Heating, Ventilation And Cooling Research Articles

Assessing Building Energy Savings and the Greenhouse Gas Mitigation Potential of Green Roofs in Shanghai Using a GIS-Based Approach

Climate change can significantly affect building energy use and associated greenhouse gas (GHG) emissions in urban areas, as fossil fuels remain a significant energy source. Green roofs can offer multiple benefits to the urban environment, but their effects on GHG mitigation have not been fully investigated, especially under climate change. This study assessed green roofs’ contribution to GHG mitigation by saving building energy and absorbing CO2 under the present (2017–2019) and future (2049–2051) climate scenarios (SSP2-45 and SSP5-85) in Shanghai, China, at the city and township scale. A Geographic Information System (GIS)-based spatial statistical method was developed based on climate change modeling and building energy simulation. The results suggested that installing green roofs can effectively save building energy regardless of building type, yet the amount of savings can vary depending on the weather conditions within the city. The contribution analysis indicated that most saved building energy was attributed to the Heating, Ventilation, and Cooling (HVAC) system, with more energy saved under warmer climate scenarios in the future, particularly during the summer months. More energy was saved from shopping malls on an annual and monthly scale, regardless of the climate scenarios and weather zones. Finally, a case study indicated installing green roofs on all five types of buildings (office, hotel, hospital, shopping mall, apartment) of less than 50 m in height can reduce 8.28% of the CO2 emitted during the building operation stage in the entire city under the present climate scenario. The annual CO2 reduction varied with the location of townships, ranging from 2.18% to 13.78%, depending on the composition of building types and local weather conditions in Shanghai. This study offered policymakers a reference on the environmental benefits and investment values of installing green roofs in large cities.

A GIS-Based Approach for Urban Building Energy Modeling under Climate Change with High Spatial and Temporal Resolution

The energy demand and associated greenhouse gas (GHG) emissions of buildings are significantly affected by the characteristics of the building and local climate conditions. While energy use datasets with high spatial and temporal resolution are highly needed in the context of climate change, energy use monitoring data are not available for most cities. This study introduces an approach combining building energy simulation, climate change modeling, and GIS spatial analysis techniques to develop an energy demand data inventory enabling assessment of the impacts of climate change on building energy consumption in Shanghai, China. Our results suggest that all types of buildings exhibit a net increase in their annual energy demand under the projected future (2050) climate conditions, with the highest increase in energy demand attributed to Heating, Ventilation, and Cooling (HVAC) systems. Variations in building energy demand are found across building types. Due to the large number of residential buildings, they are the main contributor to the increases in energy demand and associated CO2 emissions. The hourly residential building energy demand on a typical hot summer day (29 July) under the 2050 climate condition at 1 p.m. is found to increase by more than 40%, indicating a risk of energy supply shortage if no actions are taken. The spatial pattern of total annual building energy demand at the individual building level exhibited high spatial heterogeneity with some hotspots. This study provides an alternative method to develop a building energy demand inventory with high temporal resolution at the individual building scale for cities lacking energy use monitoring data, supporting the assessment of building energy and GHG emissions under both current and future climate scenarios at minimal cost.

Effectiveness of Air Filtration in Reducing PM2.5 Exposures at a School in a Community Heavily Impacted by Air Pollution

Reducing children’s exposure to air pollution is a priority among California communities heavily impacted by air pollution exposures. We conducted an observational air quality study at a school to investigate the effectiveness of improved Heating, Ventilation, and Cooling (HVAC) system filters and portable air cleaners (PACs) in reducing children’s exposure to fine particulate matter (PM2.5) under real-world classroom conditions. This study included five classrooms, three of which had PACs. Halfway through the study period, high-efficiency HVAC filters were installed in all five classrooms. Continuous measurements of outdoor and in-classroom PM2.5 concentrations were used to evaluate filtration effectiveness. The air filtration strategies, alone and in combination, demonstrated 14–56% reductions in indoor PM2.5 concentrations compared to outdoor levels. There were significant improvements in filtration resulting from HVAC filter upgrades in the two classrooms without PACs (11% and 22% improvement, p < 0.001). Upgrading HVAC filters in classrooms with PACs did not significantly improve filtration effectiveness, suggesting that utilizing both strategies simultaneously may not meaningfully improve air quality under these circumstances. CO2 data, as a proxy for ventilation, helped demonstrate that the observed filtration effectiveness was likely impacted by the variable HVAC system use and open doors.

