ENERGY CONSERVATION STRATEGIES FOR HVAC SYSTEMS V.P. Gupta

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ENERGY CONSERVATION STRATEGIES FOR HVAC SYSTEMS
V.P. Gupta, Principal Chief Engineer
(Electrical) Bharat Sanchar Nigam
Limited Tamilnadu Electrical Zone (An ISO
90012000 Unit)
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INTRODUCTION

• For Telecom Buildings, Exchange Equipment is
  compact but more powerful, fragile and very
  sensitive to high temperature.
• It is necessary to provide high reliable AC
  Systems
• HVAC Systems consume 50-60 of total power Thus
  huge potential for Energy Saving
• Innovative strategies can be applied to reduce
  Energy Bills

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INNOVATIVE STRATEGIES

• Building Orientation/Architectural Features
• Establishing Baseline Performance Indices
• High Sensible Air-Conditioning System
• Package AC Units -
• 7 TR
• 2x1.5 TR 2x2 TR
• Automation BMS
• Variable Voltage Variable Frequency Drives

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INNOVATIVE STRATEGIES

• Heat Recovery Wheel /Desiccant Cooling
• System for Fresh Air
• Panel Cooling
• Vapour Absorption Machines
• Roof Top Chillers
• Free Cooling or Cooling by Total Air Displacement

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Building Orientation/ Architectural Features

• Points to be considered
• Orientation
• Double Glass Panels
• Insulation on Roof
• No Leakage from Windows/Doors/Ceiling/Return Air
• Long side should be having minimum heat gain.
• Minimum heat gain from NORTH
• EAST
• SOUTH
• WEST

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Building Orientation/ Architectural Features

• Plant Room and AHU locations should be such that
  ducting/ piping are minimum.
• Sufficient Fresh Air Intake to avoid Sick
  Building Syndrome
• Sun Shades over glass area with proper
  inclination to avoid direct sunrays.
• Partitions and closure of air grills of
  unutilized conditioned space.

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Establishing Baseline Performance Indices

• Points to be considered
• Space Temperature (23-26C) - Task Non-Task,
  Eqpt. Room etc. (against earlier 20-26C)
• Space Humidity 30-70 (against earlier 40-60)
• Usage Time Schedule - Working Hours, Holidays
  etc.
• P.F. target 0.95, rationalise contract demand and
  A/C space.

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Establishing Baseline Performance Indices

• Total tons at worst conditions
• - At Machine End
• - At User End
• Tons / Sq. Meter
• KW / Ton
• KWH / Day
• KWH / Year

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High Sensible Air Conditioning System

• Specially designed AC Package Units to handle a
  high sensible heat factor of 0.95
• Liberal Evoporation and Condensor Coil Area
• Higher Saturation Temperature
• Higher CFM
• Air-Cooled Condensers with two/variable Speed
  Motors
• Condenser fan motor stops completely when
  compressor is stopped

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High Sensible Air Conditioning System 7 TR

• Package AC provided with dehumidification
  mechanism by reducing effective coil area to
  2/3rd whenever dehumidification is required.
• Control system enables a solenoid valve to cut
  off 1/3 of cooling coil providing a lower
  evaporating temperature and dehumidification
  without any heating
• Saving of precious electrical energy. Constant
  airflow maintained even during dehumidification

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High Sensible Air Conditioning System 2x1.5TR

• Recently Approved for Ph. V Tenders
• Highly Energy Efficient unit with Build-in
  Timers, Microprocessor Controllers to Switch from
  Active Units
• Stand-by Units and back
• Designed for continuous 24 X 7 Operations

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ENERGY CONSUMPTION RECORD / SAVING COMPARISON
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PAYBACK CALCULATION
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ASSUMPTIONS TEST PARAMETERS
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HIGH SENSIBLE AC UNITS

• Comfort type Split AC is designed at 35C
• Hi Sensible AC is designed at 43C.
• Energy saving at temperatures higher than
  35C will be even greater on using Hi Sensible
  AC unit.

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ENERGY EFFICIENCY OF SPLIT AC UNITS

• EER is the Ratio between Cooling Capacity of AC
  Unit in Kcal/Hr and Power input to AC Unit in
  Watts
• EER Output in Kcal/Hr
• Power input in Watts

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Capacity 1.5 TR Split AC Unit
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Automation and BMS

• Ensures Optimum Operation of all machines by
  avoiding energy wastage due to overcooling /
  overheating
• CO2 Sensors to control ventilation in response to
  varying people load by controlling damper
  operation
• Programmed Start/Stop of AC M/s, Ventilation
  System, Chiller, etc.
• Run-time equalisation auto adjustment of set
  points

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VARIABLE SPEED DRIVES (VV-VF)

• Step less variation of Fans, Pumps and compressor
  speed in tune with load reqmts can be achieved
  with VV-VF Drives.
• Power Consumption in Pumps/Blowers is
  proportional to Cube of Speed, eg. At 80 speed,
  power consumption is cube of 0.8 or 0.512 or
  51.2
• Reduction in mechanical wear and tear as motors
  run at low speed. Results in additional saving
  in maintenance cost.

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Variable Speed Drives (VV-VF)
The power consmp proportionality can be
explained from Affinity law governing fluid flow
Flow (F) œ Speed (N) Pressure (P) œ Square of
speed (N2) Power (E) œ F x P or N3
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Variable Speed Drives (VV-VF)

• VVVF system basically consists of a input
  rectifier and an inverter connected through a
  controller.
• V/f ratio is kept constant throughout the
  operating range of the motor to maintain torque.
• Performance depends on location and accuracy of
  sensors providing load demand feedback.

