Improved HVAC operation to preserve a church organ

The common operation of heating systems installed in churches in the Netherlands has led to typical building physics problems directly related with heating. One of the main problems is the drying related shrinkage and damage to (monumental) wooden organs under cold winter conditions. The paper presents an integrated heat, air and moisture model including modelling components for: the indoor climate of the church, the heating systems and operation, and the moisture distribution in wood. The modelling components are validated with measurements. Two types of control strategies are discussed. The first type is a limited indoor air temperature changing rate. The second type is a limited indoor air relative humidity changing rate. This preliminary study shows that a limitation of indoor air temperature changing rate of 2 K/h can reduce the peak drying rates by a factor of 20 and a limitation of the relative humidity changing rate of 2% per hour can reduce the peak drying rates by a factor of 50. The second strategy has the disadvantage that the heating time is not constant and therefore more difficult to implement in relation with early start-up.     

建筑内表面吸放湿过程对室内环境和空调负荷影响的仿真研究

提出了一个考虑室内表面材料吸放湿过程的建筑热湿过程简化模型,介绍了对室内空气湿度及空调负荷的仿真分析。仿真结果表明,室内表面材料吸放湿过程有明显的降低湿度变化幅度的作用,对潜热负荷的影响较大     

Effects of indoor environmental parameters related to building heating,ventilation, and air conditioning systems on patients' medical outcomes: A review of scientific research on hospital buildings

The indoor environment of a mechanically ventilated hospital building controls infection rates as well as influences patients’ healing processes and overall medical outcomes. This review covers the scientific research that has assessed patients’ medical outcomes concerning at least one indoor environmental parameter related to building heating, ventilation, and air conditioning (HVAC) systems, such as indoor air temperature, relative humidity, and indoor air ventilation parameters. Research related to the naturally ventilated hospital buildings was outside the scope of this review article. After 1998, a total of 899 papers were identified that fit the inclusion criteria of this study. Of these, 176 papers have been included in this review to understand the relationship between the health outcomes of a patient and the indoor environment of a mechanically ventilated hospital building. The purpose of this literature review was to summarize how indoor environmental parameters related to mechanical ventilation systems of a hospital building are impacting patients. This review suggests that there is a need for future interdisciplinary collaborative research to quantify the optimum range for HVAC parameters considering airborne exposures and patients’ positive medical outcomes.     

Double cooling coil model for non-linear HVAC system using RLF method

The purpose of heating, ventilating and air conditioning (HVAC) system is to provide and maintain a comfortable indoor temperature and humidity. The objective of this work is to model building structure, including equipments of HVAC system. The hybrid HVAC model is built with physical and empirical functions of thermal inertia quantity. Physical laws are used to build the sub-model for subsystems that have low thermal inertia while the empirical method is used to build the sub-model for subsystems with high thermal inertia. The residential load factor (RLF) is modeled by residential heat balance (RHB). RLF is required to calculate a cooling/heating load depending upon the indoor/outdoor temperature. The transparency, functionality of indoor/outdoor temperatures and simplicity of RLF makes it suitable for modeling. Furthermore, the parameters of the model can be calculated differently from room to room and are appropriate for variable air volume (VAV) factor. Nowadays, a VAV system is universally accepted as means of achieving both energy efficiency and comfortable building environment. In this research work, a pre-cooling coil is added to humidify the incoming air, which controls the humidity more efficiently inside conditioned space. The model presented here is verified with both theoretical and numerical methods.     

Development of regression equations for predicting energy and hygrothermal performance of buildings

Regression equations can be used for predicting indoor air temperature, relative humidity and energy consumption in an easier and more rapid way than building energy simulation tools. The independent variables, that is, the input data, are heating, ventilation and air conditioning (HVAC) power, outdoor temperature, relative humidity and total solar radiation. The present methodology for obtaining the regression equations is based on defining a couple of linear Multiple-Input/Single-Output (MISO) models, since two main outputs are involved, that is, indoor temperature and relative humidity. The methodology has been tested for the low- and high-thermal mass cases of the BESTest model (cases 600 and 900) and the output data is generated by using a building hygrothermal simulation tool. Validation procedures have shown very good agreement between the regression equations and the simulation tool for both winter and summer periods.     

