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Variable refrigerant flow (VRF) system has been an appealing solution of air conditioning for residential and commercial buildings, due to its flexibility and cost effectiveness, while lack of ventilation capability is a major drawback. Incorporation of dedicated outdoor air system (DOAS) is a typical practice. However, good coordination between DOAS and VRF is critical for achieving desired thermal comfort is challenging due to the possible complexity of mixed sensible and latent heat exchanges. In this paper, to handle the nonlinear dynamic characteristics of VRF-DOAS system, we propose an offset-free Koopman model predictive control (MPC) strategy for thermal comfort regulation, in which the MPC design is computationally more efficient due to the convex problem formulation and the use of reduced-order Koopman models, and the offset-free MPC structure enhances the robustness to model uncertainties and unmeasured disturbances. A control-oriented model is obtained by hybridizing the first-principle and data-driven modeling approach. The proposed controls strategy is evaluated with a Modelica simulation model of a VRF-DOAS system. A Dymola-Python cosimulation platform is developed via the functional mockup interface (FMI), for which the MPC algorithms are implemented in Python. Simulation results show significantly better performance of the offset-free Koopman MPC in thermal comfort regulation. [ABSTRACT FROM AUTHOR]

Human inhalation exposure to fine particulate matter (PM2.5), including the PM2.5 of outdoor origin, predominantly occurs indoors. To limit outdoor PM2.5 penetration into buildings, ventilation standards often require the filtration of outdoor air with a minimum efficiency. Nevertheless, the PM2.5 filter selection recommended by the standards is based on the annual average outdoor concentrations without considering seasonal or diurnal fluctuations. This could result in a waste of energy or elevated indoor PM2.5 exposures. Representative outdoor PM2.5 data from 37 cities worldwide in conjunction with a simulated office building are used to examine the impact of filtration strategies on indoor PM2.5 levels and the fan’s energy consumption. Two energy-saving methods are tested: (1) the optimum filter selection that maintains the indoor PM2.5 below the World Health Organization’s (WHO) air quality guidelines; and (2) the baseline filter recommended by standards in combination with a filter bypass. Relative to a standard recommended baseline case, the two applied methods could reduce energy demand by between 4% and 17%. This indicates that the outdoor air is over-filtered in the majority of the investigated cities. In cities with low-to-moderate outdoor PM2.5 levels, using a filter bypass can be an effective energy conservation method without compromising PM2.5 exposures indoors. 'Practice relevance' Protecting building occupants from outdoor originating PM2.5 without a high energy penalty is not a simple task. The majority of recommendations for ventilation system design typically do not consider temporal variation in outdoor PM2.5. This study’s data suggest that outdoor air filtration efficiencies required by building standards are not sufficient to protect the building occupants living in severely polluted areas. In these areas, outdoor air filtration should be supplemented with other measures to limit outdoor PM2.5 penetration. In areas with low or intermittent outdoor PM2.5 levels, bypassing the filter can significantly reduce the energy consumption from fans without compromising indoor air quality. The energy-saving potential increases with the increase of outdoor air quality. This study suggests that improved outdoor air filtration can be achieved by a stronger reliance on continuous outdoor air quality data recorded on site.

• A dedicated desiccant wheel outdoor air cooling system (DWDOAS) is proposed. • The energy, exergy and economic analyses are applied to DWDOAS. • Effect of the main operating parameters on the performance are studied in detail. • DWDOAS has a high thermodynamic coefficient in high temperature and humidity areas. In high-temperature and high-humidity environments, a large amount of energy is consumed to cool and dehumidify outdoor air by dedicated outdoor air systems in nearly zero energy buildings. Desiccant wheels have the advantages of large moisture removal capacities and continuous regeneration. However, the application of desiccant wheels in nearly zero energy buildings is limited by their large regeneration heat capacity and high temperature after dehumidification. A dedicated desiccant wheel outdoor air cooling system is thus proposed. An experimental setup is built and used to test the performances of three modes for dedicated desiccant wheel outdoor air cooling systems. The results show that mode Ⅰ (wet membrane humidifier downstream evaporation section of heat pipe heat exchanger) has a higher performance coefficient and higher exergy efficiency compared to other modes. The thermodynamic and exergy performances of the proposed mode Ⅰ system are determined. The results show that the thermodynamic coefficient decreases from 1.3 to 0.52 and the exergy efficiency decreases from 0.76 to 0.18 when the regeneration temperature increases from 60°C to 110°C. [ABSTRACT FROM AUTHOR]

