Guilherme Carrilho Da Graca

University of Lisbon | UL · Departamento de Engenharia Geográfica, Geofísica e Energia (DGGE)

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 l...

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...

The design for the new Federal Building for San Francisco includes an office tower that is to be naturally ventilated. Each floor is designed to be cross-ventilated, through upper windows that are controlled by the building management system. Users have control over lower level windows, which can be as much as 50% of the total openable area. There...

This paper presents the results of the thermal and airflow simulation of an existing naturally ventilated shopping mall located near Lisbon, Portugal. Thermal and airflow simulation is used to improve the original natural ventilation system design in order to address winter thermal comfort problems that were due to excessive cold airflow in the mal...

This study explores the feasibility of solar Net Zero Energy Building (NZEB) systems for a typical single family home in the mild southern European climate zone. Using dynamic thermal simulation of two representative detached house geometries, solar collector systems are sized in order to meet all annual energy needs. The impact of variations in bu...

Over one billion of the world’s population live in slum houses (SHs), mostly self-built. Due to their poor construction and lack of mechanical cooling in hot regions, SHs are particularly vulnerable to overheating and ongoing climate change. This paper presents the overheating mitigation results of four selected DIY low-cost roof upgrades for a typ...

This paper presents the development and experimental testing of an innovative low-pressure loss PM2.5 filter channel that can be integrated in building façades. This indoor-outdoor filter uses electrostatic precipitation (ESP) to reduce outdoor PM2.5 ingress into the indoor environment while ensuring the low airflow resistance that natural ventilat...

Ongoing concerns about electrical grid stability and existing economic interests create unattractive conditions for grid-injection of renewable energy produced in building integrated photovoltaic systems (BIPV). As a result, BIPV often fails to use the full potential of the building envelope and site. An effective approach to increase BIPV size is...

This report reviews and discusses methodologies for weather indicators, weather datasets, and production of future weather files that will be used in the context of the ABC 21 project.

Corner rooms with two or more open windows in perpendicular facades can be naturally ventilated in cross-ventilation or pumping ventilation. These two airflow regimes also occur in rooms with two openings in the same façade, in the form of single sided pumping or cross sided ventilation. This paper presents an experimental and numerical simulation...

The majority of office and other non‑domestic buildings use mechanical cooling and ventilation, even when an optimized natural ventilation (NV) system could meet cooling and fresh air requirements. However, in most large cities, the outdoor environment is contaminated with a combination of noise, fine particles, heat and toxic gases. This contamina...

Natural ventilation (NV) through a single openable window (SS1) is the most common passive cooling strategy for small rooms. SS1 NV driven by wind can be propelled by pressure variations along the opening or, in medium and large buildings, wind driven shear. This paper presents an experimental study of the impact of typical window geometries on SS1...

In this study, a grey box (GB) model for simulating internal air temperatures in a naturally ventilated nearly zero energy building (nZEB) was developed and calibrated, using multiple data configurations for model parameter selection and an automatic calibration algorithm. The GB model was compared to a white box (WB) model for the same application...

Upcoming climate change effects will vary with region, season and time of the day. Existing annual and daily temperature cycles will shift and be reshaped, leading to increased air temperatures earlier and later in the year. Buildings will be affected by these changes, especially the ones using passive design strategies, whose performance is highly...

In buildings with exposed internal thermal mass, natural ventilation (NV) can be used for nighttime pre-cooling (NVC) of the building for the next day. In many cases, these natural cooling systems are used in combination with conventional mechanical cooling systems (an approach known as hybrid cooling). The use of these systems is still limited, in...

Unstable interaction between shear layers that form in the wake of an isolated building exposed to wind can drive natural pumping ventilation in windward and leeward facing rooms with two or more horizontally separated openings. This paper presents an experimental and numerical study of pumping ventilation in a three-story cubic building with two l...

PM2.5 has significant health effects that lead to decreased life expectancy (DLE). Yet, the outdoor PM2.5 levels found in most urban environments exceed the safety limits set by the World Health Organization. In this context, using natural ventilation (NV) in urban indoor workspaces results in unhealthy increases in occupant exposure to outdoor PM2...

In the last decade, building energy simulation (BES) became a central component in building energy systems’ design and optimization. For each building location, BES requires one year of hourly weather data. Most buildings are designed to last 50+ years, consequently, the building design phase should include BES with future weather files considering...

