Carbon Friendly Thermal Energy – An Aussie Greenhouse

Just north of Perth, in the suburb of Neerabup, Western Australia, lies the country’s most advanced propagation facility of premier grafted vegetable seedlings. THG in conjunction with lead contractor, AIS Greenworks, has put together an Australian first in this 1-hectare glasshouse facility. While this project was many years in the making from initial concept through to completion, the actual opening was in September of 2011. THG is a fourth generation family-owned business, established in 1939.

The technology
Greenworks designed, supplied and installed technologies such as ebb and flood concrete floor irrigation to distribute fertilised water to the grow blocks; overhead sprinklers with multiple zones used as a secondary irrigation; high pressure fogging to control humidity and temperature in multiple zones, including grafting areas; water management systems to handle the entire operation; water treatment in the way of reverse osmosis; ultra-violet sterilisation; and copper treatment. All these systems and more contribute to making the high volume production of a high quality product efficient (in both energy and labour use) and versatile. During the conceptualisation of the project, Greenworks Engineer, Philip Jones, worked on creating processes to allow all the functionality desired by THG in a format that is simple to understand and straight forward to operate.

However, the heavy hitter in terms of reducing the energy costs and carbon footprint of THG’s business is the 4000kW biomass heating system that controls temperature in each greenhouse climate zone by the combustion of a locally sourced timber waste stream. And where does this waste stream come from? Danny Trandos, the director of THG, had the entrepreneurial insight to see a place for great improvement in their operations. This insight came in the way of replacing the traditional coal or gas thermal energy source of their business with a renewable waste stream.

The alliance he formed was with the Wesbeam factory down the road where they manufacture laminated veneer lumber for the construction industry. This lumber is sourced locally from plantation pine timber. Not only do the plantations capture carbon and energy during each growth phase, the waste streams are used in various industries such as garden mulch for the bark, MDF for the offcuts, and most importantly, to create thermal energy so THG can propagate new vegetable plants for the food production industry. The waste stream used by THG is a clean and dry wood chip as can be seen in the photograph.

The waste product is collected from the manufacturing facility and carted the short distance to the glasshouse facility by truck. From there it is loaded into a purpose built bulk fuel handling system. The fuel handling system can be loaded with 60m3 of fuel at once. And from there, the hydraulic walking floor system shifts the fuel into the main auger. After the main auger, a transition auger brings the fuel into the surge bin, which is level monitored by the thermal energy control system. The furnace auger meters the fuel into the furnace where it is combusted with the assistance of an over-fire fan providing secondary air and an induced draft fan providing primary air. The entire process is controlled by a PID algorithm matching the heating plant output with the current glasshouse thermal load. The control system influences the process via variable frequency drives on the air and fuel feeds.

Once the hot water is created within the heating plant, it is distributed to the three glasshouse zones with a transport main. The transport main takes the energy laden hot water all the way to the furthest compartment, which is over 150 metres away. Each greenhouse compartment has its own wall-mounted pumping unit, which draws the required amount of hot water through a mixing valve to supply the correct amount of energy to the zone.

Within the glasshouse is a network of heating pipes, which hang between the greenhouse trusses and the floor. This network of pipes conducts and radiates the energy from the hot water circuit into the environment. When the glasshouse calls for more heat, the pump unit reacts to increase the temperature of the hanging pipe network. More temperature in the pipe network equates to more energy being delivered to the space in the greenhouse, which in turn causes the air temperature to increase. A Priva Integro environmental control system, installed and commissioned by Powerplants, monitors and finetunes these air temperatures in coordination with all the other automated processes in the environment.

An excerpt of the water management design showing underground piping between water storage tanks and equipment in services building. Even future heating of irrigation water is catered for here.

The environmental impact
The traditional energy sources used in thermal energy applications such as this are coal and gas. Gas can be either piped natural gas or bottled LPG. All are forms of fossil fuels. What this means, is that over millions of years the decomposition of once living organisms has formed energy reserves. These energy reserves can be mined, delivered to the end user and combusted to provide the power required at the site. During the combustion process the carbon in the source fuel is quickly released to the environment, mainly in the form of CO2. Carbon dioxide is linked as a main contributor to global warming, and hence excessive CO2 emissions are looked down upon in the current environmental climate.

