BEE Paper-3 — Numericals Drill

1. A 20 MW co-generation plant operates at a daily load factor of 85% and 8% auxiliary power consumption. The power is generated at 11 kV. Out of the total energy generated, 45% is exported to the grid through a 15 MVA transformer with 99% efficiency. Additionally, 35% of the generated energy is supplied to mill motors at 600 Volts through an 8 MVA step-down transformer with 98.5% efficiency. The remaining energy is used for other LT loads and auxiliaries at 415 Volts through a 4 MVA transformer with 98.2% efficiency. Calculate the following: 1. Daily energy generation in MWh. 2. Daily energy exported in MWh to the grid at 33 kV. 3. Daily mill motors consumption in MWh at 600 V. 4. Daily LT loads and auxiliary consumption in MWh at 415 V. 5. Daily transformer losses in kWh and % transformer losses.

2. A residential colony with fixed load 250 kVA is 1 km from an 11 kV/415 V transformer. Compare LT (1×3.5c×300sqmm) vs HT (1×3c×70sqmm) distribution. Data: LT cable R=0.13 Ω/km, Rs 700/m; HT cable R=0.570 Ω/km, Rs 1300/m; unit Rs 7/kWh; transformer relocation (HT) Rs 1 lakh. Recommend and estimate payback on marginal investment.

3. L-1: Choose a 1500 kVA transformer for a load of 500 kVA for 6 h, 1000 kVA for 6 h, 1500 kVA for 12 h. Transformer-1: iron loss 2.7 kW, full-load copper loss 18.1 kW; Transformer-2: iron loss 3.2 kW, full-load copper loss 19.8 kW. (i) Annual cost of losses (365 days, Rs.6/kWh). (ii) If Transformer-1 costs Rs.25,000 more, justify it.

4. L-4: A 10 MW co-gen plant runs at 85% daily load factor, generating at 11 kV. 35% exported to grid via 7.5 MVA transformer (99% eff); 32% to mill motors at 600 V via 5 MVA transformer (98% eff); balance to LT loads/auxiliaries at 415 V via 2 MVA transformer (98% eff). Calculate: (1) daily energy exported; (2) daily mill motor consumption; (3) daily LT/auxiliary consumption; (4) daily transformer losses (kWh and %).

5. a) A small scale industry has a constant load of 380 kVA. It has installed two transformers of 500 kVA each. The no load loss and full load copper loss of each 500 kVA transformer is 750 W and 5410 W respectively. From the energy efficiency point of view should the industry operate a single transformer or two transformers equally sharing the load? b) A no load test on a three phase delta connected induction motor gave: No load power = 890 W, Stator resistance per phase at 30°C = 0.233 Ohms, No load current = 14.5 A. Calculate the fixed losses for the motor.

6. A unit has 2 identical 500 kVA transformers, each with no-load loss 800 W and full-load copper loss 5000 W. Plant load is 400 kVA. Compare transformer losses for single transformer operation vs two transformers in parallel. Also list any five options to minimise electrical distribution loss.

7. Fill in the blanks (1 mark each): a) Heat rate of a thermal power plant is expressed in ___; b) The ___ loss is independent of load in a transformer; c) ___ is used to reduce the dew point in a compressed air system; d) The speed of an energy efficient motor will be more than the standard motor of same capacity because ___ decreases.

8. a) A cold rolling mill has a maximum demand of 7 MVA at power factor of 0.95. The plant management converts the existing electrical resistance annealing furnace having steady load of 1250 kW to gas heating as a cost reduction measure. The existing capacitor banks (kVAr) continued to be in the electrical network. What will be the effect on maximum demand and power factor due to this conversion? (5 Marks) b) A cement plant has a constant load of 15 MVA. It has installed two transformers of 30 MVA each. The no load loss and full load copper loss of each 30 MVA transformer is 25 kW and 75 kW respectively. From the energy efficiency point of view the industry management wants to take a decision on whether to operate a single transformer or two transformers equally sharing the load. What is your recommendation? (5 Marks)

9. a) A cold rolling mill has a maximum demand of 7 MVA at a power factor of 0.95. The plant management converts the existing electrical resistance annealing furnace having steady load of 1250 kW to gas heating as a cost reduction measure. The existing capacitor banks (kVAr) continued to be in the electrical network. What will be the effect on maximum demand and power factor due to this conversion? (5 marks). b) A cement plant has a connected load of 15 MVA. It has installed two transformers of 30 MVA each. The no load loss and full load copper loss of each 30 MVA transformer is 25 kW and 75 kW respectively. From the energy efficiency point of view the industry management wants to take a decision on whether to operate a single transformer or two transformers equally sharing the load. What is your recommendation? (5 marks).

10. State True or False (1 Mark each): 1. In an industrial electrical system operating at unity power factor, addition of further capacitors will reduce the maximum demand (kVA). 2. In a step-down transformer for a given load the current in the primary will be much lower than the current in the secondary. 3. For the same no of poles and kVA rating, the RPM of an energy efficient motor is higher than that of a standard motor. 4. The advantage of evaporative cooling is that it is possible to obtain water temperatures below the wet bulb economically. 5. A fluid coupling changes the speed of the driven equipment without changing the speed of the motor.

11. Fill in the blanks for the following: 1. The main input energy used for refrigeration in vapor absorption refrigeration plants is _____. 2. One ton of refrigeration is equivalent to _____ kW. 3. Stray losses in induction motor generally are proportional to the square of the _____ current. 4. The unit of Ah*EPI is _____. 5. If the pump impeller diameter is reduced by 10% then head reduces by _____%. 6. A 4 pole 50Hz motor operating with slip of 3% will have a shaft speed of _____ RPM. 7. Effective Aperture Glazing (EA) = VLT × _____. 8. In an amorphous core distribution transformer, no-load loss is _____ than a conventional transformer. 9. As the condensing temperature increases, kW/TR of refrigeration system will _____. 10. The extent of drying compressed air is expressed by the term _____.

12. A textile industry had installed a 2 MVA transformer. The initial demand of the plant was 1500 kVA with power factor of 0.75. Industry has installed 450 kVA capacitor at the motor end. Calculate the following: 1. Reduction in apparent power (kVA); 2. Improved power factor; 3. Revised % loading of transformer after installing the capacitor.

13. L-6: State True or False (1 mark each): 1. The efficiency of gas turbine power plant is lower than that of a combined cycle power plant. 2. The performance of air compressor at high altitudes will be lower as compared to that at sea level. 3. Efficiency of transformer will be minimum when copper loss is equal to iron losses. 4. In cooling towers, the water droplets entrapped in the air stream is captured by drift eliminators. 5. To get the static pressure, the inner and outer tubes of pitot tube are connected to manometer. 6. The throttling of pump discharge will change the pump characteristic curve. 7. The simplest way to reduce the discharge from a reciprocating air compressor is to throttle it. 8. Cycle of Concentration (COC) is the ratio of dissolved solids in circulating water to the dissolved solids in makeup water. 9. Use of VFD will save power but also create harmonics. 10. The synchronous speed of a 4 pole motor will be 3000 rpm.

1. A steel manufacturing facility is powered by a 3-phase, 6.6 kV, 50 Hz supply and operates the following electrical loads: An electric arc furnace consumes 1.2 MW at a lagging power factor of 0.65, a bank of induction motors for rolling operations consumes 800 kW at a 0.80 lagging power factor, and the lighting and instrumentation systems consume 100 kW at unity power factor. Due to utility regulations, the overall plant power factor must be improved to 0.95 lagging. A capacitor bank will be installed for compensation. As an energy auditor evaluate the following: a. Total active power consumption. (1 Mark) b. Total initial apparent power drawn by the facility. (1 Mark) c. The operating power factor. (1 Mark) d. Determine the total reactive power required to achieve the desired power factor. (2 Mark)

2. During April-2003 a plant recorded a maximum demand of 600 kVA and an average PF of 0.82 lag. The utility requires a minimum average PF of 0.92 lag, and every 1% dip in PF attracts a penalty of Rs 10,000 per month. (a) Calculate the improvement in PF for May-2003 by installing 100 kVAr capacitors. (b) Calculate the penalty to be paid, if any, during May-2003.

3. A process plant consumes 12,500 kWh per month at 0.9 power factor. What is the percentage reduction in distribution losses per month if the PF is improved to 0.96 at the load end? Assume existing distribution loss is 4% of the plant energy consumption.

