Understanding Relative Humidity and Enthalpy

Data Capture from my home-based weather station on 27 October 2020
What do these numbers represent, with respect to relative humidity?

Basis for the calculation of enthalpy – The mean elevation of the City of Rockwall, Texas is 550 feet MSL (mean sea level). Barometric pressure at the time of measurements was 29.15 inches Hg.

The humidity of the outdoor air was greater than the value of the indoor air humidity. This discussion on humidity will mean relative humidity, the percent saturation of the air at a specific temperature.

How does relative humidity affect personal comfort?

Look at these numbers.

Real-time measurements of temperature and relative humidity in two areas of my home demonstrate how relative humidity significantly affects comfort. The master bedroom has an AirCare humidifier set to control relative humidity to 50%. My back office, served by the same air conditioning system has a relative humidity almost 10% lower than the bedroom relative humidity.

There are empirical and sensible differences. I wear a jacket to keep warm in the back office, a room ‘chilly’ to me despite both areas having the same dry-bulb temperature. It is the lower total heat, the lower enthalpy of the back office that feels ‘chilly’.

The science behind enthalpy is complex and can be difficult to understand. For the purpose of understanding how enthalpy relates to personal comfort, simply find the intersection of Dry Bulb Temperature and Relative Humidity. From that intersection, follow the line at that intersection to the left side of the chart to read the Enthalpy, the total heat in the air.

If you prefer, work out the math.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s