Modern Refrigeration and

1
Modern Refrigeration and Air Conditioning
Althouse Turnquist Bracciano
PowerPoint Presentation by Associated
Technical Authors
PublisherThe Goodheart-Willcox Company,
Inc.Tinley Park, Illinois
2
Chapter 27
Air Conditioning SystemsHeating and Cooling Loads
3
Learning Objectives

• Define heat load and identify its sources for
  both heating and cooling of space.
• Determine heat loads through the use of U- or
  R-values, square footage, and design temperature
  charts.
• Follow approved safety procedures.

4
Heat Loads
27.1

• Heat always flows from hot to cold.
• In the winter, enough heat energy (Btus) must be
  introduced into a space to compensate for the
  heat loss to the outside air.
• During summer months, heat transfers from the
  warm outdoors into the conditioned space.
• Heat must be removed from the space to cool it to
  a comfortable level.
• In both conditions, it is necessary to reduce the
  heat transfer rate.
• To reduce heat transfer, a building must be tight.

5
Heat Loads
27.1

• A building that is too tight of can cause sick
  building syndrome.
• Fresh air must continuously be brought into the
  building.
• A buildings heat transfer is determined by its
  design, construction materials, and location.
• The maximum heat load is determined for a period
  of one hour.

6
Heat Loads
27.1

• There are several major heat loads
• Heat transmitted through walls, ceilings, and
  floors (conduction).
• Heat necessary to control the moisture content in
  the air.
• Conditioning the air that enters the building by
  leakage and for ventilation.
• The sun produces heat in buildings directly
  through the windows. It also produces heat by
  heating the exterior surfaces it strikes (a
  cooling load).

7
Heat Loads
27.1

• Energy deviceslight fixtures, electric motors,
  electric or gas stoves, etc.all produce heat.
• People also release a considerable amount of
  heat.
• The heat load is considered sensible (temperature
  change) or latent (moisture).

8
Heating Loads for Heating
27.1.1

• Heat loads for heating include all means by which
  heat will be lost from the building.

9
Heating Loads for Heating
27.1.1

• Major heat losses are from
• Conduction through walls, ceilings, and floors.
• Air leakage out of the building (exfiltration)
  and into the building (infiltration).
• Combustion air leaving the flue from gas or oil
  furnaces or from fireplaces.

10
Heat Loads for Cooling
27.1.2

• Heat gain is the heat added to a space that is
  being cooled.
• Heat gains into the building include
• Heat and air leakage into the building.
• Ventilation air.
• Sun load.
• Heat from appliances, lights, and occupants.
• Heat must be removed to produce the desired
  temperature and humidity levels in the space.

11
Heat Loads for Cooling
27.1.2

• Heat gain in warm weather is produced by
  conduction through
• Walls.
• Ceilings.
• Floors.
• Windows.
• Doors.
• Heat also enters by
• Infiltrated air.
• People and animals in the room.

12
Heat Loads for Cooling
27.1.2

• Miscellaneous sources of heat are
• Electrical devices such as lights and motors.
• Gas-burning devices.
• Steam from showers, etc.
• The sun.

13
Heat Leakage
27.1.2

• Heat leakage is heat conducted through walls,
  ceilings, and floors.
• Total heat leakage is computed as follows
• Determine the area of each surface through which
  heat is leaking.
• Find the U value (heat transfer coefficient) for
  each surface. The U value represents the amount
  of heat that will pass from one side of the wall
  to the other.
• Total heat leakage Heat leakage area X U values
  of the area.

14
Heat Leakage
27.1.2

• Heat leakage can also be computed using the
  thermal resistance (R value) of the structure.
• R value is the reciprocal of conductance (C) or
  the overall heat transfer (U).

15
Heat Leakage
27.1.2

• Thermal conductivity (K) is a measure of how
  quickly heat travels through a material.
• Conductivity is the amount of heat (in Btu) that
  travels through a 1 ft2 area of 1" thick material
  when there is a 1F temperature difference. The
  unit isBtu in/ft2/F/hr

16
Heat Leakage
27.1.2

• The letter C is used to indicate heat transfer
  through a wall made of different substances. X is
  the thickness of a material in inches.
• 1/C X1/K1 X2/K2 X3/K3
• 1
• C ------------------------------
• X1/K1 X2/K2 X3/K3

17
Infiltration
27.1.2

• Air leakage between the inside and outside of the
  building is known as infiltration.
• There is a pressure difference between the inside
  and outside of a building, usually caused by
  wind.
• The force of the wind against a building causes
  air infiltration, which is the result of a
  positive pressure.

18
Infiltration
27.1.2

• The section of the building without the force of
  the wind will cause air exfiltration, which is
  the result of a negative pressure.

