LG UM42R (42,000 BTU, 12 kW) - ducted indoor unit 270 mm high for halls and workshops

The UM42R: a 12 kW ducted unit

The UM42R is a ducted indoor unit of LG's R32 semi-industrial series: 12 kW cooling, 13.5 kW heating. The dimensions are the same as the 10 kW model's: 1250 mm wide, 700 mm deep, 270 mm high, a casing of metal and plastic, supply 220-240 V, 50 Hz, with a Dual Inverter compressor in the pair. The manufacturer country and country of origin are Korea and the warranty 24 months. The card gives no pipe diameters or maximum run: these depend on the outdoor unit, and we supply the exact values from LG's combination table for the chosen pair. This is a unit for a hall of roughly 100-130 m², or for a smaller space with high heat gains.

The same casing at a higher output

Between the UM36R and the UM42R the difference in capacity is 20 per cent while the casing stayed the same - which means more air passes through the same cross-section. Physically that is achieved with a denser coil and higher fan speed, and the consequence for the design is direct: the demands on the duct network become stricter, not more relaxed. The main duct for 12 kW is taken at 450 by 200 mm or more, or 355 mm round and up, with no fewer than six to eight grilles of adequate free area. If you leave a network sized for 10 kW, the unit will work, but at higher fan speed and with more audible noise - and the gain in capacity will be partly eaten by discomfort in the hall. So when choosing between 10 and 12 kW for the same space we look not only at the heat gains but also at whether the network will take the higher airflow.

Zone supply in a tall space

In a hall 4-6 metres high there is no point cooling the whole volume: warm air collects under the ceiling anyway, while people occupy the lowest two metres. An output of 12 kW together with high static pressure makes it possible to deliver air through nozzles or long-throw grilles aimed down and forwards: the stream from such a device carries 8-12 metres and covers the occupied zone without cooling the space under the ceiling. This approach is typical for sports halls, exhibition spaces, production areas and car showrooms, and it delivers a real saving at the same comfort. The throw is calculated from the grille manufacturer's diagrams: it depends on outlet velocity, the spread angle of the stream and the air temperature. We design this from the actual geometry of the space rather than from a typical scheme, because an error in throw means either a draught over people's heads or a zone the air never reaches at all.

13.5 kW of heat in the shoulder season

A heating output of 13.5 kW turns the system into the main heat source for a hall of 110-130 m² in September to November and March to April, when the heating is not yet or no longer running. The advantage is economic: an air conditioner moves heat in from outdoors, so for every kilowatt consumed it delivers roughly three to four at moderate outdoor temperatures - an electric convector delivers one. The limits are worth knowing too: the lower bound of heating for R32 systems of this class is about -10 °C, and the colder it gets the lower the actual delivery. In frost the unit periodically enters a defrost cycle on the outdoor coil, during which heating stops for a few minutes - that is normal operation, not a fault. In a tall space in heating mode it is important to aim the stream downwards, otherwise the warm air goes under the ceiling and nothing changes at the level where people are.

Choosing the outdoor unit

For 12 kW the catalogue offers two outdoor units: the single-phase UU42WR (item 1817) and the three-phase UU43WR (item 1821), both in a 950 by 1380 by 330 mm casing. The single-phase unit draws 18-20 A from one phase and needs a dedicated 4-6 mm² copper circuit, a check on the authorised capacity and a check on the actual voltage under load. The three-phase one consumes roughly 7-8 A per phase: thinner cable, lower losses, no imbalance - where three phases exist this is unambiguously the sounder choice. We recommend the three-phase version where the site can connect it, and we help work out which is cheaper: bringing in three phases or reinforcing the single-phase line. We verify the final combination against LG's compatibility table and state the pipe diameters with the maximum run for the chosen pair.

What gets set at commissioning

A ducted unit of this capacity does not work correctly out of the box: the fan speed is set on the board to match the actual network resistance, and that is the first and most important step. The second is choosing the sensor that holds the setpoint: the built-in one in the return air or the sensor in a wired controller on the wall in the occupied zone. The third is addressing, if the site has several indoor units and central control is planned: without correct addresses a group of units will not assemble into a system. Then the fan rotation direction, the operation of the drain pump if fitted, and the actual airflow at the grilles are checked by measurement. All these parameters are recorded in the commissioning report along with pressures and currents: without such a report the next service engineer starts from scratch, and warranty questions become arguable.

Which jobs it fits and where it is out of place

The UM42R is taken for a sales floor, an open-plan office, a sports club, a production area or a restaurant room of roughly 100-130 m² with a suspended ceiling or with exposed ductwork. It works well where zone supply in a tall space is needed, or a long main duct with several distant zones. Where the model is out of place: spaces with less than 380-420 mm of void; a simple layout with two or three grilles, where the high airflow will only produce noise; spaces divided into zones at different temperatures. A kitchen, a laundry or a workshop with process emissions needs equipment of a different class and a separate ventilation calculation. If the calculation comes out above 12 kW, the series offers the UM48R (item 1832) at 13.5 kW and the UM60R (item 1833) at 15 kW - in a 360 mm high casing.

How it differs from neighbouring models in this catalogue

The UM36R (item 1830) is 10 kW in the same casing: a step down, with lower airflow and easier demands on the network. The UM48R (item 1832) at 13.5 kW and the UM60R (item 1833) at 15 kW are both 360 mm high instead of 270 mm, which calls for more void above the ceiling. If there is no suspended ceiling, 12 kW is available from the UT42R cassette (item 1839) at 840 by 840 mm or the UV42R ceiling-suspended unit (item 1845), 1600 mm long. The outdoor units are the UU42WR (item 1817) for one phase and the UU43WR (item 1821) for three; the same pair with the cassette and the suspended unit. For several rooms with independent control the alternative is a multi-split system such as the FM48AH (item 1861) at 14 kW, where each indoor unit has its own controller and its own setpoint.

Send us the area, the ceiling height and the position of the zones - we will size the air delivery for the UM42R and say which outdoor unit suits your supply better.