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Heating, ventilation, and air conditioning (HVAC) systems are the second largest energy consumers on cruise ships after the propulsion system. As a kind of HVAC system, active chilled beam (ACB) systems have been widely used for cabin service due to their performance of energy efficiency and good thermal comfort. However, conventional control strategies for ships' ACB systems are not intelligent enough and cannot balance energy consumption and cabin comfort during the voyages of ships. This study developed an optimal control strategy for cabins' ACB systems. First, a simulation environment considering dynamic conditions is established in TRNSYS. Second, an artificial neural network model is utilized to predict the energy consumption of the ACB system, while the predicted percentage dissatisfied is adopted to represent cabins' thermal discomfort. Third, an improved multi-objective salp swarm algorithm is proposed to dynamically minimize both energy consumption and thermal discomfort. A TRNSYS–MATLAB co-simulation testbed is established to simulate the cabins served by an ACB system on a small cruise ship navigating from Hong Kong to Shanghai for validation tests and a comparison study. Compared to the conventional strategies, the proposed strategy can achieve a maximum energy savings of 12% while maintaining a predicted mean vote index less than 0.5, meeting the comfort requirements set by ASHRAE. [ABSTRACT FROM AUTHOR]

Heating, ventilation, and air conditioning (HVAC) systems are the second largest energy consumers on cruise ships after the propulsion system. As a kind of HVAC system, active chilled beam (ACB) systems have been widely used for cabin service due to their performance of energy efficiency and good thermal comfort. However, conventional control strategies for ships’ ACB systems are not intelligent enough and cannot balance energy consumption and cabin comfort during the voyages of ships. This study developed an optimal control strategy for cabins’ ACB systems. First, a simulation environment considering dynamic conditions is established in TRNSYS. Second, an artificial neural network model is utilized to predict the energy consumption of the ACB system, while the predicted percentage dissatisfied is adopted to represent cabins’ thermal discomfort. Third, an improved multi-objective salp swarm algorithm is proposed to dynamically minimize both energy consumption and thermal discomfort. A TRNSYS–MATLAB co-simulation testbed is established to simulate the cabins served by an ACB system on a small cruise ship navigating from Hong Kong to Shanghai for validation tests and a comparison study. Compared to the conventional strategies, the proposed strategy can achieve a maximum energy savings of 12% while maintaining a predicted mean vote index less than 0.5, meeting the comfort requirements set by ASHRAE.

This study investigates the use of a direct ground cooling system (DGCS) using active chilled beams for the cooling of office buildings in Sweden. The methodology of the study entails laboratory experiments to develop and validate a simulation model of the cooling system. The sensitivity of the input parameters, such as borehole heat exchanger (BHE) length, internal heat gains and room temperature set point, are studied with respect to BHE outlet fluid temperature and room thermal comfort. The results provide a practical insight into designing DGCSs with regard to borehole outlet fluid temperatures. The results also show that the thermal comfort criteria in the room are met by applying the DGCS even under the most critical design conditions of undisturbed ground temperature and internal heat gains. The sensitivity study quantifies the influence of the room temperature setpoint and internal heat gain intensity on the BHE length. The BHE outlet temperature level is more sensitive in shorter BHEs than in the longer ones, and BHE length and room temperature levels are highly correlated. Thus, the sizing of DGCS can benefit from a control system to allow the room temperature to float within a certain range. • Experimental measurements are performed on a ground-coupled active chilled beam system. • A simulation model is developed for a single zone of an office building. • The system is applicable for cold climates. • Small changes in the room temperature set point have a large effect on BHE outlet temperatures. [ABSTRACT FROM AUTHOR]

