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ISO 7726:1998(E), Ergonomics of the thermal environment — Instruments for measuring physical quantities

Scope
This International Standard specifies the minimum characteristics of instruments for measuring physical quantities
characterizing an environment as well as the methods for measuring the physical quantities of this environment.

It does not aim to define an overall index of comfort or thermal stress but simply to standardize the process of recording information leading to the determination of such indices. Other International Standards give details of the methods making use of the information obtained in accordance with this standard.
 

This International Standard is used as a reference when establishing:

a) specifications for manufacturers and users of instruments for measuring the physical quantities of the environment;

b) a written contract between two parties for the measurement of these quantities.

It applies to the influence of hot, moderate, comfortable or cold environments on people.


Thermal Comfort: Everyone Wants It but Few Know the ASHRAE Standard

Copyright (C) 2012 Robert Bean, R.E.T., P.L. (Eng.), originally written for and published in the Energy Vanguard Blog, Wed, Mar 28, 2012

For additional support visit our visitor services page
 

Introduction

Let me start by suggesting that one would think that an industry with its roots grounded in thermal comfort, could roll the definition of thermal comfort right off its tongue like an old Frank Sinatra classic. I mean this should not be difficult to do right? It seems almost obvious that someone who sells comfort equipment or designs HVAC systems for comfort or repairs buildings to be more comfortable should not have to think about what it takes to be comfortable right?

Unfortunately, if you assembled a thousand people representing the professions of HVAC contracting, energy auditing, construction, engineering, interior design, architecture, and manufacturing in an exam hall and asked them only one question, that being to list the 10 key elements of an industry thermal comfort standard, approximately 30 individuals would pass. How do I know that? Because I’ve been asking that question in classes for over a decade and typically only 3% get it right and of these only half of them own a copy of ANSI/ASHRAE Standard 55 Thermal Environmental Conditions for Human Occupancy.

Thermal Comfort

The purpose statement from this standard is, “to specify the combinations of indoor thermal environmental factors and personal factors that will produce thermal environmental conditions acceptable to a majority of the occupants within the space.” This standard is as equally resourceful as other ASHRAE standards and was first published 1966 – that would be almost 37 years before ANSI/ASHRAE Standard 62.2 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings, came unto its own.

So let me take this moment to ask a few basic questions: Do you provide products or services related to thermal comfort? If so, could you right now explain ten key elements of thermal comfort? If you do promote thermal comfort, do you own a copy of ASHRAE Standard 55? If not, why not? I’m always intrigued by the answers I get. Most people don’t even know the document exists.

Along this line of questioning, how many consumers and their service providers believe comfort is defined by a numerical thermostat setting? If so, why do we have color-coded temperature controls in cars and on plumbing fixtures? Is comfort provided by high efficiency furnaces? If so why do people still complain about discomfort with the newest of appliances, especially in origami homes constructed essentially of glass? Is indoor air quality a requirement of thermal comfort or thermal comfort a requirement of indoor air quality? If so, can you explain all the thermal comfort complaints in ventilated leaky homes or how it is that you can sit back in your granddad’s La-Z-Boy™, tipping back your favourite brew, feeling all warm and cozy inside whilst inhaling radon gas, VOCs, or carbon monoxide?

The latter of these questions are definitively rhetorical and stated only to point out that neither air quality nor thermal comfort serve as proxies for each other. In fact, ASHRAE 62.2 states the standard does not address thermal comfort, referring users to ASHRAE Standard 55. Likewise, ASHRAE Standard 55 states that the standard does not address indoor air quality.

These questions should get you to start thinking about what thermal comfort really is. Now here’s the mind-blowing part: According to indoor environmental ergonomic definitions, thermal comfort is (wait for it) a “condition of mind.” That’s right – it’s in your head and your client’s head and because all heads are not alike (unless you’re in the club of medicinal marijuana licensees), thermal comfort is and always will be a subjective perception.

Ultimately one of the difficulties in discussing thermal comfort is that this definition of “condition of mind” sits, "at the crossroads of physics, physiology, psychology, culture, and climate (Solomon, 2011);" and as I like to point out, it does so amongst a competitive industry driven by public relations, marketing, and sales teams all offering products and services related to a term that it doesn’t really understand nor can it accurately define.

In the space allotted I’ve not gone into the exhaustive details of thermal comfort but I have provided in the reference section below numerous free resources for you to study at your leisure, including a link where one can purchase the ASHRAE standard; in a nutshell the ten elements for consideration when addressing thermal comfort are shown in table 1.

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*

     Humidity

     Floor Temperature*

     Air Speed

     Drafts*

Personal Factors

Metabolic Rate

Clothing

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

Most are familiar with “dry bulb temperature,” that being what 99.99% of all thermostats measure and readers of the Energy Vanguard Blog should now be familiar with “mean radiant temperature” from Allison’s infamous article, Naked People Need Building Science, but the others are equally imperative to understand when establishing conditions for thermal comfort. When all are considered, it points out why the typical thermostat is a poor “thermal ambassador” to an HVAC system since most fail to perceive what the occupants perceive.