Human inhalation exposure to fine particulate matter (PM2.5), including the PM2.5 of outdoor origin, predominantly occurs indoors. To limit outdoor PM2.5 penetration into buildings, ventilation standards often require the filtration of outdoor air with a minimum efficiency. Nevertheless, the PM2.5 filter selection recommended by the standards is based on the annual average outdoor concentrations without considering seasonal or diurnal fluctuations. This could result in a waste of energy or elevated indoor PM2.5 exposures. Representative outdoor PM2.5 data from 37 cities worldwide in conjunction with a simulated office building are used to examine the impact of fıltration strategies on indoor PM2.5 levels and the fan's energy consumption. Two energy-saving methods are tested: (1) the optimum filter selection that maintains the indoor PM2.5 below the World Health Organization's (WHO) air quality guidelines; and (2) the baseline filter recommended by standards in combination with a filter bypass. Relative to a standard recommended baseline case, the two applied methods could reduce energy demand by between 4% and 17%. This indicates that the outdoor air is over-fıltered in the majority of the investigated cities. In cities with low-to-moderate outdoor PM2.5 levels, using a filter bypass can be an effective energy conservation method without compromising PM2.5 exposures indoors. [ABSTRACT FROM AUTHOR]

Dedicated outdoor air systems (DOAS) are used to supply treated outdoor air to a cooled space. This paper focuses on a DOAS and its application in tropical climate. This DOAS is equipped with a desiccant coated Enthalpy Wheel (EW), a dehumidifying cooling coil (CC), and a sensible heat wheel (SW). A mathematical model was developed using the governing equations and validated with a TRNSYS simulation and experimental data with a coefficient of determination of 0.88 and 0.92, respectively. Simulations using the validated model showed that the DOAS configuration was applicable for the tested tropical climatic conditions. Further investigations showed that a maximum change in temperature with respect to rotational speed of SW achieved was 2.44°C, and maximum change in humidity ratio with respect to rotational speed of EW achieved was 0.38%. Also, CC showed a maximum change in temperature of 14.69°C and humidity ratio of 8.35% with respect to chilled water flow rate. Likewise, Air flow rate also showed change in temperature and humidity ratio of the supplied air. [ABSTRACT FROM AUTHOR]

• A dedicated outdoor air system with a thermoelectric radiant panel in high-speed train cabins was proposed. • A feasibility of using proposed system in cabins was investigated regarding the energy performance. • A detailed energy simulation model was developed for the proposed system. • The proposed system saved 32.6% of the annual operating energy compared to the conventional system. This paper proposes a dedicated outdoor air system (DOAS) with thermoelectric radiant panels (TERPs) for high-speed train cabins that prevents air quality problems and reduces operation energy consumption. The DOAS supplies cooled and dehumidified outdoor air for ventilation and the removal of latent loads. The cooling and heating loads can be accommodated using TERPs, which are suitable for use in train cabins owing to their simple structure. Moreover, the air flow at the exterior surface during train running can be used to remove rejected heat from the TERP. In this study, detailed energy simulations were conducted to evaluate the energy saving potential of the proposed system compared to the conventional variable air volume system. The results indicated that the proposed system can save 32.6% of the annual operation energy. In addition, the TERP system showed an annual COP exceeding 2.2 during 75% of its operational time. [ABSTRACT FROM AUTHOR]

