Displacement ventilation (DV) systems were initially developed as an efficient buoyant pollutant ... more Displacement ventilation (DV) systems were initially developed as an efficient buoyant pollutant removal strategy for Scandinavian industrial halls in the 1970s. In the following decades these systems started to be used in mechanical cooling of office buildings and auditoriums. Designing displacement ventilation systems is more challenging than conventional overhead mixing systems. Most DV system designs require simplified modeling tools. Existing simplified models of DV were validated using air temperature measurements performed in test cells that cannot reproduce the conditions that exist in large rooms with thermally active boundary conditions. There is a lack of measurements that investigate the performance of DV systems in occupied large rooms. With the goal of reducing this knowledge gap, this paper presents a set of detailed temperature and CO 2 measurements in two occupied large rooms with recently designed DV systems. The measurements were performed in two recently refurbished rooms located in Lisbon: a large Concert hall and an adjacent Orchestra rehearsal room. The measurements and subsequent analysis were used to assess the actual performance of large room, state of the art, DV systems. In addition, these measurements were used to determine the modeling error of the three-node DV model implemented in EnergyPlus when simulating large rooms. Comparison between simulations and measurements revealed a good agreement: the average simulation error obtained by averaging the error of all measurements in all temperature nodes is 5.9%, with the largest deviation occurring in the floor level node (7.1% z 0.4 C) average simulation error of 5.9% (the average of error of all measurements in all nodes).
Typically vertical temperature gradient is modelled to be linear over the room height. More advan... more Typically vertical temperature gradient is modelled to be linear over the room height. More advanced models consist of several nodes that allow different slopes for the temperature profile between the nodes. Validation and development of all those models have been based mainly on measurement using low ceiling height (below 3 m). Also, the previous studies have not covered typical flow elements that exist in office buildings. In this study, the performance of a displacement ventilation system is studied using 3.3 m and 5.1 m ceiling heights in a variety of load conditions. Typical buoyant flow elements and heat load combinations were measured in a simulated office room. The experimental study included room air temperature measurements at different heights and locations over the occupied zone in addition to surface measurement and supply and exhaust air temperature measurements. The measurement data was compared with current models. The results show that the major part of the vertical temperature gradient occurs already at low level. With some typical buoyant flow elements there is no benefit if the ceiling is lower or higher level. Also, measurements depict that modelled non-dimensional temperature profile using low ceiling height (about 3 m) is not valid for high ceiling applications (more than 4 m). Multi-node models works quite well with several buoyant flow elements. Still, the proposed multi-node models did not give good estimation of the vertical temperature gradient when warm window surface or heat gains at ceiling level were introduced in the room space.
This paper presents two case studies of stack driven ventilative cooling systems implemented in k... more This paper presents two case studies of stack driven ventilative cooling systems implemented in kindergarten schools located in the mild Subtropical-Mediterranean climate of Lisbon, Portugal. Both systems rely on stack driven natural ventilation supplemented by a larger, single-sided ventilation opening to be used in the warmer months. In both systems air enters the rooms at a low level, directly in front of the heating passive convector systems, and is exhausted in the back of the room, through a chimney. In addition to the smaller opening configuration, that is sized for the heating and mild seasons (1-3% of room floor area) both designs have larger openings to be used during the cooling season. This larger opening is fundamental to meet the minimum code requirement for total ventilation opening area (5% of floor area). The designs were developed and fine-tuned using dynamic thermal simulation (EnergyPlus). This approach allowed for straightforward statistical analysis of expected system performance, assessed in terms of thermal comfort and indoor air quality. Measurements in steady state mode show a good agreement between simulated and measured airflow rate. During the warmer months the smaller and protected heating season openings are opened for night cooling effect. The chimney exhausts were optimized to avoid opposing stack and wind effects. Both systems are user controlled. The importance of effective commissioning of passive systems is discussed and an example of a simple user manual is provided. The performance of these systems shows that a well-designed natural ventilation system can ensure adequate levels of indoor air quality in kindergartens.
