This document discusses HVAC and refrigeration systems. It provides information on types of refrigerants used in centrifugal chillers and unitary AC units. It notes that R-11, R-12 and R-22 are being phased out due to being CFCs and lists phase-out dates for various refrigerants. It also discusses vapor compression systems, properties of commonly used refrigerants, and ways to improve system performance and reduce energy consumption through maintenance and optimization of operating parameters.

1. HVAC and Refrigeration System

2. Ton of refrigeration
The cooling effect produced is quantified as tons of
refrigeration.
1 ton of refrigeration = 3024 kCal/hr
heat rejected.

3. Conceptual view of a chilled-water
air-conditioning system

4. CFCs Are On The Way Out
Eighty percent of today’s existing chillers are centrifugal chillers that use R-11 as refrigerant. The newer,
non-CFC alternative to R-11 is HCFC-123. Some centrifugal chillers use R-12; its non-CFC alternative is
HFC-134a. Unitary A/C units typically use R-22, which will be phased out in the future.
Phase-Out Dates
Refrigerants Action
1996
R-11, R-12, R-500, HCFC-152A,
CFC-114
Production of these refrigerants is stopped. Equipment
using these refrigerants is no longer manufactured.
2010
HCFC-22 Manufacture of equipment using this refrigerant is stopped.
2020
HCFC-22 Production of this refrigerant is stopped.
2020
HCFC-123 Manufacture of equipment using this refrigerant is stopped.
2030
HCFC-123 Production of this refrigerant is stopped.

5. Introduction
Refrigeration deals with the transfer
of heat from a low temperature level
at the heat source to a high
temperature level at the heat sink.
– Air conditioning for comfort
– Refrigeration for process

7. Vapour compression System

8. How do the chillers work ?
1. Boiling point of the water is a function of pressure. At atmospheric pressure water boils at 100 deg. C.
When maintained at high vacuum, water will boil and subcool itself. The boiling point of the water at
6 mmHg (abs) is 3.7 deg. C.

9. How do the chillers work ?
2. Lithium Bromide (LiBr) has the property to absorb water due to its chemical affinity. At higher
concentration and lower temperature LiBr absorbs water vapour (refrigerant vapour) very effectively.

10. How do the chillers work ?
3. As Lithium Bromide becomes dilute it loses its capacity to absorb water vapour. It thus needs to be
reconcentrated using a heat source. Heat source may be Steam or Flue gases or even Hot water.

13. Vapour absorption chillers: Types
• Single effect steam fired (0.4 to 2 kg/cm2)
– Steam Consumption for 200 TR = 8.5 Kg/hr/TR
• Double effect steam fired (3 to 9 kg/cm2)
– Steam Consumption for 200 TR = 4.5 Kg/hr/TR
– Cost of m/c = Rs. 12000 to 15000 per TR
• Low temperature hot water fired (75 – 100oC)
• High temperature hot water fired (110 – 145oC)
• Direct fired (oil, gas, kerosene)
– HSD/LDO Consumption = 0.313 lit/hr/TR
– Kerosene Consumption =0.326lit/hr/TR
– Cost of m/c = Rs. 20,000 to 25000 per TR

14. Properties of Commonly used
Refrigerants
Enthalpy *
Refrigerant
Boiling
Point
** (o
C)
Freezing
Point
(o
C)
Vapor
Pressure
* (kPa)
Vapor
Volume *
(m3
/ Kg)
Liquid (kJ
/ Kg)
Vapor
(kJ / Kg)
R - 11 23.82 -111.0 25.73 0.61170 191.40 385.43
R - 12 -29.79 -158.0 219.28 0.07702 190.72 347.96
R - 22 -40.76 -160.0 354.74 0.06513 188.55 400.83
R - 502 -45.40 --- 414.30 0.04234 188.87 342.31
R - 7
(Ammonia)
-33.30 -77.7 289.93 0.41949 -808.71 487.76

15. COP = (H2-H1)/(H3-H2)

16. Performance Assessment
The specific power consumption kW/TR is a useful indicator of the
performance of refrigeration system. By messing refrigeration duty
performed in TR and the Kilo Watt inputs measured, kW/TR is
used as a reference energy performance indicator.
The refrigeration TR is assessed as TR = Q ⋅Cp ⋅ (Ti – To) / 3024
Where TR is cooling TR duty
Q is mass flow rate of coolant in kg/hr
Cp is coolant specific heat in kCal /kg / 0C
Ti is inlet. Temperature of coolant to evaporator (chiller) in 0C.
To is outlet temperature of coolant from evaporator (chiller) in 0C.

17. Overall energy consumption
• Compressor kW
• Chilled water pump kW
• Condenser water pump kW
• Cooling tower fan kW
Overall kW/TR = sum of all above kW/ TR

18. Effect of Variation in Evaporator
Temperature on
Compressor Power Consumption
Evaporator
Temperature
(0
C)
Refrigeration
Capacity
(tons)
Specific
Power
Consumption
Increase in
kW/ton (%)
5.0 67.58 0.81 -
0.0 56.07 0.94 16.0
-5.0 45.98 1.08 33.0
-10.0 37.20 1.25 54.0
-20.0 23.12 1.67 106.0
A 10C raise in evaporator temperature can help to save almost 3 % on power
consumption.

