Abstract: This article presents the performance study of a novel decentralized ventilation system for hot and humid climates such as found in Singapore. Decentralized ventilation has a great potential for reducing pressure losses because of the short travel distances of the air. The combination of decentralized ventilation with high temperature radiant cooling offers the potential for a very energy efficient operation of buildings in hot and humid climates and to decrease their exergy destruction. Core of the ventilation system studied is a modified design of a decentralized ventilation unit incorporating a 3-stage heat exchanger. This particular heat exchanger setup ensures sufficient cooling capacity for dehumidification and offers free energy for reheating. In the process of the air treatment, the two heat exchangers’ upstream takes the roles of pre-cooling and cooling/dehumidification while the third one covers the reheating process. The results show that with the studied ventilation unit outdoor air with temperatures around 30 °C and a humidity ratio of 20 g/kg can be chilled, dehumidified and reheated such that target conditions in the supply air of 14–15 °C and 8–9 g/kg are achieved. In addition, this novel decentralized ventilation system can save around 4–5% of total cooling energy demand due to free reheating.
Permalink: https://doi.org/10.1016/j.enbuild.2014.02.021

Abstract: This research presents energy and exergy analyses of a new decentralized ventilation system to adapt to the hot and humid climate compared to general centralized ventilation systems. A zone model of an office building was applied for a heat pump cooling system in Singapore. The cooling load capacity of the zone model was simulated using the building energy simulation software “TRNSYS” and energy and exergy analyses of the new ventilation system were carried out through numerical calculations based on the measured cooling load capacity. An effective energy solution for buildings was to increase cooling and ventilation efficiency. The energy and exergy analyses evaluated the performance of the various cooling systems. The research revealed that the new decentralized ventilation system adapted to the hot and humid climate had better performance compared to a centralized all-air system and to a chilled ceiling with centralized air handling unit system.
Permalink: https://doi.org/10.1016/j.enbuild.2014.05.009

Abstract: This research discusses the use of an Airbox convector unit for cooling and dehumidification to prevent moisture condensation on the surface of chilled ceiling panels in hot and humid climates. The combination of displacement ventilation with high temperature radiant cooling offers the potential for an energy-efficient operation of buildings in tropical climates; however, it hardly avoids moisture condensation risks if there are high infiltration rates or internal moisture gain. This study presents the cooling and dehumidification performance of a novel Airbox unit hydraulically connected in series with a chilled ceiling panel. The unit is equipped with a fan and two heat exchangers that are hydraulically connected in series with a chilled ceiling panel. In the process of air treatment, the Airbox unit chills and dehumidifies indoor air while reducing the risk of moisture condensation on the panel because it not only dehumidifies indoor air but also increases the surface temperature of the chilled ceiling panel at same time. This novel system generates additional cooling capacity without the need for supplemental cooling sources due to enhanced mixed convection effects.
Permalink: https://doi.org/10.1016/j.enbuild.2014.09.031

Abstract: This paper presents the moisture performance of a novel radiant cooling system connected in series to an Airbox convector adapted to hot and humid climate. Radiant cooling systems have a major benefit in terms of energy savings; however, there is a risk of condensation on the surface of the chilled panel when a room has outside humid air infiltration or high internal moisture gains. Therefore, in order to activate the radiant cooling system, the air in the space needs to be dehumidified to a steady state humidity ratio below 13 g/kg, which causes a significant time delay before startup. Implementing an Airbox convector system connected to the radiant ceiling panel reduces the risk of moisture condensation because it simultaneously dehumidifies indoor air and increases the surface temperature of the chilled panel. This study shows the findings on its humidity performance and ability to reduce the risk of condensation by means of numerical modeling and experimentation. This novel system is sufficiently effective to be used in environments with high infiltration of humid outdoor air because the Airbox convector reduces the time delay when activating the radiant panel system, dehumidifies indoor air and increases the dew point temperature of the ceiling panels.
Permalink: https://doi.org/10.1016/j.enbuild.2014.08.005

Abstract: This study presents feasible performance of a system that combines an airbox convector unit with a radiant chilled ceiling panel for application in tropical climates. This combined system offers the potential for effective cooling and dehumidification for buildings in tropical climates because the airbox convector not only dehumidifies indoor air but also enhances the mixed convective effect, which combines natural convection with mechanical forced convection, in indoor conditions with moisture gains caused by high infiltration rates or internal heat and moisture gains. This paper presents a case study that demonstrates the enhanced mixed convection effects of the combined system as well as the cooling and dehumidification performance of the system. This novel system not only reduces the moisture condensation risk but also contributes to maximizing the temperature of the cooling system as a low exergy technology.
Permalink: https://doi.org/10.1016/j.buildenv.2014.10.012

