A greenhouse is disclosed that generally comprises a growing section, and an air or gas distribution system within said growing section, said distribution system comprising one or more conduits for distributing air or gas within said greenhouse, said conduits comprising an inner conduit within an outer conduit, said conduits carrying air or gas having different pressures along their length, with a main airflow entering said growing section from said distribution system passing into said conduits, said inner conduit comprising inner conduit holes to allow said main air flow within said conduits to pass from within said inner conduit and said outer conduit and said outer conduit comprising outer conduit holes that allow air passing from said inner conduit to pass into said growing section, wherein said inner and outer conduit holes are configured to compensate for the directional flow of said main airflow within said conduits to provide substantially equal distribution of air or gas throughout said growing sect
