Lessons in boiler efficiency

An essential component of an energy-efficient building is a heating system that integrates high-efficiency boilers for comfort heating, reducing energy consumption, and lowering emissions.

05/01/2008


An essential component of an energy-efficient building is a heating system that integrates high-efficiency boilers for comfort heating, reducing energy consumption, and lowering emissions. This also is economical.

This trend has become popular in the public sector—especially in budget-constrained school districts, where too often, not enough money is available for the basic educational requirements, let alone for increasing utility costs.

Recently, Architecture Involution LLC, Wayland, Mass., and its partners, including consulting firm Griffith & Vary Inc., Wareham, Mass., were hired to design and build a new high school in Massachusetts. When it came time to determine what type of heating system would be integrated into the design, they selected a boiler system that would achieve the greatest efficiency at all firing rates, and produce very low emissions.

Project details

Whitman Hanson Regional High School was bursting at the seams with students. The high school serves the communities of Whitman and Hanson, Mass., where an increase in student population and an aging, outdated building demanded the need for a new high school building.

The two communities contracted Architecture Involution LLC to design a new 270,000-sq.-ft facility and to assemble a team of strategic partners to assist with the project. Griffith & Vary Inc. was selected to design the new school building's mechanical and electrical systems.

Because of increasing energy costs, the design team wanted to take advantage of financial resources from the electrical and gas utilities and the Massachusetts Technology Collaborative. The team decided to sustainably design the new school building, and install high-efficiency mechanical equipment in the boiler room, lighting systems, renewable system technologies, and site considerations.

The boiler behind the savings

Because the school was being designed around the green theme, contractors wanted a boiler system that was both energy-efficient and eco-friendly. Based on experience, the engineers decided to install a Cleaver-Brooks boiler system—particularly the ClearFire Model CFC condensing boiler.

The ClearFire Model CFC achieves operating efficiencies to 99% when in full condensing mode. It does not require a minimum flow for vessel protections nor require a minimum return water temperature, providing an added value to school. And thus, the engineers selected six Model CFC boilers for a connected load of 10,800,000 Btuh input.

Energy and financial savings

According to the U.S. Dept. of Energy, utilities are the second largest single manageable item of a school budget behind personnel costs.

The typical school district of 3,000 students spends about $400,000 each year on energy-related utilities, while districts located in large metropolitan areas spend $20 million or more, according to the National School Boards Assn. On average, 25% of the energy used in a typical school is wasted due to the inefficiency of its systems and operations. In the same typical school, this amounts to $100,000 wasted annually that could be used by other instructional or physical plant programs.

Nationally, energy inefficiency related losses amount to about $1.5 billion annually. The cost of wasted energy equates to hiring 30,000 new teachers. Then consider Whitman Hanson Regional High School.

For the 2007-08 school year, there are 4,388 students enrolled in the Whitman Hanson School District, of which 1,241 attend Whitman Hanson Regional High School. By installing the Model CFC ClearFire boilers, Whitman Hanson Regional High School's annual gas savings have been approximately 11,719 therms since 2005, when the new school was completed. This contributes to an estimated yearly energy cost savings of $100,060—money that can now be put back into the classroom.

Model CFC FAQs

The Model CFC is a single-pass, vertical down-fired, full condensing firetube boiler. With the internal AluFer technology designed heating surface, the CFC delivers high performance in a compact space, offering more than 10 sq. ft of heating surface per boiler horsepower. By using the Model CFC, Whitman Hanson Regional High School was able to reduce its boiler room footprint.

AluFer heat transfer technology increases the heat transfer over a bare boiler tube by a factor of five, allowing dramatic reduction in both tube count and footprint. The AluFer tube is composed of an internal (fireside) 8 channel design aluminum alloy insert within the 316 Ti stainless steel tube (stainless steel surface on the waterside) giving it exceptional heat exchange characteristics. The efficient heat transfer is the result of three factors:

  1. The high heat conductivity of the alloy insert.

  2. The finned design with special design ridges that greatly increase the turbulence and heat transfer surface.

  3. The division of the internal tube into eight flow channels, creating maximum turbulence and heat exchange surface.

The boiler uses premix burner technology to mix the gas fuel and combustion air prior to entering the surface combustion burner canister. Combined with a variable speed fan, this technology provides low emissions levels, safe operation, and nearly 100% combustion efficiency.

To supply only the amount of heat required to the system, the variable speed fan provides modulated firing to reduce on/off cycling, load tracking, and reduced operating costs. The burner does not require mechanical linkage connections between the fuel input valve or the air control. Instead, the microprocessor control inputs the correct fan speed in accordance with system demand, which then determines the fuel input without the need for mechanical device positioning. This eliminates linkage slippage, minimizes burner maintenance, and provides precise fuel/air ratio control repeatability.

The boiler/burner control used in the Whitman Hanson Regional High School boiler room is the Model MCBA14C, which is standard on the Model CFC. The MCBA14C is an integrated, digital modulating device that controls the following functions:

  • Burner sequencing with safe start check, pre-purge, direct spark ignition, and post purge

  • Electronic direct spark ignition

  • Flame supervision

  • Safety shutdown with digital display of error

  • Control of variable speed for modulation control

  • Supervision of low gas pressure, high gas pressure, combustion air, low water, excess water temperature, and blocked flue

  • Monitoring and control of supply and return water temperatures.

With a variable speed fan, full modulation is accomplished for a 5:1 turndown ratio. The noise level at maximum firing is less than 69 dBA regardless of boiler size. Operating on natural gas, NOx emissions are less than 20 ppm regardless of boiler size.

Information provided by Earle Pfefferkorn, president of C-B Package Boiler, a division of Cleaver Brooks, Milwaukee.



AT A GLANCE

While building Whitman Hanson Regional High School in Massachusetts, engineers specified a Cleaver-Brooks ClearFire Model CFC condensing boiler for energy efficiency and an eco-friendly budget for the 270,000-sq.-ft school.

The engineers installed six of these condensing boilers in the school. The annual gas savings for upgrading to these boilers is estimated to be 11,719 therms, which contributes to predicted annual energy savings of $100,060.

The boiler features AluFer technology, which increases heat transfer over a bare boiler tube by a factor of five. This allows for a reduction in tube count and footprint. The high heat transfer comes about from the high heat conductivity from the alloy insert, the finned design that increases turbulence and heat transfer surface, and the division of the internal tube into eight flow channels, which creates maximum turbulence and heat exchange surface.



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