Venice Library Humidity Study. for Williams Building Diagnostics, LLC th Street West Bradenton, FL Report April 13, 2015

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Esther Lloyd
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1 for Williams Building Diagnostics, LLC th Street West Bradenton, FL Report April 13, 2015 Moses & Associates, Inc NW 40 th Terrace, Suite A Gainesville, FL FL License EB

2 TABLE OF CONTENTS I. INTRODUCTION... 1 II. BACKGROUND... 1 III. ANALYSIS/RECOMMENDATIONS... 2 Page i

3 I. INTRODUCTION Moses & Associates, Inc. (M&A) was contracted by Williams Building Diagnostics, LLC (WBD) to review the HVAC systems serving the Community Meeting Room (CMR) at the Venice Library. According to WBD, the CMR has been experiencing moisture and humidity problems resulted in mildew (fungal growth) and other humidity related issues. The following report is intended to be a supplement to the information provided in the WBD Report dated April 10, 2015, Building Diagnostic Report. This report findings are limited to the observations made during our site visit held on April 2, II. BACKGROUND The CMR is a 1,750 sq.ft. space with an adjacent storage room and separate mechanical room. The mechanical room contains a Trane DX Air Handling Unit (AHU). This is a split system DX unit served by a separate condensing unit located on the roof. The CMR space is an open floor plan room intended for community meetings, workshops, gatherings, etc. According to ASHRAE Fundamentals, the recommended temperature for comfort for this type of space is approximately 72 F with a relative humidity of 50%; temperature and humidity can vary over a specific range, but these are the indicated optimum values. Relative humidity should be maintained below 65% in order to prevent the formation of fungal growth. Humidity within the space is the result of 3 primary causes: 1. Occupants: The occupants in the space discharge moisture through breathing and perspiration. 2. Moisture Infiltration: Infiltration is the result of moisture entering the space through gaps or holes in the building exterior, such as doors, windows, vented eves and soffits. Site observations, as indicated in the WBD Report, verified that the exterior building envelope is not sealed; this is allowing humid outdoor air to enter the space. Additionally, the air handling equipment fan runs almost continuously. This operation draws/sucks air in through the outdoor air duct and an uncapped outdoor air ventilator located in the mechanical room. Additional outdoor air is allowed to be drawn into the space via the unsealed building exterior via opening between the CMR and main library ceiling. 3. Migration: Migration is the movement of moisture from a moist location to a dry location via vapor pressure or hydraulic force. According to the WBD Report, hydraulic force is causing water to be driven through the concrete slab and into the space below the carpet. Vapor pressure can and may be causing additional moisture to enter the space via the walls. The moist outdoor air will force its way through the building envelope if there is insufficient vapor barrier present at the exterior. M&A has not reviewed the building drawings in order to determine actual construction. In Florida, the outdoor humidity and temperature is normally higher than the recommended ASHRAE comfort level. This means that in order to lower the humidity within the space to the recommended 50% relative, the moisture must be removed from the air. Mechanical equipment (air handling and condensing equipment) achieved this by cooling the temperature of the air to at or below 55 F. This cooling causes the excess moisture to precipitate out in the form of liquid water. This dehumidified air is then discharged into the space and warmed to 72 F. In cases Page 1

The following report is intended to be a supplement to the information provided in the WBD Report dated April 10, 2015, Building Diagnostic Report.

4 where there is insufficient heat load within the space to raise the temperature of the dehumidified (55 F air) to 72 F, a method to reheat the air as required. This is usually accomplished by an electric coil in the supply duct or similar device. III. ANALYSIS/RECOMMENDATIONS M&A evaluated the HVAC unit capacity requirements, ventilation requirements and the capacity of the existing equipment. According to the Florida Building Code Mechanical 2014, the HVAC system is required to provide 15 cfm of outside ventilation air for each occupant within the space. According to ASHRAE 62.1, the space could accommodate more than 100 people. The actual occupancy was not noted during our site visit. This means that the HVAC equipment would be required to provide 1,500 cfm of dehumidified outdoor air. This equates to approximately 10 tons of cooling load. Additional cooling load would be required to provide the sensible cooling for the space due to people, lights and external building heat. This means that a total of approximately 20 tons of cooling would be required to provide proper ventilation and temperature control. The model number of the Trane unit serving the space may have the capacity to provide the required air flow. However, the unit is not sized sufficiently nor is it designed/intended to dehumidify such a high volume of outdoor air. In short, the existing equipment is not suited for dehumidifying the outdoor ventilation air. If the occupancy could be limited to approximately 50 people, the existing equipment could be modified to provide for the air conditioning loads and ventilation requirements of the space. For this to be a viable solution, the following would have to be accomplished: 1. Limit the occupancy of the room to a maximum of 50 people. 2. Seal the building floor and envelope as indicated in the WBD Report. 3. Provide outdoor air controls and ductwork to provide approximately 750 cfm of outdoor air whenever the space is occupied. 4. Provide occupancy sensors to open the outdoor air ductwork as required to provide for ventilation when the space is occupied. An alternative scheme could use CO 2 sensors to modulate the outdoor air in response to indoor air quality monitoring provided by the sensor. 5. Provide a reheat coil in the supply of the AHU. 6. Program the AHU to provide a constant 55 F supply air temperature. The reheat coil would be connected to the room thermostat and modulate as required to maintain a space temperature of 72 F. This combination would provide for dehumidification of the incoming air and mountain room temperature setpoint. While the above recommendation is feasible, it would be an energy inefficient system. The humidity being introduced into the space by the leaking floor and poor building envelope indicates that the AHU should run continuously in order to dry/dehumidify the space. This means that the air in the space, whether occupied or not, would be cooled and reheated continuously. This would result in high energy bills, but it would provide a dry environment. The estimated cost of construction to implement the above recommendations is $32,000. An alternate solution would utilize the existing equipment and modifications listed above, but also include a small 1 to 2 ton recirculating air conditioning unit. This equipment would operate as space dehumidifying equipment whenever the CMR is unoccupied. In this scheme, the large unit would be turned off during periods when the CMR is inactive and the smaller air conditioning unit would be enabled. This unit would recirculate the indoor air, provide the 55 F supply (dehumidified) air and an electric reheat coil would be provided to ensure that the space Page 2

ANALYSIS/RECOMMENDATIONS M&A evaluated the HVAC unit capacity requirements, ventilation requirements and the capacity of the existing equipment.

5 temperature remained at 72 F or greater. This combination would provide the optimum 50% relative humidity. Maintaining these conditions should prevent fungal growth from forming. The estimated cost of construction for this option is $43,000 ($32,000 + $11,000 for new unit). This would reduce the energy consumption during unoccupied periods. Note that if the moisture migration and infiltration could be mitigated and the HVAC equipment modified to provide proper temperature and ventilation control, the equipment could be turned off during unoccupied periods. Humidity sensors in the space could turn on the HVAC equipment when levels rise above specified levels. This is currently not a viable option due to the existing floor condition, building envelope and HVAC configuration. Page 3

Note that if the moisture migration and infiltration could be mitigated and the HVAC equipment modified to provide proper temperature and ventilation control, the equipment could be turned off

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