Chilled Beam Research Articles

A review of the structure and application of active chilled beams (ACBs) for central air conditioning systems

Active chilled beams (ACBs), as indoor air terminal units in heating, ventilation, and air conditioning (HVAC) systems, have been of great concern in recent years due to the requirements of energy savings and indoor thermal comfort. This paper reviews the structure and application of ACB, which is helpful in identifying current research scenarios and prospects. The results indicate that the structure of ACBs will be improved based on the entrainment ratio (ER), cooling performance and acoustic behavior as the manufacturing level evolves. The mathematical model of ACBs is constantly being optimized, although there is still room for simplification to fit practical applications. Research on airflow patterns and thermal comfort can be extended to larger spaces (including buildings with large sensible heat ratios) and various climates. Based on the optimization of the ACB mathematical model, modern control theory can be focused on the research on ACB control system. ACB system has a coupling trend with other systems to achieve the comprehensive utilization of energy due to the characteristics of high-temperature cooling. In addition, numerous technical issues remain to be resolved to reduce unnecessary energy consumption. These conclusions also provide a simple reference for research and design in the area where this technology is still in its infancy.

Stereoscopic particle image velocimetry study of the single side entrainment behaviour of multiple air jets with different nozzle cross-sections

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.

Energy Saving Quantitative Analysis of Passive, Active, and Renewable Technologies in Different Climate Zones

The purpose of this study was to provide a guideline for the selection of technologies suitable for ASHRAE international climate zones when designing high-performance buildings. In this study, high-performance technologies were grouped as passive, active, and renewable energy systems. Energy saving technologies comprising 15 cases were categorized into passive, active, and renewable energy systems. EnergyPlus v9.5.0 was used to analyze the contribution of each technology in reducing the primary energy consumption. The energy consumption of each system was analyzed in different climates (Incheon, New Delhi, Minneapolis, Berlin), and the detailed contributions to saving energy were evaluated. Even when the same technology is applied, the energy saving rate differs according to the climatic characteristics. Shading systems are passive systems that are more effective in hot regions. In addition, the variable air volume (VAV) system, combined VAV–energy recovery ventilation (ERV), and combined VAV–underfloor air distribution (UFAD) are active systems that can convert hot and humid outdoor temperatures to create comfortable indoor environments. In cold and cool regions, passive systems that prevent heat loss, such as high-R insulation walls and windows, are effective. Active systems that utilize outdoor air or ventilation include the combined VAV-economizer, the active chilled beam with dedicated outdoor air system (DOAS), and the combined VAV-ERV. For renewable energy systems, the ground source heat pump (GSHP) is more effective. Selecting energy saving technologies that are suitable for the surrounding environment, and selecting design strategies that are appropriate for a given climate, are very important for the design of high-performance buildings globally.

Comfort control and improved thermostat location in conference rooms and academic working spaces

The challenge of comfort control within commercial and academic spaces was explored in an attempt to determine what would be the optimum location and type of measurement over different occupancies and different seasons of the year. A computational fluid dynamic (CFD) simulation using Reynolds-averaged, RNG k – ε turbulence model was set up. It was verified by physical measurements of temperature and flow behavior within a commercial conference room containing a large external window and that was conditioned by an active chilled beam. Experimental measurements, supplemented by simulation, indicated a large, seasonal-varied deviation between the temperature measured by a wall-mounted thermostat and the average comfort conditions around occupants of the room. CFD results and post-processed predicted mean vote (PMV) values showed that having the thermostat located near the humans in the middle of the room (over a table in this case) improved the thermal comfort conditions compared to having it on a wall opposite the external window (PMV of 1.1 as compared to 1.8 for an Andover, MA summer scenario, respectively).The major causes of the deviations were the convective and infrared heat transfer from the window surface as well as the solar gains to the room interior. The wall thermostat errors could be moderated by including temperature measurements at the window surface as an additional input in the control algorithm. This conclusion was confirmed by experiments in a dormitory room and a large shared academic workspace.

