Low Energy Office Building Research Articles

Heating and ventilation efficiencies of a solar chimney integrated system in a low-energy office building

Mechanical air conditioning systems have a significant share of energy consumption in the building sector. Passive solar systems, such as solar chimneys, can reduce building energy demand by supplying space heating, cooling, and ventilation, significantly decreasing greenhouse gas emissions. Therefore, this study aimed to evaluate the heating and ventilation efficiencies of a solar chimney integrated system, including a roof solar chimney coupled with an air channel, for a two-story office building in Tehran, Iran. The studied system's conditions are switchable from heating to cooling by changing the opening positions. Computational Fluid Dynamics was employed to numerically investigate the heating and ventilation efficiencies of the proposed solar system. The results confirmed that the system could be utilized for pre-heating purposes during working hours but that the building should be ventilated only for 35% of this time with an air change rate of 0.8 during the year's coldest month. The arrangement could provide thermal and ventilation comfort for the occupied space only at solar intensity and ambient temperature higher than 550 W/m2 and 10 °C, respectively. In addition, the solar system could reduce 32% of the annual heating demand (918 kWh), which is equal to a reduction of 1865 kg of CO2 emissions during working hours.

Sensitivities of energy use reduction in subtropical high-rise office buildings: A Hong Kong case

Office buildings are a major contributor to energy consumption in high-density urban contexts where building high-rises is a norm. It is important to understand the parameters affecting high-rise office buildings’ energy consumption. However, previous research generally used isolated buildings as target buildings, regardless of the impact brought by the surrounding buildings. Also, there lacked a comprehensive calibration method to validate the energy baseline model. This paper aims to quantitatively analyse the energy use in high-rise office buildings by tackling these two issues and examining the impacts of various energy-saving measures (ESMs). A real-life 26-story office building in Hong Kong was selected as a base case. Multiple methods were used to calibrate the building energy model, including onsite microclimate measurement, metered data, architectural drawings and official documents, and onsite surveys. Parametric sensitivity analyses were then conducted to quantify the importance of ten selected parameters from five types of ESMs. Results indicate that fan efficiency and cooling setpoint temperature had the most significant energy-saving potential. The base case of the ESMs in use was considered as the base scenario. Two new scenarios were proposed to examine the range of total energy consumption by adopting the most and least energy-efficient ESMs, which were referred to as the “optimistic scenario” and the “pessimistic scenario”. The maximum reduction/increase in energy use is expected to be approximately 13.2%/39.3% for the optimistic/pessimistic scenario compared to the base scenario. The findings on the sensitivities and scenarios contribute to a more comprehensive understanding of the critical parameters that influence energy use in high-rise office buildings in subtropical climate. The findings also provide scenario-based design solutions for delivering low-energy office buildings.

Optimization of building demand flexibility using reinforcement learning and rule-based expert systems

The increasing use of renewable energy in buildings requires optimization of building demand flexibility to reduce energy costs and carbon emissions. Nevertheless, the optimization process is generally challenging that needs to consider the on-site intermittent energy supply, dynamic building energy demand, and proper utilization of energy storage systems. Leveraging the growing availability of operational data in buildings, data-driven strategies such as reinforcement learning (RL) have emerged as effective approaches to optimizing building demand flexibility. However, training a reliable RL agent is practically data-demanding and time-consuming, limiting its practical applicability. This study proposes a new strategy that integrates a rule-based expert system (RBES) and RL agents into the decision-making process to jointly reduce building energy costs, minimize the peak-to-average ratio (PAR) of grid power, and maximize PV self-consumption. In this strategy, the RBES determines system operation directly in less complex decision-making scenarios, while, in more intricate decision-making environments, it provides a reference decision for RL to explore optimal solutions further. This integration empowers RL agents to avoid unnecessary exploration and significantly enhance learning efficiency. The proposed strategy was tested using PV generation data and energy consumption data of a low energy office building. The results demonstrated an 85.7% improvement in RL learning efficiency and this strategy can successfully avoid sub-optimal convergence during policy learning. Compared to relying solely on the RBES, the proposed strategy led to 5.4% and 19.2% reductions in the electricity costs and daily PAR of grid power at peak hours, respectively. The strategy also achieved a satisfying PV self-consumption ratio of 62.4%, which is merely 0.4% lower than the optimal value determined by the RBES strategy that prioritized maximizing PV self-consumption. Additionally, compared with a model predictive control method developed for cost reduction, the strategy achieved similar cost savings while significantly reducing the decision time.

