Heat Balance

This section describes the Heat Balance model.

The general total heat balance for the human body is:

Q˙METQ˙STQ˙DRYQ˙EVAPQ˙RESPW=0
(49 50 51 52 53 54)

The difference between Q˙MET and W corresponds to the metabolic heat production. This heat balance can be established for all segments. The work W is equal to zero. Solving the above equation for the stored body heat flux Q˙ST for the elements of a body segment and assuming that TCloth>TCore>TMuscle>TFat>TSkin:

Core:

Q˙ST1,j=Q˙BLOOD1,j+Q˙MET1,jQ˙COND1,jQ˙RESP1,j
(49 50 51 52 53 54)

Muscle:

Q˙ST2,j=Q˙BLOOD2,j+Q˙MET2,jQ˙COND2,j+Q˙COND1,j
(49 50 51 52 53 54)

Fat:

Q˙ST3,j=Q˙BLOOD3,j+Q˙MET3,jQ˙COND3,j+Q˙COND2,j
(49 50 51 52 53 54)

Skin:

Q˙ST4,j=Q˙BLOOD4,j+Q˙MET4,j+Q˙COND3,jQ˙DRYjQ˙EVAPj
(49 50 51 52 53 54)

In addition to these heat balance equations, the central cardiovascular system must be taken into account:

Q˙ST,BLOOD=j=114(i=14(Q˙BLOODi,j))
(49 50 51 52 53 54)

In each segment, a radial heat flux is taken into account through the term Q˙COND. All elements are coupled through the central cardiovascular system of the above equation. The central blood temperature is a function of all temperatures and blood volumetric flow rates in the body.

In total, there are 57 differential equations that must be solved. At the beginning of the calculation, the temperatures must be initialized. An equilibrium condition is reached when the element temperatures no longer change (Tt=0) and the stored body heat flux becomes zero.