Project Scoping, System Design, and Documentation Planning

Why the Design Package Comes First

In professional HVAC/R practice, no equipment is ordered, no duct is cut, and no wire is pulled until a complete pre-installation design package exists. That package is the contract between the designer and every downstream worker—the sheet-metal fabricator, the electrician, the startup technician, and the building inspector. Skipping or rushing this step is the single most common cause of callbacks, code violations, and equipment failures. Your capstone project holds you to the same standard the industry does.

Manual J Load Calculation

A Manual J residential load calculation determines how much heating and cooling the building actually needs—expressed as British thermal units per hour (BTU/h). It accounts for the building's geographic location (design temperatures), orientation, insulation levels (R-values), window area and type, infiltration rate, internal heat gains, and occupancy. Using a floor plan and building-envelope data without running Manual J is guesswork; oversized equipment short-cycles, fails to dehumidify, and wastes energy, while undersized equipment cannot maintain comfort on design days.

Approved tools include ACCA Manual J worksheets and software programs that carry ACCA validation. Enter every input carefully—errors in square footage or insulation values compound quickly. Round your final load to the nearest 500 BTU/h and record every input value so the instructor can audit your work.

Equipment Selection

Once you have a calculated load, match it to actual manufacturer equipment. Your selected unit's rated capacity at the project location's design conditions must fall within the acceptable range of your calculated load. Reference the manufacturer's expanded performance data (not just the nameplate) to confirm capacity at local outdoor design temperature. Look up the unit's AHRI-certified efficiency ratings—SEER2 for cooling, HSPF2 for heat pumps, or AFUE for furnaces—from the AHRI directory rather than the marketing sheet. Document the model number, refrigerant type, factory charge, electrical data (voltage, phase, minimum circuit ampacity, maximum overcurrent protection), and physical dimensions in your equipment schedule.

Duct Layout and Static-Pressure Calculations

A duct system must deliver the right amount of conditioned air to each room without excessive noise or energy loss. Begin by assigning CFM (cubic feet per minute) to each room based on its share of the total load. Lay out supply trunk lines, branch runs, and return air paths on your floor plan. Show register locations and sizes. Select duct sizes using ACCA Manual D friction-rate method: calculate the available static pressure (equipment rated external static pressure minus accessory pressure drops), divide by the equivalent length of the longest duct run to get the design friction rate, then size each section accordingly.

On your drawing, label every duct segment with size, shape (round or rectangular), and CFM. Mark supply and return registers with their size and throw direction. Peer review catches errors you will miss in your own work—use the checklist systematically, not as a formality.

Single-Line Electrical Diagram

Your wiring diagram must show two circuits: the power circuit (line voltage from the electrical panel to the disconnect to the equipment) and the control circuit (low-voltage 24 V AC connections among thermostat, air handler, and condensing unit). On the power-circuit portion, identify:

• Disconnect location and rating
• Overcurrent protection (breaker or fuse size, not to exceed the manufacturer's maximum listed value)
• Conductor size and insulation type based on the minimum circuit ampacity
• Equipment grounding conductor

All electrical design must comply with the National Electrical Code (NEC), current edition as adopted by your jurisdiction. The NEC article covering air-conditioning and refrigerating equipment specifies disconnecting means, conductor sizing, and overcurrent protection requirements. Never guess at electrical values—pull them directly from the manufacturer's data plate and data sheet, then verify against code.

Refrigerant Piping Plan

Show the liquid line and suction line routing on your floor plan. Note line-set length, any elevation change between indoor and outdoor units, insulation requirement for the suction line, and the refrigerant type. Long line sets or significant elevation changes may require capacity correction; consult the manufacturer's installation manual and note any derating. Record the refrigerant type (e.g., R-410A or R-32 or R-454B) and the factory charge; additional charge requirements for extended line sets must be calculated per manufacturer instructions and documented.

Refrigerant safety note: Many modern refrigerants are classified A2L (mildly flammable). Before working with any refrigerant, consult the Safety Data Sheet (SDS), confirm the correct personal protective equipment (PPE)—safety glasses, gloves—and know ventilation requirements. Never vent refrigerants to atmosphere; EPA Section 608 prohibits it and requires certified technicians to handle refrigerants.

Documentation and Binder Format

Your completed design package must follow the provided binder template. Organize sections in this order: (1) project brief and site data, (2) Manual J calculations with all inputs, (3) equipment schedule with data sheets, (4) duct layout drawing with static-pressure calculation, (5) single-line electrical diagram, (6) refrigerant piping plan. Number every page. An inspector, a coworker, or your future self must be able to pick up this binder and build the system without asking you a single question.

Safety Considerations During the Design Phase

Design errors create field hazards. Undersized wire creates a fire risk. An improperly rated disconnect creates an arc-flash hazard. Duct systems with negative pressure in combustion-appliance zones can cause backdrafting. While you are not yet on the job site, every decision you make on paper has a physical consequence. Apply lockout/tagout planning at the design stage by specifying accessible disconnect locations. Design with service access in mind so future technicians can work safely.