Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
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Monika Frontczak’s Ph.D. Thesis, “Human comfort and self-estimated performance in relation to indoor environmental parameters and building features”: a must read...

Sample of content:

Of the % of respondents, these are the ten most frequently used words in descriptions of aspects contributing to comfort.

Light, sun: 46%
Temperature, warmth: 35%
Fresh/clean air, smell: 21%
Sound, noise: 16%
Peace, silence: 15%
Nature: 15%
View: 14%
Size of room: 9%
Family and friends: 8%
Room int., style, furniture: 8%

It is interesting at least from this study that light and sun both visual stimulants, dominate over view and interior decoration. Notice the combined values for temperature, warmth, smell, and sounds; all the non visual stimulants...


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Indoor Air Quality 

"In this wonderfully disruptive in-your-face inverted approach, mechanical and electrical design teams see architecture and interior design as a means of enabling maximum performance from the mechanical and electrical systems for the exclusive purpose of conditioning occupants instead of the building."

"Endorsement and enforcement of 72F (22C) air temperatures by industry has resulted in an inventory of buildings constructed over decades which have tried to solve thermal performance problems by unnecessarily creating 3150F (1750C) flame temperatures in furnaces for the exclusive purpose of excessively heating the air rather than solving the underlying thermal comfort problem which is NOT rooted in air temperature but in the mean radiant temperature (MRT) – an element intimately tied into the enclosure performance and the body’s thermal sensory system."

"...air only thermostats are and always will be poor thermal ambassadors for communicating human thermal needs to any mechanical system."


Begin With the End in Mind: A Model for Sustainability
opyright 2011, Robert Bean, R.E.T., P.L.(Eng.). All rights reserved. Edited and originally published in Commercial Building Products, March, 2012

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Many years ago, some very important words applicable to the world of architecture came from motivational leader Mr. Steven Covey in his highly acclaimed Seven Habits book - these being, “begin with the end in mind”.[1] These words are useful in many aspects of construction but their significance becomes evident when applying them to design principles for controlling the energy flows through a building for maintaining the “ergonomics of the indoor environment”.  Huh? Ergonomics? That’s for chairs and keyboards right? Ah no…the term, “Indoor environmental ergonomics” might be new to readers but it falls under the practice of indoor climate engineering and these terms imply something much deeper than the traditional knowledge of HVAC; where the latter is usually associated with the needs of the building and where the former is associated with the needs of occupants. As said in the dialect of a Maritimer …“boy’s and girl’s there be a big difference between this and that!”

The #1 message here is - if we begin with occupant needs underpinned by the unadulterated definition of sustainability, using indoor climate engineering to establish indoor environmental quality -  then the end game will result in the coveted high performance building everyone is drooling over. Even though this approach has immense benefits for contractors, designers and consumers alike it is not a trivial undertaking because it involves the busting up of egos and tradition.

So let’s first establish, by ethical requirements professionals must agree buildings at a minimum should limit the probability for occupants to become an OSHA statistic; this includes undesirable effects due in part to poor quality of air, lighting, sound, odor, vibration and thermal comfort. [2]

Secondly, the combined building, mechanical and electrical systems should meet or exceed those efficiency standards which are mandatory at the time of construction (or heaven forbid to a higher standard on a voluntary basis - he said somewhat sarcastically). Look it’s a good thing if the architect and her/his client have an obligation to the principles of earth stewardship and if so, then the principles of efficacy[3], entropy[4] and exergy[5] must then be included alongside the evaluation of energy efficiency; a principle I have labeled as an E5evaluation[6]

We’re not going to get into these concepts here but y’all should know they can’t be ignored. Accomplishing this E5 evaluation process one must remove some blockage - that being industry practice which treats architecture, interior design, HVAC and lighting systems as exclusively separate items. Why? Because from the perspective of energy and the occupants these elements are all integrated. For example, in thermal comfort your brain is like a blender except it can identify the individual ingredients so what often comes out is mixed into this, “nice view - but I’m freezing my butt off”.  It also applies to IAQ except your brain can’t always identify the ingredients so you get this, “nice flooring - is anyone else in here getting headaches?” The thing is, in solving these problems there will always be a corresponding flow of “corrective” energy and the following is just one example;

I’m cold = turn up thermostat = turn on burner/pump/fan = consumption of fuel and electricity = an act of treason against sustainability laws .[7]

So in keeping Mr. Covey’s concept of the “end in mind”, the goal is not to condition the building but to condition the occupant’s in the most sustainable way so the equipment remains off and thus the energy conserved and thus you can still show your "green face" in public.

