general air products inc - fire protection air compressors - selection and design

Air Compressors Air Compressors & Accessories & Accessories

Selection and Selection and DesignDesign

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Dry Pipe System Air CompressorsDry Pipe System Air Compressors

NFPA 13D Residential Fire PumpsNFPA 13D Residential Fire Pumps

Presenter: Presenter: Geoff PridhamGeoff Pridham

Technical Support Technical Support ManagerManager

Background:

• Electrical / Electronics Engineer

• 30+ Years Experience in Equipment Manufacture

• 16 Years Experience in Fire Protection Industry

• Email: [email protected]

What we will cover What we will cover today…today…

• Key Terms, Concepts and Codes

• Selecting a Dry Pipe Compressor by Type and Application

• Air Compressor Accessories

• How to Size an Air Compressor for a Dry Pipe Sprinkler System

• What to Consider When Writing an Air Compressor Spec

Key Terms, Key Terms, Concepts & CodesConcepts & Codes

NFPA 13 7.2.6* - Air Pressure and Supply

- This section of NFPA 13 governs most of what we will be discussing today.

Key Terms, Concepts & CodesKey Terms, Concepts & Codes

Holding Pressure

- The MINIMUM pressure at which the system needs to be maintained (13, 7.2.6.6.1)


Holding Pressure in a dry pipe system is primarily determined by the following factors:

- Valve Ratio

- System Type

- Site Variations in Water Pressure

- Trip Pressure


Holding Pressure (System) vs. Feed Pressure (from Compressor)

- Feed pressure from the air compressor must be higher than the system holding pressure in order for the compressor to flow air into the system.


Pressure Drop and the Compressor

- Trim Components

- Leaks between the Air Compressor and the Dry Pipe Valve


Pump Up Time

- The pump up time is the time for the system piping to rise to the final design holding pressure.


Air Compressor Pressure Setting

- Standard setting is 40 psi

- Low Pressure setting is 20 psi

- High Pressure setting is 60 psi


Pressure Switch Differential

- Pressure switch differential is the difference between the point at which the compressor is set to turn off and the point at which the compressor is set to turn back on.

- Note that this is different from the highest pressure and the lowest pressure the system sees.

- Expansion and contraction in the system air can change the pressures regardless of what the compressor is set for.


Pressure Regulation

- Pressure regulation is the varying (fine tuning) of the feed pressure from the compressor to the system.

- Employ an Air Maintenance Device (AMD) (13, 7.2.6.5.1)


System Capacity

- The total system capacity as far as compressor sizing is concerned should include the piping network as well as the compressor feed piping and riser volume (13, 7.2.3.1)

Selecting A Compressor Selecting A Compressor by Type and Applicationby Type and Application

Oil less… Lubricated… Parking Garage… Freezer Room…

Selecting a Compressor by Selecting a Compressor by Type and ApplicationType and Application

There are many reasons for selecting a particular compressor type:

• Listing requirements may be specified in the job specs.

• Cost. Always a factor and sometimes the deciding factor.

• Amount of maintenance available on site.

• Temperature of the ambient around the piping network.

• Physical room available for the placement of the compressor.

• Existing installation and replacement can be a factor.

• Available power supply may be in the decision.

• It can be a personal choice decision. Designers or fitters comfortable with one type over another can be the single deciding factor.


Oil less Air Compressors vs. Lubricated Air Compressors

- Oil less

Pro: Minimal Maintenance, Flexibility of Installation, Minimum Footprint

Con: Higher Initial Cost

- Lubricated

Pro: Lower Initial Cost, Simple Parts Replacements

Con: More Frequent Maintenance


Riser Mounted, Floor Mounted, or Tank Mounted?

High Pressure, Standard Pressure, or Low Pressure?

- Dictated by valve selection and holding pressure


Does Your System Require Dry Air?

- Why would dry air be important?

The act of compressing air condenses water and that water flows into the system.

Dry Air Applications:

- Freezer Rooms / Cold Storage Facilities

- Parking Garages

- Stadiums

- Data Centers

- Museums


Dry Air Also Aids in Corrosion Management…

- Less standing water in a system, the less chance there is for corrosion.