• A new mechanical dehumidification cycle for dedicated outdoor air system is proposed. • Prototype test showed energy efficiency 26% higher than the conventional one. • The new system has smaller footprint and lower cost compared with desiccant systems. Dedicated outdoor air system is drawing much attention in air-conditioning applications. However, the cooling and dehumidification process of supply air in the dedicated outdoor air system is energy-intensive. In this study, we proposed a highly energy efficient dedicated outdoor air system using novel vapor-compression refrigeration cycle which is featured by a fine combination of two-stage direct-expansion dehumidification, subcooled liquid-to-air reheating, and exhaust air heat recovery. The novel system was optimally designed and analyzed with a detailed mathematical model. A prototype was also made and tested. Test results showed that the energy efficiency of the proposed system reaches 5.42 under rated cooling conditions and 26% higher than the conventional one. The model accuracy was also validated with the measured data. Moreover, energy efficiency improvement from feature technologies was numerically analyzed. Control strategy for key operating parameters was developed and illustrated. System performance under varying operating conditions was evaluated as well. [ABSTRACT FROM AUTHOR]

Abstract The main objective of this research is to propose a dedicated outdoor air system assisted by a thermoelectric heat pump, and to evaluate the operating energy performance of the proposed system compared with a reference system. The proposed dedicated outdoor air system consists of an enthalpy wheel, a desiccant wheel, and the thermoelectric heat pump to condition the introduced outdoor air to provide required ventilation air to the conditioned zone at neutral temperature, while the reference system consists of a desiccant wheel, a sensible heat exchanger, a cooling coil, and a regeneration air heater. To develop an empirical model for the thermoelectric heat pump applicable to the energy simulation of the proposed system, a thermoelectric heat pump prototype was built, and its operating data were collected in a fully controlled laboratory environment. By integrating the existing models of each system component used in both dedicated outdoor air systems, detailed energy simulations were performed to compare the energy performance of the proposed dedicated outdoor air system with the reference system. The results showed that the proposed system assisted by the thermoelectric heat pump consumed 23% more operating energy than the reference system because of the lower coefficient of performance of the thermoelectric heat pump compared with the conventional vapor compression system. For comparable energy performance, the proposed dedicated outdoor air system should have heat exchange effectiveness values greater than 49% at least at both the process and secondary air channels of the thermoelectric heat pump, and the figure of merit of the thermoelectric modules used in the thermoelectric heat pump should be over 1.35. Highlights • A dedicated outdoor air system integrated with a thermoelectric heat pump was proposed. • A prototype of the thermoelectric heat pump was built to analyze its characteristics. • The proposed system was analyzed via energy simulation with an empirical model of the thermoelectric heat pump. • Desirable heat exchange effectiveness and figure of merit of thermoelectric heat pump for energy savings were determined. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an online air balancing method applied in dedicated outdoor air systems, named as gradient-based online adaptive balancing (GOAB) method. The GOAB method derives the damper adjustment rule based on the gradient of the objective function that quantifies the discrepancy between actual flow rate and the set point in normalized form. An adaptive mechanism is applied to capture the change of Jacobian matrix during the balancing process. The optimum direction of damper angle increment is determined based on the null space of the gradient vector to speed up the convergence and ensure at least one damper to be fully open. Compared with the existing methods, the proposed GOAB method offers the following advantages:1.) The method can be performed on a duct system in operation, which provides possibility to re-balance the system under dynamic working conditions; 2.) The energy loss on dampers is minimized without compromising the balancing accuracy. Simulations are performed in MATLAB to investigate several model parameters and provide guidance for the parameter design. Experiments are conducted on a 5-ternimal duct system to validate the proposed method under various design flow requirements. The results show that the maximum absolute percentage error can be controlled within 4.3% among all test cases. This method improves the energy efficiency of the duct system and speeds up the convergence rate towards air balance to save time and cost. Highlights • An online air balancing method is proposed to balance the flow distribution in a duct system. • A recurrent form of damper adjustment rule is proposed based on gradient descent. • The optimum direction of the damper angle increment is found to minimize the energy loss. • The proposed method requires little prior knowledge on the system topology and duct parameters. • The proposed method is suitable for variational ventilation load applications. [ABSTRACT FROM AUTHOR]

