Introduction to Heat Pumps – Key Vocabulary

These vocabulary flashcards cover fundamental terms, system components, efficiency metrics, heat-pump types, environmental concepts, and retrofit pathways introduced in the lecture.

Heat Pump

A device that transfers heat from one location to another using the vapor-compression refrigeration cycle.

Vapor-Compression Refrigeration Cycle

The four-stage process (compression, condensation, expansion, evaporation) that enables a heat pump to move heat.

Compressor

Component that raises refrigerant pressure and temperature, creating high-temperature/high-pressure superheated vapor.

Metering Device

Component that lowers refrigerant pressure and temperature, producing a low-pressure liquid-vapor mix for heat absorption.

Accumulator

Protective vessel that traps any liquid refrigerant, allowing only superheated vapor and oil to return to the compressor.

Reversing Valve

Four-way valve that changes refrigerant flow direction, switching the system between heating and cooling modes.

Check Valve (Bypass)

One-way valve that lets refrigerant bypass a metering device when flow is reversed during mode changes.

Superheated Vapor

Refrigerant vapor heated above its saturation temperature—no liquid present.

Subcooled Liquid

Refrigerant cooled below its saturation temperature—no vapor present.

First Law of Thermodynamics

Conservation of energy—energy cannot be created or destroyed, only transferred or converted.

Second Law of Thermodynamics (Entropy)

Heat naturally flows from a hotter body to a colder one to reach equilibrium.

Coefficient of Performance (COP)

Ratio of heat output to electrical energy input; values >1 indicate the heat pump delivers more heat than the energy it consumes.

Economic Balance Point

Outdoor temperature at which operating a heat pump costs more than running the backup heat source.

Heating Season Performance Factor (HSPF)

Season-long heating efficiency metric for heat pumps; higher numbers mean greater efficiency.

HSPF2

Updated heating efficiency metric that accounts for colder outdoor temperatures and higher static pressures.

Seasonal Energy Efficiency Ratio (SEER)

Season-long cooling efficiency metric for heat pumps; higher numbers mean greater efficiency.

SEER2

Updated cooling efficiency metric using more realistic static-pressure conditions.

Energy Efficiency Ratio (EER)

Cooling efficiency measured at specific indoor/outdoor temperatures rather than over a season.

EER2

Updated EER using more realistic load and temperature assumptions.

Air-to-Air Heat Pump

Transfers heat between outside air and indoor air; the most common residential type.

Water-to-Air Heat Pump

Moves heat from a water source (well, pond, loop) to the building’s air.

Water-to-Water Heat Pump

Uses a water source to heat or cool a closed water loop inside the building, often for radiant systems.

Air-to-Water Heat Pump

Extracts heat from outdoor air and delivers it to water for domestic hot water, hydronic coils, or radiant floors.

Split System

Heat-pump configuration with separate indoor and outdoor units connected by refrigerant lines.

Ductless Mini Split

Split system with a wall- or ceiling-mounted indoor unit serving a single room without ductwork.

Ducted Mini Split

Split system with a compact air handler and short duct runs; designed for low static pressure.

Multi Split

One outdoor unit connected to multiple indoor units, which may be ducted, ductless, or both.

Variable Refrigerant Volume (VRV) / Variable Refrigerant Flow (VRF)

Multi-zone system where refrigerant lines branch inside the building, allowing variable flow to each indoor unit.

Single-Stage Compressor

Runs at full capacity only; may short cycle under part-load conditions.

Two-Stage Compressor

Uses an internal unloader to operate at two discrete capacities for better load matching.

Inverter (Variable-Speed) Compressor

Modulates speed across a wide range, offering the best load-matching and cold-weather performance.

Standard-Efficiency Heat Pump

Meets (but does not exceed) the U.S. Department of Energy regional minimum efficiency standards.

High-Efficiency Heat Pump

Exceeds DOE minimum regional efficiency standards.

Cold Climate Heat Pump (CCHP)

Heat pump optimized for low-temperature operation; must have a variable-capacity compressor and COP ≥1.75 at 5 °F.

Global Warming Potential (GWP)

Measure of how much heat a greenhouse gas traps in the atmosphere compared with CO₂ (GWP = 1).

Carbon Dioxide (CO₂)

Primary greenhouse gas produced by fossil-fuel combustion; contributes to atmospheric warming and ocean acidification.

Renewable Electricity

Electricity generated from sources such as wind, solar, hydro, or biomass—over 20 % of U.S. supply in 2022.

Basic Heat Pump Retrofit

Equipment replacement with a heat pump and limited testing—may include an Air Upgrade if needed.

Advanced Heat Pump Retrofit

Comprehensive project including duct optimization, building upgrades, tiered testing, and air balancing for high performance.

System Performance Evaluation™

Flow-chart process used to decide whether a retrofit should be basic, advanced, or not recommended.