This is a break out from post `/forum/topic/6` specifically around the notion of AHU mode and the related idea of a simple on/off status. Today we have specifically avoided the notion of an AHU mode or on/off status because its a nebulous concept.

What does on or off mean? Is it simply that the main supply fan is on/off? Does it mean that any fan or mechanical cooling/heating element is on/off? I think in general most people think of the primary fan as mapping to the overall unit's on/off state. In which case do you really need another point?

So when we evaluate on/off status we really have to consider two sides. In some cases it is just a single actuator point. A non-variable speed fan is on or off. Same with a pump. A given non-dimmable light is on or off. But in those cases we are modeling individual points. An overall piece of a equipment like an AHU, boiler, or chiller has a more complex definition of on or off.

Furthermore, often when talking about "on" we are really interested in the mode of that "on" operation. For example in an AHU we might be interested in whether it's in heating or cooling mode. But often mode is multi-dimensional because we might also consider the economizer mode as part of the overall mode.

I expect we will run into many these same issues when we get into chillers, boilers, and other complex equipment.

So all of this is just background to set the stage for a series of questions which will need to be answered by those of you who are AHU mechanical engineers and domain experts:

1. Is there a simple notion of ahuMode which makes sense to standardize?
2. If so, can we boil it down to a discrete set of enumerated states?
3. Does the simplistic idea of "on/off" of the overall AHU make sense to model separately from the fan status and/or the ahuMode status (assuming we decided ahuMode was a necessary new point)

Greetings ,

1 and 2

Yes, If we tried to standardize the ahumode point a discrete set of enumerated states could be the following (cooling mode , heating mode , dead zone mode , humidify mode , dry mode , dead zone mode ) This could be used complementary to FanOn point which status (0,1) could indicate if the fan operates or not at the dead zone .

3

From our experience we believe that simple on/off status point makes sense to be modeled separately because : On status of an appliance (Rooftop , Chiller , Gas Furnace etc) indicates that the controller of the unit is at a process of calculating any variable (temperature , pressure , e.t.c.) in order to change the thermodynamic characteristics of a fluid (heating , cooling , humidification , etc ) or to improve the air quality level.Off status of a unit means that the unit takes no action except maybe of antifreeze.

I agree with the addition of "equipment mode".There are many instances when it is desirable to know if the system is ready to "run". A case in point might be that the system was shut down due to exceeding a high limit. In this case the "mode" state should show "AlarmOFF". The system would not be available to "run" until alarm is cleared. Simple fan status may not indicate this (should but). Mode states could be "run, off, AlarmOff etc. Heating or cooling Mode may be set by Cooling Coil Valve (Direct Expansion)Dx "OnOff" or "Cooling Coil Valve Modulating Value" greater than 10%. Similar for heating, may or may not be indicated by "equip mode tag" Might be additional tag under AHU or other equipment..

When I think of AHU Mode as being more of an enumeration rather than boolean. For example you could have unoccupied/occupied/unoccupied heat/unoccupied cool/night purge/morning warmup/morning cooldown.

If the mode you are refering to is on/off how does it vary from occupiedMode?