HERS Renewable Energy Systems 3

Question 1

What is the 'solar fraction' in the context of a solar water heating system?

Accepted Answer

The proportion of hot water heating load met by solar energy

Answer

Solar fraction represents the fraction of the total water heating load provided by the solar system, with the remainder supplied by a backup conventional heater.

Question 2

In a solar thermal domestic hot water system, what component prevents reverse thermosiphoning that could drain heat from the storage tank at night?

Accepted Answer

Check valve or differential controller

Answer

A check valve or differential controller prevents reverse flow when the collector is cooler than the tank, which would cause the tank to lose heat.

Question 3

What distinguishes an active solar thermal system from a passive solar thermal system?

Accepted Answer

Active systems use pumps and controls to move the heat transfer fluid

Answer

Active solar thermal systems rely on pumps, fans, and controls to circulate the heat transfer fluid, whereas passive systems use natural convection or thermosiphon principles.

Question 4

Which metric is used to compare the environmental impact of different renewable energy technologies over their full lifecycle?

Accepted Answer

Carbon intensity (gCO2/kWh)

Answer

Carbon intensity (grams of CO2 per kWh) measures lifecycle greenhouse gas emissions per unit of electricity generated, enabling environmental comparison across technologies.

Question 5

A home energy rater is evaluating a small wind turbine installation. Which site factor is MOST critical to assess first?

Accepted Answer

Average annual wind speed at hub height

Answer

Wind power output scales with the cube of wind speed, making average annual wind speed at hub height the most critical factor determining whether a turbine is economically viable.

(HERS) Home Energy Rater Certification Practice Test

(HERS) Home Energy Rater Certification Practice Test

HERS Renewable Energy Systems 3