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Energy consumption of fans is as high as the cooling energy consumption when modeling a commercial VRF air conditioner.

asked 2017-05-22 13:26:31 -0500

melanie's avatar

updated 2017-08-06 07:37:08 -0500

I'm modelling an VRF air conditioner following the classes using in the example VariableRefrigerantFlow_5Zoneand using the commercials models of the library NRREL (https://bcl.nrel.gov/) for the internal and external units. In all the cases as a result I'm obtaining that the electric consumption of the fans is nearly equal to the cooling energy consumption. Is this normal?

For example, Electricity [GJ]:

  • Cooling = 86,63
  • Heating = 20,77
  • Fans = 96,82.
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What is the schedule and total static pressure on the VRF unit fans?

mdahlhausen's avatar mdahlhausen  ( 2017-05-22 17:09:15 -0500 )edit

I'm using the Fan:ConstantVolume, the Availability Schedule I'm using is always 1, but I already verify that the fan is only available when the terminal unit is working. The Pressure Rise is the default: 600 Pa. The Fan Electric Energy is always the same:

Date/Time TUS11 VRF SUPPLY FAN:Fan Electric Energy J 07/21 01:00:00 0 07/21 02:00:00 0 07/21 03:00:00 0 07/21 04:00:00 0 07/21 05:00:00 0 07/21 06:00:00 0 07/21 07:00:00 0 07/21 08:00:00 0 07/21 09:00:00 993,989 07/21 10:00:00 993,989 07/21 11:00:00 993,989 07/21 12:00:00 993,989 07/21 13:00:00 993,98

melanie's avatar melanie  ( 2017-05-22 19:19:21 -0500 )edit

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answered 2017-05-23 16:18:42 -0500

Your fan pressure rise is 600 Pa (~2.4 in w.c.), which is unrealistically high for an indoor VRF terminal unit. I typically see around 0.3 in w.c. for external static pressure list on spec sheets, assume another ~0.1-0.2 in w.c. for coils gives around 0.5 in w.c. (125 Pa). Somewhere between 0.3-0.5 in w.c. (75-125 Pa) is a more appropriate value for a typical indoor VRF terminal unit, but the value could be anywhere between 0.25-1.25 in w.c. depending on the unit so you should look at the spec sheet.

Also check the run time for your fan. It looks like your fan may be running continuously when the VRF system is on, rather than cycling on/off as needed to meet the load in the space.

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Thank you! The problem was the pressure.

melanie's avatar melanie  ( 2017-05-25 17:10:34 -0500 )edit

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Asked: 2017-05-22 13:26:31 -0500

Seen: 366 times

Last updated: May 23 '17