Indoor Environmental Quality with Radiant Based Heating and Cooling from Healthy Heating.

Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
Not for profit educational resource on indoor environmental quality.
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Fundamentals of indoor environmental quality / thermal comfort and air quality solutions using radiant based HVAC

Some things you should know about heat...

We've heard this before, "heat rises". But this is not true for radiant energy. If it were we would need to put heat lamps on the floor; and the earth (preferably the side you're standing on) would always have to be above the sun. When you put it in those terms heat rising becomes a silly thought, agree?

There are other ways to think about everyday heat transfer. Ask yourself why you feel cool in the supermarket freezer section or underground parkade on a hot summer day.

The reason why you feel cool in the freezer section or parkade,  is your blood is much warmer than the cold display glass or concrete walls so the heat from your body travels via radiation from the skin which is warmed up by your blood, to the cooler surrounding surfaces.

Do you know what physicians and building scientists call this sensation?

That's right, its called
radiant cooling or as physician Dr. Vernon called it, "negative radiation."

HVAC designers can deliberately provide radiant cooling by sending chilled water through PEX pipes located in the floor, wall or ceiling just like a radiant heating system.

In fact, a radiant floor used for heating and cooling is called a reversible floor.

Click on the image below.  Can you imagine that the
PEX pipes might represent your arteries and veins. Can you see how a radiant heating and cooling systems is almost like your body?

Photo Credit: NRDC,
Click to enlarge.

One of the major methods  your body regulates its internal temperature is by the flow of blood to the skin.

When your body is exposed to a warm to hot surface it prevents your body from  releasing heat via radiation and it may absorb energy in the form of heat - both which make you feel warmer.

When your body is exposed to a cooler surface you release energy which takes away heat which makes you feel cooler.

A warmer or cooler surface in a building is based on its energy efficiency and/or by "conditioning" the surfaces with PEX pipes or other forms of radiators.

The less efficient a building the greater the temperature difference between your skin and the temperatures of the walls, windows, doors floors and ceilings.

It is the temperature differences between you and the building which in part, causes discomfort.

That's why conditioning surface temperature is so important in the comfort equation.

It's one of the reasons why this front entrance will feel cool.  Image how it would feel if it didn't have radiant heating to compensate for the losses.

Learn More About Thermography







Suggested Reading

Cortical, thalamic, and hypothalamic responses to
cooling and warming the skin in awake humans

Egan, Johnson, Farrell et al



Human Factors - The body as an HVAC system
For additional support visit our visitor services page.


Thermal images of the human bodyCredit: Tony McConnell/Science Photo Library

Point of interest: Wall mounted radiant panels and radiant floors operate at different temperatures and thus different wave lengths as such we experience them differently. See our study materials on radiant theory.

Figure 1. This thermograph shows a human drying off in front of a panel radiator. The different colors show the variations in surface temperatures. Have you ever heard the term "white hot"? Can you tell which way the water is flowing through the radiator? That's right, the fluid is flowing from right to left. This person feels warm because the hotter surface is radiating towards him just like the sun does. However, the temperature of the sun, radiator and radiant floor all operate in different wavelengths and because of this heat is retained or received and perceived in different ways.


Blood flow in the handCredit: Mehau Kulyk/Science Photo Library

Point of interest: Each of us has an intimate radiant relationship with the thermal environment vis--vis the temperature of our skin which, amongst many factors, is a function of blood flow circulation.

Figure 2. The variations in skin surface temperature shown in the Figure 1. thermograph are in part due to the regulation of blood flow. Blood travels through the arteries that branch out to form the capillaries. The blood then leaves through an extensive network of veins as shown in this illustration. Can you imagine the veins and arteries as radiant PEX tubes carrying warm fluid and your skin as a living radiator? Learn more about skin science.


controlling blood flow for cooling and heating regulation of body temperature.Credit: John Bavosi/Science Photo Library

Figure 3. The regulation of blood flow happens when the nerves (yellow) stimulate the artery muscle to contract, thereby maintaining blood pressure. Increase in stimulation causes constriction of the vessel and an increase in blood pressure. Decreases in stimulation causes a dilation of the vessel and a drop in blood pressure. The change in pressure regulates flow just like in a hot water heating system. The warmer the internal body temperature, the greater the blood flow to the skin where heat is radiated, convected, evaporated and conducted away for thermal cooling.