Modeling the Effect of Green Roofs for Building Energy Savings and Air Pollution Reduction in Shanghai

Building energy consumption is an essential source of greenhouse gas (GHG) and air pollution. Green roofs can directly absorb ambient CO2 and remove air pollutants through their vegetation layers, but a limited number of studies have examined their effects on GHG and air pollutant reduction associated with building energy savings, especially in the context of climate change. This research examined the performance of green roofs on CO2 and air pollutant reduction, including SO2, PM2.5, and NOx, through building energy demand savings in Shanghai, China. Climate change mitigation effects were assessed based on the energy consumption of five types of buildings before and after the installation of green roofs under 2020 and 2050 climate conditions, respectively. EnergyPlus software 9.5.0 was applied to simulate hourly energy consumption for different building prototypes with and without green roofs. Green roofs on all building types exhibited positive energy savings on annual, monthly, and diurnal scales, and they can save more energy for most of the building types under the projected 2050 climate condition. Moreover, most of the building energy saved by green roofs came from the Heating, Ventilation, and Cooling (HVAC) systems. In addition, this study discovered that the energy-saving benefits of green roofs vary based on the type of building they were installed on. Green roofs were found to have the largest energy saving on the shopping mall, especially on extremely hot summer days. Finally, a Geographic Information System (GIS)-based approach was developed with the ability to quantify the amount of GHG and air pollutant reduction associated with building energy savings for existing buildings in the Huangpu District of Shanghai. This approach was also utilized to present the spatial distribution of buildings with different levels of suitability to install green roofs by considering their location attributes and air pollutant reduction potential together, which is the major innovation of this research. The purpose of this study is to provide valuable guidance to policy makers regarding the performance of green roofs in building energy-saving and air quality improvement in the urban environment when facing the challenge of climate change, which is essential for urban sustainability.

How sociotechnical norms shape transition pathways: The co-evolution of three European heating, ventilation, and cooling (HVAC) regimes

Countries across Europe have ambitious targets to become carbon neutral. This requires a transformation in the way buildings are heated, ventilated, and cooled (HVAC), with a move away from fossil fuels. Highly divergent pathways currently exist between different European HVAC regimes. However, few studies have examined these differences in detail, or the role of social norms in sustaining or changing HVAC regimes. This mixed methods study examines the decarbonisation of HVAC systems in three European countries of Finland, Greece and the United Kingdom. Based on a quantitative survey of n = 3478 households and 40 qualitative interviews with building users, managers, and designers, we find highly divergent HVAC regimes across the three countries with considerable variability in technologies, user practices, business strategies, institutions and their relationship to ecosystems. We also discover a shifting patchwork of normative perspectives to heating and cooling. These “socio-technical” norms are highly susceptible to peer influence, broader socio-economic and political drivers, and environmental factors such as climate change. Finally, we argue that an appreciation of how these socio-technical norms are formed and influenced, is an essential yet under-explored avenue in research and public policy on sustainability transitions.

Indoor Lidar Plenoptic Array Based on Time-of-Flight Reflection

Improved energy efficiency and the associated cost savings is critical for environmental stewardship. In heating, ventilation, and cooling (HVAC) systems, occupancy sensors play an important role in system control for energy conservation. This paper introduces an integrated plenoptic device/people occupancy counting sensor for time-of-flight (ToF) measurements based on grating-coupled-waveguide, angularly resolved detection. Light from a 940 nm laser source is scattered from objects up to 5-m distant. The acceptance angle for scattered light is determined by the period of the detector grating and the waveguide properties. As a consequence of the narrow-band optical coupling, the plenoptic sensor demonstrates a good immunity to background light sources, such as sunlight and incandescent room illumination. The conical acceptance angles (azimuth and altitude) of this device are measured and confirm the device model. Importantly, the device is realized on a commercial silicon-based integrated-photonics foundry line, providing a pathway to volume manufacturing.

