Saving Ventilation Dollars

1
Saving Ventilation Dollars

• A Look at Economics of Ventilation

2
The Best Engineering Solution Is an Economical
Solution

• Ventilation cost factors
• Sources of expenditures
• Capital costs for hoods, ducts, air cleaners, fan
• Power (operating costs) for fan and air cleaner
• Cost of heating or cooling replacement air
• Maintenance of fan, labor costs, servicing etc.

3
Reducing Air Flow Saves Money

• Methodology
• Reduce air flow rates to minimum value
• Reduce flow rate by proper hood selection
• Choose heads that controls contaminants with
  minimum flow and gives access with flexibility
• Refer to the figure on the next slide

4
Reducing Air Flow Saves Money

5
Reducing Air Flow Saves Money

• Existing systems
• Locate each hood, determine type and airflow.
• Compare with ACGIH manual recommendations
• Eliminate unnecessary ventilation
• Like outdated installations and those rendered
  useless due to change in processes

6
Reducing Air Flow Saves Money

• Modify processes
• E.g. Use sulphuric acid bath instead of chromic
  acid since contaminants are less toxic and one
  third less ventilation needed hence.
• Replace dilution ventilation with local exhaust
• If practical

7
Reducing Air Flow Saves Money

• Correct poor fan inlets
• Spinning or uneven air flow reduces ability of
  the fan to move air
• Avoid sharp ducts, elbows, narrow duct diameters,
  small slots in hoods

8
Reducing Air Flow Saves Money

• Recirculate exhausted air
• -Effective for large systems where cleaned
  exhaust air can be recirculated
• -Supply of untempered make - up air to booth or
  enclosures

9
Designing New Systems to Save Money

• Reduce airflow
• Try to use enclosures or low flow hoods
  distribute receipt of air by each hood
• Install two smaller fans for each unit instead of
  a common one
• Use of dampers during ideal time
• Reduce airflow resistance
• An air cleaner for e.g. Causes air resistance so
  do scrubbers, filters or carbon beds
• High hood slot or high duct velocities cause
  pressure losses (velocity to loss factor 4)

10
Designing New Systems to Save Money

• Long runs of narrow ducts
• Should be avoided since high pressure drop
  increases resistance
• Locate fans near high suction ducts
• High pressure loss ducts need suction to overcome
  resistance, suction is greatest near the fan
  inlet
• Balance capital and operating costs
• Fan costs increase with increase in air-flow,
  duct capital costs rise with increase in
  diameters to lower resistance, however give
  priority to efficiency

11
Some Other Means and Methods

• Systems with varying air flow
• Installation of dampers in ducts to artificially
  reduce air flow
• Installation of fan inlet dampers or a motor
  speed controller to reduce work of fan on air
• Saving on maintenance
• Provide screenings to hood openings to prevent
  sucking of rags and small machinery parts
• Regularly clean ducts to prevent plugging from
  dust settling in ducts
• Careful placement and shielding of ventilation
  hoods and ducts

12
Calculating Cost Factors

• Aim is to balance capital and operating costs
• Involves calculation of following costs for
  comparison and as decision making aids
• Duct costs
• Fan costs
• Air cleaner costs
• Heating and cooling costs etc