What each category is, when you would use it, and how it is drawn here. Every kind below is published as an example you can open from the Design tab's sources and take apart, and most have a worked case — a building on its own weather year, with what it read and what it taught.
An indoor coil and fan, an outdoor compressor and condenser, one refrigerant circuit between them. Cooling by direct expansion; on a heating hour the same circuit runs backwards as a heat pump, losing capacity as the outdoor coil frosts below about 5 °C. The everyday unit for a room or a small building. Draw: mixing box (optional outside air) → DX evaporator → fan, with the compressor and condenser closing the refrigerant loop.
A split with its own outside-air mixing box, economiser and — often — a gas furnace or electric heater, sized to serve a whole floor or hall from the roof. Constant volume for one zone, or a VAV rooftop with terminal boxes for several. Heat pumps and gas variants are both drawn the same way; a gas heater is declared by its fuel.
A fan, a chilled- or hot-water coil, a mixing box and whatever else the air needs — recovery, humidifier, reheat. It makes no cold of its own: its water comes from a chiller, either inside the same drawing or from another block. An air handler serving one room runs constant-volume or SZVAV; serving several rooms it runs VAV with a box per room.
A compressor circuit whose evaporator is a water exchanger: it makes chilled water rather than cold air. Air-cooled (a condenser coil and fan bank) or water-cooled (a coaxial condenser, a condenser-water pump and a cooling tower). A modular chiller is one such circuit declared several times over. In a building a chiller is a block that serves no room and holds a leaving-water setpoint for the coils it feeds — one chiller can feed many receivers through a manifold.
A split cut along its refrigerant lines into two systems: the indoor coil and fan with its refrigerant ports open, and the remote compressor and condenser with its suction open. Each is its own block, and the pair is joined in the building by a refrigerant coupling. This is how a cold store's unit cooler, or a UPS room's indoor unit, is fed from a machine outside.
A fan and a two-pipe water coil, nothing else — the terminal unit of a chilled-water building. It has no outside air, no reheat and (two-pipe) no heat, which is why a fan-coil room usually needs an outside-air unit beside it and cannot hold a humidity ceiling on its own.
A wet pack cools air by evaporating water into it: direct when the pack is in the supply air (cooler and wetter), indirect when a small tower cools water for a coil in the supply (cooler, no added moisture), two-stage when an indirect stage runs ahead of a direct pad. Cheap to run and only useful in dry climates; a supply that is cooler than the room but nearly saturated is what you get, and the model says so.
A dedicated outside-air system is a machine whose only job is the ventilation air. It takes 100 % outside air, recovers heat (and, in a wet core, moisture) from the building's exhaust in a plate core, cools and dries the air on a coil, and delivers it at a neutral temperature; the rooms' own sensible load is carried by other machines — fan coils, splits, a VAV handler. The point of it is that ventilation air is where most of a building's moisture arrives, and drying it once, at the door, is cheaper and more controllable than asking every room's machine to do it. The example DOAS wraps a heat pipe around its coil: the air is pre-cooled before the coil and re-warmed after it by the same device, so the drying needs no reheat. In a building a DOAS is declared the lead on the rooms it serves, so it carries the latent load and the machine behind it is asked only for the rest.
A central plant serving several buildings: a water-cooled chiller or several, a tower, the pumps, with chilled water sent out through a manifold to handlers that are blocks of their own. The campus example is one — four scrolls on a coaxial evaporator and condenser, a rated tower, three buildings on a 6.5 °C loop.
A fan and a sparse-finned DX coil for a cold room or freezer, fed by a low-temperature condensing unit on R404A-class refrigerant. The supermarket example holds a frozen store at −20 °C on one.
A category is a label. If none of the ten fits, type your own when you save or publish; it filters and shows everywhere the fixed ones do.