Chiller Plant Model

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A common approach to modeling central plants is to do your building-level modeling in separate models, then output the hourly cooling loads to individual profiles that are fed into a separate central plant model. These cooling load profiles can be added to secondary chilled water loops that represent each building in the central plant model. The downside to this approach is that the building model and the plant model are not connected, so any changes to the building model means that you have to update the profiles that are being fed into the plant model, though this is pretty easy to do and does not pose a significant inconvenience.

As to whether your chillers should be connected in parallel (what I assume you mean by "horizontal") or series (what I assume you mean by "vertical"), I can say that most chiller plants will have chillers connected in parallel, so that they can be staged on and off depending on the load, and can include a low-load chiller. However, I have heard that series configurations can be very efficient in some applications and increase the available chiller capacity. If you wan to go with a "typical" configuration, though, use parallel.

If you are modeling multiple large buildings, I would suggest making the building models individually and using the district heating and cooling objects to get the plant load for each one.

Often engineers will use a separate software to model the plant to be able to better capture system operation and control. You can also refer to the engineering documentation for EnergyPlus and implement the same chiller and cooling tower logic in a spreadsheet with known loads and weather data. I would recommend this approach if you have many large buildings.

However, if you have many small buildings all part of the same project, it is possible to model this directly in the OpenStudio. If you use this approach, I recommend reading the OpenStudio tutorial on creating HVAC system plant loops to get an idea of how your setup should look.

You can see an example of this by adding a template system from the HVAC systems tab:

Your system will look something like this:

Chilled water loop - you have chillers on the supply side and cooling coils on the demand side. The little circle icons above and below the chiller indicate that it is attached to another loop (the condenser loop). Clicking the circle will bring you to the condenser loop:

On the condenser loop, your chillers are on the demand side and cooling towers on the supply side.

If you want to control the sequence of the chillers and cooling towers in a specific way, you need to specify that in your model. See these recent questions on the forum: Sequential load distribution scheme seems not working and Optimal operation of plant chillers (EnergyPlus).