Indoor Air Quality Requirements Research Articles

Retrofitting solar air heaters in New Zealand schools – A randomized crossover intervention study

Most New Zealand (NZ) schools rely on natural ventilation and are often inadequately ventilated in winter. NZ school hours typically span from 9 a.m. to 3 p.m. and are well aligned with optimum solar radiation. Existing classrooms could therefore be heated and ventilated using retrofitted solar energy applications. To investigate the suitability of a commercially available solar air heater (SAH) to improve ventilation, a randomized crossover intervention study was conducted in 12 classrooms from six primary schools in Palmerston North, NZ, during the winter of 2014. Typical performance results showed a mean (standard deviation, SD) SAH outlet air temperature of 29.2 (10.4) °C at a mean (SD) velocity of 0.7 (0.3) m·s-1. During most school periods (64–99%) classrooms maintained required thermal comfort. The concurrent use of the extant heaters was reduced, and carbon dioxide levels were improved, lowering exposure for occupants. This study confirmed that retrofitting SAHs contributed to improved classroom ventilation, increased thermal comfort and reduced energy use. Optimising performance would require design improvements to improve airflow in order to comply with NZ ventilation and indoor air quality requirements for schools.

Analysis and research on inherent angle ventilation control of residential kitchen range hoods

The emission of oil fume particles during kitchen cooking processes constitutes a significant factor that impacts indoor air quality and human health. Range hoods, as indispensable ventilation devices in kitchens, play a crucial role in reducing indoor particle concentrations. This study employs a combined approach of orthogonal experiments and computational fluid dynamics simulations to investigate the exhaust characteristics of inherent-angle-measurement-based range hoods. It analyzes the diffusion patterns of cooking-generated particulate matter under various cooking scenarios, considering factors such as the opening and closing of windows, cooking source velocities, and different airflow rates of the range hood. Based on different airflow organization patterns, a supplementary ventilation system is designed. The rationality and effectiveness of the supplementary ventilation system are analyzed to establish an effective control scheme for reducing particulate matter in various kitchen environments. The simulated research results indicate that particles disperse along the inclined surface of the side-draft range hood, resulting in higher pollutant concentrations in the breathing zone compared to the cooking zone. Increasing the exhaust airflow rate of the range hood enhances particle capture efficiency by 9.8 %. The induced airflow generated by opening windows improves particle capture efficiency by 12.9 %. However, when the velocity of the window-induced airflow exceeds 1.5 m/s, it hampers the promotion of particle capture efficiency. In the case of windows being unconditionally open, implementing a ceiling-mounted supplementary air supply system effectively improves the kitchen's particle concentration, achieving a maximum particle capture efficiency of 97.66 %. When windows can be opened, setting a baffle on the range hood, the simulation results revealed that with a baffle angle of 120° and a length of 0.3 m, the particle concentration capture efficiency in the breathing zone increased by 34.59 %. This achieved the standard limit requirement of 50 µg/m3, thus meeting the indoor air quality requirements.

Air quality and comfort constrained energy efficient operation of multi-zone buildings

Maintaining indoor air quality (IAQ) through effective ventilation is essential for the well-being and productivity of building occupants. Control strategies aimed at improving the efficiency of heating, ventilation and air conditioning (HVAC) systems must jointly determine ventilation and heating and cooling processes. In this paper, we study the problem of minimizing the energy consumption of the HVAC system in a multi-zone building, while meeting thermal comfort and IAQ requirements. We first perform a steady state analysis of the zonal carbon dioxide (CO2) concentration and the temperature dynamics. The resulting expressions are convex in the zonal mass flow rates and zonal temperatures. Guided by the steady state solutions for meeting the thermal comfort constraints, we develop two control policies for improving the energy efficiency of building HVAC systems while jointly satisfying indoor temperature and IAQ constraints. We compare the performance of our proposed approaches with those of multiple baseline approaches which implement separate regimes for controlling zonal temperature and IAQ for a typical work-day in a multi-zone campus building. We have evaluated the performance of our proposed approaches under varying levels of flexibility in zonal temperatures. We have shown that zonal temperature flexibility can result in energy savings up to 32% (for the same control strategies) as compared to the case where no such flexibility is permitted. Our proposed approaches were seen to offer potential savings of nearly 29% compared to the baseline.

