Expansion and HDPE pipe

Larger GCHP projects are being done more often as the benefits of the technology become more apparent. Larger diameter high-density polyethylene (HDPE) pipe is used in the projects as the GHX fields become larger and the flow rates increase. A question raised regularly in training workshops is how to deal with the high expansion rates of HDPE pipe. Are expansion joints or loops needed?

That depends. When HDPE pipe is used inside the building and is unconstrained, allowance must be made for the high expansion rate of HDPE pipe. When HDPE pipe is buried, it is constrained by the soil. It acts more like an elastic band and will expand radially rather than linearly. In most situations, expansion loops and expansion joints are not needed with buried HDPE pipe. 

The Plastic Pipe Institute has the Second Edition of the Handbook for PE Pipe for sale on its website. It includes information on all aspects of designing and installing PE pipe, including how to deal with pipe expansion.