JOURNAL OF THEORETICAL AND APPLIED MECHANICS

Volume 29 Number 2 1999
CONTENTS


P. O. Fanger.

Laboratory of Heating and Air-conditioning
Department of Energy Engineering,
Technical University of Denmark,
Building 402, DK--2800 Lyngby, Denmark

Ventilation for Humans: History and Future

Abstract. Over the last two hundred years, dramatic paradigm shifts have taken place in the philosophy behind ventilation. Why are we ventilating buildings and how much ventilation is required? These are the fundamental questions with which engineers, architects and hygienists are faced. The paper will review the thinking behind the very different answers that have been given to these questions in the past. Models used in new ventilation standards in progress will also be discussed, including the addition of sensory pollution sources, the acknowledgement of building materials and tobacco smoke as pollution sources, and the impact of filtration, temperature and humidity on required ventilation. Comprehensive changes in Heating Ventileting and Air-Conditioning (HVAC) technology will take place. A future paradigm shift is foreseen where indoor air is designed not only to be acceptable and to limit dissatisfaction, but also to be perceived as pleasant, fresh and stimulating.

Key words: indoor air quality, pollution sources, ventilation for humans.



S. Allwinkle.

Department of Building and Surveying,
Faculty of Engineering, Napier University,
Edinbourgh, Scotland

Energy Efficiency in Buildings: Fabric and Ventilation

Abstract. Houses are being consciously built to be more airtight in order to be energy efficient and this has been facilitated through more advanced construction techniques. As a result, natural air infiltration can no longer be relied on totally to adequately ventilate the house to ensure the comfort of the occupants and the structural integrity of the building. However, this poses problems of determining the minimum ventilation rate necessary to achieve this purpose.

As most of the housing stock is in existence, it is important that ventilation rates are established to ensure that any retrofit work does not produce adverse conditions. This paper presents some results of research work in the United Kigdom (UK) relating to the ventilation and air leakage through the building fabric.

While the total number of houses involved in the work reported here is small, the results suggest that a substantial fraction of the existing UK dwelling stock could, in principle, be made air-tight enough to justify the use of continuous mechanical ventilation on energy grounds. However, this may be significantly more difficult to achieve in dwellings built since 1970 due to changes in the method of wall construction.

Key words: energy efficiency in buildings, air tightness, condensation, heat recovery.



S. Stamov.

Present State and Perspertives of Design Practice of Heating Ventilating and Air-Conditioning Systems in Bulgaria

Department of Hydroaerodynamics and Hydraulic Machines,
Technical University of Sofia,
8, St. Kl. Ohridski Str., 1000 Sofia, Bulgaria

Abstract. The energy consumption for Heating, Ventilating, Air-Conditioning (HVAC) and hot water supply of residential and public buildings has a considerable share in the whole energy balance of Bulgaria (up to 27%). The tendency is towards increasing that share. At the same time there is a shortage of local energy sources. Import of petrol, gas, coal, and nuclear fuel meets over 70% of the existing demand. An analysis is made of standards and decrees for designing and evaluating HVAC systems and thermal insulation. The energy efficiency of residential or public buildings is represented as a measure for the optimal energy consumption in the process of construction, utilisation and maintenance. The outdoor and indoor influence can be determined by using the software package for Heat Analysis of Building Constructions, based on numerical modelling. The difficulties in handling the input data are overcome mainly by the use of a Generator of Finite Elements Mesh (GFEM). GFEM approximates two-dimensional areas with triangular simplex elements in an automatic mode. Practically this is an analogue to digital conversion of areas confined by rectilinear and curvilinear boundaries. The problem of generating arbitrary plane meshes is solved by using the possibilities of the subsystem for modifying the generated mesh. In an interactive mode of operation, the user can alter the mesh dynamically and combine its components in an appropriate manner.

Key words: design practice of HVAC systems, heat analysis of building constructions.



A. K. Melikov.

The Indoor Thermal Environment: International Standards and Considerations on the Design of HVAC Systems

Laboratory of Heating and Air-conditioning,
Department of Energy Engineering,
Technical University of Denmark,
Building 402, DK-2800 Lyngby, Denmark

Abstract. The main purpose of Heating, Ventilating and Air-Conditioning (HVAC) systems is to provide occupants with comfortable and healthy indoor climate. Investigations indicate strong evidence that workers performance and productivity depend on the indoor environment. In the present paper the requirements and methods for assessment of indoor thermal environment included in the most used standards, ISO Standard 7730 and ASHRAE standard 55 are discussed as well as requirements considered for inclusion in future standards. The design steps of HVAC systems and the role of all parties involved in creating acceptable indoor climate, i.e. architects, HVAC engineers, owners/managers and users is discussed briefly as well.

