Load Calculation and Blueprints Flashcards

When reviewing a set of mechanical blueprints for a new residential installation, where should a technician first look to understand what a specific symbol, such as a square with an 'X' inside, represents?

Answer: The legend or symbol list

The legend or symbol list on a blueprint serves as a dictionary, defining every symbol, icon, and line type used in the drawings. While other sections provide important information, the legend is the primary reference for identifying components like a supply air diffuser (often shown as a square with an 'X').

According to ACCA Manual J, which of the following factors is NOT a primary component in calculating the cooling load (heat gain) for a residential structure?

Answer: The age of the existing furnace

ACCA Manual J is a detailed procedure for calculating residential heating and cooling loads. It considers heat gain from the building's envelope (walls, windows, insulation), its location and orientation, and internal loads, but not the age of existing equipment. Equipment selection (Manual S) happens after the load is calculated.

A technician is performing a Manual J load calculation for a four-bedroom house. Based on standard ACCA guidelines, how many occupants should be factored into the internal heat gain calculation?

Answer: 5

Standard ACCA Manual J procedure for estimating the sensible and latent heat load from occupants is to use the number of bedrooms plus one. Therefore, for a four-bedroom house, the calculation would be based on five people (4 + 1 = 5).

On an architectural floor plan, a technician needs to determine the total area of windows on the west-facing wall to calculate solar heat gain. Which part of the blueprints would provide the specific dimensions for these windows?

Answer: The window schedule or elevation drawings

Window schedules and elevation drawings are specific architectural documents that provide detailed information about windows, including their dimensions (width and height), type, and material specifications. This data is crucial for an accurate Manual J calculation.

Which of the following describes a 'sensible' heat gain, which must be accounted for in a residential load calculation?

Answer: Heat conducted through a ceiling from a hot attic

A sensible heat gain is energy that increases the dry-bulb temperature of the air. Heat conducting through building materials like a ceiling is a prime example. Heat gains involving moisture (respiration, cooking, humidity) are categorized as 'latent' heat gains.

A blueprint's mechanical plan shows a duct line labeled '12x8' and an airflow value of '400 CFM'. What do these two pieces of information represent?

Answer: The duct's dimensions in inches (width x height) and the volume of air it must carry.

On HVAC blueprints, ductwork is dimensioned by its width and height in inches (e.g., 12" wide by 8" high). CFM stands for Cubic Feet per Minute, which is the standard unit for measuring the volume of airflow required for a specific space or duct run.