Analysis of Particulate and Microbiological Filtration Performance of Air Handling Unit Filters in a Low-Energy Office Building over 12 Months

Indoor air quality is an important consideration for the health and well-being of building occupants, and the SARS CoV-2 pandemic highlighted the importance of maintaining proper ventilation in buildings. Air handling units (AHUs) are used to provide fresh air and maintain occupant comfort. The objective of this work was to study the evolution of filtration efficiency in an AHU fitted with bag filters, installed to treat office air in a low-energy building, over a 12-month period. The particulate filtration efficiency (PFE) and the microbial filtration efficiency (MFE) were quantified by measuring particle size distribution and bacterial and fungal concentration in the air circulating in the AHU. The resulting microbial concentration measurements in the fresh air (between 10²–103 CFU/m3 for fungi and around 103 CFU/m3 for bacteria) were higher than those in the extracted air from the offices (between 101 and 102 CFU/m3 for fungi and around 102 CFU/m3 for bacteria). The PFE and MFE measured were almost constant throughout the 12 months, with an increase of the filter pressure drop from 70 to 90 Pa. The PFE and MFE were quite comparable for a particle diameter. Therefore, the measurement of PFE is a reliable indicator of the MFE.

Implementation of model predictive control in a large-sized, low-energy office building

Modern and energy-optimized buildings often lack an intelligent and advanced control strategy. Instead, conventional rule-based control (RBC) strategies are still mainly used today, which do not exploit the full performance potential of these buildings. Model predictive control (MPC) has proven in simulation studies and pilot cases to be a promising approach to reduce the energy consumption of buildings, while improving occupants’ comfort. However, there is still a lack of implementing MPC in real, large-scale and fully occupied buildings, to further prove this potential in real building operations. This paper describes the implementation and operation of MPC in a large-sized, low-energy office building. The MPC controller was implemented in a section of the building during a three-month test period from February to April 2020, controlling the supply temperature of heating circuits for thermally activated building systems (TABS). Its performance was compared to the default rule-based control which is active in the other building sections. This allows for a detailed evaluation of MPC versus RBC under identical environmental and operational conditions. The MPC controlled building section used 30% less heating energy than RBC controlled building sections, while the existing high level of thermal comfort could be maintained. Especially in transition periods (i. e. interseasonal periods like late winter/early spring) , the MPC is superior to the conventional heating-curve based control strategy, with heating energy savings of 75%.

Innovative HVAC System Using an Integrated Greenhouse for a Virtual Low Energy Office Building

In this paper the authors describe a HVAC innovative system using an integrated greenhouse for heating and cooling an office building. The ventilation system allows natural (night) or mechanical ventilation and the passive cooling during the summer, including cold storage in the building structure and the PCM plywood and the refrigeration energy use during the day. Natural ventilation occurs when the wind or the Venturi effect, created by the « hat » that supports the photovoltaic panels, is strong enough; otherwise, a variable speed exhaust fan mounted on top of the building is used. The plants inside the greenhouse can produce O2 under certain conditions necessary for refreshing the ventilation air. The environment of the greenhouse allows air humidification naturally, without the use of humidifiers. If the greenhouse is sufficiently insulated in winter, it can be used in the ventilation process: the air intake from offices through the greenhouse, humidified and enriched in O2 (premixed, if necessary, with fresh air) reaches the general air treatment unit, and then sent back. The process is similar in the summer, but without recirculation, due to the humidity of the air extracted from offices. Stale air humidification enhances the thermal transfer process from the desiccant collector.