4. A 37 kW, 3 phase, 415 V induction motor draws 56 A and 33 kW power at 410 V. What is the apparent and reactive power drawn by the motor at the operating load?

5. a) A 3-phase 415 V 75 kW induction motor draws 48 kW at 0.7 PF. Calculate the capacitor rating to improve PF to 0.95, the reduction in current and kVA reduction at 415 V. b) A plant consumes 2,00,000 kWh/month at 0.9 PF. What is the % reduction in distribution losses if PF is improved to 0.96 at load end?

6. State three advantages of improvement of Power Factor at Load side. Power Factor at the load side is 0.75 and average minimum load is 100 kW. What is the kVAr rating of capacitor to improve the Power Factor at the load side to 0.95?

7. A single line diagram shows a 100 kW heater load and a 200 kW motor (200 m from the 415 V LT bus). Main incoming line PF is 0.85 lag. Calculate the rating of capacitors to improve the main incoming line PF to 0.9 lag.

8. a) List five disadvantages of low power factor. b) An industry pays penalty for poor PF of 0.88; utility minimum is 0.9. Penalty = 1% of energy cost for every 0.01 PF below minimum; incentive = 1.5% for every 0.01 improvement above 0.95. Monthly energy bill Rs 6 lakhs. Calculate annual cost saving if PF improved to unity from the current level.

9. L-5: (a) A 3-phase, 50 kW rated induction motor drawing 44 kW at 0.75 lagging PF. What capacitor (kVAr) per phase is needed to improve PF to 0.96? What is the reduction in current and kVA at 415 V? (b) List five energy losses in an induction motor.

10. S-5: List any five benefits of power factor improvement in an industrial power distribution system.

11. L-1: A food processing plant has contract demand 2500 kVA; average MD 2000 kVA at 0.95 PF; MD billed at Rs.300/kVA; minimum billable MD = 75% of contract demand; incentive 0.5% reduction in energy charges per 0.01 PF increase above 0.95; average monthly energy charge Rs.10 lakhs. Plant improves PF to unity. Determine capacitor kVAr, annual reduction in MD charges and energy charge, and simple payback if capacitors cost Rs.800/kVAr.

12. A foundry draws 2500 kW. Demand during furnace operation: 5 min 2940 kVA, 7 min 2550 kVA, 3 min 2777 kVA. Billing meter monitors demand every 15 minutes. Calculate the maximum demand registered and the average PF during the interval.

13. S-8: A 100 kW heater load and a 200 kW motor (200 m from the 415V LT bus). Main incoming line PF is 0.85 lag. Calculate the rating of capacitors to improve the PF of the main incoming line to 0.9 lag.

14. L-6: (a) List five disadvantages of low power factor. (b) An industry maintains poor PF of 0.88; utility minimum is 0.9. Penalty 1% on energy cost for every 0.01 below minimum; incentive 1.5% for every 0.01 above 0.95. Monthly energy bill Rs.6 lakhs. Calculate annual cost saving if PF improved to unity from current level.

15. a) A 10 kVAr, 415 V rated power factor capacitor was found to be having terminal supply voltage of 440 V. Calculate the capacity of the power factor capacitor at the operating supply voltage. b) What would be the nearest kVAr compensation required for changing the power factor of a 500 kW load from 0.9 lead to unity power factor?

16. Fill in the blanks: (a) If the reactive power drawn by a load is zero, the load operates at __ power factor. (b) Power factor is the ratio of ___. (c) As the approach increases (other parameters constant), the effectiveness of a cooling tower ___. (d) Lower power factor of a DG set demands ___ excitation currents. (e) If voltage applied to a 415 V rated capacitor drops by 5%, its VAr output drops by about ___%.

17. L-1: The contract demand of a process plant is 6000 kVA. The average monthly recorded maximum demand is 5500 kVA at 0.78 PF. Tariff: (a) Minimum monthly billing demand is 75% of contract demand or actual recorded MD whichever is higher; no PF incentives. (b) Monthly MD charge is Rs. 400 per kVA. Find the optimum limit of PF capacitor requirement (purely to reduce MD so no excess demand charges are paid) and the simple payback period, assuming capacitor + APFC controller cost is Rs. 500 per kVAr.

18. A review of electricity bills of a process plant was conducted as a part of energy audit. The plant has a contract demand of 3000 kVA with the power supply company. The average maximum demand of the plant is 2400 kVA/month at a power factor of 0.95. The maximum demand is at 80% of the contract demand. The minimum billable maximum demand is 80% of the contract demand. An incentive of 0.5 % reduction in energy charges component of electricity bill are provided for every 0.01 increase in power factor over and above 0.95. The average energy charge component of the electricity bill per month for the plant is Rs.80 lakhs. Calculate the following: a) If the plant decides to improve the power factor to unity, determine the power factor capacitor kVAr required and the associated monetary benefits. b) What will be the simple payback period if the cost of power factor capacitors is Rs.1200/kVAr.

19. L-1(A): A trivector-meter installed in a steel plant is monitoring the maximum demand with a demand interval of 15 min. The observed maximum demand during one demand interval is given (3 min: 9634 kVA, 4 min: 10257 kVA, 3 min: 8436 kVA, 5 min: 9847 kVA). Calculate: (a) Recorded maximum demand during the cycle; (b) Demand reduction and capacitor kVAr required for improving power factor to 0.99 from average observed power factor of 0.92.

1. A private power distribution company has implemented new digital metering and billing systems to improve efficiency in a residential zone. After six months of operation, the following data was recorded: • Input energy to the system = 75 MU • Metered billed energy = 56 MU • Unmetered average billing = 4 MU • Amount billed = ₹680 million • Total amount received = ₹600 million • Arrears collected = ₹90 million • Purchased energy cost = ₹8.50 per kWh i) Estimate the Aggregate Technical and Commercial (AT&C) loss (%) and the revenue realized per kWh (4 Marks) ii) Calculate the revenue loss per kWh to the company due to AT&C loss (1 Mark)

2. A trivector-meter installed in a mini steel plant with a 15-minute cycle records the following during the maximum demand period: 1000 kVA for 10 min, 2000 kVA for 5 min, 750 kVA for 10 min, 1500 kVA for 5 min. What is the maximum demand during the 15-minute interval?

3. The maximum demand approved by a utility is 5500 kVA and the tariff provides for a minimum billing demand of 80% of approved. Records of the past 12 months show the monthly maximum demand recorded is around 4200 kVA. Will there be any benefit in surrendering part of the contract demand? If so, what kVA do you recommend surrendering? Give the cost saving, if the unit rate for kVA demand is Rs 200.

4. L-6: A distribution company has: input energy 60 MU, metered billed energy 43 MU, average (un-metered) billing 3 MU, amount billed Rs.540 million, arrears collected Rs.80 million, amount received Rs.470 million. (a) Estimate (i) AT&C loss % and revenue realised (Rs./kWh); (ii) revenue loss per kWh and monthly loss if purchased energy cost is Rs.8.10/kWh. (b) List five measures to reduce commercial loss.

1. Compute AT&C (Aggregate Technical and Commercial) Losses for the given data: Input Energy Ei=20 MU, Energy Billed Metered E1=16 MU, Un-metered E2=1 MU, Total Billed Eb=17 MU, Amount Billed Ab=Rs.800 lakhs, Gross Amount Collected AG=Rs.820 lakhs, Arrears Collected Ar=Rs.40 lakhs.

2. Harmonic measurements gave: current at 50 Hz = 300 A, at 150 Hz = 42 A, at 250 Hz = 33 A. Calculate the Total Harmonic Distortion in current.

3. Compute AT&C Losses: Input Energy Ei=11 MU, Energy Billed Metered=7 MU, Un-metered=1 MU, Total Billed=8 MU, Amount Billed=Rs.450 lakhs, Gross Collected=Rs.460 lakhs, Arrears Collected=Rs.40 lakhs.

4. One unit of electricity in end-use application is equivalent to about two units of electricity generated. Substantiate with the cascade efficiency from generating plant ex-bus to end-use. Assume: Generator yard substation efficiency 98%; T&D loss = 20%; End-use application efficiency = 65%.

