Upload
ffaulo
View
230
Download
0
Embed Size (px)
Citation preview
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 1/29
REFRIGERATION &
AIR CONDITIONING
Applications
Vapour compression cycle
Vapour absorption cycle
Energy consumption inrefrigeration systems
Air conditioning
Energy savingopportunities
Case studies
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 2/29
Integrated Systems Approach to
Refrigeration & Air-conditioning
Reducing the Need for Refrigeration
Increase Temperature Settings
Reduce Heat Ingress
Better Heat Exchanger Design and Maintenance
Better Monitoring & Control Techniques
New Developments for Relative Humidity Control
Energy Storage
Inter-fuel Substitution: Use of Absorption Chillers
Drive Transmission
Electric Motor
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 3/29
Applications
Refrigeration systems are used for process cooling by chilled wateror brine, ice plants, cold storage, freeze drying, air-conditioningsystems etc. The refrigerant temperatures for process coolingapplications may range from 15C to as low as -70C.
Comfort air-conditioning requires refrigerant temperatures in therange of 0C to 5C. Air-conditioning generally implies cooling of room air to about 24C and relative humidity of 50%-60%.
In some applications, air-conditioning involves humidification of airup to 70%-80% relative humidity (in textile industry) ordehumidification of air to less than 45% or 20% (in somepharmaceutical industries, rooms housing sophisticated electronicequipment, storage rooms for hygroscopic materials etc.).
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 4/29
Terms
1 Ton of Refrigeration (TR) = 3023 kcal/hr= 3.51 kWthermal= 12000 Btu/hr
COP = Refrigeration EffectWork done
EER = Refrigeration Effect (Btu/hr)Work done (Watts)
Specific Power Consumption = Power Consumption (kW)
Refrigeration effect (TR)
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 5/29
Vapour Compression System
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 6/29
Compressors
Reciprocating compressors are commonly used up to capacities of 250 TR.
Screw compressors are available for refrigeration capacities fromabout 200 TR to 1200 TR.
Centrifugal compressor are generally used beyond 150 ton singlemachine capacity.
Scroll compressor is of more recent origin. Suction, compression anddischarge are simultaneously performed in an ongoing sequence by
the orbiting motion of the scroll. Scroll compressors are available forcapacities up to 30 TR.
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 7/29
Performance of
Vapour Compression Machines
CapacityTR
Power kW
COP EER Btu/hr/W
Specific PowerkW/TR
Open Type Reciprocating Compressors
10.78 6.62 5.75 19.7 0.61
28.90 19.26 5.24 17.9 0.67
48.30 32.06 5.32 18.2 0.66
64.40 42.75 5.32 18.2 0.66
Semi-hermetic Reciprocating Compressors
8.77 6.25 4.94 16.9 0.71
9.26 7.00 4.62 15.8 0.76
13.90 12.10 4.03 13.8 0.87
42.00 34.50 4.28 14.6 0.82
Open Type Centrifugal Compressors
563.67 329.94 6.00 20.5 0.59
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 8/29
Single Effect Absorption Chiller
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 9/29
Performance of
Vapour Absorption MachinesCapacity
TR Steam
pressurekg/sq. cm
Steam cons.Kg/hr
COP EER Btu/hr/
W
Specificsteam cons.Kg/hr/TR
Single Effect Chiller (Steam heated)
240 3.0 2101.0 0.61 2.10 8.75
Double Effect Chiller (Steam heated)85 8.5 415.2 1.10 3.76 4.88
100 8.0 490.2 1.10 3.76 4.90
155 8.0 736.5 1.13 3.86 4.75
270 8.5 1284.0 1.13 3.86 4.76
400 8.5 2097.0 1.02 3.49 5.24500 8.0 2296.0 1.17 4.00 4.59
Double Effect Chiller (Direct fired)
78 - 27.3 m3/hrnatural gas
0.96 3.28 0.35m3/hr
150 - 54.6 lit/hr LDO 0.96 3.27 0.36lit/hr/TR
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 10/29
Centralised Air Conditioning Systems:
Comparison of Air Cooling Methods
Type DX chiller (air
cooled
condenser)
DX chiller (water
cooled
condenser)
Chilled water
system
Capacity, TR 100 100 100
Saturated Suction temp, C 6.1 6.1 4.4
Saturated Discharge temp, C 52.7 37.8 37.8
Compressor power, kW (a) 104.5 62.0 62.0
Chilled water pump, kW (b) 0.0 0.0 12.8
Condenser cooling fan/pump
(c)
7.8 13.5 13.5
Total power, kW (a) + (b) +(c) 112.3 75.5 88.3
Total Specific power, kW/TR 1.12 0.76 0.88
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 11/29
Effect of Evaporator and Condensing
temperatures on COP
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 12/29
Energy Saving Opportunity:
Operate at Higher Temperature
Increase the Chilled Water Temperature Set Point if Possible.