Case Study of Low Energy Office Building

A zero-energy building, also known as a zero net energy (ZNE) building, net-zero energy building (NZEB), net-zero building or zero-carbon building is a building with zero net energy consumption, meaning the total amount of energy used by the building on an annual basis is roughly equal to the amount of renewable energy created on the site.

Experimental And Numerical Analysis Of Modelling Of Solar Shading

The use of solar shading in future low energy office buildings is essential for minimizing energy consumption for building services, while maintaining thermal conditions. Implementing solar shading technologies in energy calculations and thermal building simulation programs is essential in order to demonstrate the effect of adaptive solar shading. In order to document the benefits of the shading technology, the description of the shading device in the thermal building simulation software must be described at a reasonably accurate level, related to the specific solar shading device.This research presents different approaches for modeling solar shading devices, demonstrating the level of accuracy in relation to measurement conducted in a full-scale façade test facility at Aalborg University. The research bridges the gap between increased complexity of solar shading technologies and the use of these technologies in thermal building simulation software.

Enhanced Sustainable Cooling for Low Energy Office Buildings in Continental Temperate Climate

AbstractDeveloping efficient, sustainable, and affordable buildings requires combinations of passive and active measures that exploit specific onsite features. However, in temperate climates, reduc...

Solar Shading in Low Energy Office Buildings - Design Strategy and User Perception

Solar Shading in Low Energy Office Buildings - Design Strategy and User Perception

Nonlinear model predictive control for a heating and cooling system of a low-energy office building

Model predictive control (MPC) is highly suitable for building heating and cooling control because it exploits disturbance predictions, obeys constraints, and enables optimal building operation in terms of user comfort and energy efficiency. This work presents a highly efficient nonlinear modular MPC concept. It optimally controls both, heating and cooling activities in a low-energy office building simultaneously. Relevant system nonlinearities are considered through a nonlinear prediction model, an LTI MPC optimization step, and an efficient mixed-integer mapping to setpoint temperatures in the building. The involved optimization problems are efficiently solvable and enable realtime control, and the controller structure allows for retrofitting and can directly be incorporated into the existing building control infrastructure. A clear formulation of thermal user comfort and energy efficiency allows straightforward tuning. Excellent control performance and robustness are observed in detailed co-simulation studies, significantly outperforming a classical rule-based reference control law. Possible approaches to analyze robust stability of the controlled system are discussed and related to results of robust TS-fuzzy system analysis.

Energy efficient office buildings in Italy

In order to support the decision-making process and to face with the European Directive, it appears overriding focusing on the analysis of administration buildings because many constructions, owned and occupied by public authorities, enclose offices. These constructions are generally complex for typological aspects, their energy-needs are relevant especially for electricity consumptions and require highlevel of indoor comfort. Hence, the present paper presents the logic reference frame of a research that has studied the influence of some design criteria on the energy performance of office buildings located in Italy and proposes an example of low-energy office building.

Lessons Learned from Field Monitoring of Two Radiant Slab Office Buildings in California

In this paper we present the results from field studies of two low-energy office buildings in California, both using radiant slab ceiling systems (thermally activated building systems, TABS) for primary cooling and heating in the buildings. Both buildings are certified LEED Platinum and incorporate a wide range of energy efficient technologies and design strategies, including TABS, advanced shading systems, underfloor air distribution, chilled beams, ceiling fans, natural ventilation, and photovoltaic panels. Findings and analysis from the following building performance assessment techniques will be discussed.•Occupant satisfaction survey. Occupant surveys are an invaluable source of information for describing how well the building is providing a high quality indoor environment for the occupants. In addition, the survey results are also compared against a large benchmark survey database of over 50,000 occupants.•Wireless measurement system. A network of wireless sensors was installed in selected zones of the buildings to provide additional more detailed information about the operation and control of the radiant slab system. This data was combined with trend data from the building management system (BMS) to examine the performance of the buildings during both winter and summer conditions. Some control issues were identified and corrected based on these measurements.•Energy performance analysis. We collected utility data for 2014 in one of the buildings and used this information to determine the building's Energy Star rating.

