The OpenStudio Application has several tabs on the left edge, each tab with an icon representing what the tab does. From the top, they are Weather, Schedules, Constructions, Loads, Spaces Types, Geometry, Facility, Spaces, Thermal Zones and HVAC, followed by a few others. The HVAC tab has two rectangular arrows stylizing a loop. Click on that tab.
Now you'll see a screen that has a green "+", a blue "x2" and a red "x" on the top left. Click on the green "+". In the dropdown that follows, select "Empty Air Loop". You'll see an empty air loop with five little circles (open dots, really) - these are where you will add coils and fan. The number of these dots will change as you manipulate this loop.
Now on the right of the screen, page down to "Coil Cooling Water", click on that, select "CHW Clg Coil" and drag that to the top right small circle. Then, on the right of the screen again, page down to "Coil Heating Water", click on that, select "HW Htg Coil" and drag that to the top right small circle (again). Then, on the right of the screen once gain, page down to "Fan Variable Volume", click that, select "Var Spd Fan" and drag that to the top right small circle (once again). You have now created an AHU with CHW cooling coil, HW heating coil and constant speed draw-through fan. If you need a blow-though fan instead, drag a new "Var Spd Fan" to the top left small circle instead, then click on the black "x" by the existing fan to delete that. if you have thermal zones already, you can drag them to the bottom center small circle.
Now on the top of the screen, there is a selection box that should read "Air Loop HVAC 1". That's the name of your AHU, for now.
Now, click back on the green "+" on the top left and this time select an "Empty Plant Loop". Similar to what you did on the air loop, you can now add a chiller to the top center dot. And, if instead of leaving the right hand side on "Library" you select "My Model", you can drop down to "Coil Cooling Water", select "CHW Clg Coil" and drag that to the bottom center dot. While you are still in the plant loop, also add a pump (you need to go back to the "Library" tab), page down to "Pump Variable Speed", select "Var Spd Pump" and drag that to the top left dot. Obviously, you can/must/will create another plant loop for the boiler.
This is just one of many ways to skin that dog, and it is by no means complete. You still need to add setpoint managers to all loops, you might want to add an OA system and and a heat recovery wheel to the air loop, etc. I am just aiming to get you acquainted (with OpenStudio 2.9.1). Important: The "Library ... (more)
