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Where are OpenStudio fan schedules?

asked 2016-03-08 15:48:44 -0500

Erik Kolderup gravatar image

I know that I can create my own fan operation schedule, but I'm puzzled that they are not included in the default OpenStudio templates. I'm hoping someone can point out that I'm missing something.

My issue is that my only default options are cycling fans or 24/7 fans.

I created a simple model using the OpenStudio plugin in Sketchup and selected the 90.1-2010 template.

In OpenStudio I assigned a PTAC system as zone equipment. The only options I have for "Supply Air Fan Operating Mode Schedule Name" are "Always On Discrete" or "Cycling PTAC Fan Mode Always Zero". Therefore, with these choices the fan either cycle's on/off or runs 24/7. There is not a schedule that matches the thermostat setpoint schedule. In other words, my default office thermostat schedules assume 6am to 10pm operation. But the fans run all the time.

Appears that I need to create a custom schedule so that fan operation matches thermostat operation.

Seems like many users would not notice this, and the result is their models would overpredict fan energy due to 24/7 operation. Is there a reason that the templates due not include fan schedules? What am I missing?

-Erik Kolderup

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I'm assuming you have setbacks defined in your thermostat temperature schedule, so are you suggesting the program infer when to turn on/off the system based on that?

Lyle K gravatar image Lyle K  ( 2016-03-08 17:14:31 -0500 )edit

Thanks for the response. No, I don't think OpenStudio should infer the fan schedules. I think the templates should include fan schedules that include the same on/off times as the thermostat schedules. The templates already include thermostat schedules; seems like they should also include corresponding fan operation schedules.

Erik Kolderup gravatar image Erik Kolderup  ( 2016-03-08 18:08:17 -0500 )edit

@Erik Kolderup I agree. See this related EnergyPlus issue.

MatthewSteen gravatar image MatthewSteen  ( 2016-03-09 08:01:09 -0500 )edit

Please bump this up higher on the priority list, to include fan operation schedules that correspond to the thermostat schedules. Mack Wallace and I are teaching a series of hands-on simulation course throughout Vietnam to about 100 people. Many are architects. PTAC systems are widely used, and we are trying to teach ways to raise efficiency and comfort. A local engineer, ng Khanh, has been writing OS Measures as templates for various PTAC solutions. The absence of fan operation schedules to match thermostat schedules has been causing unnecessary complications.

JJD gravatar image JJD  ( 2016-07-28 04:44:21 -0500 )edit

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answered 2016-03-08 16:53:16 -0500

Correct, the templates do not include fan schedules so you need to create one OS Video Showing How to Create Schedules. Why there are not HVAC schedules in the templates I have no idea, that would be a question for @macumber or another person on the NREL OS Team.

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@Kyle Benne or @aparker would know better than me for questions about the HVAC library

macumber gravatar image macumber  ( 2016-03-08 18:00:23 -0500 )edit

Thanks, Taylor. I know how to create schedules. I'm just thinking that lots of people could be running models with 24/7 fan operation and not realize that they are doing so. -Erik

Erik Kolderup gravatar image Erik Kolderup  ( 2016-03-08 18:10:11 -0500 )edit
3

answered 2016-03-08 18:49:50 -0500

updated 2016-03-08 19:24:12 -0500

In OpenStudio (and E+) thermostats do no have on/off times. Thermostats use a temperature schedule to control a zone to a specified temperature. For a PTAC, system availability and fan operation is controlled with the Availability Schedule and the Supply Air Fan Operating Mode Schedule Name.

OpenStudio includes a default Availability Schedule of 'Always On' which allows the PTAC to be available to operate at any hour during the year.

The Supply Air Fan Operating Mode Schedule tells the fan how to operate. A schedule value of 0 indicates the fan and the heating/cooling coil cycle on and off together to meet the load. A schedule value other that 0 indicates the supply fan runs continuously while the heating or cooling coil cycles to meet the load. The OpenStudio default schedule for this is also 'Always On' (value=1) which does force the fan to operate continuously 24/7.

To my knowledge, there is no way to control a system's availability based on a thermostat setpoint schedule (I think this is what you are getting at).

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Thanks, Lyle. Yes, I understand all this. I was making the point that the OpenStudio default templates do not include fan operation schedules besides "Always On" or always zero (i.e. cycling). Normal commercial operation is for the system to turn on in the morning and off in the evening. Seems to me there should be some default schedules representing this common mode of operation. As it is, it appears that the user must create their own schedules to do this. -Erik

Erik Kolderup gravatar image Erik Kolderup  ( 2016-03-08 19:28:56 -0500 )edit

Ahh ok, your comments about on/off thermostat schedules and no fan schedules in the templates had me a little confused. Yes I agree, having a cycling fan or lockout schedule that mirrors the default thermostat setbacks would be nice; many users may not be aware the PTAC fans are running 24/7 by default. It's still a little risky to assume what normal/common operation is, but I guess that's what the templates and library components are for! A simple measure or template prompt could allow a novice user to enter the hours/days of operation. Cheers!

Lyle K gravatar image Lyle K  ( 2016-03-08 20:09:44 -0500 )edit

To comply with LEED requirements on supply and return fans “Baseline supply and return fans operate continuously when spaces are occupied and cycle when unoccupied” I think for PTAC systems, in addition to creating a schedule, one need to set the “Outdoor Air Flow Rate When No Cooling or Heating is Needed” to “0”, is this correct?

Morteza gravatar image Morteza  ( 2016-04-15 14:30:03 -0500 )edit
2

answered 2016-04-15 15:57:33 -0500

Chris Jones gravatar image

You need outdoor air control so that no outdoor air is introduced when the fan cycle on during unoccupied hours.

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Thank you for your time!

Morteza gravatar image Morteza  ( 2016-04-16 17:40:39 -0500 )edit
1

answered 2016-04-15 15:16:38 -0500

Morteza gravatar image

To comply with LEED requirements on supply and return fans “Baseline supply and return fans operate continuously when spaces are occupied and cycle when unoccupied” I think for PTAC systems, in addition to creating a schedule, one need to set the “Outdoor Air Flow Rate When No Cooling or Heating is Needed” to “0”, is this correct?

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Asked: 2016-03-08 15:48:44 -0500

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Last updated: Apr 15 '16