Question

The inside temperature of a wall in a dwelling is 15°C. If the air in the room is at 21°C, what is the maximum relative humidity, in percent, the air can have before condensation occurs on the wall?

Answer 1

Given:

Wall's inside temperature,
`T_(wa) = 15^(\circ)C`

Room air temperature,
`T_(air) = 21^(\circ)C`

Solution:

To calculate percentage max relative humidity, we make use of steam table for saturated pressure of wall and air:

From steam table:

At
`T_(wa) = 15^(\circ)C`:

`P_(wa(sat)) = 1.7057 kPa`

At
`T_(air) = 21^(\circ)C`:

`P_(air(sat)) = 2.487 kPa`

Now,

`% Relative Humidity (RH)_(max) = (P_(wa(sat)))/(P_(air(sat))) * 100`

`(RH)_(max) = (1.7057)/(2.487)* 100`

(RH)_{max} = 68.58%

Therefore, max Relative Humidity of the air before the occurrence of condensation in wall is 68.85%