• An integrated air conditioning system (IACS) is proposed for a passive house. • A machine learning model is developed to quantify thermal comfort. • Multi-objective optimization of operating conditions for the IACS is presented. • The IACS consumes less energy under optimal operating conditions. • The IACS is economical, particularly in a passive house. Appropriate dehumidification systems are essential for passive houses to prevent thermal discomfort under high dehumidification loads. In this study, an integrated air conditioning system (IACS) consisting of a dedicated outdoor air system and sensible cooling unit is developed to manage dehumidification loads in passive houses. Multi-objective optimization of the operating conditions of the IACS is performed considering the energy consumption and thermal comfort of a passive house. A thermal comfort model is constructed using a big-data-driven machine learning method to improve prediction accuracy compared to a conventional model. Additionally, an artificial-neural-network-based metamodel is developed to estimate the performance of the IACS. The optimal operating conditions are determined based on the Pareto solution set obtained from multi-objective optimization. The optimized performance and economic feasibility of the IACS are compared to those of a conventional air conditioning system (CACS). For the IACS in a passive house, the optimal indoor set-point temperature and relative humidity were determined to be 27.01 ℃ and 50.35%, respectively. The energy-saving rates of the IACS were 15.96% and 7.53% in passive and normal houses, respectively, compared to the CACS. The IACS is more economical than the CACS based on its energy-saving effects, particularly in passive houses. [ABSTRACT FROM AUTHOR]

In the era of post-Coronavirus Disease 2019, the dedicated outdoor air system (DOAS), which provides 100% outdoor air for the building, is widely acknowledged as it can ensure acceptable indoor air quality by delivering fresh outdoor air to occupied space. The DOAS with a proper design and operation can provide sufficient ventilation and dehumidification while achieving energy efficiency. Nonetheless, there is limited guidance in determining the optimal control sequence of the DOAS for the designers and operators to implement in practice. Accordingly, in practice, a number of issues have been acknowledged in the design and control phases of DOAS, including insufficient ventilation and dehumidification, and increasing supply air dry-bulb temperature in fear of over-cooling, which might cause significant discomfort and energy waste. There have been efforts to develop high-performing DOAS controls for better energy efficiency. However, such controls are often complex, or difficult to interpret, for building designers and operators to consider in practice. In this regard, this paper explores a simulation-based framework for generating a supply air temperature control sequence of the DOAS not only to ensure improved energy-saving potential but also to guarantee the implement-ability of the control logic. The U.S. Department of Energy prototype primary school with dynamic occupancy profiles was modeled with a whole building simulation program, EnergyPlus. The model consists of a DOAS with an exhaust air energy recovery system for ventilation and fan-coil units for space cooling and heating. Then, a Genetic Algorithm was adopted to find the true optimal supply air temperature control sequence in terms of minimizing the energy cost of the heating, ventilation, and air conditioning system operation. Lastly, Decision Tree was adopted to extract rules out of the optimums to derive an implementable sequence of operation for the DOAS supply air temperature. A total of 12 week-simulation including four weeks of heating, cooling, and shoulder seasons, separately, under the weather condition of New York City was conducted for the case study. This case study identified that the optimization-informed rule extraction-based control, when compared to conventional outdoor air temperature-based reset control, could save about 13% of energy cost and 25% of energy consumption throughout the heating, cooling, and shoulder seasons. It is notable that the energy-saving was mainly achieved by reducing the heating energy consumption. Importantly, it nearly corresponds to the true optimal control result, which reduces approximately 14% of energy cost and 27% of energy consumption. From the results, it can be highlighted that the optimization-informed rule extraction can be as energy effective as the optimal control, while significantly reducing the complexity of the control. [ABSTRACT FROM AUTHOR]

