Heat loss, the numbers…

 

Conduction 21 BTUs Convection 92 BTUs Radiation 206 BTUs TOTAL 319 BTUs CASE 1, UNINSULATED WALL SPACE The surfaces of ordinary building materials, including ordinary bulk insulation have a low radiation or emissivity rate, and a heat ray absorption rate of over 90%. Air has low density, so conduction is slight (only 21 BTUs). Convection currents transfer 92 BTUs.

CASE 1, UNINSULATED WALL SPACE
The surfaces of ordinary building materials, including ordinary bulk insulation have a low radiation or emissivity rate, and a heat ray absorption rate of over 90%. Air has low density, so conduction is slight (only 21 BTUs). Convection currents transfer 92 BTUs.

Conduction 21 BTUs
Convection 92 BTUs
Radiation 206 BTUs
TOTAL 319 BTUs

 

Conduction 21 BTUs Convection 92 BTUs Radiation 10 BTUs TOTAL 123 BTUs CASE 2, THE SAME WALL SPACE EXCEPT that the inner surfaces were lined with sheets of aluminum foil of 3% emissivity and absorptivity. Note the drastic drop in heat flow by radiation, from 206 BTUs to 10 BTUs. Conduction and convection are unchanged. The original total heat loss of 319 BTUs drops to 123 BTUs.

CASE 2, THE SAME WALL SPACE EXCEPT
that the inner surfaces were lined with sheets
of aluminum foil of 3% emissivity and absorptivity.
Note the 
 drastic drop in heat flow by radiation, from206 BTUs to 10 BTUs. Conduction and convection areunchanged. The original total heat loss of 319 BTUs drops to 123 BTUs.

Conduction 21 BTUs
Convection 92 BTUs
Radiation 10 BTUs
TOTAL 123 BTUs

Conduction 23 BTUs Convection 23 BTUs Radiation 2 BTUs TOTAL 48 BTUs CASE 3, TWO SHEETS OF (5% EMISSIVE) ALUMINUM FOIL divide the wall space into 3 reflective compartments. Heat loss by radiation drops 94% from Case 1. The 2 interior sheets retard convection so that its flow falls 75%. Conduction rises only 2 BTUs; from 21 BTUs to 23 BTUs. The total heat loss drops 85% from Case 1.

CASE 3, TWO SHEETS OF (5% EMISSIVE) ALUMINUM FOIL divide the wall space into 3 reflective compartments. Heat loss by radiation drops 94% from Case 1. The 2 interior sheets retard convection so that its flow falls 75%. Conduction rises only 2 BTUs; from 21 BTUs to 23 BTUs. The total heat loss drops 85% from Case 1.

Conduction 23 BTUs
Convection 23 BTUs
Radiation 2 BTUs
TOTAL 48 BTUs

Reflecting Warmth