5. A DISCOM has taken initiatives to reduce Aggregate Technical & Commercial (AT&C) losses in their network. The energy supplied, received and revenue details are given below — Input energy: 50 MU; Billed Energy (Metered): 39 MU; Billed Energy (Un-metered): 2 MU; Amount Billed: Rs. 470 Million; Amount Collected: Rs. 30 Million; Gross Amount collected: Rs. 390 Million. a) Estimate the AT&C losses (in %). b) List any four strategies to reduce the commercial losses.

1. Determine the difference in heat rejected in kCal/TR to the cooling tower for two different types of air conditioning system operating at same capacity. Parameter — Centrifugal chiller / VAM: Chilled water flow (m³/h): - / 180 Condenser water flow (m³/h): - / 340 Chiller inlet temp (°C): 13.0 / 14.6 Condenser water inlet temp (°C): - / 33.5 Chiller outlet temp (°C): 7.7 / 9.0 Condenser water outlet temp (°C): - / 39.1 Specific power consumption (kW/TR): 0.6 / -

2. A 5-star business hotel operates a centralized HVAC system round the clock. Only one chiller operates at a time, the other on standby. Two centrifugal chillers, each rated 250 TR, with EER varying with load: at 85% load (212.5 TR) EER 5.2 for 180 days; at 60% load (150 TR) EER 4.6 for 120 days; at 40% load (100 TR) EER 3.9 for 65 days. No change in EER above 85% load; assume chiller motor efficiency 90% at all loading conditions. During chiller operation, two pumps run in parallel at an 80% load factor, consuming a total of 19.7 kW; two cooling tower fans operate continuously with power consumption of 5.89 kW. Both pumps and fans function 24 hours a day, with overall efficiencies of 75% and 70% respectively. Electricity tariff is ₹6.5 per kWh. Evaluate: a. The total annual energy consumption (in MWh) and cost of the HVAC system, considering part-load EERs and auxiliary loads. (4 Marks) b. Heat removal by condenser in (TR) at different loads. (3 Marks) c. The hotel is planning to use the chiller partially as a heat pump by mounting a plate heat exchanger in series between the compressor and condenser (desuperheater for partial heat recovery) for producing hot water. The heat recovery can be only 20% of the condenser heat discharge. If the hot water requirement is 2000 litres/hr with 10°C temperature rise, evaluate whether the hot water requirement can be met at 40% loading conditions. (3 Marks)

3. A process engineer develops a scheme to put 500 TR absorption-based refrigeration system to bring down process fluid temperature from 34 °C to 26 °C and this will result in higher production by 10%. 5 TPH excess steam is available in the plant and this new scheme utilizes this excess steam. COP of refrigeration system is 0.65 and available latent of steam for refrigeration system is 540 kcal/kg. A) Estimate excess steam utilization for absorption-based refrigeration system in TPH. (3 Marks) b) Estimate required Cooling water (m³/hr), if available approach in condenser is 10 °C. (2 Marks)

4. As part of a management initiative to advance green energy in a new process plant, a process engineer is assessing the economic viability of a 650 TR chiller. She is considering proposals for both LiBr-based vapor absorption chillers and vapor compression refrigeration systems. While power is sourced from renewable energy, the steam required is partially generated from excess process heat and additionally from firing furnace oil. COP of advance Vapor Absorption Chiller: 1.3 COP of Vapor Compression Chiller: 4.50 Net steam price including excess steam and from boiler: 1500.00 INR/MT Net Power cost from green source: 7.20 INR/kWh Price of Cooling water: 3.00 INR/M3 Cooling water range: 8°C Specific steam heat available for chiller: 490.0 kcal/kg Evaluate both the offers and find out the offer which is economical in terms of operating cost.

5. An energy auditor assesses the refrigeration load of each floor of a building and the efficiency of the chilled water pump. The chilled water flow of each AHU and its inlet/outlet temperatures are measured; the chilled water pump discharge pressure is 3.5 kg/cm2 with the tank water level 1 m above the pump centerline; power drawn by the refrigeration compressor and pump motor are 89 kW and 17.58 kW. Determine the floor-wise refrigeration load, total TR, chiller kW/TR and pump efficiency.

6. A 20 TR package AC plant: air velocity across suction filter 2.5 m/s; suction area 1.2 m²; inlet air enthalpy 9.37 kcal/kg, outlet 7.45 kcal/kg; specific volume 0.85 m³/kg; power: compressor 10.69 kW, pump 4.86 kW, cooling tower fan 0.87 kW. Calculate: i) air flow rate m³/hr, ii) cooling effect kW, iii) compressor kW/TR, iv) overall kW/TR, v) EER kW/kW.

7. Fill in the blanks (cross-chapter): 1) One TR = ___ kW. 2) A 4-pole 15 kW IM at 50 Hz, 1% slip has rotor input ___ kW. 3) A pitot tube measures total and static pressure to determine ___ pressure. 4) Centrifugal pump impeller diameter is generally limited to reducing to about ___ % of max size. 5) Pressure in pump suction exceeding liquid vapour pressure is expressed as ___. 6) ASME parameter to define fans, blowers, compressors is ___. 7) Pumps can run in parallel if their ___ are similar. 8) Evaporation 16 m³/cell, COC 3 → blowdown ___. 9) Pump raises water to 12 m; with brine SG 1.2 height raised is ___. 10) Installing capacitor near motor terminals increases design PF of motor - True/False.

8. A water cooled 20 TR package AC plant: air velocity across suction filter 2.5 m/s, suction area 2.4 m²; inlet air enthalpy 9.37 kcal/kg, outlet 7.45 kcal/kg; specific volume 0.85 m³/kg; power: compressor 18.42 kW, pump 2.1 kW, evaporator fan 1.25 kW. Calculate: i) air flow rate, ii) cooling effect, iii) compressor kW/TR, iv) overall kW/TR, v) overall EER in W/W.

9. Identify the type of refrigeration system in the figure and the components 1,2,3 & 4. Explain briefly the function of each.

10. Compare the performance of a centrifugal chiller with a vapour absorption chiller (VAM) from the given data (chilled & condenser water flows, inlet/outlet temps, pump and CT fan power). Centrifugal compressor 205 kW; VAM steam 1620 kg/Hr. Calculate i) refrigeration load TR, ii) condenser heat load TR, iii) auxiliary power, iv) operating cost (electricity Rs 4/kWh, steam Rs 0.45/kg).

11. a) Calculate the ventilation rate for an engine room 20 m × 10.5 m × 15 m if recommended ACH is 20. b) Air at 25,200 m3/hr, density 1.2 kg/m3, enthalpy difference inlet-outlet 2.38 kcal/kg flows into an AHU; motor draws 22 kW at 90% efficiency. Find the kW/TR. (1 cal = 4.183)

12. L-2: (a) In an AHU, filter area = 1.5 m2, air velocity = 2.2 m/s, inlet enthalpy = 67 kJ/kg, outlet enthalpy = 56 kJ/kg, air density = 1.3 kg/m3. Estimate the TR of the AHU. (b) List any five energy conservation measures for energy use in buildings.

13. L-6: Write short notes on (i) Ice Bank System in refrigeration, (ii) Vapour Absorption Refrigeration System, (iii) Harmonics in electrical system and its impacts.

14. S-2: A chilled water system runs always at full load; inlet/outlet 12 °C / 7 °C. Chilled-water pump discharge pressure 3.6 kg/cm2g, suction 5 m above pump centreline, motor power 70 kW at 90% efficiency, pump efficiency 60%. Find the operating refrigeration load in TR.

15. L-4: A 7.5 TR package A/C cools a UPS room (40 kVA UPS). Outdoor unit air velocity 6.1 m/s, fan opening radius 0.30 m, air density 1.174 kg/m3, ambient 305 K, condenser-outlet hot air 313.5 K, Cp 1.009 kJ/kgK, compressor power 5.40 kW, motor efficiency 90%. UPS on-load (16 h): input 11.94 kW, output 8.61 kW; no-load (8 h): input 1.16 kW, output 0. Calculate (a) present delivery TR, (b) power per TR, (c) annual energy savings for 7200 h if UPS relocated to a ventilated area (Rs.8/kWh).

