U
Useful energy (kWh or MJ)
The final amount of heat or work for which fuels were used; the actual demand
for energy and the purpose for its use. Useful energy is the product of delivered
energy by the efficiency of the appliance used for the task.
Useful (solar or internal) gains (kWh
or MJ)
The amount of useful heat contributed by solar or internal heat gains to help
meet a building's heating load.
U-value (or thermal transmittance) (W/(m²K))
A thermal conductance
that includes the thermal exchanges at surfaces and in cavities; the reciprocal
of the sum of the thermal
resistances of constituent layers of a composite element plus the surface
resistances at the external and internal surfaces. The U-value decreases
with thermal insulation.