Change T8 lamps to T5's in a lighting retrofit for an office ?

[Finite10]

An energy auditor I know wants to change T8 troffer lamps to T5 lamped troffers to save energy cost. This is in an office with 8' ceilings.

I thought T5's were for hi-bay lighting due to high intensity.
Do lighting retrofit guys do a retrofit to change T8 lamped fixtures to T5 lamped fixtures?

If so, what is the payback period for that? Seems like it would be too long considering you have to change the ballast and lamp-holder ends for a small savings.

 

[hurk27]

You dont really want to use the 54 watt HO T-8 lamps in this type of installation as you wouldnt really save on wattage but the office help would have to wear sunglasses.

Here is a link to swap out 32 watt T-8 to 28 watt T-5 non HO that will be a little brighter then the T-8's but use less energy:

http://www.ces-us.net/images2/Retrofit%20Spec%20sheet.pdf

Also you dont have to change the ears as they come with the adaptors

 

[steve066]

What kind of fixtures do they currently have?

There are 2 types of T5 lamps: T5 and T5HO. A standard 4' T5 lamp uses 28 watts. A 4' T5HO lamp uses twices as much: 54 watts.

Even the standard T5 is brighter than a T8 because it is a thinner lamp (a T5 is 5/8" diameter, while a T8 is 8/8" or 1", and a T12 is 12/8'.)

T5HO lamps are best for indirect fixtures, since they are so bright. There is a Lithonia RT5 fixture that uses (2) standard T5 lamps in a direct fixture. (Other manufacturers have similar fixtures). These are nice fixtures for open offices, having less glare than a traditional 2 lamp, T8 prismatic fixture.

These RT5 fixtures are very efficient. Much better than the old parabolic or louvered ice cube type fixtures.

However, the supprising thing is that a standard 2 lamp T8 prismatic lensed fixture is still more efficient than the RT5. I think that's because its harder to diffuse the brighter T5 lamp. The only problem is that nobody wants these fixtures in a open office area because they cause a lot of computer glare.

If you do a one-one replacement of standard 2 lamp T8 prismatic fixtures with RT5's, you will still save energy (every 32 watt lamp is replaced with a 28 watt lamp). However, the result will be a slightly lower light level.

 

[Finite10]

However, the supprising thing is that a standard 2 lamp T8 prismatic lensed fixture is still more efficient than the RT5. I think that's because its harder to diffuse the brighter T5 lamp. The only problem is that nobody wants these fixtures in a open office area because they cause a lot of computer glare.

If you do a one-one replacement of standard 2 lamp T8 prismatic fixtures with RT5's, you will still save energy (every 32 watt lamp is replaced with a 28 watt lamp). However, the result will be a slightly lower light level.

That's the trade-off I'm familiar with. But the light team and architect felt the T8 to T5 change-out was low hanging fruit for savings. RT5's or any fixture change-out is to expensive, T5's too intense. I've rechecked the local POCO's. Here's a new Excel lighting work-up sheet;
City Light
The fixtures are vanilla T8 troffers, don't know type since I was not on that crew during level 1 ASHRAE walk-thru.