Hydronic systems use water as a “conveyor belt” for heat.
In a heating application, thermal energy (e.g., heat) is created at a heat source, “loaded” onto a stream of water, carried by that water to where it is needed within the building, and “unloaded” from the water into the space at one or more heat emitters. The water is neither the source of the heat, nor its final destination — it’s only a means of transport.
In a cooling application, heat is absorbed into a stream of chilled water at one or more heat absorbers, carried back to a mechanical room, transferred to a medium at higher temperature, and rejected to the atmosphere, a body of water, or into the earth. Again, water serves only as the conveyance medium for the heat.
The portion of a hydronic system that lies between the heat source (or the chiller in a cooling system) and the heat emitters (or heat absorbers in a cooling system) is called the distribution system. Its function is to distribute heated water or chilled water to all areas of the building when and where heating or cooling is needed.
Figure 1-1 shows the simplest concept for a hydronic heating distribution system.
Unfortunately, the attention given to planning hydronic distribution systems is often less than that given to selecting a heat source or chiller. This could be compared to designing a race car by focusing mostly on engine selection, while overlooking opportunities to improve the aerodynamics of the body, the efficiency of the transmission, or the rolling resistance of the tires. The resulting vehicle will be less than optimal, even though the “best” engine was used.
A poorly designed distribution system can ruin the performance of any hydronic system.
Sadly, the vast majority of complaints about insufficient or poorly proportioned heat delivery or cooling ability are traceable to poorly designed or installed distribution systems, rather than improperly performing heat sources or chillers. The hydronic distribution systems used in North America often deviate from established and proven approaches. In some cases, a distribution system ends up being a “morphing” of two or more standard design approaches.
While such an approach can — with skilled design — provide a unique solution in some situations, it is much more likely to produce disappointing results, especially if the designer is not absolutely sure how the deviations will perform. Furthermore, these “one-up” distribution systems often lack proper documentation, which makes them difficult to understand and difficult to service by those not familiar with the original installation.
The preferred approach, whenever possible, is to stay with proven design concepts that properly and reliably address issues such as hydraulic separation, differential pressure control, head loss through valves, and control of supply water temperature.
This issue of idronics™ focuses on basic and proven distribution system designs that have been successfully used in a wide range of hydronic heating and cooling applications. It discusses the strengths and limitations of each approach, and provides design tips that help optimize each type of system. It also discusses many common errors related to design or detailing of hydronic distribution systems, and presents relevant solutions. Frequent reference is also made to previous issues of idronics that can provide additional information on specific subjects.