James Marston Fitch American Building: The Environmental Forces that Shape It

Transcription

1 THERMAL COMFORT Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 James Marston Fitch American 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 ( ) was an architect and a Preservationist, one of the founders of the Graduate School of Architecture, Planning, and Preservation at Columbia University in wikipedia Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 Removing the Load Must be Considered in Context ambient thermal forces bus shelter OPR hospital OR context is critical: bus shelter versus elementary school versus hospital operating room Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Thermal Comfort Why? Why should we worry about thermal comfort? What? What is thermal comfort? How? How is thermal comfort addressed during design? Who? Who is responsible? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 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 thermal comfort (not literally, but it should) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 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 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 What is Thermal Comfort? That condition of mind which expresses satisfaction with the thermal environment and is assessed by subjective evaluation. ASHRAE Standard Thermal Environmental Conditions for Human Occupancy Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 ASHRAE? Reminder The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ( A key developer and promulgator of building design standards and guidelines. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 Condition of Mind? Thermal comfort is defined as being an opinion (essentially an individual perception) Such an 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 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 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 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 Subjective Evaluation (Asking) 1. The traditional 7-point status scale: cold cool slightly cool neutral slightly warm warm hot 2. An alternative action scale: Would you prefer: to be warmer no change to be cooler Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 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 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 ASHRAE Thermal Comfort Chart (from Standard ) comfort zone(s) addressing operative temperature, relative humidity, and occupant clothing Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Midstream Thoughts Thermal comfort is an important design intent (in my opinion) and can be easily benchmarked via longestablished criteria OPR should be easy 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 concern mainly via owner s project requirements (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) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

8 Conceptual Mapping of Physical & Psychological Comfort Territories humidity? temperature Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Physical Context for Thermal Comfort -- dishealth -- dishealth conditions the body s response see required reading for more details on these responses Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 Physical Basis of Thermal Comfort Fundamentally, thermal comfort involves a heat balance (a thermal equilibrium); where: heat in heat out where heat in is the result of metabolism, radiation, conduction, convection where heat out is via radiation, conduction, convection, evaporation Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Heat Flow to/from the Environment Mechanisms three potential to mechanisms; four from mechanisms Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

10 Heat Flow to/from a 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 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 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 with bare feet for comfort, the key environmental variable is: SURFACE TEMPERATURES Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 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 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Radiation The flow of heat via electromagnetic exchange between objects that are not in direct contact but that can see each other; the objects may be a few inches or a million miles apart example: warming yourself in front of a fireplace for comfort, the key environmental variable is: AVERAGE SURFACE TEMPERATURE Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

12 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 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 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 ft 2 These factors are controllable through design a passive system should control all four factors; an active (HVAC) system is expected to control the first three (with architecture controlling the fourth) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 Heat Flow Mechanisms Conduction (sensible) Convection (sensible) Radiation (sensible) Evaporation (latent) the body has a vested interest in maintaining a consistent core temperature (around 98.6 F), and thus controlling gains and losses (see next slide) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 The Mechanisms Adapt the body automatically adapts to surrounding environmental conditions in its quest for thermal equilibrium; under high temperatures, evaporation becomes critically important Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

14 Measuring Environmental Factors air temperature, RH, wind speed data logging air speed surface temperature wet and dry bulb temperatures Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 More on 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 amount of heat by radiation as occurs in an actual (non-uniform) environment. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14

15 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 in accordance with their respective temperatures. MRT is the single 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-temperatured real space. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 Estimating MRT MRT = (angle 1)(temp 1) + (angle 2)(temp 2) deg repeat for two additional space views and then average t2 t1 1 2 MRT at point = [ MRT plan + MRT tranverse section + MRT longitudinal section ] / 3 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30 15

16 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, etc.) These factors are not controlled through design, but must be understood by a designer as they will affect occupant thermal comfort responses. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 31 Typical clo Values Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 32 16

17 Typical met Values Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 33 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 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 34 17

18 The Architect 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 as an architect, you cannot make someone be thermally comfortable; but you can ensure conditions that will tend to lead to comfort (or vice versa) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 35 Are We Happy? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 36 18