When you’re responsible for maintaining over two hundred schools, you have a number of expectations for your heating systems. As its cast iron sectional boilers reach the end of their service lifespans, the maintenance department at the Fairfax County Public School System in Virginia has high hopes—to improve energy efficiency, to reduce fuel costs, and to simplify maintenance—that are tempered by bitter experience: some boilers that had been replaced just ten years earlier are nearing the end of their life cycle.
“The key goals,” says Ben Curwin, sales engineer at The Joyce Agency, the local manufacturer’s representative for Viessmann, “are product durability and low maintenance.” Budget pressures have reduced the number of available mechanics, making maintenance a major concern. And no authority accountable to the public wants to revisit a major purchase prematurely. In Fairfax, condensing boilers proved to be the natural choice for improving efficiency; but to achieve its maintenance and durability goals the county needed to go with a boiler design built for both simplicity and endurance.
Sangster Elementary School, a building of approximately 100,000 SF, was designated as the county’s testing ground for the application of a high-mass condensing boiler manufactured by Viessmann. The Vitocrossal 200, CM2-311, holds 74 gallons of water with an exceptionally low pressure drop through the heat exchanger. Because of the large water content, or high mass, the CM2 boiler is not sensitive to flow changes and can be directly connected to an existing hydronic heating system. The titanium-stabilized stainless-steel heat exchanger is tolerant to cold return water temperatures or large temperature differentials without experiencing issues with thermal shock. The boiler’s inherent stability eliminates the need for a complex three-way valve on the return, boiler circulating pumps, buffer tanks and primary loop piping. The reduction of moving parts improves both energy and maintenance efficiency. Designed to accept a wide range of water temperatures and flow rates, the Viessmann boilers, Curwin notes,
“don’t cycle much - it’s like a fly wheel for a heating system.”
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Easy maintenance is a must. Fairfax County has seen a significant reduction in maintenance hours when using Viessmann’s CM2 boilers; compared to other condensing and cast iron sectional boilers. There are multiple layers for support locally, allowing Fairfax
County to get the proper resources for service, training and parts. The Joyce Agency and Boland Trane provide that local support to the engineers, contractors and owners, including multiple factory trained technicians to quickly respond to any service issues.
Don Kingsford, the sales and design consultant for the installing contractor, Hurley Company, admires the new boiler’s resistance to shock. Previous systems used a three-way valve to protect the boiler. With night setback, the return water could drop as low as 70° F overnight, shocking the boilers in the morning with cold temperatures that could crack sections. This would result in expensive and time-consuming repairs. The new system, built around the stainless-steel heat exchanger with a more than 30-year track record for durability, eliminates the shock threat.
Sangster now employs two CM2-311s for 2,224 MBH total input capacity. Since the conversion is designed to integrate with, rather than replace, the current plumbing and heat emitters, the boiler will maintain a 180 °F temperature only on the design day with an outdoor temperature of 14 °F. The county anticipates that it can fulfill the boiler’s potential for condensing operation and greater efficiency when higher outdoor temperatures allow for lower loop temperatures during the majority of the occupied hours of the heating season.
Given the opportunities to extend conversions to many other schools, ease of installation is a crucial virtue. “When
I get a Viessmann boiler,” Kingsford says, “boom—it’s all there. I practically just jack it up and roll it into the boiler room. We don’t have to install or wire the burner—all I have to do is bring power to it.” Unlike other boilers, the
Viessmann boilers accept gas hook-ups from the left, the right or even the back, which reduces installation hassles.
The polypropylene venting takes less than half the time to install than conventional stainless steel venting. Viessmann’s standard control platform can control the entire heating system, from outdoor reset for multiple heating circuits to pump enabling. This is essential in maximizing the boiler efficiency and further reduces complication and involvement for Fairfax County Public Schools.
Hurley Company completed the Sangster installation in the summer of 2013. With more than two hundred schools in its system, Fairfax County Public Schools acknowledges the math—the efficiency gained at each school could quickly add up to significant cost savings for the entire county. “They don’t want their boilers to be a headache,” Curwin says. “Viessmann heat exchangers have a solid history that goes back to the 1980’s. With these conversions, Fairfax County gains peace of mind while saving energy.”
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Viessmann Manufacturing
Company Inc.
Waterloo, ON Canada
1-800-387-7373 www.viessmann.ca
Viessmann Manufacturing
Company (U.S.) Inc.
Warwick, RI U.S.A.
1-800-288-0667 www.viessmann.us
Vitocrossal 200, CM2 gas-fired condensing boiler
Model
Combustion Efficiency *
Thermal Efficiency *
Minimum Input (NG)
Maximum Input (NG)
Output *
Net AHRI Rating
Overall Dimension †
Width
Height
Depth (Length)
CM2
%
%
MBH
MBH
MBH
MBH
CM2-186
95
97
133
663
643
559
CM2-246
95
97
175
878
851
740
CM2-311
95
97
222
1112
1078
937
CM2-400
95.1
95
287
1445
1372
1193
CM2-500
95.1
95
358
1800
1710
1487
CM2-620
Inches
Inches
Inches
36.5
66
73
36.5
66
73
36.5
66
73
42.4
65.6
89.5
42.4
65.6
95.6
44.3
68.75
100.7
Weight (burner, control and insulation) lbs 726 759 792 1495 1662 1929
Boiler Water Content
Heat Exchanger Surface
Maximum Operating Pressure
USG ft.
² psig
81
72.9
75
77
98.8
75
74
121.5
75
104
166.6
75
112
208.6
75
* Tested to AHRI Testing Standard Method to Determine Efficiency of Commercial Space Heating Boilers, BTS-2000.
† Includes boiler with burner, boiler panels, thermal insulation, boiler control unit and electrical connection box. Note:
For high altitude installations (5,000 to
10,000 ft.), the input will have an altitude de-ration of 15% for 5,000 ft. and 18% for 10,000 ft. Technical information subject to change without notice.
131
234
75
95.1
95
450
2245
2132
1854
H
Technical information subject to change without notice.
5547 738 - 03 03/2015 Printed in Canada
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