7.5

Moist air at 24°C, 1 atm, and 35% relative humidity enters an evaporative cooling unit operatingat steady state consisting of a heating section followed by a soaked pad evaporative cooleroperating adiabatically. The air passing through the heating section is heated to 45°C. Next, theair passes through a soaked pad exiting with 50% relative humidity. A. Determine the specific humidity of the entering moist air (to the heating section)_ B. Determine the rate of heat transfer to the moist air passing through the heating section, in kJper kg of the entering mixture. (20 of 45 points. Please input your final answer in the box below) C. Determine the specific humidity at the exit of the evaporative cooling section. D. Determine the temperature, in °C at the exit of the evaporative cooling section. (.

11.9 A duct system has branch sections to threetdifferent zones as shown in Problem 11.9 Figure. The volume flow rate and duct lengths are shown on the figure. The ducts are circular with right angle tees, diffusers with a loss coefficient of 0.2, and a sum of the loss coefficients for the fittings in each section of22. Assume a friction factor of 0.018 for each section and standard temperature and pressure.Determine the duct die a. Determine the duct diameters and pressure drops using the equal friction method. b. Determine the pressure in each zone. Using the generalized fan curve of Figure11.10, select a fan, and determine the fanpower required. d. Determine the fan power required for the same system when the total flow is reduced to 20,000 cfm with the same proportion of the flow to each zone and a variable speed fan employed. e. Draw some conclusions from your results.

Problem 2 (50 points) Consider the secondary loop of a chilled water pumping system, such as the one in the diagram below. Suppose one of the secondary pumps is active and the other is an identical backup. The performance data for each pump is provided on the next page. The provided operating conditions are the design conditions for this system. a) What is the approximate pump efficiency degradation (expressed in percentage points) due to trimming the impeller from 14" to 11.6"? Assume the 14" pump impeller serves the same system curve. b) If the 14" impeller were kept in place and a throttle valve were used at the pump discharge to regulate flow to the design condition flow, what would be the brake horsepower requirement of the active pump? What percentage increase in shaft power (relative to the 11.6" impeller pump) would this represent? c) For the scenario in part (b), how much head is lost across the throttle valve? Provide a calculation and explanation. d) If the system has zero control static head, and pump speed for the 11.6" impeller is adjusted from 100% to 70%, what would be the new pump flow, head, and brake horsepower? What percentage pump power reduction does this represent? e) Suppose the system controls pump speed to maintain a differential pressure (DP) setpoint and the DP sensor is located between the supply and return lines at one of the air handlers. Also suppose that an operator adjusts pump speed to produce 70% of the design flow. How would this scenario change your answers to part (d)? Provide qualitative descriptions (e.g., up, down, or stay the same) and explanations for each aspect. TWO POSITION ISOLATION VALVE 5 5 CHILLER #1 CHILLER #2 VARIABLE SPEED DRIVE (OPTIONAL) COMMON LEG SUPPLY AIR TEMPERATURE HIH PRIMARY LOOP VSD COIL VSD SECONDARY LOOP Page 2 of 3 KP - Horizontal Split Case Pump Head - ft NPSHr - ft 250 225 200 175 150 125 100 75 50 25 0 30 15 14.00 in 11.60 in 10.00 in 50 100 Operating Conditions Flow, rated Differential head / pressure, rated (requested) Differential head / pressure, rated (actual) Efficiency Speed, rated NPSH required Stages Impeller diameter, rated 150 600.0 USgpm 120.0 ft 119.9 ft 69.85 % 1780 rpm 13.88 ft 1 11.60 in 200 250 50 300 58 350 400 Liquid Liquid type Temperature, max Fluid density, rated / max Viscosity, rated 64 PACO KP is a single-stage, between bearings, split case pump. The axially split design allows easy removal of the top casing and access to the pump components without disturbing the motor or pipe work. (PC29) Benefits • Double suction minimizes axial load, which extends the life of the wear rings, shaft seals and bearings • Double Volute Design for increased efficiency, lower life cycle costs, & prolonged seal and bearing life • Independent bearing housing design allows access to the pump components without removing the top half of the casing • Suction baffles reduce losses and improve NPSH-R by directing flow into the eye of the impeller • High energy efficiency and low life cycle costs 68 450 500 550 Flow-USgpm Cold Water 68.00 deg F 1.000 SG 1.00 CP A 600 70 650 71 NPSHr 700 71 System Curve #1 750 800 Driver & Power Data 70 850 Motor sizing specification Site Supply Frequency Nameplate motor rating Rated power (based on duty point) Max power (non-overloading) Frame Size 900 MCSF 60 Hz 950 Max power (non- overloading) 30.00 hp/22.37 kW 26.02 hp 27.44 hp 286T Page 3 of 3 1,000