Investigation of Microclimate Parameter Assurance in Schools with Natural Ventilation Systems

Slow population growth has limited the construction of new schools, leading to the renovation of existing buildings to achieve energy efficiency goals. While improvements are made to thermal insulation, heating and ventilation systems often remain outdated, presenting challenges in maintaining indoor air quality (IAQ) in schools, where children spend a significant amount of time in densely populated classrooms, and whose health is more affected by IAQ than that of adults. Therefore, this study assessed the possibilities to achieve IAQ requirements in schools ventilated by opening the windows by monitoring the carbon dioxide (CO2) concentration, temperature, and relative humidity (RH) fluctuation. The results of the study have shown that it is not feasible to achieve the defined IAQ parameters in classrooms through window opening alone. The measured CO2 concentration during lessons in many cases exceeded the limit value of 1000 ppm and did not decrease to ambient levels when the windows were opened during the break. Additionally, the internal air temperature dropped below the normative when lessons started, and RH was significantly below the recommended minimum value on all days. It was also found that the use of thermal energy decreases evenly because of inefficient air change leaving no direct economic leverage for the installation of efficient ventilation systems.

Mathematical modelling of passive displacement dual cooling coil (PDDCC) system in a tropical climate

Unlike the conventional displacement ventilation (DV) systems, the Passive Displacement Dual Cooling Coil (PDDCC) system generates airflow in indoor environments based on natural convection and eliminates the necessity of mechanical ventilation to meet the thermal comfort and indoor air quality requirements. Investigations on such PDDCC systems, though, have been largely limited and its performance capacity and fluid flow behaviour are not fully understood. A mathematical model was, hence, developed in the current study to explore the effects of various boundary conditions on the performance of the PDDCC system. Results obtained from the mathematical model were, first, compared and validated against the measurement readings gathered from an experimental investigation conducted on the PDDCC system in a controlled test environment. The validated mathematical model was then applied to a parametric evaluation where the effects of chilled water supply (CHWS) temperature, flow rate, and return air temperature on the PDDCC system performance were examined. The varying effect of the latent and sensible cooling load was observed at the different boundary conditions applied to the PDDCC model. Slightly more than 32% of rise in total cooling load was predicted by reducing the CHWS temperature which established a much more significant contribution in comparison to the CHWS flow rate which generated approximately 5% rise in the total cooling load. Findings were supported by examining the sensible heat ratio (SHR) and the ratio of Latent cooling load: Sensible cooling load which was then was attributed to the temperature difference between the supply and return air temperature. By ensuring the maximum temperature difference, the total cooling load performance of the PDDCC system can be maximised. The contribution of both the CHWS temperature and flowrate was essential to achieve the maximum cooling load, hence, improving the total cooling performance of the PDDCC as a result.

Model predictive control of short-term winter natural ventilation in a smart building using machine learning algorithms

Natural ventilation in buildings has the potential to reduce building energy consumption and the incidence of sick building syndrome. However, controlling natural ventilation is often challenging. For instance, natural ventilation through operable windows may cause cold draughts for the occupants in winter. This paper presents the key findings of a novel machine learning-based model predicted control of single-sided natural ventilation in a retrofitted four-story smart building in Cambridge, Massachusetts, in the northeast region of the United States. A data-driven methodology is used to realize this natural ventilation modeling, including data collection, system dynamics identification, and control formulation. The prediction model of indoor CO2 and room air temperature is built through a learning process. The model predictive control (MPC) formulation step combines thermal comfort and indoor air quality requirements. Finally, the natural ventilation MPC is tested in the real building, and the results showed that indoor air quality and thermal comfort are maintained successfully, without increasing significantly the heating energy consumption in winter. This scalable data-driven methodology can potentially be applied to natural ventilation in smart buildings.