• A dedicated outdoor air system embedded with a four-coil heat pump is proposed. • The system has four operating modes integrated and can readily switch among them. • A prototype of 300 m3/h supply air provides dehumidification capacity of 101.4 L/day. • The system can keep supplying fresh air temperature above indoor dew point. Dedicated outdoor air system (DOAS) plays a critical role in building ventilation. In recent years, much attention has been paid to the DOAS with heat-pump heat recovery. It is expected to have better dehumidifying performance and more operating modes to efficiently cooperate with the parallel cooling system. This work proposes a novel packaged DOAS embedded with a four-coil heat pump. Of the four coils, supply air coil and exhaust air coil are basic components of vapor compression heat pump that facilitates heat recovery from exhaust air. Return air coil is added to reduce heat loss in the mixing of return air and additional outdoor air. Supply air coil is introduced to reheat fresh air and avoid moisture condensation on air ducts. Meanwhile, refrigerant subcooling is increased in heat pump cycle for better efficiency. With simple switch the DOAS can also operate in four modes, i.e., outdoor air dehumidification, outdoor air low-load dehumidification, outdoor air heating and return air dehumidification. A functional prototype of 300 m3/h supply air is made and tested. Dehumidification capacity of 101.4 L/day and specific moisture extraction rate (SMER) of 3.22 kg/kWh are reached under the design condition of 30 °C/27 °C. Compared to the system without supply air coil, the new DOAS can see an improvement of 46.3% in SMER at the same supply air humidity ratio of 8.5 g/kga. It also keeps the supply air temperature above indoor air dew point. At last, the system's multi-mode operation for varying outdoor conditions is discussed. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the energy saving potential of a dedicated outdoor air system (DOAS) with a thermoelectric module radiant cooling panel (TEM-RCP) by comparing it with those of both a conventional variable air volume (VAV) system and a DOAS with hydraulic ceiling radiant cooling panels (CRCP) via a detailed energy simulation. The theoretical and empirical models for each component were used to estimate the energy performance of a VAV system and a DOAS with CRCP. Additionally, the TEM-RCP was analyzed by using the developed simulation models based on the semi-black box model. Hourly simulations were conducted to measure the annual energy performance. The results indicated that the DOAS with a TEM-RCP consumed 40.7% less operating energy annually when compared with that of the conventional VAV system while the proposed system exhibited only 1.0% more annual energy consumption when compared with the DOAS with hydraulic CRCP given the relatively low dimensionless figure of merit (ZT) of the TEMs (i.e., 0.73) that is used in the TEM-RCP. However, the average coefficient of performance (COP) of the TEM-RCP for cooling was 8.3, which is significantly higher than that of the conventional CRCP (4.6) during the operation period. This is because the TEM-RCP uses a cooling tower for heat removal, and its cooling water temperature is sufficiently low without requiring additional cooling of the TEM except during summer. Therefore, TEM maintains radiant panel temperature with low electric energy consumption. The study also indicated that if the ZT value of TEMs exceeded 0.75, then the proposed system exhibited lower annual energy consumption when compared to that of the DOAS with CRCP. [ABSTRACT FROM AUTHOR]

With increased use of variable refrigerant flow (VRF) systems in the U.S. building sector, interests in capability and rationality of various building energy modeling tools to simulate VRF systems are rising. This paper presents the detailed procedures for model calibration of a VRF system with a dedicated outdoor air system (DOAS) by comparing to detailed measured data from an occupancy emulated small office building. The building energy model is first developed based on as-built drawings, and building and system characteristics available. The whole building energy modeling tool used for the study is U.S. DOE’s EnergyPlus version 8.1. The initial model is, then, calibrated with the hourly measured data from the target building and VRF-DOAS system. In a detailed calibration procedures of the VRF-DOAS, the original EnergyPlus source code is modified to enable the modeling of the specific VRF-DOAS installed in the building. After a proper calibration during cooling and heating seasons, the VRF-DOAS model can reasonably predict the performance of the actual VRF-DOAS system based on the criteria from ASHRAE Guideline 14-2014. The calibration results show that hourly CV-RMSE and NMBE would be 15.7% and 3.8%, respectively, which is deemed to be calibrated. The whole-building energy usage after calibration of the VRF-DOAS model is 1.9% (78.8 kWh) lower than that of the measurements during comparison period. [ABSTRACT FROM AUTHOR]

