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Ask the Expert: HVAC Ventilation O&Ms and FIMs

Posted by Danielle Marquis

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October 1, 2015 at 6:17 AM

Question: How can I improve the energy efficiency of my facility's HVAC ventilation?




Answer: HVAC ventilation issues, which include problems with air flow and temperature control, can take several forms. An energy audit will typically identify energy inefficiencies in one or several of the following areas:


  • Air flow to space feels unusually low or is inconsistent from one space to another
  • Large spaces having low occupancy are maintained at comfort conditions
  • Heating/cooling equipment is operating in lobbies, corridors, vestibules and/or other public areas
  • An excessive quantity of outdoor air is used to ventilate the building
  • Outdoor air intake dampers open when building is unoccupied
  • Return, outdoor air and exhaust dampers are not sequencing properly
  • Ventilation systems are not utilized for natural cooling capability
  • Exhaust system operation is not programmed
  • Air filters and heating/cooling coils do not receive scheduled maintenance
  • Duct or pipe insulation is damaged or missing
  • Fan drive belts deflect excessively
  • Air leaks from ducts or plenums are noticeable


The suggested operations and maintenance ("O&M") improvements and facility improvement measures ("FIM") will vary based on your facility's unique mix of inefficiencies, but what follows are some general guidelines.


Suggested HVAC Ventilation O&Ms:


  • Utilize ductwork access openings to check for any obstructions such as loose hanging insulation (in lined ducts), loose turning vanes and accessories, and closed volume and fire dampers. Adjust, repair or replace as necessary.
  • Inspect all room air outlets and inlets (diffusers, registers and grills). They should be kept clean and free of all dirt and obstructions. Clean and remove obstructions as necessary.
  • Clean or replace dirty or ineffective filters on a regular basis.
  • Post signs instructing occupants not to place objects where they will restrict air flow.
  • Rebalance system.
  • Reduce overall ventilation in large, low-occupancy spaces.
  • Consider regrouping activities into smaller areas, which can be conditioned separately from remainder of building.
  • Lower heating set points in public areas if there is no possibility of freeze-up. Disconnect electrical heating units (or switch off at breaker box). Maintain ventilation.
  • Close HVAC supply ducts serving public areas.
  • Reduce outdoor air quantity to the minimum allowed by codes by adjusting outdoor air dampers during hours of occupancy.
  • Repair any malfunctioning ventilation equipment.
  • Close outdoor air dampers when building is unoccupied. Be sure dampers have proper seals and adjust to ensure complete closure.
  • Where codes permit, close outdoor air dampers during first and last hours of occupancy to permit fast warm-up and cool-down.
  • Adjust damper linkage.
  • Be sure damper motors are operating properly.
  • Readjust position indicators to accurately indicate damper positions.
  • Reset linkage, repair or replace dampers if blades do not close tightly.
  • Close all outdoor air intake dampers when equipment is shut off and when building is unoccupied.
  • Whenever possible, use outside air for cooling rather than using refrigeration. Use economizer cycle, if available. 
  • Discontinue use of unnecessary exhaust fans.
  • Re-wire restrooms' exhaust fans to operate only when lights are on.
  • Establish schedules so that exhaust fans run only when needed.
  • Group smoking and other areas with similar exhaust requirements so that they may be served by one exhaust system. Reduce ventilation in remaining non-contaminated areas.
  • Develop a maintenance schedule.
  • Install filter pressure-drop gauges.
  • Repair, replace and protect damaged and/or missing pipe insulation.
  • Adjust fan belt tension.
  • Repair leaks.


Suggested HVAC Ventilation FIMs:


  • Properly adjust and balance air/water systems and controls.
  • Replace old style dampers with new high quality opposed-blade models with better close-off ratings.
  • Repair leaking or failed dampers.
  • Install controls which will automatically close dampers during unoccupied periods.
  • Install an economizer cycle with enthalpy control to optimize use of outside air for cooling.
  • Install window switches on operable windows interlocked to disable heating/cooling units so that high rise residents can get fresh air without over-running the HVAC


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Topics: CII Division, Frequently Asked Questions, HVAC Controls


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