2016 ASHRAE Annual Conference

Variable refrigerant flow (VRF) systems have been gaining popularity globally, particularly in Asia and Europe for cooling and heating in the built environment in the last two decades. In recent years, VRF systems are starting to fill a growing niche in renovation projects in the U.S. This paper describes the design and evaluation of a large scale installation of VRF systems with comparisons to traditional HVAC systems.  These VRF systems are part of a mega HVAC project that includes design, installation, commissioning, and operation of HVAC systems for 6 almost identical building complexes located in Seoul, Republic of Korea. The building complexes, with 10 above-ground floors and 4 subterranean floors, primarily house offices, conference rooms, auditoria, R&D labs, cafeteria, restaurants, utility, and machine rooms. Four of these buildings, Complex A, B, D, and E are equipped with a mélange of HVAC systems consisting of centrifugal chillers and absorption chillers, and VRF systems for their cooling and heating needs, while Complex C is 100% served by VRF systems and Complex F is 100% covered by traditional HVAC systems. The total installed HVAC equipment includes 2,000 tons of centrifugal chillers, 4,000 tons absorption chillers, 2,145 tons of geothermal VRF systems, and 6,335 tons of air- and water-cooled VRFs. Thanks to the similarities in architecture, construction, occupancy, and thermal load of these 6 building complexes, the mega project provides a unique opportunity to conduct objective evaluations and comparisons between VRF systems and traditional HVAC systems over a wide range of aspects: energy, comfort, maintenance costs, and initial investments.  The objectives of this study are (1) to evaluate the energy performance and other benefits of VRF systems in comparison with traditional HVAC systems, and (2) to evaluate if VRF is a technically and economically viable solution for large building complexes. The paper also presents several new technologies implemented in this project including (1) variable air volume (VAV) discharge temperature control technology, (2) VAV movable diffuser. The discharge temperature controls technology regulates the air flow to maintain the discharge air temperature instead of directly controlling the returning air temperature resulting in much less temperature swings. The movable diffuser utilizes Coanda effect to achieve optimal temperature distribution in air conditioned spaces. Lastly, an in-situ approach for determining the Coefficient of Performance (COP) of VRF systems is proposed for real-time energy performance evaluation.

R5 Complex, located in Suwon, Republic of Korea, is a cutting edge R&D center that focuses on research and development of consumer electronic devices. As a multifunctional building, it houses R&D laboratories, conference rooms, auditoria, offices, cafeteria, restaurants, utility, mechanical and electrical rooms. With these heterogeneous characteristics of thermal load throughout the complex, it is difficult to have a one-size-fits-all type of HVAC system that can achieve green building certification and optimal human comfort at the same time. This paper uses R5 Complex as a case study to examine and illustrate how a hybrid approach can be used to provide an optimal HVAC solution for massive R&D complexes to meet the energy and comfort requirements.   R5 complex consists of 25 floors including 4 subterranean floors with a total usable space of 300,000 m².  According to the load characteristics, the complex is divided into three big zones: outer periphery, inner periphery, and core.  The outer periphery accounts for 50% of thermal load of the entire complex. It is directly exposed to the outdoor and sunlight, thus the heating and cooling loads fluctuate the most throughout the day. The HVAC needs for the outer periphery require high energy efficiency HAVC systems that are capable of responding to changing thermal loads quickly. To meet these requirements, a total of 15 variable refrigerant flow (VRF) systems with 190 indoor units of various types are used. These systems are equipped with high efficiency inverter driven scroll compressors. In order to further improve the energy efficiency to meet green building certification, some VRF systems use geothermal sources. The inner periphery has a relatively constant heat and cooling load, is hence serviced by 4 absorption chillers. The core zone is occupied primarily by special laboratories, its HVAC needs are covered by three turbo chillers. This paper will begin with an architecture overview and design objectives of HVAC systems design, followed by in-depth analysis and comparisons of different HVAC systems design options in terms of energy efficiency, human comfort, and initial investment and system life cycle costs. Extensive Computational Fluid Dynamics (CFD) studies were conducted to investigate the impact of different types of indoor unit on indoor temperature and air flow distribution. This paper presents the key findings of these studies for optimal selection of indoor units.

Different indoor terminal units can be used to heat and cool indoor spaces. These terminal units mostly rely on convection and radiation heat transfer mechanisms but their relative ratios can vary significantly for air-based and water-based systems with implications on whole system performance, in terms of energy and exergy. In addition to the energy and exergy input required at the heating and cooling plants, the energy use of auxiliary components (fans and pumps) also vary depending on the chosen terminal unit.

In order to study the energy and exergy performances of air-based and water-based systems, an air heating and cooling system, and a radiant floor heating and cooling system were chosen, respectively. A single-family house was used as a case study assuming that different space heating and cooling systems were used to condition the indoor space of this house. In addition to the thermal energy and exergy inputs to the system, energy and exergy inputs to the auxiliary components were also studied. Both heating and cooling cases were considered and three climatic zones were studied; Copenhagen (Denmark), Yokohama (Japan), and Ankara (Turkey).

The analysis showed that the water-based radiant heating and cooling system performed better than the air-based system both in terms of energy and exergy input to the heating/cooling plant. The relative benefits of the water-based system over the air-based system vary depending on the climatic zone. The air-based system also requires higher auxilliary energy input compared to the water-based system and this difference is mainly due to the required air-flow rates to address the heating and cooling demands, indicating a clear benefit for the water-based system over the air-based system.

The auxilliary energy and exergy input to different systems is an important parameter for the whole system performance and its effects become more pronounced and can be studied better in terms of exergy than energy. In order to fully benefit from the water-based systems, the auxiliary energy use should be minimized.

Many engineering companies have used Revit and have already crossed the first major hurdles of implementation, standards, and productivity. However, firms are not using data and metrics from connected systems in Revit for design, coordination, and quality control. Time is being spent entering data and getting families to schedule as opposed to actually reviewing and using data in the model.

One of the larger sets of external information for a project is the HVAC cooling and heating loads. By exporting space properties (i.e. Name, No., Floor Area, etc.) from Revit thru gbXML to load & energy analysis software, data entry time and errors are reduced.  Once HVAC loads are completed the calculated results can be brought back into the Revit model. This allows a Space Airflow Schedule in Revit to be utilized by engineers to also show diffuser airflows.  Calculated airflows are calculated from the Load software. This removes the need to go to each view/sheet and edit and sum airflows. Once diffusers have airflows, then the ductwork sizes can be reviewed and adjusted by using velocity and pressure drop diagrams in Revit. These color coded ductwork diagrams can be setup to flag or highlight a section of duct that falls out of a company’s design standard tolerance range. The airflow from all the diffusers that connects to a piece of equipment is also able to be verified and checked in a Schedule against the scheduled airflow value. The gas load in a schedule for any piece of equipment can also be used to drive gas flow (CFH) thru the gas piping systems.  This process is dynamic which saves the time of adding up CFH values. Revit also provides the ability to perform ASHRAE 62.1-2007 ventilation calculations for constant volume single zone systems.  The setup is very easy at the beginning of a project and also dynamically updates if the design changes.

The calculations and design workflows outlined above are just the beginning of the potential productivity gains.  Other gains come from Fixture Unit propagation for Sanitary and Vent systems, and even the area served by roof drains.  These productivity gains require some investment time to set up workflows, schedules and views.  This investment will not only provide additional productivity and consistency, but also better quality control resulting from all of the information residing in one location.