Wednesday, January 16, 2008

Antique Switches

The switches we want to use are early 1900's French light switches. Aside from not being UL listed and not suitable for high-voltage use in North America, it turns out that without modification, on-off switches are at odds with California's Tiltle 24 energy law.

Light switches impact energy use. Automatic-off, for example, clearly conserves energy. Dimmers, on the other hand, often end up wasting energy. Energy standards such as California Title 24, which may have the best of intentions, are prescriptive. They say what has to be done, rather than allowing creativity and measuring results. The consequence is wasted energy.

California Title 24's (6.1.2, 6.5) regulation concerning incandescent lights in living areas: All luminaires shall either be high efficacy or shall be controlled by an occupant sensor or dimmer.
This rules out using old fashioned switches either way, since (a) if occupant sensors are used with old switches, the sensor has to be able to turn off the light. Without lighting automation, this sensor may prevent turning on the light with the switch. Furthermore, the occupancy sensors are often often visible and ugly, which impacts the feel of the house; or (b) if a dimmer is used, then an old fashioned switch can't be used, since they have no dimmer capability.

Unfortunately, if a dimmer is present, it is common practice to put in bulbs ("lamp it") brighter than the light needed on average, and then use the dimmer. The irony of Title 24 forcing the use of dimmers is that dimming incandescent lights will occur most of the time - and this wastes energy:

  • For example, it may be desirable to put in 80 watt bulbs rather than 50 watt bulbs, then dim them for typical use. Incandescent lights are less efficient when dimmed. The 80 watt bulb will use 60 watts to put out the same usable light as a non-dimmed 50 watt bulb because a dimmed bulb will be emitting more radiation in the infrared.

Here is some data from a 100 Watt Bulb, using a high-efficiency Control4 dimmer.

0% -- 0 Watts

25% -- 33 Watts

50% -- 62 Watts

75% -- 87 Watts

80% -- 91 Watts

100% -- 100 Watts

For the example above, dimming a 100Watt bulb to the same visible light output as an 80Watt bulb will consume 91Watts - the difference is extra heat from the bulb. It is far better to install incandescent lights only at the level of typical use, and avoid dimmers.

The SwitchBoard

We thought we pretty much had to go with a Lutron lighting control system to meet Title 24 requirements in various parts of the house, particularly bathrooms. To use antique switches we had to build some special electronics that converts switch signals into commands for the Lutron system.

The on and off switch functions will turn on or off Lutron "scenes" on Lutron "virtual keypads".

Touching and releasing the switch metal is interpreted to perform dimming. For example, when ON, a touch-release-touch-hold will start a dimming cycle that increases and decreases the brightness of the light. When OFF, touching the switch will turn on a nightlight for a limited period of time, and automatically turn it back off.

On-off-on behavior can change Lutron scenes as well. We'll see how intuitive it is to use this control mode.

Each antique switch has 4 wires connecting to a switch board. These connect the switch terminals, and also provide a shielded conductor to contact the switch center. The switchboard contains a low power AVR microcontroller, capacitive sensor logic, a dip switch to indicate the board device ID on the daisy chain, an LED to indicate activity, and an RS-485 connection to other daisy-chained SwitchBoards.

Software on the microcontroller triggers a capacitive sensor for variable sensitivity, monitors and debounces inputs, logs changes with timestamps, and responds to information poll requests for its ID.

A string of these SwithBoards connect (via RS-485 to serial) to a low power JStik computer that is house intranet connected. Java software on this computer polls the switchboards, interprets the switch changes into ON, OFF, ON-OFF-ON, DIM UP, DIM DOWN or NIGHT events. These events are cross-referenced in a lookup table (set via intranet web interface), which presents a Lutron command string to the Lutron controller.

In this manner, the antique light switches perform the functions as necessary required by California Title 24 energy efficiency laws, but look and work as we would like them to. This has the added benefit that most of the commonly used switches in the house are siple.

Permanent fixtures are either high efficiency (flourescent or LED), or they are incandescent but waiting for a good low-power replacement product. We intend to use the lowest wattage incandescent bulbs that do the job until we can replace them with low-power units that work. Stay tuned for a later posting about retrofitting an Iris fixture with an LED luminaire :-)