19. Effect of Variation in Condenser
Temperature on
Compressor Power Consumption
Condensing
Temperature
(0
C)
Refrigeration
Capacity
(tons)
Specific
Power
Consumption
Increase in
kW/TR
(%)
26.7 31.5 1.17 -
35.0 21.4 1.27 8.5
40.0 20.0 1.41 20.5

20. Effect of Poor Maintenance on
Compressor Power Consumption
Condition
Evap.
Temp
(0
C)
Cond.
Temp
(0
C)
Refrigeration
Capacity
(tons)
Specific
Power
Consumption
(kW/ton)
Increase
in
kW/Ton
(%)
Normal 7.2 40.5 17.0 0.69 -
Dirty
condenser
7.2 46.1 15.6 0.84 20.4
Dirty
evaporator
1.7 40.5 13.8 0.82 18.3
Dirty
condenser
and
evaporator
1.7 46.1 12.7 0.96 38.7

21. ENERGY SAVINGS
OPPORTUNITIES
• Cold Insulation
• Building Envelop
• Building Heat Loads
• Process Heat Loads Minimisation
– Flow optimization and Heat transfer area increase to
accept higher temperature coolant
– Avoiding wastages like heat gains, loss of chilled
water, idle flows
– Frequent cleaning / de-scaling of all heat exchangers
.

22. At the Refrigeration A/C Plant
Area
• Ensure regular maintenance of all A/C plant components
as per manufacturer guidelines.
• Ensure adequacy of chilled water and cooling water flows,
avoidance of bypass flows by valving off the idle
equipment.
• Minimize part load operations by matching loads and plant
capacity on line, adopting variable speed drives for varying
process load.
• Ensure efforts to continuously optimize condenser and
evaporator parameters for minimizing specific energy
consumption and maximizing capacity.
• Adopt VAR system where economics permit as a non CFC
solution

23. Select the right Cooling Medium
Type of cooling Power Consumption
1. Cooling tower water 0.1 KW/TR
2. Chilled water System at 10oC 0.7 KW/TR
3. Brine System at -20oC 1.8 KW/TR
Order of preference
Cooling water ChilledWater Brine

24. Energy Savings in Refrigeration systems
There are two broad ways by which energy
can be conserved
1.By decreasing the load
2.By optimising the refrigeration system

25. Calculating the operating load of a chiller plant
Refrigeration
plant
Refrigeration
plant
Hot well
12OC
Process
Cold well
8OC
Chilled water flow – 100 m3/hr
Refrigeration TR - 100,000 kg/hr x 1 x 4
3000
m Cp ∆Τ
- 133.33 TR
Power drawn by compressor, kW
Efficiency -
TR
120
- = 0.9
133.33

26. Energy saving measures in A/c System
• Comfort conditions: 25OC, 55 % RH
• Minimize heat load through glass windows
– Provide sun control film, Use double glass
• Insulate roof top in A/C Building
– Provide under deck insulation of 50 mm, Provide lawns at roof top
• Optimize fresh air supply into a/c room
– Conduct CO2 study to optimize fresh air quantity
– 10-15 cfm/person or 0.25 cfm/sq..ft as per ASHRAE
• Minimise artificial lighting
– Use natural lighting , 3.5 kw lighting consumes 1.0 TR load
• Provide controls
– install thermostat to control peak and base load
– Provide VSD for AHU with return air temp.sensor-set at 25oC
• Air tight the building envelop
– prevent cold air leakage, Provide door closures
• Avoid heat producing equipments inside the room
– keep away UPS Battery , ovens, other loads

27. Efficient operation & maintenance
• The suction Temperature, pressure delivery pressure of
compressors should be kept at optimum level
– Ensure all indicators are working properly
– Keep record of oil consumption
• Condensers
– Remove scale and algae and adopt suitable water treatment
– Give periodic purging of non-condensable gases
– Lesser the water temperature more the COP
– Routine defrosting of Cooling coils
– Stop condenser water pump when compressor not working
– 5OC rise in condensing temperature increases 10 % power
consumption
– 5OC rise in evaporating temperature increases 10 % power
consumption

28. Energy saving measures in refrigeration
• Look for process modifications to reduce the cooling load
• Use cooling water to remove the maximum heat before using chilled
water
• Provide VSD for condenser water pumps
– to vary the cooling water flow to maintain 4oC difference across the condensers
• Avoid primary pump operation
– Normally two pumps are operation(Chilled water supply pump from cold well
and return water pump from hot well)
– Modify to operate only return water pump
– Provide VSD for efficient part load operation
• Explore ‘Ice-bank’ system for Maximum demand reduction
• Explore application of vapour absorption with cost economics
• Replace old systems with modern energy efficient systems

29. Cold Insulation
Basis:
Ambient temperature - 35OC, emissivity – 0.8, still air conditions
Allowable heat ingress – 10 –15 Kcal/m2/hr
1915420
2711315
417310
86355
Exposed area per tonne
of refrigeration
Heat ingress
Kcal/m2/hr
Difference in temperature
between ambient and surface
• Thumb rules for cold Insulation
– Chilled water pipe insulation (Provide 2 to 3 inch thickness)
– Duct insulation (Provide 1 to 2 inch thickness)
– Suction line refrigerant pipe insulation(Provide 2 to3 inch thickness)