Improving the performance of the down-hole heat exchanger at the Alpine Motel, Rotorua, New Zealand

The township of Rotorua is situated on top of a shallow geothermal reservoir. The resource is easily accessible and is commonly used for district heating. Excessive exploitation in the 1970s and 1980s resulted in the decline of the unique thermal natural features in the Whakarewarewa geysers area, which prompted the government to set a production moratorium within a 1.5 km area around the geysers. The production wells at the Alpine Motel had to be abandoned in 1987 and the motel resorted to gas fired heaters. A down-hole heat exchanger (DHE) was used to supply the required heat, but only 22% of the heat demand was produced. Air lifting was implemented to improve the performance of the DHE, which resulted in a 125% increase in heat output. This significant increase in heat output compared to early trials was discussed. Recommendations are given to further improve the DHE performance.

► The Alpine Motel is situated within the exclusion zone of Rotorua geothermal system.
► The average annual thermal power demand of 90 kW was fully met with electricity and gas fired boilers.
► A down-hole heat exchanger (DHE) was installed, but could only provide 20 kW of thermal output.
► Installing the airlift tube increased the DHE thermal output by 125%, which is much higher than reported trails.