Design and Performance of Steel Hot Water Boilers + Tips

Steel Hot Water Boiler Tips

Want to use steel boilers to provide the required heat for your central heating system but you are not sure of the type, capacity, brand, price, and specifications that suit your purpose? Read on to find the answers to all your questions on price, technical specifications, and the best steel boilers on the market.

In the HVAC industry, stainless steel boilers supply the heat required by the central heating system of buildings using the heat from combustion in the burner and the exchange of thermal energy between absorption surfaces and a heat transfer fluid.

Regardless of capacity, dimensions and workload, steel boilers are divided into "fire-tube" and "water-tube" boilers.

Due to the importance of heat exchange surfaces in steel and steam boilers, some manufacturers use the bottom surface of the boiler for water circulation and thermal energy exchange according to the standard methods and plans in order to increase heat exchange surfaces. These boilers are called "wetback" boilers which are definitely more advantageous and have a higher fixed price than dry back boilers.

Click to view brands, models, and different types, find out the price, and Buy a Hot Water Boiler.

Steel material and design standards in hot water boilers

International standards indicate that steel boilers require a shell, furnace, or combustion chamber, and grids that are made of special steel alloys for producing hot pressurized tanks (DIN 17MN4, ASMEA516/G70 standards). The tubes must be fire-resistant and seamless according to DIN ST 35.8 standards with the capability of appropriate cold expanded connection (riveting).

One of the chief considerations in designing and manufacturing steel boilers (for hot water or steam) is the compliance of manufacturing process and components, control process, accessibility, and testing operations with conventional standards, compatibility between the boiler and its production designs, and compliance with the guidelines provided by well-known international manufactures for designing and making boilers. In other words, merely using quality steel alloys and fire-resistant tubes cannot guarantee good performance, efficiency, and durability. The device must be manufactured based on certified designs and through international standard manufacturing procedures. To emphasize, producing hot water or steam boilers without relying on internationally standard designs is unjustifiable even if using the best steel and equipment possible.

Another important point regarding the manufacture and production of standard broilers or steam boilers is how to connect the fire tubes of the boiler to the tube sheets at the beginning and end of the boiler. There should be a cold expanded connection (riveting) except for resistant tubes inside the secondary furnace which should be standardized by the cold expansion method using special ESAB welding machines for network welding of hot water or steam boilers.

For more information, read the article "Why should fire tubes not be welded to tube sheets?" on the DamaTajhiz website.

The Most Efficient and Long-Life Steel Boiler

When picking and ordering a steel boiler for your project or industrial complex, please note the following points:

1. Compliance with the recommended and accepted standards regarding the material and type of steel used in the body, furnace, and boiler tubes;
2. Compliance with all operational guidelines in accordance with the design of international authentic brands in steel boiler manufacturing;
3. Not relying on brand promotions on the quality of their products and the conscious choice of the type, capacity, and operating pressure required for the boiler.

For instance, the best choice for broilers with a capacity of over 600,000 kcal/h or 600 kilos steam per hour is a three-pass full wetback boiler with primary and secondary corrugated furnace, fully turbulent or spiral fire tubes, and the highest efficiency and longevity among fire-tube boilers.

Therefore, pay attention to the specifications and quality of furnace and boiler tubes when ordering steel or steam boilers. In addition, pay particular attention to general information like "boiler furnaces are corrugated according to the standards in certain capacities" and ask straightforwardly whether the boiler you order has a primary or secondary corrugated furnace and spiral tubes.

The differences between steel hot water-tube and fire-tube boilers

• In fire-tube boilers, the flame and smoke produced by combustion pass through tubes and boiler pass to transfer their heat to water. However, in water-tube boilers (e.g. the type used in power plants) the heat generated by the burners occupies the boiler, warming the water in tubes.
• A steel hot water tube boiler is built to operate under high pressures. This type of boiler is used in power plants under temperatures up to 550 and pressures above. On the other than, in fire tubes, the operating pressure does not exceed 30 bar. Fire-tube boilers feature long steel tubes that contain the hot gases produced in the combustion chamber. The water to be heated or vaporized circulates around these pipes.
• Fire-tube boilers offer high efficiency relative to their production costs and are easier to repair and maintain than their water-tube counterparts.