Abstract: This work reports a numerical investigation of shock focusing phenomena over concave surfaces. The study focuses on the effects of Reynolds and Mach numbers on the detailed behavior of flow features related to shear-layer instabilities and jet formation in the post-shock region. Computations are done for four incident-shock Mach numbers covering subsonic and transonic flow regimes and a wide range of Reynolds numbers. The simulations reveal a number of interesting wave features starting from early stage of shock interaction and transition from inverse-Mach reflection to transitioned regular reflection followed by very complex flow patterns at focusing and post focusing stages. Different subsequent flow characteristics develop as a result of multiple shock/shear layer interactions. During the later stage of the flow interaction, a formation of two opposing jets is predicted by the simulation in accordance with the experiments. It is shown that the formation of primary opposing jets as well as the development of Kelvin-Helmholtz instabilities can be hindered for low Mach and Reynolds numbers. However, for high flow regimes a second pair of opposing jets appears and develops far from the wall, exhibiting similar features as the primary pair of opposing jets at moderate Mach numbers. Two new bifurcations in flow patterns are observed at this stage which promote further development of vortex structures and shear-layer rollup.
Permalink: https://doi.org/10.1063/1.4890482

Abstract: In this study, passive cooling of a room using a solar chimney and water spraying system in the room inlet vents is simulated numerically in Yazd, Iran (a hot and arid city with very high solar radiation). The performance of this system has been investigated for the warmest day of the year (5 August) which depends on the variation of some parameters such as water flow rate, solar heat flux, and inlet air temperature. In order to get the best performance of the system for maximum air change and also absorb the highest solar heat flux by the absorber in the warmest time of the day, different directions (West, East, North and South) have been studied and the West direction has been selected as the best direction. The minimum amount of water used in spraying system to set the inside air averaged relative humidity <65 % is obtained using trial and error method. The simulation results show that this proposed system decreases the averaged air temperature in the middle of the room by 9–14 °C and increases the room relative humidity about 28–45 %.
Permalink: https://doi.org/10.1007/s00231-014-1366-5

Abstract: Buildings generally need serious attention in order to reduce global energy consumption and greenhouse gas emissions. Phase Change Materials (PCMs) that change phase just above normal room temperature are a promising means of reducing cooling-energy demand, and improving thermal comfort in buildings. This paper reviews the literature from studies of the thermal performance of different types of PCM and different ways of integrating them into buildings. Based on this review, the paper closes with an investigation of the potential for application of PCMs in passive-house standard dwellings and office buildings in the Nordic climate.
Permalink: https://doi.org/10.1016/j.egypro.2014.12.393

Abstract: Today, there is an obvious lack of sufficient integration of daylight in building design. The literature has been reviewed in order to see if knowledge exists to formulate an improved daylight design methodology which may be consistently integrated with thermal comfort and energy use design. Based on findings in the literature, a proposal is given on how daylight calculations and evaluations may be implemented throughout the building design. Important features in the proposed design are: early implementation of simulation tools, implementation of climate-based daylight modelling, and coupling between simulation tools for daylight, thermal comfort and energy use to ensure consistency in the design. The design proposal has been tested and the results show that the method might lead to a design with satisfying indoor environment and low energy use. Yet, more research is needed to validate and to set proper benchmark values for newly proposed climate-based daylight metrics.

Abstract: The Marienlyst School is the first educational building in Norway built according to the passive house standard. This building benefits from a super-insulated and airtight envelope. While this reduces the heating demand largely, it also enhances the risk for poor indoor air quality and overheating compared to conventional buildings. It is therefore particularly important to implement an efficient ventilation strategy in order to avoid adverse effects on the health, well-being and productivity of the pupils. In this context, the perceived indoor climate resulting from two different ventilation control strategies was evaluated in one classroom of the building. Both strategies consisted in varying the ventilation rate according to room demand, ie. Demand Controlled Ventilation (DCV). The existing strategy consisted in varying the ventilation rate in order to maintain a constant carbon dioxide concentration of 800 ppm in the classroom. A new strategy was implemented which consisted in a combined CO₂ and temperature DCV, ie. to control towards a proportionally lower CO₂ concentration when the indoor temperature increased. The aim with this strategy was to address both overheating and the fact that perceived indoor air quality decreases when temperature rises. Indoor climate measurements, as well as questionnaires on the perceived indoor air quality and thermal comfort filled up by the pupils were used to compare both strategies. The data from the questionnaires were then analyzed using a random effect linear regression model. The regression analysis revealed that the initial ventilation strategy was responsible for discomfort resulting from too high variations in the indoor temperature. The new combined CO₂ and temperature DCV strategy provided a perceived indoor climate which was significantly better than the existing strategy. Therefore, the developed ventilation strategy appears to be a relevant solution in order to address the problem of overheating and perceived indoor air quality in educational buildings with passive house standard.

