NOVELTY - The support has a base support element (30) supported by a ground surface around a borehole. An annular orientation guide element (58) is fitted to an upper surface (40) of the base support element. The guide element has an upper surface (59) at a selected angle relative to a lower support surface (57) of the base support element. A casing support ring (54) is fitted around an outer casing (46) of a geothermal borehole heat exchanger and coupled to the guide element to support the casing in the borehole. The outer casing extends through the ring, a central conduit and an aperture (36).    USE - Casing support for use in a chamber (claimed) i.e. inspection chamber, of a geothermal borehole heat exchanger utilized in ground source heat pump industry for a geothermal energy system for large scale geothermal thermal storage applications.    ADVANTAGE - The support extends through a hole in a base during an installation of the coaxial geothermal borehole heat exchanger, so that the temporary surface casing is not cemented in place in the base to enable isolation of an unstable surface rock formations to enable drilling of the main borehole, thus retrieving the temporary casing to reduce costs depending on time taken to retrieve and length used. The boreholes in a single chamber reduce a surface area of a ground required for the boreholes. The support allows an area of contact between the orientation guide element and base support element and between the casing support ring and the orientation guide element to be sealed using a sealing compound when installing the orientation guide element and the casing support ring so as to ensure that surface water from the borehole does not enter the chamber, thus protecting a well head and associated connections and flow lines against corrosion.    DETAILED DESCRIPTION - The base support element is composed of precast concrete. INDEPENDENT CLAIMS are also included for the following:    (1) a chamber comprising a casing support    (2) a method for installing a casing support of a geothermal borehole heat exchanger.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of an installation of a coaxial geothermal borehole heat exchanger illustrated during installation.    Base support element (30)    Aperture (36)    Upper surface (40)    Outer casing (46)    Casing support ring (54)    Lower support surface (57)    Annular orientation guide element (58)    Upper surface (59)