A simple airlfow path approach to sizing natural ventilation systems in a code context

Most of the existing ventilation standards are drafted in a rather prescriptive way. Growing focus on the implementation of rational energy use however, introduces an urgent need for more performance-based criteria. Optimization of energy consumption obviously encompasses minimization of ventilation airflow rates. Comfort, on the other hand, should not be reduced because of these actions. To implement this in a legal figure, one can appeal to the principle of equivalence. This principle states that all systems achieving equivalent performance to that of the systems described in the standard are acceptable. Better yet, a new standard can be devised, imposing a reference performance rather than a reference system. This avoids all discussion about the way the reference system’s performance should be interpreted. Nevertheless, practical implementation of a standard will require the definition of sizing guidelines for design purposes. The method presented in this paper is a simplified approximation of the airflow network in a building. It is conceived as a sizing guideline for natural ventilation systems in the context of a national ventilation standard. Supply, internal and exhaust resistances are the main parameters, next to overall building airtightness. These parameters are system independent and allow to describe a large scale of possible buildings. Five different dwellings, with different typologies, representative for the Flemish building stock, were evaluated for this purpose. The predicted airflow and indoor air quality are compared to that predicted by a detailed multi-zone model and acceptable agreement is found. This yields the conclusion that, for the implementation of a performance-based ventilation standard, straight forward calculation methods for sizing guidelines can be incorporated in the standard

Analysis of the influence of ventilation rate on sleep pattern

In this paper, the results from a field study on the influence of ventilation rate on the sleep pattern are presented. The testgroup was asked to sleep in their normal sleeping environment (student dorms) in order to cause as little disruption in the normal pattern as possible. For the same reason, actigraphy was used to measure sleep patterns since this is one of the least disturbing measurement techniques available. The student dorms were selected as a location because all rooms are identical and basic conditions are therefore very similar for all the participants in the study. The participants were also asked to fill out a number of questionnaires to determine their general attitude towards sleep and to get an idea of their subjective appreciation of the sleep quality experienced over the test period. The results show only a very small effect of the ventilation rate on the sleep pattern

Passive house ventilation strategies: demand control?

Since insulation levels in a passive house context are very high, energy losses trough ventilation are of relatively high importance in the total energy balance of a passive house concept. Although fully mechanical ventilation systems are at the core of the this concept, enabling both regeneration and cheap space heating, it can still be optimized. With demand controlled systems, excess ventilation can be minimized, thus reducing both redundant ventilation losses and the accompanying electrical loads. This paper reviews the possibilities for a performance based optimization of ventilation systems for passive houses within the context of the Belgian legislatio

Evaluation of a prescriptive ventilation standard with regard to 3 different performance indicators

In this paper, the performance of Belgian building code compliant residential ventilation systems is evaluated on multiple performance indicators: occupant exposure to bio-effluents, occupant exposure to other use-related pollutants (odours) and occupant exposure to building material emissions. The fitness of the proposed criteria in this context is then discussed in a broader context and this information is then used to interpret the fitness of the code prescriptions as design criteria for performant ventilation systems

Bedroom indoor air comfort : a critical analysis

The criteria that are currently used for the assessment of Indoor Air Quality in a residential context were developed in the ‘80s and relate to comfort during occupancy. More than half the time at home however, is spent in the bedroom. There is no strong indication that the criteria that are traditionally used to assess Indoor Air Quality also relate to the level of comfort while asleep. Moreover, analysis of the results of a performance assessment of frequently used residential ventilation systems based on these traditional criteria, shows that they are dominated by the pollution level in the bedrooms

Modeling cross-ventilation with multi-zone models

In the temperate climate region of Western Europe (UK/Belgium/France, The Netherlands, Germany), simple exhaust ventilation is a widely used ventilation strategy in dwellings. The merits of such systems in terms of ventilation performance have been studied intensively, mainly regarding the impact of sizing of the components (Laverge & Janssens, 2013) and demand controlled operation (Laverge et al. 2011). Cross-ventilaton strategies usually focus on window opening behaviour and exposure of the facades to the wind conditions. Maeyens (2003), however, demonstrated that the internal partitioning of the dwelling has a major impact on the expected ventilation flow rates. In conditions where the trickle ventilators of simple exhaust ventilation systems are sized for low pressure differences such as in the Belgian (2 Pa) or Dutch (1 Pa) ventilation standards, the pressure difference due to wind is often larger than that generated by the exhaust fan. Crossventilation therefore plays a major role in the performance of such systems. Below, the impact of internal partitioning of the dwelling on the share of cross ventilation in the total ventilation flow rate and ventilation heat loss will be discussed