Abstract: In this article we compare to ventilation strategies to heat a “passive house” office building using only the ventilation system. Two ventilation strategies with supply air temperature above and below the current room temperature were compared through a cross over experiment. A questionnaire was used to measure the perceived health and well being. Both strategies documented very good indoor climate with highly positive scores on the questionnaire. The strategy with supply air temperature above the room temperature resulted in a little better perceived health and well being compared to the other strategy.

Abstract: The impact of over-tempered air on the perceived indoor climate was evaluated by questionnaires filled in by the users of the first office building with passive house standard in Norway. In this building, the heating demand is covered entirely by warm air supplied into the rooms through the ventilation system. On the coldest days of January 2014, warm ventilation air was supplied into the rooms at a constant temperature during half an hour. Each user of the building was exposed to 3 different supply temperatures (around 21.5°C, 24°C and 26°C) under the minimum ventilation rate according to the Norwegian standards (17 l/s). Questions related to both perceived thermal comfort and Sick Building Syndrome-symptoms (SBS; feeling tired, headache, etc.) were answered by all the occupants on a scale of 0 (unsatisfied) to 10 (satisfied). The data from the questionnaires were then analyzed using a random effect linear regression model. The regression analysis did not report any significant relationship between the supply air temperature, and perceived thermal comfort and SBS. It enables to document with a 95% certainty that increasing the difference between supply air and room temperature by 1°C would cause a maximum reduction of the SBS score of 1.02 points on a scale of 190. The impact of an increase of the supply temperature on the perceived SBS seems therefore very limited. Using air heating to completely cover the heating demand therefore appears to be a relevant solution for office buildings in cold climate with passive house standard.

Abstract: The future is well-isolated buildings with low heating demand. The first office building in Norway satisfying the passive house standard, the GK environmental house in Oslo, was taken into use in August 2012. Low energy building is the standard for new buildings according to the building codes today, and since passive house standard seems to be included in the building codes in Norway from 2015 there is a great change in the building industry. To meet the low energy concept, the ventilation industry must cope with a massive change from use of installations with constant air volume (CAV) to demand controlled ventilation. At the same time new technology with active air handling units makes new ventilation systems more flexible to demand controlled ventilation and temperature control, air velocity and draft. The low heating demand in future buildings address the question – is it possible to use simplified heating systems, or even only air heating without any backup heating system, also for the coldest days in Norway and still have satisfied users? However, given the cold climate in Norway, totally eliminating a backup heating system for the coldest days and only use overheated supply air would be a tough decision without proper documentation. The R & D project “Simplified demand controlled air conditioning in office buildings with very low heating demand” will develop concepts for ventilation based space heating fit to buildings with very low heating demand, as well as develop documentation on the function and the conditions that must be fulfilled. (www.sintef.no/projectweb/For-Klima). The project period is three years, starting 2013. This paper reviews the results so far. So far a broad range of studies have been done: Field measurements and intervention studies with user survey on perceived indoor climate at GK environmental house, laboratory measurements, calculations and theoretical evaluations. This paper discusses the results so far after the first winter period. These are preliminary results that will have to be confirmed by further studies next winter.

Abstract: MRT model for IDA Indoor Climate and Energy (IDA ICE). The new feature of the model is that it includes the effect of shortwave radiation in the room and contributes to a more comprehensive prediction of operative temperature, e.g. of a person exposed to direct sun light. The verification of the model is carried out by comparing simulation results with fullscale measurements of a team office located in Oslo (59°N,10°E). The measurements were conducted during mid-March and April 2013. The results indicate that the new MRT model might contribute to considerable improvements in prediction of thermal comfort of persons affected by direct solar radiation. This may further have implications on the predicted energy use and design of the façade, since e.g. an enlarged need for local cooling or use of dynamic solar shading might be discovered.

Abstract: The indoor climate was evaluated in a cubicle office of the first office building with passive house standard in Norway. The office building (http://miljohuset-gk.no/) is located in Oslo and operational since August 2012. In this building, demand controlled ventilation is used to cover the heating demand by supplying warm ventilation air into the rooms when needed. The purpose of this study is to determine whether this strategy provides a good thermal comfort and ventilation effectiveness, and therefore constitutes a relevant solution for buildings with low heating demand. Measurements were carried out in the cubicle office during the coldest days of winter 2013-2014, and revealed a good indoor climate for a broad range of supplying and heat load conditions.