OTTV Equation

Question 1

What are the components of heat gain through exterior walls

Answer 1

Heat conduction through opaque parts of the wall
Heat conduction through glass windows
Solar radiation through glass windows

Question 2

What is the general procedure to calculate OTTV for walls

Answer 2

General procedure is to calculate first the OTTVs of individual walls with same orientation and construction. Then the whole exterior wall is given by the weighted average of these walls.

Question 3

Equation for walls

Answer 3

(Qw + Qg + Qs)/ Ai = (AwUwTDeq+AfUfDT+AfSCSF)/Ai
DT temperature difference between exterior and interior design
SC shading coefficient of glass times effective sc of external devices
SF solar factor for the orientation

Question 4

What parameters depend on climatic condition

Answer 4

TDeq, DT and SF. TDeq also varies with the tyoes of construction and colour of external surface finish.

Question 5

Alternative wall equation

Answer 5

(1-WWR)TDeqUw+WWRDTUf+WWRSCSF

Where WWR is the ratio of the window area to total wall area Af/Ai

Question 6

OOTV for external building tower or podium HK

Answer 6

(AwUaplhaTDEQw+AfwSCESMSF)/Aow

Question 7

OTTV of roofs HK

Answer 7

(ArUalphaTDEQr+AfrSC*SF)/Aor