IsoDim Help Temperature change in pipe/ducts module


This module is used for computing temperature increase/decrease in several linked sections of pipes or ducts

Calculation type

You have to select one out of four different types of pipe/duct. In pipes the media is some kind of fluid/gas, in ducts it is always air.

Calculate energy use

Annual energy usage due to heat loss in all sections will be calculated. Two parameters are needed to perform the calculations:
  1. Operating hours: If the system does not run the whole year this value should reflect this.
  2. Energy cost pr kWh: the cost of heating the media, can be a mix of electricity, oil, gas or other. The efficiency of the heater should be included in the calculation of the price (example: The heater efficiency is 80 % and the price of energy supplied to the heater is 0,15 /kWh, the effective energy price is 0,15 / 0,8 = 0,1875)
  3. Currency: Currency to be used for the calculations. Please note that the currency only changes the text in the calculated results, not the numbers (there's no automatic conversion between currencies).


For pipe sections three properties for the media/fluid used are needed: Density, thermal capacity and freezing point. The droplist contains properties for a selection of fluids. In addition to this the media temperature at the inlet for the first section is entered here.

Pipe/duct section

To add a section to the list you first have to set the input data for the section below and then press 'Add section'. To alter data for an existing section you first select a section in the list, make the changes below and then press 'Update section'. To delete a section simply select it and press 'Delete section'.

Section of pipe/duct

Input values for section of pipe/duct. A description (name) is needed and will be shown in the list above


Use the outside dimension of the pipe/duct (without insulation).


When calculating the external heat transfer coefficient the orientation of the pipe/duct is needed.


One or two layers of insulation can be added. Select an insulation product from the droplist. One of the standard thicknesses for the product can then be selected in droplist below or you can select and enter a user defined thickness.

Facing (outside surface)

This section sets the emissivity of the outside surface of the insulated and uninsulated pipe/duct. The droplist contains typical values for different materials.

Uninsulated suspensions

This is a simplified way of including the extra heat loss due to the pipe suspensions. For outdoor installations 25 % heat loss is added, for indoor installations 15 % is added.


Description of the conditions around and inside the pipe/duct. Ambient (surrounding) temperature, media temperature and flow are used in all calculations. For outdoor conditions the wind speed also has to be given. Normally average (yearly) values should be used (especially if annual energy usage is calculated).

Valves, fittings and flanges

Here it is possible to add equipment attached to the pipe that increases the total heat loss. Extra heat loss is calculated as an added eqivalent uninsulated pipe length. The drop list contains a fex pre-defined types.


There are two tables showing the calculated results. The first shows data for each section and second one is a summary of all sections.