CLIMATE CONTROL: INTENT/CRITERIA

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1 CLIMATE CONTROL: INTENT/CRITERIA This lecture is a review/restatement of information from ARCH 273. Thermal comfort and indoor air quality (coming up) are critical foundations for HVAC system design. Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 1 Why Climate Control Intent/Criteria? 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 American Building: The Environmental Forces that Shape It and HVAC systems are expensive and they place substantial demands upon the building designer, the building operator, and the environment Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 2 1

2 Ways to Look at Thermal Comfort As a psychological phenomenon As a physical phenomenon Both views must be tempered by statistics: although specific individuals experience these phenomena, designers typically design for groups of unknown individuals using statistical norms (know when your users are not normal ) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 3 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 2 Summer 2011 Grondzik 4 2

3 ASHRAE? Reminder The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ( Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 5 Condition (State) of Mind? Thermal comfort is technically defined as an opinion This opinion will be influenced by the environmental conditions surrounding a person and by his/her interpretation/impression of those conditions both are important to the resulting opinion Physical conditions are both group and individual Interpretation is solely individual Each individual is, in essence, evaluating the fruits of your design efforts (in one defined area of concern) This (actually, any) opinion is best assessed by asking people in-situ (building occupants) this approach is termed a POE (post occupancy evaluation) Only ask people who exist and occupy the environment of interest can be asked so POE can only be an indirect design tool Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 6 3

4 Subjective Evaluation (POE Asking) Traditional 7-point status scale: cold cool slightly cool neutral slightly warm warm hot Alternative action scale: Would you prefer: to be warmer no change to be cooler Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 7 Uses for a state of mind (psychological) approach As an exceptionally simple and quick POE tool In built spaces, to see if they are satisfactory In a lab environment, to see how people respond to a wide range of theoretical conditions As a design tool (indirectly) If enough conditions have been tested, then field/lab results can suggest what s comfortable and what s uncomfortable for the average occupant (assuming average occupants were the lab subjects) Design tools have been developed Such as the ASHRAE comfort chart Or the ASHRAE comfort software Or the Olgyay bioclimatic chart Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 8 4

5 Uses for a Physical Approach Architectural design does not directly control occupant psychological responses, it addresses comfort indirectly through the control of selected physical variables. Thus, spaciousness might be perceived as a result of proper values for length, width, and height coming together in a particular room. The same is true of thermal comfort perceptions. Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 9 Physical Basis of Thermal Comfort Heat in (via metabolism, radiation, conduction, convection) Heat out (via radiation, conduction, convection, evaporation) This will generally lead to minimal thermal stress, thus little thermal awareness, thus a neutral response the condition of thermal delight is an intriguing exception to the idea of thermal bliss via ignorance Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 10 5

6 Heat Flow Mechanisms Conduction is sensible Convection is sensible metabolism Radiation is sensible Evaporation is latent (but consumes sensible) Metabolism is internal Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 11 Conduction The exchange of heat between two adjacent and touching solids (or from one part to another part within an object) by direct interaction between molecules examples: grabbing a hot steering wheel; sitting on a cold bench (where conduction occurs through clothing) the key environmental variable is: SURFACE TEMPERATURE Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 12 6

7 Convection Heat flow from a surface of a material to/from a surrounding fluid (usually air); the ready motion of molecules of the fluid is very important in promoting heat flow examples: using a ceiling fan to improve comfort; wind chill index the key environmental variables are: AIR TEMPERATURE & AIR SPEED Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 13 Radiation The flow of heat via electromagnetic radiation 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 examples: feeling warm in front of a real fireplace; feeling cool next to single glazing in the winter the key environmental variable is: SURFACE TEMPERATURE Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 14 7

8 Evaporation Represents the substantial flow of heat that occurs as water changes state (from a liquid to a gas); this heat represents the energy required to break molecular bonds (and is called the latent heat of vaporization) examples: cooling off by sweating and fanning; blowing on a cup of coffee to cool it the key environmental variables are: RELATIVE HUMIDITY & AIR SPEED Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 15 The Relative Importance of Mechanisms Changes to Respond to Space Conditions Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 16 8

