Every HVAC system is a chain of parts that carries heat between the rooms and the outdoors. Here you build systems from those parts on a section through a building. Drag a part from the tray into an empty slot, or select the part and then the slot. A part in the wrong place goes back to the tray with the reason.
Steps 1, 2, 3 and 6 use no tab: Sanity-check the input, Test the candidate system, Scale and size, and Plant room and riser sketch.
An office like this one is cooled by four loops in a chain. Air collects heat in the rooms and gives it up at a cooling coil. Chilled water carries it to the chiller. Refrigerant inside the chiller lifts it to a higher temperature. Condenser water carries it to the cooling tower, which throws it away. Nothing in the chain makes cold. Eight parts are missing from the drawing, and each loop lights up once all its parts are in. Some parts in the tray belong to other systems. Heating here is an electric element at each VAV box, so there are no heating-water pipes.
Parts
The box on the roof is a row of sections, and the air passes through them in turn. Outdoor air comes in at the left and supply air leaves at the right; along the top deck, air from the rooms runs the other way. Some sections must come before others, and a section in the wrong place goes back to the tray with the reason. Build the air-handling unit of an all-air system first, then the outdoor air unit that serves fan coils and chilled beams, and compare the two.
Return air from the rooms is mixed with outdoor air, and the mix is supplied to the rooms.
Sections
Only outdoor air is supplied, for ventilation. Fan coils or chilled beams in the rooms do most of the cooling.
Sections
The building is the same in every case. What changes is how the cooling and heating get from the roof to the rooms: by air, by water or by refrigerant. That decides what runs up the risers, how big the ducts are and what sits in the ceiling. Build the case closest to the system you are proposing for your building first, then at least one other, and compare what crosses each floor.
Both buildings bring in outdoor air for ventilation and send stale air back out. What differs is where the room air is recirculated: in one building it travels all the way back to the roof, in the other it never leaves the room. Put a label on each duct and opening, then trace the outdoor air through the building in order. Then do the same on a typical floor of your own building.
The air-handling unit on the roof serves every floor through the duct riser, and VAV boxes share the air out on each floor.
The DOAS on the roof serves every floor through the duct riser, and a fan-coil unit in each room does the cooling and heating.
These are the questions a review panel asks of a design: does each piece of plant sit where it can work, does every loop have what it needs to run, and can the air get in and out safely. Each building below has exactly one thing wrong. Select it in the drawing, then choose the reason. Five buildings make a set, and a new set draws different faults.