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

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Heat Loss HVAC CNST 305 Environmental Systems 1 Dr. Berryman

Heating Load Componentsroofexteriorwall glassconduction floor Infiltration and Ventilation partitionwall

Design Temperatures Inside Outside

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

Conduction Heat Losses BH = U  A  T

Rates of Heat Transfer

Air Spaces

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

Heat Loss Calculation EXAMPLE Using wall section: Winter Design: 10 o F DB Indoor Design: 75 o F 100’ long; 10’ high Determine Heat Loss

Degree Day Heating load is proportional to the temperature difference between 65 o F and the average daily winter outdoor temperature. Example: Omaha, NE 65 o F - -8 o F = 73 degree days Winter Design = -8 o F w/ 6612 degree days* *From ASHRAE Handbook of Fundamentals 6612/73 = 90.6 heating days 90.6 x 24hrs = 2174 heating hours/year

Floors – Slab on Grade MildCold Climatic Conditions

Basements Heated basements: Unheated basements Use 50 o F for OA design temperature Calculate R-values through floor Note: Any exposed wall above grade has to be calculated a different wall section

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

Other Heat Losses Wall Roof Floor Windows Doors Infiltration Ventilation BTUH Total