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Heat Loss

Heat Loss. HVAC CNST 305 Environmental Systems 1 Dr. Berryman. roof. Infiltration and Ventilation. glass conduction. exterior wall. floor. Heating Load Components. partition wall. Design Temperatures. Inside Outside. 0.4%. 2%. 1%. 99.6%. 99%. DB WB. DB WB. DB WB. DB. DB.

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Heat Loss

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  1. Heat Loss HVAC CNST 305 Environmental Systems 1 Dr. Berryman

  2. roof Infiltration and Ventilation glass conduction exterior wall floor Heating Load Components partition wall

  3. Design Temperatures • Inside • Outside

  4. 0.4% 2% 1% 99.6% 99% DBWB DBWB DBWB DB DB St. Louis, Missouri 95°F [35°C] 76°F [25°C] 93°F [34°C] 75°F [24°C] 90°F [32°C] 74°F [23°C] St. Louis, Missouri 2°F [-16.7°C] 8°F [-13.4°C] Design Weather Data 1997 ASHRAE Handbook–Fundamentals, Chapter 26 Winter Summer

  5. Conduction Heat Losses BH = U  A T

  6. Rates of Heat Transfer

  7. Air Spaces

  8. AL siding (hollow back) outdoor-air film R13 insulation board 8” LW concrete block ½”gypsum board indoor-air film Determining Rates Table 2-2 (Toa) Table 2-3 Table 2-4 thermal resistance (R)

  9. Heat Loss Calculation • Using wall section: • Winter Design: 10oF DB • Indoor Design: 75oF • 100’ long; 10’ high • Determine Heat Loss EXAMPLE

  10. Winter Design = -8oF w/ 6612 degree days* 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

  11. Floors – Slab on Grade Mild Cold Climatic Conditions

  12. 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

  13. Pier & Beam (crawl space) • Same as wall/roof • Use Design OA temperatures • Calculate R-values through floor Use OA Design Temperature

  14. BTUH Total Other Heat Losses • Wall • Roof • Floor • Windows • Doors • Infiltration • Ventilation Size Furnace

  15. Sample Heat Load Form

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

  17. Next Time • Heat Transmission • Condensation • Vapor Barriers

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