Heat Pump Technology Flashcards

What is the fundamental operating principle of a heat pump that makes it more efficient than a resistance heater?

Answer: It moves heat from one place to another rather than generating heat, delivering 2-4 BTU of heat for every BTU of electrical energy consumed

A heat pump uses the refrigeration cycle to move heat from a lower-temperature source (outdoor air, ground) to a higher-temperature indoor space, delivering 2-4 BTU of heat energy for every BTU of electrical energy consumed.

What is the 'balance point' of an air-source heat pump?

Answer: The outdoor temperature at which heat pump capacity equals building heat loss—below this, supplemental heat is needed

The balance point is where heat pump output exactly meets the building's heat loss. Below this temperature (often 25-35°F for older heat pumps), supplemental heating must make up the deficit.

What is the 'Heating Seasonal Performance Factor' (HSPF)?

Answer: The total seasonal heating output in BTU divided by total electrical energy input in watt-hours; higher = more efficient

HSPF measures seasonal heating efficiency by dividing total seasonal heating output (BTU) by total electrical energy consumed (watt-hours)—higher HSPF means lower operating costs.

How does a geothermal (ground-source) heat pump differ from an air-source heat pump?

Answer: Geothermal exchanges heat with the ground (stable temperature year-round) via buried loops, achieving higher efficiency than air-source which uses variable outdoor air temperature

Ground-source heat pumps use the stable ground temperature (50-60°F in most of the US) as a heat source/sink, avoiding the efficiency penalty of extreme outdoor temperatures that affects air-source systems.

What is a 'reversing valve' in a heat pump?

Answer: A four-way valve that reverses refrigerant flow direction, switching the system between heating and cooling modes

The reversing valve (four-way valve) is the key component that enables heat pump reversibility—it redirects refrigerant flow so the indoor coil becomes the condenser (heating mode) or evaporator (cooling mode).

What causes 'defrost cycles' in air-source heat pumps and how are they handled?

Answer: Frost/ice accumulating on the outdoor coil in cold, humid conditions, reducing efficiency; handled by temporarily reversing to cooling mode to melt frost

When the outdoor coil operates below 32°F with humid air, frost forms on coil fins, insulating the coil and reducing heat absorption. The heat pump reverses to cooling mode to direct hot refrigerant through the outdoor coil to melt the frost.

What is a 'variable-speed' or 'inverter-driven' heat pump and why is it more efficient?

Answer: A heat pump with a variable-speed compressor that can modulate output from ~25% to 100%, matching actual load and avoiding on/off cycling losses

Variable-speed (inverter-driven) heat pumps use DC inverter technology to continuously vary compressor speed, operating efficiently at partial load rather than on/off cycling—providing precise temperature control and significantly higher seasonal efficiency.

What is a 'dual-fuel' or 'hybrid' heat pump system?

Answer: A system pairing an air-source heat pump with a gas furnace, using the heat pump for mild weather and switching to gas heat when it's more cost-effective at very cold temperatures

A dual-fuel system uses a heat pump as the primary heating source and a gas furnace as backup, switching between the two based on outdoor temperature and energy cost.

What is a 'water-source' heat pump (WSHP) and how is it applied in commercial buildings?

Answer: A heat pump exchanging heat with a common water loop, allowing internal heat recovery between simultaneously heating and cooling zones in a building

Water-source heat pumps are connected to a common two-pipe water loop (typically 60-90°F). Interior zones cooling reject heat to the loop; perimeter zones heating absorb heat from the loop—enabling heat transfer from interior to perimeter.

What is a 'mini-split' (ductless) heat pump?

Answer: A ductless system with a small outdoor compressor connected to one or more wall-mounted indoor units; advantages include no duct losses, individual zone control, and easier installation in retrofit applications

Mini-split heat pumps have outdoor compressor units connected by refrigerant lines to compact wall-, ceiling-, or floor-mounted indoor air handlers—eliminating duct losses and enabling individual zone control.

What is the significance of a heat pump's rated capacity at 47°F versus its capacity at 17°F outdoor temperature?