Demand controlled ventilation indoor climate and energy performance in a high performance building with air flow rate controlled chilled beams

Indoor climate and energy performance of Finnish low energy office building were studied to determine optimal control and operation solutions of demand controlled room conditioning and ventilation system with airflow rate controlled active chilled beams. Onsite measured temperature, CO2, occupancy rate were used to calibrate a dynamic simulations model. The results showed an average occupancy rate of 0.55 during office hours (OH) offering a good energy saving potential for demand control ventilation (DCV) system. DCV system used 7–8% less total primary energy compared to constant air volume (CAV) system depending on control and operation strategy used. DCV system saving was 33–41% if only heating, cooling, fans and pumps primary energy were considered. Supply air temperature controlled according to extract air temperature instead of outdoor air temperature minimized overheating problem which occurred with design solution during both seasons and systems. DCV system with active chilled beam complied at least 94% and 90% of OH with Category II indoor climate with water priority cooling and air priority cooling control respectively. Ceiling cooling panel showed an effect of decoupling cooling from ventilation resulted only in 0.9% additional primary energy saving compared to DCV system with active chilled beams.

Indoor air quality and thermal comfort evaluation in a Spanish modern low-energy office with thermally activated building systems

In the current context of a world energy situation that demands high-quality indoor environments compatible with rational energy use, the purpose of this work is to present a successful case study of a comfortable low-energy office building in Madrid, Spain. An exhaustive indoor air quality and thermal comfort field measurement survey was carried out during the summer period. The main global and local thermal comfort parameters in several workplaces, as well as CO2 concentration in supply air, exhaust air, and occupied space, were registered. Correct operation of the demand-controlled ventilation system and air distribution is observed. Also, thermally activated building systems and shading design make it possible to get high levels of indoor thermal comfort, as derived from measurements. This proves that the integration of novel energy-efficient concepts in office building design can not only contribute to a minimization of the energy use but can simultaneously favor the achievement of high indoor environmental quality.

Methodologies to Reduce Cooling Load using Heat Balance Analysis: A Case Study in an Office Building in a Tropical Country

Abstract The world is experiencing energy crisis since the 1970s due to the limitation in fossil fuel resources and increasing energy demand as a result of industrialisation and development which have taken place all over the world [1]. It is reported by International Energy Agency (IEA) that 32% of the total worldwide energy consumption was contributed by building sector [2]. Researchers found that Heating Ventilation and Air Conditioning (HVAC) system consumed the highest amount of energy in commercial building [3–7] meanwhile in tropical countries more than 50% of the building's energy were used for air conditioning [8]. This research found that standard building can be transformed into Low Energy Office building by applying heat gain reduction methodologies draws from heat balance analysis. An office building in Malaysia was audited and modelled in Design Builder software for heat balance analysis. It is found that 75% of the building's heat gain was radiated from lighting system and solar heat gain through window. It is estimated that 45.85% of building's energy can be saved by changing the zones temperature set point, modification in lighting system and building's glazing for daylight optimization and minimizing solar heat gain. Besides energy saving, the building's indoor environmental quality based on MS1525:2007 and occupants’ comfort was ensured too. A basic cost analysis estimated in the software shows that the highest increment in initial cost for the methodologies suggested was only 1.32%, hence this study shows that a sustainable building does not necessarily induced high cost for the technologies implementation if the right technologies were chosen to suit the building's condition.

Atrium cooling performance in a low energy office building in the Tropics, a field study

Despite the many advantages, naturally ventilated atria in tropical office buildings are at great risk of thermal discomfort due to the effect of the external conditions in respect of solar and heat penetration. This study reports the efficiency of different passive and hybrid cooling strategies – thermal stack flue, cross ventilation and water wall – to minimize the possible overheating inside an atrium lobby of a low energy office building in Putrajaya, Malaysia, where the weather is often warm and humid. Monitoring was carried out at ten different points of the atrium lobby at the ground floor for 14 days in November of 2013. The recorded data represent the internal thermal conditions of the atrium lobby in seven different cases by changing the opening composition, stack flue outlets, atrium lobby inlets, and water wall operating time. The study results highlight the importance of cross ventilation in improving the atrium indoor thermal conditions and enhancing the performance of other strategies. The atrium has the highest performance with the implementation of full cross ventilation via all inlet openings at the atrium lobby, together with the semi stacking flue outlet openings and water wall during the working time with high inlet to outlet opening area ratio (>15). In this case, the atrium benefits from two different airflow patterns during the working time to reduce both the indoor temperature and the humidity.

