Modeling and Analysis of Building Cooling Energy Supply System Using Variable Solar Refrigerant Flow System

Document Type : Original Article


1 PhD Candidate, Department of Renewable Energies and Environment, University of Tehran, Tehran, Iran

2 PhD Candidate, Faculty of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran

3 Associate Professor, Department of Renewable Energies and Environment, University of Tehran, Tehran, Iran


Variable refrigerant flow systems are one of the most efficient and widely used air conditioning systems to reduce energy consumption while maintaining the desired level of thermal comfort. Variable refrigerant flow systems as an efficient and flexible solution for various heating/cooling applications are gaining more attention and are widely used in commercial and residential buildings. Variable refrigerant flow systems have many advantages over traditional air conditioning systems such as chillers and fan coils or air conditioning units, including satisfactory partial load performance, individual control capability at arbitrary temperature range, and no loss in duct transmission. Easy installation and maintenance. However, variable refrigerant flow systems require a dedicated outdoor air system with an additional ventilation unit.
This section first discusses the design of a variable refrigerant flow system. The next step is to model the building located in Cyprus with the heating system in question. The parts of this modeling include the characteristics of the selected location of the building, modeling of the relevant building, modeling of variable refrigerant air conditioning system and photovoltaic systems in detail.

Variable refrigerant flow system

Variable refrigerant flow systems Among the various air conditioning systems is the DX system, based on the standard Rankin reverse steam compression cycle. Therefore, these systems are thermodynamically similar to conventional DX systems and have similar equipment such as compressor, expansion valve, condenser, and evaporator. Figure (1) shows the inside of the exterior of a variable refrigerant flow system that is installed outside the building.
A 5-storey residential building with an area of ​​1061 square meters of space has been modeled in Design Builder software (on each floor, there are two residential units with ​​110 square meters). Each floor consists of two units with an equal area; the north-facing unit has two bedrooms, the south-facing unit has three bedrooms, and the ground floor is uninhabited and without air conditioning. In addition, the corridors between adjacent apartments on each floor are also without air conditioning. This research will focus on the power consumption of the variable refrigerant flow system as an electric charge. Figure (2) shows a schematic of an integrated photovoltaic variable refrigerant flow system.
Results and Discussion
In this section, energy consumption in variable refrigerant air conditioning, power generation of photovoltaic arrays, and carbon dioxide reduction due to photovoltaics are examined according to the results obtained from the design of builder designs.
The intensity of solar radiation in this city equals 1852kWh, and the annual electricity consumption of a refrigerant flow system varies around 18500kWh. The results show that according to the duration of sunlight during the day, the total daily electricity produced by photovoltaics provides only 54% of the daily electricity required for variable refrigerant current, which has a significant impact on reducing electricity consumption from the grid and a significant impact on Reduces carbon dioxide by 14 tons per year.
Figure 1. Internal view of the outer part of the variable refrigerant flow
Figure 2. Schematic of VRF-PV integrated system
 Figure 3. DNI radiation status of the sun kW/m2 on July 21
Figure 4. Energy rate status of a building unit on July 21
Figure 5. External and indoor temperature status of a unit (dining room facing south on the 5th floor of the building), on July 21
Figure 6. Status of carbon dioxide emissions on 21 July
Figure 7. DNI and DIF solar radiation conditions kW / m2 in summer and autumn
Figure 8. Electricity status (Kw) required for cooling and photovoltaic power generation in summer and autumn
Figure 9. External temperature and temperature of the dining room facing south on the 5th floor of the building, in summer and autumn


  • Abergel T, Dean B, Dulac J. Towards a zero-emission, efficient, and resilient buildings and construction sector: Global Status Report 2017. UN Environment and International Energy Agency: Paris, France. 2017;22.
  • Yang L, Yan H, Lam JC. Thermal comfort and building energy consumption implications–a review. Applied energy. 2014;115:164-73.
  • Zahedi R, Zahedi A, Ahmadi A. Strategic Study for Renewable Energy Policy, Optimizations and Sustainability in Iran. Sustainability. 2022;14(4):2418.
  • Alberti M, Waddell P. An integrated urban development and ecological simulation model. Integrated Assessment. 2000;1(3):215-27.
  • Maghzian A, Aslani A, Zahedi R. Review on the direct air CO2 capture by microalgae: Bibliographic mapping. Energy Reports. 2022;8:3337-49.
  • Lobaccaro G, Fiorito F, Masera G, Poli T. District geometry simulation: a study for the optimization of solar façades in urban canopy layers. Energy Procedia. 2012;30:1163-72.
  • Sola A, Corchero C, Salom J, Sanmarti M. Multi-domain urban-scale energy modelling tools: A review. Sustainable Cities and Society. 2020;54:101872.
  • Hedegaard RE, Kristensen MH, Pedersen TH, Brun A, Petersen S. Bottom-up modelling methodology for urban-scale analysis of residential space heating demand response. Applied Energy. 2019;242:181-204.
  • Yu X, Yan D, Sun K, Hong T, Zhu D. Comparative study of the cooling energy performance of variable refrigerant flow systems and variable air volume systems in office buildings. Applied energy. 2016;183:725-36.
  • Zhang R, Sun K, Hong T, Yura Y, Hinokuma R. A novel Variable Refrigerant Flow (VRF) heat recovery system model: Development and validation. Energy and Buildings. 2018;168:399-412.
  • Zhai ZJ, Rivas J. Promoting variable refrigerant flow system with a simple design and analysis tool. Journal of Building Engineering. 2018;15:218-28.
  • Enteria N, Yamaguchi H, Miyata M, Sawachi T, Kuwasawa Y. Performance evaluation of the variable refrigerant flow (VRF) air-conditioning system subjected to partial and unbalanced thermal loadings. Journal of Thermal Science and Technology. 2016;11(1):JTST0013-JTST.
  • Liu J, Wang J, Li G, Chen H, Shen L, Xing L. Evaluation of the energy performance of variable refrigerant flow systems using dynamic energy benchmarks based on data mining techniques. Applied energy. 2017;208:522-39.
  • Matsumoto K, Ohno K, Yamaguchi S, Saito K. Numerical analysis of control characteristics of variable refrigerant flow heat-pump systems focusing on the effect of expansion valve and indoor fan. International Journal of Refrigeration. 2019;99:440-52.
  • Virta M, Itkonen H, Mustakallio P, Kosonen R, editors. Energy efficient HVAC-system and building design. Proceedings of Clima; 2010.
  • Hazyuk I, Ghiaus C, Penhouet D. Optimal temperature control of intermittently heated buildings using Model Predictive Control: Part I–Building modeling. Building and Environment. 2012;51:379-87.
  • Lam KP, Zhao J, Ydstie EB, Wirick J, Qi M, Park JH. An EnergyPlus whole building energy model calibration method for office buildings using occupant behavior data mining and empirical data. ASHRAE Journal. 2014:160-7.
  • Esabegloo A, Haghshenas M, Borzoui A. Comparing the results of thermal simulation of rasoulian house in Yazd by design builder software, with experimental data. Iran University of Science & Technology. 2016;26(2):121-30.