An unsupervised ensemble learning method for real-time anomaly detections in variable refrigerant flow systems

Evaluation of energy savings potential of variable refrigerant flow (VRF) from variable air volume (VAV) in the U.S. climate locations

Comparative study of the cooling energy performance of variable refrigerant flow systems and variable air volume systems in office buildings

This study presents a comprehensive analysis of the energy efficiency and sustainability of Variable Refrigerant Flow (VRF) systems in university buildings during the winter season, offering significant contributions to the field. A novel methodology is introduced to accurately assess the real Seasonal Coefficient of Performance (SCOP) of VRF systems, benchmarked against conventional Heating, Ventilation, and Air Conditioning (HVAC) technologies, such as natural gas-fueled boiler systems. The findings demonstrate outstanding seasonal energy performance, with the VRF system achieving a SCOP of 5.349, resulting in substantial energy savings and enhanced sustainability. Key outcomes include a 67% reduction in primary energy consumption and a 79% decrease in greenhouse gas emissions per square meter when compared to traditional boiler systems. Furthermore, VRF systems meet 83% of the building’s energy demand through renewable energy sources, exceeding the regulatory SCOP threshold of 2.5. These results underscore the transformative potential of VRF systems in achieving nearly Zero-Energy Building (nZEB) objectives, illustrating their ability to exceed stringent sustainability standards. The research emphasizes the strategic importance of adopting advanced HVAC solutions, particularly in regions with high heating demands, such as those characterized by continental climates. VRF systems emerge as a superior alternative, optimizing energy consumption while significantly reducing the environmental footprint of buildings. By contributing to global sustainable development and climate change mitigation efforts, this study advocates for the widespread adoption of VRF systems, positioning them as a critical component in the transition toward a sustainable, zero-energy building future.

Variable Refrigerant Flow (VRF) systems are refrigerant systems, which are generally comprised of an outdoor unit serving multiple indoor units connected by a refrigerant piping network. It is important to evaluate the performance of VRF systems, which can help the design and operate of VRF systems. Performance test done by manufactory can reveal the performance of VRF systems in designed conditions. However, it is hard to reveal effective performance in real buildings. The field test is complicated compared with the test in the laboratory and can only conduct on typical samples rather than large scale samples. However, typical samples are not enough for reflecting the performance of large scale VRF systems samples. A simple method of evaluating the performance of large scale VRF systems samples is necessary. This paper proposed and calculating model for electricity consumption and cooling demand of VRF systems based on measured operating data in the laboratory. The paper used the calculating model combined with 344 samples operating data from real residential buildings to calculate the performance of a large scale VRF. This paper analyzed the VRF systems’ performance with different influencing factors such as climate zones, cooling duration and outdoor temperature for the recommendation for VRF systems’ designing and operation.

The usage of air - conditioning in the residential and commercial buildings is becoming necessary because of the enormous demand for thermal comfort and healthy indoor environment. In achieving human thermal comfort and healthy indoor environment in a large building, there are many types of air conditioning systems that can be used, including the multi - split type unit and the variable refrigerant flow (VRF) system. The present research analyses the annual energy use of the existing ACMV system (multi - split type ceiling cassette unit) installed in the examined building, which located in the tropical area and compares it with a VRF system. The TRNSYS software is used to simulate both of these systems in accordance with the existing building’s characteristics and its operation. The existing building’s characteristics and its operation are obtained by conducting the site survey and field measurements in the building. In the current paper, the bin method is used to estimate the annual energy consumption for these systems. Based on the simulation results, the existing ACMV system consumes more energy in comparison to the VRF system by 13.62%. In addition, the annual operating cost of these systems has shown that the VRF system has a lower annual operating cost in comparison to the existing ACMV system by 13.63%. Besides that, the VRF system can accommodate an estimated payback period of around 6.6 years and an internal rate of return of 12.75%. The result has suggested that the VRF system has a great potential in energy savings and could reduce the electricity consumption in a large building significantly.

