Boilers Design and Components #3

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Continued From ---> Boilers Design and Components #2

A low water detector/cutout, which is fitted for each boiler. This safety device prevents the boiler from operating with little, or no, water and overheating, which could easily cause serious damage to the unit.

Dissolved oxygen and other chemicals in normal domestic water can cause severe corrosion and fouling of the heating system, especially with steel pipework. In closed hot water systems, water treatment chemicals may be added as the system is filled. Then, periodically, the system water quality is checked and any needed additional treatment added.

In steam systems, the makeup water must be treated to remove oxygen and dissolved solids before it enters the boiler. This is to prevent the boiler from filling with dissolved solids, since steam (pure water) is continuously boiled off. The steam is very corrosive, so a chemical treatment is included to offset the corrosive characteristics. Thus, there is a need for frequent monitoring, since any failure of treatment can cause problems in the boiler and distribution
systems.

With the two boilers in parallel, about half the water will flow through each boiler. If just one boiler is firing, the supply temperature will be based on the average temperature of the return water from the idle boiler and the heated water from the firing boiler. If the supply-temperature requirement equals the temperature that is produced by the operating boiler, then the flow through the idle boiler must be stopped, by closing the inlet valve. For systems with low summer loads, this is ideal since the efficiency is maintained and the idle boiler can be serviced with no interruption of hot-water production.

Note that with steam boilers, if one is running, both will fill with steam to the same pressure. The operating boiler keeps the second boiler hot and ready to fire.