A review of sustainable technologies for energy efficient upgrade of existing buildings and systems

Sustainable upgrades include actual case studies with before and after retrofit results, case studies with simulated results and use of computer systems to predict energy savings based on exiting building parameters. In the latter no actual renovations are done thus technologies and systems are assumed. The review used real cases including simulations and adopts a mix of systematic and content analysis approaches. Thus, over 288 articles were gathered from all the major scientific journals using Scopus, ProQuest, Web of Science etc. The sample was reduced to 230 articles based on the search themes; thereafter, a detailed focus on the methods used provided basis to trim the articles to 47. Sustainable technologies identified cover those installed to the external façade, indoor areas, air filtration, insulation systems, building elements, heating, ventilation and cooling (HVAC) systems, sensors, lighting, hot and cold water systems such as boilers, chillers, pumps, motors and renewable energy technologies. The results show sustainable technologies have been used to improve various existing buildings. Also, the results indicate high rate of adoption of insulation systems for external and internal walls, roofing and ceiling elements. This paper provides evidence to support the drive towards environmental sustainability through the adoption and installation of sustainable technologies. Policies to trigger demand and installation could further improve actions towards greenhouse gas reduction.

Evaluation of cooling setpoint setback savings in commercial buildings using electricity and exterior temperature time series data

Commercial buildings account for a significant amount of total energy produced in the US, and the Heating Ventilation and Cooling (HVAC) systems are one of the most significant components of their overall consumption. In this study, we proposed a new data-driven approach to evaluate HVAC cooling systems in commercial buildings and identify savings opportunities. The focus is an investigation of the impact of thermostat setpoint setback but using only whole building, electricity data taken at 15-min intervals for the analysis. We conducted a comparative study of setpoint setback characteristics on 432 commercial buildings with 5 building usage types across the United States. To accomplish this, both piecewise and Random Forest regression algorithms were employed using electricity and exterior temperature datasets to identify operational characteristics and the effective setpoints in the building to determine the corresponding savings opportunities. Both occupied and unoccupied time periods were studied across cooling degree days (CDD), when air conditioning is typically operational. The results show that in commercial buildings, on average, cooling systems account for 9.5% of total consumption. When a one degree setback during the cooling season is applied, an average of approximately 1.1% of annual consumption is achieved; retail and office buildings demonstrate the highest potential for savings. Additionally, we identified that the number of cooling degree days and base to peak ratio (BPR) are the most important variables for predicting the magnitude of the consumption of cooling systems.

Modeling the Effect of Green Roof Systems and Photovoltaic Panels for Building Energy Savings to Mitigate Climate Change

Green roofs and rooftop solar photovoltaic (PV) systems are two popular mitigation strategies to reduce the net building energy demand and ease urban heat island (UHI) effect. This research tested the potential mitigation effects of green roofs and solar photovoltaic (PV) systems on increased buildings energy demand caused by climate change in Los Angeles County, California, USA. The mitigation effects were assessed based on selected buildings that were predicted to be more vulnerable to climate change. EnergyPlus software was used to simulate hourly building energy consumption with the proper settings of PV-green roofs. All buildings with green roofs showed positive energy savings with regard to total energy and electricity. The savings caused by green roofs were positively correlated with three key parameters: Leaf Area Index (LAI), soil depth, and irrigation saturation percentage. Moreover, the majority of the electricity-saving benefits from green roofs were found in the Heating, Ventilation, and Cooling (HVAC) systems. In addition, this study found that green roofs have different energy-saving abilities on different types of buildings with different technologies, which has received little attention in previous studies.