Most current building thermal codes impose upper limits to the predicted annual building energy d... more Most current building thermal codes impose upper limits to the predicted annual building energy demand for heating, ventilation and air conditioning. In the building design phase these predictions are obtained using thermal simulations with variable complexity. The simplest approach uses a single lumped thermal capacitance to model the high thermal mass building elements, combined with five thermal resistances (known as the 5R1C model proposed in EN ISO 13790 standard). This model is used by many European countries as the reference simplified methodology to assess overheating risk and calculate yearly building energy demand. This paper presents a successful extension of this model that allows for its application to the prediction of the internal air temperature of free-running buildings with double skin faç ades. The extension consists in an increased number of thermal resistances used to model the double skin faç ade zone. The extended model is validated using a set of detailed thermal measurements obtained in a free-running double skin test cell. For the case analysed the simplifications used in the RC model do not reduce the overall accuracy: the mean absolute error for room air temperature is approximately 1 • C, the same order of magnitude of more detailed EnergyPlus simulations (1.2 • C).
This paper presents two case studies of stack driven ventilative cooling systems implemented in k... more This paper presents two case studies of stack driven ventilative cooling systems implemented in kindergarten schools located in the mild Subtropical-Mediterranean climate of Lisbon, Portugal. Both systems rely on stack driven natural ventilation supplemented by a larger, single-sided ventilation opening to be used in the warmer months. In both systems air enters the rooms at a low level, directly in front of the heating passive convector systems, and is exhausted in the back of the room, through a chimney. In addition to the smaller opening configuration, that is sized for the heating and mild seasons (1-3% of room floor area) both designs have larger openings to be used during the cooling season. This larger opening is fundamental to meet the minimum code requirement for total ventilation opening area (5% of floor area). The designs were developed and fine-tuned using dynamic thermal simulation (EnergyPlus). This approach allowed for straightforward statistical analysis of expected system performance, assessed in terms of thermal comfort and indoor air quality. Measurements in steady state mode show a good agreement between simulated and measured airflow rate. During the warmer months the smaller and protected heating season openings are opened for night cooling effect. The chimney exhausts were optimized to avoid opposing stack and wind effects. Both systems are user controlled. The importance of effective commissioning of passive systems is discussed and an example of a simple user manual is provided. The performance of these systems shows that a well-designed natural ventilation system can ensure adequate levels of indoor air quality in kindergartens.
Displacement ventilation (DV) flows are more complex than conventional overhead mixing systems si... more Displacement ventilation (DV) flows are more complex than conventional overhead mixing systems since the stratified room environment cannot be modeled using the traditional fully mixed room air approach. A successful DV designer must be able to control the vertical room temperature profile and manage the position of the lower boundary of the upper air layer that contains heat and pollutants. The inclusion of a chilled ceiling (CC) in the DV system increases the complexity by adding the need to manage the CC cooling power so that it does not disrupt the DV stratification. This paper presents the extension of an existing DV nodal model so that the effects of the CC in room airflow and air temperatures can be predicted. The model uses three air nodes and focuses on the thermal plumes as the drivers of the airflow and room air heat exchange. The proposed model is validated using twelve different test chamber configurations from three independent experimental studies. When compared with existing models the proposed model achieves improved precision and model flexibility while using less air nodes. The last section of the paper presents a set of CC/DV design charts that can assist system designers in early design phases.
Displacement ventilation (DV) systems are characterized by thermal stratification that cannot be ... more Displacement ventilation (DV) systems are characterized by thermal stratification that cannot be adequately modeled using the fully mixed room air approach that is common in overhead air conditioning system design. This paper presents a simplified approach for DV that models the room thermal
stratification using three air temperature nodes: lower layer (floor level), occupied zone and upper layer.
The proposed approach is a development of one of the two models currently available in the thermal simulation tool EnergyPlus. A methodology for locating the neutral height in temperature profiles was developed. This methodology was used to verify the applicability of Morton et al. (1956) plume flow equation to predict the neutral level in DV rooms. The proposed model was successfully validated using nine different scenarios from three independent experimental studies. The model provides significantly improved precision when compared to existing DV nodal models, in particular in the floor level and occupied zone temperatures.
