Heating/Cooling Loading Calcs - Equipment kW

[Designer_82]

What percent of the equipment kW is best to use when doing Heating/Cooling loading calculations?

For example, a millwork warehouse with CNC machines, cutting machines etc.

Given the nameplate of all that equipment, it adds up to 100kW. How much of that reasonably contributes to heat load... Meaning what would you enter in the software for "Electrical Equipment Wattage"?


Thank you

 

[MintJulep]

Is all the equipment operating continuously? [probably not]

Is all the equipment operating at 100% of its capacity when it's operating? [probably not]

 

[LittleInch]

Look at the load list for the site.

that usually divides equipment load into continuous (100%), intermittent (70%) and standby (10%).

Even then it is usually very conservative in terms of load ( by about a factor of 2

Then work out a day, evening, night load.

Or just monitor total current going in over a day on a hourly basis...

Many ways to skin this cat.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Compositepro]

All of the kW used by a machine ends-up as heat. The issue is that machines usually spend a small portion of the time operating at their full rated capacity. That depends entirely on your operations.

 

[Designer_82]

"All of the kW used by a machine ends-up as heat."

That's interesting. So if a machine is rated let's say 10 HP or 7.5kW, if operating full capacity, all 7.5kW goes to heat?

Now the 7.5kW is the output of the machine, if the power factor is .9 then it takes about 0.8kW to make the machine run (energize the insides)

So wouldn't it really just be this 0.8kW that ends up as heat?


Thanks

 

[EnergyProfessional]

That's not how power factor works.....

Read carefully the nameplate. they also may list peak power, nominal etc. the plant manager or team will be able to give you an idea of diversity (i.e. only 3 out of 10 machines running at any given time etc.). Obviously inquire about safety factors in case they want to add more people and run more machines at once in the future. Or if they plan to by new machines etc.
This is an educated guess and being conservative situation.

You will notice that when you ask one person about the use of the machines, they tell you what they remember from a specific day, the next person will tell you something different. Ask 10 people to get 20 opinions. I would have the client sign for that information so they are required to do the legwork of having very good idea of usage. I assume you are an outsider to that company and have no way of telling how they operate on a daily basis.

 

[IRstuff]

You seem to have that backwards. 0.9 power factor means that 90% is real power, so real heat

TTFN (ta ta for now)
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[nuuvox000]

You'll have to make an educated guess based on how many run at the same time, how long do they run, etc. I think CNC machines typically run continuously for a long time so it would be good to know how much power they're using. They might have an RLA you can use. Maybe the electrical contractor can measure the power draw for you if it's critical.

 

[Compositepro]

A 10 kW motor is capable of providing 10 kW of mechanical power continuously. If the motor is just turning at full speed with no load it may only be consuming 5% of that in electrical power. Power factor is not efficiency. Google it.

 

[EnergyProfessional]

Real vs Apparent Power

Maybe I'm mathematically challenged, but I have no idea how a 7.5kW motor and a PF of 0.9 ends up with 0.8kW. And if we assume 7.5 kW is the nominal mechanical output, the electricity going in is more due to efficiency of less than 1. And a nominal power rating can be exceeded, or be less. Look at service factor. A 7.5 kW motor also could operate at 4 kW, or 8kW, if that is what the machine uses. A machine also has other loads (smaller step motors, pumps, controls etc.). Some manufacturers also tell you the cooling load, then you don't have to guess yourself. This isn't the first time one of their machines needs cooling and they have better data than some random people on the internet.

I'd first look at the manufacturer literature or talk to a rep. Then talk to the owner/users about use diversity and future plans.

 

[IRstuff]

PF of 0.9 and 7.5kW simply means that 6.75kW is real power consumed from the mains when 7.5 kVA is measured on the mains. Assuming a flat PF, then 4 kVA from the mains means 3.6 kW actual power consumed.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[BronYrAur]

This problem has always bothered me. I can't ever seem to find a satisfactory answer. I asked a similar question years ago about motors in an air stream. I was trying to verify what temperature rise I should expect from the heat of those motors. Here is that link. Maybe it will help, but I just wasn't fully clear on the answer.

https://www.eng-tips.com/viewthread.cfm?qid=416011