Economic Operation of Thermostatic Loads Under Time Varying Prices: An Optimal Control Approach

In this paper, we consider the problem of optimal precooling of thermostatic loads by a load serving entity (LSE) under time varying electricity prices. Specifically, we propose a low complexity dynamic programming based algorithm for controlling the switching of heating, ventilation, and cooling (HVAC) units such that the cost of cooling is minimized while ensuring that the resultant temperatures do not violate the comfort constraints of consumers. Specifically, our algorithm makes use of two facts: first, the price of electricity vary discretely in time; and second, the cost-optimal state trajectory under fixed electricity price and ambient temperature, with given initial and final states, can be characterized explicitly in closed-form. We validate our algorithm with a set of numerical simulation studies using real market prices of electricity from the New York and Texas electricity markets. In addition, we also provide an approximation mechanism to implement this optimization algorithm in HVAC systems that have ON-OFF switching constraints.

Building Energy Retrofit Measures in Hot-Summer–Cold-Winter Climates: A Case Study in Shanghai

Building retrofit measures provide a significant means of mitigating the effect of climate change on buildings by enhancing building energy performance at a beneficial cost-effectiveness. An insight into the applicable building retrofit measures within a climate zone will guide the optimisation framework to attaining sustainability in architecture and the built environment. This article presents a brief overview of recent studies on retrofit measures and its application on a variety of buildings in hot-summer–cold-winter climates, with emphasis on Shanghai. Findings show that the major retrofit measures include improvement in the building envelope, heating, ventilation and cooling (HVAC) and lighting, supported by photovoltaic (PV) systems, accordingly. Furthermore, the study identifies key elements and plausible challenges for the evaluation of building retrofit measures in this region. In this regard, financial barriers and lack of standards and regulatory support are the main challenges identified. These insights provide a systematic approach to guide building researchers, practitioners and decision-makers in the design and development of existing and new retrofit measures for the future of rapidly growing cities with a broad climate variation scope.

EnergyPlus Integration Into Cosimulation Environment to Improve Home Energy Saving Through Cyber-Physical Systems Development

This paper presents a co-simulation platform which combines a building simulation tool with a cyber-physical systems (CPS) approach. Residential buildings have a great potential of energy reduction by controlling home equipment based on usage information. A CPS can eliminate unnecessary energy usage on a small, local scale by autonomously optimizing equipment activity, based on sensor measurements from the home. It can also allow peak shaving from the grid if a collection of homes are connected. However, lack of verification tools limits effective development of CPS products. The present work integrates EnergyPlus, which is a widely adopted building simulation tool, into an open-source development environment for CPS released by the National Institute of Standards and Technology (NIST). The NIST environment utilizes the IEEE high-level architecture (HLA) standard for data exchange and logical timing control to integrate a suite of simulators into a common platform. A simple CPS model, which controls local heating, ventilation, and cooling (HVAC) temperature set-point based on environmental conditions, was tested with the developed co-simulation platform. The proposed platform can be expanded to integrate various simulation tools and various home simulations, thereby allowing for cosimulation of more intricate building energy systems.

Design and analysis of a multigeneration system with concentrating photovoltaic thermal (CPV/T) and hydrogen storage

Concentrated photovoltaics (CPV) is an auspicious technology to overcome the high cost problem of highly efficient multi-junction solar cells. However, due to huge concentration of light energy, high heat flux dissipation from a confined space is a challenge. The proposed system here is first of its type to apply and thermodynamically analyze the Nucleate Pool Boiling Heat Transfer (NBHT) for thermal management of CPV. In order to increase overall efficiency of CPV system, a multigeneration system using concentrated photovoltaic thermal (CPV/T) and hydrogen storage is designed and thermodynamically analyzed to fulfill electricity, hot and cold water, heating ventilation and cooling (HVAC) requirement of a residential community with continuous operation. A part of the generated electricity from CPV is used to power the electrolyzer to produce hydrogen and oxygen. The produced gases are stored, and reused by proton exchange membrane fuel cell (PEMFC) to fulfill the system's electrical energy requirement during night time and unfavourable energy conditions in day time. The resultant thermal energy from CPV/T is used for the heating, hot water and cooling requirement of the buildings by employing lithium bromide absorption chiller (AbC). A humidity harvesting system is connected, at the outlet of the absorption chiller, to convert humid air into water and ventilation air requirement of the building. The designed system performs at 67.52% overall energy efficiency, 34.89% of overall exergy efficiency and up to 1862 times concentration ratio at designed steady-state conditions. The results show that with an increase in boiling temperature of NBHT from 353 K to 373 K, the maximum concentration ratio ability increases significantly from 1392 to 2400 times due to increase in critical heat flux, while the electrical efficiency of the CPV system decreases from 28.65% to 27.09% because of increase in cell temperature. To verify the performance of the designed system for different locations, operating conditions and capacities, the effects of Direct Normal Irradiance (IDNI), ambient temperature, relative humidity ratio and the installed capacity are also analyzed by the parametric studies.

