Detailed HVAC Templates and Support for the Airflow Network!

Some of you who have been regularly updating your plugin might already be aware of what I’m about to say but I wanted to post a more formal announcement so that people know that these features we have been developing over the last couple of months are fully-functional:

Detailed HVAC Templates
The latest honeybee-energy plugin has a fully fleshed-out tab for HVAC systems that currently allow you to assign over 100 different HVAC templates to honeybee Rooms:

This sample file here shows how to apply the templates and, while the example there is for a simple shoe box energy model, they can just as easily be applied to large multi-zone models. The HVAC templates are organized based on how they supply ventilation air:

  • All-Air HVAC systems - supply heating and cooling and ventilation air with the same air stream
  • DOAS HVAC systems - separate minimum ventilation air from the supply of heating + cooling
  • HeatCool HVAC systems - supply no ventilation air and are only concerned with meeting heating + cooling demand

In comparison to the detailed HVAC templates that were supported in legacy, we not only have more HVAC systems but the default efficiencies for the various pieces of HVAC equipment now conform to standards instead of “our intuition” that we often used in legacy. By default, ASHRAE 90.1 2013 is used, which should align with the International Energy Code (IECC) for 2015. But you can set the specific version of the standard when you assign the systems to your Rooms.

As you can imagine, the vast majority of the work to handle the application of all these templates was not done by Ladybug Tools. 95% of the work has been done by NREL and we are just using the openstudio-standards gem to apply these templates. So a huge thanks goes to NREL for enabling this feature.

The Airflow Network
I know that many of you have been asking for this for years now and so it makes me very happy to say that we now support the EnergyPlus AFN! While we all recognize the AFN’s complexity and know that it’s “impossible to master,” you may also be happy to know that we have tried to make it “easy to start” by making a 1-to-1 mapping between the simple ventilation objects that honeybee has historically used (and that honeybee still uses by default). So, if you have set up your model with operable windows and a control strategy for when the windows open, you will be able to model that exact same setup with the AFN. The only difference will be that air flow from interior operable windows and interior air boundaries will be computed using the pressure differences computed by the AFN instead of the constant air mixing that happens with simple ventilation objects. Also the infiltration will be modeled using the AFN pressure differences instead of the constant-flow infiltration objects.

This means that all that you need to start using the AFN in honeybee is a single component that’s been added under the 3 :: Loads tab:

This sample file here shows how to setup the AFN for a simple 3-zone model. You can see in that file that passing the Hoenybee Model through the AFN component before simulation will ensure that the AFN gets used in the simulation process. And there are a few inputs on that component that enable you to customize how infiltration gets translated from the simple objects to AFN objects along with some other parameters.

A huge thanks goes to @SaeranVasanthakumar , who developed the method for integrating the AFN with Honeybee’s file schema and Python libraries. He also developed and tested the method for translating the ventilation control strategies for the AFN, which are making use of E+'s Energy Management System.

Known Issues

  • The evaporative cooling HVAC templates currently aren’t implemented correctly in openstudio-standards but Matt Dahlhausen just implemented a fix for this, which will be available in OpenStudio 3.1.0 when it’s released.
  • The Airflow Network implementation currently models AirBoundaires in a manner that’s “acceptable” but it is far from the best way to model these cases in EnergyPlus. We couldn’t use this “best way” because of a bug in EnergyPlus 9.3 but Michael Witte just pushed a fix for this, which will be available in EnergyPlus 9.4 when it’s released.
  • The AFN may have some difficulty modeling operable skylights right now but we should have a fix soon (if anyone here wants to test this to make sure it’s an issue, that would be helpful)
  • This isn’t a bug but I just wanted to note that the 100+ HVAC templates do not include any radiant HVAC yet since these are in a class of their own in terms of complexity. But we plan to implement them after we have gotten a few other features checked off the list.
  • This also really isn’t a bug but I just wanted to note that the AFN can only be activated for Honeybee models right now and can’t be directly activated for Dragonfly models (so you have to convert the Dragonfly model to Honeybee in order to assign the AFN). All of the Detailed HVAC systems can be applied on the Dragonfly objects, though.

Cheers to you and all the Ladybug team. Thanks for the update. Air flow network was indeed an important addition. It would be quite interesting to compare a naturally ventilaed model both in legacy and LBT[+] using AFN. Will keep you updated. :+1:

1 Like

Those are, again, great news @chris

Thanks for the update!!

1 Like

Hi @Chris,
Is there a place where I can find more information/documentation about the standard settings of these HVAC templates? We have a lot of questions about choises that are made.

For example why are the cooling coils of the fancoilunits of the DOASwithfancoildistrictchilledwaterwithdistricthotwater system autosized and the heating coils not.

In the link above I can only find code examples.

Hi @Erikbeeren ,

The standards gem has some online documentation but, in my experience, it is not the most helpful resource since it usually does not include info about specific HVAC templates.

I know most of the assumptions about the HVAC equipment efficiencies come from the DoE Commercial reference buildings and the sample IDF files that are associated with them. So those might be a good resource to check to see if the values in those match values that you get from the templates with Honeybee.

If they don’t match, then you have most likely found a bug in the openstudio-stanadrds gem and you should open an issue on the repo that I linked to. Matt Dahlhausen (one of the primary maintainers of that repo) is usually pretty good about fixing bugs as long as you are specific about the issue that you think is a bug (I know he also gets a lot of generic “it’s not working” bug reports that are far less helpful).

Maybe it’s also worth noting that the openstudio-standards gem is not yet at version 1.0 and, while you can see that it’s good enough for us to use right now, it’s still under heavier development than the other more stable parts of OpenStudio, like the core OpenStudio SDK. So I would not be completely surprised if this hard-sized heating coil issue is a bug. Matt is the person who could tell you if it is, though.

1 Like