A minitube distribution system, he said, is a variant of variable speed injection mixing that can be used for water temperature control in both residential and commercial hydronic radiant heating applications. It takes advantage of the typically high temperature difference between a conventional boiler and a low temperature radiant floor panel. The high temperature difference allows a relatively low flow rate to carry a substantial amount of heat. Low flow rates can significantly reduce the size and cost of distribution piping. These systems also offer increased control versatility.

The benefits of using a minitube distribution system include:

• They use much smaller piping between the mechanical room and the manifold station.

• If desired, each manifold station in a minitube system can operate at a different supply water temperature or outdoor reset schedule.

• They allow the distribution circulator at each manifold station to operate continuously during the heating season.

• Minitube systems improve the rangeability of variable speed injection mixing systems.

• In some minitube systems, it may be possible to use a smaller manifold circulator.

• The small minitube piping loses less heat to surrounding air than would larger diameter distribution piping of equivalent heat transport capacity.

• The minitube concept is highly scalable.

The Webinar also discussed the effect of longer circuit length, as well as potential applications for wider tube spacing.

While the most common tube spacing used in slab-on-grade radiant floor heating is 12 inches, Siegenthaler noted, there are situations where tubes spaced as wide as 24 inches apart in concrete slabs can provide very acceptable performance.

• The interior floor areas of large industrial, retail or office buildings are good candidates for wider tube spacing.

• Occupants don’t walk barefooted on these floors, so slightly higher variations in floor surface temperature are less likely to be noticed.

• The heating loads of the spaces above such floors are often low and thus don’t require heat outputs as high as those of a typical residential floor heating system.

The benefits of wider tube spacing, Siegenthaler noted, are:

• A reduction in system fluid volume, which could be substantial in large commercial or industrial buildings where the bulk of the system volume is often in the floor tubing.

• Lower system volume also decreases the size of the expansion tank required.

• Wider tube spacing also reduces the circuit count and number of manifold connections required.

• It reduces the number of control joint crossings.

• It increases the speed at which the tubing can be placed.

• It allows larger diameter 3/4-inch tubing to be easily bent into u-turns while forming serpentine circuits.

In addition, there will be two more MEC Webinars held in 2007. They include:

Hydraulic Separation - Beyond Primary/Secondary Piping 

Oct. 25th at 2:00 pm ET; Fee $79 {Sponsor: Caleffi North America}

Distribution Efficiency-A Strong Case for Hydronics

Nov. 13th at 2:00 pm ET; Fee $79 {Sponsor: Wilo North America}

Click here for registration information.