If enough mass is used it can create a seasonal advantage. That is, it can heat in the winter and cool in the summer. This is sometimes called passive annual heat storage or PAHS. The PAHS system has been successfully used at 7000 ft. in Colorado and in a number of homes in Montana. The Earthships of New Mexico utilize passive heating and cooling as well as using recycled tires for foundation wall yielding a maximum PAHS/STES. It has also been used successfully in the UK at Hockerton Housing Project.