Occupancy sensor tied to VAV box dual minimum 1

[pgalloni]

We are designing a VAV w/electric reheat system for technical college classroom space and the VAV boxes have dual minimum (occupied minimum and unoccupied minimum airflow). The electrical engineer said they "use a slave relay controlled by the occupancy sensor for these types of loads". We typically ask the EE to spec an occupancy sensor with dual output, but I'm unsure what slave relay is, and if that will work just as well without spec'ing dual output occupancy sensors.


Thanks!

 

[walz]

Why do you need your occupancy sensor to have dual output.
isnt there any kind of AND operator in the BAS. that can decide what minimum it has to be opened in occupied as well as un-occupied.

i think that you do need to two signals in both the cases. but one signal is for occupancy and other should be temperature.

Lets goto case by case.
Case-1: Occupied minimum

this will occur when classroom is occupied but load required is minimum, so VAV should take both signals of temp and occupancy and decides that it needs to be opened (x % of toal)

Case:2 Unoccupied Minimum

this will occur when everybody is bunking. No worries. still VAV is going to decide what minimum it should be opened based on temp and CO2.

 

[VEEKRISH]

Always a good idea to couple a Temp Sensor an CO2 Sensor. Works best based on my experience.

 

[mauricestoker]

I've used "slave" to control exhaust volume, and dual technology for occupancy. The .AND. might be used for temperature reset under unoccupied mode. I've used dual technology occupancy sensors in cases where either line of sight might be lost, or occupancy does not include any amount of motion, but usually for security. Putting a motion sensor on the outside of a bathroom stall would be worst case unless you are trying to save water: having a bathroom full of unseen people waving under the stall might convince people to wait until they get home for their BM.

As above, I would not try to operate temperature and volume flow off the same sensor, especially if relative differential pressure has to be maintained.

 

[JVKS]

I am doing a project now in a college where we are wiring in the occupancy sensors to setback the VAV boxes in addition to shutting off the lights.

the DDC VAV box controllers we are using have a seperate input for an occupancy sensor that will put the box in stand-by which is just a reduced temperature setting but not full setback. basically 3 modes: occupied, unoccupied(from the day/nigh of the EMS) with a night time set back temperature and a stand by mode with a setback temperature of maybe 5 F below the occupied set point. find out from the controls mfg what theirs will do.

all of the occupancy senosrs we installed either had a dual contact on them or the power pack that several were tied into. i would rethink the dual/slave relay set up - to complicated if you can just get a dual contact sensor installed for not much more. simpler the better.