Important Aspects of Thermal and Mechanical Design in Tankless Water Heaters

March 30, 2018

Bulky industrial tankless water heaters provide substantial volumes of on-demand hot water. The tank is missing from the shrewdly engineered equipment's material footprint, yet it still occupies a large slice of real estate within its containment site. It's undeniably efficient, this trim unit, but still can't just be installed and forgotten. Before this tankless project receives a seal of approval, it had better satisfy the following commission-relevant criteria.

Tankless Thermal Management

As all heating engineers know very well, tank-style water heaters act as heat sinks. There's a massive thermal load stored inside the vessel, and that high-temperature fluid produces pressure. Tankless models don't release large amounts of heat. This energy deficit is known as standby heat loss, and it simply doesn't occur in tankless water heaters because there's no stored thermal load contained in a tank of water. There's no tank at all. Furthermore, industrial units don't utilize a direct heat mechanism. So where's the heat coming from?

Heat Exchanger Solutions

Instead of a bank of inefficient natural gas burners, tankless water heaters incorporate heat exchangers. This is where mechanical design takes charge. Indirectly fired tube stacks are mounted inside a pressure vessel, at which point a second water supply enters the containment unit. The stack is basically immersed in hot water, as supplied by an HTHW (High-Temperature Hot Water plant or a fuel-stoked boiler system. Instead of the on-demand heated fluid triggering rows of burners every few minutes, the issue of thermal efficiency is addressed by sourcing more warm fluid from the heat exchanger.

Tankless Water Heaters: Some Assorted Musings

If space is at a premium in a second-stage water heating application, the trim form of a tankless water heater can slot into the tight gap and utilize its heat exchanger assembly. The boiler or hot water plant interface with the heat exchanger, and the indirect heating unit does the rest of the work. Equipped with a three-phase electrical supply and a modulating control valve, output lag is minimized. Finally, for those demanding applications, welded carbon steel and stainless steel are superior material choices. Furthermore, pressure release valves may be required, as stated in the ASME Code, especially since this industrial-class water heater couples to a heat exchanger.

Designed to provide over 100,000 BTUs of heat, and sometimes as much as 400,000 BTUs, tankless water heaters may not use a traditional water storage shell, but they're still classed as pressurized equipment. Used in a home, a bank of natural gas flames delivers instant direct heat. Meanwhile, used in an industrial setting, it's a heat exchanger that supplies the indirectly sourced heat.

Contact Details

Fusion - Weld Engineering Pty Ltd
ABN 98 068 987619

1865 Frankston Flinders Road,
Hastings, VIC 3915

Ph: (03) 5909 8218

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