Although it is well known that there is no such thing as "cold", just an absence of heat, we often find
ourselves using phrases like "it's getting cooler". It may be a quirk of the language to assume that there is a
quantity called "coldness" or "coolness" that can increase, but the concept is useful.
It can be helpful in bulding design to assume that air conditioners and ventilation equipment (sometimes
collectively called HVAC) emit "coolth", and that bulky masses can store coolth and radiate it later. At night
building elements such as walls and floors store coolth, and emit it during the heat of the day, keeping the offices
Scientists will complain that what's really happening is that the cold walls are absorbing heat; but building
services engineers are quite happy to perform calculations on the basis that coolth really exists. Coolth is
measured in BTUs or I suppose joules1 or any other energy unit.
1- JudyT suggests "jouleth".