A well designed building will be comfortable in summer and winter and will require very little energy input to achieve this comfort. Buildings come in many different shapes and sizes and operate in many different ways. The buildings can then be compared by looking at the energy required per square metre of occupied space to maintain this level of comfort. The comfort requirement will typically be a minimum temperature in winter and a maximum temperature in summer. The comfort requirement will usually be for people, but could be for a machine, for example a computer server room, or for a product, for example cold room or humidity-controlled storage area. The comfort of the building in this case is being controlled by adding energy in winter in the form of a heating load, and in summer a cooling load. Thermal energy is also being captured from heat given off by lighting, equipment and people in the building, and from solar gain.