Heating Ventilating and Air Conditioning: Analysis and Design
Heating Ventilating and Air Conditioning: Analysis and Design
6th Edition
ISBN: 9780471470151
Author: Faye C. McQuiston, Jeffrey D. Spitler, Jerald D. Parker
Publisher: Wiley, John & Sons, Incorporated
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Chapter 3, Problem 3.53P

An interior zone of a large building is designed to have a supply air-flow rate of 5000 cfm (2.4 m3/s). The cooling load is constant at 10 tons (35 kW) with a SHF of 0.8 year-round. Indoor conditions are 75 F (24 C) db and 50 percent relative humidity (RH). (a) What is the maximum air dry bulb temperature and humidity ratio that would satisfy the load condition using all outdoor air? (b) Consider a different time when the outdoor air has a temperature of 40 F (4 C) db and 20 percent relative humidity. Return air and outdoor air may be mixed to cool the space. but humidification ill be required. Assume that saturated water vapor at 14.7 psia (101 kPa) is used to humidify the mixed air, and compute the amounts of outdoor and return air in cfm (m3/s). (c) At another time, outdoor air is at 65 F (18 C) db with a relative humidity of 90 percent. The cooling coil is estimated to have a minimum apparatus dew point of 45 F (7.2 C). What amount of outdoor and return air should be mixed before entering the coil to satisfy the given load condition? (d) What is the refrigeration load for the coil of part (c) above?

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Q2) Air is supplied to an automobile cabin from the outside, where the temperature is 20F and the relative humidity is 70%. It is desired to keep the cabin at 70F and Ø = 60%. Hoe many pounds of water must be supplied to each pound of air entering the car cabin if these conditions are to be met? The barometric pressure is 29.5 in.Hg. %3D Ans. (0.00797 lbs/Ibdry air)
Given that Initial Temperature = 28.5 deg C, Dew Point = 9 deg C, Dry Bulb = 30 deg C, Wet Bulb = 28 deg C, Saturation Pressure = 1.148 kPa Calculate the following: Humidity Ratio w = 0.622PsPt-Ps=0.622PsPa kg water/kg air Partial pressure of water vapour where: Ps = partial pressure of water vapour (Psat at dewpoint temperature )   w = humidity ratio   Pt = total pressure (standard atmospheric pressure)   Pt = Pa + Ps   Pa = partial pressure of dry air = Pt - Ps   3. Relative Humidity RH = PsPd 4. v = RaTPa   m3/kg 5. ω = 1vkg/m3 where: Pd = saturation pressure at room temperature (from steam table)      ω = density of air      v = specific volume of dry air       T = absolute temperature of room temperature       Ra = gas constant of air =0.28706 kJ/kg-K
Q.1 An air conditioning system supplying air to a space with a sensible heat load of 14 kW and a latent heat load of 9 kW has a cooling coil and a bypass path as shown schematically in Fig. The db- temperature of the space is maintained at 26°C. The dry air mass flow rate of supply air is 1.2kg/s. Outdoor ventilation air at 34°C db-temperature and 50% relative humidity is introduced into the system with a dry air mass flow rate of 0.26 kg/s. The air leaving the cooling coil is fully saturated at a db-temperature of 6°C. The pressure is constant at 101.3 kPa. Determine db-temperature and relative humidity of the supply air to the space, (ii) (i) (ii) (iv) wb-temperature of the space, temperature of the air entering the cooling coil, and refrigeration capacity of the cooling coil.

Chapter 3 Solutions

Heating Ventilating and Air Conditioning: Analysis and Design

Ch. 3 - The environmental conditions in a room are to be...Ch. 3 - Air enters a cooling coil at the rate of 5000 cfm...Ch. 3 - Air flowing in a duct has dry and wet bulb...Ch. 3 - Air is humidified with the dry bulb temperature...Ch. 3 - Air at 38 C db and 20 C wb is humidified...Ch. 3 - Two thousand cfm (1.0 m3/s) of air at an initial...Ch. 3 - Air at 40 F (5 C) db and 35 F (2 C) wb is mixed...Ch. 3 - Rework Problem 3-25, using Chart 1a, with the...Ch. 3 - The design cooling load for a zone in a building...Ch. 3 - Assume that the air in Problem 3-22 is supplied to...Ch. 3 - The sensible heat loss from a space is 500,000...Ch. 3 - Air enters a refrigeration coil at 90 Fdb and 75...Ch. 3 - A building has a total heating load of 200,000...Ch. 3 - Reconsider Problem 3-36 for an elevation of 5000...Ch. 3 - The system of Problem 3-34 has a supply air fan...Ch. 3 - An evaporative cooling system is to be used to...Ch. 3 - A cooling system is being designed for use at high...Ch. 3 - Consider a space heating system designed as shown...Ch. 3 - A variable-air-volume VAV cooling system is a type...Ch. 3 - Rework Problem 3-43 for an elevation of 5000 feet...Ch. 3 - The design condition for a space is 77 F (25 C) db...Ch. 3 - Rework Problem 3-45 for an elevation of 5000 feet...Ch. 3 - It is necessary to cool and dehumidify air from 80...Ch. 3 - Conditions in one zone of a dual-duct conditioning...Ch. 3 - Rework Problem 3-48 for an elevation of 5000 ft...Ch. 3 - A water coil in Problem 3-48 cools return air to...Ch. 3 - A multizone air handler provides air to several...Ch. 3 - Under normal operating conditions a zone has a...Ch. 3 - An interior zone of a large building is designed...Ch. 3 - Outdoor air is mixed with room return air to...Ch. 3 - Consider an enclosed swimming pool. The pool area...Ch. 3 - One particular zone served by a multizone air...Ch. 3 - A research building requires 100 percent outdoor...Ch. 3 - A space requires cooling in the amount of 120,000...

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