What Is A Multi-circuit Evaporator?

What Is A Multi-circuit Evaporator?

The evaporator is the “cold side” of the system. Low-pressure, low-temperature liquid refrigerant enters the evaporator, absorbs heat from the surrounding medium (e.g., air in a room, water in a chiller), and boils (evaporates) into a low-pressure vapor. This heat absorption is what creates cooling.

A single-circuit evaporator works for small systems, but in larger or more complex setups, it struggles with refrigerant maldistribution—uneven flow of liquid refrigerant across the evaporator’s surface. This leads to wasted heat transfer area (some parts are too dry, others are flooded) and reduced efficiency. The multi-circuit design fixes this.

The multi-circuit design enhances heat transfer uniformity and efficiency by controlling refrigerant flow. Here’s its operational flow within a vapor-compression cycle:

1. Refrigerant Distribution (Inlet Stage)

High-pressure liquid refrigerant exits the expansion valve (which reduces its pressure and temperature) and enters the evaporator’s inlet header.

The distributor (integrated with the inlet header) splits the refrigerant into equal volumes across all parallel circuits. This is critical: if distribution is uneven, one circuit might get too much liquid (causing “flooding,” where liquid refrigerant exits the evaporator unevaporated, risking compressor damage), while another gets too little (causing “starvation,” where the circuit is mostly vapor, wasting heat transfer area).

2. Parallel Heat Absorption (Evaporation Stage)

Each circuit’s tube (and its fins, if present) is in contact with the medium to be cooled (e.g., room air blown over the evaporator by a fan, or water flowing around the tubes).

Inside each circuit, the low-pressure liquid refrigerant absorbs heat from the surrounding medium. As it absorbs heat, it boils (evaporates) into a low-pressure vapor.

Because each circuit is identical and receives equal refrigerant flow, evaporation happens uniformly across the entire evaporator surface—no “hot spots” (starved areas) or “cold spots” (flooded areas).

3. Refrigerant Recombination (Outlet Stage)

After evaporating in their respective circuits, the low-pressure refrigerant vapors flow into the outlet header, where they recombine into a single stream.

This combined vapor is then suctioned into the compressor, which pressurizes it (starting the next cycle of the refrigeration system).

Multi-circuit evaporators are used in systems where efficiency, scalability, and uniformity matter:

Commercial/Industrial AC: Large office buildings, malls, or factories (high cooling loads).

Refrigeration: Supermarket display cases, walk-in freezers, and industrial cold storage (needs uniform temperatures).

Chillers: Water-cooled or air-cooled chillers for data centers, manufacturing processes, or HVAC systems (scalable heat loads).

Heat Pumps: Residential or commercial heat pumps (especially in cold climates, where efficient heat absorption from ambient air is critical).