Glycol-Water Heat Rejection: How the Trotec PT 23000 S Eliminates Gas Leak Risks

Conventional portable and split air conditioners reject heat by either exhausting warm air through a window hose or routing pressurised refrigerant lines through a wall or window gap to an outdoor condenser. Both approaches carry inherent risk at the penetration point: air exhaust creates infiltration and negative pressure; refrigerant line penetrations create potential leak sites where regulated gas can escape into the environment or, in the case of R290 or R32, into occupied spaces. The Trotec PT 23000 S takes a fundamentally different approach, using a closed glycol-water circuit to carry condenser heat from the refrigeration system to an outdoor rejection point — and the engineering consequences of that choice affect everything from installation flexibility to long-term maintenance liability.

Understanding the trotec pt 23000 s connection circuit requires grasping the key thermodynamic principle: instead of a refrigerant-to-air condenser exposed outdoors, the PT 23000 S uses a refrigerant-to-water condenser entirely contained within the indoor unit, where heat from the refrigerant circuit is transferred to a circulating water-glycol mixture. That glycol mixture then flows through insulated low-pressure water pipes to an outdoor dry cooler (a fan-assisted radiator panel that rejects heat from the liquid into outdoor air). Only water piping — not refrigerant lines — crosses any window or wall penetration.

What is the closed glycol-water circuit in the Trotec PT 23000 S?

The closed glycol-water circuit in the Trotec PT 23000 S consists of a refrigerant-to-water heat exchanger (a brazed-plate or shell-and-tube condenser where R407C or equivalent refrigerant rejects heat to the glycol-water mixture), a circulation pump, an expansion vessel, interconnecting insulated flexible hose, and an outdoor dry cooler unit. The glycol mixture — typically 30–40% propylene glycol in water to provide frost protection down to approximately −15°C — circulates in a sealed pressurised loop at working pressures of 1.5–3.5 bar, far below the 15–30 bar typical of refrigerant circuits.

The circulation pump maintains a continuous flow of glycol through the indoor condenser section, absorbing heat from the refrigerant, and then through the outdoor dry cooler, where a fan forces ambient air across finned tubes and returns the cooled glycol to the condenser. The refrigerant circuit itself — compressor, evaporator, expansion device, and refrigerant-to-water condenser — is entirely contained within the indoor unit cabinet and never exits through any building penetration. This is the architectural feature that eliminates gas leak risk at the window or wall interface.

The system is designed for commercial, server room, and professional environments where the cost of a refrigerant release is high — either due to regulatory compliance requirements, the presence of sensitive electronic equipment, or the practical difficulty of accessing the installation for refrigerant leak detection. In EU member states, fixed split installations in server rooms and telecommunications equipment spaces are subject to EN 378 leak detection requirements for charge weights above defined thresholds; the glycol-loop design sidesteps this by keeping the entire refrigerant charge hermetically sealed within the indoor unit at all times.

Why does the glycol-water design eliminate refrigerant gas leak risk at the connection point?

Refrigerant gas leak risk at connection points arises because conventional split AC installations route pressurised refrigerant — at 15–30 bar for modern HFC and HFO refrigerants — through flared copper fittings at the wall penetration. Any imperfection in a flare joint, vibration-induced loosening over time, or mechanical damage to the line set at the penetration point can release refrigerant to the outdoor environment or into cavity wall spaces. The glycol-water circuit eliminates this risk category entirely at the penetration point because the working fluid crossing the building envelope is water-glycol at 1.5–3.5 bar — a liquid whose release, while inconvenient, poses no atmospheric or safety hazard and requires no F-Gas regulatory notification.

The remaining refrigerant leak risk in the PT 23000 S system is not eliminated but re-localised: it is confined to the sealed indoor unit cabinet, where any refrigerant release would manifest as reduced cooling performance rather than atmospheric release, and where the leak would be detected in a controlled indoor environment rather than at an inaccessible outdoor wall penetration. This risk profile is broadly equivalent to that of a hermetically sealed portable monoblock unit — much more manageable than a field-installed split with outdoor flare joints exposed to vibration, thermal cycling, and mechanical disturbance.

For EU compliance purposes, the glycol-water loop is not subject to F-Gas Regulation 2024/573 requirements because it contains no fluorinated greenhouse gases — propylene glycol is an alcohol compound with zero global warming potential. The only F-Gas regulated component is the sealed refrigerant circuit within the indoor unit, which is factory-assembled, hermetically sealed, and compliant with applicable EN 378 requirements for the refrigerant type and charge weight. Maintenance personnel handling the glycol loop require no F-Gas certification.

What are the installation requirements for the glycol circuit?

