Demand-controlled Ventilation Strategy Research Articles

Simulation of Occupancy and CO2-based Demand-controlled Mechanical Ventilation Strategies in an Office Room Using EnergyPlus

Buildings are responsible for a large sharing of energy consumption worldwide. Among all energy services in buildings, heating, ventilation and air conditioning systems not only account for a significant part of energy consumption but they are also highly influential on indoor climate and occupants’ satisfaction in consequence. In this paper, four demand-controlled ventilation strategies based on occupancy schedule period, occupancy level and indoor concentration of CO2 in an office room have been studied. The indoor air quality as well as the energy consumption levels associated to each demand-controlled ventilation strategy were assessed through simulations performed using EnergyPlus. The results showed the best suited ventilation strategies for the office room that can provide acceptable level of indoor air quality with the least energy use. Furthermore, three sensitivity analyses were performed in order to assess the influence of changing different criteria on the energy consumption and indoor air quality.

The impact of design ventilation rates on the indoor air quality in residential buildings: An Italian case study

The paper investigates the effects on building indoor air quality (IAQ) resulting from the choice of different design ventilation rates. A reference residential building was analysed by means of the multizone modelling software CONTAM, by monitoring the concentration of two pollutants: occupant-generated carbon dioxide (CO2) and total volatile organic compounds (TVOC) from indoor sources. A demand-controlled ventilation strategy based on building occupancy was implemented and users' presence schedules were defined. Specifically, the evolution of indoor pollutant concentrations was investigated when the design ventilation rates, recommended by two IAQ-related standards (the Italian UNI 10339 and the European EN 15251), were implemented through a mechanical ventilation system. Different results regarding the IAQ level were achieved accordingly to the dissimilar ventilation rates. After a statistical analysis on the distributions of CO2 and TVOC concentrations, EN 15251 outcomes showed overall better results of the analysed statistical metrics, i.e. prevalence, sensitivity and accuracy. Indeed, the EN 15251 design airflows led to indoor conditions that were more often classified either in the correct air quality class or in a higher class. Finally, a better alignment between the national and European IAQ standards is recommended, especially in terms of airflows, air quality classes and pollutant limit values.

Demand-controlled ventilation for multiple-zone HVAC systems—Part 2: CO2-based dynamic reset with zone primary airflow minimum set-point reset (RP-1547)

In Part 1 of this article, a CO2-based dynamic reset was proposed and evaluated as an energy-saving demand-controlled ventilation strategy by reducing the outdoor airflow rate when the occupancy is under design occupancy. Further energy-saving potential still exists when the zone primary airflow rate is modulated or reset instead of only resetting the outdoor airflow. Two new control strategies are presented: a CO2-based dynamic reset, now combined with a zone primary airflow set-point reset in Part 2. The system level of these control strategies is the same as CO2-based dynamic reset in Part 1. The additional control features are added at the zone level. The zone primary airflow rate minimum set-point will first be reset to increase system ventilation efficiency, which will lead to a reduced system outdoor airflow rate. With this proposed dynamic reset with zone primary airflow set-point reset, the design minimum zone primary airflow rate can be designed lower than the regular set-point used in variable air volume terminal box minimum set-points. This new setting reduces the energy consumption for the system supply fan as well as energy consumption for terminal reheating. Both energy simulation and airflow simulation were conducted in different locations of a building. In this article, the results show that the proposed strategies of CO2-based dynamic reset with zone primary airflow set-point reset consume less energy when compared to CO2-based dynamic reset presented in Part 1 and the baseline case “without demand-controlled ventilation.” The average annual system outdoor airflow rates for the two options of the proposed demand-controlled ventilation are 44.1% and 45%, respectively, less than the outdoor airflow rate for the case without demand-controlled ventilation. Therefore, the proposed demand-controlled ventilation control strategies are suggested to consider for CO2-based demand-controlled ventilation for multiple-zone single duct VAV systems with terminal reheat.

