Floor Air Distribution System Research Articles

The SPA-TOPSIS-Based Evaluating Approach on Thermal Sensation Model at Different Vane Angles in UFAD–DV System

Under floor air distribution system and displacement ventilation (UFAD–DV) system is used to provide comfortable indoor thermal environment in summer, which largely satisfies overall and local thermal sensation. In UFAD–DV system, the selection of supply vane angle is particularly important to achieve the best thermal comfort. This paper studied thermal sensation of a manikin in sedentary state through the AIRPAK simulations. Firstly, in order to analyze the influence of the local thermal sensation on overall thermal sensation (OTS), the manikin model consisting of five local body parts was constructed. Then, the set pair analysis technique for order preferences by similarity to an ideal solution (SPA-TOPSIS) method was proposed to analyze the overall thermal sensation model and the combination model of overall and local thermal sensation at different supply vane angles. Finally, according to the SPA-TOPSIS analysis, the combination model of overall thermal sensation and local thermal sensation was determined and the best supply vane angle was 10° downward. The PMV and PPD values of each part of the body and overall body were 0.1932, 0.3413, 0.2287, 0.0503, − 0.0992, 0.173 and 5.9721, 7.5005, 6.377, 5.2632, 5.2579, 6.79, respectively. The weight coefficient method was used for the validation of SPA-TOPSIS-based evaluating results with p < 0.05. In addition, the thermal sensation of foot has important impact on thermal sensation, and the ideal integrated thermal sensation of five local body parts and overall body was achieved. The proposed SPA-TOPSIS-based evaluation approach can determine the best supply vane angle, which optimizes the OTS on the premise of satisfying the local thermal sensation.

A Study on Energy Saving Performance by Night Purge Cooling with Pressurized Under Floor Air Distribution System

A Study on Energy Saving Performance by Night Purge Cooling with Pressurized Under Floor Air Distribution System

A Review on Airflow and Temperature Distribution in A Residential Building with an under Floor Air Distribution System

A Review on Airflow and Temperature Distribution in A Residential Building with an under Floor Air Distribution System

Study on Thermal Behavior of an Experimental Low-energy Building in the Hot Summer and Cold Winter Zone of China

This paper is based on a study of the expansion part of the architecture department building in Huazhong University of Science and Technology (hereinafter referred to as the experimental building). Thermal environment parameters, building energy consumption and other aspects of the experimental building are monitored. The results show that indoor air temperature can be improved to about 14°C in winter and 28°C in summer by the thermal regulation system, which was limited by the underground soil temperature in Wuhan. Because of the function of the under floor air distribution system, an uneven air temperature distribution is formed in the experimental building. The building energy consumption is 10.7kWh/(m2*a), much lower than the ordinary office buildings in Wuhan. In general, the experimental building can achieve a certain indoor thermal environment with low energy consumption, meeting the requirements of buildings with no-strict thermal comfort demands in the rural areas of hot summer and cold winter zone of China. A heat pump or auxiliary heating/cooling source should be added in the system to achieve a more comfortable indoor environment.

Producing a better performance for the under floor air distribution system in a dense occupancy space

This study deals with the possibility of the under floor air distribution system usage in a dense occupied space (80 occupants) regarding to the general thermal comfort conditions of occupants, local thermal discomfort, and indoor air quality. Computational fluid dynamics methods are used to predict general thermal comfort conditions of occupants, local thermal discomfort, and indoor air quality in this space. Different locations for the diffusers and velocities of the supply air are varied to determine what produces a better performance for the under floor air distribution system. It is found that when the diffusers are installed under seats, higher temperatures are measured at relatively lower heights due to the impedance in the injection of the fresh air supply. Moreover, the mean local age of air, as indoor air quality index, is increased by reducing the supply air velocity, which means that there is a less fresh air in the breathing zone of occupants. However, general thermal comfort conditions and local thermal discomfort should be considered as determining factors in each study. Based on the overall results of the study, under floor air distribution system is capable of creating a comfortable indoor environment in a dense occupied space.

A Comparative Study of Leakage Characteristics between an Under Floor Air Distribution System and an Over Head Air Distribution System

This research aims at quantifying the leakage occurring in Under Floor Air Distribution (UFAD) systems and Over Head Air Distribution (OHAD) systems. The study also classifies the leakage occurring in the different systems into Category 1 leakage and Category 2 leakage. The study was performed between a plenum supply UFAD system (having a maximum flow rate of 1272 m3/h), a ducted supply UFAD system (having a maximum flow rate of 286 m3/h) and an OHAD system (having a maximum flow rate of 2004 m3/h). Results show that in plenum supply UFAD systems, 5.9% and 14.8% of the volume of air supplied by the Air Handling Unit (AHU) is attributed to leakage when the AHU is running at 50% and 100% fan speeds respectively. In ducted supply UFAD systems however, the leakage drops to 2.1% and 5.6% respectively at 50% and 100% AHU fan speeds. A ducted supply UFAD system in comparison to a plenum supply UFAD system lowers leakage by 62.2% when the AHU is operating at 100% fan speed and by 64.4% when the AHU is operating at 50% fan speed.