This principle applies to other conscious and below conscious responses found within the human body. For example, responses to the indoor environment can include itching, sweating, congestion, runny nose and sneezing, shivering, squinting, headaches, rashes, hives etc., and these occur with corresponding adaptive strategies of scratching, turning on a fan, pinching ones nostrils and blowing ones nose, putting on sweater, closing blinds, opening a window, and taking medications etc. (probably reminds some of you of post grad night right?).[8]  One conclusion from this is that the building in part contributes to these conscious and below conscious reactions. The qualitative and quantitative magnitude is in part, proportional to the quality of the ergonomics of the indoor environment. In layman’s terms, as one is more distracted by conscious and below conscious responses to ones environment the more one is not focusing on learning or being productive; and based on published research, this distraction or downtime expressed as a dollar cost over a few decades far exceeds the capital and operating costs of the office building itself – and yes this is true even in the presence of all that new zippy high efficient HVAC equipment.[9] So here’s a news flash for ya – smart zippy HVAC equipment does not equal smarter and zippier occupants!

In addressing this articles hypothesis, it is evident that IEQ and energy challenges could in part be simultaneously solved if the architecture were based on all human factors, but here is the caveat, all human factors except those that are stimulated by esthetics. Why? Because there is no OSHA statistics attributable to ugly buildings and ugly interiors even if ugly led to your claims of pain and suffering…and so - yes - even the most visually appealing architecture cannot compensate for the negative effects of a bad environment (nice building – but can you feel that draft?) and bad environments are in almost all cases the contributing factor to the relative excessive use of non renewable energy (nice building – but it’s still drafty- turn the heat up more).[10]

Now using thermal comfort as a surrogate for other sensory examples, let me explain how an inside-out approach to design trumps the current outside-in approach.

The human body already has its own energy management and environmental control systems; however as close to perfect as these systems are, they are no match for Mother Nature in all but the most temperate climates.  As a result, we don’t need to construct buildings to entirely replace our physiological and psychological systems, only compensate for some of their shortcomings.

The solution is a combination of passive/adaptive and active systems; where the former incorporates solar (control/convert), wind (control/convert), building orientation, shading and enclosure performance along with adjustments to activity and clothing; and the latter with the use of active elements measured in the flow of non renewable energy through the building for operating HVAC equipment and lighting.

The magnitude of energy conveyed through boilers, chillers, furnaces, heat-pumps in any given geography is intimately connected to enclosure performance; and the quantitative value used for conditioning people is remarkably similar regardless of culture due to our common human physiology; and herein lays the gem…in the absence of visual stimulation, people from all over the world would choose materials and methods of construction having a similarly agreeable effect on ones thermal, respiratory, auditory, olfactory and kinesthetic senses. In this sense, i.e. without vision we really are all the same.

Thus the second message is that sight and visual stimulation is the stressor that challenges us in making sustainability based decisions.  Unsustainable based decisions leads to architecture that compromises our comfort (great view – yes but it’s too bright and too hot so please close the blinds and turn on the a/c). Message: senses which become compromised lead to the destruction of productivity and learning ergo the inside-out approach (occupants before architecture) trumps the outside-in (architecture before occupants) approach.

So how does all this fit into the evolution of what I call T4 (see footnote vi) that being the changes from terrible, traditional, and transitional buildings into terrific buildings defined by high performance building programs?

