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Convection-radiation combined cooling systems are commonly used in residential buildings in hot summer and cold winter areas because of their high thermal comfort. When this system is used in office buildings, combined with the characteristics of office building’s working time occupancy patterns and building typologies, the operation strategy can lead to different energy consumption under the same thermal comfort. In this study, three operation strategies are compared to a system that combines two different terminal units in the same thermal zone: a radiant floor and fan coil. The performance of the combined system is assessed in terms of the thermal comfort level, hourly refrigeration performance coefficient, and energy consumption. The results indicate that the system with an intermittent operation strategy reduces energy consumption by approximately 39% compared with a continuous operation strategy, with little impact on thermal comfort. The room temperature under the three control strategies meets the temperature requirements of the office building during working hours. The fluctuation in room temperature is smaller under the continuous operation strategy than under the intermittent operation strategy, which indicates that the thermal environment of the room has better stability during continuous operation. The maximum indoor vertical gradient is always less than 3 °C, which meets the ASHRAE55-2017 standard. The room-temperature fluctuations are strongly affected by solar radiation. Therefore, building shading measures should be considered in building designs to avoid local discomfort or energy waste. When the system operates stably, the Predicted Mean Vote (PMV) value is low. The reason for this is that the radiant cooling system reduces the average radiant temperature of the building to adjust the room temperature. Therefore, it is recommended that the indoor design temperature of the radiant cooling system be increased by 2–3 °C to ensure better indoor comfort.

Space cooling of buildings shows an increasing trend in energy use worldwide. The exploitation of the energy flexibility reserve obtainable from buildings cooling-loads management can have an important role to improve the security and the reliability of the electricity power grid. Many studies in literature assess the energy flexibility potential of air conditioning systems; however, the role of the specific cooling technology is always scarcely explored. The objective of this work is to provide an evaluation of the operational energy flexibility that can be obtained involving the most common residential space cooling technologies, paying particular attention to the distribution system (e.g., all-air system, fan-coil units with and without the addition of a thermal energy storage and hydronic massive systems). The analysis is carried out with dynamic simulation models for the various cooling systems involved. Results show a great influence of the adopted distribution system in the implementation of a flexibility request. In particular, all-air systems (i.e. split systems) show the lower flexible behavior (they require up to 10 h of precooling to be off during a peak hour). Whereas the adoption of fan coil units coupled with a thermal energy storage allows to implement different peak shaving strategies without compromising the indoor air temperature with low drawback effects in terms of anticipated electricity overconsumptions (no precooling of the air is required and a maximum of 23 % increase in electricity consumed in the time before the event occurs, with a reduction of 16 % in subsequent hours). In case of ceiling cooling systems, results highlight that as the thermal inertia of the system increases, the indoor conditions are less affected, but the anticipated overconsumption of the heat pump increases (for the same Demand Response event the electricity overconsumption goes from + 67 % to +116 %, passing from ceiling panels to concrete ceiling). The results obtained from this analysis are then used to draw flexibility curves, which aim at providing a characterization of the flexibility of a cooling system. They can be used to predict, for typical installations, the system behavior in presence of a peak power reduction strategy in terms of pre-cooling duration, energy use variation and modification of the temperature comfort bandwidth. Such predictions are important because they can provide insights on the design and operation of space cooling systems in demand side management strategies.

Behavior energy conservation in buildings greatly impacts energy conservation and carbon reductions at the national level, and part-time space heating has become an important part of building operation. Under these conditions, heating terminals with different properties differ significantly in their heat consumption and heat grade demands. However, a comprehensive evaluation of the transference of quantities and grades of heat during the part-time heating of different terminals remains lacking. In this study, we developed a entransy-based analytical method and used it to compare the experimental and field-measured performances of three typical heating terminals (a radiator, radiant flooring, and a fan coil) from start-up to stabilization. The entire energy flow networks — from the heat source to the outdoor environment — were analyzed. Transient and cumulative entransy dissipation was analyzed to determine the energy utilization trends of the terminals. The dissipations between thermal nodes were also explored to intuitively reflect the key process(es) limiting heat transfer in a terminal. Further, we compared variations in heating performance under different operating durations to determine the applicability of each terminal type. Our results suggest that the radiant floor had the greatest entransy dissipation during start-up owing to its high thermal storage capacity and transfer resistance. However, because of the high thermal resistance of the terminal-to-chamber process, the entransy dissipation of the radiator was the greatest following stabilization (accounting for 57.0%), and the difference in the dissipation between radiators and the other terminal would increase with longer operating times.

