Technical Glossary.
Reference glossary of heat-exchanger, HVAC, and refrigeration terms used across Designwinds product literature and program documentation.
Last reviewed Q1 2026. Definitions are provided as general reference and are not a substitute for engineering judgment or program-specific specifications.
Air Handler / AHU
Air handling unit containing fans, coils, filters, and dampers used to condition and distribute air through a building or process. Designwinds supplies heat-exchange coils integrated into AHUs.
Ammonia (R-717)
Refrigerant used widely in industrial refrigeration. Requires materials and constructions appropriate to ammonia service.
Brazed Plate & Fin
Heat exchanger construction in which thin alternating layers of corrugated fin and parting sheets are brazed into a compact core. Used in compact recuperators and microchannel-style heat exchangers.
Brazing
Joining process using a filler metal that melts at a temperature below the base metals. Designwinds uses furnace and torch brazing for finned-tube and aluminum microchannel constructions.
BTU / BTUH
British Thermal Unit (BTU) and BTU per hour (BTUH). Standard units of energy and heat-transfer rate used in HVAC sizing.
Capacity
The thermal duty of a heat exchanger expressed in BTUH, tons, kW, or similar. Capacity depends on construction, working fluid, flow rates, and entering/leaving conditions.
CFM
Cubic Feet per Minute. Standard unit of airflow rate used in HVAC sizing.
Chilled Water (CW)
Water cooled in a central plant and circulated to fan coils, air handlers, and process loads. Designwinds chilled water coils are configured to customer-specified entering/leaving water temperatures.
CO₂ (R-744)
Carbon dioxide refrigerant. Used in transcritical and subcritical refrigeration systems. Imposes high-pressure design requirements on heat exchanger construction.
Coil
General term for a heat-transfer assembly comprising tubes, fins, and supporting structure. Coils may be fin-and-tube, microchannel, plate, or other construction.
Condenser
Heat exchanger that rejects heat from a refrigerant, condensing it from vapor to liquid. May be air-cooled or water-cooled.
Counter-Flow / Cross-Flow / Parallel-Flow
Flow arrangements between two fluids in a heat exchanger. Counter-flow generally provides the greatest temperature change for a given UA; cross-flow is common in air-side coils.
DOAS
Dedicated Outdoor Air System. HVAC system that conditions 100% outdoor air for ventilation, often with heat recovery.
DX
Direct Expansion. Cooling system in which refrigerant expands directly inside the air-side coil. DX coils are evaporators in HVAC and refrigeration.
ERV / HRV
Energy Recovery Ventilator (ERV) and Heat Recovery Ventilator (HRV). Ventilation equipment that recovers energy from exhaust airstreams. ERVs typically transfer both sensible and latent energy; HRVs transfer sensible only.
Evaporator
Heat exchanger in which refrigerant absorbs heat and changes from liquid to vapor. Air-side evaporators are commonly DX coils; water-side are typically shell-and-tube or brazed-plate.
Fin Pitch / Fin Density
Spacing of fins along a tube, typically expressed in fins per inch (FPI). Higher fin density increases surface area but raises air-side pressure drop and can complicate cleaning.
Finned-Tube
Heat-exchanger construction in which fins are bonded to a tube to extend air-side heat-transfer surface. The Series 100 product line. See Finned-Tube Heat Exchangers.
First-Article Inspection (FAI)
Detailed inspection of the first production unit against drawings and specifications. Required on many engineered programs.
Glycol
Heat-transfer fluid (typically ethylene or propylene glycol mixed with water) used in low-temperature and freeze-protection applications and in run-around heat-recovery loops.
Heat Pump
Refrigeration cycle reversed to deliver heating, or capable of switching between heating and cooling. Air-to-air, air-to-water, and water-to-water configurations are common.
Heat Recovery
General term for capturing waste thermal energy for reuse. Includes ventilation heat recovery, process waste-heat capture, and energy recovery wheels.
Latent Heat / Sensible Heat
Sensible heat changes temperature; latent heat changes phase (e.g., evaporating water from a wet coil). Total heat transfer is the sum of both.
LMTD
Log Mean Temperature Difference. Standard parameter used in heat-exchanger sizing to characterize the temperature driving force across a counter-flow or parallel-flow exchanger.
Microchannel
Compact all-aluminum heat exchanger using small parallel flow channels and brazed construction. The Series 200 product line. See Microchannel Heat Exchangers.
OEM
Original Equipment Manufacturer. Designwinds primarily supplies thermal components to HVAC OEMs for integration into finished equipment.
Plate-and-Fin
Heat-exchanger construction using stacked plates with corrugated fin layers. Common in compact and lightweight heat exchangers and in plate-style heat recovery cores.
Pressure Drop
Pressure loss as a fluid passes through a heat exchanger. Higher pressure drop increases fan or pump power; lower pressure drop typically increases physical size for a given duty.
Recuperator
Heat exchanger that transfers heat between two fluid streams that are physically separated. Brazed plate-and-fin recuperators are common in ventilation heat recovery.
Refrigerant
Working fluid in a refrigeration or heat-pump cycle. Modern HVAC refrigerants include R-410A, R-454B, R-32, R-1234yf, R-134a, and R-744 (CO₂); R-717 (ammonia) is widely used in industrial applications.
Regenerator
Heat exchanger that stores and releases heat in cycles, typically through a rotating matrix. Energy recovery wheels are rotary regenerators.
Refrigerant Charge
Mass of refrigerant in a closed system. Heat-exchanger internal volume contributes to charge minimization in modern low-GWP refrigerant designs.
Run-Around Loop
Heat-recovery configuration using a pumped intermediate fluid (typically glycol) circulated between two coils in separate airstreams. Allows heat recovery between non-adjacent airstreams.
Shell-and-Tube
Heat-exchanger construction with tubes inside a cylindrical shell. Widely used in industrial process heat transfer and process chillers.
Subcooling
Cooling of liquid refrigerant below its saturation temperature, improving system capacity and efficiency. Often controlled at the condenser outlet.
Superheat
Heating of refrigerant vapor above its saturation temperature at the evaporator outlet. A standard control parameter in DX systems.
Tube Expansion
Mechanical or hydraulic expansion of tubes into fin collars to form a tight thermal and mechanical bond. Standard operation in fin-and-tube coil production.
U-Bend
Curved tube section that turns the refrigerant or working fluid 180°, returning flow through the coil. U-bends are typically brazed copper on fin-and-tube coils.
VRF / VRV
Variable Refrigerant Flow / Volume. Refrigerant-based HVAC system with multiple indoor units served by a single outdoor condensing section. Microchannel heat exchangers are widely used in modern VRF outdoor units.
Walk-In Cooler / Freezer
Refrigerated enclosure for commercial food and beverage storage. Walk-ins use packaged evaporators and condensing units; Designwinds supplies coils to refrigeration packagers.