​Optimising your design with ALF

It is a straightforward process to identify and amend weaknesses in a design and make changes to optimise thermal performance.

ALF helps identify the ideal building orientation and the most efficient glazing sizes and materials and insulation combinations.

To locate design strengths and weaknesses after entering all the data, go to the Results & reports tab and click on the Graphs tab. This shows the gains and losses for Floors, Walls, Roofs, Windows, Skylights, Ventilation Loss, Internal gains, and Energy Use. The longest negative bars show very clearly where the largest losses are happening.

When you have identified an area that is performing poorly, go back to the Enter data tab for your design or project, and adjust the materials and insulation values. Look for the impact on the energy cost. This is specific to the schedule that you have entered in the climate details area rather than the BPI defaults.

In some cases a change of construction approach may be required. You may already have achieved the maximum insulation R-value you can with 90 mm wall framing, for example. Any improvement may require a change to 140 mm framing.

It is important to understand the concept of useful gains. For example, while a large window may gain a lot of energy during the day, only a certain amount can be used before overheating occurs. This may be balanced by including well-insulated thermal mass in the design. Glazing often has net losses because heat is lost after the sun sets. This can be made worse by very large areas of glazing and/or low thermal resistance of the window systems, such as the relatively poorly-performing aluminium double glazing with standard clear glass and no thermal break.

Orientation is a key element of good solar design. To check whether the design would perform better in a slightly different orientation, click on the house rotation buttons in the Walls & windows tab. This will change the whole orientation of the design in 45° increments.

While achieving a BPI of 1.55 or less proves Building Code compliance, that does not have to be the end of the process. Further relatively simple and inexpensive changes may reduce the BPI even more, making a house more comfortable to live in and costing less to heat over winter.