So why does the combustion of renewable fuels help? Well, because fossil fuels take millions of years to develop, and as such, the carbon released by burning these fuels will not be recaptured in the foreseeable future and therefore contributes to increasing our global carbon dioxide levels. However, if you grow a tree, you have removed carbon from the atmosphere, as a tree draws in carbon dioxide to grow. When you burn the tree, and use the energy, you release the carbon back into the environment … Well, this is the carbon that you just captured, and by growing the tree again and again you are adding no more carbon than you have just removed. Although this process takes decades, it is viewed as a renewable process and is the basis for carbon neutrality.

So when we look at the case of the Trandos’s, we look at how their carbon emissions have been reduced by the implementation of this bio-energy system. Without getting into the specifics of the maths, Greenworks knew from both experience and the theoretical calculations that this sort of 1ha development in this location will use 10,000 GJ of energy to maintain the growing temperature at around 20oC year round. Well, if they had used gas, that would be equivalent to approximately 600 tonnes of CO2 emissions per year. And if they had used coal, that number would be closer to 900 tonnes of CO2 per year. So, the result is obvious, a renewable and clean fuel in a biomass system such as this makes a huge reduction in the carbon footprint of this business.

The financial case
It’s no secret that every successful business manager wants to know how much all this will cost. Helping the environment is important, but maybe not at the risk of bankrupting the company. Of course, every case is different, depending on the costs of the various available fuels, and therefore one needs to gather all the information before making a decision. In the situation of THG, the options were relatively straightforward. Danny, with input from his coal savvy brother Steve, immediately ruled out the use of coal on this new development due to the environmental impact, the mess, and their overall poor relationship with the fuel. The option left was natural gas or LPG. Based on an approximate annual usage figure of 10,000 GJ per annum and a quoted natural gas price of $14/GJ and LPG at $0.70/L ($28/GJ), the annual thermal fuel costs came out at $140,000 and $280,000, respectively. There was room for savings, and the answer was in the wood chip waste stream. With a calculated landed price of $50/tonne (including loading/unloading and transport), the fuel value was in fact a mere $3/GJ, putting the annual running cost on the wood chip at a reasonable $30,000 per year. In summary, the options looked like this:

Fuel Type Cost/unit Cost/GJ Energy Cost 10 Year Cost
LPG $0.70/L $28 $280,000 $2,800,000
Natural Gas $14/GJ $14 $140,000 $1,400,000
Biomass – Wood Chip $50/MT $3 $30,000 $300,000

It was clear that the savings could be substantial. The additional capital cost of installing the solid fuel, biomass-powered heating station was in the order of $150,000 over a traditional gas-powered setup. The extra investment would be paid off by fuel savings in less than two years. The 10-year forecast shows close to a million dollar benefit to the business. In addition, the maximum capacity of the system, 4MW (4000kW), is enough to cater for THG’s plans for additional glasshouse development.

THG have developed a state-of-the-art propagation facility at their site in Neerabup, which not only checks off the boxes for technologies required for the production of premier grafted seedlings, but has a substantial impact on reducing carbon emission, all the while keeping the accountants happy by offering a substantial annual energy savings. This advanced development is an Australian first, and promises to produce carbon conscious seedlings for many years to come. As Danny Trandos puts it: “Aligning a renewable waste stream with our thermal energy requirements has not only given us a competitive and quality advantage, but has allowed us to meet our environmental obligations.”

About the Author
Sohum Gandhi has a Bachelor of Engineering degree from the University of Victoria, Canada. Since 2004, he has been working within the Australian Greenhouse industry. His long-term relationship with the Trandos family has been the cornerstone of many successful projects. Over the years he has witnessed THG grow in leaps and bounds to one of the most highly regarded businesses in the industry. You can contact Sohum at:

PH&G November/December 2012 / Issue 127