B.1. Calculations of „U” coefficient of partitions <br>

B.1. Calculations of „U” coefficient of partitions

In Instal-heat&energy program for thermal calculations it is possible to define partitions with homogeneous and inhomogeneous construction. As a thermal homogeneous partition is understood a partition consisting in layers of constant thickness and homogeneous thermal properties or of such properties, which can be acknowledged as homogeneous. As inhomogeneous partition is understood a partition including in its construction in plane perpendicular to heat flow direction some building elements with various thermal features.

Calculations of „U” coefficient of homogeneous partition are based on the norm PN – EN ISO 6946. The User has possibility of performing of following operations in program:

- calculations of heat transfer coefficients for partitions, floors on the ground and walls at the ground – according to normative assumptions,

- using in partition definition the aerial layers (ventilated, non-ventilated),

- taking into account the corrections DUo related to heat transfer coefficient – according to Appendix D of norm,

- taking into consideration the linear heat leakage bridges DU – according to domestic appendix NA of norm,

- control of water vapour condensation on inner surface of partition. Temperature of inner surface of partition on a heat leakage bridge can be determined on the basis of experiments or calculated by means of numerical programs,

- entering of non-homogeneous partition by declaring of repeatable homogeneous elements of partition.

Calculations of heat transfer coefficients take into consideration the heat resistance of penetration from the inside and outside of partition and heat resistance of partition layers. Heat transmission resistance depends on direction of heat flow. Heat resistance of partition layers depends on layer thickness and its heat conduction coefficient.

There are three characteristic aerial layers – non-ventilated, poor ventilated and good ventilated aerial layers. Depending on this criterion the program will select appropriate heat resistance of aerial layer.

Corrections DUO to heat transfer coefficient take into consideration following situations:

- leakages in insulation layer,

- mechanical connectors piercing the insulation layer,

- precipitations on the roof with reverse layers layout.

These corrections should be completed according to normative values.

Linear heat leakage bridges in program are taken into account in simplified way by additions to the value of heat transfer coefficient. The value of addition determining influence of heat leakage bridges on the value of heat transfer coefficient depends on the type of partition. Values of additions taking into consideration this criterion have been put together in appropriate table, in domestic appendix to norms.

Temperature of inner surface of partition is calculated according to the law of temperature drops. Its calculation and comparison with dew point temperature of considered surface (determined for the surface temperature and relative humidity of air) enables the control of condensation on inner surfaces of partitions. This method does not enable the calculation of water vapour condensation in heat leakage bridges.

An inhomogeneous partition is determined by selection of previously defined homogeneous elements of partition and determination of their share in repeatable length of inhomogeneous unit. Elements of inhomogeneous partition are selected from partitions previously defined as partitions with enforced “U”-coefficient or partitions with laminar construction.

Program does not check automatically the scope of values of „U” coefficients.