Starting to Place PEX for the Radiant Heating/Cooling

It was another beautiful blue-sky California day today.  Our goal is to complete pouring concrete inside the house before Thanksgiving so that means we need to have the radiant heating/cooling PEX loops inside the concrete before each pour.

We need to pour concrete over the hollow core concrete panels in the living area and the garage on the main level, and then pour three inches of concrete in the lower level.  On the main floor, there will be 3 inches of concrete everywhere and 5.25 inches of concrete where we are having exposed concrete.  The other areas will have hardwood flooring in a 2.25 inch system (3/4 inch subfloor, 3/4 inch PEX layer, and 3/4 inch hardwood flooring).

Bill Brown was confident that his team wouldn’t be on the ‘critical path’ and that the radiant heating/cooling (PEX) would cause delays in meeting the Thanksgiving deadline.

The gauntlet was thrown …

Silicon Valley Mechanical Improves on Our Initial Radiant Design

Several month ago we started working with Ken Martin of Silicon Valley Mechanical to design the radiant heating and cooling, and the displacement air ventilation.  Ken is a Professional Engineer and has extensive experience with innovative projects, including David Kineda’s Z-squared building in San Jose, which David won a USGBC Northern California chapter award for (and was presented at the USGBC NorCal Gala on 10/30/09).

We had engaged Monterey Energy Group for the initial design of the radiant layout, which they did.  After meeting with Ken and reviewing the preliminary design with him, Ken identified a number of innovative improvements that could be made in a cost-effective manner that would allow for simultaneous radiant heating and cooling across zones as well as heating the swimming pool and cooling the wine cellar.

The highlights of Ken’s design changes included:

  • Enabling radiant cooling by controlling humidity inside the house (to control the dew point and resulting condensation).
  • Increasing the diameter of the PEX from 1/2 inch to 5/8 inch, which reduces the pressure drop in a loop.
  • Placing the PEX on 9 inch centers (vs 12 inch).
  • Using a loop layout so the average temperature differential between the supply and return PEX yields the same differential.

Placing Our First PEX Loops

Matt Jung from 88HVAC met Bryan at the project site and showed him how to take the PEX off the spool and lay out the PEX.  Matt has extensive experience with radiant heating and this will be his first radiant heating and cooling project.

We are tying the PEX to the #3 reinforcing steel (rebar), which is placed 18 inches on center each way.  Bill Brown cautioned us to ensure that no PEX loop should be able to ‘float’ upward as he will be doing saw cuts to control the cracking in the slab.  With the PEX loops pressurized to 100 PSI, Ken Martin believes that we should be OK.  Bill would have preferred to have the PEX under the rebar; for performance purposes, we will be placing the PEX on top of the rebar so it is closer to the surface (but safe from the saw cuts).

A perfect beautiful blue-sky California day to start laying out our PEX.

A perfect beautiful blue-sky California day to start laying out our PEX.

Before Matt arrived, Bryan used our shop vacuum to clean the debris from the perimeter voids around the hollow core concrete panels.

Before Matt arrived, Bryan used our shop vacuum to clean the debris from the perimeter voids around the hollow core concrete panels.

Matt working with Bryan to lay out our first PEX loops and zip tie the PEX securely to the rebar.

Matt working with Bryan to lay out our first PEX loops and zip tie the PEX securely to the rebar.

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