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Kwang Ho Lee - One of the best experts on this subject based on the ideXlab platform.
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INFLUENCE OF Supply Air Temperature ON UNDERFLOOR Air DISTRIBUTION (UFAD) SYSTEM ENERGY PERFORMANCE
2015Co-Authors: Tom Webster, Kwang Ho Lee, Fred Bauman, Stefano Schiavon, Tyler Hoyt, Jingjuan Dove Feng, Alllan DalyAbstract:Underfloor Air distribution (UFAD) systems have received attention in recent years due to a number of potential advantages over conventional overhead (OH) systems. These potential advantages include increased layout flexibility, improved indoor Air quality and thermal comfort, and energy savings. In particular, energy performance advantages have been difficult to evaluate analytically due to the lack of simulation tools that accurately model the complex heat transfer processes of stratification in the room and “thermal decay” (Supply Air Temperature gain) in the underfloor plenum. Furthermore, the impact of key design and operating parameters cannot be easily determined without such tools. Fortunately, EnergyPlus v3.1 and beyond now contain validated calculation modules suitable to model these UFAD systems (U.S. DOE 2010). Elevated Supply Air Temperature is one of the distinguishing features of UFAD systems as compared to conventional overhead (OH) systems. In this paper EnergyPlus v3.1 simulations have been used to take a detailed look at the impact of variations in the Air handling unit (AHU) Supply Air Temperature (SAT) on the performance of one UFAD system commonly used in U.S. office buildings. The results indicate that raising design AHU SAT produces net savings in HVAC electricity consumption, even though cooling energy reductions trade off against fan energy increases; but the magnitude is climate dependent. However, heating energy (gas consumption) increases with increasing SAT, which tends to counterbalance decreases in electricity consumption. The paper includes a discussion of these somewhat counterintuitive findings.
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Supply Air Temperature impact in underfloor Air distribution systems under Korean climatic conditions: Energy, humidity and comfort
Energy and Buildings, 2013Co-Authors: Kwang Ho Lee, Sang-min Kim, Jong Ho YoonAbstract:Underfloor Air distribution (UFAD) systems have received increasing attention during the past decades due to potential advantages over conventional overhead (OH) forced Air systems. Among design and operating parameters, Air handling unit (AHU) Supply Air Temperature (SAT) has significant impacts on the overall UFAD performance. In this study, the detailed whole-building energy simulation program, EnergyPlus version 6.0, was used to perform the analysis on the impact of SAT on the UFAD system performance such as energy, humidity and comfort under Korean climatic condition. It turns out that raising AHU SAT causes increased HVAC energy consumption due to heating and fan energy increase despite the cooling energy reduction. The increase in the heating energy was mainly due to the increased central AHU heating coil demand increase with the higher SAT. In addition, raised SAT elevated relative humidity in the room space during the summer season due to the fact that higher SAT set-point in the central AHU was not able to sufficiently dehumidify conditioned Air compared to the lower SAT. However, the increased SAT reduced the number of hours when the occupants might feel cold during the heating season in the interior zone where the heating is not provided.
Jong Ho Yoon - One of the best experts on this subject based on the ideXlab platform.
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Supply Air Temperature impact in underfloor Air distribution systems under Korean climatic conditions: Energy, humidity and comfort
Energy and Buildings, 2013Co-Authors: Kwang Ho Lee, Sang-min Kim, Jong Ho YoonAbstract:Underfloor Air distribution (UFAD) systems have received increasing attention during the past decades due to potential advantages over conventional overhead (OH) forced Air systems. Among design and operating parameters, Air handling unit (AHU) Supply Air Temperature (SAT) has significant impacts on the overall UFAD performance. In this study, the detailed whole-building energy simulation program, EnergyPlus version 6.0, was used to perform the analysis on the impact of SAT on the UFAD system performance such as energy, humidity and comfort under Korean climatic condition. It turns out that raising AHU SAT causes increased HVAC energy consumption due to heating and fan energy increase despite the cooling energy reduction. The increase in the heating energy was mainly due to the increased central AHU heating coil demand increase with the higher SAT. In addition, raised SAT elevated relative humidity in the room space during the summer season due to the fact that higher SAT set-point in the central AHU was not able to sufficiently dehumidify conditioned Air compared to the lower SAT. However, the increased SAT reduced the number of hours when the occupants might feel cold during the heating season in the interior zone where the heating is not provided.
Christopher Yu Hang Chao - One of the best experts on this subject based on the ideXlab platform.
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Experimental study of thermal comfort in an office environment with an underfloor ventilation system
Indoor and Built Environment, 2002Co-Authors: Christopher Yu Hang ChaoAbstract:Frequent changes in arrangement in office space and the huge amount of cables brought about by the extensive use of computers make the implementation of raised flooring a necessity in modern office buildings. Underfloor ventilation systems that make use of the underfloor plenum for conditioned Air distribution will therefore increase in popularity as they extend the flexibility of building services and take advantage of the raised floor to accommodate the HVAC system. Previous research has revealed that the top return type underfloor system saves a significant amount of energy, as the Supply Air Temperature can be higher than that in a ceiling-based system. However, thermal discomfort due to Temperature non-uniformity was also reported. This paper presents the experiment results of a laboratory study of the thermal performance for a floor return (FR) type underfloor system under different heat load densities and Supply Air Temperatures. Vertical Temperature differences and Air velocities were found to be within the comfort limits stated in major international standards. The measured predicted mean vote and predicted percentage of dissatisfied values also satisfied the ISO Standard 7730. A comfortable environment was maintained by the FR type system under a dense internal heat load and with the Supply Air Temperature set at as high as 18°C.