Sensitivity and uncertainty analysis of measurements in outdoor airflow control strategies

Control of HVAC systems is critical to building energy efficiency and indoor environment. Almost all control systems require real-time measurements. However, the measurements inherently contain errors that inevitably impact the outputs of control systems. Therefore, it is of great interest to analyze the impacts of the measurement sensitivity and uncertainty on the control of HVAC systems. This article presents a sensitivity and uncertainty analysis method for HVAC optimal control strategies. The critical measurements in a control strategy are identified by using sensitivity analysis. The uncertainty analysis provides information for further risk analysis. A modified exponentially weighted moving average filter is developed and adopted to reduce the uncertainty of control strategies. The sensitivity and uncertainty analysis is conducted on demand-controlled ventilation strategies for multi-zone office buildings. Improvements of the control strategies based on the analysis results are also conducted. Results demonstrate the sensitivity and uncertainty analysis are effective in evaluating control strategies. The accuracy of the control strategy is significantly improved, and the uncertainty is reduced.

A new method for controlling CO2 in buildings with unscheduled opening hours

This paper proposes a novel and efficient CO2-based demand-controlled ventilation (DCV) strategy for use as an alternative to the proportional-plus-integral (PI) and the proportional-integral-derivative (PID) controls most often used for CO2 control in buildings. The new strategy “Pseudo Session DCV” divides opening hours into pseudo training sessions and breaks. For each pseudo training session, the outdoor airflow rate is calculated through the CO2 mass balance equation to keep indoor CO2 near the set point. For each pseudo break, the outdoor airflow rate is set at either the prescribed ventilation rate or the minimum outdoor air required by industry standards. Simulations were performed for a sports training center using both simulated and experimental CO2 generation rates. The results show that Pseudo Session DCV performs similar to PID for all possible cases, but achieves better energy savings performance than proportional control. For example, the Pseudo Session DCV strategy saves 34–38% of the energy required to condition outdoor air and 62–79% of fan energy compared to a proportional control strategy. Pseudo Session DCV is simple, efficient, capable of utilizing schedules for optimal ventilation control and no tuning is needed. Therefore Pseudo Session DCV control is easier to implement than PI or PID control.

Optimization of a liquid desiccant based dedicated outdoor air-chilled ceiling system serving multi-zone spaces

A liquid desiccant based dedicated outdoor air-chilled ceiling (DOAS-CC) system is proposed to serve a multi-zone space. The outdoor airflow rate and the supply air humidity ratio are two crucial variables in such a system, which significantly influence indoor thermal comfort, indoor air quality and energy consumption. Two strategies are presented to optimize these two variables in the study. They are the demand-controlled ventilation (DCV) strategy and the supply air humidity ratio set-point reset strategy. To evaluate the performances of these two strategies, a basic control strategy, i.e., the strategy adopting constant ventilation flow rate and constant supply air humidity ratio, is selected as the benchmark. Performances of the two strategies in terms of indoor air temperature, relative humidity and CO2 concentration as well as energy consumption are analyzed using simulation tests. The results show that the supply air humidity ratio set-point reset strategy is effective for the indoor air humidity control. It can save about 19.4% of total energy consumption during the whole year. The DCV-based ventilation strategy can further reduce about 10.0% of energy consumption.

Development and In-situ validation of a multi-zone demand-controlled ventilation strategy using a limited number of sensors

This paper presents a new strategy using a limited number of sensors for demand-controlled ventilation (DCV) of multi-zone office buildings. The conventional CO2-based demand-controlled ventilation strategy for multi-zone offices requires CO2 sensors and supply airflow meters being installed in all zones. However, in many practical cases, CO2 sensors might not be available or not necessary. To control the outdoor airflow based on actual occupancy variations in such cases, a DCV strategy with two implementing schemes is developed for different sensor availabilities. The first scheme is used for the situation when CO2 sensors in individual zones are not available but the airflow meters for individual zones are installed. The second scheme is used for the conditions when CO2 sensors and airflow meters in individual zones are not available. These two schemes use two different approaches to estimate the outdoor airflow fraction of the critical zone approximately. Both schemes only require the CO2 sensor in the main return air to dynamically detect the total occupancy number. The developed strategy is implemented and validated in a high-rise office building in Hong Kong. The site test results show that the strategy can achieve significant energy saving while maintaining acceptable IAQ in the situations where only limited sensors are available.

