Saving Ventilation Dollars A Look at Economics of Ventilation

Saving Ventilation Dollars2 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.

Saving Ventilation Dollars3 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

Saving Ventilation Dollars4 Reducing Air Flow Saves Money

Saving Ventilation Dollars5 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  Compare with ACGIH manual recommendations Eliminate unnecessary ventilation  Like outdated installations and those rendered useless due to change in processes

Saving Ventilation Dollars6 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

Saving Ventilation Dollars7 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

Saving Ventilation Dollars8 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

Saving Ventilation Dollars9 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)

Saving Ventilation Dollars10 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 Designing New Systems to Save Money

Saving Ventilation Dollars11 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

Saving Ventilation Dollars12 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