I'm adding the ASHRAE Outdoor Design Conditions as a lookup table to my ACCA MJE8 spreadsheet and I notice that ASHRAE don't represent RH in the same way as ACCA.
The ACCA manual gives you the RH figures for 55%, 50% and 45% for any given city. However, the ASHRAE table presents the Humidity Ratio "humidity ratio, grains of moisture per lb of dry air" (which I understand is the same thing as RH), as 0.4%, 1% and 2%. E.G.
Now both seem to describe RH in the same way, i.e. a percentage of total saturated air (grains) at a given temperature. But they represent the 3 comfort levels on a different scale. How can I convert the ASHRAE RH data into the same scale as the ACCA MJE8?