When air conditioning started gaining popularity in the early 1920s, the most "high-tech" portable tool available to the engineer was the slide rule. Consequently, the manufacturing processes at the time were limited in flexibility; these limitations are reflective of the technology and computing power of the period. In order to mass-produce, chiller manufacturers could only offer standard-size chillers at 10 degrees DT for both chilled water and condenser water flows.
Today, engineers entering the field of hvac in general and chiller plant design in particular are still being indoctrinated to the same concepts using manuals originally written in 1950s and revised in 1970s. These concepts are outdated and retrograde. It is the dawn of the 21st century and it is time to rewrite the book.