16. L-5: A textile plant had two 6 MW gas turbines + HRSG feeding process steam and a 500 TR VAM (4.4 kg steam/TR, full load). Gas turbines stopped due to gas price; two 10 TPH agro-waste boilers installed (steam cost Rs.1200/ton); plant runs 7000 h/yr. Management plans to replace VAM with an electric centrifugal chiller at 0.7 kW/TR. Compare annual operating costs of electric chiller vs VAM (grid power Rs.6.12/kWh; auxiliaries unchanged). Do you agree with running the VAM?

17. Write short notes on any two of the following: (1) Integrated Part Load Value (IPLV) for chillers, (2) Evaporative Cooling, (3) Heat Pump. (Each 2.5 Marks)

18. A 10 TR AHU operates at 8.25 TR. Inlet enthalpy 10.26 kcal/kg, outlet enthalpy 7.26 kcal/kg, specific volume of air 0.83 m3/kg. Calculate the volume of air (m3/hr) handled by the AHU.

19. S-7: Explain with the equation for COP_Carnot that (a) higher COP_Carnot is achieved with higher evaporator temperature and lower condenser temperature; (b) COP_Carnot does not take into account the type of compressor; (c) how is the COP normally used in industry given?

20. L-1: Compare centrifugal chiller vs vapour absorption chiller (VAM). Chilled water flow 192/183 m3/h, condenser flow 245/360, chiller inlet 13/14.5 C, condenser inlet 28/32 C, chiller outlet 7.8/9.2 C, condenser outlet 36.2/40.7 C, chilled water pump 32/31 kW, condenser pump 38/52 kW, CT fan 9/22 kW. Centrifugal compressor 205 kW; VAM steam 1620 kg/hr. Find (i) refrigeration load TR, (ii) condenser heat load TR, (iii) compare auxiliary power, (iv) operating cost at Rs.4/kWh and steam Rs.0.45/kg.

21. L-2: (a) Calculate the ventilation rate for an engine room 20 m L x 10.5 m W x 15 m H if recommended ACH is 20. (b) Air at 25,200 m3/hr and 1.2 kg/m3 density flows into an AHU; enthalpy difference inlet-outlet 2.38 kcal/kg; motor draws 22 kW at 90% efficiency. Find kW/TR (1 cal = 4.183).

22. a) What is the impact of condensing temperature and evaporator temperature on the COP of a refrigeration system? b) Why is it beneficial to operate induction motors in star mode at loads below 50% of rated capacity? c) In a throttle valve-controlled pumping system with oversized pump, name any 3 solutions for improving energy efficiency.

23. In an alkali chemical plant, salt brine flowing at 18 m3/hr is cooled from 12°C to 7°C using chilled water. The chiller compressor motor draws 31 kW and total input power to allied accessories is 16 kW. Motor operating efficiency is 90%. Brine density is 1.2 kg/litre and specific heat capacity is 0.97 kCal/kg°C. a) What is the refrigeration load (TR) imposed by the brine cooling? b) What is the COP of the refrigeration compressor? c) What is the overall specific power consumption in kW/TR?

24. In an AHU the actual airflow is 9300 m3/hr, inlet air enthalpy 16.12 kCal/kg, outlet enthalpy 13.33 kCal/kg, air density 1.15 kg/m3. Estimate the TR of the AHU.

25. In an alkali plant, salt brine at 20 m3/hr is cooled from 14°C to 8°C using chilled water. The chiller compressor motor draws 44.4 kW at 90% motor efficiency. Allied auxiliaries draw 20 kW. Brine density 1.2 kg/litre, specific heat 0.97 kCal/kg°C. (a) Refrigeration load (TR); (b) COP of compressor; (c) overall specific power consumption (kW/TR).

26. S-4: In a Commercial building, five window ACs each of 1.5 TR capacity were evaluated for replacement with three star labeled new ACs having Energy Efficiency Ratio (EER) of 2.50 kW/kW. The measured EER of existing ACs: AC1 = 2.05, AC2 = 2.19, AC3 = 2.30, AC4 = 2.40, AC5 = 2.17. Calculate the total kW saving potential if all the existing ACs are replaced with 3 star labeled ACs of same capacity.

27. L-2: Fill in the blanks. (a) With increase in condensing temperature in a vapor compression refrigeration system, the specific power consumption of the compressor for a constant evaporator temperature will____. (b) With increase in evaporator temperature while maintaining a constant condenser temperature, the specific power consumption of the compressor will____. (c) Lower power factor of a DG set demands ____ excitation current. (d) Slip power recovery system is used in ____ induction motor. (e) If voltage is reduced from 230 V to 200 V for a fluorescent tube light, it will result in ____ power consumption. (f) ____ fans are known as 'non-overloading' because change in static pressure do not overload the motor. (g) ____ head is the friction loss, on the liquid being moved, in pipes, valves and equipment in the system. (h) Ratio of the light reflected by a surface to the solar light incident upon it, is called ____. (i) ____ is the ratio of solar heat gain that passes through fenestration to the total incident solar radiation that falls on the fenestration. (j) luminous flux incident on an object per unit area is defined as ____.

28. L-4: An energy audit was conducted to find out the ton of refrigeration (TR) of an Air Handling Unit (AHU). Evaporator area = 10.0 m2; Inlet velocity = 1.9 m/s; Inlet air DBT = 21.5 C, RH = 75%, Enthalpy = 53.0 kJ/kg; Outlet air DBT = 17.4 C, RH = 90%, Enthalpy = 46.4 kJ/kg; Density of air = 1.14 kg/m3. Find out the TR of AHU.

29. What are the advantages of using vapour absorption refrigeration system over vapour compression system? Under what condition it would be economical? (5 Marks)

30. a) Calculate the filter area of an Air Handling Unit (AHU) for Refrigeration Load of 50 TR. The air enthalpy at inlet of AHU is 85 kJ/kg and at outlet is of 60 kJ/kg. Air velocity at filter is 1.81 m/sec and air density is 1.26 kg/m3. (5 Marks) b) A no load test was conducted in a delta connected 37 kW induction motor. Name plate data: 3 Phase, 415 V, 50 Hz, 55 Amp. Measured data on no load: Voltage V = 415 Volts; Current I = 18 Amps; Frequency F = 50 Hz; Stator phase resistance at no load = 0.23 Ohms/phase. No load power = 955 Watts. Calculate: i. The iron loss plus friction loss plus windage loss (2 Marks) ii. Stator copper loss at name plate ratings (full load), considering stator temperature as 120oC (2 Marks) iii. No load power factor of the motor (1 Mark)

31. A process plant has installed 5 MW DG set for base load operation, which is operating at 70% loading. Furnace oil is used as a fuel in the DG set. The DG set generates 8.6 kg of exhaust gas per kWh generated. The plant management has decided to install a heat recovery boiler to generate steam at 3 kg/cm2g from the exhaust gas to reduce the exit flue gas temperature from 450degC to 200degC. The specific heat of flue gas is 0.26 kcal/kgdegC. The steam generated from waste heat boiler will be used in double effect Li-Br Vapor Absorption Chiller, with a COP of 1.12. How much TR will be generated through VAM?

32. An energy audit study of a central chiller system in a commercial building was conducted and measured parameters are given below: Chilled water inlet temperature 12 °C; Chilled water Outlet temperature 7 °C; Chilled water pump discharge pressure 3.6 kg/cm²g; Pump suction 1.5 meters above the pump-center line; Power drawn by the chilled water pump motor 70 kW; Efficiency of pump motor 91%; Pump efficiency 60%. Find out the operating load of the Chiller system in TR.

33. The data for centrifugal chiller and vapour absorption chiller are given below — Chilled water flow (m³/h): Centrifugal 189, VAM 180; Condenser water flow (m³/h): Centrifugal 258, VAM 340; Chiller inlet temp (°C): Centrifugal 13.0, VAM 14.6; Condenser water inlet temp (°C): Centrifugal 27.1, VAM 33.5; Chiller outlet temp (°C): Centrifugal 7.7, VAM 9.0; Condenser water outlet temp (°C): Centrifugal 35.7, VAM 39.1; Power drawn by compressor (kW): Centrifugal 190, VAM -; Steam consumption (kg/h): Centrifugal -, VAM 1570; Chilled water pump (kW): Centrifugal 28, VAM 28; Condenser water pump (kW): Centrifugal 22, VAM 33; Cooling tower fan (kW): Centrifugal 6.0, VAM 15; Cost of Steam (Rs/kg): VAM 2.0; Cost of electricity (Rs/kWh): 9.0 both. a) Evaluate the tonnes of refrigeration (TR) of both the systems. b) Operating Energy cost per hour for both the systems.