Impact of combined moisture buffering capacity of a hemp concrete building envelope and interior objects on the hygrothermal performance in a room

In this article, a hygrothermal building model, taking into account the building envelope, indoor heat and moisture sources, indoor environment and moisture buffering capacity of interior objects, is presented and validated with the test cases found in the literature. The model is used to study the impact of hemp concrete and the moisture buffer capacity of the interior elements on the prediction of the hygrothermal comfort in the building. The numerical results show that the use of hemp concrete in buildings can ensure good hygrothermal comfort. Besides, taking into account the effect of moisture buffering of indoor objects increases the building performance. Our results also suggest that neglecting moisture transfer through the envelope increases significantly the predicted percentage of dissatisfied indices and reduces the acceptability of indoor air quality during the occupied period. This study also confirmed that the combined relative humidity-sensitive ventilation system and moisture buffering capacity of building envelope and of interior objects is a very efficient way to reduce the heating energy consumption.     

Evidence of inadequate ventilation in portable classrooms: results of a pilot study in Los Angeles County

The prevalence of prefabricated, portable classrooms (portables) for United States public schools has increased; in California, approximately one of three students learn inside portables. Limited research has been conducted on indoor air and environmental quality in American schools, and almost none in portables. Available reports and conference proceedings suggest problems from insufficient ventilation due to poor design, operation, and/or maintenance of heating, ventilation and air conditioning (HVAC) systems; most portables have one mechanical, wall-mounted HVAC system. A pilot assessment was conducted in Los Angeles County, including measurements of integrated ventilation rates based on a perfluorocarbon tracer gas technique and continuous monitoring of temperature (T) and relative humidity (RH). Measured ventilation rates were low [mean school day integrated average 0.8 per hour (range: 0.1-2.9 per hour)]. Compared with relevant standards, results suggested adequate ventilation and associated conditioning of indoor air for occupant comfort were not always provided to these classrooms. Future school studies should include integrated and continuous measurements of T, RH, and ventilation with appropriate tracer gas methods, and other airflow measures. PRACTICAL IMPLICATIONS: Adequate ventilation has the potential to mitigate concentrations of chemical pollutants, particles, carbon dioxide, and odors in portable and traditional classrooms, which should lead to a reduction in reported health outcomes, e.g., symptoms of 'sick building syndrome', allergies, asthma. Investigations of school indoor air and environmental quality should include continuous temperature and relative humidity data with inexpensive instrumentation as indicators of thermal comfort, and techniques to measure ventilation rates.     

Transfer function model and frequency domain validation of moisture sorption in air-conditioned buildings

Moisture transfer in building components and furnishings has significant effect on indoor air humidity and latent cooling load. Many mathematical models and calculation methods have been proposed to evaluate this effect. Simple but accurate models are what the users expect. Investigation shows that the one-dimensional linear moisture transfer model, which uses the vapor pressure as the unique driving potential, is both very simple and well match the real moisture transfer characteristics of most air-conditioned buildings. Frequency analysis shows completely consistent characteristics between the transfer function model of moisture sorption by interior surface materials and the one-dimensional linear moisture transfer model through the entire wall within the frequency range that should be concerned. It also shows that the moisture penetration across the wall is neglectable. The transfer function model of moisture sorption by interior surface materials is not only very simple but also has satisfactory accuracy to evaluate the moisture transfer effect of buildings on indoor air humidity and latent cooling load.     

HVAC air-quality model and its use to test a PM2.5 control strategy

This paper presents a MATLAB^® Simulink air-quality model of a commercial building with a heating, ventilation, and air conditioning (HVAC) system in Fairbanks, Alaska. Outdoor and indoor real-time fine particulate matter (PM_2.5) levels were measured at this building during a summer wild-fire smoke episode and then during a winter period. The correlation coefficient between the model-predicted and the measured indoor concentrations was 0.99 for the summer and 0.98 for the winter, justifying the usability of the model for further studies. An HVAC control algorithm was developed that reduces the indoor PM_2.5 levels. The algorithm was tested using the HVAC Simulink model and the outdoor PM_2.5 data from the summer smoke episode. The average indoor PM_2.5 level with this control algorithm was 65% lower than with the regular control. Thanks to the PM_2.5 control strategy being automatically engaged only during episodes, it was shown to have the potential of significantly reducing the indoor PM_2.5 levels without significantly compromising the purpose of the original control strategy.     

