At a recent conference in Burlington, Vermont, energy consultant Marc Rosenbaum shared insights that he’s gleaned from several energy monitoring projects. His presentation on February 7, 2018, was part of Better Buildings By Design, a conference sponsored by Efficiency Vermont.
Rosenbaum believes that energy retrofit specialists should regularly measure energy use. “We’re practitioners,” Rosenbaum told the Burlington audience. “Most of the time we try to get it right, and when we don’t we want to know why. So we grind through it. We try it again and test it.”
Monitoring a Zehnder ERV
At his house on Martha’s Vineyard in Massachusetts, Rosenbaum has a Zehnder ComfoAir 200 energy-recovery ventilator (ERV). Rosenbaum praised Zehnder’s plastic ductwork (so-called ComfoTube ducts). “I cannot find a detectable leak in the ducts,” he said.
He took temperature measurements and power draw measurements to determine the ERV’s effectiveness. “I am interested in effectiveness, not efficiency,” he said. “Most people talk about efficiency. Efficiency measurements include motor watts. Effectiveness is the measure of how much of the temperature differential between outdoor and indoor air is recovered by the ventilator. Effectiveness is affected by motor heat, heat transfer through the case, and internal condensation. You can raise effectiveness by bad design — you can heat the air with the heat from the motor and the fan.”
Summing up, Rosenbaum said, “I’m interested in in the thermal performance of the ERV — the temperature rise as the outdoor air passes through the unit.”
T(out) = outdoor air temperature T(exh) = temperature of exhaust air leaving the ERVT(sup) = temperature fresh air leaving the ERVT(ret) = temperature of stale air entering the ERV