Case study: Comparing hydronic heating systems

Two different heating systems show how different the design and specifications can be

By Jacob Haddadin, EIT and Stephanie Khouri, CCJM Engineers Ltd., Chicago September 23, 2019

The following shows the range of sizes hydronic heating systems can span. One is a relatively small hydronic heating plant in an elementary school annex and the other is one of the largest heating plants in a massive district heating plant at O’Hare International Airport in Chicago. 

The school project includes two 500 MBH (input) gas-fired, condensing watertube boilers (see Figures 1 and 2)The system operates at 150 F supply and 120 F return water temperature. It is a variable primary flow system primarily serving perimeter hydronic terminal heating equipment including cabinet heaters, fin-tube radiators and radiant heating panels (Figure 3).  

In contrast, the O’Hare International Airport heating plant consists of eight 75,000 MBH water-tube hightemperature water HTW boilers split into two fully redundant plants delivering 410 F water at 400 PSIG operating pressure. While most systems operating at this temperature are highpressure steam plants, the airport operates their system under high pressure to maintain a hightemperature water system.  

Heat exchangers at each terminal develop conventional 180 F water for air handling units and terminal devices in a decoupled tertiary loop. The plant is currently in the construction process of replacing all eight existing boilers with new, higher efficiency, lower NOXemitting watertube boilers.  

Author Bio: Jacob Haddadin is a mechanical engineer at CCJM Engineers and a recent graduate from the Illinois Institute of Technology, with hands-on commercial building mechanical design experience covering multifamily residential, educational and laboratory facilities and commissioning. Stephanie Khouri is a mechanical engineer at CCJM Engineers and a recent graduate of Marquette University developing her mechanical design experience with commercial and educational facilities.