19
Infiltration
27.1.2

• During the heating season
• Infiltrated air must be heated.
• Exfiltrated air is considered heat loss.
• During cooling season
• Infiltrated air must be cooled and is considered
  heat gain.
• Exfiltrated air causes a loss in efficiency.
• Infiltration and exfiltration can be minimized by
  sealing a building.
• Caution Care must be taken to provide enough
  fresh air for ventilation and combustion purposes.

20
Infiltration
27.1.2

• Positive pressures within a building prevent
  infiltration.
• Infiltration calculations are based on either
• Total building volume.
• Length and size of all cracks in the building.

21
Infiltration
27.1.2

• A building with a volume of 10,000 ft3 will have
  at least 10,000 ft3 of fresh air infiltration per
  hour.
• If six people occupy a 10,000 ft3 building,
  there is
• 10,000 / 6 or 1667 ft3 per hour for each person,
  or 1667 / 60 27.8 cfm (0.79 M3/min)
• Vapor barriers reduce air changes considerably.

22
Heat Transfer Rate
27.1.2

• Heat transfer rate (Q) is the amount of heat
  conducted through a structure for a given unit of
  time.
• Heat transfer rate is usually expressed in
  Btu/hr.
• To find the total heat transfer rate, multiply
  the heat transfer coefficient (U value) by the
  temperature difference and the area.
• Heat Transfer Rate Heat transfer coefficient X
  area X
  temperature difference
• Q (U X Area) X (T0 Ti)
• Where T0 Outside temperature
• Ti Inside temperature
  

23
U Value for ComputingHeat Leakage
27.1.2

• When calculating heat transfer, the U value
  includes the additional insulation effect of the
  air film.
• An air film exists on each side of the wall
  surface.
• 1
• U _____________________________
• 1/Fi X1/K1 X2/K2 X3/K3 1/F0
• Fi is heat transfer through the inside air film.
• F0 is heat transfer through outside air film.

24
U Value for ComputingHeat Leakage
27.1.2

• U value is a term indicating the amount of heat
  transferred through a structure (wall).
• U Btu/ft2/F/hour
• U values are based on a 15 mph wind on the
  outside wall surface and a 15 fpm (1/6 mph) draft
  on the inside wall surface.

25
U Value for ComputingHeat Leakage
27.1.2

• The U value for most types of construction can be
  obtained from ASHRAE reference books.

26
U Value for ComputingHeat Leakage
27.1.2

• Given the U value, the design temperature
  conditions of 70F (21C) indoors and 0F (18C)
  outdoors, and the area, calculate the heat load
  as follows
• Heat flow area X temperature difference X U
  value
• Total heat transfer (Q) U X total surface X
  temperature difference

27
U Value for ComputingHeat Leakage
27.1.2

• Example
• A structure has 400 ft2 of surface. The
  temperature difference is 70F. the structure has
  a brick veneer wall and no insulation. It has a U
  value of 0.25.
• Solution
• This U value means that 0.25 Btu will transfer
  through each square foot of wall for each one
  degree F temperature difference in one hour.
• Total heat transfer (Q) 400 X (70F 0 F) X
  0.25
• 400 X
  70 X 0.25
• 28,000
  X 0.25
• 7000
  Btu/hr.

28
U Value for ComputingHeat Leakage
27.1.2

• Example
• If total surface area is 1200 ft2 , heat transfer
  can determined as follows
• Q 1200 X (70F 0F) X 0.25
• 1200 X 70 X 0.25
• 84,000 X 0.25
• 21,000 Btu/hr.
• The same method of heat leakage is used when
  using the metric system only the units used are
  changed.

29
U Value for ComputingHeat Leakage
27.1.2

• Typical heat leakage for various materials,
  listed in watts per square foot.

30
U Value for ComputingHeat Leakage
27.1.2

• Common metric system heat transmission units are
  joules/second, kilocalories/hour, and watts.
  These values are used with square meters or
  square centimeter areas.
• Heat transmission using watts per square meter is
  most popular.
• The watt unit is used in both the US conventional
  method and the Sl metric system.
• The watt can easily be converted to heating and
  cooling capacities.

31
U Value for ComputingHeat Leakage
27.1.2

• Multiply Btu/hr/ft2/F by 5.674 to obtain
  W/m2/C.
• To change metric units to US conventional units,
  multiply W/m2/C by 0.1762 to obtain
  Btu/hr/ft2/F.
• Multiply hr ft2/F/Btu by 0.1762 to obtain
  m2/C/W.
• To change metric units to US conventional units,
  multiply m2/C/W by 5.674 to obtain hr
  ft2/F/Btu.

32
R Value for Heat Leakage
27.1.2

• The R value of a material is its thermal
  resistance.