This paper presents an application of building thermal and computational fluid dynamics (CFD) sim... more This paper presents an application of building thermal and computational fluid dynamics (CFD) simulation in the refurbishment project of the Gulbenkian great hall in Lisbon (Portugal). The thermal simulation tool EnergyPlus was used to size the HVAC system. CFD simulations where used to predict detailed airflow velocity and temperatures in the space and to access the precision of the mixed and displacement ventilation models that are currently available in EnergyPlus (E+) .
This paper presents a thermal simulation validation study of the typical precision that a trained... more This paper presents a thermal simulation validation study of the typical precision that a trained thermal simulation engineer can expect to obtain for the simulation of a room connected to a naturally ventilated double skin facade. The open source building thermal simulation tool EnergyPlus is used to predict air and surface temperatures in a free running weather exposed test cell. The validation approach used does not allow for fine tuning the simulation model by trial and error and includes a sensitivity analysis on the impact of different simulation options such as: number of thermal zones, ground heat transfer and accuracy of solar radiation data. The analysis of the results is consistent with the engineering application goal by focusing on standard indicators: average error, bias and difference between predicted and measured daily maximums. The results show good agreement between simulation and experiment, with an average simulation error in air and radiant temperature of 1.4 • C and an average daily maximum error of 2.5 • C.
Displacement ventilation (DV) systems were initially developed as an efficient buoyant pollutant ... more Displacement ventilation (DV) systems were initially developed as an efficient buoyant pollutant removal strategy for Scandinavian industrial halls in the 1970s. In the following decades these systems started to be used in mechanical cooling of office buildings and auditoriums. Designing displacement ventilation systems is more challenging than conventional overhead mixing systems. Most DV system designs require simplified modeling tools. Existing simplified models of DV were validated using air temperature measurements performed in test cells that cannot reproduce the conditions that exist in large rooms with thermally active boundary conditions. There is a lack of measurements that investigate the performance of DV systems in occupied large rooms. With the goal of reducing this knowledge gap, this paper presents a set of detailed temperature and CO 2 measurements in two occupied large rooms with recently designed DV systems. The measurements were performed in two recently refurbished rooms located in Lisbon: a large Concert hall and an adjacent Orchestra rehearsal room. The measurements and subsequent analysis were used to assess the actual performance of large room, state of the art, DV systems. In addition, these measurements were used to determine the modeling error of the three-node DV model implemented in EnergyPlus when simulating large rooms. Comparison between simulations and measurements revealed a good agreement: the average simulation error obtained by averaging the error of all measurements in all temperature nodes is 5.9%, with the largest deviation occurring in the floor level node (7.1% z 0.4 C) average simulation error of 5.9% (the average of error of all measurements in all nodes).
Typically vertical temperature gradient is modelled to be linear over the room height. More advan... more Typically vertical temperature gradient is modelled to be linear over the room height. More advanced models consist of several nodes that allow different slopes for the temperature profile between the nodes. Validation and development of all those models have been based mainly on measurement using low ceiling height (below 3 m). Also, the previous studies have not covered typical flow elements that exist in office buildings. In this study, the performance of a displacement ventilation system is studied using 3.3 m and 5.1 m ceiling heights in a variety of load conditions. Typical buoyant flow elements and heat load combinations were measured in a simulated office room. The experimental study included room air temperature measurements at different heights and locations over the occupied zone in addition to surface measurement and supply and exhaust air temperature measurements. The measurement data was compared with current models. The results show that the major part of the vertical temperature gradient occurs already at low level. With some typical buoyant flow elements there is no benefit if the ceiling is lower or higher level. Also, measurements depict that modelled non-dimensional temperature profile using low ceiling height (about 3 m) is not valid for high ceiling applications (more than 4 m). Multi-node models works quite well with several buoyant flow elements. Still, the proposed multi-node models did not give good estimation of the vertical temperature gradient when warm window surface or heat gains at ceiling level were introduced in the room space.