As a large integrated energy system, district cooling system (DCS) is widely proposed for its favorable comprehensive performance. However, due to the high complexity of DCS structure and comprehensive influential variables on cooling demand, to propose an effective operational strategy that not only enhances energy efficiency but also ensures indoor thermal comfort is quite challenging. This research proposes a novel and online multi-objective optimization strategy for DCS operations, which minimizes both energy consumption and thermal discomfort, to tackle the aforementioned challenge. The proposed strategy incorporates accurate spatiotemporal cooling demand modeling: (1) On the one hand, cooling load models of both cooling dissipations during transport networks and cooling end consumers considering comprehensive influence of outdoor meteorological parameters are described; (2) On the other hand, all power consumption components in the DCS including chiller, pump, fan coil, fan of cooling tower, are built and connected with system cooling demand. Numerical experiments based on a real-world DCS are conducted to validate the proposed strategy. The results show that by adopting the proposed strategy, energy consumption cost and thermal comfort can be effectively optimized and can save an extra 5% of energy consumption comparing with published strategies.

Several control strategies are compared for a hydronic heating system that combines two different terminal units, radiant floor and fan-coil, in the same thermal zone. The performance of the combined system is evaluated in terms of energy consumption and comfort level. The production unit is an air-water heat pump. Four control strategies are defined and compared using a TRNSYS model: one strategy is applied when only the radiant floor operates, two strategies (simply and improved) are applied when only the fan-coil operates, and one strategy is applied when both terminal units operate simultaneously. Simulations are undertaken for three major cities with different heating requirements. In terms of comfort, the combined system achieves the higher scores, ensuring comfort conditions during most of the heating season. In terms of energy consumption, the worst option is the one that uses a fan-coil with fixed air velocity and fixed inlet water temperature. Nonetheless, there are not important differences between the analysed control options. The energy consumption of the system is mainly influenced by the part load performance of the heat pump, although the differences are small.

Dynamic simulation tools that could accurately simulate operational data for both the fault-free and faulty dynamic operation of heating, ventilation, and air conditioning (HVAC) systems and equipment are needed for developing and evaluating advanced control and automated fault detection and diagnosis strategies. Among various HVAC subsystems, fan coil units (FCUs) are relatively simple, inexpensive devices that are used extensively in commercial, institutional and multifamily residential buildings. However, very little has been reported in the literature to improve FCU design and operation. There has also been a lack of dynamic simulation tool development focusing on FCUs. The work reported in this study aims at developing and validating a software tool to simulate operational data generated from FCUs that are operated dynamically under both faulty and fault-free conditions. A comprehensive and systematic validation process, using data collected from real FCUs in a laboratory building, is used to validate the tool under both faulty and fault-free operating conditions in different seasons. The validated tool not only is able to predict real-world FCU behaviors under different control strategies, but it is also able to predict symptoms associated with various faults, as well as the effects of those faults on system performance and occupant comfort.

Given the growing concern about building energy efficiency and the difficulty in applying complex simulation tools during retrofit practices, the need for easily and quickly estimating the building energy performance becomes pressing. As a pilot test, this study proposes a systematic method to develop a model, which can immediately assess the annual electricity consumption for office buildings with fan coil system in Shanghai. First, a base-case building model is established by EnergyPlus to create a pool of candidate inputs using orthogonal experiment design. Then, analysis of variance is used to identify a total of 10 key building design parameters, which are selected as the input variables in the support vector regression (SVR) model based on a well-structured database. The performance of SVR is optimized using genetic algorithm (GA) based on radial basis function kernel. Finally, two real office buildings in Shanghai with reliable measured data serve to evaluate the developed hybrid model. The resulting differences between the predicted and measured values are generally within 10%. It is expected that the developed database and model can be used to assess the likely energy savings/penalty related with certain parameter changes to some extent during the retrofit process for office buildings.