Effects of return air vent height on energy consumption, thermal comfort conditions and indoor air quality in an under floor air distribution system

In this article, an under floor air distribution (UFAD) system with separate return and exhaust air vents is investigated. The proper angle of the swirl inlet diffuser is selected by comparing the general thermal comfort conditions obtained from three different inlet angles. At this proper inlet angle, the effects of return air vent height on energy consumption, thermal comfort conditions, and indoor air quality (IAQ) are investigated. To this end, thermal comfort indices (PMV–PPD), local thermal discomfort index (temperature gradient in vertical direction), and IAQ index (mean local age of air) are probed by CFD methods. Energy consumption reduction in an UFAD system equipped with a return air vent compared to MV system is 10.9, 15.3, 18.9, and 25.7% when the return air vent height is set at 2.0, 1.3, 0.65, and 0.3m, respectively. Reducing the height of return air vent from ceiling to floor leads to an increase in exhaust air temperature and temperature gradient at the vertical direction. It is found that selection of the 1.3m height from floor (upper boundary of occupied zone in seated mode) for return air vent height will cause a 15.3% reduction in energy consumption and would maintain the thermal comfort and IAQ in the specified range.

Prediction of thermal comfort, IAQ, and energy consumption in a dense occupancy environment with the under floor air distribution system

The objective of this study is to investigate an under floor air distribution (UFAD) system with combined and separate return and exhaust air vents regarding thermal comfort, indoor air quality (IAQ), and energy consumption. This ventilation system is used in a large indoor environment (dense occupancy), and two common types of inlet diffusers (direct and swirl) are used. Computational fluid dynamics (CFD) methods are used to predict thermal comfort conditions of occupants, IAQ, and energy consumption in this space. Based on the results, direct inlet diffusers cannot lead to an acceptable temperature gradient in vertical direction in none of the examined return air vent positions, but swirl inlet diffusers can lead to an acceptable one. By precisely considering thermal comfort conditions, and IAQ made by swirl inlet diffusers, opting the upper boundary of the occupied zone (1.7 m) for return air vent position (which is the optimum case study among all the examined case studies) can lead to the best results. Moreover, the optimum return air vent position in this UFAD system can result to 10.5 percent reduction in the amount of energy consumption compared to the mixing ventilation system.

Effect of supply air temperature on conservation of energy in air conditioning of space

In HVAC applications, huge amount of energy is utilized in fans and blowers to maintain the flow. In this paper energy savings associated with air distribution is discussed. In a most commonly used air distribution system, uniform thermal environment in the occupied space is established. An alternative to this method is the under floor air distribution system (UFAD) which is in its fantasy state. Thermal stratification can be established in this method due to the buoyancy flow of the air. In this paper assessment of the impact of temperature sensors in energy savings is done in UFAD system. It is observed that by the placement of temperature sensors in the occupied space, supply air temperature can be controlled while maintaining the comfort conditions. By optimal conditions of the temperature and volume flow, energy savings can be achieved due to reduction in energy requirements in refrigeration and ventilation. The comfort criteria of ASHRAE standard 55-92 is taken.

Experimental Study on Indoor Thermal Stratification in Large Space by under Floor Air Distribution System (UFAD) in Summer

A ventilation method of down-supply up-return has grown popular in large space in recent years for comfort ventilation with low thermal load, especially in China, including gymnasium, factory space, and exhibition hall, etc. The undisturbed flow pattern in the space gives a gradient in temperature, and the vertical thermal stratification appears markedly in large space. The object for this paper is to understand the behaviour of an under floor air distribution system in a ventilated space. The thermal stratification characteristics in a real UFAD experimental space were measured. The effects of different supply conditions on the thermal stratification characteristics are investigated based on the experimental results. The relations between space air stratification and the control parameter is predicted. It can be indicated that there are 4 zones composing the vertical thermal stratification. And different zone has different control parameter.

A model for an under floor air distribution system

We present a simplified model of an underfloor air distribution (UFAD) system consisting of a single source of heat and a single cooling diffuser in a ventilated space. Laboratory experiments were carried out to simulate the flow and a model for the flow in this space is proposed. The model is based on plume theory for the heat source and a fountain model for the diffuser flow, and predicts a steady-state two-layer stratification in the room. The governing parameters are shown to be the buoyancy flux of the heat source, and the volume and momentum fluxes of the cooling diffuser. The results suggest ways to optimize UFAD design and operation.