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Thermal Load in Data Center

asked 2014-12-14 12:59:33 -0500

updated 2015-11-16 12:39:20 -0500

I'm working in a Data Center simulation project.
I have a coil for only one room, which is a Data Center. The Data Center doesn't have people and ventilation, so the Latent Load should be very small. I'm using a coil with autocalculate to calculate the needed capacity for the coil.
However, the Nominal Sensible Heat Ratio of the coil in the result Equipment Summary:Cooling Coils is 0.7. It is too high for a Data Center, so I think that there is an error.

How should I know what is the thermal latent load of the coil? Is it probable to be an error?

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answered 2014-12-15 08:31:36 -0500

updated 2014-12-15 08:32:15 -0500

EnergyPlus coil capacities and other properties are reported at rated conditions. For DX cooling coils, these are at ARI standard conditions: air entering the cooling coil at 26.7°C dry bulb/19.4°C wet bulb (80F/67F), air entering the outdoor condenser coil at 35°C dry bulb/23.9°C wet bulb (95F/75). For chilled water cooling coils, the rated conditions are rated inlet conditions are: air entering the coil at 26.67C dry bulb/19.44C wet bulb (80F/67F), inlet chilled water temperature = 6.67C (44F). Water coils report the design coil load (total). So there is probably not any latent coil load present in your simulation, but if the auto-sized coil were operating at ARI rated conditions, then it would operate at the reported SHR. I've posted as suggestion Issue #4628 to add reporting of the actual design load used for the sizing (both latent and sensible) for all coils. For now, you must report hourly coil load components for the sizing periods to confirm that there are no latent loads for that coil.

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Dear Michael,

The problem was completely solved with your answer. I report hourly load coil for the sizing periods and the latent load is less than 10 percent of the load.

But what is the reason for the report in the ARI conditions? Is this an estimate of capacity for the commercial equipment? Is there a coil that simulates a precision fan coil used in Data Centers?

Geraldo Pithon gravatar image Geraldo Pithon  ( 2014-12-20 14:49:40 -0500 )edit

Yes, the reason for reporting at ARI conditions is to help with equipment selection and to provide a common basis for comparing equipment capacities. Regarding a "precision fan coil" for Data Centers, there is some work underway to add equipment features required for data centers, but it is primarily adding options to existing equipment models. This would be better as a new question with some details on the specific modeling requirements.

MJWitte gravatar image MJWitte  ( 2014-12-23 14:47:37 -0500 )edit

answered 2014-12-15 07:12:21 -0500

updated 2014-12-15 07:18:11 -0500

Don't you have a mechanical engineer on the project responsible to size the data center cooling system?

But yes, you shouldn't have any latent load, so for your coil Total kW = Sensible kW.

Without seeing your idf file (maybe you should share it), I would definitely look at how you defined your internal loads from the server. You probably used an "ElectricEquipment" object, make sure your fraction latent is set to zero there.


  • Name
  • Zone or ZoneList Name
  • Schedule Name
  • Design Level Calculation Method
  • Design Level {W}
  • Watts per Zone Floor Area {W/m2}
  • Watts per Person {W/person}
  • Fraction Latent: set to 0
  • Fraction Radiant
  • Fraction Lost
  • End-Use Subcategory
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Hi Julien,

I thank you for your reply.

Yes, we have a team of mechanical engineers responsible for the design and that´s why we didn´t accept the high latent loads shown in the results.

I had already checked all the internal loads, including those you mentioned, but the latent loads remained high.
Mr. Michael’s response above solves the issue perfectly. There wasn´t any error in the data entry. The problem is that the report shows the design of the coil for the ARI conditions.

I am very grateful for your assistance.

Geraldo Pithon gravatar image Geraldo Pithon  ( 2014-12-20 14:48:17 -0500 )edit

answered 2014-12-15 03:28:00 -0500

Chienman gravatar image

You might want to consider just using a spreadsheet for a data center, unless you think it really needs to be modeled in energy simulation. I know this is a cop out answer, but when the internal loads begin to dominate, the envelope loads become insignificant. This is what I've done for Facebook datacenters that I've modeled and submitted to LEED.

It is pretty easy to develop a spreadsheet using hourly weather data, fan curves, and internal gains with some logic and equations for economizer hours. Hope this is helpful.

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Thank's Chienman,

I really need to do an energy simulation because the building has another spaces that aren't for datacenters but use the same cooling water. Furthermore, we need to analyze the use of free cooling and other alternatives that are more accurate when we use an energy simulation.

However, the problem with the coil still to persist. The load of the coil is too high and with a large latent part. I hoped the coil load should be approximately the load of the space, shown in the HVAC Sizing Summary, but it don't happen.

I really don't know what are happening.

Geraldo Pithon gravatar image Geraldo Pithon  ( 2014-12-15 05:58:03 -0500 )edit

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Asked: 2014-12-14 12:59:33 -0500

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Last updated: Dec 15 '14