The effectiveness of stand alone air cleaners for shelter-in-place

Stand-alone air cleaners may be efficient for rapid removal of indoor fine particles and have potential use for shelter-in-place (SIP) strategies following acts of bioterrorism. A screening model was employed to ascertain the potential significance of size-resolved particle (0.1-2 microm) removal using portable high efficiency particle arresting (HEPA) air cleaners in residential buildings following an outdoor release of particles. The number of stand-alone air cleaners, air exchange rate, volumetric flow rate through the heating, ventilating and air-conditioning (HVAC) system, and size-resolved particle removal efficiency in the HVAC filter were varied. The effectiveness of air cleaners for SIP was evaluated in terms of the outdoor and the indoor particle concentration with air cleaner(s) relative to the indoor concentration without air cleaners. Through transient and steady-state analysis of the model it was determined that one to three portable HEPA air cleaners can be effective for SIP following outdoor bioaerosol releases, with maximum reductions in particle concentrations as high as 90% relative to conditions in which an air cleaner is not employed. The relative effectiveness of HEPA air cleaners vs. other removal mechanisms was predicted to decrease with increasing particle size, because of increasing competition by particle deposition with indoor surfaces and removal to HVAC filters. However, the effect of particle size was relatively small for most scenarios considered here. PRACTICAL IMPLICATIONS: The results of a screening analysis suggest that stand-alone (portable) air cleaners that contain high efficiency particle arresting (HEPA) filters can be effective for reducing indoor fine particle concentrations in residential dwellings during outdoor releases of biological warfare agents. The relative effectiveness of stand-alone air cleaners for reducing occupants' exposure to particles of outdoor origin depends on several factors, including the type of heating, ventilating and air-conditioning (HVAC) filter, HVAC operation, building air exchange rate, particle size, and duration of elevated outdoor particle concentration. Maximum particle reductions, relative to no stand-alone air cleaners, of 90% are predicted when three stand-alone air cleaners are employed.     

Improving PAQ and comfort conditions in Spanish office buildings with passive climate control

Some researchers have demonstrated that passive moisture transfer between indoor air and hygroscopic structures has the potential to moderate variations of indoor air relative humidity and, thus, to improve comfort and PAQ [Simonson CJ, Salonvaara M, Ojalen T. The effect of structures on indoor humidity-possibility to improve comfort and perceived air quality. Indoor Air 2002; 12: 243–51; Simonson CJ, Salonvaara M, Ojalen T. Improving indoor climate and comfort with wooden structures. Espoo 2001. Technical Research Centre of Finland, VTT Publications 431.200p+app 91p]. The main objective of this study is to show the internal wall coating effect on indoor air conditions and, as a consequence of this, in comfort conditions and PAQ.     

Modell und Programm CLIMT zur einfachen Ermittlung der Raumlufttemperatur und Raumluftfeuchte bei freier Klimatisierung

In der Planungspraxis besteht Bedarf nach einem vergleichsweise (siehe TRNSYS, ENERGY PLUS) einfachen und zuverlässigen Handwerkszeug zur Quantifizierung des Raumklimas. In diesem Beitrag wird ein praktikables Modell zur Ermittlung der Stundenwerte für die Raumlufttemperatur, die Empfindungstemperatur (Mitteltemperatur aus Raumluft‐ und Umschließungsflächentemperatur) und die Raumluftfeuchte in Abhängigkeit vom Außenklima (Außenlufttemperatur, Wärmestrahlung und relative Luftfeuchtigkeit der Außenluft), von den Gebäudeparametern (Geometrie, Wärmetransportwiderstände der Hüllkonstruktion, Wärme‐ und Feuchteabsorptionsvermögen der Bauteile), von der Lüftung und der Raumnutzung (innere Wärmequellen, innere Feuchtequellen und raumluftregulierte Heizung) bei freier Klimatisierung vorgestellt. Die Ergebnisse bilden den Quelltext für das nutzerfreundliche Windows‐Programm CLIMT (CLimate‐Indoor‐Moisture‐Temperature). Modell und Programm CLIMT werden durch einen Vergleich mit Rechenwerten nach TRNSYS und Messwerten in einem Testhaus validiert. Die Ergebnisse stimmen sehr gut überein. Das Programm CLIMT ist anwenderfreundlich und praxistauglich. Model and program CLIMT for a simplified determination of room temperature and relative humidity under arbitrary climate conditions. In planning practice there is a need for a comparably simple (cf. TRNSYS, ENERGY PLUS), reliable tool for quantifying an indoor climate. In this article a practicable model is put forward for determining the hourly values for natural conditioning of indoor air temperature, the perceived temperature (average of air and enclosing surface temperatures) and the interior air humidity in relation to the external climate (external air temperature, radiant heat and relative humidity of the outside air), the building parameters (geometry, heat transfer resistance of the shell structure, heat and moisture absorption properties of the components), the ventilation and the use of the space (interior heat sources, interior moisture sources and interior air‐regulated heating). The results form the source text for the user‐friendly Windows program CLIMT (CLimate‐Indoor‐Moisture‐Temperature). The CLIMT model and program are validated in a test house by comparing values calculated using TRNSYS with measured values. The results agree very well. The CLIMT program is user‐friendly and practically‐oriented.     

