Page 215 - Alternative Energy Systems in Building Design

CALIFORNIA TITLE 24 ELECTRIC ENERGY COMPLIANCE 191

Multilevel astronomical time switches control areas with skylights that permit day-
light into a building area and are required to be calculated by the prescriptive calcula-
tion method, as well as by the mandatory automatic controls that must be installed to
reduce electric lighting when sufficient daylight is available. Multilevel astronomical
time-switch controls or automatic multilevel daylight controls specially designed for
general lighting control must meet the mandatory requirements for automatic controls
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when the particular zone has an area greater than 2500 ft .
The purpose of astronomical time-switch controls is to turn off lights where suffi-
cient daylight is available. Astronomical timers accomplish this requirement by keeping
track of the time since sunrise and the amount of time remaining before sunset. As a
basic requirement, the control program must accommodate multilevel two-step
control for each zone programmed to provide independently scheduled activation and
deactivation of the lights at different times.
In the event of overly cloudy or overly bright days, the astronomical timers are
required to have manual override capability. Usually, the override switches in a zone
are configured so that lights will revert to the off position within 2 hours unless
the time-switch schedule is programmed to keep the lights on.
To comply with power-consumption-regulation requirements, light control is not
allowed to be greater than 35 percent at time of minimum light output. Device compli-
ance also mandates that devices be designed to display the date and time, sunrise and
sunset times, and switching times for each step of control. To prevent a loss of settings
owing to a temporary loss of power, timers are required to have a 10-hour battery
backup. Astronomical timers also are capable of storing the time of day and the longi-
tude and latitude of a zone in nonvolatile memory.

Automatic multilevel daylight controls Automatic multilevel daylight controls
are used to comply with the mandatory requirements for automatic daylight controls
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when the daylight area under skylights is greater than 2500 ft . The controls must have
a minimum of two control steps so that electric lighting can be reduced uniformly.
One of the control steps is intended to reduce lighting power from 100 percent to
70 and 50 percent of full-rated power.
Multilevel daylight-control devices incorporate calibration and adjustment controls
that are accessible to authorized personnel and are housed behind a switch-plate cover
or touch-plate cover or in an electrical box with a lock. In circumstances where the
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control is used under skylight conditions and the daylight area is greater than 2500 ft ,
the power consumption must not be greater than 35 percent of the minimum electric
light output. This is achieved when the timer control automatically turns all its lights
off or reduces the power by 30 percent.
Fluorescent dimming controls, even though somewhat expensive, usually meet the
minimum power requirements. Controls for high-intensity-discharge (HID) lamps do
not meet the power requirements at minimum dimming levels, but a multistage HID
lamp switching control can.
Outdoor astronomical time switches control outdoor lighting by means of astrological
time switches, which are permitted if the device is designed to accommodate automatic