Well first know that building codes and those who adopt building codes have done a stellar job establishing “minimum” requirements as the benchmark in the neighborhoods near you. By educational standards meeting minimum requirements earns a D grade.[11] When D grade thinking is adopted en masse as it has in North America, it becomes maximum practice in the field wherein a representative code clause such as, “heating facilities shall be capable of maintaining an indoor air temperature of not less than 22C (71.6F)” has become the benchmark for establishing thermal comfort.

What adopters of D grade thinking fail to realize or deliberately ignore is that the D grade minimum in climate engineering is in fact a downgrade from the requirements of the human body as recorded in written standards (ASHRAE 55/ISO 7730) which are based on health science research. D grade thinking is one of several reasons why statistically 30% to 50% of the population is unhappy with their indoor environment which later shows up in lower academic scores, lower productivity and suppressed general happiness.[12]

Furthermore, negotiating down the price for a D grade system for economic reasons (disguised under term “affordability”) only moves the project closer to (you guessed it) the grade of “F”. Pay attention now…we’re going to get really complicated here….are you ready? Grade “F” happens because (wait for it) …people didn’t want to pay for Grade D. Duh! But you may ask why “F” is so easy to obtain in the first place? Well because the minimum benchmark is set too low. How low? Well…below the “Standards”, which is why Standards are called (you guessed it again) “Standards”. As an example, in the world of indoor climate engineering, measuring thermal comfort exclusively by air temperature is so inadequate there should be little blue pills for it. Endorsement and enforcement of 72F (22C) air temperatures by industry has resulted in an inventory of buildings constructed over decades which have tried to solve thermal performance problems by unnecessarily creating 3150F (1750C) flame temperatures in furnaces for the exclusive purpose of excessively heating the air rather than solving the underlying thermal comfort problem which is NOT rooted in air temperature but in the mean radiant temperature (MRT) – an element intimately tied into the enclosure performance and the body’s thermal sensory system.


Figure 1. There is something really freakish when you see how air temperatures around 22C (71.6F) have been programmed into our culture as representative of thermal comfort – it’s almost cult like! (Image courtesy of a Google image search for “thermostats”)

Consider Figure 1, and then consider we don’t inhale comfort we sense it through our skin – which is an almost perfect absorber and emitter of radiant energy; radiant being a dominant mechanism for body heat transfer typical of office and home environments. Translation: air only thermostats are and always will be poor thermal ambassadors for communicating human thermal needs to any mechanical system. The best way to point out the narrow sighted focus on air temperature is to drawn attention to comfort standards where air temperature is only one of ten elements considered by indoor climate engineers (see Table 1). In fact, with the exception of metabolic rates, clothing, air speed and humidity, all others are strictly a function of the enclosure performance and of specific interest to thermal comfort technicians are the interior surface temperatures which are a derivative of the combined performance of the fenestration systems, insulation values in the opaque surfaces and building tightness.

Table 1. Factors Affecting Thermal Comfort
(* strictly influenced by enclosure performance; dry bulb & rh is co-influenced by enclosures exclusively conditioned with air based HVAC systems.)

General Environmental Factors

Localized Factors

     Dry Bulb Temperature

     Vertical Air Temperature Differences*

     Mean Radiant Temperature*

     Radiant Temperature Asymmetry*


     Floor Temperature*

     Air Speed


Personal Factors

Metabolic Rate


     ref.: ANSI/ASHRAE Standard 55 Thermal Environmental Conditions for Human Occupancy  

To engage the power and simplicity between enclosure performance, radiant transfer and thermal comfort, there has to be a strategy assassination wherein the status quo goes from architect with client towards engineering of, “here’s our blueprints now design your system to make our building work” to the indoor climate and energy engineer saying to the architect and client, “here’s our systems to meet energy budgets and IEQ standards now design and build an enclosure to make them work”. In this wonderfully disruptive in-your-face inverted approach, mechanical and electrical design teams see architecture and interior design as a means of enabling maximum performance from the mechanical and electrical systems for the exclusive purpose of conditioning occupants instead of the building.[13]

Now pay attention again because this is where I’ll connect the various dots…when the engineer submits the highest possible system efficiency to the client - based on the principles of combustion and compression efficiency, it must without exception be based on the lowest return temperatures for heating and highest return temperatures for cooling. The only way to achieve the lowest and highest temperatures for heating and cooling respectively is to precede the architectural design by specifying enclosures performances by way of thermal fluxes (see Table 2) and then to incorporate large conductive low VOC interior surface areas as heat exchangers – it is serendipitous that these surfaces are readily available in the form of walls, floors and ceilings.