Improve Air Distribution and Circulation
Improve air Distribution in Cold Storages
CompressorType
Percent Increase in the COPfor each 1°F Reset
CondenserTemperature
EvaporationTemperature
Reciprocating 1.30% 1.13%
Centrifugal 0.50% 1.54%
Screw 2.30% 2.08%
Absorption 0.80% 0.59%
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 13/29
Case Study: Increase refrigerant charging to
operate at higher suction pressure
Increase of suction pressure of refrigerant compressor-chilled waterplant from 40 psig to 60 psig to increase capacity and efficiency.
This has helped in reducing the number of compressors in operationfrom 3 to 2
Under-charging of refrigerant causes poor performance of compressors
Annual energy saving was 68,000 kWh. i.e. Rs 2.8 lakhs/year ($7000)
No investment
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 14/29
Energy Saving Opportunity:
Reduce Conditioned Volume & Heating Loads
Keep Unnecessary Heat LoadsOut
Use False Ceilings
Use Small Power Panel Coolers
Use Pre-Fabricated, ModularCold Storage Units
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 15/29
Energy Saving Opportunity:
Reduce Heat Ingress
Check and Maintain Thermal Insulation
Insulate Pipe Fittings
Reduce Excessive Window Area
Use Low Emissivity (Sun Control) Films
Use Low Conductivity Window Frames Provide Insulation on Sun-Facing Roofs
and Walls.
Provide Evaporative Roof Cooling
Building Structure Cooling
Use Doors, Air-Curtains, PVC StripCurtains
Use High Speed Doors for Cold Storage
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 16/29
Energy Saving Opportunity:
Use Favourable Ambient Conditions
Use Cooling Tower Water Directly for Cooling in Winter
Design New Air-conditioning Systems with Facility for 100% Fresh Air during Winter
Use Ambiators : 2-stage Air Washers in Dry Areas to get water
below ambient wet bulb temperature Use Ground Source Cooling
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 17/29
Energy Saving Opportunity: Improve Heat Transfer
Use Heat Exchangers with Larger Surface Area
Use Plate Heat Exchangers for Process and Refrigeration MachineCondenser Cooling
Avoid the Use of Air Cooled Condensers
Evaporative Pre-coolers for Air-cooled Condensers
1C higher temperature in the evaporator or 1C lowertemperature in the condenser can reduce the specific powerconsumption by 2 to 3%.
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 18/29
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 19/29
Energy Saving Opportunity: Routine
Maintenance
Inefficient operation of refrigeration machines is usually due to fouling of
condensers. This happens generally due to the absence of water treatmentor poor water treatment practices. Specify Appropriate Fouling Factors forCondensers
Turn fans off when they are not needed.
Clean screens, filters and fan blades regularly.
Minimise fan speed.
Check belt tension regularly.
Eliminate ductwork air leaks.
