ARCH 524 Midterm Exam

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ARCH 524 Midterm Exam
2012-02-28 16:23:57
environmental systems architecture

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  1. The solar absorption value of a material refers to the
    percentage of solar radiaiton absorbed
  2. Mass walls
    operate on a cycle of storing and releasing heat, utilize direct solar gain to heat buildings, and examples are a trombe wall and a water wall.
  3. Major benefit of earth sheltering housing is derived from
    insulative capacity of earth.
  4. Infiltration can be calculated by 2 methods. Which is more accurate?
    The Crack Length Method is more accurate than the Air Change Method.
  5. If a wall has a total thermal resistance of R=25.4, what is the U-value of the wall?
    .0393 because R-value = 1/U-value
  6. IAQ
    IAQ = Indoor Air Quality
  7. VOC
    VOC - Volatile organic compound; particles, allergens, and agents of microbial origin
  8. Building Factors and Health
    • 1. Dampness
    • 2. Ventilation
    • 3. Building Materials
    • 4. Indoor Air Chemistry
  9. Designing with Climate
    • 1. Find balance between natural and man made environment.
    • 2. Try to work with, not against the natural environment.
    • 3. Need to be aware of and understand the site’s environmental conditions.
    • 4. Study the environment first, design second.
  10. Microclimate
    a climate within a climate; in cities, cloudiness, relative humidity, contaminants, temperature, etc.
  11. Embodied energy of materials
    an indicator of how much energy must be invested to mine/harvest/produce, fabricate, and transport a unit of building material
  12. Thermal Comfort
    condition of mind which expresses satisfaction with the thermal environment; influenced by temperature, humidity, air speed, materials of the building, number of windows, etc and is both psychological and physiological interaction
  13. Heat Balance
    body wants to reach equilibrium with environment
  14. M = E +/- R +/- C +/-S
    • Bodies ability to retain/gain heat to achieve equilibrium with the environment
    • M - metabolic rate
    • E - rate of heat loss by respiration, evaporation, elimination
    • R - radiation rate
    • C - conduction and convection rate
    • S - body heat storage rate
  15. Dry bulb and wet bulb temperatures
    • Dry bulb temperature - temperature measured by an ordinary thermometer
    • Wet bulb temperature - takes humidity into account
  16. 6 Primary Factors Affecting Thermal Comfort
    • 1. Metabolic Rate (met)
    • 2. Clothing insulation (clo)
    • 3. Air temperature
    • 4. Radiant temperature
    • 5. Air Speed
    • 6. Humidity
  17. Mean Radian Temperature (MRT)
    “the uniform temperature of an imaginary surrounding enclosure in which radiant heat transfer from the human body would eqaul the radiant heat transfer in the actual nonuniform enclosure”; affects the rate of radiant heat loss from the body
  18. How many occupants of a building must be satisfied with the thermal dynamics of the space to meet code?
    according to ASHRAE, only 80% of occupants need to be satisfied with thermal comfort
  19. Effective temperature
    experimentally determined index based on combination of dry bulb temperature, humidity, radiant conditions, and air movement
  20. Operative Temperature
    based on dry-bulb temperature and humidity
  21. Adaptive Approach
    if a change occurs such as to produce discomfort, people react in ways which tend to restore their comfort; little impact on performance
  22. heat transfer
    flow of heat-energy transfer between 2 regions due to a difference in temperature (from hot to cold)
  23. Rate of heat transfer is a function of
    • 1. magnitude of temperature difference
    • 2. area perpendicular to heat flow path
    • 3. resistance to heat transfer
  24. British Thermal Unit (BTU)
    a traditional unit of energy equal to 1055 joules
  25. specific heat
    energy required to raise 1 pound of a material 1 degree Fahrenheit
  26. Thermal mass (heat capacity)
    • capacity of a material to store energy
    • or
  27. E=HCᐃT
    Equation for Thermal Mass
    • E = Energy gained/stored (Btu)
    • HC = heat capacity (Btu/lb⃙F)
    • ᐃT = change in temperature (⃙F)
  28. Heat Flow R and U Value Calculation
    • (necessary for calculation of building envelope heat gain/loss)
    • * want a HIGH R value and a LOW U value *
    • K (conductivity) - the rate of heat flow through a homogeneous material, per unit of thickness
    • C (conductance) - rate of heat flow through a homogeneous material of a given thickness
    • R (resistance) - a measure of resistance to the passage of heat