Additional Note On Corrosion:

- Nitrogen Generation Systems (13, 7.2.6.7)


What ever you do,

DO NOT USE A RETAIL AIR COMPRESSOR IN A DRY PIPE SYSTEM

Why?

- Retail compressors are not industrial duty and therefore not reliable in a fire protection application

- Fire Protection air compressors are built for maximum air delivery

- Retail air compressors are not designed to perform to the standards set by NFPA 13

- They are built for high pressure / low flow usage

- Your installers will not be able to get any field support for issues at installation and beyond.


Important Note on Voltage:

- The higher the voltage used on site the smaller the wire size required.

- Take into account:

- Voltage drop due to wire run from main power source

- Start up current spike

Air Compressor Air Compressor AccessoriesAccessories

Motor Starters… Pressure Switches… Air Maintenance Devices…

Air Compressor AccessoriesAir Compressor Accessories

Motor Starters (Line Starters):

General Air Products' IEC Line Starter provide protection to motor windings from harmful currents that result in temperature rises that may be caused by either overloading the motor, sustained low line voltage, or locked rotor.

Note: We strongly recommend that a line starter accompany every General Air Products' air compressor.


Pressure Switches:

- Proper setting is vital to compressor operation and lifespan.

- Our standard pressure setting is a 13 pound differential.


Pressure Switch and Line Starter Wiring Diagram:


Air Maintenance Devices:

The AMD-2 is used forautomatic operation with a dedicated air compressor for a sprinkler system, such as a base mounted compressor.

The AMD-1 is used when compressed air is

supplied through an existing factory air supply

or when a using tank mounted unit.


Tanks (Pressure Vessels):

Riser MountedVertical Horizontal


Noise & Vibration Reduction Accessories:

- Note on Noise: Air compressors make noise and there is no getting around that. Take this into account during the design phase where possible.

- Flex hose- Vibration Pads- Intake Filter Silencer

How to Properly Size an How to Properly Size an Air CompressorAir Compressor

How to Properly Size an Air CompressorHow to Properly Size an Air Compressor

1.) The choice of unit starts with the holding pressure of the system. What is the final value you need to hold the system to? This pegs the design pressure for the compressor.

- Let’s use 35 psi as an example.

2.) Next is the system capacity. What is the total system gallon capacity of the piping structure?

- We will use 450 gallons as an example. 400 gallon system capacity plus 50 gallons ancillary feed piping.


3.) Next is the pump up time. What is the time that the inspector or designer is calling out for the system?

- Let’s use 30 minutes as an example. (13, 7.2.6.2.2)

4.) Last is the site location and elevation. Corrections for the site elevation should be compensated for in the selection. Many times this is missed and affects the final performance of the compressor.

- We will use 1000 feet above sea level. Atmospheric pressure = 14.2 psia


- 450 gallons converted to cubic feet = 60.165 (60.2) cubic feet

- This is the volume that the compressor has to fill to final pressure of 35 psi (49.7 psia)

- Atmospheric pressure at the compressor suction (1000 ft.) = 14.2 psia

- 60.2 x (49.7 / 14.2) = 210.6 cubic feet of air will be in the piping system at the 35 psig final holding pressure.

- The amount in the piping to begin with at rest was 60.2 cubic feet.

- The difference the compressor needs to add is 210.6 – 60.2 = 150.4 cubic feet. The fill time required as stated previously is 30 minutes.

- 150.4 cubic feet / 30 minutes = 5.01 cu ft/ min.


- The compressor required by the system in this example must deliver 5.01 cubic feet per minute or better to achieve the desired result.

- Our standard 425 gallon models are suitable as they are all sized to 40 psig and the requirement here is 35 psig.

- For other manufacturers be sure to check their standard conditions.

- We have made this procedure simpler in the catalog model data by rating our air compressors in system capacities (gallons) based upon 40 psi and 30 minutes at sea level.

What to Consider When Writing What to Consider When Writing an Air Compressor an Air Compressor

SpecSpec

What to Consider When Writing an Air What to Consider When Writing an Air Compressor SpecCompressor Spec

- Below is an example of an Air Compressor Spec that we have written and is available on the Spec Center Section of our web site.

Dry Pipe System Air CompressorsDry Pipe System Air Compressors

NFPA 13D Residential Fire PumpsNFPA 13D Residential Fire Pumps

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