Geothermal energy is one of the most energy-efficient systems currently available, offering the following advantages:

• can heat and cool sheds
• almost zero carbon emissions
• highly scalable
• may slash energy costs by between 50 and 70 per cent, and
• base-load energy is not reliant on sunny skies or windy days.

There is a project underway to look at its application to the poultry industry in Australia.

In a previous edition of The Drumstick, its editor wrote about biomass energy and the potential it has to cut heating costs and keep litter drier than liquid petroleum gas (LPG). That story created quite a bit of interest, he says, from growers and 'green energy providers - companies providing cheaper and green energy solutions for a range of industries, including intensive agriculture.

One of the companies introduced him to the concept of geothermal heating and cooling, also known as a ground source heat pump.

So what exactly are geothermal heating and cooling and do you need to be near hot water springs or a volcano to take advantage of this sort of energy?

The answer to the second question is: no, you definintely don't need to be near a source of hot water or mineral springs to take advantage of geothermal energy. The remained of this article deals with the first question: what is geothermal energy?

Basically, geothermal heating and cooling involves the use of constant heat (geothermal energy) that exists two to three metres below ground for heating and cooling purposes.

How Does It Work?

The temperature of the soil at approximately two to three metres below the surface remain relatively constant at around 12 to 18°C all year round, depending on where you are in Australia. A geothermal heating and cooling system is designed to draw on this heat energy using a system of fluid-filled underground pipes called a loop. The loop absorbs the heat energy in the ground and carries it to a heat pump. The heat pump compresses the heat to a higher temperature and distributes it throughout the poultry house, pulling heat from the shed and depositing it back into the ground via the same loop system.

The three main components of a geothermal system are:

• the heating and cooling pump - pretty much the same technology as a refrigerator or air conditioning pump; the more common term now is 'heat pump'.
• the underground piping system made up of HDPE poly pipe; the 'loop' and
• the ductwork to distribute the heat.

Figure 1. Basics of a geothermal heating and cooling system

The Loop

The poly pipes that make up the loop can be:

• closed or open, and
• horizontal or vertical

An open loop system uses groundwater from an ordinary bore as a heat source. The groundwater is pumped into the heat pump unit where heat is extracted and water is disposed of in an environmentally safe manner. Because groundwater is a relatively constant temperature year-round, bores are an excellent heat source.

A closed loop system uses a continuous loop of buried polyethylene (poly) pipe. The pipe is connected to the indoor heat pump to form a sealed, underground loop through which an environmentally-friendly anti-freeze and water solution is circulated. A closed loop constantly recirculates its heat-transferring solution in a pressurised pope, unlike an open loop system that consumes water from a bore.

Most closed loops are trenched horizontally in areas adjacent to the sheds. The poly pipes are laid two to three metres deep in trenches several hundred metres long. (Figure 2)

Figure 2. Trenches for laying horizontal closed poly pipe loop

If insufficient land is available for trenching. the loop can be installed vertically. Holes are bored up to 100 metres deep. U-shaped loops of pipe are inserted in the holes. The holes are then grouted to ensure consistent ground contact with the earth (Figure 3).

Figure 3. Vertical loop configuration

How Does the Geothermal Pump Work?

Simply put, a heat pump is a device that uses a small amount of energy to move heat from one location to another. Heat pumps are typically used to pull heat out of the ground to heat the poultry house but they can be reversed to cool the buildings as well. In a way, if you know how an air conditioner works, then you already know a lot about how a heat pump works. This is because heat pumps and air conditioners operate in a very similar way.

"Hold on! You said that the earth is approximately 12°C. My birds need more heat than that!"

In addition to moving heat from one place to another, heat pumps also boost the temperature from 12°C to 38°C. Some commercial units can get to 93°C. The heat pump does this using a cycle of evaporation, compression, condensation and expansion. A refrigerant is used as the heat transfer medium which circulated within the heat pump.

The system starts as the cold, liquid refrigerant passes through a heat exchanger (evaporator) and absorbs heat from the low-temperature source, i.e. fluid from the ground loop. The refrigerant evaporates into a gas as heat is absorbed. The gaseous refrigerant then passes through a compressor, where the gas is pressurised, raising its temperature to more than 82°C. The hot gas then circulates through a refreigerant-to-air heat exchanger, where heat is removed and pumped into the house at approximately 38°C. When it loses the heat, the refrigerant changes back to a liquid. The liquid is cooled as it passes through an expansion valve and begins the process again. To work as an air conditioner, the system's flow is reversed.

Scale of Heating and Cooling

The technology is highly scalable, meaning that systems are available to heat an average home all the way to an 11,000-square metre building. In fact, there are several examples in New South Wales, where geothermal energy is being used quite effectively on a commercial scale. These include Lithgow Hospital, Macquarie University, Wagga Wagga Civic Centre and may more throughout the rest of Australia.

How Efficient is a Geothermal System?

Very, according to Mr Stein.

According to the US Environmental Protection Agency (EPA), geothermal heating and cooling is the most energy-efficient method of heating and cooling currently available.

Most geothermal heat pump systems are measured by their co-efficient of performance (COP) - a scientific way of determining how much energy the system produces relative to how much it uses.

Most geothermal pump systems have COPs between 3.0 and 4.5. That means that for every dollar of energy used to power the system, A$3.0 to $4.5 of energy is supplied as heat. Using fossil fuel as an example, whereas a fossil fuel furnace may be 78 to 98 per cent efficient, a geothermal heat pump is about 500 per cent efficient.

What's the Catch?

The system is clearly very expensive to install and requires a fair size of land in which to lay the horizontal poly pipes (the loop), that are required to extract heat from the ground or to return it during the cooling cycle.

Further, the system may still require a supplemental heat source in cold conditions.

Application for Poultry Meat Growers: How Viable is Geothermal Heating?

Professor Yung-Sheng (Shawn) Xu from the University of Missouri in the US has developed a geothermal energy system for a large turkey farm in that state. The project has been jointly funded by the US Department of Energy as a demonstration project in partnership with the farm's owner. The system is being used both for brooding and grow-out. The project team estimates that they will save on energy costs between 50 and 70 per cent.

Professor Xu is working with an Australian company to develop a system that will work in local poultry houses, as it was realised that existing equipment is not suitable for an Australian style of building.

Recently, Mr Stein has met Brad Donovan from Ground Source Systems, who said they are well on their way with a re-design of the equipment after taking a farmer with many years of experience to evaluate the system in Missouri and having roundtable talks with Professor Xu on how Australian farms operate.

Mr Donovan was surprised by the level of technology and science that went into raising commercial poultry.

He said: "We need to tick all the boxes and to work with Aussie farmers to be able to do this. There is no off-the-shelf solution; it is going to take time to get it right. It's not something that can be rushed and put on the market without a full evaluation. We have seen that too many times in the past."

The boxes Mr Donovan was referring to is what will will make it appealing to the farmers - reducing operation costs, minimal maintenance, improved flock environment, reliability and return on investment.

September 2013