33
R Value for Heat Leakage
27.1.2

• Heat transfer and heat leakage calculations may
  use the R value.
• Thermal resistance (R) is the reciprocal of the
  heat transmission coefficient (U).
• 1
• Thermal Resistance (R) ______________________
• U
  (Heat transfer coefficient)

34
R Value for Heat Leakage
27.1.2

• For a composite wall (a typical building), the
  total R value equals the sum of the individual
  reciprocals of the C values.
• Rtotal 1/C1 1/C2 1/C3 1/C4 1/C5
• or
• Rtotal R1 R2 R3 R4 R5
• Individual R values for a composite wall can be
  totaled. The heat transfer coefficient will equal
  the reciprocal of the total resistance.

35
R Value for Heat Leakage
27.1.2

• R values for common materials.

36
R Value for Heat Leakage
27.1.2

• Example
• R values for a typical brick veneer wall are as
  follows
• 
  R
• Outside air film 0.17
• Face brick veneer 0.39
• Wood siding and building paper 0.86
• Airspace 0.97
• 1/2" plaster (0.09) on gypsum lath (0.32) 0.41
• Inside air film 0.68
• Total R 3.48
• U 1/R 1/3.48 0.287

37
R Value for Heat Leakage
27.1.2

• Since energy conservation has become of great
  concern, it is recommended that homes and
  apartments have thermal insulation.

38
R Value for Heat Leakage
27.1.2

• A comparison of U.S. conventional and metric
  system values follows
• US Conventional
• Specific heat at constant pressure Btu/lb./F
• Internal film coefficient Btu/hr ft2/F
• Total heat flow Btu/hr watts
• R (Total resistance to heat flow) hr ft2/F/Btu
• U (overall heat transfer coefficient) Btu/hr.
  ft2/F K
• Velocity ft./min. m/s

39
R Value for Heat Leakage
27.1.2
Metric Specific heat at constant
pressure kj/kgK Internal film coefficient W/m2K
Total heat flow kcal/hr R (total resistance
to heat flow) m2K/W U (overall heat transfer
coefficient) W/m2 K Velocity m/s
40
Wall Heat Leakage Areas
27.1.2

• In addition to finding the several U and R
  values, the areas of the walls will need to be
  calculated
• Wall heat leakage U X wall area X temp.
  difference
• Measured the outside building dimensions to
  calculate area. (Outside dimensions are
  conservative when compared to inside dimensions)
• To estimate the heat load, measure the entire
  building walls, windows, ceilings, and floors.
• To measure walls, take outside length and width
  and the inside ceiling height.

41
Wall Heat Leakage Areas
27.1.2

• Measure perimeterL W L Wor2L 2W
• The total wall area is obtained by adding these
  values and multiplying by the wall height.

42
Wall Heat Leakage Areas
27.1.2
Example A house is 24' X 32' (outside) and has
an 8' ceiling. The total area will be Perimeter
L W L W 32' 24'
32' 24" 112' Area
perimeter X height 112' X
8' 896 ft2
43
Windows and Doors
27.1.2

• You must also know the area of each window for
  heat leakage calculations.
• Measure the opening in the wall.

44
Windows and Doors
27.1.2

• Window construction may be single-pane,
  double-pane, permanent double-pane or
  triple-pane, and/or have a storm window.

45
Windows and Doors
27.1.2

• Double- and triple-pane windows have two or three
  panes of glass with sealed airspaces between the
  panes providing excellent insulation.
• The sealed airspace is evacuated and filled with
  nitrogen or other dry gas to prevent condensation.

46
Windows and Doors
27.1.2

• Widows are installed in a variety of ways. Some
  possibilities include
• Fixed (picture windows).
• Single- or double-hung (either or both sashes
  move up and down).
• Sliding horizontal.
• Casement (hinged on one side and open out with a
  crank).
• Window frames may be made of wood, metal, or
  vinyl-clad aluminum.

47
Windows and Doors
27.1.2

• Doors are constructed in a variety of designs,
  such as solid wood, wood veneers over foam cores,
  metal shell filled with insulation, and glass
  patio doors.
• When computing the wall heat leakage area, add
  the area of the doors in the outside wall
  dimension to the area of the windows.
• Then, subtract this amount from the total wall
  area.

48
Windows and Doors
27.1.2

• Example
• There are five windows measuring 2' X 4', two
  doors measuring 3' X 7', and one window measuring
  4' X 6'.
• 2 X 4 X 5 8 X 5 40 ft2
• 3 X 7 X 2 21 X 2 42 ft2
• 4 X 6 X 1 24 ft2
• Total opening area 106 ft2
• The total wall area is 896 ft2
• The net area is 896 ft2 106 ft2 790 ft2

49
Windows and Doors
27.1.2

• The two values106 ft2 of window area and 790 ft2
  of wall areawill be used later to find building
  heat load.

