Glossary of Terms

Air Permeability

Air permeability is expressed as volume flow per hour (m³ h) of air supplied to the space per square metre (m²) of envelope area for an internal to external pressure difference of 50 Pa i.e. 25 m³ hr^-1 m^-2 at 50Pa.

Atrium

In this context, a non-continuously occupied interior space within a building, often several stories high, bounded on at least one side by occupied spaces set to the conditions determined from the activity database. There may or may not be building elements (such as glazing) surrounding the atrium (although there may need to be something for smoke control in case of fire). The atrium itself is not maintained to the conditions set by the activity database for adjoining spaces. The technical purpose of the atrium can be one or more of the following:-

Providing a buffer between the thermal conditions in the adjoining spaces and the exterior, to reduce the direct impact of the exterior on those zones. In this case it should not be maintained to conditions as though it is occupied. (If it is conditioned and the features below do not apply, in this context it is not considered to be an atrium.)

Providing a means for daylight to reach the middle of deep plan spaces that would otherwise not receive it

Encouraging stack effect or other passive ventilation to draw extract air from the adjoining spaces.

Automatic Blind Control

In this context internal or inter-pane (but not exterior) blinds that are motorised so that the position can be modified to control solar heat gain and/or glare, controlled by automatic sensors. The control regime must also open the blinds as the heat gain and or daylight levels decrease, so that the use of these natural resources can be optimised for each zone. Note that exterior shading devices can be modelled using iSBEM in the definition of each window; however SBEM currently does not model the re-radiation effects of blinds where solar gain has entered the space before it is modulated by the shading device.

Demand Controlled Ventilation

Is defined as supply and/or extract ventilation that is modulated to match the needs of the actual occupation level of each zone, rather than operating at a constant level defined by the activity database. Thus the energy required to adjust the condition of the supply air and that required to move the air can be reduced. The rate of ventilation would typically be controlled by presence detectors, CO₂ sensors or another device that senses the varying requirement.

Fixed Building Services

Are those which are directly attached or connected to the building and cannot be removed/disconnected without the use of tools. A portable electric heater with a plug allowing it to be removed from the building without the use of tools is not considered a fixed building service.

Light Pipes

A light pipe is a tube/pipe, consisting of internal reflective surfaces, which channels daylight to an internal area.

Lightwell

A lightwell is a space surrounded by the walls of a building but that has no roof or glazing above it. It is therefore similar to a courtyard in appearance. The walls that surround the lightwell are exposed to external air.

Mixed Use building

A building that incorporates both commercial areas and residential spaces.

 

 

Night Ventilation Strategy

Can be defined as the presence of suitable systems, controls and operating strategy such that overnight ventilation (passive and/or mechanical) is used to cool down the exposed building mass and thereby offset daytime cooling demands. If no such operation and subsequent offset is possible through the automatic operation of systems and controls then night ventilation strategy is deemed to be not present as part of the building energy asset rating.

Self-contained dwelling

A unit designed to accommodate a single household. This would imply it has its own kitchen and bathroom.

Significant Alteration

Alterations that are covered by the Building Regulations.

Ventilation with Enhanced Thermal Coupling to Structure

This is a further development of the Night Ventilation strategy such that significant components of the building structure in addition to its ordinary surfaces are exposed to night ventilation, in order to enhance the building's capability of offsetting daytime cooling demands. An example of this procedure is the TermoDeck system where night ventilation is passed through ducts in the solid floors of the building, thereby increasing the 'coolth' contained in the thermal capacity of the building structure available to offset subsequent summertime daytime cooling loads.

Variable Speed Drive systems 

HVAC system designs are increasingly incorporating variable speed drives (VSDs) to provide control, and reduce the energy consumption of, the motors on fans and pumps.

The term Variable-Speed Drive describes the equipment used to control the speed of pumps, fans and compressors. Variable speed drives may be purely mechanical, electromechanical, hydraulic, or electronic. It is generally accepted that variable speed pumping systems offer significant benefits compared to constant flow systems.   

For alternating current (AC) electric motors this is achieved by controlling the frequency and/or voltage of the electrical power supplied to the motor. As the motor reduces the operating speed of the fan, pump or compressor the power required to operate the system is greatly reduced.