9 Environment-Based Comfort- Influencing Variables Air temperature (dry bulb deg F) Relative humidity (%) Air speed (ft per min) Mean radiant temperature [MRT] deg F (or other radiation value in Btuh per sf) These are controllable through design an active (HVAC) system can be expected to control the first three variables but the fourth is predominantly architectural and cannot be ignored during the envelope design process Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 17 MRT MRT stands for mean radiant temperature MRT is the (hypothetical) uniform temperature of surrounding surfaces with which an occupant would exchange the same heat by radiation as occurs in an actual (non-uniform) environment acts like complex simpler Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 18 9

10 Equipment to Measure Environmental Variables is Readily Available Case Study Anyone? Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 19 Occupant-Based Comfort- Influencing Variables Physical (predictable during design) Clothing (acts as insulation clo ) Activity level (changes metabolic rate met ) Mental (assumable during design) State of mind (experiences, expectations, influences of other conditions, ) These variables are not controlled through design, but must be considered as they will affect design decisions Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 20 10

11 The Designer s (Architect s) Role Understand the physical basis of thermal comfort to ensure that appropriate environmental conditions are provided (and personal variables are accounted for) Understand the influence of the psychological aspects of thermal comfort in order to adapt the physical variables to accommodate the psychological to design thermally comfortable spaces for building users Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 21 Recapping Thermal Comfort Variables (and thus Criteria) Design must control: Air temperature Relative humidity Air speed Radiant conditions Design must consider: Clothing Activity level Mental state Via HVAC system (in ARCH 373 context) Via architectural systems Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 22 11

12 One Source of Thermal Comfort Design Criteria ASHRAE Thermal Comfort Chart (Standard ) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 23 The Chart in ASHRAE Standard 55 is Explicit (under specifically assumed conditions) with respect to: Relative humidity (or humidity ratio) Air temperature * Mean radiant temperature * * via operative temperature = (air temp + MRT) / 2 Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 24 12

13 The Chart in ASHRAE Standard 55 is Explicit with respect to: Clothing (clo value) although it is given for only 2 conditions ( summer and winter ) Other clothing may be of interest how would/does the chart change for other clo values? Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 25 The Chart in ASHRAE Standard 55 is Silent with regard to: Activity level (met value) but the text of Standard 55 indicates this is assumed to be sedentary activity (as in office work) Air speed but the text of Standard 55 indicates this is assumed to be low (as in barely noticeable) Other activities and air speeds may be of interest how would/does the chart change for these? Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 26 13

14 Adjustments & Extensions to the Standard 55 Comfort Chart Reading through the text of Standard 55 can provide insight into adjustments for: Air speeds (other than nominal) Activity levels (other than sedentary) Clothing levels (other than 0.5 and 1.0 clo) And limits on: Radiant asymmetry Changes in conditions over time Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 27 ASHRAE Standard 55 Comfort Software PMV = predicted mean vote (on -3 to +3 scale) PPD = predicted percent dissatisfied Explicitly addresses all physical comfort variables as input Provides a range of output information (including the smiley face) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 28 14

15 The Comfort Zone (and Psych Chart) in Bioclimatic Design Tools: Climate Consultant Exterior conditions are plotted and the comfort zone relates to these exterior conditions (as if one is waiting at a bus stop); as expected the diagram shows that someone who spends a year at a Buffalo bus stop will be cold most of the time (and heating is the thing to focus on) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 29 The Comfort Zone (and Psych Chart) in Bioclimatic Design Tools: Climate Consultant If, however, the comfort zone is adjusted to account for the impact of the building envelope and internal loads (i.e., the balance point is shifted), then a very different picture of what s needed in Buffalo emerges (cooling is much more important). Use tools with care and understanding. Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Summer 2011 Grondzik 30 15