50
Ceilings
27.1.2

• Ceilings are generally made by fastening drywall
  to the joist.
• Heat leakage will be considerable if
• The joists do not have a floor over them.
• There is no insulation between the joists.

51
Ceilings
27.1.2

• Using the sample house, the ceiling area is
  calculated as follows
• Ceiling area W X L
• 24' X 32'
• 768 ft2

52
Basement Heat Loss
27.1.2

• Heat loss or gain for basements varies widely.
• This illustration shows the heat loss for a
  basement built five feet into the ground.

53
Basement Heat Loss
27.1.2

• The deeper the basement, the less the heat loss.
• It is usually assumed that a basement is at 60F
  (16C).
• Leakage through a basement floor is usually not
  calculated.
• Buildings built on a concrete slab have different
  heat losses than those with basements.

54
Basement Heat Loss
27.1.2

• Buildings built on concrete slabs have different
  heat losses than those with basements.

55
Basement Heat Loss
27.1.2

• To minimize ice and frost formation around the
  perimeter of a slab floor, rigid urethane is
  used.
• The slab of urethane insulation (A) should be at
  least 2" thick and installed 2' to 4' in the
  ground.

56
Basement Heat Loss
27.1.2

• Heat losses for a slab are usually calculated as
  follows
• Determine the perimeter of building.
• Total length is multiplied by 18 Btu/hr for each
  foot of length at a 0F (18C) design
  temperature.
• Another popular type of foundation is the crawl
  space.
• A space between the floor of the house and the
  ground, the crawl space, allows access to the
  underside of the floor.
• A plastic sheeting vapor barrier should be placed
  on the ground in a crawl space.

57
Basement Heat Loss
27.1.2

• The floor should be insulated.
• The crawl space must have sufficient ventilation
  to minimize moisture problems in the summer.
• During winter, vent dampers are used to prevent
  cold air from entering the crawl space area.

58
Sun Heat Load
27.1.2

• The suns heat energy adds a considerable heat
  load during summer months.
• The suns rays in the northern hemisphere shine
  on
• The east wall in the morning.
• The south wall all day long.
• The west wall in the afternoon.
• Exposed roof sections.

59
Sun Heat Load
27.1.2

• When computing total heat load, heat from the sun
  must be considered. This figure shows how the
  suns rays strike a building over a day.

60
Sun Heat Load
27.1.2

• The Sun releases different amounts of heat to
  surfaces, depending on the part of the world in
  which the building is located.
• The approximate maximum heat gain from the Sun is
  330 Btu per hr per ft2 (97 watts/ft2 1040 W/m2)
  
• This is for black surfaces at right angles to the
  Suns rays near equator.
• At the 42nd parallel (a line going from New York
  City, to Cleveland, and Salt Lake City), the
  maximum heat is about 315 Btu per hr per ft2(92
  watts/ft2 993 W/m2).

61
Sun Heat Load
27.1.2

• Heat gain for windows facing different
  directionsused when sizing air conditioning.

62
Sun Heat Load
27.1.2

• Unless windows are protected by awnings, use a
  temperature of 15F (8C) higher than the outside
  ambient temperatures for correct results.
• Also, add 15F (8C) to the ambient temperature
  to compensate for the suns rays on exposed walls.

63
Heat Lag
27.1.2

• It takes time for the heat to travel through a
  substance that is heated on one side.
• Heat lag is the time needed for heat to travel
  through a substance.
• When the sun heats the outside wall of a
  building, it may take several hours for the heat
  to reach the inner surface of the wall.
• On average, heat lag may take about three to four
  hours.
• The south wall is exposed to the suns rays all
  day long.
• The east and west walls are exposed for short
  periods.

64
Heat Lag
27.1.2

• The south wall is not affected as much as the
  east and west walls since the rays striking it
  come from overhead.

65
Heat Sources in Buildings
27.1.2

• Building heat sources are beneficial during the
  heating season, but add extra heat loads during
  the cooling season.

66
Heat Sources in Buildings
27.1.2

• There are two types of heat sources, sensible and
  latent heat.
• Latent heat loads increase humidity levels.
• During the cooling season, heat released by
  persons must be taken into account.
• A 150 lb. (68 kg) person gives off 74 watts(253
  Btu/hr) when at rest.
• The same person gives off 440 watts (1,500
  Btu/hr) when working.
• About 25 to 40 of this heat is moisture
  evaporation (latent).