This paper studies the performance of a cold storage heat pump system integrated with phase change materials (PCMs) for space cooling. An air-cooled heat pump unit comprising of two constant rotation speed compressors is selected. The PCM is an organic material that is commercially available, and has a phase change temperature of 10–12 °C. A coupled computational heat transfer model of the heat pump unit, fan coil units, and a cold storage tank filled with PCM slabs is developed. The simulations are performed under the climatic condition of Fuzhou, China. The operational behaviors of the cold charging and discharging processes of the system are analyzed. Furthermore, the overall electrical energy and electricity charge consumptions at various indoor temperature set points are compared. The results indicate that, the electrical energy consumption of the cold storage heat pump system increases as the indoor temperature increases. However, there is very little difference in the electrical energy consumption of the conventional heat pump system and the cold storage system. While under the demand tariff, the electricity charge saving ratio of the cold storage system over the conventional system is 9.07%-11.28%. In general, as the indoor temperature set point reduces, the electricity charge saving ratio increases. Moreover, the effect of cold charging temperature is also discussed. It is found that higher cold charging temperature consumes less electrical energy, however, takes longer to store the same amount of cold, and the differences relies on the required amount of cold.

Developing effective operational strategies for commercial buildings is a high priority as the global community seeks to reduce energy usage and greenhouse gas emissions. This study aims to validate the feasibility of a model predictive control (MPC) strategy for commercial building in response to occupancy variations and time-variant electricity prices in comparison to a conventional rule-based control (RBC) strategy. The building energy system included an air-cooled chiller, stratified chilled water thermal energy storage, two fan coil units, three heat exchangers, and five pumps. The optimal operations of the chiller and storage system were determined with the goal of minimizing the operating cost while maintaining the zone temperature at a cooling set point temperature during cooling operation hours. Artificial neural network was utilized as prediction models and metaheuristics algorithm was employed as optimization solver to construct a reliable and computationally manageable MPC controller. The simulation was performed for four days during the cooling season with a confirmed optimal prediction time horizon of 24 h and a control timestep of 1 h intervals. In conclusion, MPC reduced the total operating cost by 3.4% compared to the RBC, which prioritized the storage system operation to manage the thermal load.

The paper describes a study developed to estimate the energy savings potential of a radiant cooling system installed in a commercial building in India. To evaluate thermal performance and energy consumption, simulations were carried out using FLUENT and EnergyPlus software, respectively. The building model was calibrated using the measured data for the installed radiant system. Then this calibrated model was used to simulate the energy consumption of a building using a conventional all-air system to determine the proportional energy savings. For proper handling of the latent load, a Dedicated Outside Air System (DOAS) was used as an alternative to Fan Coil Unit (FCU) that was installed in conjunction with the radiant cooling system. A comparison of energy consumption calculated that the radiant system was 17.5% more efficient than a conventional all-air system and that a 30% savings was achieved by using a DOAS system compared with a conventional system. The Computational Fluid Dynamics (CFD) simulation showed that a radiant system offers more uniform temperatures, as well as a better mean air temperature range, than a conventional system. To further enhance the energy savings in the radiant system, different operational strategies were analyzed based on thermal analysis using EnergyPlus.

Traditional wall-return re-circulation air systems with ceiling-supply and wall-return air grilles are fairly common in non-unidirectional airflow industrial cleanrooms. Such re-circulation systems normally have longer airflow circulation pathways, which inherently induced higher airflow resistance, resulting in higher fan power demand per unit of airflow rate delivered. To overcome the airflow resistance, Fan Filter Units (FFUs) used in the traditional wall-returned re-circulation system are designed to operate with high external pressures, which also induce high negative pressures in supply air plenums (SAP). The negative pressures within SAP can increase the risks of infiltration of outdoor air and contaminants. A longer airflow pathway corresponds to a higher level of negativity of the air pressure inside the supply air plenum, thus inducing higher risks of cross-contamination. To overcome the above-mentioned drawbacks, a new re-circulation system using fan dry coil unit (FDCU) was proposed. This new system exhibits shorter air re-circulation paths while providing effective environmental controls (e.g., removal rate of 0.1 μm particle and temperature control) for a cleanroom. In this study, experiments were conducted in a full-scale cleanroom to investigate the energy performance of applying the innovative FDCU-return system, compared to a traditional wall-return system. Results showed that the FDCU-return system can increase energy efficiency and reduce the electric energy consumption by more than 4% compared to the wall-return system.

