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HVAC

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HVAC HEATING COOLING VENTILATION Human Comfort Zone As humans we try to maintain a body temperature of 98.6 F Three Mechanisms Heat generated within the body Heat ... – PowerPoint PPT presentation

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Title: HVAC


1
HVAC
  • HEATING
  • COOLING
  • VENTILATION

2
Human Comfort Zone
  • As humans we try to maintain a body
  • temperature of 98.6 F
  • Three Mechanisms
  • Heat generated within the body
  • Heat gained from surroundings
  • Heat lost to surroundings

3
Human Comfort Zone
  • We shiver to
  • generate heat

4
Human Comfort Zone
  • We sweat to
  • Give off heat

5
Human Comfort Zone
  • We get goose bumps

6
Human Comfort Zone
  • Blood Flow
  • Decreases to hands and feet in winter
  • Increase in summer to encourage heat loss

7
Thermal Neutrality
  • To be comfortable humans must loose heat at the
    same rate as it is produced or gained.

8
Factors Affecting Human Comfort
  • Air temperature
  • Air Speed
  • Humidity
  • Mean radiant temperature
  • Each has a direct influence on heat loss or gain
    to the human body

9
Factors Affecting Human Comfort
  • Air Temperature - This affects temperature
    differences between the body and the
    surroundings, consequently affecting the rate of
    heat loss or gain by convection.

10
Factors Affecting Human Comfort
  • Air Speed - This affects the rate at which
  • the body loses heat by convection.
  • An air temperature of 35F and a wind speed of 20
    miles/hour combine to give a wind chill
    temperature of 11.2F.
  • Air speed is also very important during summer
    when the body is trying to lose heat to maintain
    comfort.

11
Factors Affecting Human Comfort
  • Humidity - Affects the rate at which the
  • body loses heat by evaporation. During hot
  • weather, high humidity increases discomfort
  • by making it more difficult to evaporate
  • perspiration into the air.

12
Mean Radiant Temperature
  • Mean Radiant Temperature' (MRT). This is defined
    as the temperature of a sphere at the point in
    question which would exchange no net radiation
    with the environment.

13
Factors Affecting Human Comfort
  • Mean Radiant Temperature (MRT) - MRT is the
    average surface temperature of the surroundings
    with which the body can exchange heat by radiant
    transfer.
  • Radiant heat transfer to and from the body is
    quite apparent when sitting near a fireplace
    (high MRT) or large cold window area (low MRT).

14
Mean Radiant Temperature
  • In general for every 1 degree F that the MRT
    drops, the air temperature must be raised about
    1.4 degrees F to achieve comfort conditions. 
  • How can you raise the MRT?
  • Close blinds and curtains
  • Solar Film on windows
  • Seal heat leaks

15
Comfort
  • Comfort is achieved by either increasing the
    ambient temperature or by raising the mean
    radiant temperature of an environment.
  • A higher radiant temperature means that people
    become comfortable with a lower ambient
    temperature and the reverse is also true.

16
Bioclimate Chart
17
Example 1
  • Dry Bulb 73
  • Relative Humidity 50

18
In the zone
19
Example 2
  • Dry Bulb Temp. 78
  • Relative Humidity 70

20
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21
Example 2
  • Dry Bulb Temp. 78
  • Relative Humidity 70
  • Requires a wind speed of 250 FPM
  • (25060)/5280
  • MPH 2.84

22
Example 3
  • Dry Bulb Temp. 50F
  • Relative Humidity 55

23
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24
Example 3
  • Dry Bulb Temp. 50F
  • Relative Humidity 55
  • BTU/Hour 250

25
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26
Definitions
  • Conduction
  • A method by which heat is transferred from a
    warmer substance to a cooler substance by
    molecular collisions. Direct contact.
  • Convection
  • A method by which heat is transferred by
    currents in a liquid or gas.
  • Radiation
  • A method by which heat can be transferred
    through objects and empty space. Electromagnetic.