67
Window Heat Load Cooling
27.1.2

• Ordinary window glass transfers about three times
  more heat than residential roofs and ceilings.
• To reduce heat conductivity through glass, a
  storm sash is used.
• To reduce solar heat gain through glass, special
  types of glass with high heat-reflecting
  qualities may be used.

68
Window Heat Load Cooling
27.1.2

• Special heat-absorbing glass can reduce solar
  heat gain by as much as 30.
• Double-glazed windows exposed to the suns rays
  reduce solar heat absorption by 15.
• Roof extensions over a window reduce the area
  exposed to the sun.
• Awnings shade windows and can reduce the heat
  load by 55.

69
Humidifier Heat Load
27.1.2

• During heating season, water vapor is added to
  air, which creates a comfortable condition.
• The heat used to produce water vapor comes from
  heated air, furnace heat, or electric heat.
• The amount of heat needed is figured as follows
• The number of volume changes per hour must be
  known. (Generally one change per hour for
  residential.)
• The number of grains added per pound of air to
  obtain required humidity levels must be known.

70
Humidifier Heat Load
27.1.2

• Formula
• Pounds of air per 24 hours X increase in grains
• grains/day
• gr./day/7000 gr./lb. lb. of water/day
• lb. of water/day/8.34 lb/gal. gal./day
• To calculate
• Volume X changes/hr. X (gri gro) gal./day
• _______
  
  
• 
  33,000

71
Humidifier Heat Load
27.1.2

• Example
• A home has a volume of 12,000 ft3. The grains to
  be added per pound of air to change the air from
  35F (2C) at 90 RH to 72F (22C) at 40 are
  20. Find the total gallons of water to be
  evaporated per day.
• Solution
• 12,000 X 1 X 20 240,00 7.3 gal./day
• ____________ _____
• 33,000 33,000

72
Humidifier Heat Load
27.1.2

• The amount of heat needed to evaporate the water
  is found as follows
• Formula
• Volume of house X changes per hour/ 13.5 5 ft3 of
  air/lb.
• X (gr./lb. indoors
  gr./lb. outdoors)
• X 970.3 Btu/lb./7000
  gr./lb. Btu/hr.
• Volume X changes/hr. X (gri gro) Btu/hr.
• _______
• 
  97.75

73
Humidifier Heat Load
27.1.2

• Example
• Using the same numbers as before, the volume is
  12,000 ft3 the grains are 20. Find the required
  heat.
• Solution
• 12,000 X 1 X 20 240,00 2455 Btu/hr.
• ------------------ --------
• 97.75 97.75

74
Air Conditioner Heat Load
27.1.2

• This form can be used to calculate the cooling
  heat load for a room.

75
Air Conditioner Heat Load
27.1.2

• By multiplying the area of floors, walls, and
  window by multipliers, the amount of required
  energy can be determined.
• Multipliers are obtained by multiplying a
  typicalU value by the temperature difference.
• ExampleWindows in the shade have a U value of
  1.25. If the temperature difference is 12F, the
  multiplier is 1512 X 1.25 15

76
Air Conditioner Heat Load
27.1.2

• The following is a way to make a rough estimate
• The chart identifies COP, which is the ratio of
  output divided by input.
• The output is amount of heat absorbed by a
  system.
• The input is the amount of energy put into the
  system.
• On average, a medium-sized room needs 5000 to
  6000 Btu/hr of cooling.

77
Air Conditioner Heat Load
27.1.2

• The average window comfort cooling unit will
  adequately handle the cooling loads as follows
• 06000 Btu/hr 1/2 hp, COP 4.71
• 60009000 Btu/hr 3/4 hp, COP 4.71
• 900011,000 Btu/hr 1 hp, COP 4.32

78
Total Heat Load
27.1.3

• It is best to set up total heat load calculations
  in table form. This table shows the typical heat
  load calculation for a 24' X 32' house.

79
Total Heat Load
27.1.3

• The temperature difference for the ceiling is
  35F (19C).
• Consider that the roof serves as added insulation
  keeping the attic temperature higher than the
  outdoor temperature.
• Attic temperature can be accurately calculated by
  making heat leakage into attic in winter equal
  heat leakage out.
• Ceiling area X (70F attic temp.) X Uc
• Roof area X (attic temp. 0F) X Ur
• Where Uc U value of the ceiling
• Ur U value of the roof

80
Total Heat Load
27.1.3

• Most homes have an 8' (2.4m) ceiling height.
• Many homes may have a 9' (2.7m) or 10' (3.0m)
  ceiling.
• Vaulted ceilings require total wall area be
  calculated by adding dimensions of entire wall
  including the triangular area at the top of the
  walls.
• Each heat leakage value is obtained by means of
  following formula
• Heat leakage area X U value X temperature
  difference

81
Total Heat Load
27.1.3

• Using this chart is a quick method to estimate
  total heat loads. Heat load is based on room
  volume.