Experimental investigation on the control performance of an active chilled beam system under dynamic cooling loads

Abstract In this study, the control performance of an active chilled beam (ACB) system was investigated, in order to find the suitable control parameter for controlling room air temperature and preventing surface condensation when the cooling load suddenly increases. For this purpose, the impact of ACB control parameters on the cooling capacity was evaluated with mock-up experiments. Compared to the baseline condition in this study, the adjustment of the chilled water temperature and primary air flow rate raised the cooling capacity by 47% and 98%, respectively, while the adjustment of the chilled water flow rate and primary air temperature led to a relatively small increase in cooling capacity. In addition, the control performance of room air temperature was evaluated with the room air temperature drop for one hour after a step change in cooling load. It was observed that the room air temperature dropped 0.2 °C with chilled water temperature control and 0.7 °C with primary air flow rate control, whereas it dropped 1.0 °C with the simultaneous control of the chilled water temperature and primary air flow rate. The test results further showed that simultaneous control of the chilled water temperature and primary air flow rate is effective for preventing the surface condensation while providing the sufficient cooling capacity. The findings of this study can provide the information on the thermal behavior of ACB system, which is necessary for establishing control strategies for ACB systems.

An optimal design for hollow fiber heat exchanger: A combined numerical and experimental investigation

Polymeric hollow-fiber heat exchangers are a sound alternative to metallic plate fin counterparts. Plastic heat exchangers weigh much less, have significantly larger surface area per unit volume, are corrosion/erosion resistant and electrically non-conductive, have a reduced ecological footprint, and are likely to be substantially cheaper.A good passive chilled beam type heat exchanger requires its heat transfer surfaces to be distributed in optimal positions so that the thermal performance is maximized. For that purpose, a Lattice-Boltzmann model was setup in the open-source code Palabos to calculate natural convection triggered around a chilled beam made of many parallel hollow fibers with cold water running inside. In the simulations, the horizontal and vertical pitches between fibers were varied to eventually find their dimensionless optima of 6.9 and 1.3, respectively, for the Rayleigh number of 2.3. The numerical results were validated in the experiment as well as in the well-established ANSYS FLUENT.

A comparative study on borehole heat exchanger size for direct ground coupled cooling systems using active chilled beams and TABS

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.

A model-based multi-objective optimization of energy consumption and thermal comfort for active chilled beam systems

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.

Field test of active night cooling supplied by district cooling in three commercial buildings

Several previous studies have investigated active night cooling strategies to reduce the peak cooling load in buildings, primarily by precooling the building by the ventilation air during the night. In this study, active night cooling is supplied by the use of district cooling, mainly for cooling buildings by hydronic cooling systems, such as chilled beam or fan coil systems, but potentially also to cool the ventilation air if the outdoor air temperature is above the supply air temperature setpoint. A field test with active night cooling by district cooling was conducted during the summer of 2020 in three commercial buildings located in Gothenburg, Sweden. The active night cooling strategy was implemented by changing the time schedule operation of the buildings’ chilled beam systems to twenty-four hours per day for the first half of the summer and changing back to regular time schedules for the second half. The results showed that active night cooling failed to reduce the hourly maximum cooling power. However, the peak cooling load, corresponding to the 100 hours with the highest cooling power, was reduced with 6.5% for one of the buildings. Active night cooling also reduced the daytime energy usage between 0.7 and 4.6%. The field test demonstrated that some buildings and associated cooling systems are more compatible for active night cooling than others. The test also showed it was possible to achieve some cooling power and energy reductions with simple measures. However, providing active night cooling supplied by district cooling will cause additional costs for the building owners unless it is incentivized by the district cooling provider.

Spreading of SARS-CoV-2 via Heating, Ventilation, and Air Conditioning Systems—An Overview of Energy Perspective and Potential Solutions

Abstract The role of heating, ventilation, and air conditioning systems (HVAC) in spreading SARS-CoV-2 is a complex topic and has not been studied thoroughly. There are some existing strategies and technologies for health and high performance buildings; however, applications to other types of buildings come at large energy penalty: cost; design, regulations and standards changes, and varied public perception. In the present work, different factors and strategies are reviewed and discussed and suggested mitigations and solutions are provided including the required air flowrates with the presence of infectors with and without mask and disinfection techniques including ultraviolet (UV) light. Experimental and numerical research in open literature suggests that the airborne transmission of SARS-CoV-2 is sufficiently likely. However, in situ detailed experimental studies are still needed to understand the different scenarios of the virus spread. Displacement ventilation, underfloor air distribution, chilled beams, radiant ceiling panels, and laminar flow systems have varied effectiveness. High-efficiency particulate arrestance (HEPA) filters and UV light can clean viruses but at high energy cost. Suggested solutions to reduce the infection probability include recommended levels of ventilation and a combination of virus sampling technologies including cyclones, liquid impinger, filters, electrostatic precipitators, and water-based condensation.

Cooling of office buildings in cold climates using direct ground-coupled active chilled beams

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.

