The Glitch

A homeowner tells his installer that he wants a geothermal heat pump as well as a mod/con boiler to supply the radiant floor heating in his new home. The installer assembles the six-zone system shown to the right.

Once the system was put in operation, the owner began complaining that some rooms were too warm and that there were wide variations in floor surface temperature within a given room. He also mentioned that the heat pump seemed to turn on and off rapidly.

Can you spot several incorrect details?

The Fix

To start with, there are almost no situations in which two or more hydronic heat sources should be connected in series. This is certainly true with low-temperature heat sources such as heat pumps and mod/con boilers. The fix drawing shows each of these with its own circulator (with internal check valve). Each circulator operates only when its associated circulator is operating. 

Each heat source connects to a low-loss header piping that leads to a buffer tank. The latter is appropriate given the extensive zoning of the distribution system. This tank also serves as a hydraulic separator between the heat source circulators and the one variable-speed distribution circulator. By the way, that one variable-speed pressure-regulated distribution circulator, along with six zone valves, replaces all the zone circulators in the Glitch schematic.

Other errors in the glitch schematic include:
1.  Upside-down zone purging valves.
2.  Incorrect placement of the expansion tank connection.
3.  Small “header piping” under the distribution circulators.
4. “Balancing valve” at the end of the headers.
5.  Lack of hydraulic separation between circulators.
6.  Lack of a central air separator.