Effect of Fully Corrugated (Accordion) Tubes and Furnaces on Efficiency of Steam and Broilers

Today, given the role of convective heat transfer in the increased efficiency of steam and broilers, techniques that increase heat transfer are widely used. According to the comprehensive studies conducted on increasing the efficiency of convective heat transfer, also known as Vortex Heat Transfer Enhancement (V.H.T.E) as the name suggests, this method is based on creating a vortex. One of the most widely adopted applications of the V.H.T.E. method is to use an accordion or corrugates and corrugated spiral fire tubes in steam and broilers which increase convective heat transfer and efficiency of hot water and steam boilers due to the creation of more turbulence in the fluid flow.

Studies suggest that heat transfer inside the furnace and fully corrugated tubes follow a complex pattern. But, in short, according to the following graph, convective heat transfer in a fully corrugated furnace and tubes is about up to five times larger than the heat transfer in flat furnaces and tubes. In addition, in fully corrugated furnaces and tubes, radiation heat transfer increases due to many folds and increased surface area. Therefore, thanks to many folds available, steam and hot water boiler efficiency increases significantly due to the increased convective and radiation heat transfer using the V.H.T.E. method.

Challenge Faced by Consulting Engineers and HVAC Experts when Choosing Condensing Boilers

High efficiency is definitely obtained in condensing boilers due to the absorption of the latent heat of evaporation from combustion. However, obtaining this efficiency practically requires reducing the return water temperature to a temperature below the dew point as the main condition for condensing performance in a condensing boiler.

In fact, condensing boilers function within a certain temperature range of heat exchanger fluid as condensers, and in other cases, they, unfortunately, have an equal efficiency to a typical hot water boiler.

In summary, despite the claim that condensing boilers have an efficiency of 92% to 94%, this efficiency and cost-effectiveness face serious challenges due to various technical and economic issues, including the following:

1. Basically, condensing boilers face a challenge called low return water temperature. According to Figure 1, to obtain 96% efficiency in condensing boilers, the return water temperature should be 90 °F (about 50 °C). With a return water temperature of 55 °C, (about 130 °F), the efficiency of the condensing boiler reaches 87%, which is equal to the efficiency of other three-pass full wetback fire-tube boilers with fully corrugated primary and secondary furnace and spiral fire tubes. In the United Kingdom, over 90% of condensing boilers have never functioned in their condensing phase; they have operated in their non-condensing phase. Now, the main question is "how can we justify manufacturing the world's largest condensing boiler?"
   
   
   
2. The provided figures only represent maximum efficiencies and the real efficiency of condensing boilers varies between A to G similar to other boilers. However, there is currently no standard across Iran for conducting experiments to determine the efficiency of boilers by legal authorities, and the claimed efficiency is not obtained via testing.
3. Regardless of all maintenance problems, spare parts, and design problems to obtain return water temperatures of below 40 °C and the high price of condensing boilers, at best, their nominal efficiency is up to 6% higher than other three-pass full wetback fire-tube boilers with fully corrugated (accordion) primary and secondary furnace and spiral fire tubes. Thus, with scientific and economic analyses, there is no economic justification. According to the Guardian, even in countries such as the United Kingdom, despite the high fuel prices, condensing boilers have not been able to economically justify their high prices, and consumers fuss about the lack of cost reductions despite their high initial cost.

For more information on the efficiency and function of condensing boilers, read the article "Challenges of Condensing Boilers" on the DamaTajhiz website.

Notes to bear in mind when purchasing steel hot water boilers

1. The boiler and burner are the core of the central heating system and may suffer defects in long-term operation. With this in mind, and to reduce fuel consumption, in buildings with more than 8 residences or a useful area above 1,000 square meters, it is recommended to install two steel hot water boilers, each able to produce up to 60% of the total heating energy required by the building.
   