1-Introduction 2-Use program - HAP in the design of systems and devices 3 Use program - HAP in estimating your cost and energy cost SHAP 4.6- Program Description Chapter 3: Data on the establishment of the air conditioning system 1-List General 2-list System Components 3-... Zone Components 4- Sizing Data 5- Equipment 6-System account reports

5.5 A flow of 2000 cfm of moist outdoor air at 90 F and 70% RH mixes with a 1000 cfm stream of return air at 65 F and 20% RH. Determine the temperature, relative humidity, humidity ratio, and enthalpy of the mixed stream at sea level location.

5.10 SI A cooling coil with a bypass factor of 0.11 and a chilled water temperature of 12 C processes a flow of 3500 L/s. Determine the outlet state and the total, sensible and latent energy terms for entering conditions of 32 C and relative humidity between 10 and 90%.

Q2: The dimensions of room are 10-m by 6-m by 3-m high. The pressure, temperature and degree of saturation of the air in the room are 100 kPa, 25°C and 55 percent respectively. (i) Calculate the mass of air in the room. (ii) If the surface temperature of a window of the room is 10.5°C, will moisture condense out of the air?

7.7 Area The air distribution system for a restaurant is being designed. The occupancy and cooling loads for the three main areas are given in the table. The cooling design loads are based on a design ambient of 95 F db and 78 F wb and a SLR of 0.7. These loads do not include the ventilation load. Occupancy Cooling load (Btu/hr) 120,000 40,000 30,000 Dining Bar Kitchen 150 20 4 a. Specify the set points, flow rates, and capacity of the air- conditioning systems. b. Draw some conclusions from your analysis.

5.17 A flow of 4000 cfm of air at 53 F and 95% RH enters the reheat coil of a building zone. The zone set temperature is 78 F and the zone sensible heat ratio (SHR) is 0.8. 1. Determine the maximum sensible and total load that can be met by the air flow and the room RH at the maximum load. 2. Determine the reheat energy that must be supplied to keep the zone at 78 as the sensible load is decreased from the maximum value to zero with the SHR remaining at 0.8. The flow rate, temperature, and humidity of the air supplied to the reheat coil remain the same.

Problem 1 (50 points) Consider the VAV system shown in the diagram below and respond to the following. a) Sketch a pressure (y axis) versus position (x axis) chart that shows a static pressure profile of the air flow path. Begin the chart in the zones, and end the chart in the zones. On your chart, label all components that appear in the diagram below. b) If the fan is rated for 10,000 cfm and 4" TSP and draws 9.4 bhp of shaft power, what is its static efficiency? c) If the target duct static pressure (DSP) is 1.5" w.c. and the actual DSP is 2" w.c., show on a pressure-vs-flow diagram how the system can adjust its inlet vanes to meet the target DSP. d) Assume the inlet vanes are removed, and fan speed is then controlled with a VFD to maintain a duct static pressure setpoint. Show the following scenarios on pressure-vs-flow diagrams. Clearly identify the effect of VAV damper modulation and supply fan speed modulation with annotations, and show where the operating point rides the system curve and where it rides the fan curve. i. Zone temperatures are at cooling setpoint (baseline condition) and then an influx of occupants warms the zones to above setpoint. Zone temperatures are slightly above the cooling setpoint (baseline condition) and then cooler outside conditions result in zone temperatures dipping below the zone cooling setpoints. ii. OA EA RA PREHEAT FILTERS COIL []} COIL COOLING RA FAN WITH INLET VANES VARIABLE VOLUME BOX Figure 111-Variable Air Volume System Page 1 of 3