The main purpose of this research is to analyze and compare the energy performance of two different novel air conditioning systems; one is a dedicated outdoor air system (DOAS) with a parallel system and the other is a heat-pump-integrated liquid-desiccant and evaporative-cooling-assisted 100% outdoor air system (HPLD-IDECOAS). It was assumed that office buildings served by each system were located in six cities representing four different climatic regions in China. The hourly thermal loads of the office buildings meeting the local building design codes of each selected city were predicted by the TRNSYS 18 software package. The hourly thermal load data were imported into the commercial engineering equation solver (EES) program to estimate the operating energy consumption of each system via detailed energy simulations performed using valid system simulation models. The results show that the HPLD-IDECOAS has higher energy-saving potential than the DOAS with a parallel system in climate regions with high humidity, whereas, in dry regions, the difference in energy consumption between the two systems was not significant.

The main objective of this study was to develop a thermoelectric heat pump and liquid desiccant system based on a dedicated outdoor air system (THPLD-DOAS). An internally-cooled and -heated liquid desiccant system was used and a thermoelectric heat pump (THP) served as the desiccant cooling and heating energy source for dehumidification and regeneration of the desiccant solution, respectively. In order to investigate the energy-saving potential of the proposed system, its thermal performance and operating energy consumption during the cooling season were compared to those of a conventional dedicated outdoor air system with a ceiling radiant cooling panel system (DOAS-CRCP). Detailed simulations for each system were conducted under hot and humid climatic conditions. Their thermal performance under various room sensible heat factor (RSHF) conditions was evaluated to observe the energy performance, depending on the dehumidification performance, of the liquid desiccant system integrated with the THP. The results showed that the coefficient of performance (COP) of the THP ranged from 0.8 to 1.2 to maintain a sufficient dehumidification rate. The operating energy of the THPLD of the proposed system was 6.6% to 16.0% less than that of the chiller operating energy of a conventional DOAS. Consequently, the proposed system consumed 0.6-23.5% less operating energy compared to the conventional DOAS. [ABSTRACT FROM AUTHOR]

Variable refrigerant flow (VRF) refers to the ability of an air-conditioning (AC) system to control the amount of refrigerant flowing to the multiple evaporators (indoor units). This study compares the actual energy use of a building, equipped with a VRF system with simulation results obtained using EnergyPlus. Also, the aim of this study is to analyze the performance related to energy and thermal comfort when the VRF system without ventilation is replaced with the VRF system with the energy recovery ventilation (ERV) or VRF system with the dedicated outside air system (DOAS). The measured power use of the VRF system is very similar to the simulated power use of the VRF system. The mean value of the difference between simulation and measured data in monthly power use in summer and winter was 3.3% and 3.6%, respectively. The yearly energy use of the VRF system without ventilation is found to be 213.6 kWh/m 2 a. The VRF system with ERV in case 4 and the VRF system with DOAS in case 8 are found to be 16.8% and 26.0% higher than the VRF system without ventilation, respectively. Through the entire year, it was found that 17.2% of indoor air condition data provided by the VRF system without ventilation in the winter and 16.2% of the data in the summer fall within the ASHRAE winter and summer comfort zones. In order to improve the thermal comfort, the setpoint temperature in winter needs to be increased and the humidity in summer needs to be reduced. On the other hand, it was found that 93.9% of indoor air condition data provided by the VRF system with DOAS in the winter and 83.8% of the data in the summer fall within the ASHRAE winter and summer comfort zones. When the VRF system without ventilation is replaced with the VRF system with DOAS, the thermal comfort percentage is improved during the winter and summer by 76.7% and 67.6%, respectively. [ABSTRACT FROM AUTHOR]

