and see the total system capacity expand to around 1MW upon completion.
Instead of water, as is commonly used in solar evacuated tube collectors, LCI Consultants have utilised a proprietary heat transfer liquid that can not only achieve the high temperatures required, but also run through the system at low pressure.
The HTHW system serving the campus operates at temperatures ranging between 120°C and 160°C, but is designed to operate at 180°C at a design pressure of 12 bar gauge (1200kPa).
With such pressures beyond the working limit of the solar headers, and consideration given to the large number of panels (tubes), the rooftop location, maintenance requirements and health and safety, alternative fluids needed to be explored.
A number of common heat transfer fluid options were investigated, but most were unable to meet the criteria of the project, which included stability over a wide range of temperatures up to 300°C, non-hazardous and non-toxic, and resistance to oxidisation.
However after further investigation, a high performance, efficient and environmentally friendly thermal fluid was identified; Duratherm 630. Engineered for applications requiring high temperature stability to 332°C, is non-toxic, non-hazardous and non-reportable, and importantly poses no ill effect to worker safety and does not require special handling.
The Monash University Solar Farm sees this thermal fluid flow to and from the solar field, with heat transferred to the HTHW system via a shell and tube heat exchanger, specifically designed for the project.
The low load boiler then tops up the heat, if required.
Diagram 2 – System design
Beyond the challenges of heat transfer, LCI Consultants also had to overcome a number of other design obstacles, including catering for a highly variable heat source.
The system had to be designed to cater for a large variance in heat supply from the field without the low load boiler or the main system seeing any destabilising fluctuations.
The design team also had to overcome the challenges of thermal expansion and the significant amount of pipe work movement in the solar field – a consequence of long pipe runs and regular diurnal temperature swings. Some of the pipe work in the main field expands and contracts 120mm each day.
Expansion and contraction of this nature cannot be easily contained. The design allows for the entire solar field to be free-floating. In this way, anchoring and fixing systems do not have to cater for the expansion loads.
As well as matching the solar field and low load boiler to modifications made to the existing controls, significant effort was made during the commissioning process to remove moisture from the system.
Once the system was filled with the thermal fluid, the moisture in the system had to be given time to boil off. This slow process was carried out by gently raising the temperature of the boiler and venting the steam vapour at the highest point of the system.
Since reaching completion in June 2017, the solar yield from the system has been relatively low with the solar field installation optimised for summer collection.
This has provided an opportunity to complete the initial tuning and integration of the system into the main campus HTHW system, ahead of the system’s first summer of operation.
As the system is reliant on the weather, there is a 24 month turning program. Evidence from past projects, has shown the system will need to go through two cycles of the seasons, which is when the majority of hard tuning will be completed.
Although the full cost of the project remains undisclosed, a payback period of 8 years (calculated at current gas prices) is expected once Stage 2 is completed.
“This will hopefully be a test case that will allow us eliminate our dependence on natural gas,” says Dr Brimblecombe.
“Perhaps more importantly, we treat Monash University campuses as living laboratories. We feed the research into the practice that we do, and hopefully we find solutions that can be rolled out across our campuses and out into the world.”