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The latest newsletter of the IEA heat pump centre discusses how the foundation piles of a building can be applied as ground heat exchangers, leading to installation cost reductions. It provides examples of installations in Japan, including that in the headquarters of Mayekawa that employs an ammonia screw type heat pump unit.

The market for this type of system known as ‘Energy Pile System’ has been growing in recent years in Europe. The use of the building foundation piles as ground heat exchangers leads to installation cost reductions, while at the same time, the multiple building foundation piles are suitable for the underground thermal storage as the well field.

With the origins for this system dating back to a 1962 article in the Journal of Japanese Association of Refrigeration, it is now also gaining popularity in Japan, in applications such as schools and other public buildings.

An Energy Pile System employing an ammonia heat pump unit

The Energy Pile System was employed in 2008 at the head office of Mayekawa in Tokyo. To fix the U-tubes in the cast-in-place concrete pile, multiple U-tubes were inserted when the reinforced frame was set into the drilled hole from the ground , a method developed by Taisei Corp.

The system caters for a total floor area of 9,304m² and features:

• ammonia screw type heat pump unit which has a heating capacity of 140kW and can supply heat corresponding to 14 % of the peak demand and 31 % of the daily demand.

• 20 piles whose average length is 37m and average diameter is 2,000mm used as ground heat exchangers: the piles are installed at intervals of 6.4m in the horizontal direction and 13.7m in the vertical direction.