11th Conference on Advanced Building Skins

Transcription

1 11th Conference on Advanced Building Skins October 2016, Bern, Switzerland ISBN: Advanced Building Skins GmbH Hostettstr. 30 CH-6062 Wilen (Sarnen) Switzerland VAT: CHE Tel: Copyright: Advanced Building Skins GmbH

2 Thermal properties of access systems in field trials Modern doors and windows have become more thermally efficient and less permeable to air Modern access systems rely on electronic systems Therefore, locks have to be thermally efficient, have low air permeability, and do not build-up condensation inside Wolfgang Rädle 1, Bernhard Letsch 2, Urs Buehlmann 3, Urs Uehlinger 4 1 Research and Development; Architecture, Wood, and Civil Engineering; Bern University of Applied Sciences wolfgang.raedle@bfh.ch, Solothurnstrasse 102, 2504 Biel, Switzerland 2, 4 Research and Development; Architecture, Wood, and Civil Engineering; Bern University of Applied Sciences 3 Department of Sustainable Biomaterials, Virginia Tech Abstract Today's building codes and green building guidelines require building skins that prevent or at least severely limit air exchange between the inside and the outside of buildings at all points other than where specifically designed. This is particularly true for Minergie-P certified buildings, e.g., buildings with mechanically controlled climate and air exchange systems. However, due to the tightness of the building skin and discrepancies in the fine-tuning of the mechanical air exchange system, pressure differentials between the interior and the exterior of Minergie-P certified buildings are quite common. In such situations, traditional access control systems in doors and windows serve as a gateway for air, creating a potential trouble spot where condensation may accumulate. To find out more about this phenomenon, researchers at Bern University of Applied Sciences exchanged the lock of the entrance door at a single-family home built following the Minergie-P standards (Verein Minergie 2014) but not yet certified. For this field test, the door was equipped with a modern, commercially available lock including door handle, lock cover, and an electronic closing mechanism. This access system was inserted into the main entrance door of a test house in the Solothurn region. Temperature, pressure differentials, and humidity were measured in the winter of 2012/13. Results show that the mechanical air conditioning system creates sizeable pressure differentials between the outside and the inside of the house. Such pressure differentials exert pressure on all openings in the building skin including openings in the access systems and thus create the potential of moisture build-up due to condensation. Keywords: door lock, condensation, air tight, watertight, mechatronic, climate control system 1. Introduction To reduce heath losses between building interiors and the outside environment due to uncontrolled air exchange, energy efficient building skins must be non air permeable or possess limited air permeability. Also, such buildings are frequently equipped with mechanical ventilation systems, which allow reducing heath losses thanks to controlled fresh air intake. Depending on the settings of the mechanical ventilation system and depending on the design of the overflow opening, pressure differentials between the inside and the outside may occur. In times of cold (winter) weather and when the inside of heated buildings have higher air pressure than the outside, such air flow may lead to convective accumulation of moisture. Such moisture accumulations can, for example, be observed between building components with leaking vapor and airflow barriers, or at building components with high air permeability. Nowadays, with ongoing improvements of building skins in respect to air impermeability, driving rain impermeability, heat transition, and interior wall surface temperature, local weak spots are getting more

3 attention. An example of such a local weak spot in building skins are house access systems, which have not changed much over the past decades with the exception of the introduction of electronic components to the look. Such traditional access systems do not keep up with the requirements regarding air impermeability as well as with other performance expectations mentioned above. Indeed, it is assumed that current access systems sold today are the source of high levels of humidity inside the element, due to potential leakage of rain or snow into the lock or due to the occurrence of convective accumulation of moisture. This humidity affects the reliability of the electronic access system and, longer term, causes damage due to corrosion. Also, further damage can be caused to the surrounding wood-based engineered materials, if the door in question is made of a hygroscopic material. However, today, no house access system (i.e., handle and lock, Figure 1) specifically designed for energy efficient buildings that would address those shortcomings are being offered on the market. Figure 1: Example of traditional house door access system used (source: Glutz). Testing of the building skin most often does not reveal the weakness of the access system, as existing standards only apply to the entire door and not to individual components of the door. Thus, the access system, being just a relatively small part of the entire door system in terms of surface area, does not invite scrutiny. Furthermore, even when a building is tested for air tightness, the entrance door is typically used to blow air into the building (blower door measurement), and thus the door and its access system is not part of the standard test. Little is known of the performance of standard access systems in actual situations. Empirical observations of damage caused by differences in air pressure combined with high volumes of airflows through the access system exist. However, no data is currently available as to the performance of such systems in terms of temperature and pressure gradients as well as in terms of absolute and relative humidity surrounding the system. Using an actual building, this study investigated the performance of an access system available on the market today. 2. Methods To gather data on the performance of a standard access system in respect to temperature and pressure gradients as well as in terms of absolute and relative humidity surrounding the system in daily use in an actual situation, a commercially available access system made by Glutz, a leading Swiss manufacturer, was installed into an entrance door of a single family home in the suburbs of Solothurn, Switzerland build according to the Minergie-P Standard (Verein Minergie 2014). However, at the time of the test, the house was not yet certified. This entrance door in question faced east. Measurements including temperature on the inside and on the outside as well as inside the access system, differential air pressure between the inside and the outside of the building and relative humidity inside and outside as well as inside the access system were taken. Figure 2 shows a cross cut of the access system and demonstrates the locations of the measurement points inside the system with red indicating surface temperature measurements and blue indicating measurements of relative humidity and air temperature th Conference on Advanced Building Skins

