Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force.

Diabatic storage dissipates much of the heat of compression with intercoolers into the atmosphere as waste, essentially wasting the energy used to perform the work of compression.

The saturation temperature of the moisture present in the sample of air, it can also be defined as the temperature at which the vapour changes into liquid (condensation).

Deuterium (also known as heavy hydrogen) is a stable isotope of hydrogen.

A device for recovering superheat from the compressor discharge gas of a heat pump or central air conditioner for use in heating or preheating water.

A chemical process for the removal of sulfur from a material.

Destructive distillation is a chemical process in which decomposition of unprocessed material is achieved by heating it to a high temperature. The process breaks up or 'cracks' large molecules.

A specific temperature used in calculating the cooling load of a building.

A specific temperature used in calculating the heating load of a building.

Outdoor air temperatures that coincides with the peak seasonal heating or cooling load.

A design review is a milestone within a product development process whereby a design is evaluated against its requirements in order to verify the outcomes of previous activities and identify issues before committing to - and if need to be re-prioritise - further work.

Temperatures that the ground loop is designed to stay above during the heating mode and below during cooling mode.

The peak heating or cooling load used to select the equipment for a system (such as a heat pump) and to design the air distribution system (supply air diffusers, return air grilles, and the duct system).

Design controls designates the application of a formal methodology to the conduct of product development activities.

The desert climate or arid climate is a climate which there is an excess of evaporation over precipitation.

A descaling agent or chemical descaler is a liquid chemical substance used to remove limescale from metal surfaces in contact with hot water, such as in boilers, water heaters, and kettles.

Desanders and desilters are solid control equipment with a set of hydrocyclones that separate sand and silt from the drilling fluids in drilling rigs.

The tower-like structure that houses the drilling controls for a drilling rig.

Depth of Discharge (DoD) is the fraction or percentage of the capacity which has been removed from the fully charged battery.

Depth of Discharge is the fraction or percentage of the capacity which has been removed from the fully charged battery.