Heat calculation (psychometrics) 1

[NickFury]

This is my first post.
My question is:
You are designing a system for a new home. With the given conditions, what will be the final drybulb and RH after passing the air through the furnace?

Given:
Air-60 degree DB
RH-48%
Volume-1200 cfm
Btu 105,000 output

New
DB=
RH=

105,000 divided by (1200 x 1.08)
105,000 divided by 1296 = 81
81 + 60 = 141

I came up with a new dry bulb of 141 degrees by using the total heat formula. btu/hr=cfm x DT x 1.08. Which the answer to this was 81 and I add the 60 degree air and got a new dry bulb of 141 degrees. If this is coorect how do I calculate the new Relative Humidity(RH) or does the RH remain the same?

Thank you

 

[MintJulep]

141 F leaving the furnace sounds right to me.

The RH will change because it's, well, relative.

The absolute humidity will remain the same because the furnace neither adds nor subtracts moisture from the air.

The easiest way to determine the new RH would be with a psychrometric chart. Start at your air entering condition, and follow the constant absolute humidity line until it intersects 141 DB, then read the RH.

 

[imok2]

Another way is to use software I get 4.14%
Go Here:

http://www.v2cstudios.com/en/psychrometree.html