Potential infection control risks associated with chilled beam technology: experience from a UK hospital

Energy efficiency technologies are now a feature in hospital design, with active chilled beams an example of one in use worldwide. Such innovations have clear benefits but there is a paucity of information with respect to any infection control risks. We describe our experience of chilled beam technology from one of our hospitals where we faced challenges with cleaning and episodes of water ingress including condensation. We highlight the importance of infection control risk assessment in relation to new technologies and the implementation of appropriate risk mitigation.

Modelling of rooms with active chilled beams

ABSTRACT Active chilled beams (ACBs) are often modelled as generic cooling devices. Due to induction, the air flow discharged from an ACB is several times higher than supplied from the air handling unit, and due to its design, it affects the temperature of the ceiling to a greater extent than an arbitrary cooling device. This paper investigates the impact of taking these features into account when simulating air and operative temperature in a room equipped with an ACB. The building performance simulation software IDA ICE is used for analysis and the simulations are compared with full-scale experiments. The main findings are that simulations which take into account the features mentioned above correspond more closely with measurements. If designing for a certain operative temperature, this reduces the required design cooling capacity. Although negligible in many applications, the magnitude of this reduction is 9% with high-temperature cooling.

Experimental study on the performance evaluation of active chilled beams in heating and cooling operation under varied boundary conditions

This study investigates the thermal comfort, airspeed and temperature distribution, air change effectiveness and importance of the boundary conditions on the selection and performance of Active Chilled Beams (ACB). Many past studies in cooling confirm that the thermal comfort is satisfactory because the temperature gradient and airspeeds are acceptable at the occupant level without addressing the local discomfort. Similarly, no known study was found to address thermal comfort in heating. This paper reports the results of an experimental study that addresses such issues. A laboratory experiment, simulating a multi-occupant open office with an ACB subjected to different boundary conditions, was conducted. The heating test results demonstrate that there is a risk of discomfort due to radiant temperature asymmetry. It also shows no airspeed in the occupied zone, which reduces the air change effectiveness. The cooling test results demonstrate that discomfort draft risk at the ankle level is higher in ACB parallel to window configuration. The results suggest that shape and throw of ACB affect air distribution and emphasize the importance of properly selecting, orienting, and designing ACB, not just to offset the room loads, but to match the proportions and boundary conditions of the space.

Multi-objective optimization to balance thermal comfort and energy use in a mining camp located in the Andes Mountains at high altitude

The mining industry is the largest electricity consumer in Chile. Sustainability reports of Chilean mining companies show that electricity consumption of mining camps is 350–500 kWh/m2 per year. Despite cold climate conditions, mining camps show overheating, and 40% of the miners find them uncomfortable. Mining camps’ energy access is difficult because they are located in remote zones. This paper aims to optimize the building envelope and HVAC system to minimize the total energy consumption and eliminate the overheating risk of a real mining camp located at 4400 m.a.s.l. The mining camp is 30,000 m2, built of timber prefabricated lightweight modules and hosts 1700 workers. The electricity consumption of the baseline case is 330 kWh/m2year and shows overheating. Multi-objective optimization is implemented to minimizing the electricity consumption while avoiding overheating. A hybrid multidimensional optimization algorithm implemented in GenOpt, a building energy simulation program (EnergyPlus) and several scripts developed in Pyhthon for optimizing discrete variables and calculating the overheating risk of each thermal zone are coupled. Two different cases are optimized depending on the heating systems: electric heaters (Case I), which is the current situation; and heat pumps with chilled beams with free cooling option (Case II). This paper shows that an efficient HVAC system (Case II) is crucial for achieving thermal comfort and minimizing electricity consumption, which reaches 112.9 kWh/m2year, representing a significant reduction of 66% compared to the baseline case. The optimization process provides not only the optimum set of energy-efficient strategies but also a set of feasible solutions close to the optimum that allows flexibility to choose other strategies based on economic, transportation and on-site construction constraints.

Experimental comparison of thermal conditions in office rooms: Diffuse ceiling ventilation, chilled beam system, and chilled ceiling combined with mixing ventilation

Thermal environments generated by diffuse ceiling ventilation (DCV), chilled beam (CB), and chilled ceiling with mixing ventilation (CCMV) systems were compared at different heat loads. Experiments were carried out in two test chambers, in which a double office layout was investigated near heated windows. The heat load strength was increased from a normal level of 37–40 W/floor-m2 to a peak load level of 57–64 W/floor-m2 to observe effects on indoor air thermal conditions and draft discomfort. The target indoor air temperature was 26 ± 0.5 °C in the occupied zone. The results show that the air temperature, air speed, and draft rate levels were reasonable at a normal load and increased slightly at peak load conditions. The CCMV system provided the smallest share of locations in which the draft rate level was higher than 10%. None of the studied systems achieved the category A defined by EN ISO 7730. However, all the systems fulfilled the demands of category B, except for CB, which fell to category C at the peak load conditions by exceeding the draft rate limit in one location. Thermal conditions were at a similar level for the studied systems. However, CCMV may reduce slightly the draft discomfort.

