To understand how to best control comfort, we must first understand the human body's method of maintaining heat balance.

Heat production within the body

The human body must maintain heat balance if it is to survive. If it generates more heat than is needed, it must lose heat to its surroundings or its temperature will rise and it will become ill and could die. Likewise, if it loses too much heat to maintain a constant temperature, its temperature will lower and it could die. When conditions surrounding the body are not ideal, it has adaptation mechanisms that help adjust the amount of heat loss. When the body has to take adaptive measures, it is known to be under thermal stress. Thermal stress equates to discomfort while a minimum of thermal stress provides comfort.

The human body can be compared to a machine (in the engineering world) that converts fuel into energy for the purpose of doing work -- the more active the body, the more fuel that is consumed. The rate of heat production within the body is known as the metabolic rate (units=met= 360 Btu/hr) and includes all of the heat given off by all of the chemical reactions taking place in the body. Some examples of typical metabolic rates are as follows:

Introduction

Human Physiology
heat production
thermoregulatory system

Comfort Control

Animations

Like the machine, the conversion of fuel (oxidation of food) into work is not 100% efficient. That energy which is not converted to do work is in the form of heat, and if not needed to maintain a constant body temperature, it is brought to surfaces by blood flow (See Figure 1), then rejected to the body's surrounding environment. This heat is rejected in two forms, sensible and latent heat transfer.

Figure 1