Optimizing indoor air quality and noise levels in old school classrooms with air purifiers and HRV: A CONTAM simulation study

Efforts at the national level are being made to improve the indoor air quality of school classrooms. Air purifiers and heat recovery ventilation (HRV) are commonly used to achieve this objective. However, the noise generated by these systems often disrupts classes, leading students to be hesitant in utilizing them. This study proposes an operating method to minimize noise while improving indoor air quality through CONTAM simulations. The method involves operating the HRV in low wind mode during class time and strong wind mode during break time. The dissatisfaction rate (measured by the duration in which the CO2 concentration exceeded 1500 PPM) was minimal, with a rate as low as 0.2% over one year of occupancy. In the case of fine dust PM2.5, operating the air purifier 1 h earlier than occupancy time, while maintaining the existing HRV operation, resulted in a low dissatisfaction rate (PM2.5 concentration exceeded 15 μg/m3 during occupancy time for one year) of 2.6%. According to student reports, the use of weak wind mode during class and strong wind mode during break time resulted in reduced annoyance from the equipment noise. They expressed overall contentment with the experimental noise level, as long as the indoor air quality was improved. The study findings provide an effective and feasible approach to satisfying both noise and indoor air quality requirements. Furthermore, the methodology adopted in this study can be valuable for developing appropriate air purifier facility capacities in different schools.

Control logic for a novel HVAC system providing room-based indoor climate control in residential buildings

One of the major changes regarding HVAC systems in new or renovated residential buildings is the incorporation of heating in the ventilation system, providing an air heating system. In buildings equipped with air heating systems, indoor climate is commonly controlled based on a reference zone, which leads to unsatisfactory thermal condition in the other zones. In addition, this strategy is not energy-efficient for buildings due to overheating that can occur in some zones. This study presents control logic for a novel-designed demand-controlled ventilation and air heating system and develops a variable air volume (VAV) control strategy to ensure an energy-efficient operation of the system, while providing a satisfactory indoor climate conditions. The air heating system can change airflow rate and air temperature in each room quickly and accurately enabling the control of indoor climate on a room level within a dwelling. The performance of the air heating system, in terms of its effect on thermal comfort and indoor air quality in each room as well as the stability of the system has been evaluated through a full-scale laboratory experiment. The experimental result indicated the ability of the system to satisfy different temperature set-points ranging from 20 °C to 25 °C in different zones with ±0.3°C deviation from the set-points, while the system was remained stable when temperature set-points were changed in several zones during the experiment. Individual indoor air quality requirements were also satisfied with providing the required supply airflow rate to each zone, while the supply fan was running based on the critical zone reset control strategy to achieve an energy-efficient operation.

Ventilation requirements and energy aspects: the case of hospitals

Energy building design today aims to ensure thermal comfort and indoor air quality; this concern has been increased, given the recent SARS-CoV-2 pandemic. The proposed work investigates the effect of increased natural ventilation on energy requirements, ensuring low CO2 levels and acceptable Indoor Air Quality (IAQ) in general. The case of hospitals was chosen because of the stringent IAQ requirements they raise as a result of the burdened (physical, chemical, biological) indoor environment, as well as the vulnerable health of the patients. The current energy analysis was carried out in patient wards, waiting rooms, and operating rooms. The proposed correlation between IAQ and energy is infrequent in the relevant literature, especially for the case of hospitals. Different scenarios regarding the ventilation mode are examined, including pure natural ventilation, natural ventilation combined with air cleaners, as well as mechanical ventilation. According to the results, improvement of the air quality leads to higher energy demand; this is the case of mechanical ventilation, noting that not properly designed natural ventilation techniques may lead to high energy consumption, without ensuring acceptable IAQ. Air cleaners can contribute towards better environment, potentially decreasing ventilation requirements; the issue of fresh air adequacy has to be examined though. The demonstrated methodological analysis and results can help the designer to investigate the efficiency of different ventilation modes, involving the effect of thermal envelope, geometrical and operation parameters, towards the energy requirements minimization and IAQ quality maximization.

