CASE STUDIES OF HIGH HUMIDITY PROBLEMS IN HOT AND HUMID CLIMATES IN THE UNITED STATES D Turner *, P.E., Ph.D., S Deng, P.E., GH Wei, P.E. and D Claridge, P.E., Ph.D. Energy Systems Laboratory, Texas A&M University System, College Station, Texas ABSTRACT Maintenance of acceptable indoor air quality is a challenging problem in the hot and humid areas of the world. High humidity or the intrusion of water into the building can result in mold growth for a number of reasons, including poor building design, bad mechanical systems, poor construction, maintenance problems, or improper building occupant behavior. The Energy Systems Laboratory at Texas A&M University, College Station, Texas, has developed a process called Continuous Commissioning 1, (CC) 1, which improves building energy efficiency through optimization of the HVAC and controls systems. In the process of commissioning different buildings we have encountered many different mold problems, some of which have been so severe that the occupants had to be removed from the building. This paper discusses some of those problems encountered, the resolution of the problem (if found) and groups the case studies into design problems, poor maintenance, construction issues, retrofit applications, and tenant behavior. In many instances where poor indoor quality conditions exist, it is not a single problem that is found; rather it is a combination of several problems. Specific examples are given from our experiences. INTRODUCTION Over the last fifteen years it has become apparent that moisture and humidity control problems exist in buildings. The causes of these problems can be complex and involve many aspects of building design, construction and maintenance (Harriman 2001). Improper humidity control inside a building can lead to occupant discomfort, people feeling sick, building deterioration, and the development of mold, mildew or odors. At Texas A&M University the Energy Systems Laboratory has been called upon to solve many humidity problems. The group has worked on all types of buildings including dormitories, office buildings, laboratories, hospitals, and auditoriums. Several of the buildings have experienced the existence of not only high levels of humidity but also mold. Mold in buildings is a serious problem since previous studies indicate that it can lead to or aggravate health problems including headaches, breathing difficulties, allergic reactions, and aggravation of asthma systems (United States Environmental Protection Agency, 2001). Many of the problems leading to mold and inadequate humidity control can easily be identified and prevented. The problems will be divided into five categories, and examples will be given in each category. Since most of these buildings had experienced some type of mold growth it is also important to understand what mold is (how it acts) and most importantly how it can be prevented or eliminated. MOLD Over the last fifteen to twenty years, as building ventilation standards have changed, there has been a growing concern for mold and mold prevention. Monetary problems due to mold clean up, worker s compensation, and building restorations have become a major concern for the HVAC industry. In order to control and eliminate mold one must first know some basics about mold. Mold is a fungus. It is all over the world and it is crucial to the earth s ecosystem since it breaks down trees and other natural wastes. Mold is microscopic in size and travels through the air. Its survival is directly dependent on humidity, temperature, and limited exposure to ultraviolet light. As a result, different species of mold live in temperature ranges from just above freezing to just below the boiling point of water depending on the ideal conditions for growth of that particular mold species. In a particular place and building there could be * Corresponding author email: wdt5451@esl.tamu.edu 1 Continuous Commissioning and CC are registered trademarks of the Texas Engineering Experiment Station (TEES), the Texas A&M University System, College Station, Texas. 1438
hundreds of different species of mold. When temperature and humidity conditions change, one species of mold dies, but it may be quickly replaced or outgrown by the best suited species to take its place (Harriman, 2001; United States Environmental Protection Agency, 2001). Since mold travels through the air and most buildings do not have direct sunlight, the best way to prevent its development is to maintain adequate relative humidity levels inside a building. Penicillin mold, for example, starts to grow when relative humidity levels rise around the area of seventy-eight percent (Harriman, 2001), at which it thrives on surfaces with condensation present. Once mold has grown and can be easily identified with the human eye, it has already grown a protective layer called mycelium. This protective layer allows the