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Advanced Control Options for LEED v.4

Version 4 of the popular Leadership in Energy & Environmental Design (LEED) green building rating system is expected to be released at Greenbuild in November 2013.

Final balloting to approve the new LEED version is expected to occur in June, so we don’t know exactly what will be contained in the new rating system. One thing is almost certain, which is that the prerequisite for the Energy + Atmosphere section will change from the 2007 to the 2010 version of the ASHRAE/IES 90.1 energy standard.

This is because the 2010 version of 90.1 is now the national energy standard. By October 2013, all states in the country must put in place a commercial building energy code at least as stringent as ASHRAE/IES 90.1-2010 or justify why they can’t comply.

This standard is expected to be tough to beat in terms of both lighting power densities and controls. For controls, ASHRAE/IES 90.1-2010 requires automatic shutoff, bilevel lighting and daylight harvesting in a wide range of applications. These requirements are mandatory, meaning compliance translates to satisfying the LEED prerequisite.

What control options are available that can go beyond the prerequisite and earn LEED Energy + Atmosphere points?

The solution may be contained in the language of the standard. ASHRAE/IES 90.1-2010 contains mandatory control requirements (you have to do this) but also lists advanced control options that may be institute in exchange for a power credit (you do this, and you get more watts for the design as function of the control strategy and the size of the controlled loads).

The advanced control options, applicable to interior lighting systems, are found in Table 9.6.2 (applicable to the Space by Space design compliance method) and include:

• manual or programmable dimming control (must be combined with occupancy sensing in meeting and training spaces);
• multilevel occupancy sensors controlling the downlight component of workstation-specific luminaires with continuous dimming to OFF, which may be combined with occupant dimming of this downlight component;
• automatic bilevel or multilevel switching or continuous dimming daylight harvesting control in primary daylight zones under restrictive conditions related to effective aperture and size of zone; and
• automatic continuous dimming daylight harvesting control in secondary sidelighted daylight zones with a daylight aperture considered large enough.

Again, implementing these strategies above and beyond all applicable mandatory strategies is rewarded with a power adjustment credit using the following formula:

Additional Interior Lighting Power Allowance = Lighting Power Under Control (watts) x Control Factor (specific to the given control strategy by space type, from Table 9.6.2)

The control factor is specific to control strategy (manual dimming, etc.) and space type (open office, private office, meeting space and various public spaces). The factor ranges from 0.05 (manual dimming in a private office) to 0.30 (occupancy sensing controlling the downlight component of workstation-specific luminaires with continuous dimming to OFF combined with personal continuous dimming).

So if manual dimming is implemented to control a 1000W load in a retail sales area, resulting in a control factor of 0.10, 100W of additional lighting power is gained, which can be used by the designer anywhere within the building.

It’s a good addition to the code, as it provides additional options to achieve flexibility. It might also be useful for LEED. What if the additional lighting power was not claimed as additional lighting watts but instead as direct energy savings?

The Lighting Controls Association contacted the USGBC about this issue and received this reply:

“If a project is pursuing LEED certification using the building energy simulation option (modeling per ASHRAE 90.1-2010), and the optional lighting controls are installed, the additional lighting power allowance would be added to the baseline building lighting power allowance for that space. Any reduction from that value in the proposed building could be claimed as savings.”

The Lighting Controls Association has interpreted this to mean that Table 9.6.2 in ASHRAE/IES 90.1-2010 provides control options that can be used to either achieve additional lighting power using the Space by Space Method OR reduce energy consumption and thereby contribute to LEED Energy + Atmosphere points.

Suggested energy savings are built into the standard. In our above example, using manual dimming in a retail sales area to control a 1000W load would result in 100W of power savings that could be applied to LEED.

Again, this particular method of claiming energy savings would be applicable only to those projects that use the Space by Space Method of compliance.

This may be beneficial for designers of lighting systems in LEED projects, as it opens a range of lighting control strategies that can be enacted to exceed the minimum standard criteria and earn LEED Energy + Atmosphere points.

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