Smart Sensing for HVAC Control: Collaborative Intelligence in Optical and IR Cameras

Energy management of heating, ventilation, and cooling (HVAC) has become a primary concern for residential and commercial buildings. In order to save energy without compromising the comfort of occupants, various techniques have been explored to sense the real-time occupancy/vacancy of HVAC zones. Among all these approaches, wireless-camera-based sensing stands out for its potential application in surveillance and security in addition to energy management. However, limited lifetime and detection accuracy have prevented pervasiveness of wireless-camera-based occupancy detection. This paper presents a novel wireless device platform and prototype development that incorporates an infrared (IR) camera with an optical (OP) camera to provide collaborative intelligence at low power and enhanced accuracy. Compared to the single-sensor baseline design, the proposed fusion-based OP/IR design demonstrates $5\times$ miss rate improvement, $5\times$ reduction in false positive rate, and $3\times$ lifetime extension for battery usage with respect to a single-sensor-based design. Compared to a programmed thermostat and schedule-based HVAC control, the design saves a maximum of $26\%$ of HVAC energy.

Thermodynamic analysis of ventilated façades under different wind conditions in summer period

The main benefit attributed to opaque ventilated facades (OVF) is the reduction of cooling load for the building Heating Ventilation and Cooling (HVAC) achieved through ventilation led by natural convection in the ventilated chamber and the protection from solar radiation given by the outer layer of the façade.This research investigates the thermal behavior of an opaque naturally ventilated façade through Computation Fluid Dynamics (CFD) simulations during summer days. The CFD simulations have been performed in order to analyze the behavior of DSF components under different wind conditions in the summer period, utilizing the weather data of Catania city (Italy).For the different investigated scenarios, the authors have calculated the temperature and air velocity profiles inside the air gap of the façade, highlighting the different effects of buoyancy and wind forces.The results show that the wind forces in conjunction with the buoyancy forces affect significantly the performance of OVF components.Further, the reduction of the heat flux during the summer period has been evaluated by comparing the thermodynamic performance of a naturally ventilated and an unventilated façade with the same geometry and thermo-physical characteristics.The behavior of the naturally ventilated façade is an improvement in terms of passive cooling of the building compared to the non-ventilated façade since it allows the peak load to be shifted whilst offering energy savings in the range of 47% to 51% depending on climate.

Unequal access to energy efficiency in US multifamily rental housing: opportunities to improve

The energy efficiency of US multifamily rental housing is compared with other housing types. A real and growing energy efficiency gap is documented, particularly for lower income households. Findings are based on data from the 2005 and 2009 US Residential Energy Consumption Survey (RECS). Individual energy efficiency features related to HVAC (heating, ventilation and cooling) systems, appliances, and the building envelope are analysed along with weighted and unweighted total energy efficiency indices. Multifamily units occupied by low income renters had 4.1 fewer energy efficiency features in 2005 and 4.7 fewer in 2009 compared with other households. If the number of efficiency features was on par with other housing, the savings could be in the range of US$200–400 per year for most lower-income renters in multifamily buildings. There is an astonishing lack of information on how efficiency retrofits would affect property (real estate) metrics such as cash flow and value. Available evidence suggests that millions of US properties could be good retrofit investment opportunities. Better efficiency would allow renters to increase spending on food, healthcare and other essentials. This is not only an economic issue: it has implications for household health, social equity and environmental problems tied to energy consumption.

