scholarly journals The use of slotted – displacement ceiling diffuser in rooms with stationary workplaces with computer equipment

2019 ◽  
Vol 100 ◽  
pp. 00090
Author(s):  
Agnieszka Zając
Keyword(s):  
Vertical Plane ◽  
Heat Losses ◽  
Public Utility ◽  
Air Distribution ◽  
Transverse Axis ◽  
Heating And Cooling ◽  
Computer Equipment ◽  
Air Stream ◽  
Plane Passing ◽  
Winter Time

This paper presents a specification of premises with a stationary workstations. An analysis of thermal loads occurring in a public utility rooms equipped with a computer, electronic and multimedia equipment was carried out. Attention was drawn to an annual occurrence of a positive heat balances in an occupied workstations and heat losses in winter time in unoccupied premises. For an air distribution a slotted displacement ceiling diffuser was proposed, used for mixing ventilation (MV) in up-up type of air exchange in room. The results of measurements in the form of air flows in the area of its operation are provided. The graphs show the graphical distribution of air velocities and temperatures in the vertical plane passing through the transverse axis of the air diffuser. The study focused on one of the representative airflow of supply air and the behaviour of the air stream during heating and cooling was presented.

scholarly journals The slotted – displacement ceiling diffuser as an alternative to the organization of down – up air exchange in rooms with computer equipment

2018 ◽  
Vol 44 ◽  
pp. 00198 ◽  
Author(s):  
Agnieszka Zając
Keyword(s):  
Vertical Plane ◽  
Public Utility ◽  
Heat Sources ◽  
Displacement Ventilation ◽  
Computer Equipment ◽  
Air Temperatures ◽  
Air Stream ◽  
Plane Passing ◽  
Heat Loads ◽  
Air Exchange

The article analyses heat loads occurring in public utility rooms with computer or multimedia equipment. Attention has been paid to the possibility of using down – up type (displacement ventilation, DV) and up – up type (mixing ventilation, MV) of air exchange. The design of the slotted – displacement ceiling diffuser is presented. The results of measurements in non-isothermal conditions in the form of air flows in the area of its operation are provided. The graphs show the graphical distribution of velocities and air temperatures in the vertical plane passing through the transverse axis of the special diffuser. The study of the behavior of the stream flowing out of the diffuser was only in the scope of work. The velocity and air temperature distribution over the heat sources, which were located away from the diffuser, next to the external walls, was not studied. The focus was on three representative airflows of supply air and the behaviour of the air stream during cooling was presented.

scholarly journals Some Aspects of HVAC Design in Energy Renovation of Buildings

2021 ◽  
Author(s):  
Taghi Karimipanah
Keyword(s):  
Renewable Energy ◽  
Air Conditioning ◽  
Distribution Systems ◽  
Energy System ◽  
Building Energy ◽  
Hvac Systems ◽  
Heat Losses ◽  
Energy Sources ◽  
Air Distribution ◽  
Building Energy System

It is well-known fact that air conditioning systems are responsible for a significant part of all energy systems in building energy usage. In EU buildings, the building HVAC systems account for ca 50% of the energy consumed. In the U.S., air-conditioning accounts on average about 12% of residential energy expenditures. The proper choice of air distribution systems and sustainable energy sources to drive the electrical components have a vital impact to achieve the best requirements for indoor climate including, hygienical, thermal, and reasonable energy-saving goals. The building energy system components that have a considerable impact on the demand for final energy in the building are design, outdoor environment conditions, HVAC systems, water consumption, electrical appliances, indoor thermal comfort, and indoor human activities. For calculation of the energy balance in a building, we need to consider the total energy flows in and out from the building including ventilation heat losses, the perimeters transmission heat loses, solar radiation, internal heat from occupants and appliances, space and domestic water heating, air leakage, and sewage heat losses. However, it is a difficult task to handle the above time-dependent parameters therefore an energy simulation program will always be used. This chapter aims to assess the role of ventilation and air-conditioning of buildings through the sustainability approaches and some of the existing renewable energy-based methods of HVAC systems are presented. This comprehensive review has been shown that using the new air distribution systems in combination with renewable energy sources are key factors to improve the HVAC performance and move toward Nearly Zero Carbon Buildings (NZCB).