A proactive 2-stage indoor CO2-based demand-controlled ventilation method considering control performance and energy efficiency

This paper presents a novel method, named proactive 2-stage demand-controlled ventilation (P2S-DCV) method, to maintain indoor air quality (IAQ) and reduce the energy consumption of multi-zone ventilation systems. The proposed P2S-DCV method applies a proactive control scheme, which predicts future indoor CO2 concentration and supplies proper ventilation to each zone. The method includes two stages. In Stage I, a DNN prediction model is established to predict the future CO2 concentration to calculate the corresponding demand airflow. In Stage II, a reinforcement learning method is designed to achieve rapid and accurate control, and further reduce the energy consumption by optimizing the fan pressure and damper positions. A 5-zone ventilation system is established to validate the proposed P2S-DCV method. The experiment verifies that: a) it can maintain comfortable IAQ via predicting the change of future indoor CO2 and applying effective ventilation control in advance; b) it can improve the control performance, the accuracy is maintained within 8 % (satisfied the ASHRAE Standards), and the control time is maintained within minutes. It can reduce the regulating time by 83.62 % compared with ASHRAE Ratio method, and up to 51.68 % compared with PID method; c) it can reduce the fan energy consumption by 16.4 % compared with ASHRAE Ratio method, and up to 21.8 % compared with PID method; d) it has good generalization ability for various IAQ requirements and ventilation systems with different topologies.

Evaluation of Mixed-Mode Ventilation Thermal Performance and Energy Saving Potential from Retrofitting a Beijing Office Building

Mixed-mode cooling can effectively reduce the energy consumption of building cooling while satisfying the thermal comfort of occupancy and indoor air quality requirements. This paper predicted the thermal performance and energy-saving potential of an existing Beijing office building (in continental climates) operated in a mixed-mode from April to October. For the natural ventilation mode, the results predicted by simulation were validated with the results of experiments conducted in October 2021 and April 2022. Occupancy thermal comfort of the mixed-mode building was predicted using Predicted Mean Vote (PMV) and adaptive comfort models. The predictions demonstrated acceptable satisfactory thermal comfort for the occupancy. The results showed that the mixed-mode building’s annual cooling energy use is reduced by around 45% compared to the air-conditioned building. In addition, the building’s indoor temperature and velocity distributions were predicted using a Computational Fluid Dynamics (CFD) simulation. The validation showed a satisfactory agreement between CFD simulation and measurement data. It is found from CFD results that cross-ventilation can provide thermal comfort for the occupancy while improving fresh air requirements. The suggested that operational strategies of mixed-mode cooling can be used in office buildings in continental climates. Retrofitting the existing office building can bring a significant amount of energy saving.

How IoT and Artificial Intelligence can improve energy efficiency in hospitals - a North Italian case study

Because of the COVID-19 pandemic, healthcare facilities have experienced pressure of increasing occupancy rates and more demanding Indoor Air Quality requirements in recent months. In this context, the efficient management of the HVAC system in these buildings has become a crucial topic to address. The retrofit project was the result of the joint effort of a digital solution provider, Enerbrain, and the Hospital’s energy services provider, Edison. By exploiting IoT and ICT technologies and cloud-based machine learning algorithms, the HVAC-related control features of the main heating and ventilation systems of the hospital have been upgraded with no major modifications to the existing setup. The implemented solution allows energy managers to remotely verify the real-time indoor comfort conditions and to control the upgraded systems, which, thanks to the machine learning adaptive algorithms, are now effectively meeting the required set-points through advanced optimization strategies. This paper presents the implementation of a retrofit measure applied to the HVAC Building Management System of a big public hospital in Lombardy and the energy savings achieved in the 2020-2021 heating season.

A sustainable localised air distribution system for enhancing thermal environment and indoor air quality of poultry house for semiarid region

This work compares the performance of three passive cooling systems in meeting thermal and indoor air quality requirements in a poultry house located in semi-arid climate. The first two systems are a direct evaporative cooler and a cross-flow dew point evaporative cooler supplying air through a conventional tunnel ventilation that achieves uniform thermal and indoor air quality conditions. The third system is a dew-point evaporative cooler combined with a localised ventilation system to further reduce air and water consumption. To achieve these objectives, a modular analysis was adopted where mathematical models were developed for the evaporative coolers and the tunnel-ventilated poultry house module. Moreover, a computational fluid dynamics model was developed and experimentally validated for the compartment conditioned by the localised system. The evaporative coolers were sized and the hourly variation in the required fresh air and water supply was determined for the cooling season. Results of the economic analysis showed that the cost of the dew-point evaporative cooler was 6.8% lower than that of the direct evaporative cooling, with better compliance to poultry house thermal and air quality requirements. Using localised ventilation instead of conventional with the dew point apparatus further reduced costs by 4.7%, while achieving similar conditions of temperature and air quality.