Feasibility of retrofitting centralized HVAC systems for room-level zoning

Heating, ventilation, and cooling (HVAC) accounts for 38% of building energy usage, and over 15% of all US energy usage, making it one of the nation's largest energy consumers. A number of projects have attempted to optimize the control of HVAC systems by minimizing the energy wasted in conditioning occupied buildings or rooms. Researchers have proposed systems that turn off air conditioners or heaters when a house is unoccupied, or put the system into an energy saving deep-setback mode when the occupants are inactive, such as when they are asleep. These approaches enable the retrofitting of centralized HVAC systems, that are widely used within the United States, to be more energy efficient. An area that has not been as well explored is the retrofitting of centralized HVAC systems to save energy when the residents are at home and awake. In this paper, we demonstrate how to use cheap, off-the-shelf sensors and actuators to retrofit a centralized HVAC system and enable the heating, or cooling, of rooms individually, in order to reduce waste caused by conditioning unoccupied rooms. We call this approach room-level zoning. Sensors detect room state and learned activity patterns are used to predict occupancy. Based on this information, unoccupied rooms drift away from a user defined comfortable temperature if occupants are less likely to use them in the near future while occupied rooms remain at a comfortable temperature. Thus, conditioning only the rooms with a high probability of occupancy to the setpoint saves energy by decreasing the load on the HVAC system. We implement a room-level zoning system, called Dual-Zone, in a 1400 square foot house by retrofitting an existing centralized HVAC system with wireless temperature sensors to monitor room-level temperature, motion sensors to monitor occupancy, and wirelessly actuatable dampers to control the flow of conditioned air through the house. Dual-Zone statically zones the house into two zones: one conditioned at night and the other conditioned during the day. Initial analysis indicates that this method has a 20.5% energy savings over the existing single-zoned thermostat during a 20 day evaluation.

Improved firefly algorithm approach applied to chiller loading for energy conservation

Significant energy savings can be achieved by optimizing chiller operation and design in heating, ventilation and cooling (HVAC) systems. In terms of optimization, various metaheuristics have been proposed to the optimal chiller loading problem. New metaheuristics are also emerging recently, between them the firefly algorithm. Firefly algorithm is a nature inspired algorithm based on the idealized behavior of the flash pattern and characteristics of fireflies. This study proposes a new improved firefly algorithm (IFA) based on Gaussian distribution function to the optimal chiller loading design. To testify the performance of the proposed method, the paper adopts two case studies comparing the results of the developed model using IFA with those of traditional firefly algorithm and other optimization methods in literature. In this paper, the optimization problem is minimize energy consumption of multi-chiller systems, where the objective function is energy consumption and the optimum parameter is the partial loading ratio of each chiller. The results of both case studies show that the proposed IFA outperform several optimization methods of the literature in terms of minimum energy consumption solution of the optimal chiller loading problem.

Occupant comfort in naturally ventilated and mixed-mode spaces within air-conditioned offices

Contemporary concerns for improving environmental performance in buildings have led to an increased interest in natural ventilation (NV) either on its own or in combination with air-conditioning (mixed mode (MM)) as an alternative to traditional heating, ventilation and cooling (HVAC) systems. HVAC systems are widely used because they avoid many of the problems encountered with NV or MM—noise, dust, insects, odours, temperature extremes—and readily conform to steady-state conditions of thermal comfort. However, it is possible that NV or MM can provide improved indoor air quality precisely through variations associated with external climatic conditions. This article introduces an ARC (Australian Research Council) funded project evaluating comfort conditions in MM spaces, using field studies from two buildings. The first, a University campus building in Sydney, offers MM perimeter offices with air-conditioned central spaces, while the second, a commercial building in Melbourne, offers a series of MM spaces that can be used by workers from adjacent air-conditioned office spaces. The aim of the project is to evaluate the feasibility of using MM either in place of or in association with traditional HVAC systems. The outcomes of the project will be used to elaborate the justifications for inclusion of NV spaces and/or NV periods within contemporary office environments. This article presents preliminary results of the fieldwork at each location.