As far back as 1954, a 12-story office building (1) was constructed in Albuquerque that, on clear days with the outside temperature as low as 20° F at noon, received 100% of its required heating from passive solar energy and building internal heat (lights). The building was designed as a well water heat source heat pump system with provisions to utilize building cooling load energy as a heat source before using well water. The long dimension of the rectangular, curtain wall building faces south and north (with 50% insulating glass in each wall). During daylight hours in the heating season, more of the heat source is from the incident solar energy entering the south facing glass than from the well water. This proved to be a building that was accidentally solar heated, though the Architect had made provision for sun control by utilizing insulation glass (the outside pane heat absorbing) and close weave drapes.

Passive solar heating is generally understood to be solar energy utilized without the use of mechanical power, such as pumped circulation of a fluid through fluid collector panels or forced circulation of air through an air collector by means of a fan. The problem generally associated with passive solar systems is that the building space temperature control range is not close enough to satisfy the acceptable limits for commercial and institutional buildings. However, a heat pump system, which can utilize building cooling loads generated by internal loads and passive solar energy through windows or through skylights, can maintain inside temperatures within the required limits necessary to satisfy tenants that pay high rental costs and for hospitals and other types of institutional buildings. In addition, if the heat pump system incorporates thermal storage tanks which allow excess heat to be stored and recycled for early morning pick-up periods or night-time use, passive solar energy can be utilized to an even higher degree of effectiveness.