 The second air conditioning process that we're going to take a look at is that of heating and cooling with a slight modification that is where we can either humidify or dehumidify the air. So it's a minor complication over what we just took a look at. Okay so again what we'll do we'll begin with a schematic of what it is that we're talking about. So we have our standard air conditioning duct inlet state one, air is coming in at temperature one, specific humidity one, relative humidity one, and then we have our heating or cooling coil and so this could be Q dot in or Q dot out and that takes us to an intermediate state, state two, and then what we have is we have our humidification system basically just spray nozzles that are injecting either water or steam into the airstream and here we have mass flow rate water in. So we have water flowing into our system and finally the air will exit and we'll call that state three. It will be temperature three, specific humidity three, and relative humidity three. So that is what our schematic looks like. What we're now going to do is we're going to take a look at the mass balance equations for both air and water and then we'll take a look at the first law applied to this type of the system. So beginning with air and this is quite straightforward what we have is mass air at state one equals mass of air at state two equals mass flow rate of air at state three so not much going on the flow is moving through we're not adding or removing air. For water what we have is mass flow rate of water at one plus mass flow rate of water being injected between two and three is going to equal the mass flow rate of water at state three coming out of our system and we can replace the mass flow rate of water remember this is the moisture being carried by the air so we can replace it in that term there using the mass flow rate of air or multiplied by our specific humidity and then again we can do the same thing for the mass flow rate leaving the system so recasting it in terms of mass flow rate of air so that would become our water balance equation and finally for energy so applying the first law so that would be the first law now in terms of inlet what is coming in is going to be the air and the steam let's assume we're using steam and then exit is just the air and water vapor so in order to account for the steam we need a way to have the enthalpy for steam so let's assume that we are injecting steam in this particular case and for that what you would do is you would get your water in the enthalpy of that you would get that from the steam tables and for that the enthalpy value will be the saturated liquid value at whatever temperature you may say that it is coming in at so that would be the way that you could get the enthalpy for the water flowing in provide that it's you're considering it to be steam so that is how you can handle a case of either heating or cooling with humidification or dehumidification and the last thing that we'll look at in the next segment is that of evaporative coolers