Case study: Comparing hydronic heating systems
Two different heating systems show how different the design and specifications can be
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 water–tube 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 high–temperature 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 high–pressure steam plants, the airport operates their system under high pressure to maintain a high–temperature 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 NOX–emitting water–tube boilers.