A Floating‑Head Pressure Technology for Stable, Efficient Refrigeration

Liquid Pressure Amplification (LPA®) enables refrigeration and DX systems to operate at floating head pressures without losing TEV/EEV capacity, liquid stability, or system reliability. By maintaining a solid column of liquid refrigerant at the expansion device, LPA® prevents liquid line vapor, restores design pressure differentials, and unlocks the full efficiency benefits of low‑ambient operation.

Liquid Pressure Amplification (LPA)
A Floating Head Pressures Technology without a loss in TEV or
EEV Capacity: Becker/O’Brien, 2008, UK

Definitions
EEV = Electronic Expansion Valve.
TEV = Thermostatic Expansion Valve.
As head pressure is dropped:
The compressor would tend to unload because:

Why Floating Head Pressure Improves Efficiency

When condensing pressure is allowed to fall with ambient temperature:

• Liquid temperature and enthalpy decrease, increasing the specific refrigeration effect
• Mass flow reduces, lowering compressor load
• Volumetric efficiency increases due to reduced compression ratio
• Compressor power drops significantly

In many systems, reducing saturated condensing temperature from 43 °C to 20 °C can deliver up to 60% compressor power savings.

Floating head pressure is one of the most effective energy‑reduction strategies available — but it introduces new challenges in liquid stability.

Thermodynamic Changes That Cause Liquid Starvation

Floating head pressure improves efficiency, but it also triggers refrigerant mass redistribution:

Evaporator charge increases

Lower liquid enthalpy and reduced mass flow reduce flash gas, increasing the evaporator’s operating charge.

Condenser vapor density decreases

Example with R22:

• 43 °C: 71.62 kg/m³
• 20 °C: 38.34 kg/m³

This reduces the refrigerant mass held in the condenser.

Liquid density increases

Cooler liquid becomes denser, freeing volume in the liquid line — but not enough to offset evaporator charge gain.

Net effect

More refrigerant migrates to the evaporator → liquid line mass decreases → TEVs and EEVs become starved.

This is the core limitation of floating head pressure without LPA®.

Expansion Valve Capacity Loss at Low Head Pressure

When condensing pressure drops:

• TEV pressure drop decreases
• Liquid density increases
• Liquid enthalpy decreases

Estimated capacity losses from 43 °C → 20 °C:

• EEV: ~20%
• TEV: ~28%

Both valves require a solid liquid seal at the inlet. Any vapor in the liquid line dramatically reduces capacity.

Why Liquid Line Vapor Increases at Low Ambient

Liquid line vapor formation is amplified by:

• Component pressure drops
• Vertical lift
• Solar gain
• Reduced condensing pressure
• Higher ΔT/ΔP ratios at low temperature

At 20 °C condensing, saturated ΔT/ΔP increases by ~56%, meaning far more subcooling is required to prevent flashing.

Without intervention, the system cannot maintain a stable liquid column.

Why Adding More Refrigerant Doesn’t Solve the Problem

Increasing charge to restore subcooling:

• Raises head pressure above ideal
• Causes condenser flooding at high load
• Reduces suction–liquid heat exchange
• Limits floating‑head efficiency
• Often fails to eliminate vapor during low‑ambient operation

This is why LPA® is required.

Liquid Pressure Amplification (LPA®) — How It Works

LPA® adds a small, controlled pressure boost to the liquid line, ensuring:

• A solid liquid seal at the TEV/EEV
• Restoration of design pressure differential
• Re‑condensation of liquid line vapor
• Additional pressure‑induced subcooling
• Stable operation at floating head pressures

Only a small additional refrigerant charge is required — far less than what would be needed to achieve the same subcooling without a pump.

Key advantages

• Enables full floating‑head operation
• Prevents TEV/EEV starvation
• Eliminates liquid line “frothing” caused by head‑pressure control cycling
• Allows TEVs to be used where EEVs would otherwise be required
• Supports long liquid lines and vertical lift

A parallel capillary can be added to supplement TEV orifice size when pressure drop is still insufficient.

Why LPA® Is Essential for Modern Refrigerants

Low‑GWP HFO blends and CO₂ systems are more sensitive to pressure drop and more prone to flashing at low ambient conditions.

LPA® ensures:

Liquid Pressure Amplification (LPA®) is the enabling technology that allows refrigeration and DX systems to operate at maximum efficiency under floating‑head conditions without sacrificing liquid stability or expansion‑valve performance.

It is the only practical method to maintain a solid liquid column, eliminate liquid line vapor, and ensure reliable operation across all refrigerants — including modern low‑GWP blends.

Becker/O’Brien, Westfield Estate, Midsomer Norton, UK 2008