Bull Head Piping

Don't know about any other meanings specific to the chilled water application, but a "bullhead tee" is a "special" tee with relatively small, normally equal outlets on the branches (e.g. see http://www.acipco.com/adip/fittings/flanged/special.cfm#bht). I suspect this name could come from the arguable resemblance of the tee to the head of a bullhead (or catfish to many), with smaller whiskers basically branching out at right angles to the axis of the fishes head/body.

Usually this refers to the flow of the chilled water piping that comes the direction of water flows from the two opposite ends, and giving the flow on the center of the tee in one direction.

I hope this will help.