How a tri-gen facility saves money

Total Construction

Like its namesake in New York, Central Park in Broadway, Sydney is a green recreational area surrounded by buildings. Also like the one in the United States, Sydney’s version is surrounded by a diverse bunch of structures instead of a series of bland, similar-looking edifices. This was done on purpose, said Total Construction’s general manager for renewable energies James Bolton.

“The developers decided that each building would be designed by different architects,” he said. A uniform look wasn’t what the developer was after. And it works. From the hovering cantilever of One Central Park to the heritage-listed Old Kent St Brewery, the developments catches the imagination of most passers-by.

Total Construction was responsible for building the project’s Central Thermal Plant (CTP) and tri-generation facility, which supplies the heating and cooling needs to the 11 buildings that make up the development. The plant provides hot water for spatial heating and domestic consumption, chilled water for spatial cooling, as well as generating electricity. The main components are boilers for hot water, chillers for chilled water and the tri-gen plant that is fired by natural gas to produce the electricity. The buildings have Energy Transfer Stations (ETS), which is a fancy name for a group of heat exchangers. A software programme monitors the different aspects of the plant, including its tri-generation. This tells Enwave Energy’s operation manager, Atiq Rehman, whose company was responsible for developing the project, and his staff what is happening inside the building at all times.

When you delve into the depths of the CTP and tri-gen facility under the old brewery it’s easy to become over-awed at the labyrinth of wiring, pumps, transformers, engines and seven kilometres of piping that make the buildings hum. It looks like a logistical nightmare, unless you’re somebody like Bolton or Rehman. To them it is all pretty straight forward. Even so, it takes going underground to visit the home of the tri-gen plant to truly appreciate the effort and engineering that has gone into making it work.

The last building in the development is expected to be completed by mid 2018. By that time the tri-gen plant would have been running for five years. There have been no mishaps since it started – not surprising when taking into account the amount of detail and considerations that went into having it built.

“Since operations began in 2013 there have been no major issues,” said Rehman. “The plant does have some redundancy, which means you can switch loads to different boards. The plant is also N-1 rated, which means there is always a piece of kit that sits there as a backup if anything goes wrong. It gives us breathing space if we are ever off-line.”

While the plant has some built-in fail safes, there were some interesting moments during the build. As well as constructing new buildings, the aforementioned Old Kent Street Brewery had to be retained due to its heritage status. There’s nothing like the restoration of an old building to add to the aesthetics of a project, and there was one stand out feature that made the architects salivate – the brewery’s old chimney. An iconic piece of architecture that not only gave the precinct its character, but also ended up having a practical use – albeit leaving the builders with their hearts in their mouths.

“We wanted to use the chimney as a chimney,” said Bolton. “However, when we started getting into the technicalities, we thought, ‘Yeah, we’ll put hot gas at the bottom. Nice and simple – stick it in the bottom and off she goes’. But that brought another set of issues. For example, the engines aren’t running all the time. It’s a very old chimney that is going to be heating and cooling all the time. Is it going to start cracking the bricks? The gases inside there can be nasty. They can be acidic. Is it going to erode the bricks?”

The solution was one that was not only ingenious but tricky due to the mechanics of the situation.

“In the end we ended up building a 55-metre stainless-steel flue for the chimney,” said Bolton. “We first dropped in a seven-metre section through the chimney that was bolted to the foundation. We then had to drop in another 48-metre piece  down the centre of the chimney from the top to finish it off . There were only a couple of centimetres of play between the pipe and the internal edge of the chimney. ”

It took two days for the job to be completed. Good weather, hard work and a little bit of luck meant the operation went well.

Another issue that came up was the placement of two engines in the basement of the main building. These engines were a sophisticated piece of German engineering designed to drive the tri-gen plant.

“There was a massive concrete lid that opened up to the basement and we had to drop the engines in there,” said Bolton. “The issue was that the first engine had already been ordered prior to our involvement with the project. The client’s engineer had designed the size of the hole, which was already in place. Then we came along and said, ‘Is the engine going to fit through that hole?’ We went and measured the engine and checked the drawing and we realised it wasn’t going to fit. The engine was too long. As it turned out we ended up cutting the engine and dropping it in the hole and then putting it back together. We went to put in a second engine in the same hole and we knew we were going to have the same problem. We went back to the engine manufacturer and asked them to cut the engine so we could take it apart and put it back together. They said no. So we had to do the same thing again.”

The chimney piping installation and engine-fitting issues aside, there were moments when they had to do testing of the plant itself, which was an anxious time, too.

“We had a number of scenarios we had to test,” said Bolton. “A couple of interesting ones were black start tests. We basically had to shut the power off – the whole place – and see if our diesel generator kicked in. There was a 30-second pause and we’re all standing there looking at each other hoping it would kick in. And it did. It was a long 30 seconds.”
The last piece of the tri-gen puzzle is the electricity that helps run the plant. The system they set up not only provided electricity to the buildings, but generated power, too.
“With the electricity, we take high voltage – which is 11,000V – from the national grid,” said Bolton. “We bring that into a high-voltage main switchboard and from there we bring it into a number of transformers. From that we step the voltage down from 11,000V to 415V, three-phase, and we then use that electricity to power equipment within the plant – the pumps, boilers and chillers. We generate power with the engine at 11,000V and that goes into the high-voltage main switchboard. We consume less electricity from the grid because we are generating our own power.”

Because it is such a big project, it was important that every aspect was synchronised and worked well together. This was also important for the maintenance of a lot of plant.

Rehman said that all aspects of the plant were part of an asset management/maintenance system called Maximo. A lot of the instruments and plant have fixed maintenance plans that kick in either after a certain number of hours, weeks or months. Timing is also key when maintaining plant.

“Sometimes it is better to do aspects in winter. Chilled water for example,” said Rehman. “Nobody uses the chilled water in winter. There’s no load so it’s the best to do it then. In summer, it’s best to do the heat pumps because there is less load then.”

A side effect of the tri-gen plant set up was money savings for the owners of the buildings. Because it is a closed loop system, water is used to both heat and cool the buildings. This means other than the cooling towers of the CTP, no water is needed, with the exception of slight evaporation, to make the system work.

With the completion date of Central Park in sight, Total Construction and its partners are proud of what they have achieved. And so they should be. Sorting out a plethora of plant that not only supplies cooling and heating to buildings, but also does it efficiently, is no easy task. At the end of the day, tenants have a highly efficient air-conditioning system that is also eco-friendly. And looking at the Central Park precinct as a whole, the tri-gen plant fits in nicely.