advocate replacing bottled gas or natural gas with biogas. However, this is usually impractical unless live-stock are on-site. The wastes of a single family are usually insufficient to produce enough methane for anything more than small amounts of cooking. Cooling Annualized geo solar buildings often have buried, sloped water-tight skirts of insulation that extend from the foundations, to prevent heat leakage between the earth used as thermal mass, and the surface. Less dramatic improvements are possible. Windows can be shaded in summer. Eaves can be overhung to provide the necessary shade. These also shade the walls of the house, reducing cooling costs. Another trick is to cool the building's thermal mass at night, perhaps with a whole-house fan and then cool the building from the thermal mass during the day. It helps to be able to route cold air from a sky-facing radiator (perhaps an air heating solar collector with an alternate purpose) or evaporative cooler directly through the thermal mass. On clear nights, even in tropical areas, sky-facing radiators can cool below freezing. If a circular building is aerodynamically smooth, and cooler than the ground, it can be passively cooled by the "dome effect." Many installations have reported that a reflective or light-colored dome induces a local vertical heat-driven vortex that sucks cooler overhead air downward into a dome if the dome is vented properly (a single overhead vent, and peripheral vents). Some people have reported a temperature differential as high as () between the inside of the dome and the outside. Buckminster Fuller discovered this effect with a simple house design adapted from a grain silo, and adapted his Dymaxion house and geodesic domes to use it. Refrigerators and air conditioners operating from the waste heat of a diesel engine exhaust, heater flue or solar collector are entering use. These use the same principles as a gas refrigerator. Normally, the heat from a flue powers an "absorptive chiller". The cold water or brine from the chiller is used to cool air or a refrigerated space. Cogeneration is popular in new commercial buildings. In current cogeneration systems small gas turbines or stirling engines powered from natural gas produce electricity and their exhaust drives an absorptive chiller. A truck trailer refrigerator operating from the waste heat of a tractor's diesel exhaust was demonstrated by NRG Solutions, Inc. NRG developed a hydronic ammonia gas heat exchanger and vaporizer, the two essential