electrical equipment heat dissipation 1

[chiznakz25]

Good day,

I would like to ask on how to calculate electrical equipment(motors, machine shop equipment,etc.) heat dissipation
If the only given is the Input power of the equipment. this will be my consideration for my cooling load calculation.
For this type of room space, what would be the room temp requirement? Is it enough to provide ventilation only?
thank you.

 

[willard3]

Is this a homework problem?

 

[DomSh]

Hi,

The heat dissipation is not the total input power of the equipment. For a motor, you have to use the motor efficiency, the use factor, the motor load ans the power rating.

If you don't have these data, I suggest you to add a frequency and efficiency factor. For example :

Biomotor tool (200V @ 30A) = 6000W
- Factor use : 0.2, equivalent of 12min of usage in 1 hour (0.2*60min)
- Efficiency : 0.2, so 20% of the total input power is dissipated in heat
- Total heat : 6000W*0.2*0.2 = 240W, 240W*3.412 = 819 BTU/H

Unless the equipment is a electric coil, remember that not all the input power is dissipated in heat. Without these factor, your cooling load will be over estimated. Here is a rule of thumb to estimate the total cooling load :

http://bim.wikispaces.com/file/view/ASHRAE+Mechanical+Pocket+Guide.pdf

What is the function of the room ? Lab, warehouse, office, mechanical room ? The function will clarify the room temp/RH requirement.

Hope this help!

 

[Compositepro]

All the input power does eventually end-up as heat. The question is whether all that heat stays in the room or is dissipated somewhere else. With machine tools almost certainly all the heat stays in the room. However, a one hp motor is not consuming one hp of of electricity when idling. The power rating of a motor only tells you the maximum amount of work it can do in an hour without overheating. The work done in cutting metal will all turn into heat.

 

[chiznakz25]

I used this as my draft calculation, and I'm not sure if this correct:

Hm = Pm / hm

Hm = heat transferred from the machine to the room (W)

Pm = electrical motor power consumption (W)

hm = motor efficiency

The type of the room is a Laboratory. I want to determine any large cooling load caused by the equipment. Or it requires special ventilationand/ or exhaust requirements. thank you

 

[HVACMech]

You should always include all electrical equipment in a space down to copiers, computers, monitors, tvs, etc. Otherwise you could risk being undersized or oversized if you just use a generic W/sf value. If it is a laboratory, depending on the chemicals and processes being done in the space, there are absolutely special ventilation and exhaust requirements. Sounds like you need to research more about what is going on in your lab, and then read ASHRAE and your governing mechanical code to determine what you need to do for the ventilation and exhaust.

 

[dbill74]

For a lab space, I wouldn't spend too much time trying to figure out how much heat each piece of equipment is generating simply because I wouldn't expect each piece of equipment to be operating continuously all the time. If have mainly centrifuges, microscopes and other small desk top equipment, you can figure 2-3 W/SF +any special equipment that might be on for long periods and figure computers separate. You need to be talking with the end user/owner to fully understand what the lab is used for and how.
Basic desktop computers you can figure 100-150 each plus another 150-200 W for flat screen monitors or 300 W for older CRT monitors. Personally I use 350 W for each computer station.

As for special ventilation or exhaust, get with the owner or equipment manufacturer. Generally though, special exhaust is only needed for high heat generating equipment such as autoclaves and ovens; but not for hot plates. If there are hazardous chemicals and or processes, then you will probably be dealing with fume hoods which have their own unique design challenges.

I have to disagree with Compositepro's statement "All the input power does eventually end-up as heat." If this were true you would not get any work done, computers wouldn't compute, centrifuges wouldn't spin, etc.

 

[IRstuff]

The key word is "eventually"; once the computer gets done doing its calculations, all that's left is heat. Even the light from the monitor "eventually" turns into heating the room or its air. Likewise, a centrifuge spins up, but must spin back down, so its mechanical energy is converted to heat, and the work input into the sample is likewise converted to heat.

TTFN
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[Drazen]

On contrary, whoever does design work for living would use average values adjusted to own experience and checked in practice, individual counting of small equipment makes sense for unusual setups only, otherwise is overkill that nobody could take if wanting to survive.

 

[HVACMech]

I do design work for a living and use a mixture of the two personally. I use a W/sf for computers and lights, but individually count copiers, microwaves, and refrigerators.

 

[dbill74]

Unless you are dealing with a special piece of equipment, I fail to see anything wrong with using W/SF, it is much more efficient for us as designers. Now not all spaces are equal. Similarly a school lab will not have the same W/SF as a pharmaceutical lab, or a hospital lab. It is up to the engineer to determine an appropriate value to use.

With labs, diversity should also be factored into the equipment load profile. What constitutes an appropriate diversity factor for a lab? I don't know , it depends on the lab and the end users. This is why it is important for us engineers to talk with end users for these types of projects.

Getting back to Chiz's questions. You appear on the right track with figuring heat from each piece of equipment. If you haven't already done so, get with the end user/owner and talk about what is in the lab and how it will be used. If they have an existing lab they will be moving out of, try to visit it, it will give you an idea how they use their stuff.

As for space temperature requirement, again this will be an owner driven variable. Often they don't care, in which case the ASHRAE normal 75°F / 50% RH are good to design to.

Ventilation only? It depends on what type of lab and the activities in the lab - talk to the owner (see a pattern here?). Owner likely won't be able to tell if a once-through system is needed, but can tell you what is happening in the lab and from that you can review codes and standards to determine if this is what is needed.