Abstract Air-conditioning systems are employed to provide thermal comfort inside buildings. Therefore, several air-conditioning and mechanical ventilation (ACMV) systems have been tested and applied in different climates. Chilled beam systems are a new addition to it and have been in the application in Europe and North America since last two decades. In the present study, comparative performance of active chilled beam (ACB) system with conventional fan coil unit (FCU) system has been appraised in regards to thermal comfort for the tropical region of Singapore. Experiments were carried out in a simulated office building with approximately 80% glazed area under real environmental conditions. Room air temperature, air velocity, mean radiant temperature (MRT) and relative humidity which are important thermal comfort parameters were measured in perimeter zone inside the cells and assessed. It was perceived that the ACB system was providing acceptable thermal comfort as per the standard of SS 554. General thermal comfort has been assessed based on an index of PMV-PPD model and graphical method. With regard to the local thermal discomfort: indices of air draught, vertical air temperature difference (VATD) and radiant temperature asymmetry have also been evaluated. The entrance of solar radiation through window façade may have a significant impact on the asymmetry of the radiant field and can enhance thermal discomfort of the occupants. Therefore, in the study radiant temperature asymmetry has been calculated extensively. The results show that ACB system yields satisfactory thermal environment as per ISO 7730 standard and sometimes performs even better than conventional FCU system. Highlights • Comparative performance analysis of conventional FCU and ACB system with regard to thermal comfort. • Assessment of general thermal comfort criteria based on PMV-PPD model and Graphical method. • The comfort zone has been proposed to assess the data points using graphical method for tropical Singapore. • Assessment of local thermal comfort criteria based on air draught, VATD and radiant temperature asymmetry. • Extensive analysis of the impact of solar radiation on the asymmetry of radiant field. [ABSTRACT FROM AUTHOR]

Abstract Comparison in terms of energy and cost is carried out between two different air distribution systems, namely, Variable Air Volume (VAV) and Active Chilled Beam (ACB) based on a virtual building. The cooling load calculation was performed to determine the total load demand and the system design was carried out to determine the system capacity. Energy and cost analyses were carried out to determine which system gives the better saving. From the results analysis, it shows that the ACB is more energy-saving than the VAV, especially at full load and normal part-load conditions because of the reduced AHU fan's capacity. In terms of cost, the ACB has a higher initial cost than the VAV where it is mainly contributed by the secondary chilled water pipe, heat exchanger and the beam itself. However, the operation cost is lower for ACB, and for long term use, the ACB is more cost-saving than the VAV. [ABSTRACT FROM AUTHOR]

In this study, the effects of the configuration and strength of heat sources on thermal comfort are investigated in a mock-up room with an active chilled beam (ACB) system. Full-scale air temperature, speed, and humidity distributions are demonstrated. In addition, the uniformity of the distributions is evaluated. Several common thermal comfort indices, including the air diffusion performance index (ADPI), predicted mean vote (PMV), draft rate (DR), and vertical air temperature difference (VATD) are calculated and compared based on the experimental results. The results reveal that the heat sources increase the average air speed of the occupied zone. However, the air speed distribution is not significantly affected by the heat source configuration for a primary airflow rate of 32.2 L/s. In contrast, the heat source configuration has a notable impact on the temperature distribution. One humidity sensor is sufficient to measure the occupied zone humidity for ACB systems with no significant humidity source because the absolute humidity distributions are extremely uniform for all cases. The points outside the ADPI criteria ( − 1.7 ° C < T e d < + 1.1 ° C a n d v < 0.35 m / s ) are mostly because its air speed is greater than 0.35  m/s. PMV is reduced as the air speed increases. Thus, there is a higher risk of cold feeling at the ankel level where the air speed is relatively greater than other levels. The overall evaluation shows that symmetrical heat source placement results in better thermal comfort performance than asymmetrical heat sources. [ABSTRACT FROM AUTHOR]

Experimental results of the airflow pattern for Active Chilled Beams (ACB) system are investigated in this paper, where the air velocity and turbulence intensity for the air jet near the ceiling are tested and recorded under both isothermal and non-isothermal conditions. Based on the results, the velocity profile along streamwise direction is found to be significant in analyzing air detachment from the ceiling. It is revealed that the Coandă effect can be enhanced by a high pressure drop of ACB terminal unit and impeded by the temperature difference between supply air and room air. The self-similarity for the air jet is observed to be feasible for a certain downstream distance where the vertical maximum velocity is within 1.25 slot heights. A comparison study has been conducted for two mathematical models describing the self-similarity with the experimental data. It turns out that Verhoff's model has an overall better performance than Schwarz and Cosart's model. The turbulence intensity, which tends to be larger for points with lower velocity, is higher in areas where the entrainment effect is stronger. [ABSTRACT FROM AUTHOR]