   
   
   
2. In important public buildings (e.g. hospitals, hotels, etc.) irrespective of the type of boiler used in the central heating system (steel or cast iron), the international engineering standards recommend the implementation of three boilers, each capable of providing 75% of the total heating energy in order to be able to provide the majority of heating and hot water required by the building even with a single boiler in case of problems with boilers or their burners.
3. Considering the importance of boiler rooms as the central heating/cooling system and for the welfare of residents, the boiler room is recommended to meet the following criteria:
   Ease of access;
   Large entrance for equipment transfer;
   Suitable area for simpler set up, inspection, and maintenance;
   Proper lighting and ventilation.
4. The main difference between hot water and warm water steel hot water boilers is the higher operating pressure of the former;
5. Before selecting one of the fire-tube warm water boilers below, check whether the size and weight is suited to your boiler room;
6. When selecting a steel hot water boiler, in addition to the capacity and size, also check the required operating pressure. You can consult with Damatajhiz technicians if necessary;
7. After selecting the desired warm or hot water boiler, you need to implement a level, proper foundation for their installation, so the boiler can be directly placed on the foundation when transported to the boiler room.

Important recommendations for setting up steel hot water boilers

1. In boiler rooms with steel hot/warm water boilers, a water softener or anti-scaling is necessary;
2. Since the main components of boiler rooms, including the central boiler, are placed on an existing concrete foundation according to the layout plan, before installing the main equipment of the boiler room please verify the concrete foundation is built according to the designated dimensions and standards;
3. It is necessary to install a manometer and thermometer on each steel boiler to display the hot water temperature in the boiler and the pressure of the heating system;
4. it is necessary to install a submersible thermostat with a temperature range of 30-90 or 30-110 to regulate the boiler temperature and facilitate the on/off signals to the burner relay;
5. It is necessary to install at least a safety valve and a submersible thermostat with a temperature range of 30-160 or above (according to the operating temperature of the hot/warm boiler) on each boiler to regulate the boiler temperature and facilitate the on/off signal to the burner relay.

Factors that extend the durability of steel hot water boilers

• Design and production according to international standard methods and guidelines;
• Using steel alloys and fire-resistant tubes, sufficient thermal contact surface on the tubes, the appropriate number of passes in the boiler;
• Employing a water softener suited to the volume of water circulating in the heating system or installing proper anti-scaling equipment;
• Considering appropriate sizes for the head hole, hand hole, and manhole vents where necessary to enable inspection and periodic maintenance and the replacement of damaged tubes;
• The high quality of peripheral accessories, as their type and quality significantly affect the performance, safety, durability, and efficiency of steel boilers. In order to compensate for the reduced combustion efficiency of burners, their nominal capacity is recommended to be 20% more than the boiler capacity;
• The proper number and capacity of the central boilers, so that even at the coldest times of years, a single boiler is not needed to operate continuously and nonstop. For instance, in public buildings such as hospitals, hotels, government buildings, and large residential complexes the heating should not be provided by a single boiler and also, an auxiliary boiler always remains on standby for emergencies.
• The burner must fit the heating capacity of the boiler (max 20% more than the heating capacity of the steel hot water boiler);
• Periodic maintenance and services for the combustion process of the burner in steel hot water boilers, control functionality, safety valve, thermostats, and other components.
• When using a diesel burner, the angle of fuel spray from the burner nozzle is recommended to suit the diameter and length of the combustion chamber of the boiler and be based on the manufacturer's recommendations.
• Accurate calculation and implementation of the smokestack in regards to their diameter and vacuuming height based on the amount of combusted air.

After all, if you had more questions to decide on buying a steel hot water boiler or a steam boiler, you can contact to DamaTajhiz company and ask your questions.

Final speech

The specialized collection (Damatajhiz) (the first and most reliable authority in the country in the field of building facilities equipment and all air conditioning devices), offers you all kinds of sand filters and hundreds of other products, guaranteeing the originality of the product, valid warranty, and reasonable price. In addition, if you have any questions about choosing and comparing the brands of this product, you can get free advice from the heating equipment experts.

In Iran, the first and most famous specialized group in the field of building installation equipment, air conditioners, and all equipment for swimming pools, saunas, and jacuzzis since 2004, DamaTajhiz is a specialized group. Refer to the time of this group. For more information, you can get advice from the experts of DamaTajhiz Engineering and Production Company by calling 021-88822550.

We are waiting for your call and look forward to meeting you at the DAMATAJHIZ group

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