night cycle based on humidity call

asked 2023-02-01 11:34:01 -0500

nfonner
616 ●2 ●8

updated 2023-02-01 17:30:19 -0500

13830 ●76 ●24 http://bigladdersoftware.com/

Does anyone know a method or workaround within OpenStudio or E+ to activate an air handler based on high humidity (Zone RH > SP) when that system is scheduled off but "Use Night Cycle" is enabled?

(E.g. IF AHU Availability schedule = 0, zone temp <= SP, but zone humidity > SP, THEN cycle on system.)

I know with Trace 700 there is, conceptually, a workaround to create schedules with IF THEN statements (IF zone RH >SP, THEN override schedule value to 100). I've used this in the past to pin a sensible load on the zone so that it raised the temps of the zone whenever RH% > SP, thus activating the AHU, but I can't see how that even possible in E+.

This is a typical concern in buildings we work with and trying to lower zone temp to trigger more runtime hours isn't cutting it, nor is it time efficient to play a game of whack-a-mole in scheduling each individual unit available for all the individual hours where zone RH > SP.

Thanks for any input.

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answered 2023-02-01 12:29:50 -0500

ericringold

10527 ●31 ●8 https://www.nrel.gov/b...

I've done this with an EnergyPlus measure to add an EMS program and required objects. I used sensors on the AHU availability schedule 'Schedule Value' and the return air node dewpoint temperature (though you could use the Zone Control Humidistat schedules), and an actuator of AirLoopHVAC 'Availability Status'. The program logic is simple: if system is off (availabilty schedule value == 0) and DP sensor is > some limit, set availability status actuator to 'CycleOn'.

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Thanks for the direction Eric. Off to the measure writing guide.

nfonner ( 2023-02-01 15:02:29 -0500 )edit

Got it working (ish) in E+ before measure writing, but now gas usage dropped next to nothing since the units would not come out of cycling & even stayed off during winter hours.

8 Zone RH Sensors
4 AirLoopHVAC (Avail Status) Actuators
4 Programs (see below)

Should the "IF" be a "WHILE" statement or is there a fix for the "SET" statement after the "ELSE" to release the actuator back to follow the normal avail status schedule?

IF (AHU_1_NC_Status == 0) && (Zone140GymA1_RH > 60)
SET AHU_1_NC_Status = CycleOn
ELSE
SET AHU_1_NC_Status == 0
ENDIF

nfonner ( 2023-02-02 07:49:06 -0500 )edit

Careful how you're using the assignment operator (=) vs the equality operator (==); I think your line 4 won't work because the SET call should use =. See here. Also not sure about your variable names - 'AHU_1_NC_Status' seems to be the sensor name, but you're also trying to SET its value. You should SET the actuator value.

ericringold ( 2023-02-02 10:44:24 -0500 )edit

Finally (I think the Application Guide is vague on this) I'm not sure you're assigning the Availability Status values correctly. In my measure I assigned the values 'CycleOn' and 'NoAction', which I think worked. But the guide seems to indicate it should be 2.0 and 0.0. Not sure on that, may be worth trying both ways.

ericringold ( 2023-02-02 10:46:52 -0500 )edit

I'll try the suggestions and keep plugging away, but the 'AHU_1_NC_Status' is an actuator. Could be what's causing the issue is that I'm not referencing it as BOTH a sensor and actuator?

nfonner ( 2023-02-02 10:54:01 -0500 )edit

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