Re: Calculating BTU's in Computer room for Air conditioning puposes (13080 Views)
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Message 1 of 20 (13,080 Views)

# Calculating BTU's in Computer room for Air conditioning puposes

I have been asked to calculate BTU's generated in order to purcase the correct Air Conditioner in the computer room. It has been difficult to determine this. What is the best conversion? I found the following and am thingin of converting watts and kilo watts to Btu/hr.

Hustle Makes things happen
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Message 2 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

Interesting question.

Off hand, we use temperature targets. The specifications for the machine note the operating temperature range and we get enough power to keep it comfortably within that range.

I don't think power supply watts to BTU is a good approach. You need to know how much heat every device in the room gives off at full capacity, disks included.

SEP
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Message 3 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

This is what I use:

â ¢ A BTU = 3.412 * Watts
â ¢ A ton = BTUâ s / 12,000
â ¢ The 30 ton air units we use cost about \$26,638.88 to operate, per year, at full load.
â ¢ To cool a ton of air costs \$888.00 per year.

** Always use maximum wattage of a server

** Concern yourself with HOTSPOTS

Yes, it costs money to operate air conditioners. I used these numbers to justify the removal of all K-class equipment with virtually partitioned N-class servers.

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h
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Message 4 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

Well, let me put my physicist hat on:

You have to realize that for all practical purposes (and to greater than 99.9% accuracy) computers are nothing but heaters -- expensive heaters but heaters nonetheless.
This means that if you have the input power, you have the output heat dissipation --- they are one and the same. As long as you use the maximum values listed on the power supply for your calculations then what that power is doing (running disk drives, memory, powering chipmunks) doesn't matter; it's all going to be converted to heat.

To approximate power dissipation, you can multiply rated input voltage by rated current to get Volt-Amps. Then multiply by a power factor (usually about 0.8 to get watts - remember this is AC 1VA is usually not 1WA because we have those pesky phase angles) If you want to be very conservative, use a pf of 1.0 and some HP computers run a pf of 0.99. If you use a power factor of 1.0 then you will always be safe. The one other formula I should throw at you is how to calculate 3-phase power. It's simply P = IV * 3 ^ 0.5 * pf where P = power in watts, I = current in Amperes, V = Voltage, 3 ^ 0.5 ==> square root of 3 (or the appropriate number of phases), and pf = power factor (again somewhere between 0.8 and 1.0). Power factor is actually the cosine of the between the phase angle of the current and voltage.

Example :

Suppose the power supply label indicates 10 A at 200V; what is the maximum thermal dissipation?

10A x 200V = 2000VA x 0.8 (pf) = 1600W.

1600W x 3.412 BTU/HR-W = 5460 BTU/HR.

The other conversion factor you need to know is that 12000 BTU/hr = 1Ton Cooling Capacity

If it ain't broke, I can fix that.
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Message 5 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

I forgot to add that because I am in New York we have the highest energy costs in the nation (californiks pay a fraction of what we pay - they whine too much anyways - their costs could double and not be more than ours), thus using my energy costs will "CYA".

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harry d brown jr
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Message 6 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

I should also add that it is impossible to convert BTU's to Watts or vice-versa because one is a unit of energy (BTU) and the other is a unit of power. You could convert BTU's to Joules or BTU/HR to watts.
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Message 7 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

I guess I should of a took an electronics course. Thank you all for all this insight, I think this will be extremely helpful. Luckily the HP computer room has much less equipment then the Windows computer room. I just have to track down the specs of the VA7410 and 59 disks half A6193A (36gig 15k)and A6193A (73gig 15k). To the Volts and watts are not labeled anywhere.

Hustle Makes things happen
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Message 8 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

Clay,

I expected to see you pop up here, but what confuses me is this:

"1600W x 3.412 BTU/HR-W = 5460 BTU/HR."

This seems to be converting watts to BTU. However, your second reply states:

"it is impossible to convert BTU's to Watts or vice-versa", yet you seem to be doing just that. Which is it? Vice? Or versa? What am I missing?