The glycol-water circuit installation requires routing two insulated flexible hoses — a flow line carrying warm glycol from the indoor condenser to the outdoor dry cooler, and a return line carrying cooled glycol back — through a slot in an external wall or window frame. The hoses are typically 19–25 mm in outer diameter including insulation; the combined slot required is approximately 50–60 mm wide, larger than the 27 mm slot needed for a PortaSplit flat duct but substantially smaller than the 130–150 mm opening needed for a monoblock exhaust hose. Both hoses carry liquid under low pressure, so any connection fitting failure results in a liquid spill rather than a pressurised gas release.

The outdoor dry cooler unit requires its own electrical supply and must be positioned where it can draw unobstructed fresh ambient air across the fin coil — typically a minimum of 300 mm clearance on all sides. Dry cooler performance degrades as ambient temperature rises, because the temperature difference between the glycol return temperature (typically 35–45°C) and the ambient air driving the cooling is reduced. On the hottest days of the year, when outdoor temperatures approach 38–40°C, a glycol return temperature of 40–45°C leaves only 0–5°C of driving temperature differential, which significantly reduces dry cooler heat rejection and causes indoor temperatures to rise — the primary performance limitation of the glycol-loop design relative to refrigerant-circuit alternatives in extreme heat.

The high-ambient performance limitation: when glycol-loop designs reach their ceiling

The performance ceiling of glycol-water heat rejection is an important limitation to understand. A refrigerant-to-air condenser (as used in conventional split and portable split units) can reject heat to outdoor air at temperatures up to 10–15°C above the condensing refrigerant temperature, maintaining adequate performance through most European peak summer conditions. A glycol-to-air dry cooler, by contrast, requires the glycol temperature to be above ambient air temperature to drive heat flow — and as ambient approaches 38–40°C, the available temperature differential narrows toward zero, causing the refrigerant condensing pressure to rise and the cooling capacity to fall substantially.

Professional installations of PT 23000 S-class units mitigate this limitation by pre-cooling the glycol during night-time hours when ambient is lower, using thermal mass in an insulated buffer tank to extend the effective operating window during peak afternoon heat. Some commercial installations supplement with a second stage of evaporative pre-cooling (spraying water mist across the dry cooler inlet) to temporarily lower inlet air temperature and restore the driving differential. These are engineering workarounds that add cost and complexity; they confirm that the glycol-loop design is optimised for controlled-environment applications rather than residential maximum-heat performance.

Used a glycol-loop cooler for a server room in a listed building where drilling through the walls was prohibited. The building managers accepted the two small hose penetrations easily — getting permission for refrigerant lines would have been a planning process. For that application it was the right choice.

How does the glycol-loop maintenance profile compare with refrigerant circuit maintenance?

The glycol-water circuit requires annual maintenance checks that the refrigerant circuit of a conventional split does not: glycol concentration testing (the glycol-to-water ratio must be checked with a refractometer annually and adjusted to maintain frost protection at the required temperature), inhibitor concentration check (propylene glycol formulations include corrosion inhibitors that deplete over time and must be refreshed approximately every three to five years), and visual inspection of hose connections and expansion vessel pre-charge pressure.

These glycol maintenance tasks are simple and require no F-Gas certification or specialist tools — a refractometer costs under €20, glycol top-up is a standard plumbing operation, and inhibitor treatment kits are available from HVAC suppliers. By contrast, the refrigerant circuit in the sealed indoor unit requires no routine maintenance by the building operator — it is serviced only if performance degradation indicates a fault, at which point a certified F-Gas technician handles the sealed system. The split maintenance responsibility is clear: the glycol loop is owner-maintainable; the refrigerant circuit is technician-only.

When is the Trotec PT 23000 S glycol-water design the right solution?

• Listed buildings or heritage properties where drilling for refrigerant line penetrations requires planning permission but small-diameter hose slots are accepted.
• Server rooms, telecommunications equipment spaces, and laboratories where refrigerant leak detection systems are required under EN 378 for conventional split installations.
• Leased commercial premises where the tenant requires a fully reversible installation — the glycol loop can be capped and withdrawn without residual contamination.
• Environments where F-Gas maintenance records, mandatory leak checks, and certified technician requirements for refrigerant handling create disproportionate operational overhead.
• Buildings connected to district cooling or chilled water circuits where the indoor unit's glycol loop can be connected directly to the building circuit rather than requiring an outdoor dry cooler.

The bottom line on the Trotec PT 23000 S glycol-water circuit

The glycol-water heat rejection design of the Trotec PT 23000 S is a sound engineering solution for specific professional and commercial applications where refrigerant penetration risk, regulatory compliance overhead, or installation reversibility requirements make conventional split installations impractical. Its performance ceiling in extreme ambient heat and the annual glycol maintenance requirement are real trade-offs that constrain it to controlled-environment applications. For residential European buyers, a portable split with sealed pre-charged flat duct offers a more appropriate balance of performance, simplicity, and regulatory clarity.

For residential and light-commercial European buyers whose needs align with the portable split architecture rather than the glycol-loop approach, availability of the leading portable split units is the practical constraint during peak demand.