This document discusses various strategies to optimize refrigeration and air conditioning systems to reduce energy consumption and costs. It describes the basic vapor compression refrigeration cycle and how system performance is affected by evaporator and condenser temperatures. Methods to optimize compressor operation include adjusting loading/unloading, variable speed drives, and gas bypass controls. Optimizing cooling water systems, replacing shell and tube condensers with evaporative condensers, and switching to more efficient centrifugal compressors can also improve performance. The document also compares vapor absorption to vapor compression cycles.

1. Refrigeration
and
Air-conditioning system
Confederation Of Indian Industry
Energy Management Cell

2. Life cycle cost for A/C systems
• Vapour compression
• Vapour Absorption
Operating Cost 95%
Maintenance/
Consumables 1%
I nitial
I nv. 4%
Operating Cost 89%
Maintenance/
Consumables 1%
I nitial
I nv. 10%
• Life cycle : 15 years
• Cost of electricity :
Rs.3.40/kWh
• Steam Cost : Rs. 450/ton

3. Basic Cycles Vapour Compression
Cycle
Condensor
Evaporator
Compressor
Throttle
valve
Discharge
high pressure
gasHigh
pressure
liquid
Low
pressure
liquid and
flash gas
Suction low
pressure
gas
T1
T2
CHW in
or air in
CHW out
or air

4. Performance
COP = Amount of heat to be taken out
Amount of work required
= T1/ (T2 - T1)
where,
T1 = Evaporator temperature, in K
T2 = Condenser temperature, in K
Therefore,
COP = Maintain at higher T1
or
Maintain at lower T2

5. Effect of evaporator & condenser
temperatures on power
consumption
Decrease in
evaporator
temperature from
5°C to -20 °C
Increase in power
consumption by 89%
(theoretical)
Effect of evaporator temperature for same
condenser temperature
Effect of condenser temperature for same
evaporator temperature
Increase in condenser
temperature from
25°C to 45°C
Increase in power
consumption by 57%
(theoretical)

6. Cold Room
No.2
Deep Freeze
No.1
Cold Room
No.1
Deep Freeze
No.2
Condensor
- 30o
C, 100TR
Segregate high temperature and low
temperature users

7. Utilise less power intensive
cooling medium as far as possible
• Typical power consumption of different
cooling mediums are:
Type of cooling Power consumption
medium (kW/TR)
Cooling water 0.10
Chilled water @ 10°C 0.70
Brine system @ - 20°C 1.80

8. Utilise less power intensive
cooling medium as far as possible
Gas at
600°C
CW at
27 °C
CW at
30 °C
Brine
-16 °C
Brine
-20°C Liquid
at 1°C
HE - 1 HE - 2
Gas at
33 °C

9. Utilise less power intensive
cooling medium as far as possible
Liquid
at 1°C
Gas at
600°C
CW at
25 °C
CW at
30 °C
HE - 1
CHW
12 °C
CHW at
8°C
HE - 2
HE - 3
Brine at
-20°C
Brine at
-7°C
33 °c
15 °c

10. INSTALL ADDITIONAL PLATES AND
OPERATE BREW TRANSFER SECTION
CHILLER
PLATE HEAT EXCHANGER
• TO CHILL BREW FROM 38° C TO 12° C
• BRINE -4° C
• POWER CONSUMPTION 30% HIGHER – BRINE/TR Vs CHILLED
WATER
BREW IN 38 ° C
BREW OUT 12 °
C
BRINE INLET - 4°
C
BRINE INLET 1° C

11. INSTALL ADDITIONAL PLATES AND
OPERATE BREW TRANSFER SECTION
CHILLER
MODIFIED - PLATE HEAT EXCHANGER
• BRINE REPLACED WITH CHILLED WATER
• REDUCED THE RPM OF 25 %
ANNUAL SAVINGS – Rs 10.90 LACS
INVESTMENT – Rs. 5.00 Lacs
PAYBACK – 7 Months
BREW IN 38 ° C
BREW OUT 12 °
C
““CHILLED WATER” 8CHILLED WATER” 8 °
C
Additional Hx
CHILLED WATER 12CHILLED WATER 12 °
C