A novel dedicated outdoor air system consisting of a multi-stage direct expansion coil and a zero-energy heat pipe to generate extra-low temperature outdoor air to avoid moisture-related problems was proposed in this study. The proposed system’s performance in achieving the desirable air conditions and better energy efficiency objectives is compared with a conventional direct expansion system for air-conditioning of a typical office building in Hong Kong based on simulation investigations. The simulations were carried out using equipment performance data of a pilot study, and realistic building and system characteristics. It was found that the proposed system, as compared to the conventional system, could reduce the annual indoor discomfort hours by 69.4%. An energy and exergy analysis was also conducted. It was revealed that the proposed system could reduce the annual air-conditioning energy use by 15.6% and the system exergy loss rate by 13.6%. The associated overall exergy efficiency was also found 18.6% higher. The findings of this study confirm that the proposed system is better than the conventional system in terms of both energy and exergy efficiency and the desirable air conditions. [ABSTRACT FROM AUTHOR]

A VRF (variable refrigerant flow) combined system adopting a DOAS (dedicated outdoor air system) has been proposed to reduce the total energy consumption while satisfying IAQ (indoor air quality) and THC (thermal and humidity comfort) with minimum outdoor air. The objective of this study is to develop a model-based multi-objective optimal control strategy for the VRF combined system with multi-zone in order to optimize the multi-objective functions of the THC, IAQ, and total energy consumption. The performance of the VRF combined system was evaluated using the EnergyPlus model. The VRF combined system was optimized by GA (genetic algorithm) and RSM (response surface methodology) with the multi-objective functions of the THC, IAQ, and total energy consumption. The proposed multi-objective optimal control strategies (A and B) were compared with the TS (time schedule) strategy and the DCVH (demand controlled ventilation with humidifying). Optimal control strategy B reduced the total energy consumption by 20.4% and increased the ratio of the hours satisfying the extended comfort zone by 19.1% compared to the DCVH strategy. [ABSTRACT FROM AUTHOR]

Indoor air quality (IAQ) and energy consumption are becoming increasingly important in the HVAC field. This paper examines the potential of improving demand-controlled ventilation (DCV) performed under an occupant based ventilation standard. CO2-based DCV and radio frequency identification-based DCV methods are simulated in an office building model served by a dedicated outdoor air system combined with a fan-coil system. A numerical model for estimating real-time occupancy is developed. Simulations are conducted with current Chinese ventilation standard as an example. Results show that the current standard causes severe fluctuations under a CO2-based DCV strategy. It is concluded that the current standard defines the ventilation rate as a function only related to the occupancy number, which makes DCV control unstable. As an improvement, the current Chinese ventilation standard is modified to a form similar to the standard of the American Society of Heating, Refrigerating and Air-Conditioning Engineers that considers the occupant and the building separately. The modified standard is applicable to various DCV approaches and can maintain an acceptable formaldehyde concentration. This modification significantly improves the applicability of the current Chinese ventilation standard to CO2-based DCV and can be easily extended to similar ventilation standards. [ABSTRACT FROM AUTHOR]

In large commercial buildings facing high cooling loads, conventional heating, ventilation, and air-conditioning (HVAC) systems are typically based on the use of one, or few, large-capacity air handling units (AHUs) to supply conditioned air throughout a centrally-managed air distribution network. The alternative concept of ‘decentralized’ HVAC typically entails the deployment of multiple, small capacity fan coil units (FCUs) operating as dedicated outdoor air systems (DOAS) and located closest to the individual thermal zones they must condition. For this study, the authors commissioned the development of a small capacity, packaged cooling coil with built-in enthalpy recovery devices. This customised unit, intended for use in a cooling-only, decentralized DOAS configuration, includes: two rotary wheels for sensible and latent energy recovery, a single cooling coil, and both supply and exhaust fans. The unit has been intended for building air conditioning use in the Singaporean climate. This paper provides energy performance data based on laboratory testing of the unit with independent control of the following variables: outdoor air conditions, return air conditions, and chilled water flow rate. It is intended that empirical data offered by this study can be adapted for use in future building energy models of decentralized HVAC systems. [ABSTRACT FROM AUTHOR]

