Defrosting Process

The removing frost accumulation from evaporators.

Degree Day

A unit that represents a one-degree Fahrenheit deviation from some fixed reference point (usually 65° F) in the mean, daily outdoor temperature. See also heating degree day.

Dehumidification

The process of reducing the moisture content of the air; serves to increase the cooling power of the air and can contribute to occupant comfort. (see air-conditioning; humidification; cooling; heating).

Dehumidifier

A refrigeration device designed to remove water vapor from the air.  An air cooler that removes moisture from the air.

Delta-T

A difference in degrees Fahrenheit or the high and low temperature of a system such as an air conditioner or heat pump.

Demand

The term used to describe the maximum rate of use of electrical energy over a specific period of time.

Den

The same configuration as a bedroom without a closet.

Desiccant

An extremely porous crystalline substance used to absorb moisture from within the sealed air space of an insulating glass unit.

Design Specifications

Manufacturer tested specification when determining design to actual operations. This includes the chiller, cooling tower, air handlers, etc. To ensure expected performance of the equipment.

Deterioration

Impairment of condition.

Dewpoint

The temperature at which water vapor in air will condense at a given state of humidity and pressure.

Diameter

The width or thickness of a circular, or somewhat circular, object.

Diffuser

A grille over an air supply duct having vanes to distribute the discharging air in a specific pattern or direction.

Digital Manometer

Measures positive and negative air pressures in ducts, from room to room, and for taking traverses.

Dimension Lumber

Lumber which is two to five (2"-5") thick and up to twelve inches (12") wide.

Direct Expansion Equipment

'Direct expansion,' 'DX,' 'refrigeration' or 'split' units are all generic terms used to identify the same equipment. It is accepted that the terms refer to two or more units, one usually positioned externally and one or more usually positioned internally. The units are connected together by site installed refrigeration pipe work, which is charged with a refrigerant. The external unit may take one of three forms

Discontinuous Member

A member which has one or more break points and is not considered a whole unit unless tied or fastened together.

Dismantle

To take apart or remove any component, device or piece of equipment that is bolted, screwed or fastened by other means and that would not be dismantled by a homeowner in the course of normal household maintenance.

Distribution Box

A fuse box a metal box containing fuses and circuit breakers that permits access to connecting branch circuits. An underground box that receives waste from a septic tank and distributes it to the laterals of a disposal field.

Distribution Panel

An insulated board from which electrical connections are made between the main feed circuit and branch distribution circuits.

Divided Light

A window with a number of smaller panes of glass separated and held in place by muntins.

Division Wall

An interior load-bearing wall dividing a structure into rooms.

DOE

The Department of Energy is a federal agency in charge of setting industry efficiency standards and monitoring the consumption of energy sources.

DOE-2.1E

A building-simulation computer program used to calculate total annual energy use.

Door Stop

A trim piece place around the inside face of side and top door jambs to prevent damage from the door swinging too far.

Door

A moveable panel on hinges used to open or close an entrance to a room or building.  Of all the building's components, doors and windows lose or gain the most heat. A well made insulated door can contribute to your overall energy savings.

Dormer

A framed window unit projecting through the sloping plane of a roof.

Double Glazing

In general, two "thicknesses" of glass separated by an air space within an opening to improve insulation against heat transfer and/or sound transmission. In factory-made double glazing units, the air between the glass sheets is thoroughly dried and the space is sealed airtight, eliminating possible condensation and providing superior insulating properties.

Double Tap

Two electrical conductors fastened to a single safety device.

Double-Gabled Roof

See butterfly roof.

Double-Glazing

A double-glass pane hermetically sealed with an air space between the two panes to provide insulation.

Double-Hung Window

A window with two movable sashes that slide vertically.  A window consisting of two sashes operating in a rectangular frame, in which both the upper and lower halves can be slid up and down. A counterbalance mechanism usually holds the sash in place.

Double-Pitch Roof

A roof that slopes in two directions.