Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland. Mold Infestation in Buildings of Warm Humid Climate Case Studies

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1 Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland Paper ID 0039 ISBN: Mold Infestation in Buildings of Warm Humid Climate Case Studies Chin Peng Foo *, Poh San Tee, Chung Wan Wong Maek Consulting Pte Ltd * Corresponding admin@maek.com.sg SUMMARY Whilst mold infestation has been widely reported elsewhere, its phenomenon in warm humid climate like Singapore somehow yields different set of challenges. The causes are numerous, often inter-related and complex. Hygrothermal issues, material, construction, air tightness and design specific for tropical climate often interact and have an accruing effect in different ways. This paper details the background of recent cases including investigation techniques and findings. They include retail outlet in multi-storey commercial building and an art gallery within a conserved old shophouse. Investigation methodologies involving mold testing and building leakage assessment and air-condition and mechanical ventilation examination using technologies such as infra-red thermography, ultrasound leak shooter, smoke-test, pressure mapping and hygrothermal analysis are discussed. Possible causes attributed to design and construction was identified and remediation strategies, both interim and long term for an occupied premise were explored. KEYWORDS Mold infestation, hygrothermal, mold risk factor, tropical 1 INTRODUCTION Various studies have been carried out to determine apposite conditions for mold growth within the built environment. The most important factors for mold germination and growth are the presence of moisture, food (suitable substrate) and temperature. Mold spores are ever present in the environment, and as such will germinate once the factors are favourable. The strategy for its elimination is always to remove these factors from the environment, of which minimising moisture is the only practical approach. However, the causes have to be clearly determined and rectified to prevent a recurrence. Table 1 shows a profile of the tropical climate in Singapore 1 with abundant rainfall, high and uniform temperatures, and high humidity all year round. Many of its climate variables, such as temperature and relative humidity, do not show large month-to-month variation. Rainfall in Singapore shows a marked diurnal variation with rainfall occurring more frequently during the daytime, particularly in the afternoons when solar heating is strongest

2 Table 1 Singapore Long Term Climate Averages based on Climate Station Relative humidity shows a fairly uniform pattern throughout the year and does not vary much from month to month around 84%, but reaching 100% during prolonged periods of rain. Such warm and humid conditions can easily promote mold infestation within a building should there be infiltration through the building envelope.. 2 MATERIALS/METHODS Different techniques ranging from visual inspection, microwave moisture measurement, infrared thermography, ultrasonic leak detection, pressure mapping, smoke test to temperature and humidity data recording in conjunction with software simulation had been employed during this investigtion. Visual inspection of mold requires acute observation skill and experience to look for areas of potential moisture, often aided by sense of smell. Mold growth usually starts in small hidden corners and surfaces but when visibly seen, the growth would be quite substantial. Videoscope was used to inspect behind partition boards as only small openings (6mm diameter) are required. Infrared thermography (IRT) is widely used for building inspection to detect presence of moisture which can appear as hot or cold spots depending on the surrounding temperature and material. It essentially detects thermal differences between the different media. Another novel technique utilized was the ultrasound detection to comb joints for leaks that are not visible to the naked eye. An ultrasound emitter is introduced on one side of the surface to be inspected while the detector is placed on the opposite side. The detector picks up transmitted ultrasound and displays the location on the screen. The higher the signal detected, the greater the infiltration or leakage. Other methods like the pressure mapping, smoke test and environmental monitoring are common tools employed. In some cases, simulation was carried out to determine the flow pattern of air infiltration and trapped moisture via computational fluid dynamic (CFD) analysis, whilst in others mold prediction and condensation risks were made. 3 CASE STUDY 1: Retail Bank Outlet Mold growth was reported at a retail bank outlet on the ground floor of a multi-storey commercial building (Figure 1). The Air-Conditioning and Mechanical Ventilation (ACMV) is of open return system, whereby the return air from the bank is mixed with air in the plenum before re-cooled by the Fan Coiled Unit (FCU). 2

3 Initial monitoring of temperature and humidity at various locations within the bank showed that the humidity ranged from about 75% when air-conditioning (AC) is turned on (9am) to 95% (9pm). At certain location, the humidity even reached almost 100%. Both the temperature and humidity appeared to escalate quickly when the AC was turned off. Signs of condensation were also observed on stone surfaces. The water vapour content at 24⁰C and 65% RH is approximately kg/kg. (Figure 2). The vapour content increased to about 0.02 kg/kg, which is somewhat like external air. As such, it was postulated that air infiltration from the external after the air-conditioning was turned off, had caused the increase in RH internally. Checks and tests on the ACMV did not reveal any anomaly in the design and operation. Figure 1 Mold growth on wall of bank. Mold observed to start from partition board, behind wall paper Figure 2 Temperature and RH monitoring and analysis The bank has a double volume space internally and the façade comprise of glass shopfront with a canopy and double layer cladding above the canopy. (Figure 3). Initial visual survey showed that air infiltration could be coming in through the inner façade layer above the canopy and above the plenum of the bank. The outer canopy layer was not designed to be air tight. Thus pin-pointing the air infiltration path was found to be very challenging due to poor access. Follow up investigation was carried out using IRT (Figure 3) and ultrasound leak shooter (Figure 4). The IRT scan from internal of the bank revealed the presence of hot spots around columns indicating ingress of external air. In the ultrasound leak test the emitter was placed within the bank and the detector was used to trace leakage from the external and in particular the internal cladding above the canopy. Leaks were detected, again around columns where large gaps were subsequently uncovered (Figure 4). The ultrasonic leak test thus verified the IRT result. Initially, large gaps were found in the façade and rectified. Through further and repeated scanning thereafter, smaller gaps were subsequently identified until most of the detectable sources of infiltrations have been addressed. The temperature and humidity has been improved thereafter. The wall paper has also been changed and decontamination was carried out. 3

