Document v6DZX6rjEzZqV8jVpkBgjvjaR

HEATING VENTILATINC AIR CONDITIONING CUIDE 1941 Design Cooling and Dekumidifying Load. . Sensible Heat gain through walls, etc________________ __ 128,350 Heat gain from occupants (200); 44,000 Heat emission from appliances_____ _________ __ 2,000 Heat gain from lights (4 kw):--. 13,650 Heat gain from solar radiation.......................... .....12,000 Latent 36,000 Totals.:._________________________ 200,000 Outside air: 2000 X 0.075 X 60 X 0.24 X (95 - 80) = 2000 X 0.075 X 60 X (96 - 77.2) X 1060 7000 Heat gain through ducts 22,200 32,350 36,000 Btu per hour 25,600 Totala_______________________ .254,550 Total Cooling Load Tons Cooling Effect -- 316,150 Btu per hour = . 26.4 61,600 Btu per hour Ratio S.H. to T.H. - = 0.85 (Room) Design Distribution System far Heating a. Total heat loss in space Assume grille temperature , 200,000 y 60 X 0.075 X 0.24 X (90 - 72) 254,550 = 0.805 (Con- 316,150 ditioner) 200,000 Btu per hour < 90 F 10,300 cfm b. Total heat loss in ducts between unit and grilles 33,200 *f 60 X 0.075 X 0.24 X 10,300 c. 90 F plus 3 F * Design Distribution System for Cooling a. Total sensible heat gain in space Assume grille temperature n200,000________________________________ __________ . v 60 X 0.075 X 0.24 X (80 - 62) = am 33,200 Btu per hour 3F 93 F temperature leaving coil 200,000 Btu per hour 62 F 770 lb per minute b. Latent heat gain in space = 36,000 Btu per hour 600 X 7000 1060 3970 -5- 770 = 5.2 gr per pound air supplied Room condition = 80 F DB, 50% RH, 60 F DP Gain iii conditioned space Specific humidity leaving conditioner Grille temperature = 62 F DB and 58 F DP ,c. Duct gain 22,200 60 X 0.075 X 0.24 X 10,300 Leaving coil = 60 F DB, 58.7 F WB, 58 F DP 600 Btu per minute 3970 gr per minute 77.2 gr per pound 5.2 gr per pound 72.0 gr per pound 22,200 Btu per hour 2 F temperature rise These calculations are based on maximum load conditions as set forth in the design. For intermediate loads the calculations may show entirely different relationship. For example, the entering air temperature will approach the space temperature as the sensible heat gain or loss decreases, due to outside temperature change, entrance or exit of people, use of artificial lighting, direction and intensity of sun's rays. The entering dew-point will remain much more uniform as it is affected by changes in room moisture 386 CHAPTER 20. CENTRAL SYSTEMS FOR COMFORT AIR CONDITIONING gain only and this does not fluctuate greatly. If intermediate load conditions are im portant the calculations should be repeated for those loads. Example 2. Determine the cooling load for a theater if the following design con ditions are assumed. A dehumidifying air washer is to be used with and without the by-pass. Outside air dry-bulb____ Outside air wet-bulb.___ Inside air dry-bulb.. Inside air wet-bulb.. Minimum outdoor air.------- People Lights-- Transmission gain---------- . 94 F 75 F 80 F 67 F . 6300 cfm .. 600 4 kw .110,000 Btu per hour Solution. Without By-Pass. Grille Outside _ Kir w_r Return eir Conditioned space D-P.-tp h = dry-bulb temperature, room or return air, degrees Fahrenheit. It = dry-bulb temperature at supply grille, degrees Fahrenheit. ts = saturation temperature leaving washer, degrees Fahrenheit. t, -- dew-point in room, degrees Fahrenheit. 1* = dew-point at supply grille, degrees Fahrenheit. hi = enthalpy of room air, Btu per pound, ho = enthalpy of outside air, Btu per pound. As = enthalpy of air leaving washer, Btu per pound. Design Cooling Load. Transmission--------People (600)............... Lights (4 kw)---------- Sensible ____ T10.150 ...... _132,000 _______ 13,650 Latent 720,000 Totals_______________ Determine Air Quantity Sensible heat gain in space Assume grille temperature O 255,800 y 60 X 0.24 (80 - 68) Minimum outdoor air .255,800 Btu per hour 720,000 gr per hour 255,800 Btu per hour 68 F 1,480 lb per min = 19,700 cfm 470 lb per min = 6,300 cfm Return air = 1,010 lb per mih Moisture gain in space = 720,000 gr per horn- 12,000 -f- 1,480 = 8.11 gr per pound air supplied Room conditions = 80 F DB, 67 F WB, 60 F DP Gain in conditioned space Specific humidity leaving conditioner Grille conditions *= 68 F DB and 57 F DP 387 13,400 cfm 12,000 gr per min 77.21 gr per lb 8.11 gr per lb 69.1 gr per lb -i i i i