Saving Ventilation Dollars

A Look at Economics of Ventilation

Saving Ventilation Dollars 2

The Best Engineering Solution Is an Economical SolutionVentilation 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 Dollars 3

Reducing Air Flow Saves MoneyMethodology

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 Dollars 4

Reducing Air Flow Saves Money

Saving Ventilation Dollars 5

Reducing Air Flow Saves MoneyExisting 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Eliminate unnecessary ventilation Like outdated installations and those rendered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 Dollars 6

Reducing Air Flow Saves MoneyModify 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 Dollars 7

Reducing Air Flow Saves MoneyCorrect 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 Dollars 8

Reducing Air Flow Saves MoneyRecirculate 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 Dollars 9

Designing New Systems to Save MoneyReduce 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 timeReduce 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 Dollars 10

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 Dollars 11

Some Other Means and MethodsSystems 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 Dollars 12

Calculating Cost FactorsAim 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