4 Figure 2: Cross cut through Glutz access system used and measurement points. Inside the building is to the right (Drawing: Glutz and BFH). Data was registered continuously over the length of the test. The test used measurement registration equipment from Ahlborn (Almeno ), pressure measurement devices (Ahlborn DPS), thermo couples type K, humidity sensors from Sensirion (SHT 75), and a weather station. Figure 3 shows the actual door and pinpoints the locations for the outside pressure ( Luftdruck Aussen ) and for the ambient outside temperature and relative humidity ( Temperatur und Feuchte Aussen ), as well as the location of the measurement points for the air pressure inside the building ( Messpunkt Luftdruck Innen ) and the temperature and relative humidity of the inside air ( Messpunkt Temperatur, Feuchte Innen ). 11th Conference on Advanced Building Skins 595

5 Figure 3: Picture of door and measurement points for outside and inside air pressure, temperature, and relative humidity. The test was conducted from November 27, 2012 to April 16, 2013, with measurements analyzed from December 17 to December 24, Air temperature and relative air humidity as well as door access system temperature and humidity at the measurement points (Figure 2) were measured and recorded continuously over the time period of the tests. 3. Results Figure 4 shows the temperatures measured at the measurement locations (Figures 2 and 3) the period from December 17 to December 24, Figure 5 shows the differential pressure between the inside and the outside of the building at the entrance door and the absolute humidity at the measurement points over the same period. Figure 6 displays the relative humidity inside and outside the building at the access system at the entrance door as well as inside the access system from December 17 to December 24, th Conference on Advanced Building Skins

6 28 Haus Minergie P - Temperaturen Temperatur T [ C] T_innen T1Schloss_innen T4Schloss_innen T4Schloss_aussen T3Schloss_aussen T2Schloss_aussen T1Antenne_aussen T_aussen Figure 4: Temperature recorded at the measurement locations from December 17 to December 24, Haus Minergie P - Differenzdruck und absolute Feuchte 12,00 11,00 10,00 absolute Feuchte ah [g/m3] -1 Differenzdruck P [Pa] ,00 8,00 7,00 Delta P > 0Pa Delta P <= 0Pa ah_aussen ahschloss_aussen ahschloss_innen ah_innen , , , Figure 5: Differential pressure between the inside and the outside of the building and absolute humidity at the measurement points from December 17 to December 24, th Conference on Advanced Building Skins 597

