Course Description

Let us start with the fundamental physics. The vapor-compression cycle is reversed in an air-source heat pump to absorb heat from outdoor air, even at very low temperatures. In heating mode, the outdoor coil acts as an evaporator. It absorbs heat from ambient air and evaporates the refrigerant, which is why the outdoor coil feels cold to the touch in winter. The indoor coil acts as a condenser, releasing that absorbed heat into your conditioned space. In cooling mode, the reversing valve changes the refrigerant flow direction, turning the unit into a conventional air conditioner. The compressor remains the heart of the system, providing the pressure rise needed for the cycle to operate. Here is the key insight: outdoor air is not the heat source in an absolute sense. It is a carrier of sensible and latent energy. Even at minus 20 degrees Celsius, outdoor air contains usable thermal energy because absolute zero is minus 273 degrees Celsius. That is a lot of usable energy. The coefficient of performance drops as outdoor temperature falls, but modern units remain practical and efficient down to very low temperatures. Understanding this cycle is essential because sizing decisions depend heavily on how the unit performs at the extremes of its operating envelope. If you do not understand the cycle, you cannot understand why a heat pump struggles at low temperatures.

What you'll learn in this course?

• First, you will be able to explain the operating principles of air-source heat pumps, including heating, cooling, and defrost cycles.

• Second, you will differentiate between single-stage, two-stage, and variable-speed compressor systems.

• Third, you will identify key performance metrics such as COP, HSPF, EER, SEER, and the newer HSPF2 and SEER2 standards.

• Fourth, you will describe the role of the reversing valve, accumulator, and expansion device within an ASHP.

• These foundational concepts are critical before any sizing work begins.

• Do not skip them even if you have prior experience.

• A strong foundation prevents errors later in the selection process.

• Now let us move to the remaining objectives.

• Fifth, you will perform accurate heating and cooling load calculations using Manual J or simplified software outputs.

• Sixth, you will select an ASHP that meets both peak load and part-load efficiency requirements.

Prerequisites

• Basic engineering knowledge and familiarity with HVAC or industrial utility systems