When the 130-room Residence Inn by Marriott in Florence, Alabama, was replacing its water-heating system in a renovation, the original replacement system specification called for two 750-gallon boilers, each measuring 5 feet by 12 feet. The plan would have almost worked — it left a few inches of clearance in the boiler room — but with so little space, maintenance would have been impossible without shutting down the entire water-heating system.
So the hotel changed course, implementing a 17-unit gas tankless water heater array that provided enough space in the mechanical room to service the units. Plus, there were energy-efficiency benefits: The new design eliminated the energy losses from storing 1,500 gallons of hot water, reducing energy use for the hotel.
As the hotel’s successful renovation shows, propane and gas tankless water heaters offer an innovative opportunity to provide energy-efficient water heating with flexible system designs that can be tailored to a building’s space constraints and hot-water demand. A new training course from engineering consultants Newport Partners LLC and the Propane Education & Research Council, “Propane Tankless Water Heating in Commercial Building Applications,” offers insights into how commercial building professionals can use tankless systems to maximize a building’s water-heating performance for both existing buildings and new construction.
If architects, engineers, and building owners aren’t paying attention to the energy use of the water-heating systems in their buildings, they’re missing out on an important opportunity for savings, especially in certain building types. Water-heating energy represents a significant 7 percent of all energy use in commercial buildings. But a group of just six building types — lodging, healthcare, retail, education, food service, and office — represents about 85 percent of all commercial building water-heating energy consumption.
“When you look at tankless systems from a number of different manufacturers, they do provide some really key value propositions with benefits over more traditional water-heating systems,” says Jamie Lyons, senior consultant at Newport Partners. “So you see a lot of project activity, and it’s lining up because of those value propositions.” And because virtually all tankless water heaters can run on readily available propane, they’re an option even for projects that lack access to natural gas.
Flexibility for peaks and low points
One of the primary benefits the course highlights is the flexibility of tankless water-heating systems to meet a variety of water-heating loads. Many commercial tankless water-heating systems are modular: Individual tankless units can be combined together in racks or arrays to provide a range of water-heating capacity and output. That means a system could be designed for a large peak load that requires several hundred gallons per minute of hot water output but still respond well when only a small portion of that hot water is needed.
Hotels are a particularly common use case for this strategy, Lyons says. “Even though the peak demand for hot water happens really infrequently, they still have to be ready for it or else they have unhappy customers,” he says. “The value proposition for tankless there is really strong because you can use an array of tankless units that can ramp up to meet the peak when it happens, even if it only happens a really small percentage of the time. You’re ready for it, but you’re not storing hundreds or thousands of gallons of hot water all the time.”
Instead of simply keeping water hot in a large storage tank, tankless systems use sophisticated controls to modulate the heating capacity of an individual unit higher or lower to meet the demand for hot water. When additional capacity is needed, the system can bring on additional units to share the load and increase output. The controller also spreads the duty cycle out so that one unit won’t wear out before the rest.
At the Residence Inn by Marriott, for instance, the 17-unit tankless array includes 12 units to supply hot water to the 130 guest rooms and five units for the hotel’s dining and laundry operations. Each tankless unit has a capacity of just under 200,000 Btus per hour. Because each individual tankless unit can modulate as low as 11,000 Btus per hour, the overall system has a huge capacity range from over 3 million down to 11,000 Btus per hour.
More space to do business
The training course also covers important considerations for the size and ventilation considerations of a building’s water-heating system. Because boilers and tank-style water heaters store water, they have a larger physical footprint than tankless units, which can be arranged in self-supporting racks or wall-mounted, depending on project needs. While it’s unsurprising that those space savings can benefit a retrofit project like the Residence Inn by Marriott, that flexibility can be helpful in new construction as well, Lyons says.
“Even on the new construction side, we saw one or two projects where the physical footprint was a sticking point,” he says. “They want to maximize the space in the building that’s providing key services or generating revenue, as opposed to just creating space for boilers or water heaters.”
“You can use an array of tankless units that can ramp up to meet the peak when it happens, even if it only happens a really small percentage of the time.” — Jamie Lyons, senior consultant, Newport Partners
While providing ventilation for 17 tankless water heaters might sound messy, common venting options are available that save space and reduce wall penetrations. The Residence Inn by Marriott used common-vent runs for two banks of water heaters and had one standalone unit. “So they ended up with three building envelope penetrations and venting runs instead of all 17,” Lyons says.
The course highlights the diversity of tankless product offerings available from a variety of manufacturers. That includes many at efficiency levels high enough to meet the prescriptive requirements or energy-modeling savings needed for LEED v4 for Building Design and Construction. “Most, if not all, of these natural gas tankless water heaters are convertible to propane, so the offering’s pretty broad,” Lyons says.
To learn more about the contributions that tankless water heaters can make toward LEED certification and see more project examples, check out “Propane Tankless Water Heating in Commercial Building Applications” in the Propane Training Academy. Be sure to complete the course to earn learning credits from the American Institute of Architects continuing education system and the Green Business Certification Institute.
Lead photo: Contractor Anthony Crouch, owner of Crouch & Sons Plumbing in Florence, Alabama, examines the Residence Inn by Marriott’s tankless water heater array with distributor Jason Veal of the Tallman Company. Photo credit: Randy Crow.