Rethinking tankless water heater systems
In the realm of sizing up projects and providing solutions, the routine sometimes can feel like a scene out of “Groundhog Day.” However, amidst the routine, there can be found moments of intrigue, challenge, and even humor. Take, for example, conversations regarding hot water supply in an industrial or commercial setting. It’s difficult to imagine something more mundane, yet there are innumerable facets and factors to consider.
Consider this seemingly straightforward and innocuous real-world scenario:
Can a property deliver 20 continuous gallons per minute (GPM) at 140°F with two 199,000 BTU tankless units and two 119-gallon storage tanks, all supplied by a 40°F incoming water temperature?
To the layperson, this might not seem especially exciting, but to a property manager or hotelier, it’s make-or-break business.
Upon delving deeper into the specifics, it’s evident the proposed setup wouldn’t suffice. The constraints imposed by the preference for only two tankless units pose a key challenge, sure, but the issue extends beyond mere equipment choice; it’s a matter of fundamental thermodynamics.
SET YOUR BEARINGS
One common mistake many property managers make is misinterpreting a tankless manufacturers’ temperature rise and flowrate specifications. Manufacturer specifications provide a maximum flow rate or a domestic hot water delivery rate at a known temperature rise with the tankless unit’s maximum BTU capacity and combustion efficiency. However, this isn’t the temperature rise desired or achieved at a given pumped rate calculated with a unit fire rate like a domestic hot water boiler.
Instead, the solution to the quandary posted above involves a simpler approach leveraging more BTU input rather than additional storage capacity.
Thus, the problem is easily solved, with no storage needed and the 20-GPM requirement is exceeded at 23 GPM. This system would be capable of providing hot water 24/7 with no recovery time or temperature fluctuations and no need for water storage. This meets the desired flow rate and ensures an uninterrupted hot water supply without the complexities of recovery time or temperature fluctuations.
COMPARING APPLES TO ORANGES
While every situation and property are unique, the root of this problem holds a very common misconception in the tendency to equate tankless water heaters with traditional boilers, leading to misguided sizing and application. Because tankless systems operate on different principles, they require a nuanced understanding for effective implementation.
One prevalent, but misguided, practice is relying solely on manufacturer specifications for temperature rise and flow rates. These metrics, while informative, don’t necessarily translate to real-world performance in diverse applications. Two properties with identical design will have separate needs in different climates. Using the scenario above, a hotel in a chillier climate like Chicago would need more units due to colder incoming water than, say, a property in Phoenix.
Why, then, do so many properties continue to pair storage tanks with tankless units, contrary to the original goal of efficiency optimization? This inclination tends to stem from a combination of habit and uncertainty, rather than necessity. It’s a security blanket that costs us additional money as well as wear and tear on the system. Just because dad did it doesn’t make it right.
FIND YOUR FIT
While there are valid reasons for incorporating water storage, such as space constraints or peak demand loads, embracing a storage-less approach can unlock optimal efficiency in water heating systems. Understanding design criteria and the limitations of tankless units, especially concerning continuous high-flow scenarios, is crucial for informed decision-making.
Exceeding recommended flow rates or operating parameters can lead to premature wear and tear, underscoring the importance of proper system design and installation. By rethinking conventional practices and embracing innovative solutions, we can pave the way for a more efficient and sustainable future in hot water systems.
Ultimately, the path to efficiency in hot water systems lies not in clinging to outdated norms but in embracing the potential of emerging technologies and design principles.
Victor S. Reichstein is the National Hospitality Sales Manager for Navien and he can be reached at victor. [email protected].
SVETAZI/SHUTTERSTOCK.COM