7 Haus Minergie P - Temperatur und relative Feuchte relative Feuchte rh [%] Temperatur T [ C] T innen T aussen rh_aussen rhschloss_aussen rhschloss_innen rh_innen Figure 6: Relative humidity inside and outside the building and inside the access system points from December 17 to December 24, Discussion The temperature curve on Figure 4 shows that the temperatures throughout the access system follow the outside temperature. The peak outside temperatures on shows the influence of the sun shining on the door and its impact on the system s temperature. The most pronounced effect of these sun-rays hitting the surface of the building component is at the location of the antenna for the access system. The antenna in this particular access system model (and thus the temperature and humidity sensor [Sensirion SHT 75] inserted at this location) are covered by a black plastic cover, heating up the location more than at other locations of measurement, where brighter colors (silver as from galvanized metal) were less impacted by the sun. However, the impact of the sun is visible throughout the access system s surface, and can be seen even at the inside of the access system. Figure 5 shows, with the exception of a limited number of cases, that the building inside is consistently under negative pressure with pressures ranging between -2 Pa to -3 Pa, -5 Pa to -6 Pa and -9 Pa to -10 Pa. It is assumed that these consistent negative pressure readings inside the building are caused by the operation or the settings of the mechanical ventilation in place. Figure 5 also shows that the absolute humidity inside the access system is about equal to the absolute humidity outside the building. These measures are about equivalent on both sides of the access system, e.g., on the side of the access system facing the outside and on the side of the access system facing the inside of the building. The most likely explanation for this observation is that air from the outside consistently flows through the access system inside the building due to the constant negative pressure that exists inside. Actually, even minimal pressure differential of as little as 2 Pa create a air volume flow through the access system that is sufficient to greatly influence the absolute humidity on the inside of the system. This occurs consistently independent on the absolute humidity that exists inside the building. The absolute humidity inside the building partially follows the absolute humidity on the outside, partially it appears to be decoupled from the other measurements, such that in fact no clear trend can be discerned. Figure 6 shows the levels of relative humidity measured outside and inside the access system as well as the temperature on the outside of the system. The relative humidity of the outside air and on the outside of the th Conference on Advanced Building Skins

8 access system are quite similar and follow the same trends, which makes sense based on on the data in Figures 4 and 5. However, the relative humidity measured on the side of the access system facing the inside of the building is decoupled from these observations. Yet, at this location, the absolute humidity measured is more meaningful. In any case, it has to be stated that during the duration of the tests, no damaging levels of humidity to the access system were measured at any time. Modern access systems rely on electronic components to do their tasks. Thus, humidity matters much more than in the days when locks functioned purely mechanical. In the climate in question (Central Europe) and without air-conditioning being present, the potential for high humidity exists at all openings of a building where air-exchange between the inside and the outside occurs. When warm air with large amounts of humidity wander through the opening towards the colder side of the building, condensation may occur if the temperature differential is large enough. Access systems represent such an opening in the building skin and thus the levels of humidity occurring inside the system need to be understood and, in the final product, be controlled as possibly large amounts of humidity or liquid can accumulate. For example, given the situation as tested in this study, if the inside temperature of a building on a winter day is 20 o Celsius with a relative humidity of 54 percent, while the outside temperature is 0 o Celsius and the inside pressure is 4 Pa higher than the outside, as much as 0.9 g of water per hour can potentially accumulate inside the access system. To illustrate, this accumulation is equivalent to throwing the equivalent of an Espresso-sized glass of water into the access system casing every day. This study has clearly demonstrated the importance of obtaining better understanding of and, ultimately, better controlling the climatic events happening inside and surrounding modern access systems. Attention must be paid to the air penetration of such systems as well as to the thermal properties of such access systems. Additional challenges to be mastered exist in the form of protection against rain. 5. Conclusions Research was conducted on a single-family home built according to Minergie-P standards (Verein Minergie 2014) main entrance door access system (e.g., door lock) sold on the Swiss market. Focus was given on the temperature and the humidity throughout the system while in normal daily use at this single-family building in the suburbs of Solothurn, Switzerland with the door facing east. Also, differential pressures between the inside of the building and the outside were measured and recorded. Measurements were taken starting on December 17 and ending December 24, Results include that current access systems sold, such as the one tested, perform less than optimally in terms of heat transfer. Temperatures from both sides of the system were transferred through the system with relative ease, creating the potential for undesirable energy transfers. However, given the small area of building skin covered by such access systems, this effect is rather minor. More importantly are the effects of the consistent pressure differentials between the outside and the inside of the building that are caused by the mechanical air conditioning system used in this building. The existence of positive or negative pressure differences, or the existence of fairly balanced pressures between inside and outside appear to be determined by the settings of the mechanical air condition unit. However, if the inside pressure is positive, the relative ease of air flow through the access system creates an considerable potential for moisture accumulation inside the access system due to convective moisture build-up. However, during the duration of the field test, no potentially damaging levels of humidity were recorded. 6. Acknowledgements The authors would like to thank Glutz AG, Swiss Access Systems, Solothurn, Switzerland for their cooperation and the provision of materials and knowledge. The financial support by the Swiss Commission for Technology and Innovation (CTI), which supported this project, is also gratefully acknowledged. 7. Literature Cited Verein Minergie Reglement und Nachweisverfahren zur Vergabe des MINERGIE - Zertifikats für MINERGIE - Modul Türen. ARGE Minergie Türen. Bachenbülach, Schweiz. 31 pp. 11th Conference on Advanced Building Skins 599