Heating and Air Conditioning I

1
Heating and Air Conditioning I

• Principles of Heating, Ventilating and Air
  Conditioning
• R.H. Howell, H.J. Sauer, and W.J. Coad
• ASHRAE, 2005

basic textbook/reference material For ME 421 John
P. Renie Adjunct Professor Spring 2009
2
Chapter 7 Nonresidential Load Calculation

• Principles.
• Primary basis for design and selection of heating
  and air-conditioning systems and components
• First costs
• Comfort and productivity of occupants
• Operation and energy conservation
• This chapter discusses the common elements of
  load calculations and several methods of making
  load estimates focuses on the ASHRAE Radiant
  Time Series (RTS) method
• Cooling Loads Conductive, convective and
  radiative
• External walls, roofs, windows, ceilings, etc.
• Internal people, lights, appliances, equipment
• Infiltration air leakage and moisture migration
• System ventilation, duct leakage, reheat, fans,
  pump power
• Variables affecting cooling loads interrelated
  and vary over 24 hour period not always in
  phase zone dependent

3
Chapter 7 Nonresidential Load Calculation

• Principles.
• Heat flow rates for air conditioning design
• Space heat gain rate heat enters into or is
  generated within a space at a given instant
• Classified by mode in which it enters
• Solar radiation through transparent surfaces
• Heat conduction through walls and roofs
• Heat conduction through interior partitions,
  ceilings and floors
• Heat generated by occupants, lights or appliances
• Energy due to ventilation and infiltration or
  outside air
• Miscellaneous heat gains
• Classified by whether it is sensible or latent
• Sensible is directly added by conduction,
  convection, or radiation
• Latent occurs when moisture is added to space (by
  occupants or equipment) must be removed by
  condensation on cooling apparatus - coils

4
Chapter 7 Nonresidential Load Calculation

• Principles.
• Heat flow rates for air conditioning design
• Space cooling load rate at which heat must be
  removed from the space to maintain a constant
  space air temperature this doesnt necessarily
  equal the sum of space heat gains above at given
  time.
• Radiant heat gains is not immediately converted
  into cooling load first must be absorbed by the
  surfaces and objects in the space then once
  they become warmer than air temperature, heat is
  transferred due to convection
• This thermal storage effect is critically
  important in differentiating between instanteous
  heat gain for a given space and its cooling load
  for that moment.
• Space heat extraction rate the rate at which
  heat is removed from the conditioned space equals
  the space cooling load only to the degree that
  room air temperature is held constant.
• Intermittent operation of cooling system and
  minor cyclic variation or swing in room
  temperature

5
Chapter 7 Nonresidential Load Calculation

• Principles.
• Heat flow rates for air conditioning design
• Cooling coil load rate at which energy is
  removed at the cooling coil that serves one or
  more conditioned spaces equals the sum of the
  instantaneous space cooling loads (or space heat
  extraction rate if is assumed that the space
  temperature does not vary) for all the spaces
  served by the coil, plus any external loads.
• External loads include heat gain by the
  distribution system between individual spaces and
  the cooling equipment, the outdoor air heat and
  moisture introduced into the distribution system
  through the cooling equipment.
• Cooling Load Estimation in Practice
• Usually the cooling load is needed to be known
  before all parameters can be completely defined
• Heat balance fundamentals
• Engineering judgment
• Space requirements, partitions, lighting, etc.

6
Chapter 7 Nonresidential Load Calculation
7
Chapter 7 Nonresidential Load Calculation

• Principles.
• Heat balance fundamentals
• The calculation of cooling load for a space
  involves calculating a surface-by-surface
  conductive, convective, and radiative heat
  balance for each room and a convective heat
  balance for the room air.
• Requires a laborious solution of energy balance
  equations involving the space air, surrounding
  walls and windows, infiltration and ventilation
  air, and internal energy sources.
• Consider a case of a four wall, ceiling, floor
  with infilitration air and internal energy
  sources.
• The energy exchange at each surface at a given
  time can be calculated from the following
  equation.

8
Chapter 7 Nonresidential Load Calculation

• Principles.
• Heat balance fundamentals - continued

9
Chapter 7 Nonresidential Load Calculation

• Principles.
• Heat balance fundamentals - continued

10
Chapter 7 Nonresidential Load Calculation

• Principles.
• Conduction Transfer Function solved
  simultaneously with (7-1)