New concepts of removing the cooling loads in shopping centres are presented in a multi-disciplinary study. In air-quality experiments, we found that the air change rate (ACR) in shops can be reduced significantly, while still maintaining acceptable air quality. Dilution curves of typical odour-intensive retail goods were measured, which show that ACRs can be reduced down to 1.75 h−1 without impacting odour perception significantly. Then, the standard ventilation systems were replaced by air–water systems, namely active chilled beams, which allow for a combined supply of fresh air and heat removal via the water circuit. To realize low ACRs in the shops, experimental studies for developing high-induction active chilled beam systems are presented. Finally, CFD simulations were conducted in a generic shop. Aspects like room air flow, odour propagation and thermal comfort were investigated. The cold water supply was assumed to be generated in a renewable way, leading to high cold water supply temperatures. Feasible ventilation configurations with ACRs as low as 1.1 h−1 have been identified without deteriorating either air quality or thermal comfort. Primary energy consumption was assessed according to German standards and was reduced by up to 67% with the presented approach. [ABSTRACT FROM AUTHOR]

Indoor climate and energy performance of Finnish low energy office building were studied to determine optimal control and operation solutions of demand controlled room conditioning and ventilation system with airflow rate controlled active chilled beams. Onsite measured temperature, CO 2 , occupancy rate were used to calibrate a dynamic simulations model. The results showed an average occupancy rate of 0.55 during office hours (OH) offering a good energy saving potential for demand control ventilation (DCV) system. DCV system used 7–8% less total primary energy compared to constant air volume (CAV) system depending on control and operation strategy used. DCV system saving was 33–41% if only heating, cooling, fans and pumps primary energy were considered. Supply air temperature controlled according to extract air temperature instead of outdoor air temperature minimized overheating problem which occurred with design solution during both seasons and systems. DCV system with active chilled beam complied at least 94% and 90% of OH with Category II indoor climate with water priority cooling and air priority cooling control respectively. Ceiling cooling panel showed an effect of decoupling cooling from ventilation resulted only in 0.9% additional primary energy saving compared to DCV system with active chilled beams. [ABSTRACT FROM AUTHOR]

Further to a previous experimental study on the heat exchanger circuitry number for a two-way discharge active chilled beam terminal unit, an investigation of the tube connecting sequences is conducted in this paper. Given a typical air side operating condition, in situ air velocity profile across the heat exchanger is measured and non-uniformities of the air flow caused by the entrainment effect are detected. Taking the air maldistribution into consideration, heat transfer performance of the heat exchanger is simulated with a tube to tube distributed parameter model. This simulation model is calibrated with experimental results. With the calibrated model, influences of the air maldistribution on the heat transfer capacity are discovered. The heat exchanger tube connecting sequences are optimized through a particle swarm optimization program for the maximum heat transfer capacity. In addition, the potential pressure drop, manufacture difficulties, and material cost of the tube connecting sequences are qualitatively analyzed. A new heat exchanger circuitry arrangement is finally proposed for the terminal unit. Although the performance enhancement is modest, the findings obtained in the study are expected to facilitate better heat exchanger designs for the future active chilled beam terminal units. [ABSTRACT FROM AUTHOR]

The complexity and diversity of airflow in buildings make the accurate definition of convective heat transfer coefficients (CHTCs) difficult. In a full-scale test facility, the convective heat transfer of two cooling systems (active chilled beam and radiant wall) has been investigated under steady-state and dynamic conditions. With the air-based cooling system, a dependency of the convective heat transfer on the air jet trajectory has been observed. New correlations have been developed, introducing a modified Archimedes number to account for the air flow pattern. The accuracy of the new correlations has been evaluated to±15%. Besides the study with an air-based cooling system, the convective heat transfer with a radiant cooling system has also been investigated. The convective flow at the activated surface is mainly driven by natural convection. For other surfaces, the complexity of the flow and the large uncertainty on the CHTCs make the validation of existing correlations difficult. [ABSTRACT FROM PUBLISHER]

Full-scale experiments under both steady-state and dynamic conditions have been performed to compare the energy performance of a radiant wall and an active chilled beam. From these experiments, it has been observed that the radiant wall is a more secure and efficient way of removing heat from the test room than the active chilled beam. The energy saving, which can be estimated to around 10%, is due to increased ventilation losses. The asymmetry between air and radiant temperature, the air temperature gradient and the possible short-circuit between inlet and outlet play an equally important role in decreasing the cooling need of the radiant wall compared to the active chilled beam. It has also been observed that the type and repartition of heat load have an influence on the cooling demand. Regarding the comfort level, both terminals met the general requirements, except at high solar heat gains: overheating has been observed due to the absence of solar shading and the limited cooling capacity of the terminals. No local discomfort has been observed although some segments of the thermal manikin were slightly colder. [ABSTRACT FROM AUTHOR]