Key words: indoor thermal environment, design of HVAC systems.



P. Stankov.

CFD Predictions of Air Flow in a Ventilated Room as a Tool for Engineering Design

Department of Hydroaerodynamics and Hydraulic Machines,
Technical University of Sofia,
8, St. Kl. Ohridski Str., 1000 Sofia, Bulgaria

Abstract. The paper presents an analysis of Computational Fluid Dynamics (CFD) predictions of air flow in ventilated rooms with respect to the possibilities and limitations for CFD to be used as a tool for engineering design. The analysis also concerns other advanced methods for investigation and design of ventilated rooms. The possibilities of CFD predictions are demonstrated by numerical results concerning typical flow parameters i.e. velocity field, temperature field, ``local mean age'', etc. in an office room. Future perspectives of CFD predictions in ventilated rooms are also concerned. Comments on design practice are made in respect of the improvement of both the design process and energy efficiency of ventilation. Aspects of coordination between researchers and designers are also discussed.

Key words: CFD prediction, ventilated room, design practice.



J. A. Denev.

Why Do We Need the Computational Fluid Dynamics in Room Ventilation? Comments and Examples

Department of Hydroaerodynamics and Hydraulic Machines,
Technical University of Sofia,
8, St. Kl. Ohridski Str., 1000 Sofia, Bulgaria

Abstract. The Computational Fluid Dynamics (CFD) offers a powerful tool for the solution of different types of practical problems in ventilated rooms. However, the everyday practical use of CFD is rather limited and one reason for that is the restricted knowledge about the possibilities this tool offers. The present paper makes an attempt to popularize CFD and to demonstrate its natural use for the solution of practical problems. The example chosen concerns the flow conditions in rooms with cupboards. Such flows possess very complex aerodynamics and many parameters have an influence on the flow patterns. Hence, as shown by the literature review, the rules for ventilation of such rooms are always restricted to general recommendations. Thus, for every particular practical case additional investigation is required of the influence of the room flow on the performance of the cupboards positioned inside. CFD computations are very suitable for such investigations and offer the opportunity to evaluate qualitatively and quantitatively the aerodynamic processes in the room and their influence on the performance of the cupboards. CFD-supported parametric numerical studies also allow to gain basic knowledge about these aerodynamic processes. This basic theoretical knowledge could be used in analogy to other similar room flow conditions without the need for performing additional computations. An example for the latter is given in the present paper. It concerns the use of a numerically based flow analysis for the solution of a practical problem in a real industrial room.

Key words: CFD, industrial ventilation, fume cupboards.



 P. Stankov, J. Denev, P. Spassov, S. Raychev, Z. Domuzov.

The Role of Computer Simulation in Designing a New Industrial Air-Conditioning System

P. Stankov, J. Denev
Department of Hydroaerodynamics and Hydraulic Machines,
Technical University of Sofia,
8, St. Kl. Ohridski Str., 1000 Sofia, Bulgaria
P. Spassov, S. Raychev
EQE Bulgaria: Safety, Engineering and Management Consultants,
1, Hr. Smirnenski Str., Fl. 11, 1421 Sofia, Bulgaria
Z. Domuzov
Tangra Ltd., 2, Bouzemska Str., 1618 Sofia, Bulgaria

Abstract. The present paper describes the computer-simulation support for the design of a new industrial air-conditioning system. The computer simulation is based on the coupled system of partial differential equations governing the fluid flow and the temperature distribution in the room. The finite volume numerical technique is used. The role of computer simulation in the design process consists in assessing two different design variants for air-conditioning: the first one with six single pieces of ceiling-mounted split systems and the second one with a single air-cooled split system distributing the air through ducts. The numerical results obtained demonstrate the obvious advantage of the first variant. The latter is recommended for practical implementation.

All interconnections between the numerical study and the other stages of the design process are demonstrated and discussed. The current investigation presents the idea to input well-balanced efforts in the numerical computation in order to achieve a reliable assessment of the two variants rather than to perform a computer-intensive benchmark solution. To achieve this, the ``reasonable sufficiency concept'' is applied so that each modelling option is assessed in view of the resources required and the accuracy achieved. Hence, the present investigation provides useful information on how to reduce the efforts for similar computer supported design studies.

Key words: Computational Fluid Dynamics, industrial ventilation, design of ventilation systems.



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