In a simulation a controller decides, hour by hour, what each machine does to meet what its rooms ask for. The vocabulary below is the control panel's — every term is a real thing a real machine does, and the defaults are the conservative reading of a machine nobody has described.
The controller tries the cheapest thing first: fans only (ventilation, and free cooling if the outside air is good enough), then evaporative devices, then compressors; for heating, the heat pump before the heater. The first stage that can reach the required supply temperature is the one that runs. You can declare your own stages — which components each one switches on — or let them be derived from the drawing.
A stage that has more capacity than the hour needs unloads. A fixed-speed compressor cycles — runs flat out for part of the hour and stops — and its supply is the hour's average; an inverter modulates down to its minimum speed and cycles below it; a valve on a chilled-water coil modulates the water. Which one your machine does is declared on the compressor (variable speed, minimum and maximum speed) and on the strategy panel (modulate). Fixed speed is the default.
A constant-volume machine moves the same air every hour and changes how cold it is. SZVAV — single-zone variable air volume — is the other way round for a machine serving one room: the supply temperature is held at a setpoint (say 13 °C) and reset upward as the load falls, and the fan slows down so the room gets less air rather than warmer air. It saves fan energy, which is most of a light-load hour's electricity, and it is what ASHRAE 90.1 requires of larger single-zone units with variable-speed fans. Declare it on the strategy panel with the setpoint, the reset ceiling and the fan's minimum flow.
One handler, several rooms: the handler makes a cold deck, and each room has a terminal box that meters its own share of that air between a minimum and a maximum, reheating at its minimum when the room wants less cooling than the minimum air brings. The deck temperature is reset from the neediest room. Declare boxes on the block's serve links in the Simulate tab — maximum flow, minimum fraction, reheat kind and capacity — and give the handler an SZVAV strategy, which is where the deck setpoint and its ceiling live.
An outside-air mixing box has a minimum position (the ventilation the rooms need) and, with an economiser, opens further on a cooling hour when the outside air is cooler — or, in enthalpy mode, carries less heat — than the return: free cooling. Demand-controlled ventilation lets the minimum follow how full the rooms are; a damper schedule shuts it outside occupied hours. These live on the mixing box.
A condenser fan bank can be told to hold a minimum condensing temperature by taking fans off on a cool day, which is what an expansion valve needs to keep working. It costs compressor power and saves fan power; it is a constraint, not an economy, and the simulation treats it as one.
A room may declare a humidity ceiling (ASHRAE 55's 0.012 kg/kg is the usual one). To hold it the controller over-cools the coil to a lower dew point and warms the air back — with a heater downstream of the coil, or, on a machine drawn with face-and-bypass, by mixing untreated air past the coil, which costs nothing. A room may also declare a floor, which steers a steam humidifier. A machine with neither device reports the hours it could not hold.
With the fan switch on ON the ventilation stage runs through occupied hours whether or not there is a call; on AUTO an hour with no call starts from off, fans included. Rooms carry an occupancy profile and may relax their setpoints when empty (setback), and a machine may start early to recover the room by opening time (optimum start). Unmet hours are counted only while a room is occupied.
Machines serving the same room take it in turn: the one declared with the higher priority is offered the whole load, the next is offered what the first did not deliver, and the same holds for moisture. Machines of equal priority share equally. A dedicated outside-air unit is the usual lead.
Blocks are joined at their open ports: a chiller's leaving water to a coil's inlet (and back), an exhaust unit's air to a recovery unit's intake, a condensing unit's refrigerant to an indoor coil. Each coupling carries last hour's state across, one hour behind, which is how real plants behave through their pipework; a water coupling may declare the loop's volume as a buffer.