Lighting Controls

phone may 1 2014 173   Lighting Controls 9.4

As an HVAC engineer, I know that the drop in lighting power is the most obvious change in building energy performance. In the hot humid area of the country where I live, this drop in sensible heat has made the removal of latent heat from the outside air the biggest design challenge. That is a different story; today we are talking about lighting controls.

I was in Mississippi two weeks ago, talking to an AIA Chapter about 90.1 2010. An architect said that he was amazed how complicated we had made the lighting controls.

The new lighting power density tables in 90.1 2013 make the lighting control requirements much clearer. I recommend using this table, even if you are working with the 2010 requirements. In fact, I recently worked on a project where the lighting designer had modified the table format and used it on the construction plans as a room by room lighting power and lighting control matrix.

I have included a little piece of the table here, which includes offices as an example.

Picture1

 

The table has three types of offices: under 250 sq ft, over 250 sq ft and open offices. Open offices are allowed slightly less light than the enclosed offices, but have exactly the same control requirements as the larger enclosed office.

I am offen asked how you can meet the light quality requirements and the LPD requirement of a space. I remind people that the full name of the Standard is ANSI/ASHRAE/IES Standard 90.1; the IES are the illumination engineers that set the light quality requirements and their board approves every change we make to the Standard. You can find a lot of information about 90.1 on the IES website.

The second column is the room cavity ratio. The code lets you add 20% more light if your room would look like a cave without the extra lighting. The calculated value has to be larger than the table value to get the extra lighting power. The equation is 0.25 X room perimeter X fixture height(above work surface)/ room area. This is only one of several lighting power “bonuses” allowed when using the space-by-space method to show lighting power compliance.

Next in the table are the lighting controls required for that space type. “REQ” means that the lighting control listed must be included. In the office case there are two“ADD1”s and two “ADD2”s. In each case, you can chose between the two and only add one control for each “ADD”. So, a large office with day lighting would have a total of six controls.

The first requirement is for a local control. So when you walk in the office in the morning, you can flip a switch to turn on between 30 and 70% of the lights. We can either control the other lighting manually or bring on up to 50% more lighting using an automatic control. If we have side lighting, we will add light responsive control and similar top lighting controls are required if we have skylights or other roof openings such as roof monitors. Finally, we turn the lights off when we leave the room. We can either turn 50% of the lights off with a sensor within 20 minutes of the space becoming unoccupied or turn them all off within a 20 minute window.  If the partial off option is used, the building scheduled off will turn the rest of the lights off during the night. A two hour override is allowed to turn the lighting back on if you want to work late.

One set of plans I reviewed recently had vacancy sensors instead of occupancy sensors. I think that fits the 90.1 scheme better. Adjusting the lighting schedules for the Appendix G model to try to capture the energy savings of these space by space controls can be a challenge.

Opinions expressed here are solely my own and do not express the views or opinions of ASHRAE or the 90.1 committee.

 

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