34. A multi storied office has centralized air conditioning system by using the chilled water. The chilled water inlet and outlet temperatures are 13°C and 9°C respectively. The chilled water pump discharge pressure is 4.2 kg/cm²g and the suction is 10 meters above the pump centerline. The power drawn by the chilled water pump's motor is 75 kW and an efficiency of 92%. The chilled water pump efficiency at the operating point from pump characteristic curve is 65%. Find out the operating refrigeration load in TR.

35. L-3(B): Match the following (1 Mark each): 1. Pitot Tube; 2. Refrigerant Drier; 3. Condenser; 4. Spray Nozzles; 5. Occupancy Sensor — with — A. Cooling Tower; B. Lighting Control; C. Gas Velocity in ducts; D. Compressed Air System; E. Refrigeration System.

36. L-4: During the energy audit of central chiller plant, following parameters were noted: Chilled water flow 250 m³/hr; Chilled water inlet temperature 12°C; Chilled water outlet temperature 7°C; Motor Input Power 350 kW; Motor Efficiency 90%; Condenser water inlet temperature (going to chiller or outlet of cooling tower) 31°C; Condenser water outlet temperature (leaving from chiller or inlet to cooling tower) 36°C; Wet Bulb temperature of ambient air 28°C; Make up water TDS 180 ppm; Permissible limit of TDS for cooling water 720 ppm; Condenser cooling capacity 25% higher than the evaporator cooling capacity. Calculate: kW/TR of chiller compressor; COP of chiller; Effectiveness of cooling tower; Evaporation loss; Blow down quantity; Make-up water requirement (ignoring no drift loss).

1. A stream of moist air (mass flow 10.1 kg/s, specific humidity 0.01 kg/kg dry air) mixes with a second stream of superheated water vapour flowing at 0.1 kg/s. Assuming proper uniform mixing without condensation, what is the humidity ratio of the final stream (kg/kg dry air)?

2. S-3: In an air washer of a textile humidification system, airflow 3000 m3/h at 25 °C and 10% RH is humidified to 60% RH. Inlet/outlet specific humidity = 0.002 / 0.0062 kg/kg dry air; air density at 25 °C = 1.184 kg/m3. Calculate the water required (kg/hr).

3. a) Name six parameters along with units that a psychrometric chart provides to an air conditioning system. (3 Marks) b) Explain briefly about Thermal Emittance. (2 Marks)

4. a) Name six parameters along with units that a psychrometric chart provides (3 marks). b) Explain briefly about Thermal Emittance (2 marks).

5. L-3(A): State Increases or Decreases (1 Mark each): 1. If air dry bulb temperature is increased then Relative Humidity will ___. 2. In a pumping system, if the suction side liquid level is increased then NPSHa will ___. 3. If the air temperature increases at the inter-cooler outlet, then air compressor power consumption will ___. 4. A blower is retrofitted with a VFD and operated at full speed. The power consumption will ___. 5. As the design speed of the motors decreases the capacitor KVAr requirement will ___.

1. A 2-stage reciprocating compressor is supplying nitrogen from low pressure header to high pressure vessel. This high-pressure nitrogen is only used during any process upset. Compressor is cut-off once vessel pressure reaches 45 barg, and started when vessel pressure comes down to 35 barg. During energy audit, it was observed that compressor is started at gap of every 36 hrs when there is no intended consumption. Other data: Vol. of high pressure N2 vessel: 11.5 m3 Vessel temperature: 35.0 Deg.C Initial gas density: 50.3 kg/m3 End gas density: 39.4 kg/m3 Compressor load kW drawn: 30.0 kW Compressor capacity at constant suction pressure: 250.0 kg/hr i. Estimate the leak rate (kg/hr). ii. Estimate the energy saving potential (kWh/Annum), if all leaks are attended. Consider operating time of 8760 hrs/annum.

2. Calculate the free air delivery (FAD) capacity of a compressor in m3/hr for: receiver capacity 0.3 m3, initial pressure 0 kg/cm2(g), final pressure 7 kg/cm2(g), initial air temperature 35 degC, final air temperature 50 degC, additional holdup volume 0.05 m3, compressor pump-up time 4.1 minutes, atmospheric pressure 1.026 kg/cm2(a).

3. A reciprocating V-belt driven compressor operates with load pressure 6 bar, unload pressure 8 bar, load time 3 minutes and unload time 1.5 minutes. Suggest possible energy saving opportunities on a short-term basis.

4. A pump-up test on a reciprocating compressor gave: receiver + holdup volume 4100 litres, initial pressure 1 kg/cm2(g), final pressure 8.5 kg/cm2(g), atmospheric pressure 1.026 kg/cm2(a), ambient 32 degC, final compressed air temp 52 degC, pump-up time 65 sec. (a) Calculate the FAD in cfm. (b) A leakage test on the same system: on load 3 min, unloaded 13 min, drawing 145 kW on load. Calculate (i) % leakage, (ii) leakage quantity, (iii) specific power consumption, (iv) power lost due to leakage.

5. A free air delivery test was carried out before conducting a leakage test on a reciprocating air compressor in an engineering industry, with the following observations: Receiver capacity 8.0 m3; Initial pressure 0.1 kg/cm2(g); Final pressure 7.0 kg/cm2(g); Additional hold-up volume 0.3 m3; Atmospheric pressure 1.026 kg/cm2 abs; Compressor pump-up time 3.5 minutes. During the subsequent leakage test at lunch time, with no pneumatic equipment or control valves in operation: (a) compressor on-load time 24 seconds at an unloading pressure of 7 kg/cm2(g); (b) average power drawn during loading 92 kW; (c) compressor unload time 79 seconds and loading pressure 6.6 kg/cm2(g). Find: (i) compressor output in m3/hr (neglect temperature correction); (ii) specific power consumption in kW/(m3/hr); (iii) % air leakage in the system; (iv) leakage quantity in m3/hr; (v) power lost due to leakage.

6. a) Pump-up test on a reciprocating compressor: receiver+holdup 4100 litres, initial 1 kg/cm²(g), final 8.5 kg/cm²(g), atmospheric 1.026 kg/cm²(a), ambient 32°C, final compressed air temp 52°C, pump-up time 65 s. Calculate FAD in cfm. b) Leakage test: load 3 min, unload 13 min, drawing 145 kW on load. Find i) % leakage, ii) leakage quantity, iii) specific power consumption, iv) power lost due to leakage.

7. a) Calculate FAD in m³/min: receiver capacity 0.25 m³, initial 1 kg/cm²(g), final 7 kg/cm²(g), initial temp 32°C, final temp 52°C, additional holdup 0.05 m³, pump-up time 2.1 min. b) Identify as VCR or VAR: I) system operates under vacuum; II) uses water as refrigerant; III) uses large amount of high-grade energy; IV) COP decreases considerably with decrease in evaporator pressure; V) can work on lower evaporator pressures without affecting COP.

8. The rated compressor capacity is 15 m3/min. Evaluate if there is any capacity de-rating using the air-receiver tank filling method. Data: Receiver volume (incl. pipe & cooler) = 9 m3; Initial Pressure = 0.5 kg/cm2; Final Pressure = 7.0 kg/cm2; Atmospheric pressure = 1.026 kg/cm2; Time to build pressure = 5 minutes. (b) What is the deficiency in this calculation and how can it be corrected?

9. A 1680 m3/hr reciprocating compressor is driven by a 160 kW motor (90% efficiency) drawing 159 kW. Demand rises by 100 m3/hr. To meet it the compressor speed is increased by changing the compressor pulley. Existing: Motor rpm 1400, Motor pulley 300 mm, Compressor rpm 700, Compressor pulley 600 mm. Find new pulley diameter and additional power; check if motor can handle the load.

10. Determine the discharge pipe inner diameter size (in mm) for a compressed air system, given: FAD = 1000 Nm3/hr; discharge pressure = 7 bar(g); discharge temperature = 35 °C; air velocity = 6 m/s; atmospheric pressure = 1.013 bar.

11. S-8: Two 480 CFM screw compressors A & B. Compressor-A runs at full load; Compressor-B runs in load-unload. Load power of both = 74 kW; unload power of B = 26 kW. Both run all working day. B's loading is 64%; after arresting leakage, loading falls to 35%. Estimate energy savings per day.