    • R = 1/C (higher the R, more resistance to heat gain)
    • U (overall coefficient of heat transmisison) - the overall rate of heat flow through any combination of materials (including air)
    • U = 1/R
  29. Thermal Gradient
    variance in temperature through a cross-section of a construction assembly; the temperature at any point within a wall, roof, or floor assembly can be predicted if the inside and outside air temperatures and thermal properties of construction are known
  30. Building Heat Balance
    +/- M = I + S +/- T +/- O
    • M = mechanical heating or cooling
    • I = internal gains
    • S = solar heat gains
    • T = transmission of heat through envelope (loss or gain)
    • O = outdoor air load (heat loss or gain)
  31. Thermal Dynamic Laws
    • 1. Conservation of Energy
    • 2. Quality of energy
  32. Infiltration Heat Transfer
    • Q=CFM 1.08 (Ti-To)
    • Q = sensible load
    • CFM = volume of infiltration
    • 1.08 = outdoor air factor
    • Ti-To = indoor air temp - outdoor air temp

    • Air Change Method - if the AHC = 1, the entire volume of air in the room has been replaced by outdoor air in 1 hour; higher the number, higher the leakage
    • Crack Length Method - more precise but requires much more specific information about dimensions and construction details of plan
  33. Energy in Heat
    • Sensible heat - transferred via conduction (must be physically touching); measured with thermometer (DRY BULB ONLY)
    • Latent heat - change of state or phase change of a material (i.e. ice to water); takes both dry bulb temperature and humidity into consideration
    • Radiation - exchange of radiant energy between 2 bodies across open surface
  34. heat sink
    a material acts as a heat sink by absorbing heat and thus cooling a space; releases the heat later to warm the space
  35. Approaches to Cooling
    • 1. Mechanical Cooling
    • 2. Passive Cooling
    • 3. Heat Avoidance
  36. 5 Passive Cooling Strategies
    1. Cooling with ventilation
    • A. Comfort ventilation (ventilate all day/night to increase evaporative cooling)
    • B. Night flush cooling (pre-cool building for next day)
  37. 5 Passive Cooling Strategies
    2. Radiant Cooling
    • A. Direct (roof surface cools by radiation at night)
    • B. Indirect (use of heat-transfer fluid radiates - i.e. water)
  38. 5 Passive Cooling Strategies
    3. Evaporative Cooling
    • A. Direct (water sprayed into air entering)
    • B. Indirect (location of site near water, pool in courtyard, etc)
  39. 5 Passive Cooling Strategies
    4. Earth Cooling
    • A. Direct (earth-sheltered building looses heat directly to earth)
    • B. Indirect (air enters building by way of earth tubes)
  40. 5 Passive Cooling Strategies
    5. Dehumidification with a desiccant cooling
    removal of latent heat (humidity is always more uncomfortable than dry heat)
  41. Rules for Comfort Ventilation in Hot/Humid Climates
    • - maximize air flow
    • - operable windows
    • - lightweight construction
    • - windows open all the time
  42. Rules for Nightflush Cooling
    • - hot/dry climate
    • - window or whole house fans should be used
    • - airflow must be directed over mass
  43. Rules for Radiant cooling
    • - good in clear sky areas with low humidity
    • - mainly one-story buildings
    • - roof painted white UNLESS used for passive heating
    • - whole roof area should be used because effect is small
  44. Rules for Evaporative cooling
    - only dry climates
  45. Rules for earth cooling
    • - direct is best when earth’s temperature is < 60. If much colder, building needs insulation
    • - earth tubes are good in dry climates with cold winters
    • - underground structures have reduced access to natural ventilation (con)
  46. Issues with Dehumidification using a Desiccant
    • - uses chemicals to absorb water vapor
    • - 2 difficulties: 1. when water vapor is absorbed and turned into a liquid, heat is given off 2. once desiccant is saturated, it stops removing humidity
  47. Avoid heat through
    • - surface color (light reflects, dark absorbs)
    • - solar shading
  48. Sun path
    position varies according to latitude, season, and time of day
  49. Solar time
    • determined by position of sun
    • Tlocal = Tsolar + [Longitude – Longituderef) x 4]
  50. best way to passively cool a building
    keep heat from entering building in the first place
  51. Water based Thermal Storage
    water has higher capacity to hold energy than wood/stone
  52. Principles of Airflow
    • 1. Air flows either because of natural convection current, caused by differences in temperature, or because of differences in pressure. Always from high to low pressure.