Most chilled water circulation systems with fan coil units suffer from a low temperature differential between the supplied and returned water. On-site investigation shows that the relationship between total cooling consumption and total water flow rate of real systems is different from that of single coil units mainly as a result of the interaction of the terminals. When certain terminals close their water valves, the other terminals have higher water flow rates and lower water delta-T values. This study presents a quantitative analysis of terminal coupling and its effect on system characteristics. System coupling factor is used as an indicator to describe the total degree of fan coil unit coupling in a system. To observe the effect of the system coupling factor, a dynamic simulation platform is constructed and simulation tests are performed. The results show that the higher the system coupling factor is, the larger is the total delta-T loss under partial load conditions. Based on this indicator, certain problems of system design can be reviewed from the perspective of terminal coupling.

The excess flow of water increases the energy consumption of water pumps in the chilled water systems of air-conditioning units. This paper proposes a strategy to control the chilled water flow rate of a fan coil unit (FCU) using a control valve. A physical simulation test bench was built to verify valve control and energy-saving effects. Results showed that the control valve could effectively regulate the flow rate of chilled water, improve the temperature difference (delta-T) between supply and return water, and reduce the energy consumption of the chilled water pump. With a supply water temperature of 7 C and low (325 m3⋅h−1), medium (500 m3⋅h−1), and high (600 m3⋅h−1) FCU air velocity levels, the average delta-T values were 4.79 °C, 4.39 °C, and 4.97 °C, respectively, and the energy consumption of the chilled water pump decreased by 12.20%, 11.31%, and 10.66%, respectively. With medium air velocity and supply water temperatures of 7 °C, 8 °C, and 9 °C, the average delta-T between supply and return water was 4.39 °C, 3.56 °C, and 3.33 °C, respectively, and the energy consumption of the chilled water pump decreased by 11.31%, 5.10%, and 7.80%, respectively. These research results provide useful insights in relation to the problem of excess chilled water flow identified above.

This paper describes a small-scale experimental direct-expansion ground source heat pump system in typical clay soils for space heating of a building in Jinzhou, China. It uses R22 as the refrigerant, consisting of four single U-shaped copper ground heat exchangers with a uniform depth of 20 m. A special circular bend is designed on the copper tube to enhance the lubricant oil return of the scroll compressor. The operation performance and energy efficiency of the DX-GSHP system is tested in the heating mode. Results show that the present DX-GSHP system is reliable and effective. During the heating period, when the heating capacity of the indoor fan coil is 6.41 kW, the room temperature varies from 18 to 20 °C even if the door is opened or closed frequently. The average COP of the heat pump unit and the whole DX-GSHP system are 3.12 and 2.88, respectively, and the average heat-transfer rate of GHEs per depth is 54.4 W/m. In addition, the influence of the opening of the electronic expansion valve on the operation performance is analyzed. The present results can provide useful guides for the design and further improvement of DX-GSHP systems under similar geological conditions.

Solar absorption cooling systems are available from various reports, in large capacities up to several hundred kilowatts. However, in the range of small capacities ( 2 solar collector arrays, one absorption chiller with a rated cooling capacity of 8 kW, and a hot storage water storage tank of 3 m 3 in volume. The chilled water can be delivered either into fan coils or into radiant cooling panels, which are installed to satisfy the demands of the indoor thermal environment of the test room. As for the fan coil cooling mode, it was found that the average cooling output reached 4.27 kW during 9 h of operation under typical weather conditions for Shanghai. The PMV (predicted mean value, a measure of thermal comfort) inside the test room could be controlled between −0.29 and 0.32. With regard to the radiant cooling mode, an individual supply air unit was installed for the purpose of preventing condensation on the cooling panels. Comparing with the experimental results of the fan coil cooling mode, the average cooling output increased by 23.5%.