27
Conduction Examples
  • Liquid - Liquid - Pouring cold cream into coffee
  • Liquid - Gas - Ocean and Atmosphere
  • Gas - Gas Cold and warm weather systems mixing
  • Solid - Solid Touch a hot pot on a stove

28
Conduction Rate Factors
  • Contact Area
  • Type of Material Cast Iron vs Stainless Steel
  • Temperature Difference
  • Distance heat must travel

29
Convection Examples
  • In a closed room cool air will settle to the
    bottom while warm air will rise
  • Bowl of soup Hot liquid in the center moves to
    the cooler outside where it drops and is reheated
    at the center and the cycle continues.
  • Warm air rising through a heat register

30
Radiation Examples
  • The suns heat
  • A bonfire
  • Warm soil on a cool night

31
Radiation Rate Factors
  • Surface area
  • Type of material
  • Temperature difference

32
More Radiation Terms
  • Reflectance (or reflectivity) refers to the
    fraction of incoming radiant energy that is
    reflected from the surface. Reflectivity and
    emissivity are related and a low emittance is
    indicative of a highly reflective surface.
  • For example, aluminum with an emittance of 0.03
    has a reflectance of 0.97.

33
More Radiation Terms
  • Emittance (or emissivity), refers to the ability
    of a materials surface to give off radiant
    energy. All materials have emissivities ranging
    from zero to one. The lower the emittance of a
    material, the lower the heat radiated from its
    surface.

34
Emissivity or Emittance
Material Surface Emittance
Asphalt 0.90 - 0.98
Aluminum foil 0.03 0.05
Brick 0.93
Fiberglass 0.80 0.90
Glass 0.95
Steel 0.12
Wood 0.90
35
R-Value
  • R-Value is the measure of resistance to heat flow
    through the defined material. The higher the
    R-Value the less heat will transfer through the
    wall, making the system more energy efficient.
  • U-Value is the reciprocal of the R-Value
  • (1/R) and is a measure of the rate of heat loss

36
WINDOWS - 4 Ways to Evaluate
  • U-FACTOR
  • Solar Heat Gain Coefficient
  • Visible Transmittance
  • Air Leakage

37
U-FACTOR
U-FACTOR The rate of heat loss is indicated in
terms of the U-Factor of a window assembly. The
insulating value is indicated by the R-Value
which is the inverse of the U-Value. The lower
the U-Value the greater a windows resistance to
heat flow and the better the insulating value.
38
Solar Heat Gain COEFFICIENT
The SHGC is the fraction of incident solar
radiation admitted through a window. SHGC is
expressed as a number between 0 and 1. The lower
a windows solar heat gain coefficient, the less
solar heat it transmits.
39
VISIBLE TRANSMITTANCE
The visible transmittance is an optical property
that indicates the amount of visible light
transmitted. Theoretical values vary between 0
and 1, but most values are between 0.3 and 0.8
40
Air Leakage
Heat loss and gain occur by infiltration through
cracks in the window assembly. Air leakage is
expressed in cubic feet of air passing through a
square foot of window area. .3 is recommended
for Oregon
41
Low-E Windows
  • Glass is coated with silver or tin oxide which
    allows visible light to pass through but reflects
    infrared heat radiation back into the room.
  • Reduces heat loss
  • Allows visible light to pass through but reflects
    infrared heat radiation away from the room
  • Reduces heat gain

42
High number for cold climate. Low number for warm
climates
The lower the number the better the insulating
value
The best windows have air leakage rating between
0.1 and 0.6 cfm/ft.
Varies from 0 to 1.0 The higher the the more
light is transmitted.
43
Single-Glazed with Clear Glass
44
Single-Glazed with Bronze or Gray Tinted Glass
45
Double-Glazed with High-Solar-Gain Low-E Glass,
Argon/Krypton Gas
46
Triple-Glazed with Moderate-Solar-Gain Low-E
Glass, Argon/Krypton Gas
47
Ventilation
  • Multi Point Fan Systems
  • One fan located in the attic
  • Connects to baths and kitchen
  • Timed to run at high speed during high use times
    such as morning (showers, bacon ) and evening.
  • Xvent

48
Heat Recovery Ventilation
  • How it works
  • In the heating season the core transfers heat
    from the outgoing, stale household air to preheat
    the incoming, fresh air.
  • Cross-current sections, ensure the two air
    streams are always kept separate preventing the
    incoming fresh air from being contaminated by the
    outgoing stale air.

