OH HVAC Contractor flashcards
OH HVAC Contractor · Build recall with a focused review session.
31 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Sensible heat equation
- Q in Btu/h equals 1.08 times CFM times the dry-bulb temperature difference. The constant assumes standard air density at sea level and is used to size heating or cooling coils.
- Total heat equation
- Q in Btu/h equals 4.5 times CFM times the enthalpy difference between entering and leaving air. Enthalpy combines sensible and latent heat and requires a psychrometric chart.
- Superheat definition
- Suction line temperature minus the saturated suction temperature read from the gauge pressure. It confirms the evaporator is fully fed with liquid and the expansion valve is controlling.
- Subcooling definition
- Saturated condensing temperature minus liquid line temperature. Adequate subcooling proves the condenser is fully charged with liquid and the metering device receives solid refrigerant.
- Refrigerant glide
- The temperature difference between bubble point and dew point in a zeotropic blend. Superheat uses dew point, subcooling uses bubble point, and charging must follow the manufacturer method.
- CFM per ton rule
- Nominal cooling airflow is 400 CFM per ton of capacity. Lower airflow increases the temperature split and latent removal but risks coil icing; higher airflow reduces dehumidification.
- Combustion air openings
- Two permanent openings connecting an appliance space to the rest of the structure are each sized at 1 square inch free area per 1,000 Btu/h of total input for confined installations.
- A2L refrigerant classification
- ASHRAE 34 class for lower-flammability refrigerants such as R-32 and R-454B. They burn slowly, require charge limits and ignition-source controls, and need updated leak detection.
- Water column to psi
- One psi equals 2.31 feet of water column. Divide pump head in feet by 2.31 to obtain psi, or multiply psi by 2.31 to obtain feet of head.
- Hydronic heat formula
- Q in Btu/h equals 500 times GPM times the supply-to-return temperature difference for water. Use lower constants for glycol mixtures because of higher specific heat and density.
- Expansion tank precharge
- The air-side pressure of a bladder tank set before filling the system. It typically equals the cold fill pressure so the tank accepts expanded water without exceeding relief pressure.
- RPZ backflow assembly
- A reduced-pressure zone device with two check valves and a relief valve. It is required for high-hazard cross-connections and must be tested annually by a certified tester.
- Water fixture unit
- A dimensionless load value assigned to a fixture. Total water supply fixture units convert to probable demand in gallons per minute through the Hunter curve for pipe sizing.
- Drain slope rule
- Horizontal drainage pipe smaller than 3 inches slopes at 1/4 inch per foot. Pipe 4 inches and larger may slope at 1/8 inch per foot while maintaining self-scouring velocity.
- T&P relief discharge
- The water heater temperature and pressure relief valve must discharge through a full-size pipe to within 6 inches of the floor or outdoors. It cannot be trapped or reduced.
- Series loop hydronic system
- A piping arrangement where water flows through each terminal unit in sequence. It is simple and inexpensive but delivers decreasing temperature to downstream emitters.
- Ohm's law and power
- Voltage equals current times resistance. Power in watts equals voltage times current, and for reactive loads multiply by the power factor to get true power.
- Three-phase power equation
- P in watts equals 1.732 times line voltage times line current times power factor for a balanced three-phase load. The 1.732 factor is the square root of three.
- Motor branch circuit sizing
- Branch-circuit conductors are sized at 125 percent of the motor full-load current from the NEC tables, not from the nameplate current, before ampacity adjustments.
- Motor overload protection
- A device that protects the motor winding from sustained overcurrent. It is sized from nameplate service factor and separate from the short-circuit protection that clears faults.
- Equipment grounding conductor
- The conductor that provides a low-impedance fault path back to the source. Its size comes from NEC Table 250.122 and is based on the overcurrent device rating.
- Voltage drop formula
- Single-phase voltage drop equals 2 times conductor constant K times current times length divided by circular mils. Three-phase replaces the 2 with 1.732.
- GFCI protection locations
- Ground-fault circuit interrupter protection is required in bathrooms, garages, outdoors, kitchens, and near sinks. It interrupts the circuit when current leaks to ground.
- Motor disconnect location
- The disconnecting means must be within sight of the motor and its controller. A horsepower-rated switch or circuit breaker is required unless the breaker is lockable.
- ORC Chapter 4740 scope
- Ohio law that licenses heating, ventilating, air conditioning, refrigeration, plumbing, hydronics, and electrical contractors. The OCILB administers licenses and enforces standards.
- OCILB role
- The Ohio Construction Industry Licensing Board issues, renews, and disciplines contractor licenses. It adopts administrative rules covering exams, continuing education, and fees.
- Experience requirement
- Applicants must document at least 5 years of business experience in the trade, or equivalent education and experience the board accepts, before taking the licensing exam.
- Continuing education requirement
- Licensees must complete board-approved continuing education hours each renewal cycle. Certificates must be kept and produced on audit or the license may not renew.
- Surety bond requirement
- Contractors must maintain a bond and liability insurance as a condition of licensure. Failure to keep coverage can result in suspension of the license.
- License non-transferability
- A contractor license belongs to the named licensee and cannot be sold, assigned, or used by another person or entity. Work must be performed under the licensed contractor.
- Unlicensed practice penalties
- The board may seek civil penalties and injunctive relief against unlicensed contracting. It may also refuse, suspend, or revoke licenses for violations of the chapter.