ASHRAE 90.1-2007 Overview

Scope of 90.1-2007: Section 2 of the Standard describes what buildings and building systems (e.g.lighting) are covered under 90.1-2007.  It also enumerates what the Standard does NOT cover (e.g. low rise residential buildings where low rise means three stories or less above grade.)

Lighting Scope: Section 9.1.1 of the Standard points out that the following types of lighting are exempt from this section of the Standard:

• any emergency lighting that is automatically turned off during normal business hours,
• any lighting within 'dwelling units' as defined in section 3.2 of the Standard,
• any lighting that has been required by statue, ordinance or regulation, and
• any decorative gas lighting systems

Interior Lighting Power Allowance: Sections 9.5 and 9.6 of the standard describe the two methodologies by which a user may calculate how many watts may be used for the interior lighting:

• Building Area Method: this method allows the user to look up (in Table 9.5.1 of the Standard) the allowance in watts per sq.ft based on building types (e.g. 'Office'); this allowance is then multiplied by the area of the building type to come up with the interior lighting power allowance.  A single project may end up using more than one building type and the individual allowances should be summed to come up with the interior lighting power allowance for the project. Additional considerations include:
  • This method, while easier to use than the Space-by-Space Method, will typically yield a lower number of allowed watts.
  • If the user is unable to find their specific building type in Table 9.5.1, the user may use a 'reasonably equivalent' type from the table.
  • When calculating the area:
    • dimensions to exterior walls should be taken to the outer surface of that wall, and
    • dimensions to interior walls should be taken to the centerline of that wall
• Space-by-Space Method: this method allows the user to look up (in Table 9.6.1 of the Standard) the allowance in watts per sq.ft based on space types (e.g. 'Office-Enclosed'); this allowance is then multiplied by the area of that space to come up with the interior lighting power allowance for the space.  The individual allowances should then be summed to come up with the interior lighting power allowance for the project. Additional considerations include:
  • This method will typically yield a greater number of allowed watts then the Building Area Method.
  • If the user is unable to find their specific space type in Table 9.6.1, the user may use a 'reasonably equivalent' type from the table.
  • The standard describes when the user may claim additional allowance when using decorative lighting or, in the case of retail situations, when using display accent lighting.

Exterior Lighting Power Allowance: Section 9.4.5 of the Standard describes a process similar to the Space-by-Space Method..  Individual area types are looked up in Table 9.4.5 and the listed allowance is then multiplied by either the square feet (e.g. of a parking lot) or linear feet (e.g. along street frontage) of that area.  Additional considerations include:

• The user is allowed 5% more than the sum of the individual allowances.
• Some area types are tradable in that the user may borrow watts from one area and use them in some other tradable area.
• Some area types are 'nontradable'; the watts in those areas are use-it-or-lose-it.
• Section 9.4.5 contains a list of exterior lighting that is exempt from this section.

Installed Interior/Exterior Lighting Power: Sections 9.1.3 and 9.1.4 of the Standard are then used to determine how many watts have been actually installed for the lighting.  Additional considerations include:

• The installed interior lighting power is calculated separate from the exterior.
• In general, the input watts to the luminaire must be used for these calculations, not the lamp watts.
• Section 9.2.2.3 of the Standard contains a list of interior lighting that does not have to be included in this calculation
• The resultant requirement is that:
  • the interior lighting power allowance must be no less than the installed interior lighting power, and
  • the exterior lighting power allowance must be no less than the installed exterior lighting power

Mandatory Provisions:

• Lighting Controls:
  • Auto Shutoff: the lighting in all buildings over 5,000 sq.ft, with certain exceptions, must be on auto shutoff
  • Space Control: the lighting in each individual space must be separately controlled with occupancy sensing being required in certain space types.  There is also a limit on how large an area any one device can control.  This section does allow for remote control in certain situations involving safety or security.
  • Exterior Lighting Control: the types of device options are discussed in section 9.4.1.3 of the Standard dependent on whether or not the lighting is designated as 'dusk-to-dawn'.
  • Additional Controls: section 9.4.1.4 of the Standard lists certain applications where additional control of the lighting is required; this typical means the control must be separate from the general lighting in the space.
• Tandem Wiring: in certain situations, section 9.4.2 requires that the ballasts of linear fluorescent luminaires be tandem wired.
• Exit Signs: Section 9.4.3 sets an upper limit on how watts internally illuminated exit signs may use.
• Exterior Building Grounds Lighting: for exterior lighting not under the control of a motion sensor, Section 9.4.4 sets a minimum efficacy for the lamp(s) being used.