Numerical Simulation of Convective-Radiative Heat Transfer in a Solar Chimney

2014 ◽  
Author(s):  
Bernardo Buonomo ◽  
Oronzio Manca ◽  
Sergio Nardini ◽  
Gianluca Tartaglione
Keyword(s):  
Kinetic Energy ◽  
Electrical Power ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Three Dimensional Model ◽  
Solar Chimney ◽  
Ansys Fluent ◽  
Heating And Cooling ◽  
Air Stream

Solar chimney is a new method to produce electrical power. It employs solar radiation to raise the temperature of the air and the buoyancy of warm air to accelerate the air stream flowing through the system. By converting thermal energy into the kinetic energy of air movement, solar chimneys have a number of different applications such as ventilation, passive solar heating and cooling of buildings, solar-energy drying, and power generation. Moreover, it can be employed as an energy conversion system from solar to mechanical. A component, such as a turbine or piezoelectric component, set in the path of the air current, converts the kinetic energy of the flowing air into electricity. In this paper, a numerical investigation on a prototypal solar chimney system integrated in a south facade of a building is presented. The chimney is 4.0 m high, 1.5 m wide whereas the thickness is 0.20 m for the vertical parallel walls configuration and at the inlet 0.34 m and at the outlet 0.20 m for convergent configuration. The chimney consists of a converging channel with one vertical wall and one inclined of 2°. The analysis is carried out on a three-dimensional model in airflow and the governing equations are given in terms of k-ε turbulence model. The problem is solved by means of the commercial code Ansys-Fluent. The numerical analysis was intended to examine the effect of the solar chimney’s height and spacing. Further, comparison between radiative and non-radiative model is examined and discussed. Results are given in terms of wall temperature distributions, air velocity and temperature fields and transversal profiles for a uniform wall heat flux on the vertical wall equal to 300 W/m2. Thermal and fluid dynamics behaviors are evaluated in order to have some indications to improve the energy efficiency of the system.

scholarly journals Investigation on Relative Heat Losses and Gains of Heating and Cooling Networks

2021 ◽  
Vol 25 (1) ◽  
pp. 479-490
Author(s):  
Violeta Madan ◽  
Ingo Weidlich
Keyword(s):  
District Heating ◽  
Energy System ◽  
Heat Losses ◽  
Heat Sources ◽  
Temperature Level ◽  
Near Surface ◽  
Heating And Cooling ◽  
Surface Soil Temperature ◽  
Steady State Heat ◽  
Sustainable Energy System

Abstract The integration of district heating (DH) and cooling (DC) in the sustainable energy system of the future requires a significant reduction in operating temperatures. Supply temperatures below 70 °C are required for new 4th Generation DH. Main benefits are the use of low exergy heat sources and the reduction of heat losses. The reduction of heat losses is achieved by reducing the driving temperature difference between the medium pipe and the ground. The decrease of the return temperature level is limited by the consumer behaviour and the ground temperature level. As a consequence, the reduction of the supply temperature is accompanied by a reduction of the maximum transmittable heat flow. For energy efficiency and economic reasons, the relative heat losses are therefore an important design value for DH networks. The study proposes an approach to estimate the relative heat losses by using steady-state heat loss models and analyses the values for different DH generations. In particular, due to the rising of the near-surface soil temperature, the relative cold losses are also studied.

scholarly journals A Transient Method for Determining Thermal Diffusivity of Tobacco Stems

1989 ◽  
Vol 14 (5) ◽  
pp. 321-326
Author(s):  
NN Barthakur ◽  
NP Arnold
Keyword(s):  
Thermal Diffusivity ◽  
Cooling Curves ◽  
Microwave Generator ◽  
Unsteady State ◽  
Transient Method ◽  
Flow Rates ◽  
Heating And Cooling ◽  
Air Stream ◽  
Stem Temperature