surface in which the mold is growing to be kept moist. Due to this protective layer, mold is very difficult, if not impossible, to completely remove from a building once it is present. When mold is treated by ultraviolet light or toxic chemicals such as bleach, only the top layer of the mold is usually killed. If the original spore is unaffected, it will continue to live on the surface in a dormant state. Once there is additional moisture present, the mold will again reproduce and develop (Harriman, 2001; United States Environmental Protection Agency, 2001). CAUSES OF HUMIDITY PROBLEMS Humidity control has been a major concern in areas that experience warm temperature and high humidity. Excess humidity not only causes discomfort for the building s occupants but it also allows for the growth of mold in these buildings. ASHRAE standard number 62 states that an office environment should have a relative humidity in the range of 30 to 60% (ASHRAE, 1989). There are many causes for lack of humidity control in buildings. Most of these causes can be avoided if a concerted effort is made to control the relative humidity inside a building. Some of these causes can be prevented before the building is built by having adequate and proper design of the HVAC system and proper construction techniques. Other ways to prevent the lack of humidity control are proper building retrofit and proper maintenance. This paper will focus on five major categories of causes for humidity problems in buildings: Design, Construction, Retrofit Applications, Maintenance Issues, and Tenant Behavior. Category 1: HVAC Design The first of these categories, the one in which an engineer has the most control over, is HVAC design. A building should be designed properly to provide a comfortable environment for its occupants to work or live. The building should be installed with proper type of equipment to supply adequate cooling or heating. It is also crucial for a building to have a positive differential pressure to the outside atmosphere. If the building pressure is negative, the engineer will have no control as to what type of air will be drawn into the building making it impossible to control the humidity level. A paper (Chen, et al, 2004) summarizes the results of 31 case studies of buildings which have high humidity/mold problems. Approximately one-third of the problem buildings were found to have poor HVAC design. Another important factor in HVAC design is the building s location. It is necessary to take into account the position of the building with respect to wind direction, speed, and outside air humidity content. The engineer should try to minimize any direct openings to the outside to control infiltration. Case Study: Lecture Hall, University Campus A lecture hall had experienced high relative humidity levels, and mold was starting to grow on the surfaces of walls, tables, and chairs. Measurements in the room indicated temperatures near the comfortable range of 70-72 F but relative humidity levels near 80%. (Chen, et al. 2000) A single-zone air handling draw-through unit configuration served the lecture hall. Of all the air handling systems, the single-zone air handling system is perhaps the simplest and most common type of system. The unit is controlled to respond to the room conditions as indicated by a room thermostat. No reheat coil was designed for this system, so dehumidified primary air or recirculated room air could not be reheated. The original design data of the AHU and the measured air condition data both indicate that the cooling capacity and supply airflow volume was adequate for the sensible load, but not the latent load. The single-zone AHU 1439
system with no reheat capacity originally chosen was not adequate for the space due to the lack of humidity control. Different geographic locations have different ratios of latent load to sensible load and different AHU types have different advantages. The ratio of latent load to sensible load should be considered as a criterion to design the HVAC system and select equipment for different climates (Harriman, Plager and Kosar, 1999). The engineering solution to this problem is to retrofit the AHU with a reheat capability to maintain proper humidity control. Category 2: Construction Sometimes the way a building was designed or planned is not the way it was ultimately built. Such problems can be seen in many buildings throughout Texas and elsewhere. In (Chen, et al, 2002) 37 percent of the case study buildings with humidity problems were categorized as having a construction problem. Case Studies: #1 Dormitory on College Campus A building on a campus had the distinction of being a building plagued by humidity issues. The ceilings in many of its bathrooms were weeping to the point that water was raining on the occupants. This condensation problem had no obvious cause since room humidity levels were