Trench heating is the term which describes a heat source set in a floor trench, covered by a grille and almost always sited in front of glazed facades. The primary purpose of trench heating is to create convection currents that prevent heat loss through the glazing and condensation forming on the glass. Trench heating can be configured to also contribute to space heating, reducing demand on the primary space heating system.
Trench heating is often specified in buildings that are glazed from floor to ceiling, where other types of perimeter heating (such as radiators) would be unsightly and encroach on the views. Trench heating takes up less floor space, an important consideration in offices.
The heat source for trench heating may be hot water piping or electric elements. Heat distribution may rely solely on natural convection or be fan-assisted.
The positioning of the pipes or heating elements within the trench also influences the distribution of the warmed air. For example, positioning the heating element on the room side of the trench creates an air convection loop adjacent to the glazing, but contributes very little to room space heating. By contrast, location of the element on the window side of the trench encourages cold entrained air to be brought in from the room floor, thus encouraging a stronger convection loop for space heating. Mid-positioning of the element in the trench is effectively a compromise, contributing to both façade and space heating.
Other factors to be taken into account in the design of trench heating include:
- Depth of trench
- Width of trench
- Distance of trench from façade
- Trench usage as a ventilation pathway
- Choice of grille and its resistance to air flow