- Damper
- Flap or similar used to regulate, divert or stop flow of air or gases in a duct
- Darkness, hours of
- Measurable factor which may act as a good driving factor for
management of lighting demand.
Download Excel table of monthly and weekly standard figures (for
latitude 52°N but suitable for most of England and Wales)
- DC
- Direct Current Mode of electricity transmission in which the polarity is fixed (contrast AC).
- DCF
- Discounted Cash Flow. Method of evaluating future cash flows (for example investment in energy-saving measures and resultant savings) in a manner which gives progressively less weight to
savings and costs occurring further in the future.
Download an Excel workbook which explains and illustrates the principle and can be used
for your own evaluations.
- Dead band
- Either deliberate separation of (say) heating and cooling control set points to inhibit
simultaneous operation or switching differential of a thermostat or other similar control
- Decarbonise
- To reduce the carbon dioxide emissions associated with energy derived from fossil fuels
- Degree days
- Measure of how cold (or hot) the weather was at a given location over
a particular interval of time (usually monthly or weekly), expressed as
a single numerical index. See data and related articles
or download tables of annual regional totals for
heating or
cooling.
- Dehumidification
- Removal of water vapour from the air, usually to achieve a
comfortable relative humidity. Achieved either by dessicant drying
system or by cooling the air to condense surplus water and
then reheating it. Read an article about how to account
for variable energy demand driven by humidity
- Display Energy Certificate
- For UK buildings regularly visited by the public, gives an A-G grading based on energy intensity per unit floor area. Must be displayed in a prominent position and can also be downloaded from epc.opendatacommunities.org
- Destratification
- Elimination of the blanket of warm air that otherwise collects under a high ceiling when the
heating system is running
- DHW
- Domestic Hot Water, i.e. provided for washing, bathing, kitchens etc
- Draught proofing
- Reduction or prevention of unwanted air ingress into a building.
Incoming air displaces heated air and then itself needs to be heated. Read an article about building fabric
- Driving factor
- An independently-measurable factor (e.g. production throughput, mileage, degree-day value)
that determines or explains the required quantity of energy or other consumable resource.
- DUoS
- Distribution use of system: (UK) charges for local transportation of electricity from a grid supply point to the consumer