    • 2. Conservation of air.
    • 3.Air has mass ( and thus momentum) and it will tend to continue in its direction until altered by an obstruction of adjacent airflow.
    • 4. The overall effect of wind at a site is so large that locally deflected airflow will tend to return to the direction and speed.
    • 5. Laminar airflow is smooth with adjacent air moving in similar direction and speed. Slow, gentle alterations of flow direction preserve laminar flow, while abrupt alterations result in turbulent flow.
    • 6.Bernoulii effect - an increase in the velocity of a fluid decreases its static pressure; velocity of air increases with height above ground; Result: air pressure at roof is lower than at ground level resulting in exhaust of air through roof openings
    • 7. Venturi effect - causes an acceleration when laminar airflow is constricted in order to pass through an opening; if constriction is so abrupt to create turbulence, Venturi acceleration is minimized
    • 8. High and low pressure areas - as air hits the windward side of a building, it compresses and creates a positive pressure. At the same time, air is sucked away from the leeward side, thus creating negative pressure.
    • 9. Cross-ventilation requires an outlet as well as an inlet
    • 10. Stack effect - can exhaust air by natural convection (because hot air rises)
  53. Solar chimney
    induce heating of air to draw ventilation through building
  54. Approaches to Heating
    • 1. Mechanical Heating
    • 2. Passive Solar Heating
    • 3. Heat Retention
  55. Passive Heating Strategies
    • 1. Maximize solar radiation
    • A. southern exposure
    • B. thermal storage
    • 2. Avoid winter wind
    • A. heat loss through convection
    • B. infiltration
    • 3. Buffer north exterior wall with less frequently used spaces
    • A. bathrooms, storage, mechanical, etc.
    • 4. Passively warm outdoor air before it enters space
  56. Greenhouse Effect
    collects and traps solar radiation during the day; glass allows short radiation to pass through and change to a long wavelength therefore it becomes traps and can no longer pass through
  57. Thermal mass/color
    massive floors should be medium to dark in color while the finish of non-massive materials should be light
  58. Trombe wall
    uninsulated wall operates by convection while insulated are fan assisted; air between glass and wall is heated, rises, and enters living space; has the ability to reduce building heating load by up to 35%
  59. Water wall
    a wall built with a water surface is more efficient in storing heat than timber, stone, and brick
  60. Exposed surface area
    the greater the exposed surface area, the greater the rate of heat loss/gain
  61. Degree Days (DDs)
    • - there are Heating DDs (HDD) and Cooling DDs (CDD)
    • - refer to average daily temperature below or above a base temperature; each day’s mean temperature is subtracted from base temperature which equals the number of DDs for that day
    • i.e. high: 70 F low 32 F = mean 51
    • 60-51 = 9 HDD60
    • - good for comparing buildings within a climatic region
  62. Importance of IAQ
    • - health and well-being of building occupants
    • - productivity
    • - lawsuits
    • - professional responsibility
    • - 90% of time spent indoors
  63. Sick Building Syndrome (SBS)
    symptoms improve with time away from problem building and recur on return to building; temporary
  64. Building Related Illness (BRI)
    illness brought on by exposure to building air where symptoms of diagnosable illness are identified and can be directly attributed to environmental agents in the air
  65. Possible Sources of IAQ
    • 1. Building materials
    • 2. HVAC
    • 3. Construction/design
    • 4. Landscaping and site planning
    • 5. Indoor equipment
    • 6. People
    • 7. Animals/insects
  66. Strategies to Improve IAQ
    • - sustainable green design
    • - space planning
    • - avoid cross contamination of supply air
    • - maintenance schedule
    • - construction site maintenance
    • - displacement