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Design help

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

Internal Gains


Internal gains consist of :

Hot water: 100W accounting for the cylinder losses and for hot water used in the building for bath, showers etc.

Appliances: For each m2 building area 5.3W for waste heat from appliances and lighting.

Occupants metabolic heat release: Each occupant in the building contributes metabolic heat.

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Internal Gains Background

Internal heat gains from household appliances (including house lighting), and the metabolisms of the occupants contribute to space heating when a house is occupied. Like all other occupant effects, internal heat gains vary greatly in practice.

In ALF software takes the following simplified approach:

A base internal gain rate of 100W is taken. This mainly takes account of the heat losses of the hot water cylinder and heat of hot water used in the building (showers, laundry etc.). Older hot water cylinders can have losses up to three times as high. Also the location of the cylinder in or outside of the house influences the amount of gains.

Instant gas cylinders have no standing losses at all. If the pilot light is constantly burning it will on the other hand contribute to internal gains.

The heat release of lighting and appliances is then linked to the total floor area of the building. This approximation is based on the experience that larger houses generally have a larger number of lights and other appliances. Special features like heated fish-tanks contribute, as well.

The metabolic heat release of occupants in the building is considered by a contribution linked to the number of occupants. It is assumed that the metabolic heat release rate of people in a house is similar to that of people typing.

Both the length of the heating season and the timing of the internal gains in respect to the heating schedule have to be considered when calculating the seasonal metabolic heat release. If for example most of the gains occur during the morning hours and the 'evening heating only' schedule is applied few of the gains would be useful in terms of reducing the required evening heating energy.

In the development of the internal gain figures, two time of day periods (day and night) have therefore been taken into account. 75W per person with 60% availability was used during daytime (7:00-23:00) and 100% during night time (23:00-7:00). Equipment gains are 16W/m2 with 25% available during the day and 5% during the night. Lighting gains are 8.5W/m2 with 15% available during the day and 0% during the night. A constant 100W was assumed for hot water. The different timings and contributions of the internal gain components were then approximated through an average power and an Internal Gain Factor. The Internal Gain Factors therefore reflect the relation of the time of internal gains in respect to the heating schedule and the number of heating months determined by the climate of the location.

As for the solar gains a five-hour acceptable delay time for the internal gains is used, i.e the gains from up to five hours before heating commences are included.

The estimations of the internal heat releases of appliances and metabolic heat are based on data from Wright and Baines, (Wright, J. and Baines, J. 1986. Supply curves of conserved energy - the potential for conservation in New Zealand's houses. Centre for Resource Management, University of Canterbury and Lincoln College. Published by the Ministry of Energy, 1986. Wellington)

For BPI calculations three occupants for buildings under 120m2, four occupants for buildings between 120m2 and 180m2 and five occupants for buildings larger than 180m2 are assumed.

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