SUMMARY: Volts, Watts, & BTUs

From: Rick Schieche (
Date: Tue Feb 18 1997 - 13:19:11 CST

Original Question:
We are moving a bunch of equipment to another building that will have an
air-conditioning unit cooling all of our sun boxes. They wish to know how
many BTUs all of my equipment is generating. Is there any simple way to
do this? The only thing that I can find is that my Sparc10's and 20's
have a 140 Watt power supply.

The equipment is:

3 Sparc 20's with monitors
2 Sparc 10's with monitors
1 Sparc 670MP with WYSE terminal
1 IPC with WYSE terminal
6 external disks (Artecon 1Gb boxes)
2 external Sun CD-ROMs
2 Dell PCs with 15" monitors <---- thought I might as well add'em...

Heck, just a close estimation will suffice for me. Grab all of your geeky
electrical engineer friends and take a survey. I will summarize to the

After many good replies from those trusty engineers (and some not), the
overwhelming consensus was to just give the HVAC people the VA ratings
from the nameplates on the Sun boxes and let them deal with what that
might mean in BTUs. About half of the respondents said that you could
assume that VA = Watts, but the others said "It's almost correct". I
guess I should have paid attention in college...

A real thermodynamic problem lies in the fact that not all of the energy
going into the box is necessarily turned into heat, but most people just
assume that is the case to account for future growth or a worst case

It was also noted that BTU/hour = .29 Watts for all of you

John Hough ( was nice enough to give me an
estimate of what some of my Suns' power requirements were (in case I
couldn't get to the machine or was too lazy). His response is at the end
of this message.

Many thanks to the following electron-heads!

Bob Woodward <>
Rich Kulawiec <>
Vasu Srisanan <>
John Justin Hough <>
Danny Johnson <>
Lidio Presutti <>
Wis Macomson <>
Colin J. Wynne <>

 Take all the monitors as secondary issues and then

   SPARC 10 & 20's <= 180 VA each
   SPARC 670 (depends on #CPU, how much memory and #disks) 1000 VA
   IPC < 100 VA
   External SCSI devices < 60 VA
   PC ~ 200 VA
   15" monitors (color) ~ 350 VA
   17" monitors (color) ~ 450 VA
   Terminals (monochrome) ~ 200 VA

 You have to determine the power factor to convert to WATTS but a rule
 of thumb is to go long and multiply the VA by the square root of two.

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