MA HVAC flashcards
MA HVAC · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Superheat
- The difference between the actual suction-line temperature and the saturation temperature at the suction pressure; used to verify TXV or orifice performance and charge.
- Subcooling
- The difference between the saturation temperature at the condensing pressure and the liquid-line temperature; indicates liquid seal and charge condition at the condenser outlet.
- TXV function
- A thermostatic expansion valve modulates refrigerant flow to maintain a set evaporator superheat, responding to bulb temperature and evaporator pressure.
- Sensible heat formula
- Qs equals 1.08 times CFM times the dry-bulb temperature difference; used to calculate airflow or capacity at standard air conditions.
- Latent heat formula
- QL equals 0.68 times CFM times the moisture difference in grains per pound; used to size dehumidification and check latent capacity.
- Manual J
- ACCA residential load calculation method that estimates heating and cooling loads from envelope, orientation, infiltration, and internal gains.
- Manual D
- ACCA duct design method that sizes ducts using friction rate, equivalent length, and available static pressure from the equipment.
- External static pressure
- The total pressure the blower must overcome across the air handler, including filter, coil, supply, and return ductwork; must not exceed the equipment rating.
- Combustion air rule
- For indoor air, two permanent openings each sized at 1 square inch per 4,000 Btu/h of total appliance input; outdoor air through vertical ducts uses 1 per 2,000.
- Category I venting
- Negative-pressure, non-condensing appliances vented into a listed chimney or Type B vent sized per the gas code and the appliance listing.
- Expansion tank
- A tank that absorbs the volume increase of heated water in a hydronic system; pre-charged to system fill pressure and located near the circulator suction.
- Zone valve
- A motorized valve that opens or closes to direct hot water to a specific zone, controlled by a thermostat and wired to the zone control panel.
- Motor branch circuit
- Conductors sized at 125% of motor full-load current, with short-circuit protection sized from the nameplate or code tables.
- MCA and MOP
- Minimum circuit ampacity and maximum overcurrent protection printed on the equipment nameplate; wire and breaker must not exceed these values.
- Disconnect location
- The disconnecting means must be within sight of and within 50 feet of the motor or controller it serves.
- Section 608 certification
- EPA credential required to purchase, handle, or dispose of regulated refrigerants; types I, II, III, and Universal cover different equipment classes.
- A2L refrigerant
- A mildly flammable refrigerant class requiring ignition-source control, ventilation, and charge limits per ASHRAE 15/34 and equipment listing.
- Recovery cylinder fill
- Recovery cylinders are filled to 80% of capacity by weight unless equipped with a float switch and rated for liquid fill.
- Venting prohibition
- Intentional release of ozone-depleting refrigerant to the atmosphere is prohibited; recovered refrigerant must be recycled, reclaimed, or destroyed.
- Duct gauge selection
- Duct steel gauge is chosen by pressure class and duct size; typical residential trunks use 26-28 gauge and branches 28-30 gauge.
- Pittsburgh seam
- A folded lock seam used to join longitudinal duct edges; the flat pattern adds about 1/2 inch for the seam allowance.
- Fire damper
- A listed device installed where a duct penetrates a rated assembly to close on fire and maintain the assembly's fire-resistance rating.
- Flex duct limits
- Flexible duct must be fully extended, supported, and limited in length per manufacturer and code; it cannot be concealed where inspection is impossible.
- Home Improvement Contractor
- Massachusetts registration required for residential remodeling contracts; the registration number and cancellation notice must appear in the written contract.
- Mechanic's lien
- A statutory claim against property for unpaid labor or materials; Massachusetts requires notices and filing within deadlines measured from last furnishing.
- Gross margin
- Gross margin equals price minus cost divided by price; it differs from markup, which is cost times a percentage added to cost.
- 780 CMR
- The Massachusetts State Building Code, which adopts and amends the model building code and includes energy and mechanical provisions for HVAC work.
- 248 CMR 5.00
- The Massachusetts Gas Code regulating gas piping, appliance venting, combustion air, and pressure testing of gas systems.
- Condensate disposal
- Condensate must discharge through an approved air gap or trap to a receptor per the plumbing code; direct connection to a drain is restricted.
- Fall protection threshold
- OSHA requires fall protection in construction at 6 feet; guardrails, personal fall-arrest systems, or designated anchor points are acceptable.
- Lockout/tagout
- A procedure to isolate and verify zero energy state before servicing equipment; required for electrical and rotating HVAC components under OSHA rules.
- Hot work permit
- Authorization required before brazing or other open-flame work on many jobsites; a fire watch is maintained during and after the work.