not excessive. Removal of the lighting fixtures in one bathroom revealed that the crawl space above the bathroom was filled with very hot (90 F), very humid (95%) air that was condensing on all the surfaces with temperatures below the air s dew point. The condensate would then leak into the bathrooms below. An examination of the crawl spaces discovered numerous pathways for this humid air through large unsealed holes originally cut for piping. These gaps allowed the humid air to freely migrate from a steam tunnel to the rest of the building. Once the humid air came in contact with a cold surface, it would condense (Chen, et al, 2002). #2 Dormitory on a Military Base Although this was not a severe mold problem, this case study represents how much attention needs to be paid to small details in construction. Mold was growing on the supply air grille to the occupied space. Conditioned air at 55 F was supplied in the duct, but there were small gaps (1/4 to 1/2 ) between the end of the metal duct and the diffuser grille. This small gap allowed hot, moist attic air to come in contact with the cold supply duct and grille, and moisture condensed on the surface of the grille. This led to mold growth. Figures 1 and 2 show the small gaps between the supply duct and the ceiling. Lack of attention to even small construction details can cause problems. Figure 1. Junction of the supply air duct and the ceiling 1440
Figure 2. Junction of the supply air duct and the ceiling #3 - Military Hospital After about seven years of operation, severe mold problems were observed in a number of rooms. The mold was first discovered during a renovation when vinyl wallpaper was removed from a wall, and mold was found growing on the underside of the wallpaper. Further investigations showed similar growth in several locations. Energy Systems Lab engineers investigated the humidity and mold areas and found a number of problems. Figure 3. Smoke test showing negatively pressure at an electrical wall plug 1. The building had a lot of cracks in the outside walls. There were many locations where daylight could be seen through the brick walls. 2. Many rooms in the building were negatively pressurized. Figure 3 shows a smoke test at an electrical outlet. 3. Most of the severe mold was occurring on the backside of the vinyl wallpaper, around windows, or around electrical wall plugs, as shown in Figures 4 and 5. Figure 4. Mold behind the vinyl wall. 1441
Figure 5. Mold around windows and electrical wall plugs During the subsequent investigation, it was determined that the flow tracking stations on some of the air handling units had failed, and that there was not a correct differential between supply and return air, resulting in some areas of the building having negative pressure with respect to the outside conditions. Further, during windy days, the cracks in the outer walls allowed for greater infiltration of untreated air. With the untreated air and moisture moving into the building, the vinyl wallpaper served as a vapor barrier, and moisture was trapped on the underneath side of the wallpaper. As with the situation with many of the case studies presented herein and summarized in (Chen, et al 2004), the mold growth is not attributable to just a single cause. In this example construction problems related to the exterior wall cracks and the installation of the vinyl wallpaper were major causes of the mold problems. However, the problems were made worse by the negative pressurization caused by the air flow station failures in the air handling units. Category 3: Building Retrofits and Alterations Once a building has been in place for several years changes have to be made to it in order to better fulfill its purpose. For example, a conference room may be changed into new offices, or a classroom may be converted into a computer or server room. There are also advancements in the technology utilized in the office environment. Offices must now have fast and reliable Ethernet connections. There is also the need for additional telephone lines for fax machines and other office equipment. All this wiring has to be distributed throughout the building. In order for this to be done, electrical conduit has to be run through walls and from floor to floor. Often the breaks made in walls and ceilings are not properly sealed. In Chen, et al 2004 15% of the observed humidity problems were categorized as having been caused by retrofits and alterations. Case Studies: #1 Classroom/Office Building Built in the 1980 s, construction retrofits and alterations occurred to account for the upgraded information technology equipment installed. Ethernet wiring had to be distributed throughout the building, which caused holes to be placed in walls for wiring conduit. These holes were often not sealed correctly, and they allowed for undesired air flow throughout the building. In particular, holes in