The architect and building engineers knew they were going to have to provide for the comfort of as many as 14,000 travelers on any one day. That meant a 250,000 square-foot facility with gates for 25 airplanes.

But cooling demand was going to ebb and flow with passenger load. At peak times of travel the parallel hot-and-cold water systems would run at full capacity to serve busy washrooms and kitchens as well as the building's heating and air-conditioning systems.

At night and other times of fewer arrivals and departures, load requirement was reduced. System designed to meet and continuous operate at peak demand would waste energy unless a reliable way could be found to modulate with the load.

Using computer modeling, systems designers at Bell & Gossett's Packaged Systems Group, a suburban Chicago fluid handling subsidiary of ITT Fluid Technology Corp., showed variable speed pumps could supply hot and cold water to the terminal at less than half the cost of pumps set to run at one constant speed. Following is their rationale.

Assuming a nominal 10 cents per kilowatt hour (KWH) cost of operating the pumps, the Bell & Gossett engineers found it would cost $20,200 a year to run a 1,090 gallon per minute (GPM) chilled water pump, but only $8,800 to operate a pump of the same capacity at variable speeds to match the system load.

For hot-water requirements, the computer modeling showed it would cost over $4,200 a year to operate a constant-speed 155 GPM pump at 10 cents pre KWH, but only about $1,800 to run the same pump at variable speeds.

Savings in terms of efficiency of operation would also be dramatic, the study revealed. During the 2 hours a day when the chilled water system would be running at minimum (218 GPM), the constant speed pump would be running at 25.6 brake horsepower. The variable-speed pump would be operating at about 40% speed and consuming only 3.1 horsepower.

The variable-speed pump would be operating at 50.3% efficiency while the constant-speed pump would be operating at only 24.7%. In terms of operating cost, the variable speed pump was running at $.56 per day rate versus a $4.59 rate for the constant-speed pump. Of course, overall efficiency would be greater for the constant-speed pump during the 1º hours a day when the system would be running at 100% of design. Efficiency for the variable-speed system during that short period would be slightly lower due to the power consumption of the adjustable frequency drive (AFD). The cost of operation during those 1º hours would be nearly equal, however: $3,74 a day for the constant-speed system and $3.78 a day for the variable-speed.

Cost of operating the variable speed system would be less than one-third that of the constant-speed pump during the longest daily stretch of constant demand - those 7.2 hours when the American Airlines terminal would require 545 gallons of cool water a minute. Both systems would be running at 50% of design capacity, but the horsepower draw for the variable-speed system would be 9.3 horsepower. Cost of operation during that load would be $5.01 for variable-speed: $16.55 for constant-speed.

Computer modeling for both the variable-speed and constant speed systems was performed on the basis of using a 50 horsepower, size 6E Bell & Gossett series 1510 end suction pump for chilled water circulation. Impeller diameter was 10.625 inches, and RPM was 1,770. The 1,090 peak GPM systems produced system design discharge pressure at 98 feet of head.

For the smaller hot-water system, modeling was done on the basis of using a 10 horsepower, size 2E Bell & Gossett end suction pump with a design RPM of 1,750. Impeller diameter was 10.75 inches and the 155 GPM systems produced a system design discharge pressure of at 113 feet of head.

It was assumed the hot water system would operate continuously. The chilled water system would operate an average of 22.8 hours a day for 365 days of the year.

Convinced of the potential cost savings, American Airlines ordered complete Bell & Gossett PowerSav pumping systems. The variable speed hot-water system consists of two 10 horsepower pumps, two adjustable frequency drives (one for stand-by), a Technologicô 2000 pump controller and two differential pressure sensor/transmitters.

Programmable and interfaced with the airline terminal's energy management system, the Technologic 2000 pump controller monitors four zones, calculating pump speeds to match the demand. Set points of the sensor/transmitter can be reset individually at the Technologic Pump Controller.

All Bell & Gossett controllers are designed to safeguard against potentially damaging pump conditions such as improper staging and destaging while maintaining smooth operating through PID algorithms. They are programmed to perform diagnostic fault-finding on the pumps, motors, sensor/transmitters, adjustable frequency drives, and the controller itself.

Bell & Gossett adjustable frequency drives are all fitted with fault detection/trip circuits, manual speed controls indicating meters, status lights, alarm lights, ground fault protection, elapsed time meters and H-O-A Switches.