Answer: Capacity at 47°F (standard AHRI rating condition) is always higher than at 17°F; the ratio shows how much capacity decreases in cold weather—important for sizing in cold climates

Standard heat pumps are AHRI-rated at 47°F outdoor. Capacity at 17°F is typically 50-75% of the 47°F rating for conventional heat pumps. Cold-climate heat pumps maintain higher ratios at 17°F, critical for sizing in northern climates.

What is 'refrigerant charge' management in heat pump systems?

Answer: The proper amount of refrigerant ensuring correct superheat and subcooling values, affecting both efficiency and reliability

Proper refrigerant charge ensures the system achieves target superheat at the evaporator outlet and subcooling at the condenser outlet—both too much and too little refrigerant dramatically reduce efficiency and can damage the compressor.

How does a heat pump water heater work?

Answer: It uses refrigeration cycle (heat pump technology) to extract heat from surrounding air to heat water, achieving COP of 3-4 (200-400% efficient)

A heat pump water heater uses a refrigeration cycle to extract heat from ambient air and transfer it to the water tank, achieving 200-400% efficiency versus 100% for electric resistance heaters.

What is the purpose of an 'accumulator' in a heat pump system?

Answer: A vessel in the suction line before the compressor that traps any liquid refrigerant, allowing only vapor to enter the compressor and preventing liquid slugging

The accumulator is a suction line vessel that separates liquid refrigerant from vapor, allowing only refrigerant vapor into the compressor—protecting against liquid slugging damage, especially critical during defrost cycle transitions.

In a heat pump system, what does the 'supplemental' or 'auxiliary' heat do?

Answer: Provides additional heating capacity (typically electric resistance strips in air handlers) when heat pump output is insufficient to maintain indoor setpoint

Supplemental heat (usually electric resistance heating strips in the air handler) provides additional BTUs when outdoor temperature drops below the heat pump's balance point, when demand exceeds heat pump capacity, or during defrost cycles.

What is 'Cold Climate' or 'H1C' specification for air-source heat pumps?

Answer: NEEP's specification requiring heat pumps maintain at least 70% of rated capacity at 5°F outdoor and provide capacity down to -13°F or lower

The Northeast Energy Efficiency Partnerships (NEEP) Cold Climate Air Source Heat Pump (ccASHP) specification requires maintaining ≥70% of rated capacity at 5°F outdoor and operation down to -13°F.

What is 'thermal mass' or 'buffer storage' and why might it be beneficial with a variable-speed heat pump?

Answer: A water tank or hydronic mass that stores thermal energy, allowing the heat pump to run at optimal efficiency rather than cycling with building loads

A buffer tank (small hydronic tank) stores thermal energy, decoupling the heat pump's operation from short on/off cycling—the heat pump heats the buffer tank, which then serves load, allowing the compressor to run longer at efficient conditions.

What is 'EER' (Energy Efficiency Ratio) versus 'SEER' (Seasonal Energy Efficiency Ratio) for cooling equipment?

Answer: EER measures efficiency at a single standard test condition (95°F outdoor, 80°F/67°F wet bulb indoor); SEER integrates efficiency across the full cooling season at varying conditions

EER is a single-point efficiency measure at standard peak conditions, while SEER represents a weighted seasonal average that better predicts real-world energy consumption and annual operating cost.

What is 'hot gas defrost' versus 'reverse cycle defrost' in heat pump systems?

Answer: Hot gas defrost bypasses hot refrigerant from compressor discharge directly to the outdoor coil without reversing the refrigerant cycle; reverse cycle defrost reverses the entire refrigeration cycle to heating mode

Hot gas defrost uses a bypass valve to send hot discharge refrigerant directly to the outdoor coil without full cycle reversal—maintaining indoor coil in heating mode. Reverse cycle defrost fully reverses the system to cooling mode, temporarily heating the outdoor coil at the expense of indoor comfort.

What is 'transcritical CO2' (R-744) heat pump technology and where is it most applicable?

Answer: A refrigeration cycle where CO2 operates above its critical point on the high-pressure side; particularly advantageous for heat pump water heating and cold climate heating applications

Transcritical CO2 systems operate the high-pressure side above CO2's critical point (88°F/1071 psi), which makes them highly effective for heat pump water heating (achieving 150°F+ outlet temperatures) and heating in cold climates.