Prefabricated ground coil assembly

A prefabricated ground coil assembly coiled in an annular configuration for storage and openable to an uncoiled configuration for use, comprising:

• a first header providing an inlet means for connection to a fluid supply circuit;
• a second header providing an outlet means for connection to the fluid supply circuit;
• a plurality of flexible elongate coil elements connected in parallel between the headers, each coil element comprising a first pipe connected at one end to the first header and a second pipe connected at one end to the second header, and a footer interconnecting the other ends of the first and second pipes, the first and second pipes being of the same length or of different lengths wherein the difference in length is the same for each coil element;
• the coil elements being coiled spirally in contiguous relation to form an annular package whose axial length is equal to the sum of the diameters of the pipes, the package being openable to a substantially planar configuration in which the pipes of the coil elements lie parallel to one another.