Ice-on-coil thermal storage apparatus and method

A method for storing thermal energy comprising:

• placing a freezable liquid in a container;
• placing a cooling coil assembly in the container, the cooling coil assembly including a plurality of tubes, each tube having a non-circular cross-section with a horizontal dimension and a vertical dimension, the vertical dimension being greater than or equal to the horizontal dimension, the tubes being oriented generally horizontally and being arranged in a plurality of spaced apart, generally vertical rows, with neighboring tubes in adjacent vertical rows being horizontally spaced apart sufficiently such that unfrozen, generally vertical passageways remain between the envelopes of frozen storage liquid;
• passing a refrigerant through the tubes to create an envelope of frozen storage liquid around each tube during a storage cycle, the envelope of frozen storage liquid on each tube conforming to the non-circular cross-section of the tube to increase packing efficiency of the frozen storage liquid per unit volume of available space for frozen storage liquid around the coil assembly, and forming vertical bridging of storage liquid between the envelopes of frozen storage liquid on adjacent tubes in the vertical rows;
• extracting thermal energy in the form of cooling from the frozen storage liquid during a usage cycle;
• and
• passing storage liquid vertically between the envelopes of frozen storage liquid of adjacent vertical rows to increase heat transfer efficiency compared to the heat transfer efficiency of a method using an otherwise comparable coil assembly of tubes having a circular cross-section of the same cross-sectional area as the tubes having a non-circular cross-section.