By Bob Baker

In an earlier article, we described a new medical office where the moisture level in the attic space was so high that water was condensing on ceiling panels and light fixtures and dripping on the Physician and his patients. This resulted from a building design change decision during construction that was incompletely implemented.

We made two types of recommendations. Several were "musts" because the building operation would continue to fail occupant expatiations unless these were completed. The rest were highly recommended for long term owner satisfaction.

Must - These changes were required to conform to current codes or natural law in order for the building to perform in line with the planned use.

• Seal the roof assembly to the same level as the below ceiling building envelope. This primarily consists of minimizing heat, air and vapor movement through openings in the soffit assembly. One possibility is to remove the soffit panels, construct a sealed barrier system above them and then replace the panels. Another possibility might be to secure some gasket or other sealing system that will make the current soffits effective air-flow barriers. Whichever choice is made, insulation with a vapor barrier facing toward the interior space must be installed on top of either the new structure or the soffit panels.
• Maintain building pressurization as positive regardless of status (on cycle or off cycle) of the two air handlers. Although this could be done by setting the fan controls to continuous operation we noted that option should not be considered under any condition as operation of the fans without removing moisture from outside air will make the current moisture problem even worse. We suggested several options for doing this without risk of increasing moisture levels. We referred them to the design engineer who completed the design of the current system for his advice on which strategy to follow:
  • Minimal option - An economizer type control could be installed on the Pre treatment unit so the fan would run at all times, and the compressor would cycle as needed to maintain correct psychometric conditions (ASHRAE Standards for energy and comfort). This would take advantage of free cooling when outside conditions allow.
  • We also suggested several sources for ducted dehumidifiers for residential/light commercial use and suggested one of these could be installed on the outside air input to AHU #1 and the controls set to provide full time fan operation with cycling of the refrigeration system as needed to maintain acceptable psychometric conditions in the outside air supply. Implementing both of the above would provide slight positive pressurization at minimal cost. It still would not be optimal but would improve considerably on the current situation.
  • Second option - An enthalpy energy recovery unit could be installed on the exhaust system so as to remove heat and moisture from the outside air supply and eject it to the exhaust stream then furnish the processed outside air to the conditioned space. The unit would have to be sized to assure a net positive pressure to the building. Under this option, the operation of the current units could remain unchanged if a recovery unit of sufficient size were installed and could be made to provide adequate conditioned outside air.
  • Other options could also be considered including a redesign of the entire HVAC system. Whatever solution is chosen, the Florida Healthcare Facility Design standards would have to be consulted to assure that the resulting system meets regulations for total supply air and outside air for the surgery space.
• Finally we noted that the pre-treatment air handler condensate line did not have a trap and one must be installed.

Highly Recommended - These modifications/activities are required for the facility to perform in the manner expressed by the owner as desired, to prevent deterioration of the building asset and facilitate maintenance.

• HEPA Vacuum all surfaces in the attic areas to remove any settled spores present followed by fogging of all areas with a growth inhibitor registered by the US EPA for control of fungal growth (BBJ Microbiocide for floors and walls or equivalent). Although eliminating the excess moisture in the attic space will probably stop the growth that was starting to form, it is good practice to remove what is existing and the inhibitor acts as an insurance policy against regrowth.
• Rework all filter racks so that they meet the guidelines contained in the National Air Filtration Association IOM (Instillation Operation and Maintenance) Manual. This includes providing gaskets and fillers as needed to eliminate existing filter bypass (currently estimated to be in excess of 15%) and providing convenient change access to the final filter on the system serving the surgery area plus installing a differential pressure gauge to monitor the condition of that filter (the gauge should be calibrated to indicate the pressure maximum pressure drop recommended by the media manufacturer prior to change out. The existing filter installation was far below standard and, although not part of the immediate complaint, would eventually result in unsatisfactory operation.
• Replace the filter rack on the Carrier system with a rack capable of supporting a higher efficiency media. (MERV 6 minimum) MERV 6 is the minimum considered adequate under current ASHRAE and other guidelines for commercial buildings. For this type of facility, MERV 11 would be preferable.
• Rework all fiberglass duct board plenums so they meet the NAIMA Fibrous Glass Duct Construction Standard using pressure sensitive tape (or fiberglass tape) and mastic rated for UL 181A.
• Rework all flexible duct connections (including those to register boots) so they conform to the Air Diffusion Council Flexible Duct Performance and Instillation Standards (Alternate Method 4.6) using clamps and mastic that conform to UL 181B. There were many air leaks throughout the duct system that were both wasting energy and promoting moisture condensation.
• Remove air handler internal insulation that has become wet and replace with new insulation. Inspect balance of HVAC system interior as indicated in NADCA Standard ACR 2005 and clean or repair to that standard as needed. It was incredible how soiled the system was for a building that had been in operation for only three months. We speculated that the system had been operated during construction without filters in place and not cleaned before the building was occupied.
• Have Insulation Contractor reinstall insulation between rafters using retaining netting so the insulation will form a uniform thermal, air and vapor barrier. We also considered that the owner consider one of the new spray insulation systems as these would be less likely to be dislodged than the bats and provide a more effective air and vapor barrier.

What Happened?

When we last checked, some of the recommendations had been implemented. The insulation had been reinstalled, The duct system had been sealed according to current industry standards and the existing mold had been removed. The sealing of the soffit space was to be completed the next week.

The HVAC contractor initially resisted any additions to the system insisting that control modifications (adding a humidistat) would handle the problem. The day after the control modifications were completed, water dripped on the Physician and now a heat/moisture recovery system is on order.

Bob Baker is a member of IAQA, ASHRAE, CSPA and Chairman and CEO of BBJ Environmental Solutions, Inc., "The Standard of Care for Indoor Air". BBJ has offices in Tampa and Hong Kong and Mr. Baker follows indoor air quality developments throughout the world. For additional information, Mr. Baker can be reached at (800) 889-2251 or through the company web site at www.bbjenviro.com.