Turning off florescent lights to cool the building?

[nanette1985]

We're sitting here in the office discussing the notice we had from the building, asking us to turn off all lights (etc) to conserve energy and keep the building cooler.

Okay, turning off incandescent light bulbs I get, we know that heat is generated. I guess it would make a difference if the entire building turned off those.

Florescent lights, or the power source, must generate some heat too, but how much? Is it really important to turn off florescent lights to keep the heat down?

Anyone an expert on this? Thanks.

 

[tasmanian]

I dont think that the lights make enough heat for it to really matter.

 

[bsobel]

The ballast may, not to the extent of incadescents, but heat is heat.

 

[DnetMHZ]

So you are supposed to work by the light of a monitor?

 

[So]

It will make a difference, but a small fraction of the difference that an incandescent would.

 

[destrekor]

For some reason, when we turned off the fluorescent lights and closed the blinds in class (as opposed to only closing the blinds) it would feel much cooler. I think most of it was in the mind, because I'm not aware of fluorescent lights making any noticeable amount of heat.

+

 

[MiniDoom]

just turn off all the servers.

 

[Jeff7]

Very little. Part of the reason to use fluorescent lights in the first place is efficiency - most of the electrical energy is converted into visible light, versus incandescent bulbs, where a LOT of it is in the infrared.
Some of the ballasts that GE has out are rated as >90% efficient.

So going just on that, every tube might be 32W. 3.2W waste per tube, possibly 4W.

Multiply that by the number of fluorescent tubes in the place, and that's how much heat is being generated by the lights.

 

[BurnItDwn]

From GE lighting webpage ...
http://www.gelighting.com/na/h..._compact.htm#heat_rads

How much heat (or infrared radiation) is emitted by regular, halogen, and compact fluorescent light bulbs?
Regular light bulbs, known as incandescent bulbs, create light by heating a filament inside the bulb; the heat makes the filament white-hot, producing the light that you see. Halogen light bulbs create light through the same method. Because incandescent and halogen bulbs create light through heat, about 90% of the energy they emit is in the form of heat (also called infrared radiation). To reduce the heat emitted by regular incandescent and halogen light bulbs, use a lower watt bulb (like 60 watts instead of 100).

Fluorescent light bulbs use an entirely different method to create light. Both compact fluorescent bulbs and fluorescent tubes contain a gas that, when excited by electricity, hits a coating inside the fluorescent bulb and emits light. (This makes them far more energy-efficient than regular incandescent bulbs.) The fluorescent bulbs used in your home emit only around 30% of their energy in heat, making them far cooler.


So, they use about 1/4 to 1/3 the power that incandescents use, and then they only create about 1/3 as much heat as incandescents per watt. So, A florescent bulb at 60 watts creates about 54 watts of heat, or about 184 BTU's of heat per hour.. A CFL at 17 watts creates about 5 watts of heat, or about 17 BTU's of heat per hour.

The heat generated by fluorescent lighting isn't totally negligible, but it is really quite minimal compared to incandescents.

 

[sdifox]

It may put out little heat compared to incandecent, but there is a large quantity of them.

 

[Kaervak]

If they really want to cool off the building, paint the roof white if it's black. You'd be surprised how much of a temp drop that will provide.

 

[Howard]

Certainly. Almost 100% of the energy drawn by the ballast is converted to heat (yes, the light also turns to heat eventually).

 

[nanette1985]

Wow, thanks. Great info. I didn't even think about my desk lamp, which is halogen, and I know how hot that is.

Sounds like we can keep some of the florescents on with a clear conscience. I don't know how much difference all this makes, but if this is the rule, I'll follow it.

Next question is, which generates more heat, running the coffeemaker, or sending someone out for coffee?

 

[DrPizza]

As Howard pointed out, it's simple conservation of energy. Every single watt of energy used by the lights is eventually turned to heat. Of course, if the light shines out the window, that energy is lost (then again, during the daytime, the sunlight is going to add more heat than you lose via this process.)

Coffee-maker: it wouldn't reduce the amount of heat by as much as people might think it would. When it's brewing, it's probably operating at about 1500-1800 watts. (edit: and it's only brewing for a few minutes at a time.) However, most of that heat goes into the liquid. While a pot is just sitting there, being kept warm, however many watts are in the warming plate (I'm guessing 2 or 3 hundred watts; wild guess though) are being disipated.

For what it's worth, there are some programs with various energy companies where your company may be selected to voluntarily reduce energy consumption by as much as possible for an hour or so. I'm not sure of the details, but you get about 24 hours advanced notice, and it's supposed to be practice in case there ever have to be rolling brown-outs or something like that. In such instances, cutting back by quite a bit over the course of an hour can lead to some nice kick-backs from the energy company.

Oh, and just for the sake of comparison, I'm in a classroom right now with 27 fluorescent lights at 40 watts each. Not including the energy disipated by the ballasts (which are wired up really screwy, hence the odd number) that's 1080 watts; about the equivalent of me leaving a blow dryer on low/med setting running all day (at ceiling level, since some heat is radiated through the ceiling to the floor above.) Since I don't have air conditioning, the difference is quite noticeable by 3pm. If I leave my shades most of the way down, providing just enough light, and turn the lights off, my room is about 10 degrees cooler at the end of the day than an adjacent room that leaves the lights on, shades up, and windows open.

 

[JulesMaximus]

Originally posted by: destrekor
For some reason, when we turned off the fluorescent lights and closed the blinds in class (as opposed to only closing the blinds) it would feel much cooler. I think most of it was in the mind, because I'm not aware of fluorescent lights making any noticeable amount of heat.

+

They do produce heat, not nearly as much as an incandescent light bulb, but they do produce some heat.

 

[Howard]

Originally posted by: DrPizza
Every single watt of energy

I see what you did there.

 

[imported_Imp]

They produce some heat, less, but with so many in an office building, it adds up. Also, I think I heard from my building science professor that the visible light is also converted to heat once it hits a surface (kinda makes sense if you think about the sun as an extreme example), so that will also add in.

Not sure if you should do it or not though. Office building heating/cooling is designed with the lighting in mind (i.e. partly why it's on 24/7).