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What are mechanical systems?
Published in Samuel L. Hurt, Building Systems in Interior Design, 2017
The refrigerant compressors that provide the cooling for cooling systems can be air-cooled or water-cooled. Most people are familiar with air-cooling because that is what most people have at home. Air-cooling means that the compressor has a fan (a large fan, relative to the size of the compressor) that pulls a large amount of air across the condenser coil and the compressor, thereby putting the heat that has been removed from inside the building into the atmosphere and cooling the compressor in the process. This is why the typical outdoor “air-conditioner” (actually called an Air-Cooled Condensing Unit, or ACCU) is noisy and blows lots of hot air around. But large commercial systems can use ACCUs too, including chillers, so ACCUs can be as small as the one at someone’s small house or 30′ 0″ long, 10′ 0″ wide, and 6′ 0″ tall (or even bigger). A dry cooler is another form of air-cooling, but it is indirect because the cooler only cools water in a loop, which is then used to cool indoor compressors (this is one form of a “geothermal” system; geothermal is used incorrectly here though. Such a system is really an “earth-coupled” system). Air-to-air heat pumps are simply ACCUs that can run backwards to provide heating; unfortunately, typical equipment like this becomes highly inefficient in heating below 30 °F or so, but they are air-cooled compressors all the same. The latest technology is VRF (or VRV) which is a large outdoor air-cooled heat pump (often called a heat-recovery unit) that serves multiple indoor zones.
Variable Volume Systems
Published in Samuel C. Sugarman, HVAC Fundamentals, 2020
There are several names for variable volume refrigerant systems. I’ll use the generic term variable refrigerant flow (VRF) which refers to the ability of the system to control the amount of refrigerant flowing between indoor units (evaporators) and outdoor units (condensers, Figure 9-7). In other words, in a VRF system varying amounts of refrigerant is piped to an indoor unit to heat or cool the conditioned space and then back to a condensing unit. VRF systems are either two- or three-pipes.
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Published in Clark W. Gellings, The Smart Grid: Enabling Energy Efficiency and Demand Response, 2020
VRF technology uses smart integrated controls, variable-speed drives, refrigerant piping and heat recovery to provide products with attributes that include high energy efficiency, flexible operation, ease of installation, low noise, zone control and comfort using all-electricity technology.
Local vs. integrated control of a variable refrigerant flow system using artificial neural networks
Published in Science and Technology for the Built Environment, 2020
Kiuhn Ahn, Kyung Jae Kim, Kwanwoo Song, Cheol soo Park
A variable refrigerant flow (VRF) system is generally composed of one outdoor unit and several indoor units. The outdoor unit changes its capacity by varying the discharged refrigerant mass flow rate through an inverter-driven variable speed compressor in order to meet required cooling or heating loads (Aynur 2010). A schematic drawing of a typical VRF system is shown in Figure 1. The refrigerant mass flow rate is regulated by an electronic expansion valve (EEV) located in each indoor unit according to the difference between a zone air temperature and a zone air set-point temperature (Aynur 2010) (Figure 1). With recent advances of inverter-driven technology, VRF systems have been favored because of their convenient installation, easy maintenance, centralized management, and flexible layout (Tu et al. 2016). In cooling mode, the refrigerant discharged from a compressor enters a condenser (an outdoor unit heat exchanger) through a four-way valve (Aynur 2010). The pressurized refrigerant is then throttled to a low pressure through an EEV and enters an evaporator located in an indoor unit. Then, the refrigerant returns back to the compressor and the refrigeration cycle ends. In heating mode, the flow path of the refrigerant is reversed via the four-way valve (Figure 1). Specifically, individual zone control and switchover between cooling and heating operation modes are the main reasons for the widespread use of VRF systems in buildings such as offices, schools, retail space, and hotels (Lin et al. 2015; Yun, Lee, and Kim 2017).
Mode switching control for a multi-functional variable refrigerant flow system
Published in Science and Technology for the Built Environment, 2018
Liujia Dong, Yaoyu Li, John M. House, Timothy I. Salsbury
Variable refrigerant flow (VRF) air-conditioning systems feature multi-split ductless configurations using one outdoor unit (ODU) and multiple indoor units (IDUs; Park et al. 2001). Using a variable capacity compressor and electronic expansion valves (EEV), a VRF system can control the refrigerant flow to the evaporators of multiple IDUs, thus enabling operation of individual zoning with variable capacities. VRF systems offer many advantages, such as elimination of duct loss from air distribution, design and installation flexibility, compactness, integrated controls, quiet operation, and reduced maintenance cost (Goetzler 2007; Lin et al. 2015a). The so-called multi-functional variable refrigerant flow (MFVRF) system enables simultaneous heating and cooling via the mode change unit (MCU), which is effectively a valve array that regulates the refrigerant flow through the IDUs (Aynur 2010; Masuda et al. 1991; Xia et al. 2002) to achieve five possible operation modes: (1) cooling-only; (2) heating-only; (3) cooling-dominated; (4) heating-dominated; and (5) heat recovery (Hai et al. 2006; Jiang et al. 2014a, 2014b; Shi et al. 2003; Xia et al. 2004). Joo et al. (2011) studied the performance of various modes of a MFVRF system having four IDUs all operating at part-load conditions. Kwon et al. (2014) studied a MFVRF system in heating and shoulder seasons. Lin et al. (2015b) presented an experimental study of a MFVRF system operated in heat recovery mode with a water heating system, which demonstrates performance improvement with increased heat recovery ratio and compressor efficiency.
Development of TRNSYS model for energy performance simulation of variable refrigerant flow air-conditioning system combined with energy recovery ventilation
Published in International Journal of Green Energy, 2021
The necessity for green energy usage on building energy consumption is becoming more demanding these days. The reason why every building constructed or renovated to become a so-called “green building” is to reduces the detrimental impact for these buildings on natural energy sources and to achieve sustainable development, which is one of the leading goals of the organization of the united nations (Tariq et al. 2019). The impact of the HVAC (Heating, Ventilation, and Air Conditioning) systems on buildings has a strong effect on building energy consumption. Implementing an efficient HVAC system has a key role in saving energy toward a green building. Therefore, a VRF (Variable Refrigerant flow) is considered an efficient HVAC system to be used in buildings to become more sustainable.