Principle of Indoor Climate Engineering

As I wind down this post, I want to point out one of the principles that indoor climate engineers understand full well – there exists an intimate relationship between building performance and that “condition of mind” and ultimately HVAC must start with the choice in architectural systems where energy consumption and system complexity is inversely proportionate to the performance of the enclosure. As David Butler pointed out in his excellent guest post, the enclosure should do the bulk of the thermal comfort work.

In support of this principle, I have stated on several occasions that if building codes dropped the reference to controlling air temperatures and switched the requirements to controlling mean radiant temperature, building performance specifications would have to change overnight. Bad buildings have low MRT’s in winter and high MRT’s in summer; this contributes to large differences in the vertical air temperature; creates excessive drafts and increased radiant asymmetry. Bad buildings also have uncomfortable floor temperatures and are challenged to maintain reasonable levels of humidity.

I believe once you read and digest the linked content, you will be motivated to purchase the ASHRAE standard and embrace its messaging as it relates to improving building enclosures and reducing energy demands for conditioning people…because at the end of the day people don’t feel the heat loss or heat gain of the building, they feel the heat loss and heat gain within their bodies and this will effect a “condition of mind”, that being our individual perceptions of thermal comfort.<>

The views and opinions expressed in this post are strictly those of the author and do not necessarily reflect the views of The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE).


Heat Balance and Thermal Comfort Equations (Fanger, (1934-2006))
source/credit: ASHRAE Fundamentals (2001) Thermal Comfort, F.08, pg 8.2


Formulas for calculating comfort? Was there any doubt? Fanger did his Ph.D. thesis on calculating thermal comfort including a study in angle factors, mean radiant and operative temperature. He left us with a means of predicting the percentage of people dissatisfied (PPD) using the predicted mean vote (PMV) methodology described today in ANSI/ASHRAE 55 and ISO 7730 standards.

M - W = qsk + qres + S = (C + R + Esk ) + (Cres + Eres) + (Ssk + Scr)

M = rate of metabolic heat production, Btu/h ft2

W = rate of mechanical work accomplished, Btu/h ft2

qsk = total rate of heat loss from skin, Btu/hft2

qres = total rate of heat loss through respiration, Btu/h ft2

C + R = sensible heat loss (convection and radiation) from skin, Btu/h ft2

Esk = total rate of evaporative heat loss from skin, Btu/h ft2

Cres = rate of convective heat loss from respiration, Btu/hft2

Eres = rate of evaporative heat loss from respiration, Btu/h ft2

Ssk = rate of heat storage in skin compartment, Btu/h ft2

Scr = rate of heat storage in core compartment, Btu/h ft2

 

Resources:

  1. Title, Purpose and Scope of ANSI/ASHRAE Standard 55

  2. Turner, S., What’s New in ASHRAE’s Standard on Comfort, ASHRAE Journal, pages 42-48, June 2011
    H. Rohles , Temperature or temperament: a psychologist looks at thermal comfort. ASHRAE Transactions 86 1 (1980), pp. 5–13. 11.

  3. Solomon, N.B., The Comfort Zone, Architectural Record, McGraw-Hill, April 2011

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

  5. Bailes, A., Naked People Need Building Science, Energy Vanguard, Dec. 2011

  6. Butler, D., Lessons Learned by a Reluctant Owner-Builder, Energy Vanguard, Mar. 2012

  7. Bean, R., The Big Picture: Enclosures, indoor environmental quality and HVAC systems cannot be treated as isolated and independent systems – they are in fact one of the same, Better Buildings – Beyond the Benchmark,  Fall 2011

  8. Bean, R., Thermal Comfort and Indoor Air Quality, 2012 Conference Slides – Online version (allow 120 seconds to load)

  9. Bean, R.,  Begin with the End in Mind, Commercial Building Products, March, 2012

  10. Egan, G.F., Johnson, J., Farrell, M., McAllen, R., Zamarripa, F., McKinley, M.J., Lancaster, J., Denton, D., Fox, P.T. (2005) Cortical, thalamic, and hypothalamic responses to cooling and warming the skin in awake humans: A positron-emission tomography study. National Academy of Sciences, U.S.A., 10.1073/pnas.0409753102 PNAS April 5, 2005 vol. 102 no. 14 5262-5267

  11. McAllen, R.M., Farrell, M., Johnson, J.M., Trevaks, D., Cole, L., McKinley, M.J., et al. (2006) Human medullary responses to cooling and rewarming the skin: a functional MRI study. Proc Natl Acad Sci U S A. 2006;103:809–13

  12. Alter, L. (2015) There's more to comfort than just picking a furnace or an air conditioner. Mother Nature Network.

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