Pete

Pete
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Message 9 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

Simple, I wasn't converting BTU's to watts but rather BTU's per hour to watts and that is perfectly legal. The distinction is that power is the time rate of delivering energy so that dividing a unit of energy (e.g. a BTU) by a time unit (e.g. an hour), you now have a unit of power (BTU/hr). Similarly a watt is actually another unit of energy (a Joule) divied by a time unit (a seconds) so that 1 Joule/second = 1 watt.
If it ain't broke, I can fix that.
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Message 10 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

I have gotten all the information from the back up the equipement. But would any of you know the following:
VA7410 (labeled on each of 2 power supplies)
100-240v
8.2-3.4A 50/60hz

3 of the 2405 enclosers (labeled to on each one)
4.1-1.7A 50/60hs

1) These are plugged into a 110 power strip. So am I to read it as 8.2 amps max but if I had it plugged into 240 the amps would be 3.4 amps max?

2) This is probably a silly question. it seems low, so I guess I to add the hard drives on to this too? they are not visable so I guess I need to grab the white papters?
Hustle Makes things happen
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Message 11 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

All you have to concern yourself with are the power supplies. The disk drives (as long as you include their power supplies don't matter). You are treating the power supplies as heaters whether or not they themselves dissipate the heat. All other components can then be considered to emit zero thermal power. When determining the power consumption of devices with redundant power supplies (those with N + 1 power supplies where N is the minumum number to carry the load) is to consider the ratings of N power supplies. For example, if you server has 2 power supplies and only 1 is required to actually operate, you can calculate the power consumption of 1 power supply and ignore the other. You suppostion about current for 120/240 V is correct. A power supply operating at 240V will draw half the current as it does at 120V. Note that the product of current and voltage remains constant (or very nearly so). Calculating power this way based upon the power supply maxima is a very safe and conservative method of not exceeding maximum thermal ratings of your HVAC system.
If it ain't broke, I can fix that.
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Message 12 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

I should add that one of the heat sources you should not overlook is lighting. Depending upon the type of lighting used and how much there is, lighting can add significantly to the thermal load. For your purposes, you do not have to count UPS's units within the data center; they are not quite 100% efficient but can be safely ingored as long as you count the devices that they will be powering -- which you already are.
If it ain't broke, I can fix that.
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Message 13 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

Thanks again Clay I just finished it up now. Thanks for clarifying the UPS. You are right it came out extremely high. But I was abled to get the correct BTU per hour from from APC.
Hustle Makes things happen
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Message 14 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

Ahhh, I see - thanks, Clay!

Pete

Pete
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Message 15 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

You should be aware that simply calculating equipment BTU's will not be a complete answer. This is just a sensible heat gain. All equipment does both sensible and latent work and the BTU rating of the equipment reflects that.

Equipment designed for computer rooms is designed with this in mind, but there is still latent work being performed.

It would be a good thing to consult with a HVAC professional or forum dedicated to HVAC to answer more questions.

And, no... you don't have to buy Liebert to make it work correctly.
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Message 16 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

That is funny you said that. That is what we wound up getting was Liebert. Noisy machines aren't they. But it sure is cool in there.
Hustle Makes things happen
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Message 17 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

Dear John,

I just read your blog about converting watts to BTU's/hr for sizing air conditioning needed for your computer room. As a Data Center Facilities Designer, I have been designing data centers for 7+ years.

Based on the method described (maximum input ratings of the power supplies), you would derive numbers which are way too high.

The numbers indicated on the power supplies are the maximum input power, assuming every available device option is installed, and all these devices are running 24 hours/day.

In my experience, typical computer systems draw less than half of the rated input power stamped on the power supply. As a result, using these numbers would derive a figure approximately tripple your actual loads. And you probably bought way too much air conditioning for your data center (don't worry about it. I once made the same mistake myself).

Just guessing, but I would bet that you still have plenty of cooling capacity in your data center, even after two years of adding equipment. Am I correct?..

Jeff
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Message 18 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

More servers and still working well. Funny you should respond. Next year we are combining our 2 server rooms into 1 and making it larger. I have a feeling we are going to be asked to redo our numbers for the new room.
Hustle Makes things happen
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Message 19 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

I have found that individual UPS units (like Belkin 1100VA) generate a lot of heat. This one in particular drew 24 Watts all by itself (no devices attached). From that experience, I'm leery of the statement that you can ignore UPS's.
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Message 20 of 20 (13,080 Views)

# Re: Calculating BTU's in Computer room for Air conditioning puposes

How would I handle a server with dual power supplies? Since one power supply is sufficient to handle the server, with two supplies, the server should be drawing roughly half the load from each supply (plus a little extra for inefficiency in the power conversion, or just running the extra supply). Anyone have some numbers on this?
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