12. L-2: Write short notes on the following with respect to the compressed air system: (a) Refrigeration drier, (b) Heat of compression drier, (c) Role of air receiver, (d) Dew point.

13. Two 270 cfm compressors operate at 7 kg/cm2(g), on-load 80% of the time; load power 40 kW and unload power 15 kW each. Cleaning air requirement is 60% of air generated. Calculate the daily energy consumption for cleaning air alone (continuous operation).

14. L-5: A 220 cfm screw compressor: Shift I load 60 s/unload 10 s; Shift II load 45/unload 25; Shift III load 25/unload 45 (8 hrs/shift). Load power 37 kW, unload power 11 kW. Calculate: (1) energy loss per day; (2) shift-wise average air requirement in cfm; (3) energy savings after installing VFD with VFD loss 3% of load power.

15. Calculate the free air delivery (FAD) capacity of a compressor in m3/min for the following data: Receiver capacity 0.5 m3, Initial pressure 0 kg/cm2(g), Final pressure 7 kg/cm2(g), Initial air temperature 32°C, Final air temperature 51°C, Additional holdup volume 0.03 m3, Pump up time 4.5 minutes, Atmospheric pressure 1.026 kg/cm2 absolute.

16. A compressed air leakage test was conducted in an industry running 3 nos. of 500 cfm reciprocating compressors, maintained at loading-unloading settings of 6.6 and 7.0 kg/cm2g. Trial 1 (before): On load 30 secs, Unload 110 secs. Trial 2 (after attending leaks): On load 18 secs, Unload 145 secs. Average power was 71 kW during load and 16 kW during unload. Calculate the annual cost savings for 4000 hr/year operation at energy charge Rs. 6.00 per kWh.

17. Calculate the free air delivery (FAD) of a compressor in m3/hr from a pump-up test: Receiver 0.5 m3; initial 0.0 kg/cm2(g); final 7.0 kg/cm2(g); atmospheric 1.026 kg/cm2(a); ambient air 40°C; final compressed air 60°C; additional holdup volume 0.005 m3; pump-up time 5 min 30 s.

18. L-3: A free air delivery test was carried out before a leakage test on a reciprocating air compressor. Receiver capacity = 12 m3; Initial pressure = 0.2 kg/cm2(g); Final pressure = 7.0 kg/cm2(g); Additional hold-up volume = 0.3 m3; Atmospheric pressure = 1.026 kg/cm2(a); Compressor pump-up time = 4.8 minutes. Leakage test (lunch time): (a) on load time 40 s, unloading pressure 7 kg/cm2(g); (b) average power during loading 95 kW; (c) unload time and loading pressure are 90 s and 6.6 kg/cm2(g). Find (i) compressor output m3/hr, (ii) specific power consumption kW/(m3/hr), (iii) % air leakage, (iv) leakage quantity m3/hr, (v) power lost due to leakage.

19. A small foundry has installed a reciprocating air compressor of 14.25 m3/min. The plant could not meet the compressed air requirement and hence conducted a capacity test to determine the derating in the compressor capacity. Calculate the actual FAD delivered after considering necessary temperature correction in m3/min, and the percentage derating. Operating parameters: Volume of air receiver including pipe and cooler 9 m3; Atmospheric temperature (T1) 35degC; Receiver temperature (T2) 44degC; Initial Pressure 0.5 kg/cm2(g); Final Pressure 7.0 kg/cm2(g); Atmospheric pressure 1.026 kg/cm2(a); Time taken to build up the pressure 5 minutes.

20. In an engineering industry, compressed air delivered is 500 CFM (FAD) and the compressor discharge pressure is 6 kg/cm² (gauge). Calculate the size of the header by considering velocity of compressed air 6 m/s. Assume Temperature remains constant.

21. L-6: An engineering industry operating three shifts per day has replaced its old reciprocating compressors with 1000 CFM screw compressors. During the energy audit, run hours counter readings: Load Hours start 7956, end 8401 (166 Loading kW); Un-Load Hours start 4918, end 5121 (58.1 un-loading kW). Calculate: 1. Capacity Utilization (%) of the compressor; 2. Monthly energy consumption for the present loading of the compressor; 3. Plant management is considering to install a 750 CFM compressor for energy savings. Estimate the energy savings for the same operating load, if loading power is 125 kW and unloading power is 43.75 kW; 4. To meet the present air requirement, if VFD is to be installed in the 1000 CFM compressor, what should be the percentage reduction in speed.

1. A pump is used to fill a rectangular overhead tank measuring 5 m × 3.5 m with a height of 10 m. The inlet pipe to the tank is positioned at a height of 25 m above ground level. The following additional data is available: The pump draws water from an underground sump situated 4 meters below the pump level and delivers it to a tank whose overflow line is positioned 8 meters above the tank bottom. The motor driving the pump draws 7.5 kW of power. The operating efficiencies of the motor and the pump are 90% and 70% respectively. Calculate the time taken by the pump to fill the tank up to the overflow level.

2. A) A clear water pump with rated flow of 125 m³/hr, head 55 m at rated speed of 1460 rpm and 79% efficiency supplies clarified water to a residential colony's water treatment facility. The daily water requirement is 3000 m³. The pump is directly coupled and driven by a three phase 50 Hp, 415 V, 64A, 0.9 pf, 1460 rpm induction motor with 90.5% full load efficiency. During an internal energy audit, the motor is found to operate with only 65% loading at pump rated conditions. The plant considers replacing the standard motor with a 30 kW IE3 motor. Operating parameters before and after motor replacement: Flow (m³/hr): 130 / ? Head (m): 52 / 51 Supply Voltage (V): 415 / 415 Current (Amp): 42 / 39 Power Factor: 0.9 / 0.92 Motor Eff (%): 0.88 / 0.932 The slip of the new IE3 motor has decreased by 20 rpm. Validate the savings, calculate: i) % Loading of motor after replacement. (1 Mark) ii) Flow after replacing the standard motor with 30 kW IE3 motor. (1 Mark) iii) Operating Pump Efficiency before and after motor replacement. (2 Marks) iv) Daily energy saving during operation due to motor replacement. (1 Mark) B) Mark True/False: i) Totally enclosed, fan cooled (TEFC) motors are less efficient than screen-protected, drip-proof (SPDP) motors. ii) Stray loss in induction motors is inversely proportional to load current. iii) As per BIS standard, the motor output should not be affected with voltage variation up to +/- 6%. iv) Motor life doubles for each 10°C reduction in operating temperature. v) Starting torque of energy efficient motors is higher than standard motors.

3. A cooling water pump has a positive suction head of 5 meters. The discharge pressure is 3.0 kg/cm², and the water flow rate is 150 m³/hr. Determine the pump efficiency given that the actual power input of the connected motor is 18.0 kW and the motor operates with an efficiency of 85%.

4. Analyse the following data collected for a water pump. If the operating head is 16m explain what will happen to other parameters. Design Parameters / Values: Flow (Q): 40 lps Head (H): 20 m Power (P): 15 kW Efficiency: 51%

5. A pump is delivering 50 m3/hr of water with a discharge pressure of 3.5 kg/cm2. The water is drawn from a sump where water level is 5 meter below the pump centerline. The power drawn by the motor is 9.5 kW at 90% motor efficiency. Find out the pump efficiency.

6. A cooling water pump connected to a pillar furnace has specifications Q = 12.5 lps, H = 60 m, P = 13.4 kW. The furnace manufacturer requires only 12.5 lps at 3.0 kg/cm2. What energy conservation measure can be proposed and estimate the reduction in power consumption.

7. A centrifugal pump pumping water operates at 35 m3/hr and 1440 RPM. Pump operating efficiency is 68% and motor efficiency is 90%. The discharge pressure gauge shows 4.4 kg/cm2 and the suction is 2 m below the pump centerline. If the speed of the pump is reduced by 50%, estimate the new flow, head and power.

8. a) Pump suction head 3 m below centreline, discharge pressure 2.8 kg/cm², flow 120 m³/hr. Find pump efficiency if actual motor input is 15.0 kW at 0.90 motor efficiency. b) A V-belt reciprocating instrument air compressor maintains 7 kg/cm²g. 20% of air goes to boiler-house control valves needing 6.5 kg/cm²g; balance 80% needs 2 kg/cm²g. What do you advise?