11
Chapter 7 Nonresidential Load Calculation

• Principles.
• Space Air Energy Balance also simultaneously

12
Chapter 7 Nonresidential Load Calculation

• Principles.
• Total Equivalent Temperature Difference Method
  (TETD)
• Series of representative wall and roof assemblies
  used to calculated TETD values as a function of
  sol-air temperature and room temperature
• See text for methodology
• Transfer Function Method
• Use of CTF followed by room transfer function
  (RTF)
• Heat Balance Method (HB)
• Exact solution computer essential
• Use of simplifying models, thus approximate
• Well-mixed model
• Uniform surface temperatures
• Diffuse radiating surfaces
• Uniform long wave (LW) and shortwave (SW)
  irradiation
• Radiant Time Series Method (RTS)
• New simplified method rigorous but not
  iterative, transparent for peak load
  calculation only

13
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations.
• Building characterizations
• Configuration
• Outdoor design conditions
• Indoor design conditions
• Internal heat gains and operating schedules
• Areas
• Gross surface area
• Fenestration area
• Net surface area
• Additional considerations

14
Chapter 7 Nonresidential Load Calculation

• Heat Gain Calculation Concepts
• Primary weather-related variable influencing a
  buildings cooling load is solar radiation
• Heat gain through exterior walls and roofs
• Sol-Air temperature the temperature of the
  outdoor air that, in the absence of all radiation
  changes, gives the same rate of heat entry into
  the surface as would the combination of incident
  solar radiation, radiant energy exchange with the
  sky and other outdoor surroundings, and
  convective heat exchange with outdoor air.
• Heat gain through exterior surfaces

15
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations.
• Heat gain through exterior walls and roofs -
  continued

16
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations.
• Heat gain through exterior walls and roofs
  Sol-Air Temperatures

17
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations.
• Sol-air temperatures any other air temperature
  cycle can be determined from Table 7-1
• Average Sol-Air Temperature

18
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations.
• Hurly air temperature Table 7-1 is based on a
  design temperature of 95 F and 21 range. For
  something different, take the percent of range
  and subtract it from the design temperature.
• Say design temperature is 88 F and range is 19.9
  (FW)
• At 800 pm, 88 (0.47)19.9 78.6 F

19
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations.
• Heat Gain Through Fenestration

20
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations.
• Heat Gain Through Fenestration

21
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations.
• Total instantaneous rate of heat gain HB model

22
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations.
• Fenestration heat gain

23
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations.
• where

24
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations Table 7-3 Solar
  Heat Gain

25
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations Table 7-3 Solar
  Heat Gain

26
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations Table 7-3 Solar
  Heat Gain

27
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations Table 7-3 Solar
  Heat Gain

28
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations Table 7-4 Glazing
  and Windows

29
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations Tables
• Table 7-5 Solar Heat Gain Coefficients for
  Domed Horizontal Skylights
• Table 7-6 Solar Heat Gain Coefficients and
  U-Factors for Standard Hollow Glass Block Wall
  Panels
• Table 7-7 Unshaded Fractions (Fu) and exterior
  Solar Attenuation Coefficients (EAC) for Louvered
  Sun Screens
• Table 7-8 Interior Solar Attenuation
  Coefficients (IAC) for Single or Double Glazing
  Shaded by Interior Venetian Blinds or Roller
  Shades
• Table 7-9 Between Glass Solar Attenuation
  Coefficients (BAC) for Doubling Glazing with
  Between-Glass Shading
• Table 7-10 Properties of Representative Indoor
  Shading Devices Shown in Table 7-8 and 7-9
• Table 7-11 Interior Solar Attenuation
  Coefficients for Single and Insulating Glass with
  Draperies

30
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations
• Effect of horizontal projection to provide for
  shading and considerable reduction in solar gain.
• Applicable to south, southeast, and southwest
  exposures in late spring, summer, and early fall.
  East and west all year and south in winter the
  lengths would be to large.
• Geometry

31
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations

32
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations gain into a
  window

33
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations gain into a
  window

34
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations gain into a
  window

35
Chapter 7 Nonresidential Load Calculation

• Initial Design Considerations gain into a
  window

36
Chapter 7 Nonresidential Load Calculation

• Solar Angles

37
Chapter 7 Nonresidential Load Calculation

• Solar Angles
• Determine the Earth-Sun line at given time, data,
  position
• The angles QV and QH are measure of this E-S line
  from the local vertical and a line normal to the
  vertical surface
• Dropping a projection from the E-S line to the
  horizontal ground plane, forming a right angle
• The angle b, the solar altitude, is the angle
  between the E-S line and this ground projection
• The angle f, the solar azimuth, is the angle from
  the base leg of the E-S projection to the south
  direction.
• The angle g is the angle between the base leg of
  the E-S projection and the perpendicular to the
  surface wall solar azimuth
• The angle y are the angle between south direction
  and the perpendicular to the surface
• The profile angle W is determined from g and b
  tabulated in Table 7-13

38
Chapter 7 Nonresidential Load Calculation

• Table 7-13 Solar Position and Profile Angles for
  40 deg N Lat.