1- Is this possible to break down the “Mechanical air exchange per hour” output into % of outside air and recirculated values?
Yes, though it all depends on which type of HVAC template you are hoping to apply this to. In Legacy, this really only worked for the DOAS HVAC systems and you can similarly recreate this behavior on the DOAS systems in the LBT plugin by editing the ventilation parameters. Essentially, you just want to set up the ventilation load (either per-area, per-person, or ACH) to include both the outdoor air volume and recirculated air volume together. Then you can apply a ventilation schedule that has the fraction of the total air volume that the outdoor air should occupy. This will result in the constant DOAS fan to be sized to deliver the full volume of recirculated + outdoor air. However, the outdoor air controller will only mix enough air into the stream to meet the ventilation schedule value.
2- Is this possible to define recirculation fractions as well as different MERV filters in HVAC definition or room program?
This question is a little unclear but MERV filters are generally accounted for by editing the pressure rise across the Fan. You will need to do this manually in the OpenStudio Application or with some OpenStudio SDK code like what you see described here since we have not exposed fan pressure rise in the Honeybee model schema.
3- I noticed Air Detail component is no longer available in your advanced versions. Does it mean users can no longer design manual HVAC systems and must adhere to HVAC templates? Is it possible to modify templates?
All of the components that assign HVAC templates have properties that you can adjust on them and most of them align with what was exposed on the Legacy AirDetails component (eg. heat recovery, DCV, economizers, availability schedules, etc.).
4- How can users read more about the assumptions used in developing HVAC templates in more details?
All of the template HVAC systems in the LBT plugin come from the OpenStudio Standards gem and all of the default efficiencies for HVAC equipment come from ASHARE 90.1. So I would refer to those if you want more details.