Built in 1901, during the golden age of Washington, D.C., apartment houses, the seven-story Mendota is the oldest luxury cooperative apartment building in the district.
“While many other D.C. buildings of the era have lost their visual character, the configuration of nearly every apartment unit in the Mendota is identical to when it was built,” Jim Wood, head of the building and grounds committee for the Mendota’s board of directors, said.
The Mendota’s 50 apartments include such architectural details as 10-ft ceilings, ornate crown molding, tall windows, heart-pine floors, built-in cabinetry, and Victorian-tile fireplaces. Another historic feature is the original heating system, which still is in place, but long has been disconnected. The Mendota is heated with a one-pipe steam system connected to column-style cast-iron radiators.
After many years in operation, the gas steam boiler that replaced the original coal-fired boiler was becoming less and less reliable.
“We allocated approximately $75,000 annually for natural gas, and this expense was a huge portion of our budget,” Wood said. “Also, many tenants complained it was either too warm—requiring them to open windows—or that they didn’t have enough heat. We had to do better.”
System Repairs Pick Up Steam
Dan Foley, president and owner of Lorton, Va.-based Foley Mechanical Inc., was enlisted to help remedy the heating woes.
“When we started working with Mendota, a 40-year-old steam boiler provided heat,” Foley said. “Upon inspection, we noticed the boiler fired all day long and never shut off.”
Foley’s team also noticed the main venting system was not appropriate for the two 6-in. steel mains that circled the basement. The boiler flooded regularly, and condensate would lag as it percolated through the clogged wet returns.
“When the condensate would finally return, the boiler would flood, which required a service call,” Foley said. “Water continuously drained from the boiler as fresh water was added, causing the boiler to disintegrate from the inside out.”
Foley and Wood decided first to make incremental improvements to the aging boiler. Enhancements included replacing ribbon burners that had rusted and replacing the boiler relief valve and safety controls. Next, the team rebuilt the main venting system.
“The vents were undersized, and the two mains were not balanced,” Foley said. “We had a welder cut in two 1-in. threadolets into the end of the steam mains, and then we built vent headers on each main.”
Another improvement involved the removal of an old electromechanical control that had not functioned properly in years.
All of the boiler-system improvements had a fairly dramatic effect on tenant comfort and energy use. The boiler heated the building more evenly, and annual fuel expenses fell to $55,000 to $60,000. Still, Foley believed there was room for improvement.
When service calls began to become a weekly occurrence and most of the operational parts of the boiler had been replaced, building management decided the time for a boiler replacement had come.
Boiler Replacement Full Steam Ahead
After several years of maintaining the aging boiler, Foley recommended installing a new boiler, re-piping the header, and replacing the rotted, clogged wet returns.
“I submitted a six-figure proposal, and at first the board balked at the price,” Foley said. “When I suggested they review what they paid in fuel over the past five years and add in the service calls and tenant complaints, they quickly came around.”
Foley recommended the installation of a 2.5-million-Btu Weil-McLain LGB-20 atmospheric draft steam boiler. At up to 84-percent combustion efficiency, LGB boilers are among the highest-efficiency commercial cast-iron atmospheric gas boilers available from Weil-McLain. Their compact design allows more piping and venting headroom, while their short draw rods permit faster, easier assembly of boiler sections.
The boiler was sized to the connected radiation using a 1.5 pickup factor. The header was re-piped to manufacturer specifications.
“Before we removed the old boiler, we conducted a system overhaul to optimize the distribution piping, vents, and the radiators in every room,” Wood said. “We then installed new main-line steam vents, both at the beginning and the end of the line, checked all the mud legs, and replaced the near boiler piping because it had been clogged.
“Our preparatory work and due diligence ensured the whole system would work much more efficiently and we could slip the new unit right in,” Wood added.
The project took two weeks to complete. Installation challenges included navigating stairs and working in a small space.
After the new boiler was installed, the team cleaned the system with steam cleaner and ran it for several weeks to flush out all of the sediments. After flushing the boiler and wet returns, Foley skimmed the water line until it ran clear.
Loop seals also were clogged with sediment. Foley and his team meticulously flushed out each loop seal with water, which allowed the condensate to drain and the steam to flow freely. This process helped to balance the system.
New System Benefits
With the new boiler optimized and in service, several benefits quickly were realized. Radiators that had not heated in years were hot. Steam circled the mains quickly and the risers received steam at the same time. Windows previously opened in January were closed.
“We actually installed a couple of dozen additional radiators that had been removed with the previous system because it had been run at such a high level that the building was overheating in some areas,” Wood said.
Wood likes the fact he does not have to change the operational parameters of the boiler throughout the year.
“The controls are such that we don’t make adjustments at all,” Wood said. “The system learns and fine-tunes settings as needed.”
One of the most significant benefits of the installation of the new, higher-efficiency Weil-McLain boiler was the energy savings realized. Fuel costs for the building decreased to about $30,000 annually, a reduction of more than 40 percent from gas bills years earlier.
Additionally, the system operates quietly.
“When the boiler turns on and the radiators are operating, you sense the heat, but you don’t hear anything,” Wood said. “It just purrs.”
Most importantly, tenant complaints have been reduced.
“I believe that steam boilers with radiators really is just the most perfect, comfortable heating method,” Wood said. “We have been absolutely pleased and impressed since the new boiler was installed. And we’ve saved a lot of money.”
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