Residential Energy Efficiency & Load Calculations Flashcards

A building has 2,400 sq ft of wall area with an overall U-factor of 0.065 BTU/hr·ft²·°F and a DTD of 65°F. What is the wall heat loss?

Answer: 10,140 BTU/hr

Heat loss = U × Area × DTD = 0.065 × 2,400 × 65 = 10,140 BTU/hr.

In Manual J calculations, the 'latent load' refers to:

Answer: Heat associated with moisture removal from the air

Latent load is the cooling energy required to condense and remove moisture from indoor air, distinct from sensible (temperature-related) heat.

Which window property most directly affects the cooling load from solar radiation?

Answer: Solar Heat Gain Coefficient (SHGC)

SHGC measures the fraction of incident solar radiation admitted through a window, making it the primary factor for solar-driven cooling loads.

For a geothermal heat pump with an EWT of 50°F in heating mode, which effect does a lower entering water temperature have on capacity?

Answer: Capacity decreases and power consumption increases

As EWT drops, the heat pump must work harder, reducing heating capacity and COP while increasing electrical consumption.

Which of the following best describes 'degree-days' as used in energy consumption estimation?

Answer: Cumulative sum of daily mean temperature deviations from a base temperature (65°F)

Heating degree-days (HDD) sum the daily differences between 65°F and the average outdoor temperature, providing a seasonal measure of heating energy demand.

Air sealing a home before sizing a geothermal system is important because:

Answer: Reduced infiltration lowers the design load, potentially allowing a smaller, more efficient system

Reducing infiltration directly decreases both sensible and latent loads, so the designer can right-size the geothermal system rather than oversize it.

Which ACCA manual covers the design of duct systems to properly distribute conditioned air from a geothermal air handler?

Answer: Manual D

ACCA Manual D provides the procedure for sizing residential duct systems to distribute airflow from any HVAC system, including geothermal air handlers.