Adding a Load Profile for an AirLoop

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While @ericmartinpe is correct that there isn't one object like the LoadProfile:Plant for air system demand loads, you can do the following:

1. Create a "dummy zone" that doesn't represent a real space in the building you are modeling. All zones in EnergyPlus need at least one surface, so make the surface(s) of this dummy zone adiabatic with no sun or wind exposure to prevent envelope loads.
2. Assign an OtherEquipment object to this zone. This can have "None" assigned to it's fuel type (no energy meter consumption), and then the equipment power (total, per area, or per person), schedule, and heat gain/loss fractions can be set to mimic the load profile you desire.
3. If this air handler you want to model only serves the dummy zone, you could use the Ideal Loads Air System. Otherwise, place the dummy zone in parallel with other zones on the demand side of the air system that the air handler serves (air handler is on the supply side).

No, I don't believe there is something similar for air loops. Plant loops are closed systems whose load simply depends on supply/return temperature and flow rate, as opposed to AHUs which are subject to return air conditions that fluctuate based on internal gains specified elsewhere, in addition to ventilation requirements and infiltration which impart loads on the AHU based on fluctuating ambient weather conditions.