Modeling of the heating system in small building for control

Model identifications for the heating system of small building are presented. Basic problems of data acquisition and preprocessing are detailed. Specially designed wire-less data collection and control system to conduct real-world experiments are described. The model structure choice based on analysis of weather condition influences on the system performance are presented. Finally, the general structure of two-layered heating control strategy for the heating system is proposed. Instead of heating, ventilating and air conditioning (HVAC) standard, the proposed strategy controls only indoor temperature and changes the set point according to additional measurements of indoor humidity to keep thermal comfort. Non-linear compensation of outdoor temperature and wind speed is also introduced.     

Determination of indoor humidity profile using a whole-building hygrothermal model

During the design of a new building or retrofitting of an existing one, it is important to reliably assess the indoor humidity levels of the building as it can potentially affect the building envelope durability, occupants’ comfort and health risks associated with mould growth. Simplistic assumptions of indoor humidity profiles, which ignore the dynamic coupling of the indoor environment and building enclosure, may lead to inaccurate conclusions about the indoor environment and moisture performance of the building enclosure. In this paper, a whole-building hygrothermal model called HAMFitPlus, which takes into account the dynamic interactions between building envelope components, mechanical systems and indoor heat and moisture generation mechanisms, is used to assess the indoor humidity condition of an existing occupied house. HAMFitPlus is developed on SimuLink development platform and integrates COMSOL multiphysics with MatLab. The basic input parameters of the model are discussed in detail, and its simulation results are presented. In general, the HAMFitPlus simulation results are in good agreement with the measured data.     

新建建筑围护结构热质传递对室内温湿度环境的影响

新建建筑第1年由于较大的内表面散湿量会影响室内的温湿度水平,严重的会引起围护结构内表面霉菌。为分析新建建筑第1年围护结构的湿传递对室内温湿度环境的影响,本文对哈尔滨地区新建建筑综合热质耦合传递进行了模拟,分别建立了围护结构和室内空气的质能平衡方程,并讨论了夏季不同的室内通风率对围护结构内表面散湿量及室内温湿度的影响,得出了几点重要结论。     

长江中下游地区梅雨季节的室内热湿环境

经过调研得到长江中下游地区(以南京为例)梅雨季节住宅建筑室内热湿状况,并分析3种不同建筑能耗计算模型(整体建筑热湿空气流动耦合模型HAM,传递函数模型CTF,有效湿渗透深度模型EMPD)的准确性。数值模型基于Matlab-Simulink编写,使用调研数据进行验证,进而使用梅雨季节典型气象参数模拟分析。调研结果显示在2013年梅雨季节,多数时间内建筑室内温度高于28℃,相对湿度高于70%。数值模拟结果显示3种能耗模型对室内温度模拟的差异较小,而对室内湿度的模拟存在较大差异,特别是CTF模型误差最大。结果显示在长江中下游地区梅雨季节,当房间换气次数小于2ACH时,围护结构对于室内环境湿缓冲的作用明显,选择合适的吸放湿材料可有效降低建筑能耗30%以上。     

