Heat Loss

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Heat Loss

• HVAC
• CNST 305
• Environmental Systems 1
• Dr. Berryman

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Heating Load Components
partition wall
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Design Temperatures

• Inside
• Comfort
• Outside climate conditions
• Occupancy
• Outside
• Design Temperatures

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Design Weather Data
1997 ASHRAE HandbookFundamentals, Chapter 26
Winter
Summer
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Conduction Heat Losses
BH U ? A ? ?T
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Rates of Heat Transfer

• A materials ability to conduct heat
  ()
• Conductance (C) non homogeneous
• BTU/HR/SF/oF
• Conductivity (k) homogeneous
• BTU/HR/SF/IN/ oF
• A materials ability to resist heat (-)
• Resistance (R)
• Overall heat Transfer Coefficient (U)
• 1/RTotal

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Air Spaces

• Thickness of air space
• Orientation of heat flow
• Reflection plus Absorption Emissivity (h)
• 3x for 1 or better

R 1/h
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Determining Rates
Table 2-2 (Toa) Table 2-3 Table 2-4
thermal resistance (R)
U 1/16.91 0.059 BH/SF/oF
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Heat Loss Calculation

• Using wall section
• Winter Design 10oF DB
• Indoor Design 75oF
• 100 long 10 high
• Determine Heat Loss

EXAMPLE
BH (0.56 BH/SF/oF)(65oF)(1000 SF) 3640 BH
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Degree Day

• Heating load is proportional to the temperature
  difference between 65oF and the average daily
  winter outdoor temperature.
• Example Omaha, NE

65oF - -8oF 73 degree days
6612/73 90.6 heating days
90.6 x 24hrs 2174 heating hours/year
From ASHRAE Handbook of Fundamentals
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Floors Slab on Grade
Mild
Cold
Climatic Conditions
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Basements

• Heated basements
• Unheated basements
• Use 50oF for OA design temperature
• Calculate R-values through floor

Note Any exposed wall above grade has to be
calculated a different wall section
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Pier Beam (crawl space)

• Same as wall/roof
• Use Design OA temperatures
• Calculate R-values through floor

Use OA Design Temperature
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Summary of Heat Losses

• Wall
• Roof
• Floor
• Windows
• Doors
• Infiltration
• Ventilation

Size Furnace
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Sample Heat Load Form
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Assignment

• Wall Section
• Sketch (on graph paper)
• Show in one section roof, wall, floor/foundation
• Provide dimensions, material call-outs
• Determine rates of heat transfer
• R values of materials, spaces, films, etc.
• R Total of each construction (i.e roof, wall,
  floor)
• U value
• Determine indoor/outdoor design temperatures

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Next Time

• Heat Transmission
• Condensation
• Vapor Barriers