ACCA Residential HVAC Design flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Manual J purpose

It calculates room-by-room heating and cooling loads from envelope, infiltration, internal, and duct gains. Equipment selection must follow this calculation rather than precede it.

Sensible vs latent load

Sensible load changes air temperature; latent load removes moisture. Manual J computes both separately, and equipment must satisfy each at design conditions.

Manual S sizing rule

Total capacity must meet or exceed total load, and sensible capacity must meet sensible load at design entering wet-bulb. Permissible oversizing is explicitly limited.

Oversizing consequences

Excess capacity shortens runtime, increases cycling losses, reduces latent removal, and causes temperature swings. Manual S limits oversizing for these reasons.

Available external static

Total external static pressure minus pressure drops of devices and coils. This remainder is apportioned across supply and return duct runs to set friction rate.

Equivalent length in Manual D

Straight-run length plus fitting allowances. At fixed available static, higher equivalent length lowers friction rate and requires larger ducts.

Design wet-bulb role

Coincident wet-bulb with design dry-bulb sets latent load and coil entering conditions. Sensible capacity is rated at a specific entering wet-bulb.

Room airflow allocation

Manual D assigns cfm to each room consistent with Manual J room loads, so delivered airflow matches calculated space requirements.

ANSI/ACCA 5 QI

The HVAC Quality Installation Specification. It defines verifiable criteria for design, installation, commissioning, and documentation of residential systems.

Superheat charging method

For fixed-orifice systems, charge is set by measuring superheat and matching manufacturer tables at specified indoor and outdoor conditions.

Subcooling charging method

For TXV systems, charge is set by measuring subcooling at the condenser liquid line and matching the manufacturer's target value.

Target residential airflow

Roughly 350 to 450 cfm per ton of cooling. Lower airflow risks coil icing and compressor overheating; higher airflow reduces latent removal.

Deep vacuum target

Evacuation to about 500 microns or below, held to confirm stability, removes moisture and non-condensables before charging the system.

Combustion safety testing

Draft measurement and CO testing on gas appliances. Spillage or elevated CO requires correction before the installation is accepted.

Duct leakage testing

Quantifies distribution losses from the duct system. Sealed and tested ducts reduce effective load and improve delivered capacity to rooms.

Commissioning records

Documentation of static pressure, temperature split, charge method, airflow, and combustion results. These support warranty and quality verification.

Section 608 certification

Clean Air Act requirement that technicians handling refrigerants be certified for the equipment class they service, including small appliances and high-pressure systems.

R-410A pressure characteristics

An HFC blend with zero ozone depletion but high GWP. It operates at roughly 50 to 70 percent higher pressures than R-22, requiring rated equipment.

A2L refrigerant safety

Mildly flammable classification. Handling requires ignition-source awareness, ventilation, adherence to charge limits, and proper labeling per applicable standards.

Recovery cylinder limits

Cylinders must be DOT-approved and not overfilled, typically capped near 80 percent fill. They must be labeled with refrigerant type and amount.

Leak repair requirements

EPA rules require repairing leaks above threshold rates for appliances of specified charge sizes, followed by verification testing to confirm the repair.

No venting rule

Refrigerant must never be vented to atmosphere. Recovery, recycling, or reclamation are the only permitted disposition paths under federal rules.

Permit requirements

New installations, changeouts, and duct alterations typically require permits and inspections. Exact scope varies by jurisdiction and must be confirmed locally.

Load calc as submittal

Load calculations and equipment selection documents are commonly required for permit review and for utility or rebate program qualification.

Energy code sizing link

Many energy codes, such as the IECC, reference Manual J, S, and D compliance as the basis for equipment sizing and duct design.

Contract essentials

A written agreement should define scope, equipment model numbers, warranties, payment schedule, and change-order procedures to limit disputes.

Refrigerant recordkeeping

Purchase and handling records support EPA compliance and may be requested during audits of refrigerant use and disposal.

Warranty documentation

Manufacturer coverage often depends on documented commissioning data such as charge verification, airflow, and static pressure. Missing records can void coverage.

Change order practice

Written change orders approved before work proceeds protect both margin and legal standing when scope or conditions differ from the original contract.

Temperature split check

Measured difference between return and supply air. It is a commissioning indicator of airflow and charge performance against expected values.

Infiltration estimation

Derived from envelope tightness, often blower-door ACH50 converted to natural ACH, plus wind and stack factors rather than fixed rules of thumb.

HFO lower-GWP blends

Refrigerants such as R-454B with substantially lower global warming potential than R-410A, increasingly used in new residential equipment.