AbstractA microwave generator and a closed-circuit wind tunnel were used to measure the thermal diffusivity of tobacco (Nicotianatabacum L.) stems in vivo by the unsteady-state method. A simple mathematical model for heat flow, based on Fourier's heat-conduction equation and Newton's law of cooling, was used in this study. The microwave method was found to be relatively rapid as both heating and cooling of a cylindrical stem in an air stream could be completed in approximately 30 minutes for thermal-diffusivity determinations. Thermal-diffusivity value of the tobacco stems, containing 94 % moisture and a mean stem temperature of 30°C, was found to be (1.38 ± 0.06) × 10-7 m2 s-1. The coefficient of variation for the measurements did not exceed 1.4 % as determined through the analysis of cooling curves for five different air-flow rates over the stems. This study showed that the microwave technique could be effectively used to determine both accurately and reliably the thermal diffusivity of tobacco stems in vivo.

Using POD to Characterise Panel Backside Heat Losses

2014 ◽  
Author(s):  
A. F. Emery
Keyword(s):  
Composite Structures ◽  
Heat Losses ◽  
Short Paper ◽  
Alternative Analysis ◽  
Temperature Variations ◽  
Metal Structures ◽  
Repair Site ◽  
Heating And Cooling ◽  
High Thermal Resistance ◽  
Proper Orthogonal

Repairing composite structures requires heating the repair site to a specific temperature and holding it at this temperature for a length of time. This is usually accomplished by placing a heating blanket over the repair site or by thermally radiating it. In either case, significant heat conduction occurs through the composite repair zone resulting in spatial variations in temperature. In general, one has access only to one side of the structure and is not aware of the specific nature of conditions on the backside. It is not uncommon for the backside structure in the neighborhood of the repair site to be such that the heat transfer is inhibited by pockets of trapped air or increased by metal structures. If the applied heat can be spatially controlled it is possible to eliminate temperature variations in the repair zone. This short paper describes attempts to estimate backside heat losses, or at a minimum to detect the presence/magnitude of these losses. Early attempts to estimate these losses by parameter estimation proved not to be adequate. The test was modified to include a backside heat sink, but thermocouple measurements suggested that there was negligible effect. The use of proper orthogonal decomposition of thermographic images taken during heating and cooling was considered as an alternative analysis. The POD indicated that there was no substantial heat loss to the sink because of the high thermal resistance of the panel. Given this finding, it appears that eliminating spatial temperature variations can only be done by active control of the heat source.

scholarly journals The Right Amount of Technology in School Buildings

2020 ◽  
Vol 12 (3) ◽  
pp. 1134 ◽  
Author(s):  
Thomas Auer ◽  
Philipp Vohlidka ◽  
Christine Zettelmeier
Keyword(s):  
Energy Demand ◽  
Age Groups ◽  
Heat Losses ◽  
School Buildings ◽  
School Construction ◽  
Passive House ◽  
Technical Aspects ◽  
Heating And Cooling ◽  
The Right ◽  
Indoor Comfort

What is an adequate school building nowadays and which amount of technology does it need? How high is the indoor comfort in terms of thermal, visual, hygienic, and acoustical comfort? Are there technical aspects that stand out to other solutions? How do users feel and act in the buildings? For this purpose, the Chair compared, in total, twelve selected modern, older, and renovated school buildings from different building age groups. For the comparison, it was essential to intensively analyze each of the twelve schools. This included visiting the schools, talking with the participating architects, specialist planners, builders, and school managers, procuring and analyzing planning documents and, where available, publications and reports, performing simulations and measurements in the classrooms, and surveying the buildings’ users. The predominant energy demand in schools is the energy expenditure for heating and cooling the air, especially for heating the air in the winter. Nevertheless, it turns out that from a purely energy-focused perspective, mechanical ventilation cannot be justified. It is also evident that transmission heat losses play a negligible role in school construction, which is why the “passive house” as a goal for renovations must be called into question.