This paper presents two case studies of stack driven ventilative cooling systems implemented in k... more This paper presents two case studies of stack driven ventilative cooling systems implemented in kindergarten schools located in the mild Subtropical-Mediterranean climate of Lisbon, Portugal. Both systems rely on stack driven natural ventilation supplemented by a larger, single-sided ventilation opening to be used in the warmer months. In both systems air enters the rooms at a low level, directly in front of the heating passive convector systems, and is exhausted in the back of the room, through a chimney. In addition to the smaller opening configuration, that is sized for the heating and mild seasons (1-3% of room floor area) both designs have larger openings to be used during the cooling season. This larger opening is fundamental to meet the minimum code requirement for total ventilation opening area (5% of floor area). The designs were developed and fine-tuned using dynamic thermal simulation (EnergyPlus). This approach allowed for straightforward statistical analysis of expected system performance, assessed in terms of thermal comfort and indoor air quality. Measurements in steady state mode show a good agreement between simulated and measured airflow rate. During the warmer months the smaller and protected heating season openings are opened for night cooling effect. The chimney exhausts were optimized to avoid opposing stack and wind effects. Both systems are user controlled. The importance of effective commissioning of passive systems is discussed and an example of a simple user manual is provided. The performance of these systems shows that a well-designed natural ventilation system can ensure adequate levels of indoor air quality in kindergartens.
Most current building thermal codes impose upper limits to the predicted annual building energy d... more Most current building thermal codes impose upper limits to the predicted annual building energy demand for heating, ventilation and air conditioning. In the building design phase these predictions are obtained using thermal simulations with variable complexity. The simplest approach uses a single lumped thermal capacitance to model the high thermal mass building elements, combined with five thermal resistances (known as the 5R1C model proposed in EN ISO 13790 standard). This model is used by many European countries as the reference simplified methodology to assess overheating risk and calculate yearly building energy demand. This paper presents a successful extension of this model that allows for its application to the prediction of the internal air temperature of free-running buildings with double skin faç ades. The extension consists in an increased number of thermal resistances used to model the double skin faç ade zone. The extended model is validated using a set of detailed thermal measurements obtained in a free-running double skin test cell. For the case analysed the simplifications used in the RC model do not reduce the overall accuracy: the mean absolute error for room air temperature is approximately 1 • C, the same order of magnitude of more detailed EnergyPlus simulations (1.2 • C).
This paper presents two case studies of stack driven ventilative cooling systems implemented in k... more This paper presents two case studies of stack driven ventilative cooling systems implemented in kindergarten schools located in the mild Subtropical-Mediterranean climate of Lisbon, Portugal. Both systems rely on stack driven natural ventilation supplemented by a larger, single-sided ventilation opening to be used in the warmer months. In both systems air enters the rooms at a low level, directly in front of the heating passive convector systems, and is exhausted in the back of the room, through a chimney. In addition to the smaller opening configuration, that is sized for the heating and mild seasons (1-3% of room floor area) both designs have larger openings to be used during the cooling season. This larger opening is fundamental to meet the minimum code requirement for total ventilation opening area (5% of floor area). The designs were developed and fine-tuned using dynamic thermal simulation (EnergyPlus). This approach allowed for straightforward statistical analysis of expected system performance, assessed in terms of thermal comfort and indoor air quality. Measurements in steady state mode show a good agreement between simulated and measured airflow rate. During the warmer months the smaller and protected heating season openings are opened for night cooling effect. The chimney exhausts were optimized to avoid opposing stack and wind effects. Both systems are user controlled. The importance of effective commissioning of passive systems is discussed and an example of a simple user manual is provided. The performance of these systems shows that a well-designed natural ventilation system can ensure adequate levels of indoor air quality in kindergartens.
