Industrial Utility Efficiency    

Level 1 NFPA Medical Compressed Air Systems

Located in the bowels of most hospitals, you will find the source of the Level 1 Medical Air compressed air system. Per the NFPA Section 99 Specification (National Fire Protection Association), Level 1 air compressor systems provide air for human consumption within the hospital facility. Level 2 Systems are used where patients are not dependent upon mechanical ventilation (such as driving pneumatic tools). Level 3 Systems are used to drive hand pieces in dental offices or hospitals. Medical air may be supplied from cylinders, bulk containers and/or medical air compressors. The definition of a medical air compressor (per NFPA) is a compressor that is designed to exclude oil from the air stream and compression chamber and that does not, under normal operating conditions or any single fault, add toxic or flammable contaminants to the compressed air.

A Level 1 medical compressed air system is made up of four major sections; the compressors, control panel, receiver, and purification. The air system supplies compressed air through hundreds, if not thousands, of feet of copper pipe that has been cleaned and installed per requirements established by the NFPA Section 99 Specification. The pipeline leads to many areas of the hospital with the most vital area being surgery. Surgery and patient rooms are equipped with medical outlets that act as quick connections for attaching respirators and ventilators.

Powerex SOS Scroll Medical Compressors

Air compressors used in medical systems have been evolving over the last twenty years. Historically, air compressors were mostly of two different technologies; liquid ring and oil-free reciprocating. Liquid ring pumps are very reliable, however, they require water to cool and seal the pump, which increases operating costs due to the additional cost of the water and sewage. Oil-free reciprocating air compressors have a oil-free piston and cylinder with an oil-lubricated crankshaft and crankcase. The piston and crankcase areas are separated by a extension shaft. This extension shaft is required, by NFPA 99, to be within visual access, to insure that the extension seals are not leaking oil that could find its way to the piston and cylinder.

 

Oil-less Scroll Air Compressors

The primary technologies used today are oil-less reciprocating and oil-less scroll air compressors. Reciprocating oil-less pumps have proven to be reliable in applications requiring less than a 50 % duty cycle. A lower duty-cycle reduces the temperatures of the piston and cylinder areas. Powerex reciprocating pumps are designed and built with composite piston technology that greatly reduces the temperature of the cylinder areas and the temperature on the wrist pin bearing.

 

Powerex Oil-less Reciprocating Compressor

Oil-less scroll technology has become the technology of choice. Scroll technology is capable of a 100% duty cycle, because its low bearing loads, and higher speeds, allow the pump to be air-cooled with high-velocity cooling fans. Scroll compressors are physically smaller and provide high output.

Powerex offers the scroll pumps in 3 and 5 horsepower sizes. Smaller horsepower compressors provide lower operating costs and extend service intervals. These relatively small horsepower systems, with multiple compressor pumps, fit the demands of a hospital system very well. Medical air systems in the hospital have varying demands all day long. The morning hours, when most surgeries are scheduled, provide the greatest demands on the air system. At night, these systems experience very low air demand. Banking multiple 3 to 5 horsepower air compressors allows energy costs to more closely match air demand by turning off un-needed air compressor horsepower.

 

Multi-unit Scroll Compressor Package

 

Control Systems and Panels

Powerex combines scroll technology with its demand control system to drive down the costs of ownership. Newly released enclosed scroll compressor systems offer lower noise levels of 53 dbA (similar to the noise level of a microwave oven) and come in 15 and 20 horsepower models. Each module comes with a solid-state circuit board to allow the operation of each module while alternating between each enclosure. Powerex enclosed systems allow the advantage of adding cooling air ducting and hot exhaust air ducting which will lower the temperature and noise of the mechanical room. Control panels manage the operation and protection of the systems electrical components. These control panels contain all of the regulator components used in industrial electric motor applications as well as a circuit of alarms.

