ball state architecture | environmental systems 1 | grondzik 1 thermal comfort

Ball State Architecture | ENVIRONMENTAL SYSTEMS 1 | Grondzik 1

THERMAL COMFORT


James Marston FitchAmerican Building: The Environmental Forces that Shape It

“The fundamental thesis of this book is that the ultimate task of architecture is to act in

favor of man: to interpose itself between man and the natural environment in which he finds

himself, in such a way as to remove the gross environmental load from

his shoulders. The central function of architecture is thus to lighten

the very stress of life.”James Marston Fitch (1909–2000) was an architect

and a Preservationist, one of the founders of the Graduate School of Architecture, Planning, and

Preservation at Columbia University in 1964. (wikipedia)


“Removing the Load” in Context

context is critical: bus shelter versus elementary school versus hospital operating room


Thermal Comfort

• Why?– Why should we worry about thermal comfort?

• What?– What is thermal comfort?

• How?– How is thermal comfort addressed during

design?


Why Worry About Thermal Comfort?

• Designers have an ethical responsibility to cause no harm – my personal opinion

• Gripes about thermal comfort are consistently the number one complaint heard by building managers/owners

• Comfort decisions can have substantial energy and resource consumption implications

• Comfort is the basis for a substantial investment (in a climate control system)

• Green design demands (sort of ) thermal comfort


Two Ways to Look at Thermal Comfort

As a psychological phenomenon

As a physical phenomenon

Both views are valid, both must be tempered by statistics, and both views are important to building design efforts


What is Thermal Comfort?

“That condition of mind which expresses

satisfaction with the thermal environment

and is assessed

by subjective evaluation.”

ASHRAE Standard 55-2010 Thermal Environmental Conditions for Human Occupancy


ASHRAE?

Reminder The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

(www.ashrae.org)

A key developer and promulgator of building design standards and guidelines.


Condition of Mind?• Thermal comfort is defined as being an opinion

(essentially an individual perception)• This opinion will be influenced by the

environmental conditions surrounding a person and by his/her interpretation/impression of those conditions– Physical conditions are both group and individual

• Room air temperature is typically common to a group• MRT (mean radiant temperature) is often experienced

differentially by those in the same space

– Interpretation is solely individual• Nevertheless, a group consensus might be ascertained


Condition of Mind?

• A perception (condition of mind) is best assessed by asking people (occupants) how they feel

• A critical note: one can only ask people who exist and occupy the environment of interest—thus, “asking” is a POE (post occupancy evaluation) activity … there is no one to ask about conditions in a space until that space is built and occupied

• Information from existing situations, however, can be collected, collated, and provided as guidance (or precedent) for future designs


Uses for a “condition of mind” (psychological) approach

• As a post-occupancy evaluation (POE) tool– If people are in the space being evaluated

• Not directly usable as a design tool– There is no occupied space during design

• But ... POE/laboratory studies can provide useful information (trends and patterns) to help develop a design tool– Such as a “comfort chart”


ASHRAE Thermal Comfort Chart (from Standard 55-2010)

comfortzone(s)

addressing operative temperature, relative humidity, and occupant clothing


Midstream Thoughts• Thermal comfort is an important design intent (in my

opinion) and can be easily benchmarked via criteria• Thermal delight might be an even better intent here

and there (see Lisa Heschong: Thermal Delight in Architecture)

• Thermal comfort is not typically required by building codes (it is rarely required, in fact) so it will become a design issue mainly via intent/criteria (or through general practice or by accident)

• Thermal comfort as a psychological-statistical concept should be straightforward

• But …. we need to understand the physical basis of comfort to really use it in design (since environmental elements will need to be manipulated)


Mapping Physical & Psychological Comfort Territories

temperature

hum

idity


Physical Context of Thermal Comfort

-- dishealth

-- dishealth

conditions the body’s response

see required reading for more details on these responses


Physical Basis of Thermal Comfort

Fundamentally, comfort involves a heat balance (a thermal equilibrium) … where:

heat in ≈ heat out

where “heat in” is provided by metabolism, radiation, conduction, convection

where “heat out” is via radiation, conduction, convection, evaporation


Heat FlowMechanisms

three external “to” mechanisms; four “from” mechanisms


Heat Flow to/from Human Body

Sensible Heat– Flows via conduction, radiation, and convection– Flow rate is generally related to space temperatures

