Making trigeneration work
Faculty Management spoke to the Spotless facility management team at the new Royal Children’s Hospital about the practicalities involved in trigeneration, the challenges presented and how they can be overcome, and the advantages gained.
The new Royal Children’s Hospital in Melbourne is supported by a trigeneration power plant that provides base load power 24 hours a day, thereby reducing the hospital’s dependency on the grid and reducing electricity costs. The plant will also assist in reducing the hospital’s greenhouse gas (GHG) emissions.
Facility Management interviewed the Spotless facility management team at the new Royal Children’s Hospital to learn more about the installation at the Royal Children’s Hospital and to gain their perspective on investing in a trigeneration system.
At the time of writing, it was still early days regarding the evaluation of the effectiveness of the system and related issues; however, the team strongly believes that trigeneration systems are “well worth the investment in time and capital as they provide very tangible benefits”.
THE BUSINESS CASE FOR TRIGENERATION
Why was it decided to install a trigeneration system at the new Royal Children’s Hospital?
A variety of reasons were involved. One was a desire to reduce the peak demand that the building made of the grid supply, which reduces the costs of electricity and the design capacity requirement of the electrical chiller plant capacity. In addition, the improved energy conversion efficiency would reduce overall fossil fuel use and GHG emissions compared to the traditional split of mains gas and mains electricity. The plant would also make a cost-effective contribution to the overall energy redundancy strategy.
In addition, the nature of the electrical, cooling and heating demands of the site was a good fit with the optimum operating strategies for trigeneration systems. For instance, the site has high and reasonably consistent base loads. These made it a good solution to the requirement.
Under the public-private partnership (PPP) model, the hospital did not prescribe a trigeneration solution, but it did prescribe continuity of supply and a reduction in GHG (greenhouse gas) emissions. The private sector consortium determined this arrangement to be the best overall method to deliver these reduced GHG emissions, when considered over the 25-year life of the project.
Do the cost savings achieved through the reduction of energy costs make the upfront costs worthwhile and what is the expected payback period?
Cost savings against budget are yet to be established. In 2009, the payback period was forecast to be fewer than seven years, although utility prices, particularly peak electricity prices, are not yet as high as were anticipated in the 2009 analysis. If one assumes that electricity prices will increase over the coming years – and at a greater rate than gas prices – then the original business case is likely to remain true.
What environmental benefits are gained through trigeneration?
The benefit gained is essentially the increased efficiency (less waste) in turning fuel into heat and power. Whereas most centralised grid power stations waste the heat that is a by-product of their electricity generation, when we generate our own electricity, we use that heat in the facility to supplement heating and cooling water – thereby reducing our overall fuel use.
A significant amount of electricity is also wasted in the transmission and distribution system of electricity networks. Because we are generating electricity at the point of use, these losses are reduced to virtually nil. The more efficient the conversion of fossil fuel, the less needs to be used.
Victoria’s grid electricity generates particularly high levels of GHG, so burning gas instead of coal-derived electricity creates an additional GHG reduction. In areas of the world where grid electricity is generated from 100 percent renewable sources, however, this particular benefit does not apply.
What practical decisions were involved in choosing a trigeneration solution for the hospital?
Key decisions start with understanding the electrical, cooling and heating loads, and their daily and annual profiles to establish whether the profiles would suit a co- or tri-generation plant. Then, the quantum of the loads must be assessed as accurately as possible to allow sizing of the engine and chillers, so they can operate to their optimum parameters.
A reciprocating engine was chosen over a turbine because a local supplier, Cummins, was selected for the generator and alternator supply to reduce risks in control and synchronisation, and Broad chillers were selected. Both companies have strong track records regarding these installations and Melbourne-based support operations.
What do facility managers need to consider before choosing to install a trigeneration system in their facility?
The first question facility managers should ask themselves revolves around the load for electricity and heat – the size and their daily/annual profiles. The desire is to try and match electricity generation with a heating or cooling load.
Given the capital investment required, it is sensible to have a reasonable degree of certainty or control over the heating or cooling load for some years forward, as these load assumptions form the business case for the capital investment.
A good first point of call, particularly for a facility manager lacking the necessary expertise, might be one of the number of companies that design, install and maintain these systems.
What challenges were there during installation and how were these overcome?
A key challenge was arrangements concerning connection of the plant to the grid. While the system is not designed or expected to export electricity to the grid, its operation depends on connection to the grid. In other words, it is not designed to run in island mode. This generated a number of challenges for the design team and created significant uncertainty during the design development process. These challenges were overcome through a process of redesign and negotiation.
THE FUTURE OF TRIGENERATION
Do you believe that the use of trigeneration systems will become widespread in the future?
A key barrier to the installation of a trigeneration system is the technical and commercial uncertainties associated with connection to the grid network. Determining the technical configuration – and hence the financial cost – for safe connection to the grid can be complicated. This can be costly in time and money, which can cause major projects in particular to err on the side of the more conventional power supply arrangements.
This technical barrier is not, however, the only one. The barriers to wider implementation of this mini power generation distribution throughout the grid are quite diverse and, therefore, are unlikely to be easily or quickly altered. These barriers include ignorance, regulatory issues and mispricing.
A small number of facilities will perhaps always appear to be good candidates for a trigeneration system and will proceed. The question is whether currently more marginal business cases will ever become stronger.
THE TRIGENERATION SYSTEM AT THE ROYAL CHILDREN’S HOSPITAL
The trigeneration system at the new Royal Children’s Hospital simultaneously produces electricity, cooling and heating. Heat recovered from the gas engine’s exhaust and jacket water is used by two absorption chillers to produce chilled water. The chillers use a lithium bromide solution as a refrigerant and supply the primary chilled water ring main. The generator and absorption chiller jacket water is also used via a heat exchanger to produce hot water for the primary heating hot water ring main.
The trigeneration system features two 1160-kilowatt (electrical) Cummins C1160N5C (QSK60) lean-burn gas generator sets. The gas gensets and diesel units were installed and integrated by Cummins, PSG Elecraft (the principal electrical services contractor working on the project) and the mechanical services contractor, RACAH – a joint venture between AG Coombs and AE Smith. Cummins also installed the standby power system at the hospital, incorporating three 2250-kilo volt-ampere Cummins C2250D5 (QSK60) diesel generator sets.
Each genset will operate for around 6000 hours a year during peak demand. The diesel units can synchronise with the gas gensets and load share in the event of a blackout. Cummins assisted with the design of the two digital master controllers, one each for the gas and diesel gensets.
According to Nathan Saffery, project manager for PSG Elecraft, Cummins’ ability to provide a fully integrated system of trigeneration and standby diesel gensets was critical. “The fact that we didn’t have to make two separate electrical systems and then try to interface these systems was hugely beneficial,” he notes.
The three diesel gensets are fed with fuel from two 50,000-litre underground tanks, which are sited 200 metres from the generator room. There are two fully separate supply and return lines (adding to the total length), as well as three 1000-litre day tanks with a fully automatic fuel control and monitoring system. Cummins, together with its contractors, also installed the complete noise and engine exhaust attenuation system for the diesel standby generators to achieve 75db(A) at 1 metre.