12. What should be the ideal control
system for R & A/C ?
Control should start at the user point
What are the control systems for
Chilled Brine ?
 2 Port Control
 3 Port Control

13. Install Two Port Valves Instead of
Three Port Valves at Chilled Water
Users
Typically Three Port Valves Used in Chilled Water
Three Port
System
Cold
Well
Hot
Well
Chilled Water User
Chilled Water User
Bypass depending on load
3 - Port
Valve
Quantity
Constant

14. Annual savings = Rs.11.50
lakhs
Investment = Rs.6.00 lakhs
• Installed two port
valves for all users
& VFD for one pump
• One pump operation
stopped completely
• At design stage -
Investment also
comes down
Two port system
Cold Well Hot Well
Chilled Water
User
Chilled Water
User
2 -Port
Valve

15. What Are The Ways Of Capacity
Control of Compressors?
Reciprocating
 Loading / unloading facility
 Variable speed
motors
 Dual speed motors
 On-Off control

16. Variable frequency
Hot gas by pass
Suction throttling
What Are The Ways Of Capacity
Control of Compressors? (continued)
Reciprocating

17. Part Load Control By Gas By-pass
Condenser
Evaporator
Compressor
Throttle
valve
Cooling effect reduction α Fraction of total flow through by pass

18. What Are The Ways Of Capacity Control
of Compressors?
Centrifugal
 Inlet vane control
 Variable speed drives

19. Automatic Unloading/loading For
Refrigeration Compressor At LCP
• Present condition varies from - 7o
C to
-22o
C
• At -22o
C the suction pressure is too low and
compressor capacity utilisation is poor
• Results in higher power consumption per
ton of refrigeration

20. Automatic Unloading/loading For
Refrigeration Compressor At LCP
• Install automatic loading/ unloading in 20TR
and 40TR compressor
• Depending on load choose either 20TR or
40TR compressor

21. Automatic Unloading/loading For
Refrigeration Compressor At LCP
(contd.)
Loading -10o
C Unloading -
15o
C
• Savings - Rs.84,000/-
• Investment - Rs.40,000/-
• Pay back - 6 months

22. Performance Of Compressors
At Part Load
Reciprocating%fullloadCOP
% full load
Twin screw or
centrifugal

23. Which Compressor To Choose?
150 TR 150 TR 150 TR 150 TR
(A) (B) (C) (D)
(A) or (B)
(A) or (B) (C) or (D)
(A) & (B) (C) or (D)
Capacity Base Load Variable Load
150 TR
250 TR
400 TR

24. How do you optimise the number
of compressors in operation?
Operation of a compressor in full load
gives highest COP
In a battery of compressors, micro-
processor controls is the latest trend
Continuously monitor the load of all the
compressors and load optimally

25. Optimise the Cooling Tower Water
across Refrigeration condenser
Refrigeration Condenser
 Measured ∆T across the condenser - 2°C
 Increased to 4 °C – By throttling
 Reduction in pump power – 6.5 kW
 Increase in compressor power – 2.5 kW
 Net reduction – 4 kW
 Savings – Rs 1.28 lakhs

26. kW/TR at various Evaporator
Temperatures
Reciprocating – Full load operation
Evaporator
Temperatures
kW / TR
10°C 0.80
0°C 1.14
-4°C 1.26
-6°C 1.35
-8°C 1.44
-20°C 1.80

27. Comparison of Centrifugal,
Reciprocating & Screw Compressors
Reciprocatin
g
Centrifugal Screw
kW/TR at 10°C
chilled water
temperature
0.8 – 0.9 0.65 – 0.70 0.65 – 0.70
Capacity range > 0.5 TR > 150 TR > 100 TR
Cost
comparison
w.r.t
reciprocating
- 50% higher 50% higher

28. Earlier
• 1 x 120 TR - 83% load (10 out of 12 cylinders
loaded)
• 2 x 60TR - 66% load (6 out of 8 cylinders loaded)
Optimise Refrigeration Compressors
Operation
Modified
• 1 x 120 TR - 100% load & 1 x 60TR - 66% load
• 3rd compressor stopped for 10 months in a year
Annual Savings - Rs.3.00 lakhs (in amps - 28)
Investment - Rs.5.00 lakhs
Payback - 20 months

