Split Arctic

What a split unit is, and why it suits a cold climate

In a monobloc the whole refrigerant circuit is sealed outdoors and heating water is piped through the wall. In a split, only refrigerant crosses the wall, so the water circuit stays entirely inside the heated envelope. The consequence in a continental winter is direct: no antifreeze in the heating water, no external pipe insulation to degrade in UV light, and no reliance on a frost protection routine that itself needs mains power.

• No frost risk in the line. The refrigerant connection between the outdoor and indoor units stays freeze-proof even during a prolonged power outage, because there is no water in it.
• Lower outdoor noise. The condenser and circulation pump are indoors, so the outdoor unit is essentially a fan and a compressor in an acoustically treated casing.
• Certified commissioning. The trade-off is that the refrigerant side must be evacuated, charged and leak tested by an F-gas certified engineer under the EU F-gas regulation.
• Indoor space is required. A monobloc needs almost nothing inside. A split needs a wall or floor position for the hydraulic module plus service clearance.

Inverter modulation, output range and matching the heat loss

The compressor is driven by a frequency inverter, so it varies its speed continuously instead of switching on and off at full output. A building spends the overwhelming majority of the heating season somewhere between 20 and 60 % of its design load, which is exactly where a modulating machine earns its efficiency: it settles at a low frequency, runs for hours, and holds a steady flow temperature.

• Minimum modulated output matters more than maximum. A unit that turns down to roughly 30 % of rating rides a mild October far better than one that only reaches 60 %.
• Short cycling is the enemy. Start, satisfy a small volume in four minutes, stop, repeat. Each start costs energy and compressor life, and it never appears in a laboratory COP.
• System water volume is part of the specification. A buffer of 60, 100 or 160 L, or a low-loss header, gives the inverter something to work against when thermostatic valves close.
• Weather compensation should always be on. A fixed setpoint throws away the benefit of modulation by forcing the machine to the same high flow temperature in November as in January.

Size from a room-by-room heat loss calculation to EN 12831 at your local design outdoor temperature, never from floor area. Then read the manufacturer's capacity table at that outdoor temperature and at your real flow temperature, because a unit rated at 12 kW for A7/W35 delivers noticeably less at minus 10 °C outdoor and 50 °C flow.

• 6 to 8 kW covers well-insulated houses of roughly 120 m², or smaller buildings with moderate insulation.
• 10 to 12 kW suits medium houses of about 120 to 200 m² with standard insulation.
• 14 to 16 kW is for larger properties, poorer fabric or a higher share of high-temperature emitters.
• Do not stack safety margins. A heat loss figure is already a steady-state worst case. Adding another 30 % produces a machine that spends the season below its minimum modulation.

Flow temperature: radiators or underfloor

Flow temperature is the single largest efficiency lever on any heat pump. As a working rule, each 1 °C reduction in flow temperature improves COP by roughly 2 to 2.5 %, so the same Arctic unit in the same house can be cheap or expensive to run depending only on the emitters.

• Underfloor heating runs at 30 to 40 °C because the emitting surface is huge. This is the natural pairing and gives the best seasonal figures.
• Oversized or replaced radiators work comfortably at 40 to 45 °C. Enlarging the emitters in the two or three worst rooms is usually cheaper than living with a high curve for twenty years.
• Radiators sized for a 70 °C gas boiler will function, but the seasonal penalty is severe and the machine spends more of the year near the top of its envelope.
• Mixed systems need zoning: an underfloor circuit and a radiator circuit on one uncontrolled flow temperature always ends up running at the higher of the two.

COP, SCOP and defrost behaviour

COP is heat output divided by electrical input at one declared operating point, written as A7/W35 for 7 °C outdoor air and 35 °C flow. SCOP is the seasonal average calculated to EN 14825 over a defined climate profile and a defined flow temperature, and it already includes part-load running, standby and defrost losses. Compare SCOP figures only when both are quoted at the same flow temperature, because a 35 °C number and a 55 °C number are not the same measurement.

• Defrost is normal, not a fault. Between roughly minus 5 °C and plus 5 °C with high humidity, moisture freezes onto the outdoor coil and the unit briefly reverses the cycle to melt it.
• Expect steam and a puddle. Vapour rising from the outdoor unit for a few minutes is melting frost. Provide a free-draining base and, in hard frost areas, a heated condensate tray or gravel bed.
• Frequent defrosts pull the season down. Frost forms fastest in damp still air, so a unit tucked into a shaded, unventilated corner ices up more often than one in open air.
• SPF is the honest field number. The measured seasonal performance factor includes pumps, controls and the backup element, so it sits below the brochure SCOP.

Electrical supply, indoor module, hot water and photovoltaics

Units up to roughly 10 kW are commonly single-phase at 230 V; larger units and most 3 to 9 kW electric backup elements need a three-phase 400 V supply for balanced loading. Confirm the available connection capacity, breaker rating and RCD type at the distribution board before ordering, and remember that the outdoor unit and the backup element are usually separate circuits.

• Indoor module space. Allow a clear wall or floor area plus front and side service clearance. All hydraulic components should remain reachable without dismantling the casing.
• Hot water connection. This version has no built-in cylinder, so the module drives an external DHW tank through a three-way diverter valve and a tank sensor.
• Cylinder coil surface is the limiter. A heat pump works at a much lower water temperature than a boiler, so an old cylinder with a small coil will reheat slowly even when its volume is adequate.
• Condensate and safety. Route the outdoor condensate away from paths and doorways, and terminate the discharge from the safety valve to a visible, frost-free point.

A heat pump is the strongest self-consumption load most households have, because each surplus kWh becomes three or four kWh of heat. A photovoltaic array with export detection can lift the hot water setpoint or nudge the heating curve while the sun is on the roof, storing energy as heat far more cheaply than as battery capacity. The gain is largest in spring and autumn and smallest in midwinter, when demand peaks and yield does not.

Key parameters compared

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