Why use interior surfaces as on site fabricated heat exchangers? Because indoor climate engineers know that if the environmental ergonomics influenced by warm and cool surfaces can suppress or encourage body heat loss based on the radiant exchange, they can easily and efficiently address almost all of the parameters required to meet both thermal comfort and energy restrictions. Thus the control of the radiant exchange between occupants and the building trumps control over air temperature and is first solved with enclosure performance and then augmented with a radiant cooling and heating system incorporating dedicated outdoor air system for deodorization, decontamination and dehumidification in what this author refers to as a radiant based HVAC system[14].

Table 2. Enclosures level performance (T4): based on combined convective and radiative flux per unit of floor area (sensible loads only in the long wave range).

Enclosure performance level

Thermal flux, Btu/ft2hr, (W/m2)

Terrific (high)

< 10 (31)

Transitional (good)

10 to 20 (31 to 63)

Traditional (moderate)

20 to 30 (31 to 94)

Terrible (poor)

> 30 (94)

I came up with these parameters by tying surface flux back to boiler efficiencies based on potential return temperatures using conductive floors and tight tube spacing in radiant floor heating systems. I’m not saying it should be used universally but hey it’s as good as any definition that I have seen elsewhere

To put a scope around fluid temperatures typical of radiant floor surfaces, I provide nominal requirements in Table 3, for various heating and cooling fluxes using low VOC[15] conductive floors and tight tube spacing’s. These are based on typical space temperatures of approximately 72F (22C) for heating and approximately 78F (26C) for cooling.

Table 3. Typical average fluid temperatures for radiant floors: based on flux, tiled concrete floors, 9” (225mm) tube spacing(a)

Building performance and mid range example for thermal flux, Btu/ft2hr, (W/m2)

Avg. heating fluid temp.
 F (C)

Avg. cooling
fluid temp.
F (C)

Terrific, (high performance)
flux = 5 (16)

78 (26)

70 (21)

Transitional, (good performance)
flux = 15(47 )

92 (33)

54 (12)(d)

Traditional, (moderate performance)
Flux = 25 (9)

105 (41)

38 (3)(d)

Terrible, (poor performance)
Flux = 35 (110)

120 (49)(c)

18 (-8)(d)

(a) Applies to floors only. Walls and ceilings would have different characteristics and thus different temperatures.

(b) All ranges listed would be in the condensing mode for gas/oil boilers.

(c) Out of the range of a water to water geothermal heat pump.

(d)Denotes ranges exceeding 12 Btu/ft2hr (37 W/m2), flux limited by a 66F (19C) floor temperatures  in accordance with ASHRAE 55 Thermal Environmental Conditions for Human Occupancy

The equipment manufacturers and related mechanical contractors and designers should immediately recognize the potential efficiencies in condensing boilers, heat pumps and chillers with some of the parameters above. Using traditional differential temperatures, for example a 20F (11C) in heating for a high performance building (i.e. terrific enclosure), supply temperatures become 78F + (20F/2) = 88F (31C)…putting that into perspective, its cooler than blood temperature. Return fluids back to the boiler become at design temperatures, 78F – (20F/2) = 68F (20C).[16] At such low return temperatures the combustion efficiency climbs into a high 90% range and with the use of weather compensators this type of efficiency can be maintained throughout the entire heating season.  Likewise you can see the efficiency destruction when the buildings are inefficient particularly in the cooling modes. Beyond the transitional building in cooling, radiant surfaces are useful as a base system, engaging supplemental systems during peak loads[17].