Heating and cooling terminals can be classified in two main categories: convective terminals (e.g. active chilled beam, air conditioning) and radiant terminals. The mode of heat transfer of the two emitters is different: the first one is mainly based on convection, whereas the second one is based on both radiation and convection. In order to characterise the advantages and drawbacks of the different terminals, steady-state simulations of a typical office room have been performed using four types of terminals (active chilled beam, radiant floor, wall and ceiling). A sensitivity analysis has been conducted to determine the parameters influencing their thermal performance the most. The air change rate, the outdoor temperature and the air temperature stratification have the largest effect on the cooling need (maintaining a constant operative temperature). For air change rates higher than 0.5 ACH, differences between terminals can be observed. Due to their higher dependency on the air change rate and outdoor temperature, convective terminals are generally less energy effective than radiant terminals. The global comfort level achieved by the different systems is always within the recommended range, but differences have been observed in the uniformity of comfort. [ABSTRACT FROM AUTHOR]

Highlights: [•] This paper presents the first reported ACB terminal unit model. [•] The model encapsulates mechanical and thermal aspects. [•] A compromise is made between underlying physics and suitability for applications. [•] The model is obtained under the unique condition of ACB. [•] The model is accurate and robustness. [ABSTRACT FROM AUTHOR]

Highlights: [•] This paper gives the first reported research about heat exchanger issues for ACB. [•] Four different circuitry arrangements are investigated. [•] The effectiveness of circuitry adjustment to ACB terminal unit is confirmed. [•] The unexpected conclusion indicates much potential improvement of ACB system. [Copyright &y& Elsevier]

Achieving energy savings in the building sector while maintaining high air quality of indoor environments requires efficient ventilation systems. Active chilled beams (ACBs) are a promising solution for the ventilation in non-residential buildings. Their functionality is often based on the single side entrainment of multiple air jets. In order to enhance this entrainment and thus increase the efficiency of ACBs, this study investigates the specific flow situation of a single side entrainment experimentally. Additionally to the reference circular type, three different cross-sections (elliptic, cross-like, lobed) of an orifice nozzle are investigated with different experimental methods. The unique flow situation in ACBs with multiple interacting jets entraining air from one side is extracted to a test bench. First, the general nozzle efficiency and total entrainment is investigated. Then, the detailed understanding of the entrainment process is achieved with stereoscopic particle image velocimetry (stereo-PIV). The results show that a minimum distance between the jets is necessary for the development of individual flow behaviour affecting the entrainment. For a larger nozzle distance we measured an increased overall entrainment for the non-circular nozzle geometries, with the lobed geometry showing the greatest improvement. The PIV results show how the jets from the different nozzle geometries pass through different stages of entrainment behaviour and profile transformation. [ABSTRACT FROM AUTHOR]

• Experimental measurements are done on a direct ground-coupled cooling system. • A simulation model is developed for a single zone of an office building. • ACBs require longer BHEs compared to TABS. • Operating strategies shall consider peak hourly loads reduction methods. Direct ground cooling is a method for cooling buildings whereby free cooling is provided by circulating water through borehole heat exchangers (BHEs). Since no refrigeration cooling is involved, supply water temperature to the building's cooling system is dependent mainly on BHE sizing. This study investigates the sizing of BHEs for direct ground cooling systems, with a particular focus on the influence of terminal unit types and their operating strategies. Experimental results using a direct ground-coupled active chilled beam (ACB) system are used to develop a simulation model for an office building. The model is also modified for thermally activated building systems (TABS). The simulation results show that using TABS instead of ACBs for a similar BHE reduced the ground peak hourly loads, resulting in a lower borehole outlet temperature. Resizing BHE depth to reach similar maximum borehole outlet temperatures according to the actual heat extraction rate from the cooling systems resulted in a significantly shorter BHE depth with TABS compared to ACBs. However, indoor temperature was generally warmer with TABS, due to their slower heat extraction rate from the room. The findings are practical for analysing the design and operation of BHEs for different types of terminal units. [ABSTRACT FROM AUTHOR]

