Energy Efficiency and Renewable Energy
What this domain covers
Energy questions center on water heating, typically the second-largest energy end use in a U.S. home, and on renewable systems that preheat or replace conventional water heating. You are expected to size, compare, and troubleshoot these systems rather than recite brand names.
Core rules
- Solar thermal certification runs through SRCC: OG-100 covers collectors, OG-300 covers complete factory-packaged systems including freeze protection and controls.
- A common sizing rule is 1.5 to 2 square feet of collector per gallon of daily hot water storage; tilt is set near site latitude; freeze protection is by drainback or a closed glycol loop.
- Heat pump water heaters reach a COP of roughly 2 to 3 but need conditioned space, air volume, and condensate drainage; a cold garage erases the advantage.
- Drain water heat recovery units are rated to CSA B55.1 and B55.2 and recover roughly 40 to 60 percent of shower drain heat in vertical falling-film units.
- Recirculation saves water and wait time but wastes energy unless controlled by a demand button, timer, or aquastat; on-demand control beats continuous pumping.
- Insulate hot water piping and place the heater near high-use fixtures; every foot of uninsulated pipe is standby loss.
Worked example
A house uses 60 gallons of hot water per day at a 70 degrees F temperature rise. Energy = 60 gal × 8.34 lb/gal × 70 degrees F = 35,028 Btu per day. A solar system delivering 20,000 Btu per day net covers about 57 percent of that load, a solar fraction of 0.57, leaving the backup heater to supply the remaining 43 percent.
Traps
Mixing up OG-100 and OG-300; claiming recirculation always saves energy; ignoring standby and distribution losses when comparing systems; specifying a heat pump water heater in an unconditioned space; sizing collectors without matching storage, which causes stagnation and overheating.