An integrated modeling tool for simultaneous analysis of thermal performance and indoor air quality in buildings

To analyze the thermal performance and indoor air quality (IAQ) in building simultaneously and quickly, we have developed an integrated modeling tool to simulate the dynamic indoor multi-parameters distributions and concentrations. The tool can take the parameters including indoor temperature, indoor humidity, and pollutant concentrations (e.g., volatile organic compounds (VOC) CO₂, particulate matter (PM)), as well as the heating/cooling load of heating, ventilating, and air-conditioning (HVAC) system into account. It couples a new zonal approach based on room air age. This paper presents the basic concept and flow chart in developing the modeling tool, and demonstrates the tool's application in a hypothetical health care building. The tool could be used for design of HVAC system with IAQ control devices and for the simultaneous analysis of thermal performance and IAQ in buildings.     

The effect of structures on indoor humidity--possibility to improve comfort and perceived air quality

The research presented in this paper shows that moisture transfer between indoor air and hygroscopic building structures can generally improve indoor humidity conditions. This is important because the literature shows that indoor humidity has a significant effect on occupant comfort, perceived air quality (PAQ), occupant health, building durability, material emissions, and energy consumption. Therefore, it appears possible to improve the quality of life of occupants when appropriately applying hygroscopic wood-based materials. The paper concentrates on the numerical investigation of a bedroom in a wooden building located in four European countries (Finland, Belgium, Germany, and Italy). The results show that moisture transfer between indoor air and the hygroscopic structure significantly reduces the peak indoor humidity. Based on correlations from the literature, which quantify the effect of temperature and humidity on comfort and PAQ for sedentary adults, hygroscopic structures can improve indoor comfort and air quality. In all the investigated climates, it is possible to improve the indoor conditions such that, as many as 10 more people of 100 are satisfied with the thermal comfort conditions (warm respiratory comfort) at the end of occupation. Similarly, the percent dissatisfied with PAQ can be 25% lower in the morning when permeable and hygroscopic structures are applied.     

Transfer function method to calculate moisture absorption and desorption in buildings

A transfer function approach has been described to calculate dynamic moisture absorption and desorption by building materials in the hygroscopic range, and the dynamic moisture absorption and desorption processes have been theoretically modeled. Their surface vapor pressure and moisture absorption and desorption flux can be evaluated by this approach. It has turned out mathematically that the material surface attains instantaneous moisture equilibrium with the surroundings at high Biot number (Bi → ∞), and that the material moisture behavior can be described through a lumped-parameter modeling at low Biot number (Bi → 0). For building materials at intermediate Biot number, comparisons with experimental results and numerical solutions have shown satisfactory agreement with the proposed approach. Using this approach, the dynamic response of moisture absorption and desorption in interior building materials to the variation of indoor air humidity and the dynamic effect of moisture absorption and desorption by building interior materials on indoor air humidity and space latent cooling load can be simultaneously calculated.     

Moisture-induced stresses perpendicular to grain in cross-sections of timber members exposed to different climates

In variable humidity conditions, wood absorbs or desorbs moisture from the air. Unless the change in humidity is very slow, this will develop moisture gradients in the wood sections. These gradients will develop stresses due to constrained swelling or shrinkage strains. These stresses are named moisture-induced stresses. The present paper investigates the main parameters affecting such moisture-induced stresses, including the type of climate, the size of the timber cross-section, and the type of protective coating. A first attempt to identify moisture-induced stresses in different European climatic regions was made. For each climatic region, relative humidity and temperature histories were identified, and characteristic and mean values of yearly and daily variations were calculated. Using a finite element model implemented in Abaqus, the moisture content and stress distribution were computed on different timber cross-sections exposed to the climatic regions and protected with different types of coating. A Fickian moisture transfer model was used to compute the moisture distribution, and a mechanical model for time-dependent behaviour of wood was implemented to calculate the corresponding stress distribution. The variation of moisture was found to result in stresses of magnitudes that would probably cause cracking of wood in the perimeter of any uncoated cross-section size. The use of a protective coating, however, reduced considerably the moisture-induced stresses, and can be regarded as an effective protective measure to avoid cracking due to humidity variations. Considering European climates, Northern climates were found to result in higher surface tensile stresses than Southern climates.