When designing their first portable air conditioning unit, the owners and designers at NorthWind Inc. focused on the needs of their customers. Precision cabinetry, unit size and performance were vitally important considerations, and noise reduction ranked as top priority.

“To satisfy our customers,” says company co-founder John Spencer, “keeping noise level of our units to a minimum is essential. Excessive air conditioner noise can be annoying in most applications so reducing noise was our number one design priority.”

The desire to reduce unit noise was paramount to both Joe Pius, president, and John Spencer, vice-president sales and marketing, two men with nearly 80 years of combined refrigeration experience. After founding their Elk Grove Village, Ill.-based company, they worked with designer Bill Jackson, to create a line of low noise industrial/commercial portable air conditioners. Reducing noise and vibration generated by fans and blowers — the biggest source of noise in an HVAC/R unit — emerged as a predominant challenge to NorthWind.

In less than a year’s time, NorthWind designed and built portable air conditioning units for the rugged conditions of the rental market. These units are used in applications such as computer-server rooms, offices, emergency cooling, and even the sand fields of Iraq.

Going to the source

Rosenberg Ecofit fans and blowers inside the Tundra unit.

NorthWind realized that most blower/motor combinations are bought independently, then assembled and installed in equipment. Typically, those components are not balanced as an assembly. This method often causes vibration. NorthWind spent months researching technology that would best reduce noise and vibration, while also meeting size constraints and air-flow requirements.

They found the blowers they needed in France, made by Ecofit, a company owned by German-based Rosenberg. According to Pius, the external rotor blower system is not found on any other portable air conditioner, but is found in the state rooms of the Queen Elizabeth II cruise ship.

This wasn’t a case of buying blowers off the shelf and putting them into existing designs. “Instead,” says Spencer, “we designed our units around the blowers.”

The product series they created, the Tundra, is the result of that effort. Tundra units come in two sizes: 1-ton and 1.5-ton capacities, 115V, with an operating range of 50 DegF to 115 DegF, which Spencer says has a much broader range than most units. The 1.5- ton unit has a capacity of 16,900 BTU/HR at 95 degree dry bulb (DB) and 83 degree wet bulb (WB) at 60 percent relative humidity (RH) and 17,200 BTU/HR at 115 DegDB/95 DegWB at 50 percent RH as verified by UL performance testing.

The Tundra series is so vibration-free that it can pass the nickel test. A nickel can be balanced on its edge during start up and will remain balanced while running, regardless of the fan speed selected. The Tundra series features a 2-speed Ecofit blower in both the evaporator and condenser sections. The forward curved blowers feature an external rotor, totally enclosed, ball bearing, and thermally protected motor. The motors have a lower starting current. The wheel and motor are balanced in two planes as an assembly, which is the secret to vibration-free operation.

The Tundra series went through several iterations before a final design was approved. One version had the blower discharge mounted close to the unit’s discharge, but that was too noisy. The final solution involved lowering the blower in the cabinet and attaching a duct that acts as a plenum. “Attaching the duct helped attenuate the noise. This system is the best solution for balancing cost vs. noise,” Spencer says.

Another unique feature of the Tundra series is a two-speed condenser blower that automatically switches speeds. NorthWind contracted with Texas Instruments Sensors & Controls Division, which is now Sensata Technologies, to design a custom switch attached to the liquid line on a Schrader valve, which automatically turns the condenser fan to high or low speed depending on the heat load. “This control will provide fan cycling capability on all of our units,” Spencer said.

Improved air flow

Mounting the motor with a three-leg bracket allows for greater airflow.

Another benefit of the external rotor motor being installed inside the squirrel cage is that this provides improved airflow in a more compact size. “A triangle bracket holds the assembly in place without the motor blocking the inlet air,” says Spencer, “and that helps air flow.”

He added that typical direct-drive blowers block 30 to 40 percent of the opening on the motor side of the blower opening, requiring a bigger blower. But, “bigger doesn’t work for us because we are trying to make a compact unit.”

In portable air conditioning units, size is important. The blowers need to provide good airflow, but not take up too much space. “Efficiency is nice, but it isn’t the primary consideration,” says Spencer. “There are no energy guides for special purpose air conditioners. If we had to build a 13 SEER portable unit, we couldn’t get it through the door. The coils would be huge, and the customer would be hot.”

Other features

A NorthWind Tundra portable air conditioning unit.

NorthWind’s Tundra units feature a 14 FPI evaporator coil with a thermostatic expansion valve that helps assure precision flow of R-22 refrigerant through the entire operating range of the unit. A constant pressure expansion valve controls refrigerant flow at lower ambient temperatures and at lower airflow conditions. It helps prevents evaporator icing and allows the unit to operate in conditions to 50 DegF.

Other features include a hermetic compressor equipped with a thermal overload, accumulator, and capacitor. Each unit also includes Permatron electrostatic UV protected air filters. “This helps reduce the amount of dust being drawn into the computers in server room applications,” says Spencer.

An Advanced Condensate Removal System (ACRS) features a 5-gal. condensate tank, with a condensate pump mounted side-by-side. A diverter valve switches between the two. “In the past, this task alone would take a couple hours to convert, and the customer might need a technician.” says Pius. “Now, you just have to turn a valve.”

This simple solution is part of an overall goal of “plug and cool functionality” which makes units easy to use, whether for limited, short-term use or for more extended needs. For ease of operation, for instance, the Tundra has no electronic or digital controls. “The rental market wants easy-to-operate equipment without a long learning curve,” says Spencer. “And most of our component parts are available at any HVAC wholesaler around the country, making our units easy to maintain and service.”

For more information, enter email: krosenberg@rosenbergusa.com