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 20/29
Energy Saving Opportunity: Heat Recovery
Devices
Heat Pipes, Heat Wheels, Plate Heat Exchangers
Reducing Heat Load due to Ventilation
Low Relative Humidity Air-Conditioning
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 21/29
Demand Saving Opportunity:
Thermal Storage
Ice banks
Salt hydrates
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 22/29
Case Study: Optimising Speed of Compressors
Description Brine Chiller Water Chiller
Compressor make Kirloskar Kirloskar
Compressor model KC4 KC4
Motor rating, kW 55.0 90.0 Motor power input, kW 53.0 74.1
Speed, rpm 750 780
Operating hours/day 14.5 9.0
Refrigeration capacity, TR 29.1 57.0
Specific power consumption, kW/TR (compressor shaft power)
1.6 1.2
Average energy consumption,kWh/day
768.5 666.9
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 23/29
Case Study:
Optimising Speed of Compressors
Description Brine Chiller Water Chiller
Motor power input, kW 32.3 35.6
Speed, rpm 480 409.5
Refrigeration capacity, TR 23.0 44.0
Specific power consumption,kW/TR (compressor shaft power)
1.23 0.7
Operating hours/day 18.0 14.0
Average energy consumption, kWh/day
581.4 498.4
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 24/29
Case Study: Low Relative Humidity Air
Conditioning
The Air-to-Air Heat Exchangerwas installed recover heat fromthe return air duct to eliminate orreduce the requirement of ductheaters.
The room condition at the time of
measurements was at 23.9ºC and50% relative humidity. Total HeatLoad was 7 TR (i.e Room HeatLoad plus Air Re-heating Load).
Heat Recovery was 2.8 TR (equivalent to electrical heat loadof 9.9 kW).
The annual energy saving is about97,000 kWh/annum i.e. Rs. 5.0lakhs (12,500 $) per annum. Thisis a saving of about 70%.
C t d R d i i diti i l d
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 25/29
Case study: Reducing air conditioning load –
Green Building
The CII-Godrej Centre for
Environmental Excellence isIndia’s first Green Building
In the air conditionedauditorium, the design freshair requirement is 4000 cfm,which would increase the air
conditioning load. A uniquemethod of natural pre-coolingof warm fresh air has beenattempted called “wind tower”.
On an average, the airconditioning load reduction is
about 10 TR. The net saving is about 76.5
kWh/day in cool climate. Thesavings are expected to behigher in summer.
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 26/29
COOLING TOWER
Temperature Range: It isthe difference between thecooling tower inlet andoutlet water temperatures.
Temperature Approach: It is the difference betweenthe cooling tower cold watertemperature and theambient wet bulbtemperature.
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 27/29
Common Causes Of Poor Cooling Tower
Performance
Scale Deposits —When water evaporates from the cooling tower, it
leaves scale deposits on the surface of the fill from the minerals thatwere dissolved in the water.
Clogged Spray Nozzles — Algae and sediment that collect in thewater basin as well as excessive solids that get into the coolingwater can clog the spray nozzles. This causes uneven water
distribution over the fill.
Poor Air Flow —Poor air flow through the tower reduces theamount of heat transfer from the water to the air. Poor air flow canbe caused by debris at the inlets or outlets of the tower or in the fill.Other causes of poor air flow are loose fan and motor mountings,
poor motor and fan alignment, poor gear box maintenance,improper fan pitch, damage to fan blades, or excessive vibration.
Poor Pump Performance — An indirect cooling tower uses acooling tower pump. Proper water flow is important to achieveoptimum heat transfer.
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 28/29
Energy Saving Opportunities
Automatic ON/OFF control of fans with temperaturefeedback
Multi-speed motors for fans
Variable speed drives for fans
More efficient fans
Fan inlet cone
Velocity recovery stack
Fan tip clearance
PVC fills
7/28/2019 Refrigeration & Air Conditioining
http://slidepdf.com/reader/full/refrigeration-air-conditioining 29/29
Case Study: Cooling Tower Rationalisation
Description Unit Induceddraft CT-1
Naturaldraft CT-2
Water flow m3/hr 278 380
Water inlet temp. C 35 35
Water outlet temp C 30 30
Heat load TR 460 630
CT pump power KW 18.7 30.5
CT fan power KW 6.8 fanless
As the natural draft cooling tower had a capacity of
1200 TR, CT-1 was shut down and the entire load wasdiverted to the natural draft tower after change of pump impeller
Net saving of 10 kW.