The data are from a solar panel simulation case study.
The original source that Box, Hunter and Hunter used is http://www.sciencedirect.com/science/article/pii/0038092X67900515
A theoretical model for a commercial system was made. A 2^4 factorial design was used (center point is not included in this dataset).
The factors are dimensionless groups (https://en.wikipedia.org/wiki/Dimensionless_quantity)
A: total daily insolation,
B: the tank capacity,
C: the water flow through the absorber,
D: solar intermittency coming in.
The responses variables are
y1: collection efficiency, and
y2: the energy delivery efficiency.
The coded values for
D are given, with -1 representing
the low value and +1 the high value.
A data.frame containing 16 observations of 6 variables (A, B, C, D, with y1 and y2 as responses.)
Box, Hunter and Hunter, 2nd edition, Chapter 5, page 230.
Box, G. E. P. and Hunter, J. S. and Hunter, W. G., 2005, Statistics for Experimenters, Second edition. Wiley."