49
Heat Recovery Ventilation
  • During the air-conditioning season, the HRV
    reverses this process, removing some of the heat
    from the incoming air and transferring it to the
    outgoing air.

50
Heat Recovery Ventilation
51
Ventilation
  • Heat Recovery System - uses fans to maintain a
    low-velocity flow of fresh outdoor air into the
    building (incoming air stream) while exhausting
    out an equal amount of stale indoor air (exhaust
    air stream). Fresh air is supplied to all levels
    of the building while stale air is removed from
    areas with high levels of pollutants and moisture.

52
Ventilation
  • Heat Recovery System
  • Air Exchange - Expels stale, polluted indoor air
    and gaseous pollutants and continually exchanges
    them with a continuous flow of fresh, revitalized
    outdoor air to improve Indoor Air Quality.

53
Ventilation
  • Heat Recovery System
  • Excess Humidity Control - Helps prevent
    uncontrolled excess humidity by expelling excess
    humidity from the air, thereby reducing the risk
    of window condensation, mildew and mold, which
    prevents  structural damage and deterioration to
    your home.  

54
Ventilation
  • Heat Recovery System
  • Heat Recovery Core - As warm air is expelled from
    your house, it warms the incoming cold, fresh air
    before its circulated throughout your home. The
    result is a constant supply of fresh air, no
    unpleasant drafts and greater home comfort.

55
HRV
56
HRV
  • Sized to ventilate the entire house at a minimum
    of .35 air changes per hour.
  • Minimum CFM requirement can be calculated as
    follows
  • Determine square footage and multiply times
    ceiling height.
  • Divide by 60 minutes
  • Multiply times .35 (minimum air changes)

57
HRV Calculation
  • Example
  • Determine square footage and multiply times
    ceiling height.
  • Divide by 60 minutes
  • Multiply times .35 (minimum air changes)

58
HRV
  • Calculate the minimum CFM for a home
  • with 2000SF main level, 1000SF second level
    and 750 SF finished basement
  • Note Main and second level have 9 foot
  • ceilings and basement has 8 foot
  • ceiling.

59
Solution
  • 3000 SF x 9 27000
  • 750 x 8 6000
  • Total 33000
  • 33000/60 550
  • .35 x 550 192.5 CFM

60
HEPA Filter
High Efficiency Particulate Air Filter
61
Energy Recovery Ventilators
62
How are HRVs Installed?
63
How are HRVs Installed?
64
How are HRVs Installed?
65
Radiant Floor Heat
  • Three types
  • Radiant Air Floors
  • Electric Radiant Floors
  • Hot Water (Hydronic)

66
Radiant Floor Heat
  • Types of installation
  • Wet Installations
  • Large thermal mass of a concrete slab floor
  • lightweight concrete over a wooden subfloor
  • Dry Installations
  • Where the installer "sandwiches" the radiant
    floor tubing between two layers of plywood or
    attaches the tubing under the finished floor or
    subfloor.

67
Radiant Floor Heat
  • Air Heated Radiant Floors Not recommended for
    residential applications
  • Electric Radiant Floors -

68
Electric Radiant Heat - Wet Installation
69
Wet Installation
70
Wet Installation
71
Dry Installation
72
Dry Installation
73
Hydronic Radiant Heat
74
Wet Installation
  • PEX piping in Concrete (thick slab)

75
Wet Installation
  • Thin Slab Application Gypcrete over plywd

76
Electric Toe Kick Heat
77
Toe Kick Electric Heat
78
Heat Pump and Furnace
Indoor Cooling Coil
Thermostat
Furnace
Heat Pump
Air Cleaner
79
Heat Pump and Air Handler
Thermostat
Air Handler
Heat Pump
Air Cleaner
80
Air Conditioner and Furnace
Thermostat
Indoor Cooling Coil
Air Cleaner
Air Conditioner
Furnace
81
Air Conditioners and Air Handlers
Thermostat
Air Handler
Air Conditioner
Air Cleaner
82
Cooling
83
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