To increase the penetration of photovoltaic renewable energy (PV RE) in the residential building sector energy mix, the mismatch between midday production and evening electrical energy demand must be bridged. The use of heat pumps for space heating of residential buildings creates an opportunity for energy flexible residential buildings that rely o...

Airborne fine particulate matter (PM2.5) is a pollutant that is found in all urban environments. PM2.5 is predominantly generated by traffic and domestic fuel combustion and has significant negative health impacts. The ever-growing urban population spends most of their time in indoor environments where it is exposed to PM2.5 that is brought in from...

During cooling seasons, a progressively warmer and increasingly urban world is leading to hostile internal thermal environments in many high-performance buildings. Correctly Implemented, Ventilative Cooling can mitigate unwanted building overheating while minimising cooling loads. Identifying different solutions with proven performance can be inval...

A substantial part of the energy demand of residential buildings is due to fossil fuel powered space and domestic hot water heating. Reductions in the energy use of these buildings can be achieved by improving the thermal envelope, installing efficient building energy systems and improving user behavior. Alternatively, it may be possible to use hyd...

Single sided ventilation is a commonly used room natural ventilation strategy. Small, single occupant offices, often use single sided ventilation through a single opening (SS1). In most multistory buildings, the ratio between building façade and SS1 window opening area is 0.1% or less. In these cases, wind driven SS1 flows are caused by entrainment...

This paper presents a two-stage numerical study of the effects of airborne fine particle pollution on the usability of natural ventilation in three Asian megacities (Beijing, Shanghai and New Delhi), using measured weather and PM2.5 data. The first stage assessed the impact of personal comfort systems on NV availability and their combined effect on...

In recent years, concerns about global warming and greenhouse gas emissions have motivated designers to reduce building energy consumption through the implementation of passive solutions without compromising users' thermal comfort. This evidence has stimulated a renewed interest in designers for the exploitation of natural ventilation as means of p...

Most natural ventilation (NV) systems used in non-residential buildings are single sided (SS). These systems are easy to integrate in the building layout, since, unlike in cross-ventilation (CV), these systems do not require access to two facades or a central stack. Current knowledge about SS NV flow penetration away from the façade can be found in...

In recent years, concerns about global warming and greenhouse gas emissions have motivated designers to reduce building energy consumption through the implementation of passive solutions without compromising users' thermal comfort. This evidence has stimulated a renewed interest in designers for the exploitation of natural ventilation as means of p...

Overheating is an unwanted consequence of modern building designs and internal gains that will be aggravated by the effects of climate change on local climates within urban and suburban areas. To minimise the energy cost of limiting overheating several different approaches exist for passive cooling dissipation techniques. Free cooling by ventilatio...

In California, the majority of office and other nondomestic buildings use mechanical cooling and ventilation even when an optimized natural ventilation (NV) system could meet cooling and fresh air requirements. Unfortunately, in most large California cities, the outdoor environment is contaminated with noise, fine particles, heat, toxic gases or, i...

This paper presents a numerical analysis of the effect of fine particle pollution on the natural ventilation potential of office buildings in nine European cities. Several years of measured weather and PM2.5 concentration data were used to perform statistical and dynamic thermal and airflow simulation analysis. The statistical analysis confirmed th...

Displacement ventilation (DV) systems were initially developed as an efficient buoyant pollutant removal strategy for Scandinavian industrial halls in the 1970´s. 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 co...

Children spend the majority of their weekdays in classrooms that often have low indoor air quality and limited financial resources for the initial and running costs of mechanical ventilation systems. Designing effective natural ventilation (NV) systems in schools is difficult due to the intense use of the classroom spaces and the dependence of NV o...

This paper presents a study of the impact of horizontal aperture separation in single-sided ventilation flows with two apertures (SS2). The study is based on wind tunnel measurements and dimensional analysis. The results show that the SS2 ventilation flow rate, scaled with incoming wind velocity and aperture area, depends on the incoming wind angle...

This paper presents a study of the impact of horizontal aperture separation in single-sided ventilation flows with two apertures (SS2). The study is based on wind tunnel measurements and dimensional analysis. The results show that the SS2 ventilation flow rate, scaled with incoming wind velocity and aperture area, depends on the incoming wind angle...

Throughout history, natural ventilation has remained the preferred choice for the majority of residential buildings, while, in commercial buildings, natural ventilation went from being the single option to somewhat of a lost art as mechanical ventilation systems and air conditioning became the standard during the second half of the twentieth centur...