Latching relays are used to control the sequence of operation along with timers. Many manufacturers are using more advanced control circuits that include solid-state circuit boards or PLC’s (Programmable Logic Controllers). Powerex is registered by the Underwriters Laboratory to manufacture control panels per UL508A. This listing is required by the NFPA. Receiver Tank The receiver tanks vary in size and configuration. The receiver is required to be registered by the National Board and must comply with ASME (American Society of Mechanical Engineers). The receiver tanks are required to be lined with a coating to prevent corrosion. Most corrosion-resistant materials are epoxy linings or galvanized coatings. Powerex uses an FDA (Food and Drug Administration) approved phenolic lining, that is baked on, to prevent any chance of off-gassing after being applied. Receivers are required to provide bypass piping per NFPA 99. Air Purification It is critical to remove moisture from the compressed air system. Compressed air leaving the air compressor flows through the receiver tank and into compressed air dryers. The NFPA 99 Specification requires the installation of two dryers - keeping one dryer in reserve in case of a malfunction.

The two acceptable types of air dryers are refrigerated and desiccant-type dryers. The NFPA requires that the dryer produce a dew point of 32 degrees F or lower. The alarm system for this requirement is set at 39 degrees F. Refrigerated dryers are not able to deliver the 32 F requirement at the commonly used pressure of 100 psig (pounds per square in gauge). In-order for refrigerated-type dryers to deliver the required 32 F dew point, the air must be expanded. This is accomplished after the final line pressure regulator, which is to be set at 55 psig. The average refrigerated dryer would provide a 39 F dew point at 100 psig and when expanded to 55 psig would deliver a 21 F dew point which is well within the 32 F requirement of the NFPA 99 code. Lower-pressure, liquid-ring compressor systems make it even more difficult to achieve the 32 F requirement and can cause frequent nuisance dew point alarms. The trend today is to move towards systems using desiccant-type air dryers. These regenerative drying systems utilize chemical drying techniques to adsorb the moisture and then have the moisture vented back to atmosphere. Desiccant dryers are constructed of two towers filled with either molecular sieve or activated alumina. Powerex desiccant dryers have four modes of operation that provide clean dry compressed air:

  1. Expansion Phase- pressure in one tower is released to ambient with a blast of air through the muffler
  2. Dehumidification Phase- dried compressed air is bled by orifice through the decompressed chamber
  3. Pressure Phase- after dehumidification the chamber will pressurize so that the switchover from regeneration to adsorption can take place
  4. Standby Phase- the dew point monitor signals when the chambers are to switch. This reduces the amount of purge air consumed, lowering the operating of the system.

 

Medical Air Installation With Desiccant Air Dryers

After the air leaves the dryer it then flows through a particulate filter and a carbon filter. These filters remove particles of .01 micron, oil vapors and odor from the air stream. These filters are required to be backed-up by a secondary set of filters to enable replacement without interrupting the air stream. The plumbing throughout the air system must be cleaned for oxygen service per CGA (Compressed Gas Association) 4.1, the specification which outlines the process for pipe cleaning. Final-line pressure regulators are then placed in the pipeline to reduce the air pressure before entering the hospitals’ pipeline. This regulator is required to be backed up by a second regulator. After leaving the regulator, the air is monitored for carbon monoxide (CO) and dew point. Carbon monoxide must not exceed 10 PPM. When levels of CO register higher than this, a visual and audible alarm will sound locally at the air compressor and at a location that is manned 24 hours - typically the nurses station or the security department. A second alarm system is usually found in the mechanical room of the hospital. The required alarms and defined locations are listed in the NFPA 99 code. The dew point alarm is required to activate when moisture levels go above a 39 F dew point.

Medical Air Level 1 compressed air systems reliably provide purified air for hospitals. The four major components of the system (compressors, control panels, receivers, and purification) meet with very specific specifications, which ensure safe and reliable air for the hospital.

 

For more information, please contact Don Baer, Product Manager, Powerex Inc., tel: 888-769-7979 ext. 8580, email: dbaer@powerexinc.com, www.powerexinc.com

Powerex (Pure Air Technology) Inc. is located in Harrison, Ohio and was established in 1982. Powerex manufactures compressed air and vacuum systems for healthcare, laboratory, process, and environmental applications.