Design of central heating systems

The principle aim behind designing a heating system is to achieve a simple balance between a high performance system with an economical one. However, the science behind the design is in fact quite a complex one, with many factors being accounted for on each project.

Every building will have rooms of different shapes and sizes, different outside wall and window areas, and will be built with different materials with varying levels of insulation. Therefore, to achieve a system with a high performance/economical balance, each building, be it a domestic or commercial property, will need to have a room by room heat loss calculation.

To do this we use a sophisticated piece of software, which calculates heat loss to BS EN 12831. We look at the every aspect of the building and its surroundings  including:

• Climatic data to include design temperature & annual mean temperature. These are key factors for the heating design
• Air tightness of the building and any mechanical extraction system proposed
• Shielding coefficient i.e. is the building in a rural area or surrounding by other buildings?
• Defining the building such as storey heights, height above ground and what space any given room is adjacent to, i.e. a room adjacent to a roof space will need more heat input than one adjacent to a bathroom
• The building’s heat up capacity ie solid floors and walls or suspended floors with light walls
• Floor slab evaluation to determine ‘b’- value
• Use default building elements or construct tailored layers specific to your project. For example if you know your building has a brick external layer, followed by 100mm air gap, followed by 4” block followed by plaster board internal we can use this information to get a specific u-value for that wall. Also if you know you are using a specific manufacturer’s doors and windows we can input their specific thermal data.
• All windows, walls, doors ceilings can now be drawn to scale over the plans provided
• All rooms can be given a target temperature and ventilation rate, for example it is normal to design bathrooms to 24 degrees whilst a living room would be 20 degrees

With this information the software can perform the heat loss calculations and provide: building data, room design heat load, room list, building heat load summary and heat loss chart.

Underfloor Heating Design

Once the above has been carried out we can now proceed to the underfloor heating design. Again the scope is endless and anything can be considered and entered such as:

• The type of insulation used
• The installation method and material, i.e. is it a screeded system, are spreader plates between joists being used, and just about any variation can be accounted for
• Mark areas to be heated, but also areas not to be heated such as where the kitchen furniture will be going, where the stairs are etc. Peripheral zones can also be marked to allow a higher design temperature to be used if needed.
• Consider any floor covering to enable accurate target floor temperatures and heat up response times
• Areas for connecting pipes
• Area for the manifold(s)
• Allocate zones

Using all this information we can now calculate to BS EN 1264 the correct flow temperature, the pipe spacing for individual rooms, the exact flow rates required for each loop along with the loop length and the temperature difference between flow and return. The software will most importantly tell you where there is an output shortage, this enables us to look at adding an extra loop or supplementary heating such as a towel rail.

This information also gives us an exact materials list requirement so the installer will definitely have the right materials for the project and minimalise waste. This allows for highly accurate quotations.

Finally, all this information can be transferred to a CAD layout drawing so the installer can see exactly the layout he needs to follow.

For further examples of CAD designs, please have a look in our downloads section.