Regulating Supply Temp

The Glitch

Overview:A manually set three-way mixing valve was installed to regulate the supply temperature to the concrete-slab radiant floor system. A bypass valve is also installed to help boost the boiler inlet temperature.

Exercise: Assume the system undergoes a few modest nighttime setback periods as it operates through the heating season. What are the problems with this design?

The Fix (#1 & #2)

The Fix

One of the problems with the design is the boiler is still not “guaranteed” to be protected against flue gas condensation. A high-mass slab can easily absorb heat from the water faster than the boiler can reproduce that heat by burning fuel. When this happens, neither the manually set 3-way valve nor the bypass will prevent the boiler temperature from dropping "