Ground Source Heat Pump Systems

in Australia, ground source heat pump systems are uncommon, yet they have their place, but only in very cold climate areas or as hybrid systems combining ground source and solar collectors for special projects.

Are ground source heat pumps and geothermal heat pumps the same?

Ground source heat pumps are also known as geothermal heat pumps* because they use the stable temperature of the earth at a depth of 3-5 metres. If you have ever visited Cooper Pedy  and spent time in an underground home, you'll know how stable the temperature is below ground level!   * (Definition of geothermal: of or relating to the heat in the interior of the earth.)

A ground source system is configured so the inlet water to the storage tank comes from deep underground and is at a relatively stable temperature all the time.

In a very cold climate this means that in winter time, the water entering the storage tank will be at a higher temperature than if the water came from the tap, so less heat must be "pumped" into it to reach your target hot water outlet temperature. 

Graphic and information with permission of David Darling's Encyclopedia of Renewable Energy and Sustainable Living

How does a geothermal pump get its heat?

A heat pump works not by burning a fuel or passing electricity through an element to make heat. It works by "pumping" heat from one region to another.

But it firstly has to have a source of heat to "pump".

A regular air source heat pump (ASHP) uses the air outside your house as its source of heat.  The ASHP does fine in the vast majority of Australian climates, but as the air gets colder, the heat pump can’t get as much heat, and in particularly cold or frosty locations, a ground source heat pump may have advantages.

Why is a geothermal heat pump well suited to very cold climates?

A geothermal heat pump (GHP) uses the temperature of the ground as its source of heat. In our region, below –ground is about 10-15°C all year round, so the unit has a constant source of heat that never drops to that 0°C range,.

Hence, the efficiency of the heat pump can be improved as the temperature difference between the water entering the tank and the target temperature of your hot water is less - it requires less heating.  

In these circumstances, a ground source heat pump will use about half of the electricity of an air source heat pump in very cold weather. This is great news.

But that good news is tempered with the very high cost of a GHP.  To get that ground temperature, you have to either dig wells to pull water from deep in the earth, or dig a swimming pool sized hole in the yard that is then lined with pipework which carries liquid to pick up the ground temperature. 

As with everything, the total cost versus the total savings must be taken into account before you make this important decision.

In Australia, with few exceptions, we have few very cold climate areas where air source heat pumps might lose efficiency (i.e. use more electricity) over prolonged very cold periods making geothermal heat pumps a less viable option than an air source heat pump for hot water.

In many locations overseas, for example in Canada, Alaska or Northern Europe where winter temperatures below -15°C are commonplace, ground source heat pump systems work extremely effectively. 

However, some projects in Australia are designed to take advantage of the high temperatures of the earth a kilometre below the surface where aquifers can be tapped, or water pumped to that depth and brought back to the surface considerably hotter.

There are a number of projects in Western Australia where council swimming pools are heated in winter using this geothermal source during winter.

What are Hybrid Geothermal Systems?

In some cases, a geothermal heat source is combined with a split system heat pump where it can be used for all a homes heating requirements - space heating via fans and underfloor, and for hot water - see the picture above.

These hybrid systems may have applicability in Australia, as the stable geothermal heat source works to your advantage both in summer and winter -  water heating all year round, plus lower space heating costs in winter, and lower cooling costs through our hot summers.

These hybrid systems are both "air-conditioners" and hot water heaters.

So in your mind's eye, combine the concepts shown in the two pictures on this page and you'll have an understanding of a hybrid geothermal heat pump system.

Effective, but considerably expensive to set up.

Veraahdy Pty Ltd does not supply or install geothermal systems, however we have contacts to people who do, so feel free to give as a call if you would like an introduction to these vendors.

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