9. Water level is 4 m below the pump centreline. Discharge pressure 2.60 kg/cm². Flow 1.5 m³/min. Find pump efficiency if motor draws 14 kW at 0.88 motor efficiency.

10. Fill in the blanks: 1) Cavitation occurs when local static pressure falls below the ___ pressure of the liquid. 2) In an ammonia VAR system the absorbent is ___. 3) System resistance of a fan is proportional to the ___ of flow rate. 4) DBT=30°C and WBT=30°C → RH = ___. 5) Slip ring induction motors are ___ efficient than squirrel cage of same rating. 6) Suction static head 3 m, friction head 21 m → total head ___. 7) Lowest theoretical temperature water can be cooled to in a cooling tower is the ___ of atmospheric air. 8) Measure of illuminance in metric units is ___. 9) Pumps run in parallel if their ___ heads are similar. 10) When heat load, range and WBT held constant, cooling tower size is ___ proportional to approach.

11. Cooling water is pumped to three heat exchangers via pipes A, B, C. Pipe A: 0.1 m dia, 1.5 m/s; Pipe B: 0.1 m dia, 1.8 m/s; Pipe C: 0.2 m dia, 2.0 m/s. Measured motor power 50.7 kW, motor efficiency 90%, pump discharge pressure 3.4 kg/cm², suction head 2 m. Determine pump efficiency.

12. A pump delivers 64 m³/hr of water with a discharge head of 26 m. Water is drawn from a sump 3 m below the pump centreline. Motor draws 8.89 kW at 88% motor efficiency. Find the pump efficiency.

13. A centrifugal pump runs at 60 m3/hr, 1470 RPM, pump efficiency 65%, motor efficiency 89%. Discharge gauge 3.4 kg/cm2, suction 3 m below pump centerline. Auditor recommends replacing the motor with a 4-pole 91% efficient motor at 1% slip. Determine new flow and motor power; throttle fully open and system head purely frictional. Comment.

14. Three identical parallel cooling-water pumps (two running, one standby) all develop 3.4 kg/cm2(a). Flow meter at common header reads: Pumps 1&2 = 545 m3/hr; 2&3 = 535; 3&1 = 550. Motor power: P1 33 kW, P2 31.5 kW, P3 32.5 kW. Motor efficiency 92% (P1,P2) and 91.5% (P3). Suction 3 m below pump centerline. Find i) individual pump efficiencies, ii) specific energy consumption (kWh/m3), iii) best operating combination.

15. A pump fills a rectangular overhead tank 5 m x 4 m, height 8 m. Inlet pipe is 20 m above ground; pump suction is 3 m below pump level; overflow line is 7.5 m from tank bottom; motor power 5.5 kW at 92% efficiency; fills to overflow in 180 minutes. Assess the pump efficiency.

16. A centrifugal pump pumps 80 m3/hr of water into a container at 3 kg/cm2(g). Discharge head 5 kg/cm2(g); water level 5 m below pump centre line. Motor draws 22 kW, motor efficiency 90%, water density 1000 kg/m3. Find pump efficiency.

17. L-3: Three identical cooling water pumps in parallel (two running, one standby), all combinations give 3.4 kg/cm2(a) discharge. Flow: pumps 1&2 = 545, 2&3 = 535, 3&1 = 550 m3/hr. Motor power 33/31.5/32.5 kW; motor eff 92%/92%/91.5%; suction 3 m below pump centre line. Find (i) individual pump efficiencies, (ii) specific energy consumption kWh/m3, (iii) best operating combination.

18. A pump is delivering 40 m3/hr of water with a discharge pressure of 29 metre. The water is drawn from a sump where water level is 6 metre below the pump centerline. The power drawn by the motor is 7.5 kW at 89% motor efficiency. Find out the pump efficiency.

19. A centrifugal pump pumps 90 m3/hr of water with discharge pressure 3 kg/cm2(g) and a negative suction head of 3 m. Motor power drawn is 13 kW. Find pump efficiency. Motor efficiency 91%, water density 1000 kg/m3.

20. A water pump is delivering 400 m3/hr. The impeller diameter is trimmed by 8% and its speed reduced by 10%. Find the water flow at the changed conditions.

21. S-5: The following data of a water pump of a process plant have been collected. Flow: 70 m3/hr, Total head: 24 meters, Power drawn by motor 7.2 kW, Motor efficiency 89%. Determine the pump efficiency.

22. S-6: List any 5 energy conservation opportunities in agriculture pump sets.

23. A process plant is situated 100 m above the ground level on the top of the hill. The plant requires 100 kL of water per hour. The management decides to install a pump at the ground level, with suction 3 meter below the ground level. The friction head is 12 meter. Evaluate the rating of the motor required considering 10% extra margin with respect to actual input pump power. The design pump efficiency is 65%. Also calculate the motor input power if the motor efficiency is 93%. (5 Marks)

24. Rated capacity of a fresh water shut-discharge pump flow rate is 485 m3/hr and discharge pressure is 13.5 kg/cm2 at rated speed of 2950 rpm. It has been observed that 450 m3/hr water is sufficient to dispose the ash. The suction pressure of the pump is 0.5 kg/cm2. The management has decided to trim the impeller to satisfy the reduced flow requirement. Calculate: a) % reduction of impeller diameter (5 Marks) b) Annual energy savings after modification, if the pump is operating for 6 hours/day and 330 days in a year. (5 Marks)

25. A process plant is situated 100 m up the side of the hill. The plant requires 100 kL of water per hour. The management decides to install a pump at the ground level, with suction 3 metre below the ground level. The friction head is 12 metre. Evaluate the rating of the motor required considering 10% extra margin with respect to actual input pump power. The design pump efficiency is 65% and motor efficiency 93%.

26. Rated capacity of bottom ash disposal pump flow rate is 485 m3/hr and discharge pressure is 13.5 kg/cm2 at rated speed of 2950 rpm. It has been observed that 450 m3/hr water is sufficient to dispose the ash. The suction pressure of the pump is 0.5 kg/cm2. The management has decided to trim the impeller to satisfy the reduced flow requirement. Calculate: a) % reduction of impeller diameter (5 marks). b) The annual energy savings after modification, if the pump is operating for 6 hours/day and 330 days in a year (5 marks).

27. L-5: A 30 MW coal fired thermal power plant uses conventional wet ash disposal system for ash evacuation. During an energy audit at ash slurry disposal pump house it was observed that only one ash slurry disposal series is continually operated out of installed three numbers of series. Data collected for one series: two pumps per series; rated parameters each pump flow 815 m³/hr, head 33 mWc; slurry flow rate measured at second series pump discharge 752 m³/hr; suction head to 1st pump +2.6 mtr; final slurry discharge pressure 5.2 kg/cm²g; differential pressure across 1st slurry pump 2.44 kg/cm²; differential pressure across 2nd slurry pump 2.5 kg/cm²; ash water ratio (by weight) of the slurry 1:15; ash slurry density 1032 kg/m³; electric power input to motor of 1st slurry pump 141 kW; electric power input to motor of 2nd slurry pump 139 kW; motor rating of each pump 200 kW; full load motor efficiency 93%; belt transmission efficiency 92%. Evaluate: (i) Individual pump efficiencies if the operating motor efficiency is 92% for all pumps; (ii) Specific energy consumption of each pump (kWh/m³); (iii) Specific energy consumption of the series (kWh/m³); (iv) As water conservation measure the energy auditor recommended to maintain ash water ratio at 1:7 and slurry density of 1067 kg/m³, calculate the incremental power consumption of each pump and series if all other parameters are unchanged.

1. a) In a large-scale steel manufacturing facility, a cooling tower is used to reject heat from continuous casting operations. The circulating water flow rate is 2000 m³/hr. The cooling tower is currently operating at a Cycles of Concentration (COC) of 3. The evaporation loss is estimated at 1.0% of the circulating flow, and the drift loss is 0.1% of the circulating flow. The facility is planning to improve the COC from 3 to 6 through advanced water treatment. Evaluate the following: i. Calculate the make-up water requirement at the current COC of 3. ii. Calculate the revised make-up water requirement if the COC is increased to 6. iii. Estimate the total water savings per day. iv. Discuss one limitation or risk associated with increasing the COC. b) True or False: i. Cooling towers primarily reject heat through evaporative cooling. ii. The approach temperature in a cooling tower is the difference between the hot water temperature and the ambient dry bulb temperature. iii. Blowdown in a cooling tower is required to prevent the build-up of dissolved solids. iv. Drift losses in a cooling tower refer to water carried away with the exhaust air. v. Cooling tower effectiveness improves with higher approach temperatures. vi. Cycles of concentration in a cooling tower relate to how many times the water is reused before discharge.