The brain is the perfect thermostatCredit: Health Archives (Publisher Unknown)

Figure 4. The instruction to dilate or constrict blood flow comes from the brain which gets input from nerve sensors in the body. The name for the part in your brain that is responsible for your bodies temperature regulation is called the hypothalamus. Your hypothalamus is the perfect thermostat and its wired to your skin sensors through your nervous system.


Thermal sensors in the skinCredit: Francis Leroy, Biocosmos/Science Photo Library

Figure 5. The average adult body is covered by a nominal 20 sq. ft. of skin, which has over 166,000+/- thermal sensors which are connected to the brain through your nervous system. These and other sensors in your skin are stimulated by  pressure, heat, cold and pain. That stimulation is sent to the brain for interpretation. The skin is also rich in blood vessels; shown here, arterial capillaries appear red, venous blue. To protect vital organs, the blood flow is reduced to the skin when the body gets cold. Goose bumps are caused by the skin tightening up around your hair follicles. Picture your head popping out of your coat after buttoning it up on a cold winter day. Likewise the sweat pores in your skin open up when your body begins to overheat. Learn more about shivering and sweating.


thermography for studying human physiology

Credit: Dr. Arthur Tucker/Science Photo

Figure 6. The human body is a living heating and cooling systems which can be very effective at staying healthy with radiant transfer. Can you now imagine how this baby might feel exposed to (radiant and convection)) and crawling (conduction) across a cold floor defined by cold walls and ceilings? The colors represent different temperatures, from the cold feet to the hotter forehead. The body at rest absorbs and releases over 50% of its sensible heat by radiation and the temperature of the skin is regulated by blood flow. With this knowledge in mind, knowing humans, (especially babies) like warm surfaces in winter and cool surfaces in summer, what combination of architecture and heating and cooling systems makes sense for you and your family? What would you recommend to others?

The objective of using radiant solutions for thermal comfort.

The objective with low temperature radiant heating is to warm the interior surfaces of the room thereby reducing the radiant heat transfer from your body to the building. You see it is the heat you retain which provides the thermal comfort sensation.

The objective with radiant cooling is to lower the interior surface temperatures of the room thereby encouraging the radiant heat transfer from your body to cooler surfaces. You see its the heat leaving your body which causes the cooling sensation.

Spaces heated with forced air may have warm air but the surfaces can still be cool and so you can experience radiant cooling in a forced air heated can experiment with this by standing next to a cold window or wall...see how it makes you feel even though the room air thermostat may say 72F.

With high performance buildings some or all of the radiant challenges can be solved by the enclosure thus the reason why HVAC begins with the structure.


Additional studies:

Want to know how other industries do thermal comfort research?
Visit our web page on Comfort Instrumentation, Thermal Manikins, Thermal Comfort Surveys

Want to expand your knowledge on human physiology and comfort?
Visit our web pages on
Indoor Environmental Quality

Want to familiarize yourself with the basics of architectures and radiant based HVAC systems? Visit our schematics pages.

Want to read about insulation, working with contractors, heat pumps, radiant cooling, hardwood floors and radiant systems? Visit the links at one of our solutions page where you can find many articles on several topics.

Want to have fun simulating your ideal environment by playing with air velocity, clothing, activity, and humidity? Visit the Comfort Calculator page.

The images on this page were made available through the financial generosity of our corporate sponsors and individuals who have downloaded the Guide to Indoor Quality Comfort and the Architectural Guide to Radiant Based HVAC Systems. If this material was of use to you, please consider sponsoring a page or donating so we can continue to offer high quality educational materials on indoor comfort quality (ICQ).

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