Mixed Deck — All HVAC Topics Flashcards

What is the significance of 'HSPF2' rating for a mini-split heat pump?

Answer: Heating Seasonal Performance Factor 2 — measures heating efficiency over a full heating season. Higher is better

HSPF2 (Heating Seasonal Performance Factor 2) is the heating efficiency rating for heat pumps, measured over a full heating season. Higher values indicate better efficiency. Mini-splits typically achieve HSPF2 of 8-14+, significantly better than electric resistance heating (HSPF2 equivalent of 3.41).

What is the typical fin spacing (fins per inch) for a residential evaporator coil?

Answer: 8-14 fins per inch

Residential evaporator coils typically have 8-14 fins per inch, balancing heat transfer efficiency with acceptable airflow resistance and ease of cleaning.

What is the saturation temperature of a refrigerant?

Answer: The temperature at which refrigerant changes state at a given pressure

Saturation temperature is the temperature at which a refrigerant changes between liquid and vapor states at a specific pressure.

What is 'load calculation' software (like Manual J or HAP) used for?

Answer: Calculating heating and cooling loads to properly size HVAC equipment for a specific building

Load calculation software (Manual J for residential, ASHRAE Handbook or HAP/Trace for commercial) calculates the heating and cooling loads for a specific building based on construction, climate, occupancy, and internal gains. Proper load calculations prevent over- or under-sizing equipment.

What is MERV rating and why are commercial HVAC filters rated higher than typical residential filters?

Answer: MERV rates particle capture efficiency; commercial buildings have higher air quality standards, more occupants, and more pollutant sources requiring better filtration

MERV (Minimum Efficiency Reporting Value, ASHRAE 52.2) rates particle removal efficiency. Commercial buildings require higher MERV filters (MERV 8-14) due to more occupants, regulatory requirements (ASHRAE 62.1), and higher expectations for air quality, despite the increased pressure drop.

What is the purpose of a refrigerant recovery machine's oil separator?

Answer: To separate compressor oil from recovered refrigerant

The oil separator in a recovery machine removes compressor oil that may have mixed with the refrigerant during the recovery process, keeping the recovered refrigerant cleaner.

What is superheat in an HVAC system?

Answer: Refrigerant temperature above its boiling point at a given pressure

Superheat is the number of degrees the refrigerant vapor is heated above its saturation (boiling) temperature at a given pressure.

What chemical treatment is commonly applied to drain pans and coil surfaces to prevent biological growth?

Answer: Copper-based biocide tablets or pan strips

Copper-based biocide tablets or pan strips are placed in drain pans to slowly release antimicrobial agents that prevent algae, mold, and bacterial growth.

A building's VAV system delivers poor cooling to perimeter offices in the afternoon despite adequate static pressure at the AHU. What is the MOST likely cause?

Answer: VAV box actuators in perimeter zones are failing to open due to solar heat gain overloading the zone controllers

Afternoon solar gain dramatically increases perimeter zone loads, and if the VAV boxes cannot fully open or are undersized for peak solar load, those zones will overheat despite adequate system pressure.

What is the purpose of the 'follow me' remote control feature on a mini-split?

Answer: The remote control's built-in temperature sensor reads the temperature at the occupant's location, and the mini-split conditions to that point rather than the wall sensor

The 'follow me' feature uses the remote control's built-in temperature sensor to measure temperature where the occupant actually is (not at the wall-mounted unit). The mini-split conditions to meet the setpoint at the remote's location, providing more accurate comfort control for the actual occupant position.

Which refrigerant has been the standard for new residential split systems since R-22 was phased out?

Answer: R-410A

R-410A replaced R-22 as the standard residential refrigerant after the EPA phased out R-22 production due to its ozone-depleting properties.

In a BAS, what is the purpose of the 'priority array' in BACnet commandable objects?

Answer: Manage multiple competing commands to an output by assigning priority levels 1-16

The BACnet priority array allows up to 16 commands at different priority levels to compete for control of an output, with the highest active priority winning.

What happens to system efficiency when evaporator coil fins become coated with a thin layer of dirt?

Answer: Efficiency decreases because heat transfer is impaired

A dirt coating on coil fins acts as thermal insulation, significantly reducing heat transfer between the air and refrigerant and decreasing overall system efficiency.

What is a key code difference between residential and commercial HVAC installations regarding refrigerant room requirements?

Answer: Commercial facilities with large refrigerant charges require mechanical equipment rooms with ventilation, refrigerant detectors, and emergency shutoffs per ASHRAE 15

ASHRAE Standard 15 (Safety Standard for Refrigeration Systems) requires mechanical equipment rooms for large refrigerant charges in commercial facilities, with ventilation systems, refrigerant leak detectors, emergency shutoffs, and occupancy sensors. Residential systems have much simpler requirements.

Which document must accompany refrigerant shipments and identifies the type and amount of refrigerant?

Answer: Material Safety Data Sheet (MSDS/SDS)

A Safety Data Sheet (SDS, formerly MSDS) must accompany refrigerant shipments. It provides hazard information, handling procedures, and emergency response details.

What is 'sensible heat' versus 'latent heat' in HVAC load analysis?

Answer: Sensible heat changes air temperature; latent heat changes air moisture content without changing temperature

Sensible heat causes a measurable temperature change, while latent heat is the energy associated with moisture (phase change) that does not change the dry-bulb temperature.

What tools are required for proper installation of mini-split refrigerant line sets?

Answer: Tubing cutter, deburring tool, flaring tool, torque wrench, and vacuum pump are essential; manifold gauges and refrigerant scale also needed

Proper mini-split installation requires: tubing cutter (clean cuts), deburring tool (smooth flare seats), quality flaring tool (proper flare geometry), torque wrench (specified tightening), vacuum pump (evacuation), manifold gauges (pressure checking), and refrigerant scale (if additional charge needed).

After replacing a compressor, a technician pulls a vacuum to 500 microns and the system holds for 15 minutes. The technician then charges the system and it trips the high-pressure switch. What was MOST likely missed during the compressor replacement?

Answer: The filter-drier was not replaced

Replacing a failed compressor without replacing the filter-drier leaves acid and contaminants in the system, which can cause the new compressor to fail or cause restriction that raises head pressure.

How does a dirty air filter affect evaporator coil performance?

Answer: Reduces airflow, lowering suction pressure and potentially causing coil freeze-up

A dirty filter restricts airflow, reducing the amount of air passing over the evaporator coil. Less airflow means the coil absorbs less heat, suction pressure drops, and coil temperature can fall below 32°F causing freeze-up.

An air handler blower runs on high speed only, regardless of the thermostat fan speed setting. What is the MOST likely cause?

Answer: Failed ECM motor control module or incorrect dip-switch settings

An ECM blower that ignores speed commands usually has a failed control module or incorrect programming/dip-switch configuration that defaults to maximum speed.