The American Airlines Systems are also equipped with the unique PowerSav Type C automatic AFD bypasses. Since operation of this system is considered to be critical for passenger comfort, the Technologic pump controller is programmed to monitor not only AFD, but also the pump motor, sensor/transmitters, and the system differential pressure for fault conditions. If a fault is detected in any of the above components, the Technologic 2000 C pump controller will turn off the lead system and automatically tart the stand-by variable speed system and give an alarm. This ensures continuous energy saving variable speed operation even if a failure occurs.

ITT Bell & Gossett has a complete line of PowerSav systems to match users' various needs. The full line includes three job specific Technologic pump controllers, a full range of adjustable frequency drives, five varieties of sensor/transmitters and large selection of Bell & Gossett pumps.

So, how's the system operating? Very well, says facility maintenance engineer Patrick Nadua, It's well suited to an installation like this one, where needs are changing all the time, and seems to be matched to the requirements of our facility very well.

Variable Speed Pumping System Keeps
Medical Research Center Pumping Cool

What's the most efficient way to control the climate in a medical research building, where minor variations in temperature and humidity can upset delicate scientific experiments? And, how can it be done effectively when the building is a sprawling, one-story 135,000 square foot structure in the humid Southeastern city of Durham, North Carolina?

These were two critical questions facing Glaxo, Inc., a prominent international pharmaceutical manufacturer, when construction plans were being developed in 1988 for the firm's Venture Center in Research Triangle Park.

The design engineers were faced with maintaining temperatures between 72 and 74F 24 hours a day. Glaxo's research personnel and equipment would be housed here, including delicate animal and chemical experiments. Humidity was a concern, since a moisture imbalance could do costly damage. Another concern was the emission of destructive RFI (radio frequency) and EMI (electro-magnetic) interference.

Moreover, the entire job had to be specified, designed and built in about six months, where a project like this normally requires a year or more.

To meet these challenges, design engineers from Glaxo and O'Brien Atkins, P.A., a Durham-based consulting engineering firm, could have gone with the conventional solution: Install constant speed pumps and regulate the flow through the building distribution loop using two-way valves. This is a proven solution with a lower initial investment than some other options.

However, a constant speed pump doesn't maintain high efficiencies under varying operating conditions. The pumps would be sized to meet peak demand, and valves would have to be throttled for the pumps to work close to actual block load design, which would occur the majority of the time.

Early projections indicated that pumping chilled water throughout the Venture Center was going to require two 75-horsepower pumps capable of 2400 GPM at 90 feet TDH and 1750 RPM. The yearly cost of operating both constant speed pumps in parallel and staging to a single pump under low load conditions was calculated at $46,034.

The design engineers opted for a more effective solution. Working closely with the Packaged Systems Group of Bell & Gossett (B & G), a Chicago area subsidiary of ITT Fluid Technology Corp., they quickly determined that the superior option was a PowerSavô Variable Speed Pumping System.

Running both of the 2400 GPM variable speed pumps in parallel and operating only one of the pumps to carry the load when demand was light (while automatically staging on the other as load increased) would cost only $17,461 a year. The savings, $28,573 a year, would pay for the variable speed pumps in less than two years.

Four differential pressure sensor/transmitters were installed around the Glaxo distribution loop. Set points for each are adjusted individually. Additional sensor/transmitters can be installed in the future, if necessary.

The B & G Technologic 3000 Pump controller can be used to monitor up to 15 zones throughout the laboratory building and adjust the pump speed to match actual system demand.

based on specific compliance requirements, Glaxo chose B & G's variable voltage inverter (VVI) adjustable frequency drive (AFD). The VVI/AFD is a logical choice for a laboratory installation because it can meet IEEE 519-1981 and FCC Para 15 subpart J RFI/EMI noise and interference standards without a need for costly and inefficient filters or isolation transformers.

Standard equipment on the VVI drive includes fault detection/trip circuits, manual speed control, indicating meters, status lights, alarm lights, ground fault protection, elapsed time meters and H-O-A switches.

Bell & Gossett was chosen as the pump systems supplier for this rush job. B & G stood ready to deliver a complete system (pumps, pump controllers, adjustable frequency drives and sensor/transmitters) within the required schedule. And the company would take complete unit responsibility for the system, a single source for ordering, delivery, operation and any questions regarding system components or the system as a whole.