Conduction within building elements

In ESP-r conduction within layers of a building construction is, by default treated as 1D. It is possible to increase this to 2D and 3D conduction but this requires much more information about the composition of the building and the nature of the junctions. Because of this the facility is rarely used and few people know how to setup and work with such models.

Air layers

Heat transfer across an air gap is typically represented as an equivalent air gap resistance. Resistance values for horizontal, vertical and sloped instances are supplied by the user. These are static values. It is possible to treat an air gap as a thermal zone and explicitly represent heat transfer.

In the case of slightly ventilated layers (i.e. rainscreens) heat transfer can be represented at considerable detail if the air layer is defined as one or more zones with an air flow network describing the air leakage paths.

Conduction adjacent to the ground

Heat transfer for ground-connected surfaces is represented as a high heat transfer coefficient at the outer face of a surface to the current months ground temperature. An alternative approach for basements is to use the BASESIMP technique (pre-computed heat transfer correlations based on the topology of basements).

Naturally ventilated cavities

Many construction types include slightly ventilated cavities. A ventilated cavity is, in ESP-r an additional thin thermal zone and the air flows would be either scheduled or included in a flow network. Radiant heat transfer across the void is explicit. In a recent project the use of a flow network and additional zones was found to closely match measurements for a range of rain-screens.

Temperature dependencies

Heat transfer sensitivity to the temperature of the material is represented as additional attributes to the standard thermophysical properties and the solution technique recognises this specification and applies a revised conductivity during the assessment.

Alternative material attributes

In ESP-r it is possible to schedule alternative constructions (it must have the same number of layers) or to alter the optical properties of a construction based as part of a control law.

Heat transfer in phase change materials

Where a PCM is embedded within a building element an additional set of attributes for the PCM need to be added to the model. During the assessment these are recognised and applied. There are several models of PCM available as so-called special materials.

Conduction in liquids

In ESP-r it is possible to nominate a zone as being water-filled and the simulator recognises this. Liquid within a construction is approximated by altering the basic thermophysical attributes. Lastly, it is possible to describe adsorption and advection properties of layers and to treat water vapour as a contaminate and thus explicitly carry out HAM modelling. Note this is considered as an advanced topic and it may be difficult to acquire the required information.

Heat transfer via thermal bridges

Heat transfer attributable to thermal bridges is represented as one or more static heat transfer coefficients and lengths within zones. A facility automates the detection within a room via geometry rules and boundary conditions. Users then attribute these with psi values. These are included in the analysis and the zone energy balance. An alternative is to create an alternative material with an equivalent thermal conductivity and insert additional surfaces in the zone using these alternative materials. Lastly, the 2D and 3D conduction facilties could be used to represent thermal bridges (but this has not been attempted recently).