HVAC Systems Encyclopedia

A comprehensive encyclopedia of heating, ventilation, and air conditioning systems

Natural Gas Distribution Infrastructure

Natural gas distribution infrastructure comprises the extensive network of pipelines, compressor stations, storage facilities, and pressure regulation systems that deliver natural gas from production fields to end users. Understanding this infrastructure is essential for HVAC professionals working with gas-fired equipment, as system pressure, composition variability, and supply reliability directly impact equipment performance and safety.

Interstate Pipeline Systems

Interstate pipelines form the backbone of natural gas transmission across regional and national boundaries. These high-pressure systems operate at 500-1400 psi and transport gas over hundreds or thousands of miles. Pipeline diameters range from 16 to 48 inches, with larger diameters providing greater transmission capacity while minimizing friction losses. Interstate systems connect production areas to major consumption centers and storage facilities.

The Federal Energy Regulatory Commission (FERC) regulates interstate pipeline operations, establishing safety standards, tariff structures, and capacity allocation procedures. HVAC applications indirectly depend on this interstate network for fuel supply reliability, particularly in regions distant from production areas.

Intrastate Pipeline Distribution

Intrastate pipelines operate within state boundaries and bridge the gap between interstate transmission and local distribution networks. Operating pressures typically range from 200-500 psi, stepping down from interstate transmission levels. These systems include branch lines, lateral connections, and regional distribution mains that serve multiple distribution companies.

Pressure regulation stations at key points reduce pressure to levels suitable for local distribution systems. Understanding pressure levels at equipment connection points is critical for proper gas valve sizing and burner orifice selection in HVAC applications.

Local Distribution Companies (LDC)

Local distribution companies operate the final delivery infrastructure serving residential, commercial, and industrial customers. LDC networks consist of medium-pressure mains (60 psi or less) and low-pressure distribution lines (0.25-2 psi). Service lines connect individual buildings to the distribution main, with pressure regulators reducing pressure to appliance-level requirements.

LDCs maintain responsibility for gas quality, pressure stability, and odorization (typically with mercaptan compounds for leak detection). HVAC contractors must coordinate with LDCs for service upgrades, meter sizing, and pressure verification when installing large gas-fired equipment.

Pipeline Pressure Levels

Natural gas distribution employs multiple pressure tiers to optimize transmission efficiency and end-use safety:

  • Transmission pressures: 500-1400 psi for long-distance transport
  • High-pressure distribution: 60-200 psi for industrial feeders
  • Medium-pressure distribution: 0.5-60 psi for commercial areas
  • Low-pressure distribution: 0.25-2 psi for residential neighborhoods
  • Appliance pressure: typically 3.5-14 inches water column (0.13-0.5 psi)

Multiple pressure reduction stages prevent excessive velocity, minimize leakage potential, and provide operational flexibility. HVAC professionals must verify available supply pressure and size pressure regulators appropriately for equipment gas input requirements.

Compressor Stations

Compressor stations located every 50-100 miles along transmission pipelines compensate for friction-induced pressure drops and maintain gas velocity. Reciprocating and centrifugal compressors driven by natural gas engines or electric motors add 50-150 psi per stage. Station spacing depends on pipeline diameter, flow rate, and terrain.

Compression increases gas temperature, necessitating aftercoolers to prevent pipeline thermal expansion issues and improve efficiency. Understanding the compression-heating relationship helps HVAC professionals recognize gas temperature variations at delivery points.

Underground Storage Facilities

Underground storage provides seasonal supply balancing, meeting peak winter heating demand and absorbing summer production surpluses. Storage types include:

Depleted gas fields: Former production reservoirs with proven containment geology, offering large capacity and moderate injection/withdrawal rates.

Aquifer storage: Underground water-bearing formations displaced by natural gas, requiring more extensive geological characterization than depleted fields.

Salt cavern storage: Solution-mined cavities in salt deposits providing rapid injection/withdrawal cycling capability despite smaller total capacity.

Storage working gas capacity (gas available for withdrawal) differs from total capacity, with cushion gas remaining permanently in storage to maintain pressure. HVAC loads contribute significantly to seasonal storage cycling, particularly in heating-dominated climates.

Peak Shaving Facilities

Peak shaving facilities supplement pipeline supply during extreme demand periods, typically cold winter days when heating loads surge. These facilities include:

  • Liquefied natural gas (LNG) storage with vaporization equipment
  • Propane-air mixing plants producing synthetic natural gas
  • Compressed natural gas storage in high-pressure vessels

LNG peak shaving plants liquefy natural gas during low-demand periods and revaporize it during peak events, effectively providing short-term storage at atmospheric pressure. Propane-air facilities blend propane with air to match natural gas heating value and combustion characteristics, though Wobbe Index differences may affect some burner systems.

Understanding peak shaving operations helps HVAC professionals anticipate potential gas composition variations during extreme weather events and verify equipment compatibility with supplemental gas sources.