load calculations

**advantage** · 01-22-2002, 11:36 AM

I have a telemarketing account that has aproximately 100 computers in approx. 1600 sf. The client is adding 56 more computers in this area. My question is, "Is there a rule of thumb for calculating cfm per computer in the space?". The space was originally used by insurance company which didn't have this heat load in it. I know I could get all the data on the space (ie.# of people, windows etc.) and use a program or ask an engineer. Any help would be appreciated.

Thanks,

Advantage

**Don Sleeth** · 01-22-2002, 11:51 AM

Hi - I don't think you mean CFM per computer, you mean BTUH per computer. What you should do is download the trial version of HVAC-Calc Commercial (t is included in the main download as long as you don't select "only for your own home") Download it here HVAC-Calc

Then, with the commercial program, I would enter it in as a lighting load. Find the wattage of each computer (roughly 200 watts but you should try to get it close since there are so many of them). If you want, after you download the program and play with it a bit, give me a call and I will show you what I mean. 1-888-736-1101

don

**MarcPollo** · 01-23-2002, 03:50 PM

Make sure you do an accurate survey of the equipment. don't forget about the monitors, they produce more heat than the computers do. You can't just count them all up and assume that is the load. (You couldn't afford to cool the place.) You will have to make assumptions that they are running at 60% to 80% capacity. (Same way electricians do it for their panel sizes.) Computers don't pull any where near their capacity as stated on the name plate. Monitors do, so run those at 100%.

Be sure and look for thing likes Laser printers, modems, network hubs, they make a lot of heat. Inkjets are ok.

Manual-N has tables with computers included, but I would calculate them manually based on actual draw.

Figure the building and people separately so you when your customer complains about the cost you can show them why it so high for the computers.

Plan on using an economizer or low ambient controls for winter time.

**Don Sleeth** · 01-23-2002, 03:58 PM

Those are all excellent points MarcPollo, thank you.

The back of one of my monitors says 1.8 amps at 100V so that would be 180 watts for that 19 inch monitor. I have a bigger one that says 1.7 amps (170 watts) so I guess 180 watts/monitor would be pretty close.

thanks

don

**tech-man** · 01-23-2002, 05:07 PM

The rule of thumb is simple do a load calculation.

**MarcPollo** · 01-23-2002, 10:05 PM

Originally posted by Don Sleeth
Those are all excellent points MarcPollo, thank you.

Thanks Don.

I have fixed many a computer room. Most comupters have a 150 watt - 200 watt power supply but will almost never need that much power. If you used all the devices in the computer then you would probably only use 50 - 60 watts.
60 watts = 205 Btuh. However monitors are either off or on. A monitor that pulls 1.8 amps x 120 volts = 216 watts = 737 Btuh. Throw in a 500watt laser printer and you got a lot of heat. Put 10 of these systems in a room and that will be about 26,000 Btuh.

My advice to these type customers is turn off those montitors and laser printers when not in use.

**BamaCracker** · 01-23-2002, 10:18 PM

And, don't forget operators. Most of the time, more computers means more people. If my memory serves me correctly, people at rest (computer work is considered rest, although it makes me tired) is 400BTUh. 200 sensible, 200 latent. Is that still considered right Don?

**MarcPollo** · 01-23-2002, 10:30 PM

Be sure to add one dummy thermostat for every 15 women.
You would be surprised how much more comfortable they will be.

**BamaCracker** · 01-23-2002, 10:31 PM

It's true! Dummy stats add to the comfort level!

**advantage** · 01-24-2002, 08:01 AM

Thanks for the information. I will start on this asap. It's not such a rush right since it's winter and the other computers are not installed. Now I know which direction I need to go, I really appreciate everything.

**advantage** · 01-24-2002, 08:06 AM

Thanks Marcpollo for all the useful info. I'm sure it will be very helpful in determining the load. I do appreciate the help.

**kim** · 01-24-2002, 05:45 PM

Bama
I have always used 400 btu sensable 200 latent for sitting people. Actually I just use 400 btu and make my latent load 1/3 of the sensible. I use 1200 BTU for bars and party rooms or anyplace they will be dancing. I use 800 for resturants. I use 90% of max seating capacity. If it is a crouded bar, I use 120% of max seating capacity.

**cem-bsee** · 09-07-2003, 11:38 PM

With that much equip, better plan on supply on one side of room, returns on other.

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