Underground Temperature Regulation

Aerial view of the Ghost Gully Farm

In the summer of 2009/10, a severe heatwave hit South-East Queensland, shutting down the Ghost Gully Produce farm in Gatton for five weeks. Farm losses are, of course, costly in terms of lost product and production, and potential lost customers. Temperatures of up to 45°C were being routinely reached. Overhead sprays were used to cool the systems, but were blown over the systems by westerly winds.

We were desperate to cool the systems, but the best cooling towers were only capable of reducing temperatures by 4–6°C. Their effectiveness, pricing and running costs made us wonder if there could be a better way.

Gatton is not only prone to extreme summer temperatures, but also to sub-zero winter temperatures. What was needed was a solution to thermal dormancy (and worse!) in summer, and growth shut down in winter.

I stumbled across heat pumps with underground piped heating used in European homes to maintain an even temperature through summer and winter—could that work here? I tried to research ground temperatures, but data was difficult to come by. A customer knew of a farmer who had trialled a similar installation, but only achieved limited success. The idea was clearly not new, but if we could make it work well, it would be a solution for summer and winter, with reduced overheads compared to other heating and cooling methods. Still, we were flying into this blind.

I met with Gary from Ghost Gully Produce—a long term customer, and the farm most affected by the 2009/10 heatwave. Ghost Gully Produce is also a fully automated farm, which meant data on air and water temperatures would be logged and available for analysis. We set our price point as the price of cooling towers for the systems.

Overhead view of the trench at Ghost Gully Produce after earthworks

The decision was made to utilise a 350 metre circuit, and an excavator was hired for the necessary groundworks. We knew we would need to use significantly more pipe than that used in the other known installation, and it would have to be sufficient to cool five 10,000 litre tanks.

The installation was completed in full, but the overall initial outlay meant that there would be no PLC controllers to achieve variable flows, although this was accommodated in the design. A lack of power to the most distant systems meant that only two systems of the five would be brought online to begin with. Our worst fears were realised when we only achieved marginal improvements initially… but with modifications, we finally saw the results we had been looking for.

The following charts show the system air and nutrient temperatures before and after installation of the underground temperature regulation system (click to enlarge):

Summer 2008/09 Pre-Installation

Winter 2009 Pre-Installation

Summer 2009/10 Pre-Installation

Winter 2010 Post-Installation

Summer 2010/11 Post-Installation

Winter 2011 Post-Installation

Data for Winter 2011 is only available on one system, as the temperature probe has failed and is awaiting replacement. Anecdotal evidence is that the underground temperature regulation is still working to improve growth in line with the other system.

The Summer of 2010/11 was a mild one, as far as temperatures go, and not a full test of the system’s capacity. I look forward (with some trepidation) to the next heat wave arriving, and really putting the system to the test. In the meantime, I’m happy knowing that overall, the plants are growing better than usual, with the regulated nutrient solution’s temperatures. In particular, observations by Gary are that there has been particularly constant, consistent growth during the seasonal transitions, and a shortening of the winter growing period on the systems that are temperature-regulated.