Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
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radiant cooling for thermal comfort

Glossary of Terms
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Featured articles:
Tres Bien for Large Scale Radiant Cooling

Sample radiant cooling calculation procedure.

There are radiant cooled projects all over the world including many projects in America.

One the largest radiant cooling projects in the world is the Bangkok airport having over 1,500,000 sq. ft. of cooled floors to absorb sensible heat from solar gains and travelers.

Photo credits various sources including TransSolar, Dr. Olesen, Project Team, Uponor et al.


Designers use programs like this to easily calculate the dew point of surfaces

Online radiant design presentation for professionals.

Infloor Radiant Design Guide: Heat Loss to Head Loss

Typical Radiant Based HVAC Schematics

Validating radiant cooling and heating designs

"...man does not feel the room temperature, he feels the heat loss from the body." Credit Innova

Increasing the heat loss from the body can be done with cooled surfaces;  similar to the sensation you get when standing next to a window on a cold winter day...except the cooled surface is controlled for comfort.


Radiant Cooling - Part I, Fundamentals

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Let's get the #1 myth out of the way before we discuss radiant cooling in greater detail...

Fact #1: 100% of all condensation problems in buildings conditioned exclusively with air did not have radiant cooling panels to blame (go figure).

Fact #2: Regardless of the HVAC system, moisture must be controlled for biological concerns (bacteria, viruses, mites and molds), for hydrolysis and the control of VOC emissions (formaldehydes, phthalates, terpenes etc.), for the dimensional stability of hygroscopic materials (woods), for the preservation of materials, and for occupant respiratory and thermal comfort; moisture must be regulated for these greater priorities making the condensation on radiant cooling panels a moot point.

Radiant Cooling for Sceptics: How to do radiant cooling in high humidity geographies. Make your request for the presentation password through our Linked-In group.


The two most common myths around radiant cooling is that it will cause condensation and you will have cold floors - that's it...go to any online chat site and ask about radiant cooling and watch what happens.

The reason why these radiant cooling myths get spread has to do with misunderstanding four principles:

  • the true definition of heating, ventilation and air conditioning (HVAC)

  • the difference between latent and sensible loads and,

  • the concept of a "lean" mixture (grains of moisture per pound of dry air)

  • how comfort cooling works.

First we need to remind ourselves that HVAC is not exclusively about conditioning the building, rather its primarily about conditioning you and I which includes both conditioning the air and our bodies.

What does this mean?

It means you have to learn to separate comfort quality from air quality which is hard thing to do if you've spent your whole life thinking they are the same or believing you can effectively do both with one HVAC system. Look at it this way...have you ever considered the body has independent system to deal with thermal comfort (skin to brain) and respiration (lungs to brain)...and have you ever considered there are two separate standards one for thermal comfort (ASHRAE 55) and one for air quality (ASHRAE 62)? The problem with most builders and HVAC people is they try to do two separate tasks with one system which is contrary to what the body does and contrary to what is reflected by standards.

So when do we feel cooling comfort? Well when our body loses more heat than it can generate we experience a cool sensation. If the heat loss from our body is such that it goes from cooling comfort to cold it causes a reduction in skin temperature and goosebumps...if the body can't shed its heat fast enough it goes from heating comfort to hot which leads to a rise in skin temperature and perspiration. If the body continues to loose excessive heat we can go into hypothermia...if we can't get rid of excessive heat we go into hyperthermia - both scenarios can lead to death - which is really hard to recover from...

To cool our body just enough to be comfortable we can lower the mass temperature in our home a few degrees cooler than our skin temperature which creates the same experience you get when you walk into an underground garage on a hot summer day or into the frozen food section at the super market.  Why do we feel cool in the underground garage or freezer section? It's because the temperature of the concrete or glass in relation to our skin is lower so our body releases its heat via radiation to the cooler surface  - thus the reason we feel cool. The best part of it all, is a body at rest, transfers over 50% of its heat via radiation so radiant cooling makes perfect sense. In fact the transfer of our body heat to the cooler surface via radiation is called "sensible" heat transfer. So now you know that radiant (sensible) cooling works because you have experienced it a thousand times before just like the cave dwellers of years past…you just never thought about it.

Where most uneducated voices speak up and against radiant cooling has to do with condensation. You see they don't know about sensible vs. latent cooling. Sensible can be thought of as dry heat or heat without moisture. The solar heat inside a greenhouse is a great example of sensible heat. In Sensible Heata building, sensible cooling is the absorption of the radiant energy from the sun and other radiant heat sources such as your body, lights, motors, compressors, stoves, ovens, dryers, computers and home theatre systems.   All of these loads which raise the mass temperature and mean radiant temperature of the home can be removed by absorbing the excess heat with a cool surface. 

Think of a cooled surface as 'sponge' for sensible heat

What shouldn't be absorbed by a cool surface is the heat being held in the moisture content of the air.  This heat is called the "latent" load. Latent means dormant, hidden or concealed. Latent heat shows up every time you sit outside on a hot humid day with a cool drink in your hand...water actually forms on the glass surface. Where did the water come from?  It Latent Heatwas actually hidden in the air and the amount is based on an every day term that you are familiar with called relative humidity. The visible presence of moisture or condensation occurred because the ‘humid’ air (latent heat) met a chilled surface (sensible). Can you guess where some of the heat in the moisture went to? That's right...it went into the glass via conduction.  It's one of the reasons why you need to keep putting ice into the glass to keep the drink cool. The rest of the heat went back into vapor or dripped all over your  shirt or shorts.

So what does this mean? It means a radiant cooling surface is used to absorb heat it can thermally feel in the absence of moisture.

This is very important to understand because in some climate regions of North America the relative humidity in the summer is very low almost desert like. In other parts of the country the humidity is very high.  In other parts it changes based on how much rain falls in the region and for how long.

Regardless whether there is a radiant cooling system present or not, the latent load must always be controlled for thermal and respiratory comfort, to prevent moisture damage in buildings, to enable dimensional stability in hydroscopic materials and to disable the environmental support of pathogens and allergens.

So the key to confidently cool with radiant is to first control the moisture in the air (lean) through dehumidification for the reasons stated above and then control the surface temperature of the floor (dew point) which is easy to do.

Radiant cooling - 1st control the moisture then the dew point

go to part II - click here., Controlling the Relative Humidity
go to part III - click here, Heating and Cooling Comfort Systems
go to part IV - click here, Radiant Cooling Educational Movie Clips
go to part V - click here, Featured Project, Manitoba Hydro Office Building

People who visited these radiant cooling pages have also visited our Radiant Design Guide, Psychrometrics - Made Easy and Introduction to Indoor Environmental Quality.

Suggested reading:

Leach, M., Lobato, C., Hirsch, A., Pless, S., Torcellini, P., Technical Support Document: Strategies for 50% Energy Savings in Large Office Buildings, National Renewable Energy Laboratory, Technical Report, NREL/TP-550-49213 , September 2010, <http://www.nrel.gov/docs/fy10osti/49213.pdf>
Radiant Cooling Systems: Condensation Concerns Part 1 of 6, Preservation of Materials
Radiant Cooling Systems: Condensation Concerns Part 2 of 6, Microbial
Radiant Cooling Systems: Condensation Concerns Part 3 of 6, Hydrolysis
Radiant Cooling Systems: Condensation Concerns Part 4 of 6, Dimensional Stability of Hygroscopic Materials


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