The energy slab is a hybrid structure to utilize geothermal energy by encasing heat exchange pipes with a horizontal layout. However, the ambient air temperature may interfere with the thermal performance of the energy slab due to direct exposure. Such an unfavourable situation can be improved by installing a thermal insulation layer on the energy slab. This study experimentally investigated the applicability of the two types of energy slabs (floor-type and wall-type) equipped with the aerogel-type thermal insulation, which were constructed in an underground parking lot. During the thermal performance tests, the thermal performance of the energy slabs was investigated by measuring the inlet and outlet temperatures of the energy slabs. In addition, the structural integrity of the energy slabs was assessed from the measured temperature and thermal strain at the energy slabs. It was found that the installation of the thermal insulation layer enhanced the thermal performance of the energy slab and prevented surface condensation. In addition, it was realised that the induced thermal stress especially during the cooling operation of the energy slab should be carefully handled to prevent damage to parking lot structures.