high dry bulb temperature, low relative humidity area
Your money will be best spent if you chose humidifiers, if this is the case.
Why?
Humidifiers will introduce water vapour into your air. Since the relative humidity is low, the water vapour will absorb heat and occupy the air space.
Relative humidity will increase to the comfort region and dry bulb temperature will decrease as a result of heat transfer
low dry bulb temperature, high relative humidity area.
You have two options in this case.
If the absolute humidity of the space is within the comfort region, then an air heater will do the trick. Air will be heated through sensible heating.
If the absolute humidity of the air is higher than the comfort region, then a dehumidifier is the best option. Outlet temperature of the humidifier will be higher, at a lower humidity.
Air conditioner for heating, plus humidifying action is the best.
As the temperature rises through sensible cooling, relative humidity will decrease. Thus, addition of water vapour into the heated air will increase its humidity.
That’s it for psychrometric chart analysis for air conditioning. I promised you it’s simpler than it sounds.