82
Total Heat Load
27.1.3

• A duct sizingmethod.

83
Total Heat Load
27.1.3

• Standard sheets are available for calculating
  total heat load. Samples of these worksheets are
  found in Figure 27-27 of the textbook.

84
Total Heat Load
27.1.3

• Heat gain calculations use a temperature
  difference based on the location being
  considered.
• Indoor temperature is usually designed to be 75F
  (24C) at 50 RH.
• If summer design temperature is 100F (38C), the
  temperature difference is 25F (14C).
• This temperature difference is for load
  calculations only.
• In practice, a 15F to 20F (6C to 8C)
  difference is recommended.
• Other sources of heat must always be considered
  (solar gain, electrical appliances, lighting,
  etc.).

85
Design Temperatures
27.2

• Design temperature can be found at a local ASHRAE
  chapter or the local weather bureau.
• Always choose the low side of the outdoor design
  temperature (ODT) for energy efficiency.
• ODT usually varies with latitude and elevation.

86
Design Temperatures
27.2

• ASHRAE charts give three different values for
  each location
• Lowest temperature for residential and
  uninsulated office buildings.
• 99 temperature indicates that outdoor
  temperature is at or above stated temperature 99
  of the time. This number may be used for
  well-constructed and well-insulated buildings
  having a standard amount of windows.
• 97.5 temperature indicates that outdoor
  temperature is at or above stated temperature
  97.5 of the time. This number may be used for
  large buildings having a considerable thermal
  capacity and small window area.

87
Design Temperatures
27.2

• Example Detroit once used 10F (23C) as ODT
  for all buildings.
• Now, 0F (18F) is recommended be used for
  small, uninsulated buildings.
• For well-constructed, insulated buildings with
  standard window area, 4F (2C) (99 factor) is
  used.
• For large buildings with a standard number of
  windows, 8F (4C) (97.5 factor) is used.
• If inside design temperature (IDT) is 72F
  (22C), an ODT of 0F (18C) means a 72F (40C)
  temperature difference (TD).

88
Design Temperatures
27.2

• The 99 ODT (4F 2C means a 68F (38C) TD.
• The 97.5 means a 64F (35C) TD.
• 72 64 X 100 8 X 100 11
• ---------------- ---------
• 72 72
• This represents an 11 savings in equipment size
  on this installation.

89
Degree-Day Method
27.2.1

• The degree-day method is used for determining
• Fuel consumption and heating cost during a
  season.
• Average temperature of each day during the
  season.
• The degree-day method uses a 65F indoor
  temperature as a standard.
• If average temperature outside is 15F, the
  temperature difference is 50F. That day would be
  50 degree-days.

90
Degree-Day Method
27.2.1

• Each degree-day requires a certain heat load to
  keep inside temperature at 65F (18C).
• Knowing the degree-days when a fuel oil tank was
  last filled helps you to accurately calculate the
  amount of fuel left in the tank.
• If degree-days are known for a season, the
  heating cost can be calculated.

91
Insulation and Vapor Barriers
27.3

• Insulation is necessary to reduce heat loss.
• Vapor barriers are added to insulation to reduce
  the amount of moisture transfer through walls.
• Insulation that is hygroscopic (moisture
  absorbing) must be hermetically sealed.
• Moist insulation will lose its insulating value.
• Insulation should
• Have sufficient strength to support itself.
• Not shrink or settle.
• Not deteriorate.
• Be fire resistant.

92
Insulation and Vapor Barriers
27.3

• Bulk insulation can be blown into the space
  between studs of an existing building.

93
Insulation and Vapor Barriers
27.3

• Flexible insulation comes in rolls and is easy to
  install.
• The Mineral Insulation Manufacturers
  Association, Inc. (MMA) recommends certain
  insulation for electrically heated and air
  conditioned homes
• Ceilings R-19 through R-2 8
• Walls R-11 through R-19
• Floors over unheated spaces R-11 through R-19
• R values always depend on location increase if
  the building is above 42nd parallel.

94
Ponded Roof
27.3.1

• Ordinary roofs may be heated by the sun to 100F
  to 150F (38C to 66C), causing ceilings to
  become warm.
• Many flat-roof buildings provide summer comfort
  cooling by using ponded roofs.
• A 2" to 3" (5cm to 8cm) pond of water covers the
  roof surface.
• To be effective, the roof area should be as large
  as the floor area.
• The cooling effect comes from the evaporation of
  water from the roof.

95
Ponded Roof
27.3.1

• Ponded systems are most effective in areas with
• High temperatures
• Low relative humidity.
• Bright sunshine.
• Ponded roofs require a means of maintaining a
  constant water level.
• Drains are used to carry away excess water.
• Wave breakers are used to prevent waves during
  high winds.