2. A steel industry has 100 MW of captive power plant with 2 nos. of identical extraction condensing steam turbine. Power demand is 80 MW. The turbine specific condensing load is 3.20 kg/kWh and heat rejection in condenser is 560 kCal/kg. Cold cooling water temperature: 32.0 °C Hot cooling water temperature: 39.2 °C Calculate the following: a) The Cooling Water circulation flow (m³/hr) through both condensers, if only one cooling tower supplies water to condenser of both the steam turbines. b) Make-up water flow rate (kg/hr) to basin, assuming blowdown loss is 1.0 % of circulation flow.

3. Estimate the cooling tower capacity (TR) with: water flow rate 120 m3/h, sp. heat 1 kcal/kg C, inlet water temperature 37 C, outlet water temperature 32 C, ambient WBT 29 C.

4. In a cooling tower the cooling water circulation rate is 1250 m3/hr and the operating range is 7 C. If the blowdown rate is 1% of the circulation rate, calculate the evaporation loss and COC.

5. A cooling tower cools 1565 m3/hr of water from 44 C to 37.6 C at 29.3 C wet bulb temperature. The fan air flow rate is 989544 m3/hr (air density 1.08 kg/m3) and it operates at 2.7 cycles of concentration. Find: a) Range, b) Approach, c) % CT Effectiveness, d) L/G ratio in kg/kg, e) Cooling duty in TR, f) Evaporation losses in m3/hr, g) Blowdown in m3/hr, h) Make-up water in m3/hr.

6. An induced draft cooling tower is designed for a range of 7°C. An energy manager finds the operating range as 4°C. What could be the reasons for this situation?

7. Estimate the cooling tower capacity (TR) and approach: water flow 2 m³/min, specific heat 1 kcal/kg°C, inlet water 43°C, outlet water 35°C, ambient WBT 30°C.

8. a) Cooling tower circulation rate 1200 m³/hr, water enters at 38°C, ambient WBT 26°C, approach 4°C, blowdown 1% of circulation. Calculate evaporation loss and COC. b) An industry with 450 kVA load has two 500 kVA transformers (no-load loss 760 W, full-load copper loss 5400 W each). Should it run one transformer at full load or two sharing the load? Recommend with reasons.

9. Power plant cooling tower audit: Generation 785 MW; Circulation 107000 m3/hr; Range 10.5°C; COC 3.8. Find a) total water consumption per hour, b) specific water consumption in m3/MW. If COC is increased to 7.0, c) potential water savings in m3/hr and m3/MW.

10. a) Two streams of cooling water 9000 m3/hr at 41°C and 6000 m3/hr at 52°C are mixed and fed to one cooling tower; measured heat rejection 45,000 TR at 31°C WBT. Calculate effectiveness and evaporation loss. b) In a 0.5 m × 0.5 m AC duct, average air velocity 28 m/s; suction static −20 mmWC, discharge 30 mmWC; 3-ph motor draws 10.8 A at 415 V, 0.9 PF; motor efficiency 88%. Find fan efficiency (neglect density correction).

11. An 18 MW cogeneration plant: max condenser load 7 MW; extraction steam 57 TPH for process and VAM. Condenser heat load 550 kcal/kg steam; steam rate 5 kg/kW for condenser power; VAM heat load 127 kcal/min/TR with VAM capacity 1100 TR. Estimate cooling tower heat load (kcal/hr). For 6°C range, calculate cooling water flow. Design approach 5°C.

12. S-1: Operating data of an induced-draft cooling tower: range 8 °C, cooling water flow 12,500 m3/hr, drift loss 0.1% of circulation, WBT 27 °C, ambient DBT 35 °C, effectiveness 67%, COC 3. Estimate evaporation loss, make-up water requirement and TR load.

13. A 4-cell cooling tower has 45 kW CT fans per cell operating at 40 kW at 1450 rpm. Fans are replaced with two-speed motors at 1450 rpm and 740 rpm. High-speed mode 5300 hours, low-speed mode 1800 hours/year. Estimate annual energy savings vs continuous fixed-speed 1450 rpm operation.

14. L-6: (a) What is L/G ratio and how is it useful in cooling tower operation? (b) Functions of fill media. (c) Calculate L/G ratio: water flow 4540 m3/hr, approach 4.45 C, air entering enthalpy 24.17 kcal/kg at 26.67 C, air leaving enthalpy 39.67 kcal/kg at 37.8 C, hot water 47.77 C, cold water 31.11 C.

15. S-6: Power plant cooling tower audit: generation 785 MW, circulation rate 107000 m3/hr, range 10.5 C, design COC 3.8. Find (a) total water consumption/hr, (b) specific water consumption (m3/MW). If COC raised to 7.0, (c) potential water savings in m3/hr and m3/MW.

16. L-4: (a) Cooling water 9000 m3/hr at 41 C and 6000 m3/hr at 52 C mixed and fed to one cooling tower. Measured heat rejection 45,000 TR; WBT 31 C. Calculate effectiveness and evaporation loss. (b) AC duct 0.5 x 0.5 m, air velocity 28 m/s, suction static -20 mmWC, discharge 30 mmWC, motor draws 10.8 A at 415 V, 0.9 PF; motor eff 88%. Find fan efficiency (neglect density correction).

17. L-5: An 18 MW cogeneration plant: max condenser load 7 MW, extraction steam 57 TPH for process and VAM. Condenser heat load 550 kcal/kg of steam, steam rate 5 kg/kW for condenser power. VAM heat load 127 kcal/min/TR, VAM capacity 1100 TR. Estimate cooling tower heat load (kcal/hr); for 6 C range and 5 C approach calculate the cooling water flow.

18. Estimate the cooling tower capacity (TR) and approach with the following parameters: Water flow rate = 120 m3/hr, Specific heat of water = 1 kCal/kg°C, Inlet water temperature = 42°C, Outlet water temperature = 36°C, Ambient WBT = 32°C.

19. a) Define Range, approach and effectiveness in cooling tower operation. b) An induced draft cooling tower is designed for a range of 8°C. The energy auditor finds the operating range as 2°C. What could be the reasons for such a situation?

20. Find the blow down rate of a cooling tower: cooling water flow 600 m3/hr; operating range 8°C; TDS in circulating water 1500 ppm; TDS in make-up water 300 ppm.

21. (a) Estimate the cooling tower approach and capacity (TR): water flow 150 m3/hr; sp.heat 1 kCal/kg°C; inlet water 42°C; outlet water 34°C; ambient WBT 30°C. (b) A 180 kVA, 0.80 PF rated DG set has a diesel engine rating of 240 BHP. What is the maximum power factor maintainable at full load on the alternator without overloading the diesel engine? (alternator losses + exciter power = 5.44 kW; no derating.)

22. S-8: An induced draft-cooling tower is designed for a range of 8 C. The energy auditor finds the operating range as 2 C during the conduct of energy audit. In your opinion what could be the reasons for this situation?

23. L-6: A cooling tower cools 1450 m3/hr of water from 43 C to 36.6 C at 30 C wet bulb temperature. The cooling tower fan air flow rate is 9,50,000 m3/hr (air density = 1.08 kg/m3) and operates at 2.7 cycles of concentration. Find (a) Range, (b) Approach, (c) % CT Effectiveness, (d) L/G Ratio in kg/kg, (e) Cooling Duty Handled in TR, (f) Evaporation Losses in m3/hr, (g) Blow down requirement in m3/hr, (h) Make up water requirement in m3/hr.

24. In a steel industry, cooling water of 7500 m³/hr and 4200 m³/hr from two different sections with temperatures of 38 °C and 55 °C respectively, are fed to cooling tower after proper mixing. If the measured heat rejection by the cooling tower is 38,000 TR, calculate the effectiveness and evaporation loss of the cooling tower at 28 °C WBT.