Thermal Performance of Water Permeable EPS as Pipe Insulation
Paper in proceeding, 2004
The purpose of this project was to study the function and strength of the EPSPEX pipe under unfavorable moisture conditions, in order to enable a comparison to traditional pipes. The EPSPEX pipe construction consists of cross-linked polyethylene (PEX) medium pipes placed in—and thermally insulated by—blocks of expanded polystyrene (EPS). The EPS blocks have a square-shaped cross-section and are laid directly in the ground with a polyethylene foil as only external protection. Laboratory tests were done on two different EPS alternatives: The standard density DC 200 and the lighter DC 100. These designations refer to the materials’ nominal compressive strength: 200 kPa and 100 kPa respectively. The pipes, laid in a watertight box backfilled with drainage shingle, were subjected to repeated flooding and drying. During the tests, the temperatures in both flow and return pipes were 80 ºC. The heat losses from the EPSPEX pipe increased after each repeated flooding and subsequent drying. The increase occurred at a diminishing rate and the insulation capacity recovered better if longer drying periods followed the floods. After four repeated floods and month-long drying periods, the heat losses had increased with approximately 40 % for the DC 200 alternative, and about 20 % for DC 100. During a final additional drying period the pipes recovered significantly. After this, the corresponding heat loss increase was about 20 % and 6 % respectively. The compressive strength of the EPS dropped somewhat during the tests, and a significant decrease in modulus of elasticity was seen.