Tri Harder The Final Chapter – Why do we have so many trigen systems and 6 reasons to install one
So what has driven the recent plethora of trigeneration systems? Why do we put them into buildings? Will there be more trigeneration systems in the future? I’ve covered a lot about trigeneration from Part 1 of Tri Harder where I talked about the different carbon intensities of grid electricity around the world to Part 6 of Tri Harder where I talked about flue emissions and maintenance.
This final chapter in the tri-harder series answers the questions of why trigeneration, when would I use it and how do I know if its right for my building.
Why do we have so many trigeneration systems in buildings?
Driver #1 – Carbon Emissions
As covered within the Tri Harder series, carbon emission reduction is one of the biggest drivers to installing trigeneration systems in buildings. Depending upon on which state you are in savings of upto 50% in carbon emissions year on year can be achieved.
Driver #2 – NABERS Ratings
Rightly or wrongly NABERS ratings are calculated using carbon emissions rather than energy. In a normal Class A or Premium office buildings a 4.5 – 5* NABERS rating should be achievable with normal well designed VAV air conditioning and without trigeneration, on-site power generation or chilled beams. A 5.5 – 6* NABERS rating cannot be achieved without trigeneration or mixed mode air conditioning, in large floor plate office buildings natural ventilation is not practical – only remaining solution for 5.5 – 6* NABERS is onsite power, in a tall CBD office building that means trigeneration.
Driver #3 – Green Star Ratings
As well as trigen giving you good energy points – well its carbon emissions but its called energy points in Green Star, if it was energy then trigen wouldn’t give you a better score than grid. Anyway, back to the point. Under Green Star not only does trigen get you points under ENE-1 it can also get you peak load reduction points. Under version 3 office design tool, you can get one point for 15% reduction and 2 points for 30%.
So if you are already spending money on trigen for energy points, it makes sense to increase the size of the engine for not much more money and get the peak load reduction points. Well not really because in an office building if you install one trigen engine to meet a 30% peak load reduction it will only be on for 30-40% of the year, not generating a lot of carbon savings or if your building is only part occupied it won’t get turned on.
It is not the intention of the Green Star credit to encourage large trigeneration systems, the intention is to reduce the peak demand on the grid. This credit can still be obtained with smarter use of a variety of onsite generation sources rather than just trigeneration.
Why would I put a trigeneration system into buildings?
Reason #1 – Carbon Emissions
When designed well, operated correctly and in the right type of building trigeneration and cogeneration can reduce the carbon emissions of a building. But, it will cost more over a 10 year period than a comparative emission reduction from offsite renewables.
But, if you require a NABERS rating you won’t be able to take into account the carbon savings of off site renewables so you end up with trigeneration.
Reason #2 – Peak and Shoulder Electricity Costs
The cost of electricity during peak times can be as much as twice the daily average and three times more than off peak. In NSW the average daily NEM price is 5.9 c/kWh and peak average is 9.8 c/kWh. Through operating a trigeneration system it is possible to reduce the amount of grid electricity being used during peak times, thereby reducing costs.
It may also be possible to reduce the peak demand costs through implementing trigeneration systems. This needs to be carefully looked at on a project by project basis.
Reason #3 – Onsite Standby Power
If you are designing a project that has a significant onsite standby power requirement, such as a hospital or data centre, it may be possible to use a trigeneration engine in place of the standby generator. The cost of a trigeneration engine tends to be about the same as a standby generator, thereby changing the financial investment and the payback of the trigeneration system considerably. It is likely that you can only replace 25% of the standby generators but this still may create a good return on investment.
Reason #4 – Large Heating Requirements
Cogeneration is inherently more efficient than trigeneration – using the heat source directly rather than converting it to into chilled water. If you have a project with a large heating demand such as a swimming pool or industrial process needs then cogeneration systems can save a lot of money as well as carbon emissions. Basically generating electricity as a by-product of generating heat.
Reason #5 – Onsell to domestic size tenants
Domestic scale tenants such as single owner retail stores or residential apartments and houses pay at least 30-50% more than larger users such as landlords. Using a trigeneration it is possible to generate heat to create cooling within the building and then onsell the electricity at a higher cost than the basebuild pays for it. This option has the potential to create carbon and cost savings to both the landlord and the tenants / residents within a fair payback period.
Reason #6 – Large Mixed-Use Developments
The more hours a trigeneration system runs the great the opportunity to obtain a carbon and financial payback, in an office building a trigeneration system that cant export to grid is likely to only run between 8am and 6pm.
Mixed-use developments have the opportunity to extend the operating hours through the varying demands – residential peak demands are early in the morning and in the evening, hotel demands extend to later in the day and casinos operate 24 hours.
Creating a trigeneration system that can operating 24 hours a day can change a payback period from 12 years to 8 years or less.
In summary from the Tri Harder series there are some areas that you need to be very careful of in order to reap the potential benefits of trigeneration
– grid carbon intensity varies across Australia, trigen wont always generate carbon savings
– dont oversize a trigen unit to meet a Green Star credit, it may not operate as intended
– trigeneration wont always provide a cost saving, in many states in Australia trigeneration will cost more upfront as well as more than grid every year
But if you carefully consider each trigeneration system on a project by project basis then there are many reasons to consider trigeneration just make sure you are clear about the risks and rewards of those benefits.
Calculating the exact benefit and cost of a trigeneration system should be done for each individual building as the profile of electrical demand, cooling demand and operational profile will vary the calculations. If you are looking at a trigeneration system and need help please email me at email@example.com