Latent Heat– Flows via evaporation– Flow rate is generally related to space humidity

Total Heat Flow = sensible + latent flows


Heat Flow to/from Human Body

Conduction (sensible)

Convection (sensible)

Radiation (sensible)

Evaporation/Condensation (latent)


Conduction

The flow of heat between two adjacent and touching solids (or from one part to another part within an object) by direct interaction between molecules

example: walking on a beach in your bare feet

for comfort, the key environmental variable is: SURFACE TEMPERATURE


Convection

The flow of heat from the surface of a material to/from a surrounding fluid (usually air); the free motion of molecules of the fluid is very important in promoting heat flow example: fanning yourself with a newspaper

for comfort, the key environmental variables are: AIR TEMPERATURE | AIR SPEED


Radiation

The flow of heat between objects that are not in direct contact—but that can “see” each other via electromagnetic radiation; the objects may be a few inches or a million miles apartexample: warming yourself in front of a fireplace

for comfort, the key environmental variable is: SURFACE TEMPERATURE


Evaporation The flow of heat that must be provided as

a material changes state (from a liquid to a gas); this heat represents the energy required to break molecular bonds (called the latent heat of vaporization)

example: feeling cool coming out of a swimming pool on a breezy day

for comfort, the key environmental variables are: RELATIVE HUMIDITY | AIR SPEED


The Mechanisms Adapt

the body automatically adapts to surrounding environmental conditions in its quest for thermal equilibrium; under high temperatures, evaporation becomes critically important


Environmental Comfort Factors

• Air temperature (dry bulb – deg F)• Relative humidity (%)• Air speed (ft per min)• Radiant conditions

– Mean radiant temperature [MRT] in deg F – or other radiation value in Btuh per sf

These factors are controllable through design – a passive system should control all four factors; an active (HVAC) system is expected tocontrol the first three (with “architecture” controlling the fourth)


Measuring Environmental Factors

data logging

air temperature,

RH, wind speed

air speed

surfacetemperature

wet and dry bulb temperatures


MRT

MRT stands for mean radiant temperature

MRT is the (hypothetical) uniform temperature of surrounding surfaces with

which the human body would exchange the same heat by radiation as occurs in an

actual (non-uniform) environment


MRT

Surface temperatures in a typical room are often not all the same (for example, cold

window glass, warm radiators); the human body will radiate to/from these different surfaces. MRT is the temperature (if all

surfaces were at this one temperature) at which the body would exchange the same heat by radiation as occurs in the messy,

many-temperature real space.


Estimating MRT

MRT = (angle 1)(temp 1) + (angle 2)(temp 2) + ….

360 deg

repeat for two additional space views … and then average

11

2

2


Personal Factors Affecting Comfort

• Physical– Clothing (specifically its insulation value in “clo”)– Activity level (specifically metabolic heat

production in “met”)

• Mental– State of mind (experiences, expectations,

influences of other conditions, …)

These factors are not controlled through design, but must be understood by a designer as they will affect occupant thermal comfort responses


Typical clo Values

http://www.homeenergy.org/


Typical met Values

http://www.homeenergy.org/


Physical Basis of Thermal Comfort

The potential for thermal equilibrium is:– Influenced by environmental factors

• Often common to all occupants in a space• Designer must control these conditions

– Influenced by personal physical factors• Individual to each occupant in a space • Designer must be aware of and consider these

conditions


The Designer’s Job

Understand the physical basis of thermal comfort and related variables

Appreciate the influence of the psychological aspects of thermal comfort

Use this understanding and appreciation to design spaces that building users will decide are thermally comfortable


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ball state architecture | environmental systems 1 | grondzik 1 thermal comfort

Documents

environmental forces

gross environmental

wikipedia slide

ultimate task of architecture

human occupancy slide

condition of mind

conditions physical

perception condition