Experimental and numerical analysis of the energy performance of a large scale intensive green roof system installed on an office building in Athens

The aim of this study is to investigate the thermal behaviour and the energy efficiency of an intensive green roof system composed of indigenous aromatic plants with low irrigation needs, installed in the 10,000m2 roof of a fully insulated, low energy office building in Athens, Greece. It consists of almost 16,000 Mediterranean plants of at least 14 different kinds and a running track of a stabilized ceramic floor. The urban heat island mitigation potential of the green roof as well as its energy contribution is investigated using experimental and theoretical methodologies. The surface temperature of the green roof is found to be up to 15K lower than that of a conventional roof. Plants having a low absorptivity to solar radiation together with a dense foliage are found to present a much lower surface temperature and a higher mitigation potential. The surface temperature of the plants is found to be highly influenced by the ambient air temperature. Using simulation techniques it is calculated that such a type of green roofs can decrease the average indoor temperature of a non air conditioned building up to 0.7K, while it may decrease substantially its annual cooling and heating needs.

Potential of Night Ventilative Cooling Strategies in Office Buildings in Spain - Comfort Analysis

Night ventilation has been applied successfully to many passively-cooled or low-energy office buildings. This paper analyses the thermal comfort achievable in office buildings in Spain according to European standard EN 15251:2007. Furthermore, the comfort level is evaluated using the Degree Hours (DH) criteria and the maximum indoor temperature. Considering the high interest of architects and engineers in the evaluation of optimal comfort condition as a function of building typology (8 typologies), glazing ratio (30% and 60%) and climate (12 different Climate Zones), a total of 192 different study cases were simulated. For every case, an optimal air change per hour (ac/h) that can range from 1 to 50 ac/h was then determined. The research shows that passive night ventilation should be considered as an effective strategy for all Spanish Climates to reduce cooling demand in buildings with high daily internal gains (i.e. office buildings), improving comfort conditions and flattening peak temperatures.

A novel approach of integrating ventilation and air cleaning for sustainable and healthy office environments

Abstract A wise integration approach using well-developed and innovative existing scientific/engineering tools can be a good answer to rising core questions of sustainability science. Many research works have been conducted to protect and satisfy occupant health and comfort in a sustainable way. The present study investigates a novel approach to the control of ventilation, dynamically integrated with the use of air cleaning technology toward a substantial reduction of building energy/cost with cleaner indoor air than what the standard provides. To demonstrate the proposed methodology, a low energy office building was used as a testbed, subject to the variation of outdoor pollution due to nearby traffic. A detailed building model was constructed by utilizing DesignBuilder and ContamW based on the building design/actual construction documents for the analyses of combined IAQ and energy benefits. Target contaminants included formaldehyde, other 16 representative VOCs and CO 2 for IAQ analysis. Dynamic profiles of outdoor pollution were based on actual monitoring data and EPA_2008_AirData. By setting up a suite of usage scenarios under four representative climate and outdoor air quality conditions throughout the U.S. including Syracuse (cool), Los Angeles (mild), Houston (cooling dominant) and Duluth (heating dominant), the approach of dynamic integration of ventilation and air cleaning was assessed. Results showed that the minimum ventilation rate requirements in ASHRAE 62.1-2010 might not be sufficient for meeting the exposure limit constraints for IAQ (especially for formaldehyde) at all times. The integration strategy would provide satisfactory IAQ, and also could bring most energy/cost benefits (∼11% annual savings) for the case building.