Rightsizing = Green Design & Operations

As we all know, pumping less water in a hydronic system is an easy way to save money on monthly bills. In existing buildings and new buildings, you’ll find that engineers often opt to overdesign systems, leading to too much water in systems. In existing buildings, to reduce energy costs, there’s a tendency for operators to reduce water flow, but not always in the best ways. So here are some tips to optimize water flow for new and existing buildings.

To reduce water flow in an existing building, you can’t just reset a thermostat or VFD setting. It would be like using a 2×4 to keep fresh air dampers from opening to cut down on conditioning outside air. In an existing building, a good first step is to re-examine the loads to ensure that the systems in place are responding to the heating and cooling loads they were designed to. The load forecasts may have been wrong, or the design out of whack; or the loads may have changed with shifts in occupancy and configuration of interior spaces. After examining the loads, examine the system to find oversized and undersized equipment; unbalanced flows; controls that have failed or are out of calibration, etc.

For projects still in design, it takes more than just a simple calculation to reduce flow rates. In hydronic systems, everything is connected not only by pipes and pumps, but by the water flowing through them. Pumping flow rates must consider the roles of coils, terminal devices, chillers, cooling towers and boilers. Even the diameters and pitches of piping come into play, and the elevation of the pumps. But before getting to components, engineers and owners need to work together to forecast the loads the system will be responding to.

Engineers love safety factors – they keep them safe from lawsuits because, “no one ever got sued for providing too much cooling or heating. “ Yet…between design safety factors, and installation modifications, it’s very easy for a systems to be designed with 15%-20% more water than needed. Over-sizing leads to higher first costs (bigger components), wasted energy (components operating inefficiently), and premature service life (components suffering from operating outside optimal parameters). Oversizing = anti-green.

In summary, there are lots of ways to save energy in hydronic systems in new and existing buildings!  We covered a bunch of them above. Here are a more:

  • Design systems around high differential temperatures for higher efficiencies and right-sized components
  • Limit hydronic system head losses in distribution systems to one-half the head losses of branch piping
  • Use two-way modulating valves instead of three-way/two-position valves
  • Use variable speed pumping techniques to limit pump horsepower input to the system
  • Consider using advanced pumping strategies such as primary-secondary-tertiary with variable speed drives to hydraulically organize systems into more manageable sub-systems.
  • Use dual-function balancing valves like circuit setters to help adjust sub-system pressure losses, and replace extra and unnecessary shutoff valves.
  • Don’t add any unnecessary pressure losses to hydronic systems to help assure design flow to all circuits.

What are your tried and true methods of reducing water flow in hydronic systems?

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