• Develop a novel multi-objective optimization model for active chilled beam systems. • Build energy models with fundamental equations for active chilled beam systems. • Propose a parameterless selection strategy for Pareto optimal solutions. • Steady-state experiments of various heat loads are compared with optimized cases. • A good trade-off is achieved between energy consumption and thermal comfort. Active chilled beam (ACB) systems provide two highly-coupled cooling capacities due to its unique structure through combining primary air nozzle and cooling coil, whose energy consumption is difficult to be estimated and balanced against thermal comfort. This study considered the trade-off between energy consumption and thermal comfort as a multi-objective optimization problem and proposed a novel and practical solution by utilizing empirical energy models of the ACB system and an evolutional non-dominated sorting genetic algorithm II. The energy models are established for components of fans, pumps, and chillers based on fundamental equations which are validated by experimental data. The thermal comfort of each room is quantified by the predicted percentage dissatisfied (PPD) model. Chilled water flow rate, primary airflow rate, and room temperature in ACB systems are specifically chosen as control variables due to the control convenience. Besides, a parameterless selection strategy that considers both thermal comfort and energy consumption is proposed to select the most appropriate solution among Pareto optimal solutions. Three steady-state experiments with different heat load conditions are conducted. Compared to experienced operation, the proposed strategy demonstrates a maximum of 39.32% of energy saving and 12.21% of PPD reduction by increasing the water flow rate and room temperature, and reducing the primary airflow rate. Furthermore, this study investigates the distribution of capacities in ACB systems and suggests to assign more capacity to the cooling coil based on energy efficiency considerations. A good trade-off is achieved between energy consumption and thermal comfort through the proposed multi-objective optimization strategy. [ABSTRACT FROM AUTHOR]

• Experimental measurements are done on a direct ground-coupled cooling system. • A simulation model is developed for a single zone of an office building. • Thermal performance of a ground-coupled active chilled beam system is investigated. • Operation strategy can significantly influence the required borehole depth. • Building peak load reduction methods shall be considered in operational strategies. Sizing of borehole heat exchangers (BHEs) for direct ground cooling systems (DGCSs) is a critical part of the overall system design. This study investigates the thermal performance and sizing of a DGCS with two different operation strategies using experimental and simulation approaches. The traditional on/off operation strategy keeps a constant room temperature. The continuous operation strategy has the potential to reduce the building peak cooling loads by precooling the space and having a variable room temperature measures. The experimental results from the laboratory-scale setup show the differences in the hourly room heat extraction rates and the room temperature pattern for the operation strategies applied. The experimental data is also used to develop a simulation model. The simulation results show that applying the continuous strategy reduces the building peak cooling loads and lowers the heat injection rates to the ground. For new BHEs, applying the continuous strategy can result in shorter BHEs, owing to the significantly lower ground heat injection rates. For existing BHEs, applying the continuous strategy can decrease the borehole outlet fluid temperature and thus, increase the cooling capacity of the building cooling system. The findings of this study have implications for developing the widespread use of DGCSs. [ABSTRACT FROM AUTHOR]

Active chilled beams (ACB) are gaining popularity worldwide as a potentially energy-efficient air-conditioning technology for buildings. However, the control of ACB system is challenging, as it needs to handle multiple cooling coils and the relatively slow response to cooling load dynamics. This paper reports the implementation of a model predictive control (MPC) system for an ACB system, which employs a linear white-box building model for building energy and indoor condition predictions. A multiple-objectives function is employed in the MPC controller to optimize the energy efficiency in air-conditioning system and indoor thermal comfort while fulfilling the constraints of indoor comfort range (−0.5 < PMV < 0.5). The MPC controller was implemented in the BCA SkyLab test facility in Singapore. The control characteristics and performance of the MPC controller in controlling a conventional fan coil unit (FCU) and an ACB system were investigated experimentally. A conventional feedback control based building management system (BMS) originally installed in the SkyLab test facility was employed as a reference for comparison with the MPC controller. Compared to the original BMS, the MPC controller achieved 14.7% and 20% electricity savings for the conventional FCU and ACB systems, respectively. The MPC controller also kept the indoor PMV within acceptable thermal comfort range at all time. This study demonstrated the real-time multi-objectives optimization capability of the MPC controller in enhancing the performance of ACMV systems. [ABSTRACT FROM AUTHOR]