Question about btu/hr and kW/hr calculation

[JLaw]

Funny question here.

I'm working on some calculations for going from 50W halogen light bulbs to 5W flourescent light bulbs for commercial buildings. I need to sell the idea to my boss.

No problem on calculating the actual energy savings, that's okay. My question relates to how can I calculate the amout of heat in btu's the halogen lamp and the flourescent lamp put off? I can tell him the the halogen lamp get's too hot to touch and the flourescent lamp doesn't, but that's not proof positive enough to convince an engineener.

So...is there a formula that allows me to enter my known values, such as voltage and wattage of an electrical load, and get the resulting heat load generated by that load in btu or btu/hr?

JLaw

[WildBill]

Edited: My post didn't answer the question of the OP.

[Frost]

If the waste heat numbers are not available the next thing I would look for is the efficiency numbers. Don't forget about the ballast.

[tetralaw]

1 kw = 3413 BTu's

Might I suggest running a halogen bulb for an hour and a flourescent bulb for an hour. Take both bulbs and hold them against his neck.

Answer should be pretty easy.

[seamusTX]

OK. Nearly all the energy consumed by a light bulb is converted to heat within the building. Some light energy goes out the window and says bye-bye, but not much.

50 W equates to about 41 BTUs in a 12-hour day, assuming you are talking about a typical office that is lighted for a normal work day.

5 W would, of course, cut that by 90%.

In my opinion, the savings are close to negligible compared to air conditioning, elevators, escalators, computers, and so forth.

I have replaced the light bulbs in my house with compact flourescents as the old incandescent bulbs burned out, simply for the longer life and less hassle of the compact flourescents (which is a also consideration for a large building).

I don't think wholesale replacement of incandescents makes economic sense.

I am not a rocket scientist and didn't stay at a Holiday Inn Express last night, but I have a bachelor of science in electrical engineering from Illinois Institute of Technology in Chicago, class of 1978.

- Jim

[7075-T7]

Funny question here.

I'm working on some calculations for going from 50W halogen light bulbs to 5W flourescent light bulbs for commercial buildings. I need to sell the idea to my boss.

No problem on calculating the actual energy savings, that's okay. My question relates to how can I calculate the amout of heat in btu's the halogen lamp and the flourescent lamp put off? I can tell him the the halogen lamp get's too hot to touch and the flourescent lamp doesn't, but that's not proof positive enough to convince an engineener.

So...is there a formula that allows me to enter my known values, such as voltage and wattage of an electrical load, and get the resulting heat load generated by that load in btu or btu/hr?

JLaw

If you have to convince an engineer that fluorescent bulbs are more thermally efficient than halogen bulbs, then his degree should be taken away.

You could always go about it by speaking of the lumens per watt for each of the bulbs, then you can tell the manager that if the halogen is 1000lumen for 50W, and 1000 lumen for 5W, then your "lumen efficiency" is 20 lumen/watt and 200 lumen/watt respectively (or .05 W/lumen and .005 w/lumen).

Nerd-out-time.

So, for any desired luminosity of the building, lets say 100,000 lumens total at any given time, you will consume 5000W with halogen and 500W with fluorescent, with a net difference of 4500W. that 4500W is mostly heat (among other things). 4500W is 4.5KW and with 1kW = 3412 BTU/hr then you're eliminating 15,354 BTU/hr of heat from the building. with a Ton of air conditioning being 12,000 BTU/hr your saving approximately 1.279 Tons of AC power just to eliminate waste heat from the bulbs. Additionally, assuming a SEER efficiency of 15, you are consuming 853W of power just to run the AC to remove the extra heat. If we add the savings in the bulbs, and the saved energy from the AC heat removal, you come up with 5353W total power saved coming through the meter at any given moment, and assuming a 12 hour day, 64.24 kW/h per day less, and assuming a 25 day month, 1606kW/hr, assuming $.35/ kW/hr electrical cost, about $560 a month in electricity costs.

Subsituting the lumen/watt (or watt/lumen) numbers should carry though, and the total lumens can be found by counting the # of lights run, etc etc.

YMMV (I think I did the math correctly) but I did graduate from The University of Texas with a BSME class of 2005.

Edit: Mis-spelling of fluorescent corrected by request...

[WildBill]

If you have to convince an engineer that florescent bulbs are more thermally efficient than halogen bulbs, then his degree should be taken away.

Either that or make him write it 100 times on the blackboard. Thanks for your calculations.

[TxKimberMan]

...assuming $.35/ kW/hr electrical cost...


That's about three times what most people pay...

At work, we use roughly 350,000kWh's/month and pay $0.0876/kWh inclusive of delivery charges, taxes and fees.
At home I pay about $0.12/kWh inclusive of delivery charges, taxes and fees.

[philip964]

Halogen is normally in an MR16 bulb which is a spot reflector bulb. (condenses the light into a small area) Fluorescent bulbs are generally not made for spot applications.

LED has made great advances in the last year. It is made for spot applications and is even more efficient than the fluorescent. There is a lot of junk LED out there so look for lumens produced for the bulb and compare it to the halogen lumens.

LED is still expensive even when you consider the long life of the bulb.

[JLaw]

Thanks for all the great replies. The 1kW=3412btu/hr is what I was looking for.

I guess I didn't make myself clear, what I have to do is have all the numbers ready for the engineer to approve, MR16 vs flourescent vs LED comparison weighing cost vs. bulb life, light levels at given distance, wattage, amp draws and wasted heat energy for each. We are trying to decide which way to go in one of our relamping projects, which will involve ~60 bulbs in over 120 locations.

JLaw

[seamusTX]

How can you have 60 bulbs in 120 locations? Are they quantum bulbs or something?

The numbers are all there, but it sounds like they are making you do the homework. The complaint about traditional fluorescent lighting was the bluish light that a lot of people (including me) disliked. But the newer CFs are more in the solar spectrum. They also make CF floods that occupy another niche that was one of the holdouts of incandescents.

- Jim

[WildBill]

How can you have 60 bulbs in 120 locations? Are they quantum bulbs or something? - Jim

Maybe they're dim bulbs.

[philip964]

How can you have 60 bulbs in 120 locations? Are they quantum bulbs or something?

Jim

Ha Ha Ha Ha

[tetralaw]

I think he meant 60 bulbs in each of 120 locations.
maybe??

[JLaw]

Quantum bulbs, you guys are great! We only let one store have a bulb for a week then they have to share...

No, 60 bulbs in EACH location is correct. And yes, I'm having to do the homework for them. Can't complain, though, it's actually my job. Kind of a "paralegal" of the energy maintenance department.

JLaw