29. Higher Compressor Discharge
Pressure
• Higher pressure leads to Higher
power consumption
Reasons
Scaling of tubes
Air ingress
Plugged
tubes

30. Lower Suction Pressure
• Results in less capacity
utilisation
• Higher specific power consumption
Reason
• Over design

31. Effect of cooling water system on
refrigeration compressor
• Cooling water temperature
- Cooling water temperature should be as
low as possible
- For every 1°C drop in approach, the
reduction in compressor power : 4
to 5%

32. Effect of cooling water flow on
refrigeration compressor
Typical design ∆T of cooling water (CW) across
condenser : 4 to 10 ° C
30°C 34°C
∆T = 4°C
Refrigeratio
n condenser CW outCW in
High ∆T
- Means less cooling water flow (reduction in
pump power)
- Slight increase in compressor power
• Can be off-set by increase in condenser area

33. CW Flow Optimisation Across
Condensers
• Adjust the valve, such that the temp. rise of
cooling water reaches the design value
• Cooling water requirement drastically comes
down
• Simultaneously, measure the amps of
refrigeration compressor
• Estimate the net saving (reduction in cooling
water pump power minus the increase in
compressor power)

34. 400 m3
/h
Condenser - 1
∆ T = 3-4°C
• If area is double, cooling water requirement
becomes half
Utilisation of two condensers for one
compressor
• Generally, spare condensers are available
• Excellent potential

35. 100 m3
/h
Condenser - 1
∆ T = 6-8°C
100 m3
/h
Condenser - 2
∆ T = 6-8°C
Utilisation of two condensers for
one compressor

36. Replace Conventional Shell & Tube
Type Ammonia Condensers with
Evaporative Condensers
 Evaporative condenser – latest
technology
Vapour condensing
 Operating cost very low ∼ 20% of ST
condenser

37. Replace Conventional Shell & Tube
Type Ammonia Condensers with
Evaporative Condensers
 Features
 Improved water to air contact within coil
 Greater water flow rate over coil
 Enhanced heat transfer η
 Lower condensing temperatures
 Reduced system power

38. Case Study
Existing System
MC Brine
compressor (204
m3
/hr x 2 no.s)
408 m3
/hr
MC Brine APV (1 no) 193 m3
/hr
MEG Brine 200 m3
/hr
Total cooling water 801 m3
/hr

39. Case Study
Modified – After
EvapcoOne cooling tower stopped – 600 m3
/hr
Power Savings
Pumps 2 nos. x 75 kW + 1 no. x
30 kW
180 kW
Fans 3 nos. x 7.5 kW 22.5 kW
Total 202.5 kW
MC Brine – Fan + Pump
(How)
(7.5 + 1.5) kW x 2 18 kW
MC Brine – Fan + Pump
(APV)
(7.5 + 1.5) kW x 1 9 kW
MEG Brine – Fan + Pump (7.5 + 1.5) kW x 1 9 kW
Total 36 kW

40. • Centrifugal compressors
- Energy efficient
- Less maintenance prone
• kW/TR comparison
- Centrifugal : 0.65 to 0.80
- Reciprocating : 1.00 to 1.20
• Centrifugal ideal for high capacities
(say 200TR and above)
Replace Reciprocating Compressors
With Centrifugal Compressors

41. Replace Reciprocating Compressors
With Centrifugal Compressors
• Better to incorporate at initial stage
• 200TR reciprocating compressor replaced
with centrifugal compressor
Savings - Rs. 15.00 lakhs
Investment - Rs. 50.00 lakhs
Pay back - 40 months

42. Approach for energy savings in
cooling tower pumps
Typical reasons for excess power consumption
• Excess capacity
• Excess head
• Under loaded process
Approach is different from conventional pumps
• Unique approach

43. • Excess cooling water flow on account of over-
sizing - May go unnoticed
Heat exchangers designed with following ∆T’s
Criteria for estimating excess flow
- Temp. difference (∆T) between supply and
return water across heat exchanger
Air compressors : 10°C
Process applications : 5-10°C
Turbine condensers : 10°C
Refrigeration condensers : 7-8°C

