ALF help

What is ALF?

ALF is a tool for designers, builders, building contractors and others involved in the planning of residential buildings. The tool can also be applied to evaluate energy efficiency retrofits for existing buildings. The ALF calculation method will allow you to

• estimate the annual heating energy requirement for your house design
• evaluate whether and how much increased insulation and double glazing will reduce heating energy use
• find out whether the use of heavy thermal mass increases or decreases the heating energy required
• compare how different building orientations affect the heating energy requirement
• determine Building Performance Index (BPI), which is one of the compliance options with the Energy Efficiency Clause H1 of the New Zealand Building Code, Approved Documents (view more information about BPI)
• estimate what impact heating habits have on the heating energy
• estimate the cost benefits of increased insulation by taking account of the energy costs from your power supplier and insulation costs
• evaluate energy efficiency retro-fit options for existing buildings.

Good thermal design also has implications for condensation levels, thermal comfort and therefore occupant health. ALF does not address these additional issues explicitly but as a general rule of thumb, a thermally well designed building has lower condensation risks, higher indoor comfort levels and provides a healthier living environment than a thermally badly designed building.

The ALF calculation method:

• follows an easy step by step path which means that it is also useable by any interested person who wishes to minimise space heating costs
• the method is quick. It is expected that the user does not have to spend more than 20 minutes creating the calculation for a design
• it is very transparent. Almost all the actual heat loss mechanisms (wall losses, window losses, window gains etc.) are dealt with in separate steps. This allows the designer to systematically target particular design options like house insulation, use of thermal mass, insulation levels and others
• because the method is linked to realistic heating behaviours and heating seasons it estimates realistic annual heating energy consumption. This allows the designer to conduct useful cost-benefit analysis for different design options

In addition to above features, the computer program:

• provides extensive and transparent graphs and reports. It could therefore be used to demonstrate benefits of good thermal design to clients during the design process
• it is very user-friendly. Most of the sections of the BRANZ House Insulation Guide are implemented into the software so that the need to reference other documents is minimised.
• the program is very flexible in that the user can define and store their own construction types for walls, roofs and windows. Most of the input files are in ASCII format so that the user can modify and update input data easily.