Düşük Yoğunluklu Gaz Yakmalı Radyant Sisteminin Pratik Ve Ekonomik Açıdan İncelenmesi Ve Standart Isıtma Sistemleri İle Karşılaştırılması

Abstract

Düşük yoğunluklu, gaz yakmalı, radyant borulu ısıtma sistemleri, çoğunlukla konvansiyonel ısıtma sistemleri ile ısıtılması ekonomik olmayan, büyük endüstriyel binaların ısıtılmasında kullanılmaktadır.Daha önce bu konuda yapılan çalışmalarda gaz yakmalı, radyant borulu ısıtma sistemlerinde %30 ile %50 arasında bir enerji tasarrufu sağlanabileceği saptanmıştır.Gerçekleştirilen bu çalışmada öncelikle radyant ısıtma işlemi ve radyant ısıtma sistemleri tanıtılmıştır. Radyant sistemlerin hem kendi aralarında, hem de konvansiyonel sistemler ile karşılaştırmaları yapılmıştır.Radyant ısıtma sistemi seçimi için yerine getirilmesi ve dikkat edilmesi gereken hususlar incelenerek, seçilen bir bina için ısı kaybı hesabı yapılmış, ortamın ısıtılması için yeterli ısıtıcı gücünde bir gaz yakmalı, radyant borulu ısıtma sistemi üretici katalogundan seçilmiştir.Verilen sabit ısı yüklerinde duvar Ti, tavan T2, taban T3 ve iç hava Ti -■ ■-■-i— 1—D!n^nm Hm/or tav/an tahan ve ic havası için avrı

