I would like to submit the new tag bypass for AHU unit where a bypass damper (installed in a duct connectiong supply with return) is used instead of a VFD to maintain discharge air pressure to setpoint.

tag would be bypass damper cmd

We already have faceBypass - isn't this the same thing?

faceBypass is a dual duct giving one way for air to "bypass" a heating coil... the other duct has a heating coil (face coil).

It's a way to heat air with (often) a steam coil.

Bypass damper closes a path for air to pass directly from supply ...to return (it bypasses the VAV boxes).

It's a way to lower the duct static pressure. Fan keeps its speed and supply air has a path to return even if the boxes are closed.

I agree with Christian. I think that the bypass tag description just needs to change.

Current

• bypass - Indicates a valve used to by-pass a piping system.

Suggestions

• bypass - Indicates an actuator used to by-pass a medium in the system.
• bypass - Indicates a controlled variable used to by-pass a medium in the system.

Okay after talking to John now I understand the difference between face by-pass and what we are talking about here.

I suggest we take Christian's proposal to add a bypass damper cmd to the ahu point list.

We will also add the following text to the bypass tag:

This tag is used in combination with the damper tag on an ahu to indicate a damper in the ductwork to by-pass the VAV boxs and create a direct circuit between the discharge and return of the unit.

Comments, tweaks, rewrite welcome.

I think adding that description to the existing bypass tag works well.

Hi There, wondering about the definition of a PAU. The use of PAU's in warmer climates is very common. There is a difference between a PAU and an AHU in that a PAU (Primary Air Unit) provides treated outside air to other AHU's and not a space as an AHU typically does. I my humble opinion tbese units need to be identified differently even though they may have the same basic functionality. They could be identified as different type like the Packaged RTU? They can be very large in warmer climates especially when associated with Hotel kitchens and Guest room fresh air treatment for example.

Does a PAU have the same basic components like outside air damper, fan, heating/cooling coils, and sensors in the same places? If so then I agree just creating a new tag like rooftop which you stick on a ahu would make sense.

The tag would probably be pau if that abbreviation doesn't collide with any other common type of equipment.

Can you propose a formal definition for a PAU is?

Wouldn't ERV be a more common description for a fresh air unit?

Raymond, PAUs do not necessarily have energy recovery, so no, they are not an ERV. They are very similar to AHUs and are intended to dehumidify, and sometime pre-condition fresh air serving AHUs or FCUs.

As to the original subject, I noticed a number of typical AHU points also that appear to be missing (such as "chilled water coil valve", "hot water coil valve", etc). Do these simply not exist yet? Is the forum the best place to make recommendations for addition?

Also, I recognise that terms already recommended are currently being utilized and that revision to implemented systems would be difficult. That being said, from the mechanical engineer control design perspective, there may be some very good arguments to do so (both to distinguish purpose and to stay consistent with other standards). What is the process to suggest revision to existing tags?

As to the original subject, I noticed a number of typical AHU points also that appear to be missing (such as "chilled water coil valve", "hot water coil valve", etc). Do these simply not exist yet? Is the forum the best place to make recommendations for addition?

These are defined as cool cmd and heat cmd - if they are valves they are 0 to 100%. Otherwise they might be staged binary commands in which case the stage tag should also be used.

Thanks Brian. If I find any other points that appear to be missing, is the forum the best place to bring this up?

For instance, I work with IDEC systems that also utilize direct evap cooling sections, which are usually in place in addtion to moduling chilled water coils and direct expansion (the first and last of which are both staged cooling).

Thanks Brian. If I find any other points that appear to be missing, is the forum the best place to bring this up?

Yeap this is the exact place to discuss missing points or new equip types.