Variable refrigerant flow (VRF) or variable refrigerant volume (VRV) systems provide many benefits over traditional air-conditioning systems, with great potential to decrease energy cost and increase thermal comfort in buildings. This paper presents a method to size and select VRF systems and to compute its annual energy consumption. The study compares the cooling energy usage of a VRF system against a conventional chiller-based variable-air-volume (VAV) system and a packaged VAV (PVAV) system for a typical light commercial building. The results reveal that the peak electrical demand of the VRF system for the cooling season is about 60% of the chiller-based VAV system and 70% of the packaged VAV systems, and the operating energy usage is about 53% of the chiller-based VAV system and 60% of the packaged VAV system for the building studied.
Efficient heating and cooling systems and renewable energy sources are crucial for effectively designing net-zero energy homes (NZEHs). The study proposes using a multi-functional variable refrigerant flow system with hydraulic heat recovery (MFVRF-H2R) to reduce HVAC and hot water energy usage, offering a practical approach to enable NZEH solutions. Photovoltaic (PV)-based on-site power generation is utilized to achieve zero-energy performance in residential buildings. A building energy simulation study is conducted to assess the effectiveness of the combined systems in various climate conditions. To develop the simulation model, the US National Institute of Standards and Technology (NIST)'s net-zero energy residential test facility is used as the benchmark for NZEH baseline models. The MFVRF-H2R system is incorporated into the NZEH baseline to propose a more-energy efficient design with heat recovery technology. eQUEST and post-processing calculations are used to simulate NZEH performance, comparing whole-building energy end-use and PV capacity for the baseline and alternative models with MFVRF-H2R. Results demonstrate that the proposed VRF-based NZEH design can provide potential energy savings of up to 32% for cooling energy under various climate zones. Moreover, the NZEH design with the proposed MFVRF-H2R can achieve up to a 90% reduction in domestic hot water usage compared to an NZEH design without VRF heat recovery technology. The study suggests that the MFVRF-H2R system can provide practical and realistic solutions for making HVAC energy-efficient by minimizing thermal waste and reusing it for other thermal parts of the building, such as hot water applications. Consequently, this study highlights the effectiveness of the MFVRF-H2R system in designing NZEHs while considering heat recovery and renewable energy technologies.
Net-zero energy homes (NZEHs) have been studied widely from different perspectives to provide realistic and practical solutions. Among various approaches to enable NZEH designs, energy-efficient heating, ventilation, and air-conditioning (HVAC) systems play a key role in providing thermal comfort and good air quality in a cost- and energy-efficient manner. This study proposes a NZEH design using photovoltaic (PV)-based distributed energy generation and multi-functional variable refrigerant flow (VRF) systems with electric and thermal energy storage systems. Simulation-based NZEH performance evaluation is conducted based on case studies under various US climate conditions. To develop a validated NZEH simulation model, the net-zero energy residential test facility (NZERTF) constructed by the US National Institute of Standards and Technology (NIST) is used for benchmarking the NZEH reference model. Changes in monthly energy consumption and on-site power generation before and after the VRF application are analyzed to capture the potential impact of the VRF system application for the NZEH design. This study shows that the alternative NZEH design with the proposed VRF and electric and thermal energy storage systems can achieve around 13% through 32% of cooling energy reductions under different US climate conditions. With the proposed VRF system, the savings potential of domestic hot water energy consumption is significant up to 90% reduction compared to the original NZEH before the proposed VRF and energy storage systems were considered.
Recent energy and economic analysis of a cogeneration system has been implemented by a manual calculation that is based on monthly thermal loads of buildings. In this study, a cogeneration system modeling validation with a detail building energy simulation, eQUEST, for a building energy and cost prediction has been implemented. By analyzing the hourly building electricity and thermal loads, it enables designers to decide proper cogeneration system capacity and to estimate more reliable building energy consumption. eQUEST also verified economical and environmental benefits when the heat pump system is integrated with the cogeneration system because the mechanical system configuration benefits from the high efficiency heat pump system while avoiding the building electricity demand increase. Economic analysis such as LCC (Life Cycle Cost) method is carried out to verify economical benefits of the system by applying actual utility rates of KEPCO (Korea Electricity Power COmpany) and KOGAS (KOrea GAS company). As results, the proposed system consumed approximately 40% less energy than the Alt-2 in terms of source energy. LCC analysis results also show that the proposed system could save about 10–14% of energy cost during the life cycle compared to the Alt-1 and Alt-2. It could save 6–7% of the total life cycle cost and it is equivalent to around 1–1.3 billion Won in cost.
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