A Hydrodynamic Study of the Oscillation Motion in Swimming

1988 ◽  
Vol 4 (1) ◽  
pp. 21-37 ◽  
Author(s):  
Yi-Chung Pai ◽  
James G. Hay
Keyword(s):  
Vertical Plane ◽  
Mass Effect ◽  
Flow Conditions ◽  
Transverse Axis ◽  
Low Frequencies ◽  
Competitive Swimming ◽  
High Frequencies ◽  
Fluid Forces ◽  
Static Approach ◽  
Hydrodynamic Study

The purpose of this study was to determine the validity of the quasi-static assumption—that fluid forces exerted under unsteady flow conditions are equal to those exerted under similar steady flow conditions—in the case of a cylindrical model oscillating in a vertical plane about a transverse axis normal to the flow. The findings indicated that the quasi-static approach is applicable only to cyclic motions with low frequencies and small accelerations. For swimming motions that involve high frequencies and high accelerations, like those that occur in competitive swimming, the vortex shedding effect and the added mass effect must be taken into account if accurate values are to be obtained for hydrodynamic forces.

Location of the Centre of Resistance for the Nasomaxillary Complex Studied in a Three-Dimensional Finite Element Model

1995 ◽  
Vol 22 (3) ◽  
pp. 227-232 ◽  
Author(s):  
Kazuo Tanne ◽  
Susumu Matsubara ◽  
Mamoru Sakuda
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Sagittal Plane ◽  
Three Dimensional ◽  
Vertical Plane ◽  
Element Model ◽  
Occlusal Plane ◽  
Dimensional Finite Element ◽  
Plane Passing ◽  
Three Dimensional Finite Element

The purpose of this study was to investigate the location of the centre of resistance (CRe) for the nasomaxillary complex by the use of finite element analysis. A three-dimensional finite element model of the craniofacial complex, consisting of 2918 nodes and 1776 elements, was used for displacement analyses. Anteriorly and inferiorly directed forces of 9·8 N were applied at five different levels, parallel and perpendicular to the functional occlusal plane, respectively. For each loading condition, horizontal and vertical displacements of eight anatomic points in the complex and on the maxillary dentition were analysed. The complex exhibited an almost translatory displacement of approximately 1·0 µm in the forward direction when the horizontal force was applied at a point on the horizontal plane, passing through the superior ridge of the pterygomaxillary fissure, whereas the complex experienced clockwise or counter clockwise rotation when the forces were applied at the remaining levels. Furthermore, the downward forces produced anteriorly upward, or posteriorly upward rotation. However, the force applied at a point on the vertical plane passing through the posterior wall of the pterygomaxillary fissure, produced almost equal displacements of approximately 6·0 µm in an inferior direction for all the anatomic points. It is suggested that CRe of the nasomaxillary complex is located on the posterosuperior ridge of the pterygomaxillary fissure, registered on the median sagittal plane.

scholarly journals Trombe Wall Application with Heat Storage Tank

2019 ◽  
Vol 5 (7) ◽  
pp. 1477-1489 ◽  
Author(s):  
Kıvanç Topçuoğlu
Keyword(s):  
Reinforced Concrete ◽  
Heat Storage ◽  
Heat Losses ◽  
Paraffin Wax ◽  
Concrete Wall ◽  
Heating And Cooling ◽  
Reinforced Concrete Wall ◽  
Trombe Wall ◽  
Wall System ◽  
Heat Store

In this study, an investigation was made of the performance of a Trombe wall of classical structure used together with a heat store. Most Trombe walls are able to supply the heating needs of a space to which they are connected without the need for extra heating at times when the sun is shining. However, the heat obtained from the Trombe wall can be in excess of needs at such times, and measures must be taken to provide ventilation to the heated space. It is thought that the heat energy can be used more efficiently and productively by storing the excess heat outside the building and using it inside the building when there is no sunlight. To this purpose, a tank full of water and marble was built as a heat store as an alternative to the general Trombe wall design, and an attempt was made to minimise heat losses by burying it in the ground. It was concluded that in place of a traditional Trombe wall system using a massive wall heat store, a heat store could be constructed in a different position and with different materials. The Trombe wall system which was developed and tested met up to 30% of the energy needed for heating and cooling the building, and reduced the architectural and static disadvantages of Trombe wall systems. As a result of the study, it was seen that where a standard reinforced concrete wall could supply heat to the inside for 7 hours and 12 minutes, the figure for a wall made of paraffin wax was 8 hours and 55 minutes. In the same study, the heat storage thickness of a reinforced concrete wall was calculated as 20 cm, while that of a paraffin wax wall was calculated as 5 cm.

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