Pennsylvania DCNR seeks renewable fuel to fire a district hydronic heating system, Part 2

Feb. 12, 2014
Part 2 of this Hydronic Heating System article covers: What makes up the pressurized side of the heat exchanger. A field analysis of the different fuel sources.

PINE GROVE, PA. — On the pressurized side of the heat exchanger, insulated pipes drop into a covered manhole in the floor of the mechanical room. From here, water heads to the buildings. There are three Rehau radiant manifolds throughout the shop, and seven radiant manifolds located in the office building across the parking lot about 300-ft. away. 

The boilers share a main mechanical room with a super-insulated, 400-gallon buffer tank. All supply and return lines to both buildings run underground.

To deliver the water safely and economically, flexible, pre-insulated tubing was buried below the frost line. The blue, corrugated outside carrier houses thick foam insulation and 1¼-in. PEX lines.

“We went with double pipes on the home runs to the office buildings” said Adams, who was involved with the design of the pressurized portion of the system. “Each corrugated line contains two pipes, just in case one is ever compromised. The spare remains capped and unused. The price increase between dual and single pipe was minimal, so it seemed worth the expense to have the extra insurance.”

The manifolds in the shop are shrouded in steel cabinets, and deliver water to ½-in. PEX lines to heat the floor slab. The same is the case at the office buildings, except that there’s an additional 80-gal. buffer tank between the underground supply pipe and the manifolds. A Wessels Automatic glycol makeup system keeps the pressurized portion of the system safe in the event of a system rupture.

The radiant manifolds throughout the service bays are shrouded in custom-fabricated steel cabinets.

Hands-free renewable energy

“About a year ago, I did a field analysis of the different fuel sources we have available in the Northeast,” said Longenecker. “Cord wood — when used in a high-efficiency gasification boiler — was the least expensive. The downside is that you need to be around to light and stoke the unit, not to mention cut, split and stack. Then came natural gas, but that’s not always an option. Wood pellets were a very close third, roughly half the cost of LP and oil.”

Longenecker prefers wood pellets over other fuels because, in the correct boiler, it’s a no-fuss fuel. Additionally, it’s a sustainable byproduct. Hardwood sawdust is pressed into pellets that resemble large rabbit food. And it’s available nearly anywhere in the Northeast. A delivery truck literally blows the pellets into a 29-ton outdoor silo, from which the indoor boilers draw automatically. 

When pellets were delivered before commissioning in September, the price was $170/ton. According to the UDSA Forest Products Laboratory, a ton of pellets contains 16.4 million BTUs. The BTU equivalent of No. 2 fuel oil would have cost over $400. 

The vacuum tubes that move pellets from the outside bin to the boilers are shrouded in black corrugated plastic pipe to keep the sun from degrading the lines.

To get pellets from the silo, a high-velocity vacuum on each boiler draws pellets through flexible thermoplastic tubing, filling a roughly bushel-sized day bin attached to the unit. Two fire gates and an inclined fuel drop tube in the boiler keep flame from ever reaching the stored pellets.

“The boilers are nearly silent during operation. Because filling the day bin is noisier, you can program the boiler to draw pellets at a certain time of the day,” said Nichols. “Or for example — avoid filling between 9 p.m. and 8 a.m.” To light itself, the boiler uses an electric heat gun whenever there’s a call.

Anything but average

“I wish I’d have crossed paths with ATI Systems sooner,” said Adams, who is C.B.C.P. certified through AEE. “I commission, design and trouble-shoot the systems — both structural and mechanical— that DCNR operates.”    

The Weiser State Forest job strays slightly from the ATI Systems modus operandi, where full system design, from beginning to end, is the norm. In a way, they’re both a distributor and a mechanical engineering firm. But the way they see it, they’re a value-added equipment marketer. Depending on the product line, they sell both to mechanical contractors and wholesalers. 

“Retrofit, addition or new construction, we’ll pick up a project at any phase. But we prefer to be brought in at the design stage,” said Longenecker. “Sitting in front of blueprints allows us to design a system that will optimize fuel efficiency and comfort, while minimizing ecological impact.”

That’s what they’ve done at countless Pennsylvania jobsites, not to mention a host of other states across the country. The Weiser State Forest DCNR facility is now ready for all that winter can throw at it. An Amarillo, Texas, Toyota dealership is up next.

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