walls in or near mechanical rooms, which shared a wall with one of the stairwells, allowed humid outside air to be sucked into the stairwell. This was a major factor for the growth of mold in the building. #2 Hospital Mold Problems This case study falls into all five categories, i.e., design, retrofit, construction, maintenance, and occupant behavior. However, since the humidity problems and subsequent mold problems occurred after an energy retrofit, it will be discussed within this category. After an energy retrofit, a geriatric hospital began experiencing some severe mold problems. When engineers from the Energy Systems Lab were asked to investigate the problems, excessively high humidities (> 80%) were found. There was severe mold growth in bathrooms and on many of the hospital walls. While this mold would be bad for any hospital, it was particularly bad for this facility since it largely housed elderly patients, many of whom had severe respiratory problems. 1442
The retrofit that had occurred was a chiller replacement, where direct expansion units had been replaced by two small chillers. The chillers supplied chilled water to outside air pre-treatment AHUs and fan coil units. There were several major problems noted in the site analysis: 1. The outside air pre-treatment units were handling nearly twice as much outside air than design, resulting in less dehumidification and discharge air temperatures in the high 60 s. 2. Chilled water supply temperatures ranged from 48 F to 51 F during the site visit. 3. Fan coil units had high discharge air temperatures, 67-68 F. (Thermostats controlled chilled water valves.) 4. Neither of the chillers had isolation valves. 5. During fall and spring operation, and during summer evenings where only one chiller was used, the supply water to the hospital was blended with the return water through the off chiller. 6. The high chilled water temperatures could not dehumidify adequately during low load, high humidity conditions. 7. There were numerous unsealed penetrations in the building which allowed infiltration of untreated outside air (also caused from prior retrofits and poor maintenance). 8. The air distribution system was poor. To complicate matters even further, a decision was made by facility administrators to open all the outside air vents fully open to allow more fresh air into the building. This occupant behavior decision exacerbated the problem because too much outside air was already being admitted into the building. This case study presents an example of how bad an IAQ problem can be when there is a poor design, construction problems, maintenance issues, improper retrofit application, and bad decisions by occupants/administration. Fortunately, there was a successful ending to the story. The mold/mildew was cleaned and mitigated, isolation valves were installed on each of the chillers, and the chillers were programmed to supply 44 F water to the hospital. A Testing, Adjusting, and Balancing (TAB) firm was hired to balance the air distribution system, including bringing in the proper amount of outside air. Facility maintenance staff and the contractor worked to seal as many of the building penetrations as they could. The building was restored to an acceptable living environment. Category 4: Poor Maintenance One of the main causes of mold within buildings is poor maintenance. In many institutions, where there are a large number of buildings to maintain, regular scheduled maintenance is often delayed in order to fix new and last-minute complaints from building occupants. As a result, problems that could have been prevented begin to accumulate. In some instances problems will not be fixed until complaint calls are made to the maintenance office (Chen, et al, 2000; Chen, et al, 2004). In the Chen, et al paper, which analyzes some 31 case histories, there were some maintenance issues in 95% of the cases. This is by far the category with the highest cause for lack of humidity control and also the easiest to prevent. Case Study #1 - Dormitory Humidity Problems This dormitory had high levels of humidity inside bathrooms and bedrooms. Relative humidity levels reached the 80 percent mark and residents constantly complained about comfort. Upon careful inspection of the building, it was discovered that all the outside air grilles were partially or completely obstructed, effectively forcing the units to circulate only inside air. Exhaust fans operated continuously. As a result, the building was being operated very negative and untreated air was entering through doors, windows, and any available cracks. This problem could have easily been corrected by proper maintenance and inspection of HVAC equipment. Case Study #2 Dormitory on Campus This dorm s humidity problems could have very easily been prevented. During inspection, it was noticed that the two outside air AHUs designed to dry out the outside air and provide the building with positive pressure were off-line due to component failures. It was further noticed that the coiling coils were still active, flowing chilled water. Even with the air handling units off, air flow was detected through the units due to the negative pressure in the building. Simultaneously, untreated air was infiltrating through doors and cracks of the building. Once the hot, humid air came in contact with the cool ductwork fed by the off-line AHUs, it condensed and dripped onto the hallway below. 1443