Ventilation is necessary for good indoor air quality (IAQ) in air-conditioned buildings. However, the ventilation causes a substantial load and resulting energy consumption of the air-conditioning system particularly for buildings in tropical region. To address the issue, this paper investigates the dedicated outdoor air system (DOAS) for the energy-efficient ventilation. In the study, performance of various DOAS configurations is evaluated for a typical office building under the hot and humid climate of Thailand. The results from the simulations using TRNSYS software show that the DOAS of the combination of a cooling coil, a run-around coil and an enthalpy wheel is the most energy efficient by which it offers the smallest total air-conditioning loads in obedience with the Thai's ventilation standard requirement. [ABSTRACT FROM AUTHOR]

• A revised radiant time series method (RTSM) was proposed for radiant systems. • We find the revised RTSM has good accuracy compared to the heat balance method (HBM) • The revised RTSM slightly underestimates/overestimates the load for radiant terminal/DOAS. • The RTSM is preferred due to its simple and practical advantage compared to HBM. Cooling load calculation can significantly affect the first cost, energy consumption, and performance of air-conditioning systems. Current peak cooling load calculation theories and methods are developed based on all-air systems, which remove the room heat gains through purely convective heat transfer. Studies found that they are not suitable for radiant systems that remove room heat gains through both radiation and convection, especially for the integrated operation of radiant terminal and dedicated outdoor air system (DOAS). This study proposed a revised radiant time series method (RTSM) to calculate the cooling load for radiant systems. The method assumes the heat transfer rate of the radiant terminal as a negative "heat gain" and uses radiant time series factors to calculate the cooling load for DOAS. From the results of an example room, we find that the proposed RTSM has good accuracy compared to the heat balance method (HBM), while it slightly underestimates/overestimates the cooling load for radiant terminal/DOAS. Besides, a parametric simulation with 34,992 cases considering nine impact factors was performed. We find that compared to HBM, the relative errors of the peak cooling loads for the majority of the cases are within ± 10%, and the peak load occurring time differences are very minor, which are within the accuracy range of engineering applications. In summary, the revised RTSM was developed to offer a rigorous cooling load calculation approach for radiant systems, yet does not require complicated iterative calculations. Moreover, though originated from HBM, it has additional advantage of quantifying the cooling load converted from different heat gains separately, which is preferred in engineering applications. [ABSTRACT FROM AUTHOR]

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 CO 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. [ABSTRACT FROM AUTHOR]

Abstract: Condensation is prone to occur at the startup moment in chilled ceiling systems, due to the infiltration and accumulation of moisture during system-off. To prevent condensation, an effective method is to operate the dedicated outdoor air system (DOAS) to dehumidify indoor air before operating chilled ceiling system. The pre-dehumidification time is critical. However, there is little experience in determining the pre-dehumidification time in both research and practice. In this study, neural network (NN) is used to predict condensation risk and the optimal pre-dehumidification time in chilled ceiling systems. Two NN models are developed to predict the temperature on the surface of chilled ceiling and indoor air dew-point temperature at the startup moment so as to evaluate the risk of condensation. The third NN model is developed to predict the optimal pre-humidification time for condensation prevention. Both training data and validation data are obtained from simulation tests in TRNSYS. The results show that 30min pre-dehumidification is sufficient for the simulated building in Hong Kong. The influence of infiltration rate on the pre-dehumidification time is also investigated. This study also shows that NN-based method can be used for predictive control for condensation prevention in chilled ceiling systems. [Copyright &y& Elsevier]