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ESBE VTN100 frost protection valve: protecting your heat pump against freezing
Monobloc air-to-water heat pumps have one vulnerable feature: the water circuit runs all the way to the outdoor unit, which is exposed to freezing conditions. As long as the heat pump is running, the water circulates and does not freeze. The problem arises during a power cut in severe frost – the circulation pump stops, the water stops moving and begins to cool down. When the temperature drops below freezing point, the expanding ice can rupture both the plate heat exchanger and the pipework in the outdoor unit. Repairs are costly, and frost damage is also typically excluded from the warranty.
Author: Jaromír Bittner - Sales Representative
The ESBE VTN100 frost protection valve is designed precisely for this scenario. It is a simple, purely mechanical safety device that starts draining water from the system when needed, before it has a chance to freeze.
How the VTN100 works
At the heart of the valve is a highly precise wax (thermostatic) element that responds to the temperature of the flowing medium – no electronics, no power supply. The principle is intentionally simple:
- Opens at 3 °C (±1 °C): as soon as the water temperature at the valve drops below 3 °C, the valve begins to open and discharge water.
- Warmer water flows in: by draining off the colder water, warmer water from another part of the circuit reaches the valve. This means the system does not empty all at once – only as much water is discharged as is strictly necessary to prevent freezing.
- Closes at 4 °C (±1 °C): once the medium temperature rises again to approximately 4 °C, the valve closes automatically.
Automatic closing and controlled discharge
Once the risk of frost has passed and the medium has warmed up, the valve closes automatically and requires no manual reset. It also includes a vacuum valve which, if necessary, allows the protected section of the circuit to be completely drained – air enters the pipework and the water can drain away fully.
The maximum discharge flow rate is approximately 2 l/min (at 1 °C and a differential pressure of 3 bar; Kvs 0.07 m³/h). This is therefore not an emergency drain-down of the entire system, but a controlled, economical discharge of only the water at risk.
VTN100 vs. VTN200 – what is the difference
The VTN range is available in two versions. VTN100 responds only to the temperature of the medium. VTN200 also features an ambient (outdoor) temperature sensor that blocks the discharge function if the surrounding air temperature is sufficiently high (above approx. 6 °C). This prevents unnecessary draining of the system in summer, when the heat pump is operating in cooling mode and the medium may be cold even though there is no risk of frost outdoors. So if your heat pump also provides active cooling, consider the VTN200 instead; for standard heating without cooling, the VTN100 is entirely sufficient.
ESBE VTN100 technical parameters
| Parameter | Value |
|---|---|
| Opening temperature (medium) | 3 °C ±1 °C |
| Closing temperature (medium) | 4 °C ±1 °C |
| Operating medium temperature range | 0 °C to 90 °C |
| Ambient temperature range | −30 °C to 60 °C |
| Discharge flow rate | 2 l/min (at 1 °C and 3 bar; Kvs 0.07 m³/h) |
| Pressure class / max. operating pressure | PN 10 / 10 bar |
| Connection | male thread (G), ISO 228/1 B – G 1" or G 1¼" |
| Medium | heating water in accordance with VDI 2035 |
| Body material | brass |
| Seal (O-ring) | EPDM |
| Spring | stainless steel |
| Installation position | vertical, with a tolerance of ±45° |
| Maintenance | maintenance-free |
| Compliance | PED 2014/68/EU, Article 4.3 |
Specific types: VTN102 DN25 (G 1", order code 35100100, weight 0.35 kg) and VTN102 DN32 (G 1¼", order code 35100200, weight 0.42 kg).
Principles of correct installation
For the valve to protect the system effectively, where and how it is installed matters. Key rules from the manufacturer's instructions:
- Outdoors and at the most exposed point. The valves are installed (outside the building) on both the flow and return pipework in the part of the system where the risk of freezing is highest – that is, where they can allow the outdoor unit and exposed pipework to be drained.
- Away from heat sources. The valve must not be installed near a heat source or a wall, as radiant heat would distort the measured temperature and affect operation.
- Take care with discharged water. Install the upper valve so that the discharged water does not run onto lower pipework or system components.
- Do not cover. The vacuum valve or the ambient temperature sensor (on the VTN200) must not be covered.
- Vertical position ±45°. Observe the recommended clearances in accordance with the installation instructions (Figures 1–3).
If removal is ever required, first depressurise the system – there is a risk of scalding, as hot water may escape from the system.
Who the VTN100 is worth it for
A frost protection valve is an inexpensive safeguard against costly damage. It makes sense wherever a monobloc air-to-water heat pump is installed outdoors and there is a risk that, during a prolonged power cut in freezing weather, the water will remain stationary. The cost of the valve is only a fraction of the price of a plate heat exchanger, so from a risk perspective the payback is clear. The valve is purely mechanical and maintenance-free, so once correctly installed, you will hardly need to think about it in practice.
Frequently asked questions (FAQ)
Usually two – one on the flow pipe and one on the return pipe, so that both branches leading to the outdoor unit are protected.
No. It discharges only a small amount of water (max. approx. 2 l/min) until warmer water reaches it. The aim is to prevent freezing, not to empty the entire circuit.
No. As soon as the medium temperature rises to approximately 4 °C, the valve closes automatically. After that, simply check the system pressure and top up with water if necessary.
Yes, and that is precisely the point. It operates using a wax thermostatic element, so it requires no power supply – it protects even during a power cut.
According to your pipe size: the VTN102 DN25 has a G 1" male thread, while the VTN102 DN32 has G 1¼".
If the heat pump also operates in active cooling mode. Thanks to its ambient temperature sensor, the VTN200 does not discharge water in summer when the medium is cold due to cooling, but there is no risk of frost outdoors.
It is intended for heating water in accordance with VDI 2035 in systems up to PN 10 (max. 10 bar) and a medium temperature of 0–90 °C. Before use in a specific application, always check local and national regulations.
