GG Dehumidification Coil Condensation

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go to Labs Sessions - Q1 2015

  • Prep - Overview
    • Email request from Tom Brennan to investigate as follows:
      • "We have a need for the Labs group to make a recommendation for how to deal with the condensation coming off the bottom of the dehumidification coil.
      • The issue is there is condensation coming off the drain pan on the dehumidification coil when the outdoor humidity gets very high.
      • We're looking for an effective, low cost answer. A complete redesign is not possible.
      • Would like to address this in June before the humid weather gets here."
    • J Gallagher observations from past summers also recorded below.
  • Hands-On
    • Visual observation for signs of past moisture
      • Rust on outside of coil/drain pan section
      • Some white residue on wood from water on floor in Annex
    • Activated dehumidification mode
      • Dehumidification activated, but Altherma not coming on
      • Communication to Altherma failed, low water alarm indicator communication failed
      • Traced back and found GFI in bathroom was tripped; power to I/O module is from power outlet in Janitor's Closet that is connected to same GFI
      • Reset breaker and power came back on; Altherma functioning
      • Time clock on Jace scheduling was another 2 hours off; set ERV schedule two hours later so ventilation on during occupied hours
    • Screenshot of system taken during thermal imaging of coil, noting Outside Air T/RH and Annex T/RH
    • Thermal imaged coil / duct area to check for extent of colder areas
    • Checked duct joints / coil drain pan for moisture leakage - indoor conditions not humid enough to cause condensation yet
      • Rust at border between drain pan and coil near bottom of section
      • Listened for air leakage; does not appear to be an issue
  • Brain Work
    • Analyzed thermal imaging
      • No extreme cold spots shown
    • Observations
      • Water on floor in Annex observed mid-July to end of August, generally
      • Condensation is worst during weekend recirculation dehumidification cycle
      • Coil pan was not originally sloped to drain correctly; improved by adjusting hangers for better slope, but still an issue
      • Condensation only observed in bottom area of coil drain pan where cold water collects, not around air duct area
    • Ideas Discussed
      • Secondary drain pan under coil drain pan with more definite slope (additional cost, might still condense on new pan)
      • Fabricate new coil drain pan with better slope and dimensional control to manage condensation collection (additional cost, might still condense on high humidity days)
      • Externally insulate drain pan where condensation occurs (minor cost; recommended option)
    • Recommendations
      • Insulate sections where condensation occurs with self-adhesive elastomeric insulation, minimum of 1/2" thick
  • Conclusions - Suggestions
    • Provide access panel upstream / downstream of coil for cleaning coil and drain pan and for observing duct, coil, and air conditions
    • Add note about GFI in bathroom if no power to that outlet again in building operating notes and with local sign
    • Future Improvement: Could revise wiring so Janitor's Closet power for controls is on separate GFI from bathroom
    • Repeat thermal imaging and take dewpoint readings on hot, humid day to check results
    • With insulation on exterior of coil casing, condensation is reduced, but water is still pooling on both sides of the Tank Town roof.
    • Reviewed further and determined that drain pan is integral to coil and coil was installed backwards, so drain is on the wrong side of the coil. Condensation on coil front (downstream side) has no place to drain to.
    • Also found rust and other dirt and debris blocking drain.
    • Cleaned, but also need to turn coil around and/or extend drain pan downstream of coil and provide positive drainage.
    • JG to pursue.



  • Plan / Do / Check / Act / Repeat