Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question
2

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

asked 7 years ago

melanie's avatar

updated 7 years ago

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.
Preview: (hide)

Comments

What is the schedule and total static pressure on the VRF unit fans?

mdahlhausen's avatar mdahlhausen  ( 7 years ago )

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  ( 7 years ago )

1 Answer

Sort by » oldest newest most voted
2

answered 7 years ago

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.

Preview: (hide)
link

Comments

Thank you! The problem was the pressure.

melanie's avatar melanie  ( 7 years ago )

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Training Workshops

Careers

Question Tools

3 followers

Stats

Asked: 7 years ago

Seen: 463 times

Last updated: May 23 '17