Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
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Fundamentals of indoor environmental quality / thermal comfort and air quality solutions using radiant based HVAC

Human Physiology 1
Human Physiology 2
Human Physiology 3
Human Physiology 4
Human Physiology 5


Unless otherwise noted, the content and animations on this page have been lent to us by
David Scheatzl
e, Ph.D
and the team at the
College of Architecture and Environmental Design

Copyright (c) Arizona Board of Regents 2002, All Rights Reserved

RB's Comment

One Btu is about the amount of heat a single wooden match puts off.

So imagine your body at rest burning 360 matches in one hour.

Now you know why when you work or play hard you feel hot and sweat.

Sensible and Latent Heat includes radiant, conduction, evaporation and convection
Sensible & Latent Heat

Radiant heating is natural

This Living Entity Needs Radiant do you.

"Our environmental preferences are based on value judgments which are learned through past experiences and influenced by our background and social-economic level and age is an important catalyst."
F. Rohles,Jr., Ph.D.
Professor Emeritus,
Kansas State University

Human Physiology 2 - Homeostasis - Thermal Balance
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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:


Metabolic rates or Met Rates


No. of Mets



Seated, quiet (office work)


Walking (3 mph)


Tennis, singles







Figure 1. 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.

Human Physiology - Sensible Heat Loss

Figure 2. There are three sensible heat loss mechanisms : Radiant loss to cooler surfaces (or gain from warmer surfaces); Convection loss to cooler air (or gain from warmer air) which is heated and rises; and dry respiration heat loss to cooler air that enters the lungs and is exhaled warmer

Human Physiology - Latent Heat Loss

Figure 3. The latent heat loss mechanisms include: latent respiration heat loss; water diffusion through the skin; and the evaporation of sweat (skin wettedness).

Here's an exercise you can do at home...look at everything around you and ask what natural interactions are going on with respect to heat? Then ask yourself, if you were a plant how would you thrive in an environment without radiant energy, proper humidification, fresh air, or had to live with cold surfaces...your HVAC system should represent nature - it can be therapeutic or threatening...
its your choice.

Click here to visit Human Physiology 3



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