Fundamentals of Heating. Ventilating, and Air-Conditioning

Solar radiation with a clear sky

Solar radiation with a clear sky consists of three parts: • Direct radiation, Gd • Diffuse radiation, Gd • Reflected radiation, Gr Total solar radiation on a horizontal surface, GtH GtH = Gdh + GdH, Gr=0 Total radiation on a tilted surface Gte = G ne + Gde + Gr All the three parts are […]

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Solar angles

• Sun’s position The sun’s position can be determined by two angles: Solar altitude, (3 Solar azimuth from the south, $ Sin (3 = cos L cos 8 cos H + sin L sin 8 cos c[) = (sin (3 sin L — sin 8)/(cos (3 cos L) Where L = local latitude decime’.ion 8 […]

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Solar time

Mreh21 Su "liner StJStiCS Winter solstice June El or 22 December 21 Of 22 Hgo n. 6-1 Hie effect of the earth’s till and rulaunD — ibout the sun. Apparent solar time (Local solar time) is determined by a sundial (The sun’s position in the sky). 15° longitude —» I hour 1° longitude —» 4 […]

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Solar radiation

The earth’s orbit is elliptical. The sun’s surface temperature is approximately 6,000°C (10,000°F). The radiant heat flux outside the atmosphere of the earth is 2200 W/m2. The extraterrestrial radiant flux, E0, is 1418 W/m2 on January 4 1325 W/m2 on July 5 1360 W/m as mean value The solar radiation at sea level is 1370 […]

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Infiltration

Infiltration is from combined effect of buoyancy and wind. Infiltration rate: O Where Q = infiltration rate (L/s) L = effective leakage area (cm2) Cs = stack coefficient (L2 s’2 cm’4 K’1) AT = average indoor-outdoor temperature difference (K) Cw = wind coefficient (L2 s’4 cm’4 K’1 m’2) V = average wind speed measured at […]

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Natural convection

Driving force of natural convection: • pressure difference caused by wind • air density difference due to buoyancy (stack effect) • pressure difference caused by appliance operations (combustion devices, hood, etc.) Ap = Po + Pw — Pir + Aps Where Ap = pressure difference between outdoors and indoors at location (Pa) p0 = static […]

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Forced convection

Forced ventilation is used to remove/add heat in a space to maintain appropriate thermal conditions. Sensible heat exchange: O Where Q s = sensible heating/cooling load(W) V = airflow rate (m3/s) p = air density (kg/m3) Cp = specific heat of air (J/kg K) Ti = indoor air temperature (°C) Ts = supply air temperature […]

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Definition

• Ventilation: intentional and controllable air exchange between indoor and outdoor air • Infiltration: unintentional and uncontrolled air exchange between indoor and outdoor air • Forced ventilation: powered ventilation • Natural ventilation: unpowered ventilation

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Other assemblies

• Below-grade walls Q = U A (Tground " Ti) Where Q = heat flow rate U = U-factor of basement wall (Table 5-8 in the textbook) A = area of basement wall below grade Tground = ground surface temperature T; = inside air temperature Tground — Tavg — Amp Where Tavg = average winter […]

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Walls

U= 5.5 W/m K U= 2.7 W/m2 K U= 1.8 W/m2 K R-l (ft2 °F h/Btu) R-2 R-3 The following conditions are assumed in calculating the design R-values: 1. Equilibrium or steady-state heat transfer, disregarding effects of heat storage 2. Surrounding surfaces at ambient air temperature Example 5.4 Calculate the U-factor of the 38 mm […]

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