Energy Saving Options

1
Energy Saving Options

• Electricity

2

• Electricity Generation

3

• Electricity Generation

During Electricity Generation, thermal energy is
converted to work. The process is subject to
the Carnot principle
4

• Carnot Principle

Heat Supplied, Qs at Ts
W Qs -Qr Efficiency W/ Qs Qs -Qr
Qs (Q m cp T) So, Efficiency Ts -Tr
Ts
Work, W
Heat Rejected, Qr at Tr
(Temperatures in degrees K)
5

• Efficiency Heat to Work

If Ts 600oC (steam) 873 K and
Tr 350 oC 623 K Efficiency
873 - 623 873 28.6 Thus,
71.4 of the heat energy is rejected to the
environment
Heat Supplied, Qs at Ts
Work, W
Heat Rejected, Qr at Tr
(Temperatures in degrees K)
6

• Supply Capacity

7

• Supply Capacity

The maximum kVA that can be taken from an
electricity mains supply cable is limited by a
fuse. Utilities charge a fixed amount monthly
for each kVA of available supply capacity
8

• Maximum Demand

9

• Maximum Demand

The kVA being taken by the supply cable is
measured continuously, or at given intervals.
The user pays a premium to the electrical
utility according to the maximum value of kVA
(the maximum demand) which occurs during the
month
10

• The Reduction of Maximum Demand

The user should monitor the kVA readings to
ascertain when the peak occurs and its magnitude
11
The user will then be in a position to reduce
maximum demand charges by

• identifying activities that contribute to maximum
  demand
• rescheduling activities that occur at maximum
  demand time (peak lopping)
• staggerong start-up times
• using stand-by generators to peak-lop
• maximising power factors
• switching-off plant when not required

12

• The Reduction of Maximum Demand

It should be noted that each kW saved by
electricity conservation, also saves 1 kVA of
maximum demand charges
13

• Electric Motors and Variable Speed Drives

14

• Electric Motors

Both the efficiency and the power factor of an
electric motor vary with the load The largest
potential savings with electric motors is to
match motor to load so that the motor runs at
maximum efficiency
ac
15

• Electric Motors

A survey of all motors at a site should be made
and efficiencies estimated. Those motors which
are too large should be changed. Many times this
involves swapping motors around the plant and
buying only a few new motors
ac
16

• Variable Speed Drives

In situations where the load on the
motor fluctuates, the use of variable
speed drives should be considered to avoid large
heat losses at lower loads
ac
17

• Fans and Ducts

DUCT
AIR
FAN
18
Fans and Ducts
Power flow rate of fluid x specific volume
of fluid x pressure rise across fan /fan
efficiency
ac
19
Fans and Ducts

• To Reduce Power Requirements

1. Reduce flow-rate of fluid 2. Decrease pressure
drop in the duct
ac
20
Fans and Ducts

• Flow Control can be achieved in two ways

1. A damper can be used to restrict the
flow 2. The fan speed can be altered
ac
21
Fans and Ducts
Reducing Head Losses (Pressure Drops)

• Minimise
• bends and elbows
• restrictions, filters, dampers
• and frictional forces

22

• Pumps and Pipes

PIPE
LIQUID
PUMP
23
Pumps and Pipes

• feed water pumps
• chilled water pumps
• condensate return pumps
• oil pumps
• process fluid pumps
• cooling tower water pumps

24
Pumps and Pipes
Power flow rate of fluid x specific volume
of fluid x pressure rise across pump / pump
efficiency
ac
25
Pumps and Pipes

• To Reduce Power Requirements

1. Reduce flow-rate of fluid 2. Decrease pressure
drop in the pipe
ac
26
Pumps and Pipes

• and similarly, Flow Control can be achieved in
  two ways

1. A flow control valve can be used to restrict
the flow, just as a duct damper 2. The pump
speed can be altered just as the fan speed
ac
27
Pumps and Pipes

• Considerations of selecting optimal pumps and
  speeds to match pipe flow rates are exactly as
  for fans and ducts.