44. Phase - I
• Fix the required header pressure
- Pressure meter to be fixed
• Measure the inlet and outlet cooling water temperature across
condensers
- By comparison of measured ∆T with design ∆T, flow is
sufficient or excessive
• Select the condensers, where ∆T is less than design value
- Throttle the delivery side valves of the
condensers, till the design ∆T is achieved

45. • While throttling valves, process conditions to be monitored
continuously
- Increase in header pressure
• Pump delivery valve to be throttled to maintain the required
header pressure
- Optimum cooling water requirements will be
achieved
• Partial energy savings can be achieved with the steps in
phase - I

46. Phase - II
• Critical condensers to be studied for their Log Mean Temp.
Difference (LMTD)
- Heat transfer area can be increased
• Estimate cooling water requirements after increasing the areas
• Install correct size pumps (matching capacity and head)
- Possible to tap full savings potential

47. • Alternatively, a VFD can be installed for the existing pumps
- Can be operated at lower speed
- ∆T across condensers as the control
parameter
• Combination of Phase - I and Phase - II to be attempted
- Will result in maximum energy savings

48. Vapour Absorption Cycle
Condensor
Evaporator
Throttle
valve
Absorber
Generator
Weak
Stron
g
Hea
t

49. SINGLE EFFECT TYPE

50. Vapour Compression vs
Vapour Absorption
• Air conditioning load : 200TR
• Recip. comp. consumption : 220 kW
• Double effect VAHP selected
• Specific consumption : 4.5 kg/TR
• Steam requirement : 0.9 TPH

51. Vapour Compression vs
Vapour Absorption
• Vapor comp. oper. cost : Rs.60 lakhs/yr
• VAHP operating cost : Rs.22 lakhs/yr
(live steam cost @Rs.300/Ton)
• Savings : Rs.38 lakhs/yr
• Investment on VAHP: Rs.60 lakhs
• Simple pay back : 1.6 years

52. Details VAC VAHP
Capacity 65TR 65TR
Steam consumption Nil 325 kg/hr
Steam cost Nil Rs.152/hr
Electricity consumption 72 kW 3 kW
Electricity cost Rs.216/hr Rs.9/hr
Total cost Rs.216/hr Rs.161/hr
Capital cost Rs.10 lakhs Rs.20 lakhs
Vapour Compression vs
Vapour Absorption

53. • Annual savings - (216 - 161) Rs./hr
x 8000 hrs/yr
- Rs.4.40 lakhs
• Investment(differnce)- Rs.10.00 lakhs
• Pay back - 2.2 years
• Going by initial cost alone is
misleading
Vapour Compression vs
Vapour Absorption

54. Possibilities at Coke
Optimisation Chilled Brine
Temperature Present Operating Temperature -2° C
 Is it possible to increase temperature ?
 CO 2 Absorption ?
 Higher Operating Temperature
-2 ° C 1.20 KW/TR
-4 ° C 1.26 KW/TR
-6 ° C 1.36 KW/TR

55. Possibilities at Coke …
Replacement with Screw Chiller With VFD
 Lower KW/TR – 25 % Lower
 Lower Loads – KW/TR Nearly Same
 Chiller at Coke
33 % ____ KW/TR
66 % ____ KW/TR
100 % ____ KW/TR

56. Possibilities at Coke …
Chilled Brine Pumping System
– Any Possibility
 3 Port Valve
 Conversion to 2 Port System
 VFD – For Tapping Full Savings

57. Possibilities at Coke …
Conversion of Chilled Brine System
– One Pass
 Possible ?
 What Advantages ?
 Equipment Reduction
 Pump Energy Saving
 More Chilled Brine Storage

58. Possibilities at Coke …
Cooling Water Use In Chiller Condenser
 Operating “ T” – ie.,
 Design “ T” - ?
 Any Possibility ?

59. At Coke …
Develop a Template for Monitoring
Month Pump
(kW)
Compre
(kW)
Chilled water
temp (°C)
Amb. Temp
(°C)
01.01
02.01
03.01
04.01
05.01

60. Thank you