CLIMATE CONTROL: OPR

Transcription

1 CLIMATE CONTROL: OPR A review/restatement of information from ARCH 273. Thermal comfort and indoor air quality (coming up) are critical foundations for active climate control (HVAC system) design. OPR stands for Owner s Project Requirements. Ball State Architecture ENVIRONMENTAL SYSTEMS 2 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 Plus HVAC systems are expensive; they place substantial demands upon the building designer, the building operator, and the environment understanding true owner project requirements allows for a focus on relevant design problems. Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 2 1

2 Two Ways to Look at Thermal Comfort As a psychological phenomenon As a physical phenomenon Both views are informed by statistics: although specific individuals may differentially experience comfort phenomena, designers typically design for groups of unknown individuals using statistical norms (thus, it is really important to know when your building users are not normal ) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 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 Grondzik 4 2

3 What is ASHRAE? The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ( Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 5 A Condition of Mind? Thermal comfort is technically defined as an opinion This opinion will be influenced by (1) the environmental conditions surrounding a person and by (2) 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 results of your design efforts (in one defined area of concern) An opinion regarding thermal comfort is best assessed by asking people in-situ (building occupants) this approach is termed a POE (post occupancy evaluation) Only people who exist and occupy an environment of interest can be asked so POE can only be an indirect design tool (with design always preceding occupancy) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 6 3

4 Subjective Evaluation of Comfort (How to Ask in a POE) Traditional 7-point status scale: Are you: cold cool slightly cool neutral slightly warm warm hot An alternative action scale: Would you prefer: to be warmer no change to be cooler The 7-point scale provides more information than the action scale and is the basis of ASHRAE s thermal comfort zone Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 7 Uses for a State of Mind (Psychological) Approach to Comfort Directly: As an exceptionally simple and direct POE tool In built spaces to see if they are deemed satisfactory In a lab environment to see how people respond to a wide range of potential conditions Indirectly: As a design tool If a variety of thermal conditions have been tested, then field/lab results can suggest what s comfortable and what s uncomfortable for a typical building occupant (assuming typical/normal occupants were the POE subjects) Practically: Design tools have been developed Such as the ASHRAE comfort chart Or the UC-Berkeley comfort software Or the Olgyay (or Climate Consultant) bioclimatic chart Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 8 4

5 Uses for a Physical Approach to Comfort Architectural design does not directly control an occupant s psychological responses. The design process addresses comfort indirectly through the control of selected physical variables. Thus, spaciousness might be perceived by a user not because of brainwashing, but because proper values for length, width, height, and colors come together in a particular room in a particular culture. The same is generally true of thermal comfort perceptions. Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 9 Physical Basis of Thermal Comfort Heat In (via metabolism, radiation, conduction, convection) approximately equals Heat Out (via radiation, conduction, convection, evaporation) Such an equilibrium will generally lead to minimal thermal stress, thus little overt thermal awareness, and thus a neutral thermal response the condition of thermal delight is an intriguing exception to the idea of thermal bliss via ignorance Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 10 5

6 Heat Flow Mechanisms Conduction is sensible Convection is sensible metabolism Radiation is sensible Evaporation is latent (but consumes sensible heat) Metabolism is internal Ball State Architecture ENVIRONMENTAL SYSTEMS 2 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 is mitigated by clothing) the key environmental variables are: SURFACE TEMPERATURES Ball State Architecture ENVIRONMENTAL SYSTEMS 2 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 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 variables are: SURFACE TEMPERATURES Ball State Architecture ENVIRONMENTAL SYSTEMS 2 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 Grondzik 15 Human Heat Flow Mechanisms Adapt to Varying Space Conditions latent sensible Ball State Architecture ENVIRONMENTAL SYSTEMS 2 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 aspects of the built environment are controllable through design. An active climate control (HVAC) system is expected to control the first three variables but the fourth is predominantly architectural and must be addressed during the building envelope design process or be compensated for by the HVAC system. Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 17 More on 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 Grondzik 18 9

10 Equipment to Measure Environmental Variables is Readily Available Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 19 Occupant-Based Comfort-Influencing Variables Physical (predictable during design) Clothing (acts as insulation clo ) Activity level (surrogate for metabolic rate met ) Mental (assumable during design) State of mind (experiences, expectations, influences of other conditions, ) These occupant-based variables are not controlled through the design process, but must be considered by the designer as they will affect occupant heat flow patterns and comfort perceptions. Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 20 10

11 Equipment to Measure Occupant Variables is Not Readily Available neurosky.com/ gbmnews.com/ Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 21 The Architect s Role in Providing for Thermal Comfort Understand the physical basis of thermal comfort to ensure that appropriate environmental conditions are provided through design (appropriately accounting for occupants personal variables) Understand the influence of the psychological aspects of thermal comfort in order to adapt the physical variables to accommodate the project-specific psychological context Understand how specific project expectations (the Owner s Project Requirements OPR) will affect design for thermal comfort Overall: to coordinate design decisions that will result in thermally comfortable spaces for building users Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 22 11

12 Recapping Thermal Comfort Design Variables Design must control: Air temperature Relative humidity Air speed Radiant conditions Design must consider: Clothing Activity level Mental state Via precedent Via climate control system (active or passive) Ideally, via architectural enclosure systems Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 23 One Source of Thermal Comfort Design Criteria ASHRAE Thermal Comfort Chart (Standard ) Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 24 12

13 The Comfort Chart in ASHRAE Standard 55 is: Explicit (under assumed and expressly stated 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 Grondzik 25 The Comfort Chart in ASHRAE Standard 55 is: Explicit with respect to: Clothing (via clo value) although it is given for only 2 conditions ( summer and winter ) Other clothing values may be encountered; raising the question: how would/does the chart change for other clo values? Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 26 13

14 The Comfort Chart in ASHRAE Standard 55 is: Silent with regard to: Activity level (via 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 encountered; how would/does the chart change for these? Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 27 Adjustments and Extensions to the Standard 55 Comfort Chart Reading through the text of Standard 55 can provide insight into recommended 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 thermal conditions over time Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 28 14

15 ASHRAE Standard 55 Comfort Software PMV = predicted mean vote (on 7-point scale ranging from -3 to +3) 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 Grondzik 29 The Comfort Zone (and Psychrometric Chart) in 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 Grondzik 30 15

16 The Comfort Zone in 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 temperature 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 Grondzik 31 Considering the wide range of conditions we experience, thermal comfort occupies some prime psychrometric real estate (which we pay for with energy, carbon, design effort, and design constraints) GET IT RIGHT Ball State Architecture ENVIRONMENTAL SYSTEMS 2 Grondzik 32 16