The trials of trigen revealed
Willow Aliento | 22 February 2017
Trigeneration and cogeneration technology was once the go-to technology for buildings whose owners wanted strong Green Star or NABERS ratings.
In more recent times, though, many of those big kits have been sitting idle, victim of rising gas prices and other factors.
According to Ausnviro managing director Jay Gualtieri, many of the systems were simply oversized in terms of the building’s actual energy use, meaning many simply don’t get switched on.
“Green Star looks favourably on commercial office buildings that use technology like trigeneration,” Gualtieri says.
“The problem is from a design perspective Green Star is quite bullish on trigen, essentially the bigger the system the better.”
This makes the technology often a “classic non-practical” initiative once the building goes live.
Trigen is only efficient in terms of producing lower emissions energy when it is sized correctly, he says.
At the core of the conundrum is a conflict between energy efficiency and cleaner energy generation.
By burning gas as a fuel, trigen generates around two-thirds less carbon emissions than grid electricity derived mainly from coal-fired power stations.
But when a building becomes more energy-efficient, the energy loads become lower and fail to reach the set points that will kick trigen into action.
“Trigen has only recently started to evolve in terms of how it is specified or sized,” Gualtieri says. “In so many buildings the systems are all too big, so they don’t run or only run occasionally.”
One of the solutions is to tune the trigen system down. This allows it to come on at a lesser load than it was originally designed for.
This solution was put in place by Ausnviro and Cogent at Investco’s 321 Exhibition Street property. The result, in combination with a few additional energy conservation measures, was the building went from 5.5 star NABERS to 6 star NABERS.
Before the intervention, the trigen wasn’t coming on early enough or running late enough – both times of day when loads are lower. That meant both the base building and Origin’s tenancy pulled from the grid at those times.
The tuning down process meant the trigen started operating optimally, coming on “as soon as humanly possible” because it was being triggered at optimal set points.
“It has been optimised to the point where it is running like a finely tuned machine. The building is using very little grid-fed allocation – and the trigen energy is two-thirds cleaner than grid energy.”
However, even with tuning down, Gualtieri says there are still risks to be managed. Any system will have been built to run at a certain capacity, and even if it is tuned to attempt to chime in with the actual building loads, it may trip out because the engine is too big for the job it is doing.
He says that many commercial buildings during their development have registered agreements to achieve 5 Star NABERS or 5.5 Star NABERS ratings. This is generally based on modelling where the trigen is assumed to be online.
However, the building may not actually get there in operation due to how it has been tuned during commissioning and operations. If all the other systems are “fine, well commissioned technologies” that operate at optimum efficiency, the trigen assumed to be working in the modelling may not kick in.
As well as the downside of not obtaining lower emissions electricity, it also means the building is unlikely to be able to achieve the highest possible NABERS rating of 6 stars.
Gualtieri says he does not know of any building that has reached 6 stars in Melbourne or has a shot at getting there without trigen, cogen or onsite solar to provide cleaner energy and reduce draw from the grid.
“To get from 5.5 stars to 6 stars – it is very difficult to get there without help with how you generate energy.”
Another factor that is influencing the trigen technology is the steep hike in gas prices. This has smashed the business case of using cheaper gas to replace mains electricity.
“There are a lot of crosswinds,” Gualtieri says.
The majority of buildings in Melbourne that have trigen and a 6 star rating are only using trigen to supply the base building.
To supply tenants as well puts the trigen within the building in the situation of being a utility. That is “not something that just anyone can do”, Gualtieri says.
At 321 Exhibition, because the system was installed by Cogent, the tenant was already a utility as was the system provider.
In other buildings Cogent had installed trigen, the business model enabled trigen energy for tenants to be provided under an agreement, with Cogent as the utility providing the cleaner power.
The EPA building at 200 Victoria Street uses trigen for both base building and tenant under this type of model, Gualtieri says.
There is one advantage for owners and managers of only using trigen for base building supply – it is an easier pathway to get to that 6 star rating because the owner or manager cannot generally control the energy loads of tenants.
The bottom line is that the key factor in making trigen work and getting to the top of the NABERS class is having the system sized correctly.
“With all the crosswinds, that’s the most pivotal part to getting there.”