96
Ponded Roof
27.3.1

• Ponded roofs may reduce required air conditioning
  capacity by as much as 30.
• Weight of water must be taken into consideration
  when the roof is built.
• A ponded roof must never be added to an existing
  roof unless the roof structure can support the
  extra weight.

97
Building Insulation and Ventilation for Electric
Heating
27.3.2

• The problem with electric heating is
• The need for insulation and ventilation.
• Excess relative humidity.
• Excessive cost.
• Reducing heat loss through walls, floors, and
  ceilings will reduce the electric heating costs.
• Electric heating requires a well-insulated and
  tight structure.

98
Building Insulation and Ventilation for Electric
Heating
27.3.2

• Systems using electric heat may have heating
  elements located in the
• Plenum chamber.
• Duct branches.
• Individual rooms.
• Since there is very little infiltration into
  buildings that use electric heat, high humidity
  levels may be a problem.

99
Building Insulation and Ventilation for Electric
Heating
27.3.2

• Dehumidifying equipment may be needed to lower
  humidity levels.
• In some areas electrical companies provide lower
  price for electricity as an incentive to install
  electric heat.

100
Energy Conservation
27.4

• When reviewing calculations for determining heat
  loads, certain steps should be followed that will
  increase energy savings such as
• Increase R values where possible.
• Use latest design temperatures when calculating
  HVAC system capacity.
• Use proper inside design temperature and relative
  humidity.
• Eliminate heat leakage around doors and windows.
• Use secondary heat sources as much as possible
  (motors, machinery, etc.).
• Use the most efficient construction materials
  (shaded glass, thermopanes, and foam-insulated
  metal doors).

101
Construction Types and Designs
27.5

• A buildings design may affect the
• Type of heating and air conditioning system.
• Air or water distribution network.
• HVAC installation.
• A technician should have an understanding of
  common construction practices.
• A residence can be classified as a
• Single-story ranch.
• Two-story colonial.
• Tri-level or split-level.

102
Construction Types and Designs
27.5

• Each type may be built on a
• Basement.
• Crawl space.
• Cement slab.
• The materials used for construction (brick,
  aluminum, insulation, etc.) will have an effect
  on heating and cooling loads to a building.

103
Construction Types and Designs
27.5

• Technicians should be able to read construction
  prints or floor plans, which are useful when
  sizing and installing HVAC equipment.

104
Roof Design and Construction
27.5.1

• Heat loss through roofs is influenced by
• Construction.
• Ventilation.
• Covering.
• The most common type of roof is a pitched roof
  using a prefabricated truss.

105
Roof Design and Construction
27.5.1

• The slope of a roof is the vertical rise over the
  horizontal run.

106
Roof Design and Construction
27.5.1

• A typical ranch home may have a 4 in 12 roof
  slope.
• The pitch of a roof is the ratio of the vertical
  rise to the span (twice the run).
• The same 4/12 roof has a 4/24 or 1/6 pitch.
• The pitch of the roof will
• Minimize snow weight at the center of the roof.
• Affect energy conservation when taking into
  consideration cathedral ceilings and solar panel
  installations.

107
Roof Design and Construction
27.5.1

• Proper ventilation is also important for roofs.
• Attics are used to vent household air through
  ceiling and exhaust fans.

108
Roof Design and Construction
27.5.1

• Most attic areas are vented by overhangs and
  exhaust through roof or gable vents.

109
Roof Design and Construction
27.5.1

• Roofing shingles are based on surrounding
  climate.
• Dark shingles help absorb heat during winter, but
  this also works against cooling during summer
  months.
• Insulation can be used beneath roof sheathing.
• R values for pitched roofs are higher than those
  for flat roofs.
• Design as well as color of roof must be taken
  into account when selecting a roof.

110
Wall Construction
27.5.2

• This is a typical brick veneer outside wall
  construction.

111
Wall Construction
27.5.2

• During heating season, the wall vapor barrier
  keeps moisture inside the home.
• During the summer, the vapor barrier keeps
  moisture from entering the home.
• The temperature of the wall must not reach the
  dew point temperature of the air or condensation
  will form at the inside vapor barrier.

112
Wall Construction
27.5.2

• The following should be avoided
• Having indoor RH above 21 when the outdoor
  temperature is below 20F (29C).
• Having indoor temperature below 67F (19C) when
  outdoor conditions are higher than 98F (37C)
  and higher than 97 RH.
• Tightly seal vapor barriers when used.
• Vinyl siding and brick are the two most commonly
  used exterior wall coverings today.