Low intensity gas fired radiant tube heating systems are mostly used for heating large industrial buildings which cannot be achieved economically with conventional heating systems. Preceding studies show that low intensity gas fired infrared radiant tube heating equipment's energy savings are 30% to 50% or more. The principle of radiant energy is that it heats solid objects and the floor, not the air. In spaces which are heated with radiant heating systems, normal comfort levels are provided at a lower ambient temperature. In this study all radiant heating system alternatives have been introduced and some comparisons for advantages, disadvantages, costs, maintenance have been made for these systems. A calculation for a selected building with a low intensity gas fired radiant tube heating system has been made and the results have been shown in figures. Introduction Installation of radiant heating systems has begun in the United States in about 1 955. In Europe with becoming widespread of the use of natural gas, the use for these systems has begun twenty years ago. Gas fired radiant systems can also be used with L.P.G., but it is more logical to use natural gas for these systems, depending on the fuel costs. In 1 950's when these systems were installed, there was little information on the practical application of "infrared" radiation for comfort heating. Up to now many studies have been made to develop radiant heating systems. XIII A wide range of radiant system applications shows that this kind of heating systems are necessary for the heating of large industrial buildings. Instead of total building heating it is also possible to heat a selected area with the spot heating alternative of radiant heating. Radiant systems, are systems that deliver more than half of their useful heat output by means of infrared radiation. In practise this means systems with emitter temperatures greater than 100 °C, such as gas radiant tubes and plaques, electric quartz linear heaters, steam radiant panels and others. In this work, the low intensity gas fired radiant tube heating equipment and its calculation has been studied in detail. To understand, how radiant heating system works, basic principles of heat transfer has been summarized. There are three modes of heat transfer: conduction, convection and radiation. Radiation is an electromagnetic process of which heat radiation is one form. Heat radiation is the emission from a source of electromagnetic waves having wavelengths in the infrared band between visible light and radio waves. Simply, heat radiation is further defined as an electromagnetic transfer between two surfaces. The heat generation occurred with striking of infrared rays onto a solid body which stimulates the molecules within that body with causing them to move rapidly. This process does not require an intermediate medium as in the case of convected heat. Convected heat uses air as the medium to transfer the heat energy. With radiant heat the objects, bodies and surfaces are heated directly. The air is not heated directly with the effect of radiant heat. It is heated with the effect of convection from the heated bodies and surfaces. Radiant appliances can be classified in several ways. In this study radiant appliances are classified according to the operation temperatures of their emitting surfaces. Simply, radiant appliances can be classified in two groups, according to their emitting surface temperatures. The first group of this radiant appliances can be defined as high and medium intensity radiant appliances which emitting surface temperatures are above 815 °C. High and medium intensity radiant appliances can be classified again in two groups. These two groups can be described as linear quartz radiant tubes and gas plaque radiant heating appliances which have both a high temperature emitting surface. These systems which take the form of open flame, unvented appliances with incandescent ceramic faces, are normally utilized in intermittent, localized or spot heating situations. XIV The second group of this radiant appliances, can be defined as low intensity radiant appliances which emitting surface temperatures are between 260 °C and 815 °C. Gas fired radiant tube heating appliances can be given as an example for this second group of radiant systems. These systems were used widely for total building heating applications in industrial buildings. Examples and explanations for this kind of radiant appliances were given in this study. « Low intensity units are designed to operate below incandescent temperatures and frequently use steel pipe (as used for the calculations in this study) as the emitter. A typical low intensity system may be constructed of 4 inch steel tubing 3,5 m to 16 m in legth with gas combustion units inserted through the top of the tube. Combustion takes place in this tube, elevating the tube temperature to initiate radiant heat emission from the tube surface. Products of combustion are then normally vented to the outside. Low intensity systems are used extensively for heating large structures with Intermediate to high ceilings. Appliances such as manufacturing plants, workshops and in the last years mosques are typical installations effectively utilizing these systems. This study covers the practical and economical study of low intensity gas fired radiant tube heating systems and a comparison with conventional systems. Low intensity gas fired systems are provided with reflectors to direct the radiant energy downward. With this systems, floors and occupants are heated directly. The air is heated indirectly by convection from contact with the warm objects and the floor. The warming of the floor provides additional comfort to the space as the floor reradiates this absorbed heat. It is also important to note that the resulting localized convected air currents are secondary and do not represent heat emitted directly from the heated source. Consequently, air temperature stratification from floor to ceiling is subtiantally reduced. This reduces heat loss through ceiling areas in contrast to heating systems that rely on convected or forced air to distribute heat throughout the space. Due to the high surface temperatures in the building, the building heat losses will be more than for a conventional system. This shows us also the importance of the insulation of the building. Common radiant heating system types and the advantages and disadvantages of these systems have been shown and a comparison have been made between radiant systems and conventional systems. The total heat input required for the selected building has been calculated and a low intensity gas fired linear radiant tube has been selected from the manufacturers catalogue. xv Mathematical Model A mathematical model has been developed to calculate the temperatures of the wall Ti, ceiling T2, floor T3 and ambient air Ti. 1. Energy equation for the wall kd*(Td-Ti) + hd*(Ti-Ti) + -^-[Fi2*(E2-Ei) + Fi3*(E3-Ei)] + FRAi*p* - = 0 (8.1) 1-81 Ai 2. Energy equation for the ceiling kç*(Td-T2) + hç*(Ti-T2) + -^-[F2i*(Eı-E2) + F23*(E3-E2)]+FRA2*p*- = 0 (8.2) 1-S2 A2 3. Energy equation for the floor hı*(Tı-T3) + -^-*[F3i*(Eı-E3) + F32*(E2--E3)] + FRA,*p* - = 0 (8.3) 1-83 A3 4. Energy equation for the inside air Aı*hd*(Tı-Tı) + A2*hç*(T2-Tı)A3*ht*(T3-Tı) + f*(Td-Ti)*Q + (1-p)*Q = 0 (8.4) With respect to heat loss to the outside air it is noted that the floor is adiabatic. It does exchange heat by convection with the inside air and radiation exchange with the other surfaces. Unknown temperatures and roots of the above shown nonlinear equation have been solved with the EUREKA Solver software. The calculation has been made for different Q total heat inputs and for different p fraction of radiant heat. All results have been shown in figures, to display the results better. XVI Conclusion Calculated results for the gas fired radiant system in this study have been shown in several figures. These are: - Changes between total heat input and inside air temperature, Q - Tj - Changes between total heat input and all temperatures, Q - T(i,2,3,0 - Changes between all temperatures and fraction of radiant heat, T(i 2,3,0 " P - Changes between gas rate and and inside air temperature, Q0 - T\ - Relative prices of radiant heating equipment - Life cycle costs Low intensity radiant heating equipment support an overall reduction in the input energy requirement for radiant heating system installations. Converting energy savings to cost savings demonstrates the cost advantage that is available with radiant heating. As result low intensity radiant heating provides a cost effective, energy efficient alternative for space heating.