CRD Residential Energy Efficiency & Load Calculations 2 — Questions and Answers
Question 1: Which method is most commonly used for residential cooling load calculations in geothermal system design per ACCA standards?
- Manual J (Correct answer)
- Manual D
- Manual S
- ASHRAE Handbook
Correct answer: Manual J
Manual J by ACCA is the industry-standard residential load calculation method used to size geothermal and other HVAC systems.
Question 2: A house has a design heating load of 48,000 BTU/hr. If a geothermal heat pump has a COP of 3.5, what is the approximate electrical input required?
- 13,714 BTU/hr (4.02 kW) (Correct answer)
- 48,000 BTU/hr (14.07 kW)
- 168,000 BTU/hr (49.2 kW)
- 24,000 BTU/hr (7.03 kW)
Correct answer: 13,714 BTU/hr (4.02 kW)
Electrical input = 48,000 / 3.5 ≈ 13,714 BTU/hr; dividing by 3,412 BTU/kWh gives approximately 4.02 kW.
Question 3: In residential load calculations, infiltration is typically measured using which unit?
- ACH (air changes per hour) (Correct answer)
- CFM per square foot
- BTU/hr per degree-day
- Tons of refrigeration
Correct answer: ACH (air changes per hour)
Infiltration in residential buildings is expressed as ACH (air changes per hour), representing how many times the home's air volume is replaced by outdoor air.
Question 4: Which insulation metric directly describes how well a material resists heat flow per inch of thickness?
- R-value per inch (Correct answer)
- U-factor
- SHGC
- AFUE
Correct answer: R-value per inch
R-value per inch (specific R-value) describes a material's thermal resistance per unit thickness, enabling comparison between insulation types.
Question 5: The Design Temperature Difference (DTD) used in heat loss calculations is defined as:
- Indoor design temperature minus the outdoor design dry-bulb temperature (Correct answer)
- The difference between summer and winter outdoor temperatures
- The difference between supply and return air temperatures
- Maximum minus minimum indoor temperature swing
Correct answer: Indoor design temperature minus the outdoor design dry-bulb temperature
DTD = indoor setpoint (typically 70°F) minus the outdoor winter design temperature, representing the worst-case temperature difference driving heat loss.
Question 6: For geothermal system sizing, the peak cooling load is most influenced by:
- Solar heat gain through windows and roof (Correct answer)
- Duct leakage into unconditioned spaces
- Ground loop entering water temperature in winter
- Thermostat setpoint differential
Correct answer: Solar heat gain through windows and roof
Solar heat gain through glazing and roofing materials is typically the dominant driver of residential peak cooling loads in summer.
Question 7: Which building code energy standard sets minimum envelope efficiency requirements that directly affect geothermal system sizing?
- IECC (International Energy Conservation Code) (Correct answer)
- NFPA 70 (National Electrical Code)
- ASHRAE 90.2
- IRC Section P3000
Correct answer: IECC (International Energy Conservation Code)
IECC establishes minimum insulation, window, and air sealing requirements for residential buildings, directly reducing the loads that geothermal systems must meet.
CRD Residential Energy Efficiency & Load Calculations 2
Which method is most commonly used for residential cooling load calculations in geothermal system design per ACCA standards?