CRD Residential Energy Efficiency & Load Calculations 4 — Questions and Answers
Question 1: A geothermal designer notes that a home has a high window-to-wall ratio on the south facade. How should this affect load calculation?
- Increase both heating and cooling loads due to greater conductive and solar gain area (Correct answer)
- Only increase winter heating load due to conductive loss
- Only increase summer cooling load due to solar gain
- Have no significant effect if windows are double-pane
Correct answer: Increase both heating and cooling loads due to greater conductive and solar gain area
Large south-facing window area increases winter conductive heat loss and summer solar heat gain, raising both heating and cooling loads.
Question 2: The 'balance point' of a building is best defined as:
- The outdoor temperature at which internal gains equal heat losses, requiring no heating or cooling (Correct answer)
- The point at which the heat pump switches from heating to cooling mode
- The entering water temperature where system COP equals 1.0
- The soil temperature at the ground loop depth
Correct answer: The outdoor temperature at which internal gains equal heat losses, requiring no heating or cooling
The building balance point is the outdoor temperature at which internal heat gains exactly offset envelope losses, requiring no mechanical heating.
Question 3: Which of the following insulation locations has the greatest impact on reducing heating loads in a cold climate home?
- Ceiling/attic insulation (Correct answer)
- Basement wall insulation
- Crawl space floor insulation
- Interior partition walls
Correct answer: Ceiling/attic insulation
Ceiling/attic insulation addresses the largest area of heat loss in most homes and benefits from stack effect and the large temperature differential at the top of the thermal envelope.
Question 4: In hot-humid climates, latent loads typically represent what approximate percentage of total cooling load?
- 30–50% (Correct answer)
- 5–10%
- 60–75%
- Less than 5%
Correct answer: 30–50%
In hot-humid climates like the southeastern US, latent (moisture) loads commonly represent 30–50% of total cooling load, making dehumidification a critical design factor.
Question 5: Which factor is NOT typically included in the internal heat gain component of a residential cooling load?
- Ground loop pump heat rejection (Correct answer)
- Lighting heat dissipation
- Occupant metabolic heat
- Appliance and cooking heat
Correct answer: Ground loop pump heat rejection
Ground loop pump heat is a system efficiency parameter, not an internal building heat gain source used in Manual J cooling load calculations.
Question 6: What effect does adding thermal mass (e.g., concrete floors) have on peak cooling load calculations in a well-designed passive solar home?
- It reduces peak cooling load by absorbing and time-shifting solar heat gains (Correct answer)
- It increases peak cooling load by storing and re-radiating heat at night
- It has no effect because Manual J ignores thermal mass
- It increases heating load by keeping floors cold in winter
Correct answer: It reduces peak cooling load by absorbing and time-shifting solar heat gains
Thermal mass absorbs solar heat during the day and releases it slowly, flattening the peak load curve and reducing the maximum cooling demand.
Question 7: The Manual S procedure, used after Manual J calculations, is specifically designed to:
- Select properly sized HVAC equipment based on calculated loads and performance data (Correct answer)
- Design the duct distribution system
- Determine ventilation rates per ASHRAE 62.2
- Calculate ground loop lengths for the geothermal system
Correct answer: Select properly sized HVAC equipment based on calculated loads and performance data
ACCA Manual S uses the Manual J load results along with manufacturer performance data to select correctly sized heating and cooling equipment.
CRD Residential Energy Efficiency & Load Calculations 4
A geothermal designer notes that a home has a high window-to-wall ratio on the south facade.
How should this affect load calculation?