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close this book National design handbook prototype on passive solar heating and natural cooling of buildings
close this folder VII. Detail design
View the document A. General
View the document B. Solar access, shading and window protection
View the document C. Control of conductive heat flow
View the document D. Evaluation of internal heat loads
View the document E. Cross-ventilation and air flow
View the document F. Glass-mass relationship
View the document G. Air infiltration

D. Evaluation of internal heat loads

The total energy used in dwellings throughout Australia varies largely because of climatic differences. The use pattern for a typical four-person household in Sydney is illustrated In figure 92 while data for other localities can be found in the annexes.


Figure 92. Energy used within the home - Sydney (kWh per annum)

In an energy-efficient building the heat generated inside by the occupants and appliances or equipment in use will compensate for some of the heat lost through the outer fabric. In some of the "super-insulated" houses built in northern Europe and North America, the casual internal heat gain is sufficient to counter the structural heat losses. Very little auxiliary heat is Fresh air is passed through an air-to-air heat exchanger to retain even the heat in the exhaust air.

Table 15. Daily profile of internal heat input from the activities of a tour- person household d. ("Time' is the starting time for the Indicated load, which applies for one hour.)

Time

Living zone

(Wh)

Bed zone

(Wh)

Service zone

(Wh)

Total

Comment

0000

75

225

 

300

 

0100

75

225

 

300

 

0200

75

225

 

300

 

0300

75

225

 

300

 

0400

75

225

 

300

 

0500

75

225

 

300

 

0000

75

225

 

300

 

0700

400

450

800

1 650

Breakfast,showers etc.

0800

325

 

325

650

 

0900

100

 

200

300

Early morning cleaning

1000

150

   

150

 

1100

150

   

150

 

1200

225

   

225

 

1300

150

   

150

 

1400

150

   

150

 

1500

150

   

1500

 

1600

800

200

 

1000

Children home: cooking

1700

1200

200

 

1400

 

1800

800

100

 

900

 

1900

800

100

 

900

 

2000

800

100

 

900

 

2100

800

100

100

1000

 

2200

500

150

650

 

Bed time

2300

75

225

 

300

 

Total (Wh)

8100

3400

1225

12725

 

The magnitude and source of casual internal heat gains will vary from one situation to another. Cultural differences in lifestyle will also impact on energy use. In a typical Australian household the casual internal heat gains can be assumed to be in the order of 8kWh/day in the living zone of a three bedroom-dwelling, with a peak around the time of the evening meal. In mild climates this reduces auxiliary heating for energy-efficient houses. As the stove is the largest single heat source (other than auxiliary space heaters) in the living area, its pattern of use is a key factor in this picture.

The knowledge of internal heat gains is important when determining the thermal behaviour and auxiliary heating and cooling loads of a specific design. Most computer programs require an hour by hour estimate of internal heat gains. Table 15 illustrates the internal heat gains assumed for a typical family home being assessed in the 5-star design rating system, during colder months. Where the maximum outdoor temperature exceeds 27°C the profile should be reduced progressively from 81 00Wh/day to 6670Wh/day when the outdoor maximum is 33°C and above. The reduction should be made to the evening end of the day to reflect the reduced cooking load in warmer weather. The occupancy pattern of the two zones of the building is reflected clearly in the times of significant heat gain.

A table of energy use for a wide range of equipment and domestic appliances is included in annex IV. It must be noted that the main difficulty is to estimate realistic use patterns for these appliances. In many simple evaluations the inclusion of minor appliances is an unnecessary complication.