113
Commercial Construction
27.5.3

• Small commercial buildings may us the same
  construction material as residential homes.
• Many low-rise shopping centers are made of
  concrete blocks set on a concrete slab.
• Shopping centers usually have flat asphalt roofs.
  
• Water drainage is essential with flat roofs.
• High-rise and large industrial buildings are much
  more complex in construction.
• Always study blueprints before doing any HVAC
  work involving the building structure.

114
Questions

• Heat always flows from ______to ________.

hot
cold

• During summer months, heat transfers from the
  _______________ to the ____________________.

warm outdoors
conditioned space

• ________ must be removed from the space to cool
  it to a comfortable level.

Heat

• Name three heat loads that add heat to a building
  during the cooling season.

1. Heat transmitted through walls, ceilings, and
floors (conduction).2. Heat necessary to control
moisture content in the air.3. Energy
deviceslight fixtures, electric motors, electric
or gas stoves, etc.
115
Questions continued

• Name three major heat losses during the heating
  season.

1. Conduction through walls, ceilings, and
floors.2. Air leakage out of the building
(exfiltration) and into the building
(infiltration).3. Combustion air leaving the
flue from gas or oil furnaces or fireplaces.
heat leakage area

• Total heat leakage ___________________ X
  ________________.

area U values
116
Questions continued
conductance (C)

• The R value is the reciprocal of
  ________________ or the overall
  ___________________.

heat transfer (U value)

• Thermal conductivity (K) is a measure of how
  quickly heat travels through a _______________ of
  material that is _________ thick when the
  temperature difference is ____º F, or
  ________________.

one square foot
one inch
1
Btu in./ft2/ºF/hr

• Air leakage from the outside of the building to
  the inside is known as ___________.

infiltration
117
Questions continued
Fi

• The ________ is heat transfer through the inside
  air film.

FO

• The ________ is heat transfer through outside air
  film.

• What is the calculation for the U value?

U Btu/ft2/ºF/hour

• The FO U value is based on wind speeds of
  ___________.

15 mph
118
Questions continued
R value

• The __________ of a material is its thermal
  resistance.

• The R value is the reciprocal of the _________.

U value

• Which side(s) of a house do the suns rays shine
  on in the northern hemisphere?

The east wall in the morning. The south wall all
day long. The west wall in the afternoon.

• What is the definition of a heat lag?

Heat lag is the time needed for heat to travel
through a substance.
119
Questions continued

• Name two types of heat sources added to a
  building that must be removed during the summer
  months.

Sensible and latent.

• Awnings and shaded glass windows can reduce the
  heat load by _______

55

• What is used for determining fuel consumption and
  heating cost during a season?

The degree-day method.
120
Questions continued

• When using the degree-day method with a 65ºF
  (18ºC) indoor temperature as a standard and an
  average outside temperature of 15ºF (9ºC), the
  degree-day temperature would be _____________.

50ºF (27ºC)

• What is the purpose of the vapor barrier that is
  added to insulation?

It is used to reduce the amount of moisture
transfer through walls.

• Name three disadvantages of using an electric
  heating system.

The need for insulation and ventilation
increases. Excess relative humidity. Excessive
cost.
121
Questions continued

• Name three ways to increase R values in a
  building.

1. Use the proper inside design temperature and
relative humidity. 2. Eliminate heat leakage
around doors and windows. 3. Use the most
efficient construction materials (shaded glass,
thermopanes, and foam-insulated metal doors).

• Which roof has a higher R value a pitched roof
  or a flat roof?

A pitched roof.
122
Safety
27.6

• For safety, a heating system must have enough
  capacity to heat a structure without becoming
  taxed or overheated. The heating system should be
  slightly oversized, not undersized.
• All designs of heating and cooling systems should
  be checked carefully. Be sure that enough fresh
  air enters the structure. It must provide
  adequate ventilation for the maximum number of
  occupants. It must also provide for adequate
  combustion air during the heating season.

123
Safety
27.6

• In some well-insulated homes, it may be necessary
  to open a basement window or provide some other
  air inlet. This enables the furnace and fireplace
  flues to draw properly smoke and carbon monoxide
  will not be released into the building.

124
Glossary

• COP
• The ratio of output divided by input.
• heat leakage
• Flow of heat through a substance.
• heat load
• Amount of heat removed during a period of
  twenty-four hours.
• heat transfer rate
• The amount of heat transfer through a given
  material per unit of time.
• infiltration
• Passage of outside air into building thorough
  doors, cracks, windows, and other openings.

125
Glossary

• joules
• Metric unit of heat.
• kilocalories
• Great calorie (1000 calories) used in engineering
  science.
• R value
• The thermal resistance of a given material.
• thermal conductivity
• The ability of a material to transfer heat.
• watt
• Unit of electrical power.