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Variable Speed Drives (VV-VF)

3 Ph Supply





DC REACTOR




L






RECTIFIER

M

O

INVERTER

CAPACITOR

SECTION


A



D









MOTOR










MAIN


CONTROLLER





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Heat Recovery Wheel/ Desiccant Cooling

• Induction of fresh air into building is necessary
  to reduce Sick Building Syndrome
• ASHRAE 62-99 specifies 20 cfm of outdoor air per
  person.
• Creates additional load on A/C system
• Desiccant cooling helps in reducing the
  additional load due to fresh air (applicable for
  areas with 80-90 humidity throughout year)

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Heat Recovery Wheel / Desiccant Cooling

• The wheel is positioned typically in the duct
  system so that return air is drawn through its
  one half and outdoor air is drawn through its
  other half in a counter flow pattern.
• The wheel is rotated at 2 to 20 rpm
• Sensible heat is transferred as the metallic
  substrate picks up and store heat from the hot
  air steam and gives it up to the cold one.
• Latent heat is transferred as the desiccant on
  the wheel absorbs moisture from the higher
  humidity air stream and releases the same into
  the air stream that has a lower humidity ratio

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Heat Recovery Wheel / Desiccant Cooling

• Capable of recovering 80 of heating or cooling
  energy exhausted from building and reduces energy
  cost of fresh air.
• Enthalpy wheel is usually 4 to 10 deep packed
  with a heat transfer medium i.e. numerous small
  air passages or flutes parallel to direction of
  air flow. This honeycomb matrix is produced by
  interleaving flat and corrugated layers of a high
  conductivity material usually aluminium surfaced
  with a desiccant.

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Heat Recovery Wheel / Desiccant Cooling
Universal Rules of Total Energy Wheels
1. Heating/Cooling Energy (e.g. 80) Is Always
Returned To Where It Came From
Heat In
Cooling Energy Out
Heat Out
Cooling Energy In
2. Moisture and Dry Air (e.g. 80) Is Always
Returned To Where It Came From
Moisture In
Dry Air Out
Moisture Out
Dry Air In
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Heat Recovery Wheel / Desiccant Cooling
UNIVERSAL HEAT RECOVERY ENERGY WHEEL
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Panel Cooling

• The telecom equipment heat load is only 40 and
  another 60 heat load is due to the surrounding
  space/ room. Due to shrinkage of equipment size,
  improvement in technology , the exchanges are not
  required to be manned.
• Substantial energy saving is possible by
  mounting small panel coolers instead of window/
  split AC units only for cooling the switching
  equipment and not the entire room.

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Panel Cooling

• Panel cooler - a mini AC unit delivering a
  fractional TR,directly clamped to eqpmt panel
  with a close loop air cycle so as to cool the
  space within the equipment.
• Power consumption - only 2.7 KW against earlier 6
  KW with 3 number window AC units.
• On experimental basis a Pilot Project has been
  carried out in Hyderabad.
• Requires further studies. Vendors to come forward
  for optimum solution.

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Vapour Absorption Machines

• VAM uses primary energy in the form of heat viz.
  Steam, CNG, HSD, Kerosene and superior Kerosene.
  (Whereas VCM uses secondary energy in the form of
  electricity.)
• VAM uses Lithium Bromide as absorbent and water
  as refrigerant.
• Becoming popular due to

• High cost of secondary energy. Easy avail. of gas
  
• Noiseless, No Moving Part, Low Cost of Mtce.
• Uncertainty in view of CFC phase-out

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Vapour Absorption Machines - Principle
of Operation
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Roof Top Chillers

• Costly built up space inside the building can be
  saved used as they can be mounted on the roof.
• All components like Compressor, Compressor
  Motor, Evaporator, Chiller and Air Cooled
  Condenser along with the micro-processor based
  control panel forms part of the roof top chiller
  and are highly compact.
• A considerable saving of energy as the
  refrigerant pipes become very small

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Roof Top Chillers

• Factory made and designed with best of
  components.
• All the protecting device and safeties are
  factory fitted and thus, ensure high level of
  reliability.
• The microprocessor based panels monitor the set
  points precisely and thereby, save energy.
• Designed with energy efficient scroll or screw
  compressors.

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Free Cooling or Cooling by Total Air Displacement

• Whenever ambient dry bulb temperature is in
  between 16 to 20 C, cooling of inside space can
  be achieved by total displacement of inside air
  with the fresh air
• When the temperature is in between 11 to 16 C,
  a of mixture of return air and ambient air can
  give the required inside conditions
• In both cases, the ambient air needs to be 100
  filtered

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Free Cooling or Cooling by Total Air Displacement

• Dampers in both the cases to be operated with
  suitable sensors for free cooling.
• Mechanical Refrigeration is needed only when the
  ambient temperature is more than 20C.
• Free cooling assures power saving of about 80,
  we require power only for the operation of fans
  for exhaust and circulation of air.
• Manufacturers have to come forward to fine tune
  Filters, Sensors and Control of Dampers.

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Free Cooling or Cooling by Total Air Displacement
D1 DAMPERS
D2
RETURN FILTER COOLING
FAN COND. AIR COIL
SPACE PLENUM
  EXHAUST RETURN
AIR TO ATMOSPHERE
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Conclusion
The above strategies can be suitably applied for
optimization of airconditioning system and energy
savings. Manufacturers/Vendors to come forward
for providing optimum solution with Panel Cooling
and Free Cooling Strategies.
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Thank You