A4 Energy and Efficiency in Buildings

Topic

A heat pump does not generate heat from electricity the way a resistive heater does; instead, it transfers heat from a cooler environment to a warmer one while consuming only a fraction of the energy equivalent to the heat delivered. This is the physical reason why it is generally the most efficient system available for climate control in a building: for every unit of electricity consumed, it delivers multiple units of transferred heat.

However, there is a theoretical limit to this efficiency that depends solely on the temperatures between which the equipment operates: the smaller the difference between the temperature at which it captures heat and the temperature at which it delivers it, the closer the equipment comes to that ideal limit; conversely, the greater that difference, the further it moves from that limit and the less efficient it becomes in practice. This means the same heat pump performs very differently on a mild day compared to an extremely cold one, even though the equipment itself remains unchanged.

To compare buildings beyond their individual equipment, energy certification classifies each structure based on its primary energy consumption per square meter per year, using a letter-based scale ranging from the most efficient to the least efficient buildings. Solar photovoltaic generation, meanwhile, depends on the available solar radiation at the site, the installed panel area, and the conversion efficiency of those panels—a factor that has improved substantially with modern technology.

Thus, this module—which begins with a heat pump that transfers heat rather than generating it—concludes by showing that a building's energy efficiency depends on two independent decisions: how effectively its equipment transfers or generates heat, and how much of the energy it consumes can instead be produced on-site.

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