Convective Heat Transfer coefficients in mechanical night ventilation: a sensitivity analysis

Since the Energy Performance for Buildings Directive (EPBD) was accepted and implemented over the course of the last years, buildings are audited energetically to receive the necessary construction licenses. This augmented the already high attention to research on innovative (passive) energy-saving system concepts even further. Previous research suggests that, although the effect of commissioning can be significant, specific fan power is the most important factor influencing the energetic viability of mechanically driven night ventilation as an active cooling replacement. This parameter should thus be the central point of focus during the design process. In this paper, we present an analysis of the effect of detailed convective heat transfer modeling on the predicted performance, in order to determine the level of detail needed to assess feasibility of this kind of system in early design phases. Results indicate that the effect amounts to 20-50% of the predicted performance and therefore cannot be neglected. It is within the range of effect of the dominant parameter, specific fan power. In light of these results, it is suggested that detailed convective heat transfer coefficient modeling is taken into account whenever forced convection due to large volume flow is introduced

Overcoming condensation problems in a closed cavity double skin façade

For highrise office buildings, double skin façades offer a attractive alternative in building envelope conception. A recurrent problem in concepts with single outdoor and double indoor glazing (“passive façade”) is condensation on the cavity side of the single glass pane. Permasteelisa Group developed a innovative concept, employing a fully sealed cavity and a very modest dry air flow (“closed cavity façade”), that prevents condensation at all times, thus preventing dirt offset on the window panes and eliminating the need for cleaning inside the cavity over the lifetime of the façade. This paper presents a coupled multizone airflow / thermal model developed to assess condensation risk inside the cavity under different climate conditions and the initial validation. Additional validation experiments are held in the 2008-2009 winter season. This model is now implemented as a R&D tool and to size the system components in actual projects

Performance assessment of demand controlled ventilation controls concerning indoor VOC exposure based on a dynamic VOC emission model

The performance assessment of ventilation systems often focusses only on CO2 and humidity levels. The indoor Volatile Organic Compounds (VOC) emissions of building materials or other products is thereby overlooked. The new generation of ventilation systems, Demand Controlled Ventilation (DCV), are systems that do not supply the nominal airflow continuously but are controlled by CO2 or humidity sensors in order to save energy. This poses potential problems for exposure to VOCs. In this study, a dynamic VOC model, which takes into account changing temperature and humidity that was derived from literature, is implemented in a CONTAM model of the Belgian reference apartment. The impact of a DCV system on the indoor VOC levels is investigated. Results show that the use of a dynamic model is necessary compared to the previously used approximation of a constant emission. Furthermore, on a system level, the influence of the ventilation system control on the indoor VOC levels shows. The overall VOC concentration in the different rooms will be higher because of lowered ventilation rates. Especially in rooms that are often unoccupied during the day, the accumulation of VOCs shows. In the development of DCV system controls, the aspect of VOC exposure should not be overlooked to be able to benefit from both the energy savings and improved Indoor Air Quality (IAQ)

A comparison of different ventilation strategies for dwellings in terms of airflow rates and airflow paths

The context of ventilation in Belgian dwellings has changed since the publication of the Belgian standard NBN D 50-001:1991. Due to the higher energy performance of these dwellings, ventilation plays nowadays a more essential role in maintaining a good indoor air quality. Therefore, new rules for improved ventilation strategies are needed to accomplish high energy-efficient ventilation while providing a good indoor air quality. A first step is to compare different ventilation strategies, including strategies that don’t comply with the current standard, in terms of airflow rates and airflow paths. This comparison also includes the influence of demand controlled ventilation. This paper covers a simulation study using multi-zone airflow and contaminant transport calculation software (CONTAM) which compares the performances of the different ventilation strategies in terms of indoor air quality and average airflow rates. The evaluation of the indoor air quality is based on the exposure of the occupants to CO2 and VOC and on the relative humidity in the rooms. The different ventilation strategies can achieve a comparable indoor air quality, including the strategies not conform to the Belgian standard. However, some strategies require up to twice the airflow rate than others