Natural heat transfer air-conditioning terminal device and its system configuration for ultra-low energy buildings

In consideration of the lowered heating and cooling load of ultra-low energy buildings, a natural heat transfer air-conditioning terminal device (NHTACTD) is presented by the authors. The terminal device is able to undertake heating, cooling and moisture load of a room according to the inlet water temperature. Its comparative advantages are pointed out by comparing it with radiators, fan coil units, chilled beams and radiant heating and cooling terminals. After the actual thermal properties of the NHTACTD are provided, three air-conditioning system configuration schemes based on the NHTACTDs are presented: (1) In the NHTACTDs plus fresh air system, the NHTACTDs and the fresh air handling unit undertake all the air-conditioning load of the system together, and it is used where high indoor air quality is demanded; (2) In the scheme of the air-conditioning system including the NHTACTDs only, all the air-conditioning load of the system has to be undertaken by the terminals alone and it is used where high indoor air quality is not rigidly demanded. (3) In the scheme of the air-conditioning system including both the NHTACTDs and radiant panels, the NHTACTDs undertake all the moisture load of the system, and the remaining sensible cooling load is undertaken by the radiant panels. The scheme can be used where there is large sensible cooling load while high indoor air quality is not rigidly demanded. Then an ultra-low energy residential building is taken as a case project to elaborate the design method of an air-conditioning configuration scheme based on the terminal device with the help of psychrometric chart.

Performance evaluation of a direct ground-coupled self-regulating active chilled beam system

Active chilled beams support high temperature cooling which enables the opportunities of direct ground-coupling and self-regulation. Direct ground-coupling implies cooling through a ground heat exchanger without use of a chiller and self-regulation refers to the elimination of individual room control systems. This paper presents the operation and indoor air temperatures in such an office building located in Stockholm, Sweden, and the analysis includes the unprecedented hot summer of 2018.The results show that the system is capable of supplying the building with enough cooling to not exceed desired indoor air temperature levels. It is also concluded that the self-regulation kept the indoor air temperature satisfactory uniform. The difference between the highest and lowest temperature is 1.9 K on average and below 2.4 K during 90% of the time. Regarding stability, the least stable temperature recorded has a standard deviation of 0.8 K while the average standard deviation is less than 0.5 K. The indoor air temperature during summer is about 2 K lower than suggested by standards. This calls for conducting a thermal comfort survey and may be remedied by increasing the chilled water temperature. To increase the performance of the system, the ground is cooled during winter by preheating the supply air. During 2018, slightly more cooling was extracted in the summer than recharged during winter.

Study on Performance of Ground Source Heat Pump System Based on Active Chilled Beam

This paper takes the ground source heat pump unit of a research and development centre in Beijing as the research object. This collected the operation data in the cooling condition and the heating condition respectively. Based on the measured data, this paper calculated the coefficient of performances and the energy efficiency ratio of the unit. The results show that when the active chilled beam is used as the air-conditioning terminal device, the inlet temperature of the heat pump unit is greatly improved. The ground source heat pump unit meets the standard and has a higher energy efficiency ratio; The operation of a single unit is more efficient than that of multiple units at the same time.

Performance evaluation and design guide for a coupled displacement-ventilation and passive-chilled-beam system

Displacement ventilation (DV) can provide good air quality to indoor spaces while saving energy. Research has shown that, since the supply air temperature in DV cannot be very low, its capability to remove a high cooling load is limited. Previous studies found that passive chilled beams (PCBs) could be coupled with DV to enhance the cooling capability of the latter and reduce the vertical temperature gradient. However, PCBs also recirculate airborne contaminants downward, reducing the air quality in the occupied zone. Therefore, it is essential to design a DV-PCB system for optimal thermal comfort and indoor air quality. This study established a database of 70 cases that include four typical types of indoor spaces with DV-PCB systems and developed mathematical models for predicting the thermal and ventilation performance of a DV-PCB system based on various design parameters. With the models, this investigation then proposed a step-by-step procedure for designing a DV-PCB system to create a thermally comfortable and healthy indoor environment without causing condensation on the chilled beams. Moreover, a user-friendly design interface was developed that can be used by engineers to make design decisions conveniently.