Humidity control problems could easily have been prevented with proper air handling unit maintenance and inspection. Once one of the components was not working properly it should have been replaced, and the humidity problem could have been avoided. The fact that both outside air AHUs were not working points to improper maintenance. Category 5: Tenant Behavior It is important that tenants be educated to understand how their behavior impacts the HVAC system and indoor air quality. With so many buildings now being built with central HVAC systems, many windows are not operable and, therefore, cannot be opened by the occupants. However, some buildings have operable windows, and these are sometimes opened to allow fresh air into the building. There are also instances when building occupants will leave outside doors open or forget to close large delivery doors in conditioned storage areas. Wind effects will cause a positively pressurized building to become negative under high-wind conditions, but this is a transient effect. Even though buildings may be positively pressurized by the HVAC system, the systems are not designed to handle long periods of time with windows or door open. Occupants should be educated to keep windows and doors closed, especially during periods of potentially high humidity. Case Study: Military Hospital Energy Systems Laboratory engineers made a site visit to a major military hospital which was experiencing severe comfort problems. Like several of the case studies previously discussed, this case study is not just related to tenant behavior. The indoor humidity problems were caused by a poor retrofit design, poor maintenance, not enough chilled water being supplied, and tenant behavior. The occupants were sensing both high temperature (77-80 F) and high humidities (65-80%) and were naturally uncomfortable. To get some improved comfort, they were opening their windows (and sometimes leaving them open), which allowed a large, direct path of untreated air into the facility. Their behavior only made the IAQ conditions within the facility even worse. CONCLUSION Causes for lack of humidity control and the development of mold come from many different sources. They are related to every stage of a building s life from the original design to construction to retrofits to poor maintenance to uneducated tenant behavior. The existence of mold in a building is a serious concern and should be treated immediately. The easiest way to deal with the mold problem is to prevent it by having a properly designed building HVAC system and to keep it performing adequately with proper maintenance. Once mold has been identified in the building, it should be treated, the cause of the high humidity eliminated if possible, and steps should be taken to see that future problems will not reoccur. REFERENCES 1. ASHRAE, 1989. ANSI/ASHRAE 62-1989, Ventilation for Acceptable Indoor Air Quality. Atlanta: American Society of Heating, Refrigeration and Air Conditioning Engineers, Inc. 2. Chen, Hui, Homer L. Bruner, Song Deng, Claridge, D. E. and Turner, Dan, 2002, Eliminating Humidity and Condensation Problems in University Dormitories Case Study, International Conference for Enhanced Building Operations, Dallas, Texas, October 15-17, 2002 3. Chen, Hui, Song Deng, Homer L. Bruner, Claridge, D. E., 2000, Control of Humidity with Single-Duct, Single-Zone, Constant Air Volume System A Case Study. The Proceedings of the Twelfth Symposium on Improving Building Systems in Hot and Humid Climates, San Antonio, Texas, May 15-17, 2000, pp. 416-423 4. Chen, Hui, Song Deng, Homer Bruner, and Jerry Garcia, Roots of Mold Problems and Humidity Control Measures in Institutional Buildings with Pre-Existing Mold Condition. Proceedings of Fourteenth Symposium on Improving Building Systems in Hot and Humid Climates, May 17-20, 2004, pp. 51-59 5. Harriman, L., Brundrett, G., Kittler, R., Humidity Control Design Guide for Commercial and Institutional Buildings, ASHRAE 2001, pp. 100-105 6. Harriman, III., L. G., Plager, Dean and Kosar, Douglas, 1999 Dehumidification and Cooling Loads from Ventilation Air, Journal of Energy Engineering, Vol. 96, No. 6, pp. 31-45 United States Environmental Protection Agency, Mold Remediation in Schools and Commercial Buildings, http://www.epa.gov/iaq/molds/images/moldreme diation.pdf.march 2001 1444