Displacement ventilation (DV) flows are more complex than conventional overhead mixing systems si... more Displacement ventilation (DV) flows are more complex than conventional overhead mixing systems since the stratified room environment cannot be modeled using the traditional fully mixed room air approach. A successful DV designer must be able to control the vertical room temperature profile and manage the position of the lower boundary of the upper air layer that contains heat and pollutants. The inclusion of a chilled ceiling (CC) in the DV system increases the complexity by adding the need to manage the CC cooling power so that it does not disrupt the DV stratification. This paper presents the extension of an existing DV nodal model so that the effects of the CC in room airflow and air temperatures can be predicted. The model uses three air nodes and focuses on the thermal plumes as the drivers of the airflow and room air heat exchange. The proposed model is validated using twelve different test chamber configurations from three independent experimental studies. When compared with existing models the proposed model achieves improved precision and model flexibility while using less air nodes. The last section of the paper presents a set of CC/DV design charts that can assist system designers in early design phases.
Displacement ventilation (DV) systems are characterized by thermal stratification that cannot be ... more Displacement ventilation (DV) systems are characterized by thermal stratification that cannot be adequately modeled using the fully mixed room air approach that is common in overhead air conditioning system design. This paper presents a simplified approach for DV that models the room thermal
stratification using three air temperature nodes: lower layer (floor level), occupied zone and upper layer.
The proposed approach is a development of one of the two models currently available in the thermal simulation tool EnergyPlus. A methodology for locating the neutral height in temperature profiles was developed. This methodology was used to verify the applicability of Morton et al. (1956) plume flow equation to predict the neutral level in DV rooms. The proposed model was successfully validated using nine different scenarios from three independent experimental studies. The model provides significantly improved precision when compared to existing DV nodal models, in particular in the floor level and occupied zone temperatures.
This paper presents an application of building thermal and computational fluid dynamics (CFD) sim... more This paper presents an application of building thermal and computational fluid dynamics (CFD) simulation in the refurbishment project of the Gulbenkian great hall in Lisbon (Portugal). The thermal simulation tool EnergyPlus was used to size the HVAC system. CFD simulations where used to predict detailed airflow velocity and temperatures in the space and to access the precision of the mixed and displacement ventilation models that are currently available in EnergyPlus (E+) .
This paper presents a thermal simulation validation study of the typical precision that a trained... more This paper presents a thermal simulation validation study of the typical precision that a trained thermal simulation engineer can expect to obtain for the simulation of a room connected to a naturally ventilated double skin facade. The open source building thermal simulation tool EnergyPlus is used to predict air and surface temperatures in a free running weather exposed test cell. The validation approach used does not allow for fine tuning the simulation model by trial and error and includes a sensitivity analysis on the impact of different simulation options such as: number of thermal zones, ground heat transfer and accuracy of solar radiation data. The analysis of the results is consistent with the engineering application goal by focusing on standard indicators: average error, bias and difference between predicted and measured daily maximums. The results show good agreement between simulation and experiment, with an average simulation error in air and radiant temperature of 1.4 • C and an average daily maximum error of 2.5 • C.
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Papers by Nuno Mateus
stratification using three air temperature nodes: lower layer (floor level), occupied zone and upper layer.
The proposed approach is a development of one of the two models currently available in the thermal simulation tool EnergyPlus. A methodology for locating the neutral height in temperature profiles was developed. This methodology was used to verify the applicability of Morton et al. (1956) plume flow equation to predict the neutral level in DV rooms. The proposed model was successfully validated using nine different scenarios from three independent experimental studies. The model provides significantly improved precision when compared to existing DV nodal models, in particular in the floor level and occupied zone temperatures.
stratification using three air temperature nodes: lower layer (floor level), occupied zone and upper layer.
The proposed approach is a development of one of the two models currently available in the thermal simulation tool EnergyPlus. A methodology for locating the neutral height in temperature profiles was developed. This methodology was used to verify the applicability of Morton et al. (1956) plume flow equation to predict the neutral level in DV rooms. The proposed model was successfully validated using nine different scenarios from three independent experimental studies. The model provides significantly improved precision when compared to existing DV nodal models, in particular in the floor level and occupied zone temperatures.