The temperature and humidity independent control (THIC) system, which controls indoor temperature and moisture separately, may be an attractive alternative to existing conventional HVAC systems for its prominent improvement on the overall system performance and utilization of low grade energy resources. In order to verify the effectiveness of THIC system, a pilot project has been implemented in an office building in Shenzhen, China. In the system, liquid desiccant fresh air handling units driven by heat pumps are utilized to remove the entire latent load of outdoor air supplied for the whole building, and chilled water at the temperature of 17.5 °C from chiller is pumped and distributed into dry fan coil units and radiant panels to control indoor temperature. This paper presents the results of field test of the system, which shows that the system can provide a comfortable indoor environment even in very hot and humid weather. The COP of the entire THIC system can reach 4.0. According to the energy usage data recorded from the year 2009, the energy consumption of the THIC system in the tested office building was 32.2 kWh/(m 2 yr), which demonstrates magnificent energy-saving potential compared with the conventional air-conditioning system (around 49 kWh/(m 2 yr)).

The performance of different HVAC systems varies when coupled with different buildings. This paper examines the relationship between building heating and cooling load and subsequent energy consumption with different HVAC systems. Two common HVAC systems in use throughout the UK office building stock, variable air volume (VAV) system and fan coil (FC) with dedicated outside air system, have been coupled with a typical narrow plan office building with and without daylight control and for both cellular and open plan. The results presented in this paper clearly indicate that it is not possible to form a reliable judgment about building energy performance based only on building heating and cooling loads. For the two investigated systems, variable air volume system and fan coil with dedicated outside air system, the difference between system demand and building demand varied from over −40% to almost +30% for cooling and between −20% and +15% for heating. If a heat recovery unit is used, the difference in heating performance is even greater, rising to −70%.

This study deals with exergetic assessment of an educational building heated by a conventional boiler in a heating center. The heating system is examined from the generation stage to the envelope of the building. In general the heat loss calculations are made using both energy and exergy analysis methods. The energy and exergy flows between the stages are obtained using a pre-design tool for an optimized building design. Energy and exergy losses are obtained to evaluate the performance of the system. A conventional boiler in the heating center and a fan coil unit in a room are considered in the analysis. Total exergy input rate is calculated to be 694.5 kW, while the largest exergy loss rate is obtained to be 333 kW. Exergetic efficiencies of the conventional boiler and the fan coil unit are also found to be 13.4% and 37.6%, respectively.

A discrete model characterizing heat and fluid flow in connection with thermal fluxes in a building is described and tested against experiment in this contribution. The model, based on a cellular automaton approach, relies on a set of a few quite simple rules and parameters in order to simulate the dynamic evolution of temperatures and energy flows in any water or brine based thermal energy distribution network in a building or system. Using an easy-to-record input, such as the instantaneous electrical power demand of the heating or cooling system, our model predicts time varying temperatures in characteristic spots and the related enthalpy flows whose simulation usually requires heavy computational tools and detailed knowledge of the network elements. As a particular example, we have applied our model to simulate an existing fan coil based hydronic heating system driven by a geothermal heat pump. When compared to the experimental temperature and thermal energy records, the outcome of the model coincides.

An experimental investigation on operation characteristics of cool storage air-conditioning system with spherical capsules packed bed was performed in this paper. The experimental system of cool storage air-conditioning system with spherical capsules packed bed was set up. The performance parameters such as the evaporation pressure and the condensation pressure of refrigeration system, the refrigeration capacity and the coefficient of performance (COP) of the system, the cool storage rate and the cool storage capacity in the cool storage tank, the inlet and outlet coolant temperatures in the cool storage tank during charging period, and the cool discharge rate and the cool discharge capacity in the cool storage tank, the outlet and inlet coolant temperatures in the cool storage tank and the outlet and inlet air temperatures in room fan coil unit during discharging period were investigated. The experimental results indicated that the cool storage air-conditioning system with spherical capsules packed bed has better performances and can stably work during charging and discharging period.

In this work, the combined effect of the energy conservative variable refrigerant volume (VRV) system and the variable air volume (VAV) system was experimentally investigated using genetic fuzzy optimization method that yielded better thermal comfort, indoor air quality (IAQ) requirements without compromising on the energy savings potential. The proposed system was tested using the demand controlled ventilation (DCV) combined with the economizer cycle ventilation (ECV) techniques and examined for a year-round building air conditioning (A/C) application. The supply air temperature (SAT) set points were varied under three distinct strategies and the optimal solutions obtained for the fuzzy systems designed resulted in an enhanced energy conservative potential. The test results of the proposed system were compared with the conventional fan coil A/C system. Based on the three strategies of the supply air temperature, the proposed system yielded an improved per day energy savings potential of 54% in summer and 61% in winter design conditions. Furthermore, for the strategies considered the proposed system achieved an annual energy conservative potential of 36% and exhibited more possible ways to achieve thermal comfort, IAQ and energy conservation.