Throughout history, natural ventilation has remained the preferred choice for the majority of residential buildings, while, in commercial buildings, natural ventilation went from being the single option to somewhat of a lost art as mechanical ventilation systems and air conditioning became the standard during the second half of the twentieth centur...

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...

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...

This paper presents an application of building thermal and airflow simulation tools to the design of a naturally ventilated office building located in the center of Lisbon (Portugal). The seventeen-story building will have a hybrid ventilation system. The facade and natural ventilation system design were optimised using three interrelated simulatio...

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 syst...

This paper presents a validation of airflow network (AFN) and computational fluid dynamics (CFD) simulations for a naturally ventilated office building using wind tunnel measurements as the reference for external pressure coefficients and effective airflow rate prediction. The CFD simulation model is also used to study the effect of partially open...

Cross-ventilation flows (CV) are characterized by significant inflow momentum conservation as fluid flows across an enclosed rectangular volume as a confined jet. When the inflow area is smaller than the volume cross-sectional area the CV flow has distinct jet and recirculation flow regions. The simplified model presented in this paper characterize...

Energy efficiency in buildings is of particular importance in the pursuit of international objectives in the area of climate and energy, as it is a sector that represents approximately 40% of the total primary energy demand in the world, with expected strong growth. In Portugal, the current Building Energy Certification and Indoor Air Quality Syste...

This paper presents an application of building thermal and CFD simulation in the refurbishment of the HVAC system of the Gulbenkian great hall in Lisbon (Portugal). The existing overhead mixing ventilation system was converted into displacement ventilation. The thermal simulation tool EnergyPlus was used to size the HVAC system. CFD simulations whe...

Energy efficiency in buildings is of particular importance in the pursuit of international objectives in the area of climate and energy, as it is a sector that represents approximately 40% of total primary energy demand, with strong growth prospects for absolute consumption [1]. In Portugal, the implementation of the energy certification system (SC...

This paper presents a building energy simulation study of the impact of electrical peak demand reduction strategies in a large office tower in New York that has extensive use of daylight responsive dimmable ballasts, and under floor air distribution systems (UFAD). The complexity and large size of the building imposed careful simplification of the...

The climate indicators that are currently used in the building energy area, summations of degree-days, are not suitable for net-zero and low energy analysis, because they fail to characterize the building-climate interaction. This paper presents a new set of climate indicators that focuses on overall climate and building performance, as well as spe...

This thesis evaluates the performance of daytime and nighttime passive ventilation cooling strategies for Beijing, Shanghai and Tokyo. A new simulation method for cross-ventilated wind driven airflow is presented . This method decouples the airflow model from the thermal model allowing for fast real weather simulation of the building thermal perfor...

This paper presents a study to integrate photovoltaic (PV) production larger than micro-generation in urban areas, using the school roofs as installation sites. This initiative is part of a more comprehensive effort to increase dispersed electricity production as opposition to a conventional policy of centralized electricity production often locate...

This paper presents a study of room cross-ventilation airflow. A simplified model is developed using scaling analysis, experimental correlations, and computational fluid dynamics. The model distinguishes two regions in the room, the main jet region and the recirculations, and models relevant flow features that are essential inputs when predicting h...

This paper presents a performance evaluation of two passive cooling strategies, daytime ventilation and night cooling, for a generic, six-story suburban apartment building in Beijing and Shanghai. The investigation uses a coupled, transient simulation approach to model heat transfer and airflow in the apartments. Wind-driven ventilation is simulate...

This paper presents two simplified models of building natural ventilation. The models improve existing approaches by incorporating momentum conservation effects. The first model predicts the main temperature variations and heat transfer in the airflow in a room. The second model predicts the flow rates through different rooms in a cross-ventilated...

Buildings protect their occupants from the outside environment. As a semi-enclosed environment, buildings tend to contain the internally generated heat and air pollutants, as well as the solar and conductive heat gains that can occur in the facade. In the warmer months of the year this generally leads to overheating, creating a need for a cooling s...

This paper presents an analysis of the thermal behaviour of the new San Diego Children's museum and the subsequent development of a low energy climate control system. The museum is designed as a naturally ventilated building with no mechanical heating or cooling. The exhibition space consists of two galleries on the first and second floors and an a...