Geothermal vs. traditional air conditioning - Geo Air Services

These cost to run comparisons are based on the figures found on the www.energyrating.gov.au website for normal inverter ducted systems. Also the "star" power efficiency rating given on the units is based on an outside air temperature test for the outdoor unit for summer and winter temperatures of in this case, 24 degrees Celsius humid air for summer and 7 degrees Celsius humid air in winter. Indoor temps are for traditional systems are at 20 degrees Celsius dry air for winter and indoor of 19 degrees humid air for summer testing, all as per Australian Standard AS3823. Remember this, once those outdoor temps go above and below what is tested, the unit will use more power than listed.

Geothermal units are tested based on ground temperatures, which are more consistent than air and more stable, even at 0.5-1m deep. For this comparison, I will use Sydney temperatures of 18 degrees Celsius in winter and 25 degrees Celsius in summer at a depth of 600mm down. The deeper you can go, the better the stability of the temperature. Outdoor air temps in Sydney can get as high as 40 degrees Celsius in summer during the day and as low as 0 degrees Celsius in winter at night. These temperatures are from metropolitan areas. Coastal areas are only slightly more temperate for winter nights and summer days, usually only by 5 degrees though. Mountain areas are as always colder in winter.

Indoor temps are for geothermal systems are the same as traditional systems, at 20 degrees Celsius dry air for winter and indoor of 19 degrees humid air for summer testing.

The price of electricity is compared at 16 cents per KW hour for 8 hours per day over 30 days of summer or winter.

For a geothermal unit of 9kw and allowing for a pump of 250watts the figures are as follows:-
At 9kw cooling at ground temp of 25 degrees Celsius , approximately 2.0kw per hour, and at 9.8kw heating at ground temp of 16 degrees Celsius, approximately 2.4kw per hour.

A comparative Fujitsu inverter unit of 8.5kw cool uses approximately 2.8kw per hour, and at 10kw heat uses approximately 2.75kw heating. Not much for a small unit, but about $30 more expensive in summer, based on the rated temperature of 24 degrees and around $18 more expensive in winter, based on outdoor temp of 7 degrees. Watch the power bill go up in extremes of temperatures outside.

Not convincing enough, then lets look at a geothermal unit of 15kw and allowing for a 400 watt pump the figures are as follows:-
15kw cooling at a ground temp of 25 degrees Celsius, approximately 3.8kw per hour and at 16.8kw heating at a ground temp of 16 degrees uses approximately 3.9kw heating.

A comparative Actron Air inverter unit of 15kw cool uses approximately 5.25kw power, and 16kw heating uses approximately 4.75kw heating. That's about $60 more to run in summer and $40 more in winter.

Once again, remember that normal inverter units with an outside fan compressor/condenser will use more power once the temperature goes up in summer over 24 degrees, and how many people switch their air-conditioning at an outdoor temp of 24 degrees. Winter at night, the outside fan compressor/condenser will use more power once the outdoor temp goes below 7 degrees. A geothermal unit heating is still running at a ground temp of 16-18 degrees, even when the outdoor air temp is 2 degrees.

Also remember that if you live in an area where there is no town gas supply or in the country areas where electricity is charged at a higher rate, you will save more.