A research project “Evaluation of Variable Refrigerant Flow (VRF) Systems Performance and the Enhanced Control Algorithm on Oak Ridge National Laboratory’s (ORNL’s) Flexible Research Platform” was performed to (1) install and validate the performance of Samsung VRF systems compared with the baseline rooftop unit (RTU) variable-air-volume (VAV) system and (2) evaluate the enhanced control algorithm for the VRF system on the two-story flexible research platform (FRP) in Oak Ridge, Tennessee. Based on the VRF system designed by Samsung and ORNL, the system was installed from February 18 through April 15, 2014. The final commissioning and system optimization were completed on June 2, 2014, and the initial test for system operation was started the following day, June 3, 2014. In addition, the enhanced control algorithm was implemented and updated on June 18. After a series of additional commissioning actions, the energy performance data from the RTU and the VRF system were monitored from July 7, 2014, through February 28, 2015. Data monitoring and analysis were performed for the cooling season and heating season separately, and the calibrated simulation model was developed and used to estimate the energy performance of the RTU and VRF systems. This final report includes discussion of themore » design and installation of the VRF system, the data monitoring and analysis plan, the cooling season and heating season data analysis, and the building energy modeling study« less

The variable refrigerant flow (VRF) air conditioning system usually needs to be operated with a ventilation system, since the VRF system cannot provide fresh air. The commonly used ventilation unit with the VRF system is the heat recovery ventilation (HRV) unit due to its merits of energy saving. In this study, a novel solid desiccant heat pump unit (DESICA) is introduced and mathematical model of DESICA is developed based on the dynamic building energy simulation software—EnergyPlus. The mathematical model is validated with experimental results. Based on the model, performance comparison study is conducted among the novel joint DESICA and VRF (DES&VRF) system, the conventional joint HRV and VRF (HRV&VRF) system, and the original VRF standalone with ventilation (VRFSA) system in an office building in Shanghai. Simulation results show that, HRV&VRF and VRFSA can handle the sensible load, though both of them cannot well deal with the latent load. On the contrary, DES&VRF system can keep both indoor temperature and humidity ratio at the target value, resulting in the best indoor thermal comfort than the other two systems. In addition, through the whole year, DES&VRF consumes 5% more energy than VRFSA and 20% less energy than HRV&VRF.

Operation and performance of VRF systems: Mining a large-scale dataset

Integration of variable refrigerant flow and heat pump desiccant systems for the heating season

A novel variable refrigerant flow system with solar regeneration-based desiccant-assisted ventilation

Field test and simulation evaluation of variable refrigerant flow systems performance

Ensemble 1-D CNN diagnosis model for VRF system refrigerant charge faults under heating condition

Space cooling energy consumption is a significant component of building energy consumption, and in recent years it has attracted much attention worldwide owing to its significantly increasing usage. The variable refrigerant flow (VRF) system is one common type of cooling equipment for buildings in China and is applied extensively to residential and office buildings. The performance of VRF systems significantly influences the cooling energy consumption of buildings. The system energy efficiency and electricity consumption are the main indicators employed to evaluate the performance of VRF systems. It is hard to obtain the actual energy efficiency and electricity consumption of VRF systems in buildings because of the high cost of the required complicated measurements. This study proposes a virtual sensor modeling method to determine the actual energy efficiency and electricity consumption of 344 VRF systems in residential buildings. Statistical and clustering analyses are conducted to determine the energy efficiency and electricity consumption to obtain distributions and typical operation load patterns of VRF systems in residential buildings in China. The main findings are as follows: the main range of the Seasonal Energy Efficiency Ratio (SEER) for the cooling season is from 2.9 to 4.4; the median SEER in the Hot Summer and Cold Winter zone is lower than in another climate zones; the longer cooling duration may lead to greater electricity consumption, and the electricity load for VRF systems electricity load is periodic for each day. The oversizing issue is common for VRF systems in the dataset, which also led to the lower energy efficiency of VRF systems. The high usage of VRF systems appeared from July 27th to August 26th. The findings provide recommendations for designing VRF systems in residential buildings.

Modularized PCA method combined with expert-based multivariate decoupling for FDD in VRF systems including indoor unit faults

Although variable refrigerant flow systems have become attractive due to good energy performance in part-load conditions, the shortcoming of the variable refrigerant flow system in outdoor air ventilation has not been well solved. A variable refrigerant flow and variable air volume combined air-conditioning system was proposed to solve this problem. The variable air volume part of the combined system consists of an outdoor air processing unit and air supply and distribution devices. The combined system was found having potential to obtain high-level energy efficiency without compromising thermal comfort by an intelligent control system. Therefore, a so-called global coordinated optimization strategy based on a local coordinated optimization strategy is proposed in this study. The local coordinated optimization strategy decreases energy consumption of the combined system through optimizing load allocation between the variable refrigerant flow unit and the outdoor air processing unit. The global coordinated optimization strategy has a much deeper coordination of the variable refrigerant flow and outdoor air processing units, as it combines the local coordinated optimization strategy with stopping and restarting of the outdoor air processing unit. Performances of the combined system in heating conditions under this strategy are evaluated in the simulation platform. Results show that the global coordinated optimization strategy can effectively reduce the energy consumption of the combined system.