Negative pressure produces positive results at St. Mary Schools
The steam systems at two Church of Saint Mary schools in Manhasset, NY were in need of a serious overhaul. High fuel cost and inadequate comfort presented officials at both the high school and elementary school with a quandary.
"It was costing us approximately $40,000 annually to heat the high school, and another $14,000 to heat the elementary school," said Joe Cascone, facilities manager for the Church of Saint Mary. Given the size of the two schools, 40,000 sq ft and 18,000 sq ft respectively, no one could argue that fuel cost had gotten out of hand.
In both schools, the major source of inefficiency was poor distribution. It took 6 lbs of steam pressure to get steam to all the elementary school zones and 8 lbs to the high school zones. These high pressures resulted in longer run times on both boiler systems, increasing overall fuel consumption.
TYPICAL PROBLEMSThe problems at these two schools were typical of many facilities where aged steam systems still provide the primary source of heat. Invariably, over time, the ability of the system to efficiently deliver steam to all zones becomes impaired by faulty or poorly maintained traps and other distribution issues. Given these typical realities of older steam systems, the challenge is getting steam to flow quickly through the system without having to generate an inordinate amount of pressure. Fortunately, Ed and Frank Burke of Burke Mechanical Corp., had a solution: A vacuum condensate unit from HT Pump Specialties.
Burke Mechanical Corporation and Cascone were aware of the difference that a properly applied vacuum system could make to a facility's bottom line. Burke Mechanical had successfully applied such systems in the past and Cascone had experienced the transformation at a similar project while employed at another church. Both were eager to see what a vacuum system could do for St. Mary's.
A 120-gal vacuum/boiler feed unit was selected for the combination oil/gas fired steam boiler system at the elementary school. The system is designed to maintain 8 to 10 in. of vacuum pressure at all times. (As a safety, a Heat-Timer Digi-Span setpoint control is installed on the unit control panel, which deactivates the pumps if temperature sensors register that condensate temperatures are approaching high limit.)
As a result, the elementary school now heats up much more quickly and is able to do so at one-quarter the pressure, said Cascone. Since the boiler is operating less often, the school is paying noticeably less for fuel.
NIGHT AND DAYA similar system was applied to the high school steam system. A 36-gal vacuum condensate system was selected for the steam system, which consists of two boilers. Because of space limitations, the high school system did not include a boiler feed tank. Otherwise, the system operates the same as the elementary school, with the Venturi valve assembly serving to create the vacuum in the system.
Results at the high school have been even more dramatic. Operationally, the school is able to maintain heat by running only one boiler at a time, and rotating them every two weeks, whereas before two boilers were required to meet demand. Additionally, the system now operates on a mere ¼ lb of steam - so small that a vapor stat (calibrated in ounces) had to be installed just to be able to register the exact pressure. Boiler runtimes last approximately 18 min/hr compared to the 40 min/hr runtimes of heating seasons past, and it takes only 15 min to get steam to all parts of the high school, whereas it once took two hours.
Fuel consumption is also down - a fact that Cascone has been able to document and attribute directly to the vacuum system, since this was the only change made to the high school. Based on a comparison that takes degree-days into account, the high school system is consuming approximately 1,200 gal less of fuel per month during peak heating season. This reduction in fuel consumption just happened to coincide with a $0.22 increase in oil cost, saving St. Mary's even more.
The difference is like night and day to the occupants and the mechanical staff at both schools. Comfort is up, while fuel usage and maintenance headaches are down.
"It's nice when you can go back to the board and show them the system you recommended is really working," remarked Cascone. "We've got the numbers now to do that."