An all-air central air-conditioning system with an exhaust fan incorporated with a supply fan is presented in this article. With the proposed system, detailed year-round energy-efficient operation strategies and control methods for the air-handling unit are presented. Further, the method of determining the pressure head and air volume of the exhaust fan is also presented, which is needed for designing this presented system. As opposed to conventional one supply-fan systems in the all-air central air-conditioning system, the proposed system is shown to not only maintain indoor pressurization required for controlling indoor air quality but also operate in an improved energy-efficient manner, achieved by having proper variable fresh-air ratios during the period of intermediate season. Due to its increased outdoor air, the proposed system can improve indoor air quality further.

An innovative low temperature differential variable air volume fan-coil unit (LTD-VAV FCU) was developed to improve the defects of variable air volume (VAV)and coldairdistributionenergy-savingtechnologies.A testbenchand proceduresaccording toitsuniqueair supplyfeatures were established to investigate the energy-saving and IAQ improving potential experimentally. The experimental results of the prototype indicated the supply air volume can be continuously varied between 0.09 m 3 /s (200 CFM) and 0.38 m 3 /s (813 CFM), controlled by the bypass damper giving an air supply/air return temperature difference from only 2.30 to 8.09 8C. The effect of reducing the supply/return air temperature differential not only makes people feel comfortable, but also improves the cold draft and condensing at the outlet generated by ordinary air supply method. In addition, continuous capacity variations range from 0.45 kW (383 kcal/h) to 5.29 kW (4550 kcal/h) rendering to achieve the effect of comfort at a stable indoor thermal condition. Moreover, the temperature difference of chilled water ranges from 0.42 to 5.05 8C, the chiller plant not only can be unloaded at a low temperature difference to enhance energy-saving, but also complement other areas for multi-area application. # 2006 Elsevier B.V. All rights reserved.

During the design process of heating and air conditioning systems, the designer must analyse various factors in order to determine the best design options. Therefore, the environmental aspects of a product should be included in the analysis and selection of design options if an environmentally aware design is to be produced or selected. The comparison between three different heating systems was made with the Eco-indicator 95 method. The study included the environmental impact at the production phase of the system, because alternative production methods have different kinds of environmental burdens. The results showed that the three different concepts of heating systems with different construction materials varied the Eco-indicator value. For radiator heating system the Eco-indicator value is far superlative than for floor or fan coil convector heating system. Copper pipes and other copper parts contribute to the greatest environmental impact. Radiator heating Eco-indicator showed three times higher value for copper pipes than for the steel pipes despite smaller dimensions. The lowest values are obtained for floor heating systems. Reasonable values are obtained for fan coil units; analysis shows up, that heat exchanger contributes the main part of the value.

Two modern office buildings in Shanghai with typical variable air volume (VAV) systems were selected for research. Four separate spaces on a standard office floor in each building facing different directions (north, south, east, and west) were selected for thorough site measurements of outdoor airflow rates and indoor air quality (concentrations of CO 2 and PM10) during typical days of the four seasons (summer, autumn, winter, spring). Computer simulations and calculations were also done of outdoor airflow rates and CO 2 concentrations in the four-test spaces on an hourly basis for the entire year. In addition to the site measurements, monthly electrical consumption for the two buildings was recorded or estimated. Simulations and calculations were performed of the buildings’ energy consumption and energy cost using two different outdoor air control strategies of a typical VAV system as well as a fan coil unit (FCU) system. The site-recorded data, or estimated data, and simulation results are compared and analyzed. The study reveals that in a VAV system, the outdoor airflow rate distributed to each zone varies greatly, especially during part-load hours, making it difficult to always ensure sufficient outdoor air in each zone and avoid indoor air quality (IAQ) problems. However, this problem can be prevented by using appropriate outdoor air control strategies—e.g. a fixed high level total outdoor airflow rate. © 2002 Elsevier Science B.V. All rights reserved.