IR(Infrared) 센서기반 제어방법에 따른 공동주택 멀티 존 환기시스템 평가 연구

In previous research, most occupant said that they have not operated ventilation system installed in the house, because of increasing of energy consumption and unconcern of ventilation. Therefore, it is necessary to applied the sensor based demand controlled ventilation for the IAQ(Indoor Air Quality) and improvement of energy efficiency in ventilation strategy. The propose of this study is to present a application method of IR(Infrared) sensor for multi-zone DCV(Demand Controlled Ventilation) in the apartment house. It is possible that IR sensor could be used for DCV, because that could detect the occupant and action. IR sensor based DCV strategies are established to evaluate characteristic of application in the apartment house and simulated by Contam program. As a result, they have some week points though, if they would be applied DCV with optimum strategy, it would be useful to improve IAQ, to reduce energy consumption.

Model-based Optimal Control of Outdoor Air Flow Rate of an Air-Conditioning System with Primary Air-Handling Unit

This paper presents a model-based outdoor air flow rate optimal control strategy for multi-zone variable air volume air-conditioning systems with the primary air-handling units. An adaptive optimisation algorithm is adopted for optimising the set point of the outdoor air flow rate to minimise the energy cost, which could compromise the energy consumption of the primary fan and the cooling energy saving by the cold outdoor air. The primary fan energy consumption can be predicted using a simplified incremental fan model and the main parameters of this model are identified online. The cooling energy saving by the outdoor air is estimated online using the enthalpies of the air streams. The lower limit of the outdoor air flow rate is determined by a CO2-based adaptive demand-controlled ventilation strategy using the dynamic multi-space equation to maintain the satisfied indoor air quality (IAQ). Tests were conducted to evaluate the performance of the control strategy applied to a practical building system in simulation environment. The results show that the proposed optimal control strategy can reduce energy consumption significantly, while maintaining a satisfactory IAQ.

A novel and dynamic demand-controlled ventilation strategy for CO 2 control and energy saving in buildings

Although conventional CO 2-based demand-controlled ventilation strategies, such as proportional and exponential controls, can ensure buildings/spaces meeting the minimum requirements of outdoor air by industry standards, they are operated under the assumption of equilibrium condition which can hardly be reached in practice and therefore there is still much space to improve on conventional strategies in terms of energy saving. In this paper, a novel and dynamic control strategy was developed for hourly scheduled buildings. The strategy utilized schedules by setting a base ventilation rate for unoccupied periods and calculating ventilation rate dynamically at each occupied period by solving the CO 2 mass balance equation to keep indoor CO 2 near the set point during the occupied period. Experimental simulations were made over a sports training center using both simulated and experimental CO 2 generation rates. Results show that the new strategy can save +34% of energy related to ventilation air compared to proportional control. The new strategy was also extended to common buildings which are occupied for almost all opening hours. In the case of common buildings, the new strategy can save about +26% of energy related to ventilation air compared to proportional control. The new strategy is simple, dynamic, flexible and efficient.

In-situ implementation and validation of a CO 2-based adaptive demand-controlled ventilation strategy in a multi-zone office building

This paper presents the in-situ implementation and validation of a CO 2-based adaptive demand-controlled ventilation (DCV) strategy in a super high-rise building in Hong Kong. The adaptive DCV strategy employs a dynamic multi-zone ventilation equation for multi-zone air-conditioning systems, in which a CO 2-based dynamic occupancy detection scheme is used for online occupancy detection. This strategy is implemented in an independent Intelligent Building Management and Integration platform (IBmanager), which communicates with the main station of the Building Management System (BMS) through a communication protocol and interface. The performance of this DCV strategy is practically tested and validated by comparing with that of the original fixed outdoor air flow rate control strategy used in site. The implementation architecture and test results including energy and environmental performances represented. Since the accuracy and reliability of the major measurement instrumentations affect the actual performance of the DCV strategy significantly, the commissioning and calibration of major measurement instrumentations are presented as well.

