ALF help

Design help

On the Design pages you enter information about the particular house design and location to perform an ALF analysis on it.

Climate & Heating


This page contains information about the location of the building and on the heating habits of the occupants.

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The location selection determines the:

  • coldness of the climate (ALF-values)
  • the length of the heating season (ALF-values)
  • the windiness of the location (Air Leakage Zone) and
  • the Climate Zone according to NZS 4218:2004 (Copyright of the standard is property of the Standards Council and is protected as described in the NZS 4218:2004 document.) and the climate location according to the Energy Efficiency Clause H1 of the NZBC. In order to comply with Clause H1 (2007) of the New Zealand Building Code a building has to have a BPI of less than 1.55 kWh/(m2.°C.month) in any location.

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The heating is described in terms of the timeframe during which heating is applied (Heating Schedule) and the temperature to which the building is heated during those times (Heating Level).

The available heating schedulesare:

  • Evening only (5:00pm-11:00pm)
  • Morning and evening (7:00am-9:00am & 5:00pm-11:00pm)
  • Morning to evening (7:00am-11:00pm)
  • Continuous (24 hours)

The available heating levels are:

  • 16°C
  • 18°C
  • 20°C

This version of ALF does not consider the efficiency and responsiveness of the heater. It assumes that the Heating Level is instantly achieved with whatever heating appliances are installed. If the evening only heating schedule is used it does not therefore take account of any energy needed before 5:00pm.

Climate & Heating Background

The thermal performance of a particular design depends to a large degree on the behaviour and requirements of its occupants. A particular building design might have benefits in the case of intermittent heating whereas it has disadvantages in the case of 24-hour heating schedules. In particular, the benefits of thermal mass are largely dependent on the applied heating schedule. Intermittent heating generally favours lightweight buildings whereas continuous heating favours heavy thermal mass buildings (Pollard, A. and Stoecklein, A. 1997, The Effect of Thermal Mass on Energy Consumption and Indoor Climate, Report for the Cement and Concrete Association of New Zealand) .

The winter season is defined on the basis of long term average monthly temperatures. The threshold temperature was decided through a small heating habit survey. The subjects were asked during which months of the year they usually apply heating. The results were then compared with long-term average monthly temperatures from the National Institute of Water and Atmospheric Research Ltd. (Penney, A. 1997. Climate Database (CLIDB) User's Manual, NIWA Technical Report 4, Wellington). This comparison led to a threshold average monthly temperature of 11.5°C. Thus the winter season in the ALF calculation procedure is defined as all the months with an average monthly temperature of 11.5°C or less.

Using this method some of the warmest climate zones did not have any heating season assigned to them because all months had a long term average temperature of over 11.5 °C. Experience, however, shows that even in these locations some heating is applied during individual cold spells. Therefore a minimum ALF-value of 10% of the Wellington (Kelburn) ALF-value is used in those cases. This minimum ALF-value was then applied when the ALF-value based on the average monthly temperature led to an ALF-value smaller than 10% of the Wellington one.

ALF provides four heating schedules and three heating levels.

The available heating schedules are:

  • Evening only (5:00 pm - 11:00 pm)
  • Morning and evening (7:00 am - 9:00 am & 5:00 pm - 11:00 pm)
  • Morning to evening (7:00 am - 11:00 pm)
  • Continuous (24 hours)

The available heating levels are:

  • 16°C
  • 18°C
  • 20°C

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Interpolation and Extrapolation

Other temperature levels can be interpolated or extrapolated.

Example of interpolation:
The interpolation works in the following manner:

  • Choose the temperature which you are interested in, i.e. 17.5°C
  • Calculate the heating energy for the heating level below (16°C) and the one above (18°C): and .
  • The heating energy for 17.5°C is then given by:

Example of extrapolation:
In order to extrapolate the heating energy to, for example, 22.5°C use the following method:

  • Calculate the heating energy for the two closest available heating levels (18°C and 20°C): and .
  • The heating energy for 22.5°C is then given by:

It should be noted that extrapolating the energy to levels lower than 16°C in warm climates may result in unreliable results because the energy consumption becomes very sensitive to small changes in temperature levels.

The three different heating levels were selected based on other available information of monitored internal temperatures in New Zealand houses. Most research indicates that New Zealand houses are generally heated to comparatively low temperatures. A winter indoor temperature of 20°C is very uncommon. Temperatures under 16°C, on the other extreme, are not recommended for health reasons.

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Total Floor Area

The total floor area is the area of the whole building. This includes the floor areas on all building levels.

It is used for calculating:

  • the house volume by multiplying it with the average room height for air leakage calculation and
  • the amount of internal gains through appliances and lighting (for each m2 building area 5.3 W for waste heat from appliances and lighting, see section 'Background' for more detailed information) and
  • the usefulness of gains and
  • the Building Performance Index (BPI).

The total floor area is necessary to calculate the annual purchased heating energy because the heating energy is the heat requirement minus the amount of useful gains. Unless the usefulness of gains can be calculated (using the total floor area) no annual energy consumption can be calculated.

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Average Room Height

The average room height is multiplied by the total floor area to determine the volume of the building. The volume of the building is used for calculating losses from air leakage.

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Number of Occupants

The number of occupants is used to determine metabolic heat gains. Each occupant in the building contributes metabolic heat. The amount of annual metabolic heat gains depends on the heating schedule and the heating season.
The metabolic heat gains are part of the total internal gains.

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 Create an ALF account

Register now to create your free ALF account.

Every user needs to create an ALF account. Creating an ALF account will ensure:

  • Confidentiality for your project.
  • Allow BRANZ to record usage of the ALF tool – BRANZ cannot access any individual projects. Your privacy is assured.

 Contact and Feedback

Contact us at Branz for further information about the ALF 3.2: Annual Loss Factor.