Boilers, Chillers

Series counterflow chiller arrangement benefits

Configuring water-cooled chiller plants in a series counterflow (SCF) arrangement splits the lift between two machines to enhance the operating efficiency of the plant.

By Cory Duggin, PE, LEED AP BD+C, BEMP; TLC Engineering for Architecture, Brentwood, Tenn. October 8, 2020
Courtesy: TLC Engineering for Architecture

Water-cooled chiller plants are traditionally designed with the evaporators and condensers piped in parallel, which makes the compressor in each machine have to do the entire cooling delta T and lift. Lift is the difference between leaving evaporator pressure and leaving condenser pressure.  This is often approximated by the leaving temperatures.

Figure 1: Above is a chilled water system diagram illustrating a series counterflow arrangement. Courtesy: TLC Engineering for Architecture

Figure 1: Above is a chilled water system diagram illustrating a series counterflow arrangement. Courtesy: TLC Engineering for Architecture

Configuring water-cooled chiller plants in a series counterflow (SCF) arrangement splits the lift between two machines to enhance the operating efficiency of the plant. In a SCF configuration the chiller making the coldest chilled water also gets the coldest condenser water. Now one machine will cool the water from 56 to 49 F° and the second machine cools it from 49 to 42 F°. Just like in life, splitting the work results in a more efficient outcome.  Our analysis has shown SCF configurations saving 15 to 20% compared to typical parallel configurations with full load efficiencies below 0.5 kW/ton (COP=7).

Figure 2: Annual chiller efficiency map of a single parallel chiller. Courtesy: TLC Engineering for Architecture

Figure 2: Annual chiller efficiency map of a single parallel chiller. Courtesy: TLC Engineering for Architecture


This article originally appeared on TLC Engineers’ websiteTLC Engineers is a CFE Media content partner. 


Cory Duggin, PE, LEED AP BD+C, BEMP; TLC Engineering for Architecture, Brentwood, Tenn.
Author Bio: Cory Duggin is the energy modeling wizard at TLC Engineering for Architecture, providing building-performance simulation efforts and high-performance design solutions. He is a member of the Consulting-Specifying Engineer editorial advisory board.