Your facility most likely has some HVAC schedules already in place for your day-to-day operation of your HVAC equipment. To use Events2HVAC, you will eventually either need to deactivate those schedules or take steps to override them so that Events2HVAC can send commands to equipment automatically. Ideally, you want to leave your existing schedules in place in case the server is shutdown and automatic scheduling through Events2HVAC is disabled. It is always a good practice to have a backup plan.
Most schedule objects in HVAC systems can be setup to work on a fixed daily schedule, a manual event schedule, or a holiday schedule. The schedule object commands one or more individual points that turn the equipment on or off. The command sent to these items are sent at a specify priority level. When setting up Events2HVAC, you will need to determine the individual points to command and the priority level at which the schedule object is sending the commands. When you define the actions for equipment, you will need to send the commands to those same points using a priority that is higher than your existing schedule object.
There are several schedule override strategies that can be employed when integrating Events2HVAC to your existing systems. Some require little, if any, preparation of the existing HVAC system. Others may require your HVAC technician to make some programming changes and/or add some additional objects. This document describes four different methods for overriding schedules in the case of an outage.
1. Overriding at a Higher Priority
Note: This method has minimal impact to your existing HVAC system, but requires more manual steps to revert back to backup scheduling.
Figure 1- Overriding Priorities
This example shows a BACnet schedule object that has a weekly schedule assigned to turn on AHU-1,2,3 from 8am to 8pm. This object sends start commands at a priority of 15. In Events2HVAC, we created 3 equipment items AHU-1, 2, and 3. For each item, we created an action that sends a command on each events start/stop time. This action will send the command at priority 14 (higher) so that it will override any command that is sent from the schedule object.
In this scenario, individual rooms can be assigned to each AHU in Events2HVAC, allowing individual room schedules to turn on/off each AHU.
The proper method to reverting back to default schedules in this case is to release the priority 14 commands on each of the commanded zone objects. The objects will then revert to the commands coming from the schedule objects at priority 15.
2. Override at Higher Priority and Release
Note: This method has minimal impact to your existing HVAC system, but requires more manual steps to revert back to backup scheduling. This method well suited for the need to have existing base schedules for equipment or a method create exception schedules on the HVAC side. EventsHVAC will turn the system on when needed at an overriding priority and when done the equipment is release back to the base scheduler.
Figure 2 - Overriding and Releasing Priority
Use this strategy if you want your default base schedules to operate during normal business hours. For after-hours events, E2H will override the individual HVAC equipment for the start of the event. When the event is finished, the override priority (14) is released so that the last commanded priority 15 state will take over.
This method also allows users a way to enter exception schedules using there HVAC scheduler whenever they have an event that may not be entered in the reservation system.
The proper method to reverting back to default schedules in this case would be to release the priority 14 commands on each of the commanded zone objects. The objects will then revert to the commands coming from the schedule objects at priority 15.
3. Isolating and Adding Logic for Events2HVAC commands
Note: This method is probably the most eloquent and user-friendly switching method, but will require additional programming and object creating on the HVAC system.
Figure 4 - Switchover Logic
This option adds logic to the controllers and binary points to regulate the commands coming from Events2HVAC. Additional binary points are created in the HVAC system for each item that Events2HVAC is commanding; and a global binary object is created to indicate how you want to control your rooms.
If the global switch point (SCHED-SW) indicates that you want default schedules, all of the commands originating from default schedules are sent to the room points. If the global switch point indicates that you want Events2HVAC to control rooms, default schedules are blocked and the binary room points that you added for each control point will command the direct room points.
This kind of control takes more time because you have to add all of the binary points and the necessary programming logic. However, it will allow the Events2HVAC binary points to be tracked using point history and provide a more orderly switch over when it is needed.
For automatic switch-over strategies see: Schedule Fail-over Strategies
4. Pushing Schedules Instead of Occupied States
Starting in 1.5.x, if you are using the BACnet Device interface, you can push 24 hrs of BACnet exception schedules into a dedicated zone schedule object instead of sending the occupancy state (binary) to the zone.
The above 3 choices still applies only E2H would be sending schedule data into the a local schedule object instead of a BV point. In most cases you will need to create a single schedule object for each zone you want to control and link the output to the controlled device. You may still decide to keep a BV point that will indicate what the zone schedule object is outputting to the end device, but it is not necessary.
Figure 5- Overriding Priorities using Schedules
Whatever method you choose, make sure you discuss it with you HVAC representative and/or your local HVAC operators. They may have some insight into a better way of accomplishing the end result. Also, remember to document the procedure so that the person on-call knows what to do in case of an outage.