4 Figure 3: Left image shows the cross section of the façade of the bank with glass shopfront below the canopy. The façade above the canopy comprises of 2 layers of cladding. The images on the right show hot spot from thermograms taken from inside the bank. The hot spots which indicate ingress of warm air from external are found around the columns. Figure 4: Images from the ultrasound leak showing locations with high sound leakage (higher decibel) demarcated in red boxes. The yellow boxes indicate lower decibel, i.e., lower degree of air leakage. The left photo shows a large gap found in the cladding around the column. 4 CASE STUDY 2: Art Studio A pre-war (constructed ~1927) two-storey shop house and the adjoining warehouse were conserved and converted to a fully air-conditioned Art Studio. In the conversion, the original clay roof tiled had been reconstructed to include a skylight made up of glass roof tiles and glass panel immediately below. Mold was later found infesting the ceiling and partition board within the studio and threatening the artwork within. (Figures 5 and 6). Initial investigation involving IRT, temperature, RH and air flow measurements and smoke test indicated that there was infiltration of external air through the glass tiles and poor ventilation within the studio. In order to verify this, a series of analyses were conducted and summarised in table 2. Figure 5: Left image shows the cross section of the studio with mold infestation. The photos above show mold staining on the boards and algae around the glass panel 4

5 Figure 6: (Left) Glass tiles above the skylight on the roof and (right) cross section of the skylight with glass roof tiles and glass panel below Table 2 Thermal measurement and evaluation parameters Measurement Evaluation 1. Ambient temperature and relative humidity a) Dew point of skylight and ceiling panel board 2. Skylight and board surface temperature b) Mould risk factor c) Hygrothermal simulation The dew point of the artist studio was calculated and plotted with the surface temperatures of the glass and ceiling panel and depicted in figure 7 shows high risks of condensation in the early morning on these surfaces. Mould Risk Factor2 (MRF) is a mould growth prediction through analysis of measured temperature and relative humidity to determine if the environmental conditions are susceptible to biological decay, including the growth of xerophilic mould and mildew and any risk of insect infestation. The method takes into account the variability of temperature and relative humidity over time of day and months while it computes the potential for mould growth. The results show a mold risk factor of 2.27 indicating high risk for its growth on the glass panel. See figure 8. Figure 7 Results from temperature and RH analysis for condensation and mold risk factor A hygrothermal simulation of the simplified skylight glass system model was conducted using WUFI which performs dynamic simulations of coupled heat and moisture transfer. The simplified model consists of air gap between the external roof tiles and the internal glass panel (Figure 8) and the simulation used typical Singapore weather and measured ambient condition at the skylight. Other solar and directional parameters were not taken into account. The results show that mold growth is highly likely the hygrothermal results are beyond the limiting isopleths for mold growth (Figure 8)

6 Figure 8 (Left) Simplified model of glass panel and (right) results showing mold growth high likely CFD was conducted to study the air flow externally and internally. The former was based upon the prevailing wind direction in Singapore whilst for the later, the locations of supply and return air was adopted. External air flow simulation shows infiltration through the glass roof tiles whereas internal air flow simulation shows stagnation of air at the top of the ceiling. It would appear that external humid air was infiltrating through the glass tiles and skylight which was then trapped around the pitch roof/ceiling due to the arrangement of the supply and return air duct. This trapped humid air then led to mold infestation around the ceiling boards and glass panels. As a final confirmation, smoke was introduced at the roof which then quickly infiltrated the glass tiles and trapped at the ceiling apex as predicted. (Figure 9). Figure 9 Simulation results of external (top) and internal (bottom). Smoke test shows air infiltration and stagnant air near the roof. 5 CONCLUSIONS Humid in tropical climate often aggravate the occurrence of condensation when external air infiltrates the buildings. Tracing the path of infiltration and studying the air flow based on local climate and wind directions have proven to be invaluable approaches. Poor positioning and layout of air conditioning system can also exacerbate the problem without a full understanding of air movement within, as experienced in the Arts Studio case. 6 ACKNOWLEDGEMENT Supervisor and colleagues who have contributed to the investigation. 7 REFERENCES United States Environmental Protection Agency (USEPA). Mold Remediation in Schools and Commercial Building. World Health Orgnization. WHO guidelines for indoor air quality: dampness and mould. 6