Differences between Direct and Indirect Hot Water Cylinders

Blog | September 10th, 2018

In principle, direct water heating systems apply energy straight to the base of a water-filled cylinder. The immersion elements or gas flame directly affect the hot water cylinder. Indirect heating, on the other hand, employs a secondary system mechanism. For this scenario, a heat exchanger carries hot water from a boiler. This incoming fluid medium never mixes with the cylinder water. Let’s break down the system differences further.

Direct Heated Systems 

Two-stage direct hot water cylinders are mounted on hardened platforms. There’s gas or electrical power entering the lower half of the housing, where the thermal emitters are installed. Gas nozzles burn fuel. Alternatively, the electrical resistivity of a heated element discharges large volumes of thermal energy. Located directly below the cylinder, the energy conducts through the shell casing, where it enters the cool water and sets up a convective current.

Indirectly Fueled Hot Water Cylinders 

Indirect heating units remove the primary fuel stage. Instead of electrical resistivity or gas-fired nozzles, there’s a heated copper coil inside the hot water cylinder. It’s hollow and full of hot water, which has just arrived from the heat generating equipment. Essentially, that cylinder-interred copper coil is coupled to a boiler, one that could be in a completely different room. Providing the boiler flame, an electrical transformer is sparking. As the H.T. (High Tension) wires spark, a fuel source ignites.

Mulling Over Cylinder Applications 

Indirectly heated water cylinders are found in countless industrial and commercial applications. It just makes sense to keep the high-pressure steam line in its self-contained lane, where it can’t blow the top off of a regular room radiator. In this manner, lower pressures and lower temperatures spread throughout buildings and large complexes via heat exchangers. The same system has been in use in homes for several decades. For instance, old homes sometimes use basement furnaces, and it’s this oil-fueled equipment that heats basement boilers. Loaded with super-heated water, the pressurized, highly excited fluid is channeled into a heat exchanger unit, where it’s then sent to the floors above.

Integral gas or electric assemblies’ burn fuels and heat elements, and they do so while in close contact with a direct hot water cylinder. They’re fast and efficient. Elsewhere, an indirect hot water heating system is using the cylinder as storage. The fuel is electric or solar, propane or diesel, and the burner/boiler equipment is self-contained. Again, indirectly heated cylinders are efficient, plus they separate heat sources from radiator water. This separation also applies to the pressures and steam-hot temperatures that flow in the primary boiler’s lines.

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