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how to control DOAS supply fan and damper?

asked 2019-03-15 03:57:39 -0500

xzb86 gravatar image

updated 2019-03-17 11:12:00 -0500

Hi everyone, I'm simulating FCU + DOAS system in energyplus, when I get the result, I checked with the variables, I tried to change controller: outdoor air and air terminal: singleductVAV: Noreheat, but I still can't control DOAS supply fan as scheduled, it always constant. can anybody tell me how to control DOAS supply fan (fan: variable volume) as schedule?

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answered 2019-03-19 11:42:05 -0500

The fan does not control the flow, it reacts to flow. Other objects control flow such as the air terminals as you describe or the outdoor air controller. The outdoor air controller can adjust the OA flow rate as specified in the inputs for that object. See example file DOAToFanCoil.idf as a start. Alternately, and since you mentioned schedule, you can use the Minimum Outdoor Air Schedule Name, Minimum Fraction of Outdoor Air Schedule Name and/or Maximum Fraction of Outdoor Air Schedule Name to control the flow. Also see the Controller:MechanicalVentilation object for demand controlled ventilation. See the InputOutputReference document for more information.

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it's very strange that I checked the system node of outdoor air node and air terminal unit, they are worked as schedule, the air flow rate are exactly correct.

But all the other nodes in air loop are totally different from OA flow rate, and the flow rate of fan: variable volume is constant.

that's what I confused, why in one loop, there is two different air flow.

xzb86 gravatar image xzb86  ( 2019-03-20 09:57:57 -0500 )edit

There are 2 types of systems, an outdoor air system (to meet the OA need) and a recirculation system (to meet the load). The recirculation system blows air into the zone(s) and brings that air back to the inlet or return of the HVAC system ("recirculate"). The air flow rates in these systems are rarely the same. Consider the VAV box in a zone, where the flow rate is chosen at some supply air temperature to meet the zone load. If you sum the flow rate in all zones I would not expect that "recirculation" flow rate to be the same as the amount of outdoor air you need.

rraustad gravatar image rraustad  ( 2019-03-20 10:05:10 -0500 )edit

yes, I set two systems. FCU+DOAS, FCU deal with Zone load, and DOAS system deal with OA load, I checked FCU Mixing box, OA and exhaust are both 0, even I change the outdoor air flow rate, FCU flow rate doesn't change, so I think FCU is no problem. for the DOAS system, whatever how I change, the air loop flow rate is always strange. can you leave a mail address, I can send the model to you.

xzb86 gravatar image xzb86  ( 2019-03-20 10:51:11 -0500 )edit

is there any way I can send the idf to you?

xzb86 gravatar image xzb86  ( 2019-03-20 10:52:22 -0500 )edit

click on my name for email address

rraustad gravatar image rraustad  ( 2019-03-20 13:28:51 -0500 )edit

answered 2019-03-17 16:16:58 -0500

In the Fan:VariableVolume object there is a field called Availability Schedule Name. You can create an On/Off or fraction schedule and specify it in this field to turn off the fan whenever the schedule value is 0.

Alternatively, the fan may not be turning off if your minimum flow fraction or fixed minimum air flow rate is greater than zero in the AirTerminal:SingleDuct:VAV:NoReheat object. Setting this field to zero on all the terminal units should turn off the fan when the building is unoccupied and has no heating/cooling load, even if your fan availability schedule is always 1.

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As I know, availability schedule can only realize on/off, what if I want to simulate the 0~1 fraction schedule?

xzb86 gravatar image xzb86  ( 2019-03-19 08:52:23 -0500 )edit

Yes the availability schedule would only control when the fan is allowed to operate, it would not vary the fan speed. If the fan is operating at constant speed, perhaps this is because there is a constant ventilation requirement that the DOAS is providing, or some other continuous load. If you share your model I could take a look.

ericmartinpe gravatar image ericmartinpe  ( 2019-03-19 11:32:04 -0500 )edit

how can I send you my idf file? can you leave a mail address?

xzb86 gravatar image xzb86  ( 2019-03-20 09:37:32 -0500 )edit

upload it to dropbox or googledrive and post the link here.

ericmartinpe gravatar image ericmartinpe  ( 2019-03-20 11:05:55 -0500 )edit

The issue is similar to this, but you need an AirLoopHVAC:OutdoorAirSystem so that you can control the ventilation requirement with a Controller:OutdoorAir. First change, the Return Air Node in ZoneHVAC:EquipmentConnections to Zone A Relief Air Outlet (to prevent return air to DOAS). Then, change the terminal to AirTerminal:SingleDuct:Uncontrolled, and specify Zone A Outdoor Air. Then, add DOAS Return Air Outlet and Zone A Return Outlet to an OutdoorAir:Nodelist. See here.

ericmartinpe gravatar image ericmartinpe  ( 2019-03-24 14:15:34 -0500 )edit

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Asked: 2019-03-15 03:57:39 -0500

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Last updated: Mar 19 '19