Sustainable Energy - Without the Hot Air

http://www.ck12.org Chapter 4. Technical Chapters

useries combination=

1

(

1

u 1 +

1

u 2

).

There’s a worked example using this rule.

Ventilation loss

To work out the heat required to warm up incoming cold air, we need the heat capacity of air: 1. 2 kJ/m^3 /K.

In the building trade, it’s conventional to describe the power-losses caused by ventilation of a space as the product
of the number of changesNof the air per hour, the volumeVof the space in cubic metres, the heat capacityC, and
the temperature difference∆Tbetween the inside and outside of the building

TABLE4.11:

kitchen 2

bathroom 2

lounge 1

bedroom 0.5

Air changes per hour: typical values ofNfor draught-proofed rooms. The worst draughty rooms might haveN= 3
air changes per hour. The recommended minimum rate of air exchange is between 0.5 and 1.0 air changes per hour,
providing adequate fresh air for human health, for safe combustion of fuels and to prevent damage to the building
fabric from excess moisture in the air (EST 2003).

TABLE4.12:

U-values(W/m^2 /K)

old buildings modern standards best methods

Walls 0.45-0.6 0.12

solid masonry wall 2.4

outer wall: 9 inch solid

brick

2.2

11 inch brick-block cavity

wall, unfilled

1.0

11 inch brick-block cavity

wall, insulated

0.6

Floors 0.45 0.14

suspended timber floor 0.7

solid concrete floor 0.8

Roofs 0.25 0.12

flat roof with 25 mm insu-

lation

0.9

pitched roof with 100 mm

insulation

0.3

Windows 1.5

single-glazed 5.0

double-glazed 2.9

double-glazed, 20 mm

gap

1.7

triple-glazed 0.7-0.9