An Adaptive Demand-Controlled Ventilation Strategy with Zone Temperature Reset for Multi-Zone Air-Conditioning Systems

In air-conditioning systems serving multiple zones, conventional ventilation strategies often result in over-ventilation in some zones with under-ventilation in the other zones when the heating/cooling load and occupancy profiles of zones differ greatly. This article presents an adaptive demand-controlled ventilation (DCV) strategy for multi-zone air-conditioning systems, which employs real-time occupancy identification using the dynamic multi-zone ventilation equation and zone temperature set-point reset of critical zones. The strategy identifies the critical zones, and fully considers the outdoor air demand of critical zones and the unvitiated outdoor air in the re-circulated air from the other zones. The air temperature reset of critical zones results in the increase of their supply air fractions and therefore the amount of outdoor air delivered to the critical zones. Consequently the total outdoor airflow demand and the overall energy consumption are reduced while the ventilation of critical zones is satisfied. This adaptive DCV strategy is validated by comparing its energy and environmental performances with other typical ventilation strategies under various weather conditions.

96/04238 The design, layout and maintenance of ventilation and air conditioning on the basis of hygiene requirements in standards

This paper presents the in-situ implementation and validation of a CO2-based adaptive demand-controlled ventilation (DCV) strategy in a super high-rise building in Hong Kong. The adaptive DCV strategy employs a dynamic multi-zone ventilation equation for multi-zone air-conditioning systems, in which a CO2-based dynamic occupancy detection scheme is used for online occupancy detection. This strategy is implemented in an independent Intelligent Building Management and Integration platform (IBmanager), which communicates with the main station of the Building Management System (BMS) through a communication protocol and interface. The performance of this DCV strategy is practically tested and validated by comparing with that of the original fixed outdoor air flow rate control strategy used in site. The implementation architecture and test results including energy and environmental performances represented. Since the accuracy and reliability of the major measurement instrumentations affect the actual performance of the DCV strategy significantly, the commissioning and calibration of major measurement instrumentations are presented as well.

Demand-Controlled Ventilation in a Multi-Zone Office Building

This study applies indoor air quality modelling to investigate the potential advantages and drawbacks of demand-controlled ventilation as an indoor air quality control strategy. The study uses a multiple zone pollutant transport model to evaluate the performance of several indoor air quality control strate gies under a variety of conditions. The pollutant transport model is incorpo rated into the TRNSYS simulation program to allow simultaneous calculation of both building pollutant concentrations and building energy use. A specific office building situation consisting of a main zone and a conference room was studied. The simulations showed that a carbon dioxide-based demand con trolled ventilation system can provide better control of indoor air quality than a constant outdoor airflow at the ASHRAE Standard 62-1989 prescribed level under a wide range of building conditions. The constant outdoor air approach lacks the capability of providing additional outdoor air when required by poor building conditions such as a low pollutant removal effectiveness and a high occupant density. The demand-controlled ventilation system saves energy compared to the constant outdoor air approach under all conditions consid ered. It was also found that a demand-controlled ventilation strategy consist ing of a step controller combined with scheduled 100% outdoor air purges can protect building occupants from exposure to high concentrations of non-occu pant-generated pollutants while still providing energy savings.

Designing the green skyscraper

The construction of high-rise residential buildings has increased dramatically in line with the expansion of cities. However, this type of buildings has relatively higher annual energy consumption and further relies on comprehensive use of fossil fuels. Furthermore, these buildings are rather expensive compared to other types of residential buildings by the global costs throughout their economic life cycle. The present study aims to contribute in improving the energy performance of high-rise residential buildings based on the cost-optimal framework methodology as provided in Recast Directive on Energy Performance of Buildings (EPBD 2010/31/EU). Recognized as an EU candidate and engaged in accession talks for full membership, Turkey is required to comply with the provisions stipulated in this Directive. In the scope of the present study, advanced retrofit measures aimed to improve the energy performance of heating, ventilation, and air-conditioning systems are suggested based on a high-rise residential building, a representative case study in Turkey. The results indicated that use of decentralized heat recovery ventilator systems combined with demand-controlled ventilation strategy would decrease the energy consumption by an annual rate of 39% in high-rise residential buildings. Besides, it was concluded that use of photovoltaic and waste heat recovery systems was associated with significant superiority in improving the energy efficiency level of high-rise residential buildings at cost-optimum scenarios. In the present study, the aforementioned retrofit measures helped decrease the annual energy consumption and global cost by 50% and 23%, respectively. Accordingly, it was suggested that the utilization of photovoltaic and waste heat recovery systems in high-rise residential buildings should be mandatory through an increase in incentives intended for renewable energy systems and amendment of the building codes in Turkey.