28
Reducing Head Losses (Pressure Drops)
Pumps and Pipes

• Minimise
• bends and elbows
• restrictions, orifices, valves
• vertical rises
• frictional forces

29

• Compressors

30

• Compressors

Work in pressure energy change in
internal energy m cp dT pV m cv dT m cp
dT m R dT m cv dT cp R cv for
air, 1005 287 718 J/kg K
m mass of gas cp,cv specific heats at
constant pressure and volume p pressure dT
change in temperature R characteristic
gas constant
31
Compressors
Thus 1005 units of work are required to produce
287 units of pressure energy, even at
100 efficiency of compression. Furthermore, the
work (electricity) has been produced in the
first place in the conversion of heat to work
at 30 efficiency.
32
Compressors
So it requires at least 3350 units of heat
energy to produce 287 units of pressure energy,
or 11.7 units of heat for 1 unit of pressure
energy.
33
Compressors
Compressed air is the most expensive energy
commodity and should only be used as a last
resort. Question every use for compressed
air. It certainly should not be used for swarf
blowing and cleaning purposes.
34
Compressors

• check conditions of plant
• check efficiency
• check position of inlet duct
• check maintenance procedures
• check control arrangements
• check the amount of compressed gas supplied
• check delivery temperature and pressure
• check for leaks

35
Compressors

• check uses for compressed gas
• check pressures at points of use
• reduce generating pressure to minimum
• consider interstage cooling
• consider interstage bleed-off at different
  pressures
• consider the use of localised booster
  compressors
• switch off compressors when not in use

36
Compressors

• consider the introduction of compressed gas
  accumulation so that off-peak electricity can be
  used or to peak lop maximum demand
• use outside air/water for cooling/intercooling
• recover heat from cooling and intercooling

37
Compressors

• avoid condensation and concomitant blockage of
  pipelines
• reheat compressed gas to increase discharge
  pressure
• meter compressed air usage
• look for heat recovery opportunities

38
Lighting
39
Lighting

• check zonal lighting requirements
• zone lighted areas
• check that parts of the building are not being
  lit unnecessarily
• use infra-red detectors/time switches
• check the maintenance procedures
• replace lamps when their efficiency drops
• check lighting controls
• use automatic controls

40
Lighting

• challenge the need for large areas of glazing
• eliminate glazing
• obtain economic balance of artificial lighting
  and day-lighting
• use separate circuits for day-lighted peripheries
• use separate circuits for use outside working
  hours

41
Lighting

• check colours of room surfaces
• check conditions and cleanliness of luminaires
  and windows
• keep windows and roof-lights clean
• avoid dark background colours
• never use low-efficiency filament lamps
• use low-energy fluorescent or discharge lamps
• look for heat recovery opportunities

42
Refrigeration and Air Conditioning
43
Refrigeration and Air Conditioning

• check maintenance and operating procedures
• evaluate load patterns and operating cycles
• check conditions of plant and equipment
• check for and seal leaks
• check insulation levels and conditions of
  insulation
• consider the use of thermal (cold) storage

44
Refrigeration and Air Conditioning

• check operation of condenser fans
• check cleanliness of heat transfer surfaces
• check water treatment systems
• check cooling tower operation
• check control arrangements
• check operating temperatures and pressures
• look for heat recovery opportunities

45
Refrigeration and Air Conditioning

• Select proper design points - temperature and
  humidity - thermal comfort chart
• Select minimum airchange rates - vent off
  pollutants at source
• check control arrangements
• check that heating and cooling systems cannot
  conflict
• reduce heating and cooling loads
• check zonal requirements

46
Refrigeration and Air Conditioning

• check for unoccupied areas
• consider zoning, partitioning, false ceilings and
  destratifiers
• minimise infiltration
• look for opportunities for heat recovery
• check insulation levels
• isolate system from the surroundings

47

• On-site Cogeneration

48

• On-site Cogeneration

Examine the annual heating and power
requirements for the site and consider whether
the on-site generation of power with use of the
heat generated might be an economic option. Such
a system could also produce refrigeration via an
absorption refrigeration system using the heat
rejected from the power generator