Modeling the Applicability of a Displacement Ventilation System

Due to its significant role in improving indoor air quality, displacement ventilation system is widely adopted in current literature. This paper proposes a displacement ventilation system for room conditions with ceilings that are relatively low, internal heat load could be high, walls could be sunlit, and occupants doing the low physical activity. These conditions are prevalent in the Philippines, being a tropical country. Input parameters to the design process such as heat load, the height of the ceiling, comfort, and indoor air quality requirements were generated, and the main output parameters are the stratification height and ventilation airflow rate. To demonstrate the proposed displacement ventilation system, four cases were generated. Results show that the ventilation airflow rates obtained from the four cases were greater than the minimum outdoor air requirements for health in conference rooms and large assembly areas which are 17.5 and 3.5 liters/sec*person respectively, for smoking and no smoking rooms.

Using long-term measurements of airflow, electrical power, indoor temperature, and CO2-concentration for evaluating sizing and performance of an all-air HVAC system in an office building - a case study

Monitoring performance of heating, ventilation, and air-conditioning (HVAC) during building operation enables to evaluate the appropriateness of the system’s design. Such insights can help to reduce energy consumption while ensuring satisfying indoor conditions in the monitored building. Additionally, such insight can help to improve future HVAC design. The aim of this paper is to present a case study demonstrating how HVAC engineers can evaluate whether the monitored air-handling units (AHUs) were appropriately sized and performed as intended based on design requirements regarding energy-efficiency, thermal conditions, and indoor air quality (IAQ). Three months of measurements of airflow, electrical power, indoor temperature, and CO2-concentrations were collected from an office building with six AHUs. The results showed that three of the AHUs were appropriately sized and satisfied the thermal condition, IAQ and energy-efficiency requirements. The remaining three AHUs were apparently appropriately sized and satisfied IAQ requirements, but they did not satisfy the required energy-efficiency and thermal conditions. The applied approach seemed to be suitable for supporting building operating managers for on-going performance monitoring as it was able to identify discrepancies from intended performance. But it remains the task for the operating personnel to identify the cause of the identified discrepancies.

Development of a procedure for estimating the parameters of mechanistic VOC emission source models from chamber testing data

In order to evaluate the impacts of volatile organic compounds (VOCs) emissions from building materials on the indoor air quality beyond the standard chamber test conditions and test period, mechanistic emission source models have been developed in the past. However, very limited data are available for the required model parameters including the initial concentration (Cm0), in-material diffusion coefficient (Dm), partition coefficient (Kma), and convective mass transfer coefficient (km). In this study, a procedure was developed for estimating the model parameters by using VOC emission data from standard small chamber tests. In the procedure, initial values of the model parameters were refined by multivariate regression analysis of the measured emission data. To verify the procedure and estimate its uncertainty, simulated chamber test data were generated by adding 10% experimental uncertainties on the theoretical curve from the analytical solution to a mechanistic emission model. Then the procedure was applied to the generated data to estimate the model parameters. Results indicated that estimates converged to the original parameter values used for the data generation and the error of estimated parameters Dm, Cm0 and Kma were within ±10%, ±23%, and ±25% of the true values, respectively. The procedure was further demonstrated by applying it to estimate the model parameters from real chamber test data. Wide application of the procedure would result in a database of mechanistic source model parameters for assessing the impact of VOC emissions on indoor pollution load, which are essential input data for evaluating the effectiveness of various indoor air quality (IAQ) design and control strategies as well as the energy required for meeting given IAQ requirements.