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Experimental Study of Thermal Comfort in an Office Environment with an Underfloor Ventilation System
Indoor and Built Environment, 2002Co-Authors: M.p. Wan, Christopher Yu Hang ChaoAbstract:Frequent changes in arrangement in office space and the huge amount of cables brought about by the extensive use of computers make the implementation of raised flooring a necessity in modern office buildings. Underfloor ventilation systems that make use of the underfloor plenum for conditioned Air distribution will therefore increase in popularity as they extend the flexibility of building services and take advantage of the raised floor to accommodate the HVAC system. Previous research has revealed that the top return type underfloor system saves a significant amount of energy, as the Supply Air Temperature can be higher than that in a ceiling-based system. However, thermal discomfort due to Temperature non-uniformity was also reported. This paper presents the experiment results of a laboratory study of the thermal performance for a floor return (FR) type underfloor system under different heat load densities and Supply Air Temperatures. Vertical Temperature differences and Air velocities were found to be within the comfort limits stated in major international standards. The measured predicted mean vote and predicted percentage of dissatisfied values also satisfied the ISO Standard 7730. A comfortable environment was maintained by the FR type system under a dense internal heat load and with the Supply Air Temperature set at as high as 18degreesC. Copyright © 2002 S. Karger AG, Basel
Li Song - One of the best experts on this subject based on the ideXlab platform.
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Air-Handling Unit Supply Air Temperature Optimal Economizer Control Experiment
Volume 6: Energy Parts A and B, 2012Co-Authors: Wesley M. Thomas, Li Song, Gyujin Shim, Gang WangAbstract:Most Air handling units (AHUs) in commercial buildings have an Air economizer cycle for free cooling under certain outside Air conditions. During the economizer cycle, the outside Air and return Air dampers are modulated to seek Supply Air Temperature at its setpoint. The Supply Air Temperature is typically set at 13 °C (55 °F) to control humidity in the space. However, dehumidification is not necessary when the outside Air is dry. Meanwhile, the space may have less cooling load due to envelope heat loss and/or occupant schedule changes. These facts provide an opportunity to use higher Supply Air Temperature to reduce or eliminate mechanical cooling and terminal box reheat. On the other hand, a higher Supply Air Temperature requires increased Air flow as well as fan power. Therefore, an optimization question was formed, through which an optimal Supply Air Temperature is identified to minimize total energy consumption. In our previous studies, through simulation, 90% of energy savings were concluded and a universal control sequence was also proposed for implementing the optimal control strategy. In this paper, experiments were conducted to validate the previously documented theory concerning the optimal Supply Air Temperature reset. The previously recommended universal control sequence is implemented into the building automation system for an Air-handling unit control to make the program ready for the next step of verifying energy savings previously simulated. This paper presents optimization control system setup and experimental results showing the program tuning procedures, through which the program is ready for the next step.© 2012 ASME
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Air handling unit Supply Air Temperature optimal control during economizer cycles
Energy and Buildings, 2012Co-Authors: Gang Wang, Li SongAbstract:Abstract Most Air handling units (AHUs) in commercial buildings have an Air economizer cycle for free cooling under certain outside Air conditions. During the economizer cycle, the outside Air and return Air dampers are modulated to seek Supply Air Temperature at its setpoint. The Supply Air Temperature is typically set at 55 F (13 °C) to control humidity in the space. However, dehumidification is not necessary when the outside Air is dry. Meanwhile, the space may have less cooling load due to envelope heat loss and/or occupant schedule changes. These facts provide an opportunity to use higher Supply Air Temperature to reduce or eliminate mechanical cooling and terminal box reheat. On the contrary, a higher Supply Air Temperature requires increased Air flow as well as fan power. Therefore, an optimization question is formed, through which an optimal Supply Air Temperature is identified to minimize total energy consumption. In this paper a steady-state energy consumption model is established for AHU systems under the economizer, and then an analytical optimization method is used to seek an optimal Supply Air Temperature setpoint to minimize the energy cost. This paper presents AHU system energy modeling, Supply Air Temperature optimization, simulated energy savings, and control sequence development.
Sang-min Kim - One of the best experts on this subject based on the ideXlab platform.
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Supply Air Temperature impact in underfloor Air distribution systems under Korean climatic conditions: Energy, humidity and comfort
Energy and Buildings, 2013Co-Authors: Kwang Ho Lee, Sang-min Kim, Jong Ho YoonAbstract:Underfloor Air distribution (UFAD) systems have received increasing attention during the past decades due to potential advantages over conventional overhead (OH) forced Air systems. Among design and operating parameters, Air handling unit (AHU) Supply Air Temperature (SAT) has significant impacts on the overall UFAD performance. In this study, the detailed whole-building energy simulation program, EnergyPlus version 6.0, was used to perform the analysis on the impact of SAT on the UFAD system performance such as energy, humidity and comfort under Korean climatic condition. It turns out that raising AHU SAT causes increased HVAC energy consumption due to heating and fan energy increase despite the cooling energy reduction. The increase in the heating energy was mainly due to the increased central AHU heating coil demand increase with the higher SAT. In addition, raised SAT elevated relative humidity in the room space during the summer season due to the fact that higher SAT set-point in the central AHU was not able to sufficiently dehumidify conditioned Air compared to the lower SAT. However, the increased SAT reduced the number of hours when the occupants might feel cold during the heating season in the interior zone where the heating is not provided.
