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Diagnostics – Case Study 1


Client Need

Provided an indoor air quality survey of an existing 27,000 SF building space utilized as an administration area. The area is divided into private offices that average roughly 200-300 SF each. Occupants had complained about noise and particulate issues in their spaces.


  • Surveyed all relevant HVAC systems serving occupied spaces.
  • One to three offices served by a single, ducted fan coil unit that provides both heating and cooling functions with downstream terminal electric re-heat.
  • Fan coil units installed above the ceiling with return air plenum above ceiling.
  • Return air path included return air grilles in ceiling and lined transfer ducts connecting adjacent return air plenums.
  • Make-up air distributed to the back of each fan coil unit from a central make-up air unit where it is filtered, cooled, dehumidified and heated as necessary prior to discharging to the return section of the fan coil unit.
  • The fan coil units had low-efficiency spun glass insulation filters, dual forward curved fans, and a single coil used for both heating and cooling (2-pipe change over system).
  • The fan coils discharged into a ducted supply system with individual electric re-heat coils serving each space.
  • The closed cell foam liner inside the units was mostly deteriorated or gone with remaining liner easily crushed to dust.
  • Multiple leaks found on both sides of fan coil units, bypassing air around the filter and discharging air prior to attached ductwork- loss of efficiency.
  • Reviewed balancing reports which showed the quantity of make-up air exceeded design by approximately 40%.
  • Upon further review, changes to original sequence of operation for the make-up air unit reduced dehumidification effectiveness further reducing overall fan coil efficiency. Make-up air was not sufficiently dehumidified prior to delivery to fan coils.

Recommendations and Benefits

  • Provided client with multiple options for remediation based on different budgeting scenarios, moving forward with selected option.
  • Option #1: Upgrade the individual components in place including new higher quality fan coil units, higher efficiency supplemental filters, and refurbishing the existing make-up air handling unit including modification of existing controls.
  • Option #2: Replacement of the entire system including higher quality air and hydronic system including custom air handling equipment specifically engineered to reduce noise and vibration, reduce particulate significantly relative to current levels, improve both temperature and humidity control and improve overall system efficiency and operating costs.

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