An optimal control method for discrete variable outdoor air volume setpoint determination in variable air volume systems

In multi-zone variable outdoor air (OA) volume air-conditioning systems, there is often a mismatch between OA volume flow supply and demand, because variable air volume (VAV) systems exhibit nonlinear, multivariable, and long delay characteristics. Traditional methods ensure indoor air quality (IAQ) by increasing OA volume flow, which leads to a waste of OA flow energy. To address this problem, an optimal control method for determining discrete variable OA volume flow setpoints, based on differential pressure control, is proposed in this study. In this method, changes in indoor CO2 concentration and the total air volume flow demand of terminals are regarded as constraints of OA volume flow setpoints. A Proportional-Integral (PI) calculation method and trial-and-error method are used to discretize continuous OA volume flow setpoints to increase system stability. Two types of experiments were conducted to compare the characteristics of the two discrete OA volume flow setpoint determining methods, and to verify the feasibility of our new approach. The results show that the OA volume flow control loop can be well fitted with other control loops of VAV systems, and ensure OA volume flow demand for a target area. The proposed method provides greater energy savings than maximum OA ratio control strategy (7%–22%) and typical on-demand ventilation method (6.1%), and better control performance than continuous OA volume flow setpoints control system. The PI calculation method is suitable for conditions with high IAQ requirements, while the trial-and-error method can be used for comfort air-conditioning systems to adjust the indoor environment.

Assessing low energy school buildings using the new Building Bulletin 101

This paper reports an assessment of a school building design using the newly published Building Bulletin 101 2018. The requirements on thermal comfort and CO2 based indoor air quality from this new guidance document are very different from its earlier version published in 2006. Existing research reported that the new requirements are much tougher to meet compared with the previous version. The aim of this research is to examine whether design alternatives on an existing school building with 10 learning and teaching spaces can help in passing the new requirements using dynamic thermal simulation tool - IESVE. It is found that promoting ventilation, shading and night purging can all help mitigating overheating in the ten learning and teaching spaces evaluated. With the ‘as built’ condition, these learning and teaching spaces failed all three overheating criteria from the new BB101. Promoting ventilation can help some of the spaces pass the overheating occurrence criterion but not the overheating severity criteria. With added shading to block excessive solar gains, half of the evaluated spaces were able to pass the thermal comfort requirement. Boosting the night purging also helps to some extent in bridging the gap against the target requirements on overheating severity, however, there are still spaces which will not pass the comfort requirement. This may indicate that natural ventilation itself may not be able to provide thermal comfort for the given design. CO2 based indoor air quality requirements are less of an issue as higher CO2 concentrations always happen when the outdoor air temperature is low, boosting ventilation using automatic or manual control can easily resolve this. The research also highlights that one of the overheating criteria is much more difficult to meet, the appropriateness of this criterion is therefore in question. As the new BB101 was only launched very recently, it will be subject to further tests and evaluations in order to examine whether it fits for purpose.

Research on the performance of sidewall perforated plate air supply system that suitable for prefabricated buildings

Taking the rural prefabricated residential building as research object, prefabricated sidewall partitioned perforated plate air supply model and traditional jet air supply model were established respectively. Then, CFD commercial software was used to simulate the temperature field, velocity field, formaldehyde concentration of indoor air-flow distribution of the two air supply model that mentioned above. Simulation results show that in the indoor breathing zone, the valuation index of prefabricated sidewall partitioned perforated plate air supply system, such as the velocity non-uniformity coefficient, air diffusion performance index, ventilation efficiency are entirely superior to the traditional jet air supply system. Moreover, the maximum vertical temperature gradient and maximum horizontal temperature gradient of the prefabricated sidewall partition perforated plate air supply system were also small which means the new air supply system could satisfy the indoor air quality and human thermal comfort requirements.

Performance of a heat recovery ventilator coupled with an air-to-air heat pump for residential suites in Canadian cities

Heat recovery ventilation (HRV) technologies are used to satisfy indoor air quality requirements while reducing building energy consumption. In a typical installation, an HRV system is expected to decrease energy demand; however, the actual benefit depends on the mechanical system, climate conditions, and building design. Here, we assess the energy savings from sensible heat recovery in residential apartment buildings across Canada by modeling the building thermal demands and the HVAC system's energy use. We compare the annual performance of a commercial air-to-air heat pump coupled to a balanced ventilation system with and without the HRV. A hypothetical residential suite is modeled under eight different building orientations for fifteen Canadian cities. Results show that HRV use always reduces the annual heating energy consumption; however, energy consumption may increase in cooling seasons.