School building graduates from oil to propane heating
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Keene Central School serves about 170 students in Keene Valley, New York. In 2019, voters approved a $7.85 million capital project to expand the K–12 school building, enhance security, and upgrade infrastructure.
Students began the 2022/23 school year with a new lab space, main office with a secure vestibule, fitness center, and a more comfortable environment. The school district worked with the Albany, New York–based architectural firm CSArch for the project. The firm then engaged the mechanical, electrical, and plumbing group at AES Northeast, in Plattsburgh, New York, to overhaul the facility’s aging boiler plant and other building systems.
The result is a more functional facility that will help meet the district’s academic goals and improve energy performance.
Modernizing the space heating
The original heating system comprised two oil-fueled cast iron boilers nearing their end.
“I rarely had both of them running because one of them was usually down,” says Jake Riggins, Keene Central School’s director of facilities.
Temperature control, or lack thereof, was another issue. The school’s space heating is divided into three zones — two served by air handlers and another by in-floor radiant heat. The problem: The distribution pumps were pushing too much water past the radiant zone’s three-way valves. That meant classrooms and hallways were stifling during winter. Not only was it uncomfortable for the students, but Riggins’ night crew would open windows for relief.
“Some of those hallways would get up to 85 degrees,” Riggins recalls.
An upgrade was in order. To make way for cleaner, more-efficient heating, Riggins recommended an oil-to-propane conversion. Propane for space heating produces 10 percent fewer greenhouse gas emissions than oil.
“We had 300 psi of oil running through the building, and I just saw that as a nightmare one day,” says Riggins, who has a background in environmental remediation. He was glad to be rid of the 10,000-gallon underground oil tank. Riggins had three 2,000-gallon propane tanks installed in its place.
AES Northeast specified four condensing boilers to replace the two cast iron units. The new propane-fueled boilers have a maximum firing rate of 1.5 million Btu but can run as low as 300,000 Btu. That’s a 5:1 turndown ratio per boiler, which means the system can modulate between high and low outputs based on demand.
“The new boilers, being propane-fired, are a much smaller footprint. So we went from a two-boiler plant arrangement with fuel oil to a two-boiler plant arrangement with gas, which allowed us to load match the building better. They’ve got a much higher turndown ratio than they had before,” says Nathan Bull, P.E., principal engineer at AES Northeast’s building systems group.
Intern engineer Jacob Jacques adds, “Last winter, instead of running 180-degree water, [Riggins] found that most of the year, he can run much lower than 180 degrees, which he couldn’t do with the cast iron boilers before. He’s getting through most of the season with 140-degree supply temperature.”
The upgrade also included a dedicated pump for the radiant zone, with electronically activated three-way valves for temperature control to prevent overheating.
Upgrading the water heating
A 600 Mbh oil-fired tankless water heater provided the school’s hot water, but the kitchen would routinely run out.
“I was getting calls every day for hot water,” Riggins says.
The solution: A 200-gallon indirect water heater with a coil drawing heat from the boilers, along with a thermostatic mixing valve and precise temperature control, distributes ample hot water throughout the building. The indirect water heater also lowers the temperature returning to the condensing boilers for optimal efficiency.
A Lochinvar Armor condensing tankless water heater adds redundancy while also being the facility’s primary hot-water source during the summer.
For Riggins, the makeover of the building’s space- and water-heating systems more than alleviated headaches; it created comfortable conditions and energy savings.
“Our fuel consumption is down significantly,” Riggins says. “The return on investment is already showing itself.”