A year-round air-conditioning system employing refrigeration equipment in a manner which enables usable heat to be supplied to a space during the winter period, and by reversing the operation cycle to extract heat from the same space during the summer period. When operating as a heating system, heat is absorbed from an outside medium (either air, water, or the earth) and this heat, together with the heat equivalent of the work of compression, is supplied to space to be heated. When operating on the cooling cycle, heat is absorbed from the space to be cooled and this heat, together with the heat equivalent of the work of compression, is rejected to the outside medium.