As we initially stated, if we begin with human factor design underpinned by the unadulterated definition of sustainability, using indoor climate engineering to establish indoor environmental quality - then the end game will naturally deliver high performance buildings.

When designers can focus on controlling occupant heat transfer to and from interior surfaces using enclosure performance, it will result in warmer interior surfaces in winter and cooler interior surfaces in summer. Such passively controlled surfaces temperatures using low VOC finishes improve the health of the environment while reducing the operating time of active systems and thus contribute to conserving energy - a key component in sustainability. When heating and cooling equipment must run during swings in extreme seasonal loads, it can and must run at maximum efficiency enabled by the low heating temperatures and high cooling temperatures associated with radiant based HVAC systems. The beauty of these is how well they play so well with natural materials and the multiple sources of renewable energy found in the earth, wind, water and sun.


Note: All of what has been explored in general terms above reveals significant contributions in meeting the requirements of several key and LEED recognized ASHRAE standards including 55, 60.1(.2) 90.1(.2) and 189.1 

[1] I know its hard to believe that someone with a professional designation in building construction engineering and another in HVAC engineering would care about motivational speakers….well I sorta of do and besides it made for a nice introduction.

[2] Wall Street is no longer allowed to use the word professional and ethics in the same sentence but in architecture it’s still acceptable.

[3] Efficacy – Roman buildings heated with the hypocausts had good efficacy compared to the following generations of rich but stupid land owners who tried to heat entire castles with fireplaces – hot to the left of me, cold to the right, here I am stuck in the middle of a big ole damp cold castle…apologies to 1972’s band Stealers Wheel

[4] Entropy – thermal accounting for why cold beer becomes warm and warm coffee becomes cold.

[5] Exergy – using the temperatures of a flame thrower to heat your skin is bad exergy…Btu dad to Btu son…you could have done so much more with your life! See “Master Yoda - The E5 Jedi”.

[6] E5 the original article had lots of formulas and after editing this was the only mathematical term I was allowed to keep – sorry to all you who still own pocket protectors and carry mechanical pencils.

[7] Ok so there are no sustainability laws yet but just wait and see what happens over the next two generations.

[8] I wouldn’t know since we were all angels in our construction programs…urp.

[9] Rather than list the exhaustive research, Google search using these terms: +office +productivity +“indoor environment”…enjoy the reading.

[10] People that study linguistics will tell you that the word “but” essentially erases everything said up to the word “but” so “a nice building “but” its still cold…means they don’t care about how the building looks if they are uncomfortable.

[11] I stole this – I just don’t remember who I stole it from…sorry to whoever came up with this wonderful analogy….you get an A+ for creativity and dealing with reality. Side note: no professional sports team tries to be the last team to make it to the finals…go ahead and think about it…building codes & D grades & last team to make the cut off…do you need a map?

[12] Google search, “Thermal Comfort Surveys” +satisfaction, and read to your hearts delight.

[13] Search online for my long ago rant, “In a Town Called Comfort Only the Blind Can See”. It needs an editor but you’ll get the idea.

[14] Message: the silly battle over hydronics versus air is moot – one is not better than the other…you need both systems if you want to reach energy and IEQ objectives…I learned this right after graduating in 1983 - radiant for thermal comfort quality and air for air quality; use liquid to move Btu’s – use air to ventilate, decontaminate and control humidity. It’s the way your body works (blood/fluid and lungs/air), it’s the way standards are written (ASHRAE 55 and 62) and it’s the way we should do buildings...enough said.

[15] VOC, volatile organic compounds, i.e. aldehydes, benzene, toluene etc…nasty stuff found in finishes

[16] Folks, at 88F (31C) supply fluid temperatures there is no room for the word “hot water heating” in modern buildings…tepid yes, hot - definitely not!

[17] If you’re freaking out over condensation and radiant cooling have you ever considered that 100% of all condensation problems in buildings exclusively conditioned with air didn’t have radiant cooling to blame? 100% as in all - as in…the problem isn’t the radiant it’s the moisture.  Keep the rh below 55% and the surface above 66F (19C) and you’ll have ample safety factor in a good to high performance building.

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