Air Conditioners For Home

Most buyers arrive at this category already knowing the number they want. They have a room, they have a rule of thumb about BTU per square metre, and they ask for the unit that matches. That is a sensible way to buy a mains powered air conditioner, because the electricity is somebody else's problem. It stops being sensible the moment the electricity is yours.

A 24,000 BTU machine is roughly seven kilowatts of cooling. To deliver that, the compressor and fans draw a certain number of watts, continuously, for as long as the room is above set point. In a grid connected house that shows up as a bill. In an off grid house it shows up as battery state of charge at four in the morning, and as the number of panels on the roof. The panel count is the real specification of an off grid air conditioner, and it is set by the DC efficiency of the unit, not by its BTU figure.

24,000 BTU is the same as about 7.0 kW of cooling capacity. As a rule of thumb, that is the class of unit used for a large living room, an open plan kitchen and dining space, a small shop floor, a consulting room, or two connected bedrooms in a hot climate. The number is nominal: it is measured at a standard test condition, and every unit delivers a little less when the outdoor air is hotter than the test point and a little more when it is cooler. That is true of every brand and every model, and it is the reason a 24,000 BTU unit that feels weak in a 40 °C afternoon is not necessarily faulty.

What matters for sizing is not the headline number but the relationship between the room and the outdoor coil. A room with west facing glass and a dark roof needs more capacity than the same floor area on a shaded ground floor. A room with a ceiling fan and good insulation needs less. If you are choosing between 18,000 and 24,000 BTU for a space that sits on the boundary, the larger unit will reach set point faster and then cycle, which is fine on grid power and wasteful on a battery, because the pull down is the most expensive part of the day.

A conventional solar installation puts an inverter between the panels and the house, and the air conditioner then runs on 230 V AC as if nothing had changed. Each conversion in that chain costs energy. A DC driven unit takes the array voltage, regulates it to a 48 V DC bus, and feeds the compressor and the fans from that bus directly. There is no inverter stage between the sun and the compressor, which is why a DC unit of the same nominal capacity can be run from a smaller array than an AC unit plus inverter.

The 48 V level is also the reason the cabling is manageable. At 48 V the current for a given power is four times lower than at 12 V, so the copper stays reasonable and the voltage drop across a ten metre run stays small. It is the same reason 48 V has become the default for off grid homes, telecom sites and small commercial solar systems.

Two details from the installation guide are worth repeating here, because they are the ones installers get wrong. First, a 40 A DC breaker belongs on both sides of the controller, not just one: one between the panels and the controller, one between the controller and the battery cabinet. Second, the cable from the controller to the battery cabinet is specified at 4 mm² in the manual, and it should be run as a pair with the breaker close to the battery end, so that a fault in the run cannot be fed by the bank.

A split system separates the noisy half from the quiet half. The indoor unit carries the evaporator coil, the fan and the louvres, and it hangs on the wall of the room being cooled. The outdoor unit carries the condenser coil, the compressor and the condenser fan, and it stands where it can reject heat to open air. The two are joined by an insulated copper pair, a condensate drain and a multicore cable. Almost everything that goes wrong at commissioning is in that join.

Both copper ends are flare connections. The manual calls for two spanners, one to hold the body of the fitting and one to turn the nut, because a single spanner twists the pipe and work hardens the flare. A vacuum pump and a pressure gauge are on the tool list for the same reason: the line set has to be evacuated before the charge is released, and it has to hold pressure before the unit is started. None of this is exotic, but all of it is invisible once the trunking is closed, which is why the photographs in the guide concentrate on the moment before the wrap goes on.

The wiring order matters on a DC unit more than on a mains unit, because the control boards are alive as soon as the bus is up. Land the earth first, then the numbered cores, then check that the numbers match at both ends before the outdoor cover goes back on. The guide shows the terminal strip with L, N, 1, 2, 3 and an earth stud, and it is worth taking a photograph of that strip at commissioning: it is the single most useful record if the unit is ever serviced by somebody else.

The indoor unit is fixed to a steel wall plate, and the plate is fixed with four expansion screws. Before drilling, three things decide whether the installation will be quiet and dry for the next decade: the height, the drain route, and what is on the other side of the wall.

Height: the head should sit high on the wall, with the top of the unit far enough below the ceiling that the air intake is not starved. A unit pushed into a ceiling corner will run, but it will pull its own return air and the room will feel flat. Drain route: gravity is the only pump in this system, so the drain must fall continuously from the tray to the outside. If the only exit is above the tray, the installation needs a condensate pump, and that is a different job. Other side of the wall: the copper pair leaves through a single sleeve, and the outdoor unit needs to be within the line set length and reachable for service. Drilling a 65 mm sleeve in the wrong place is the most common reason a one day installation becomes two.

The outdoor unit is a heat rejector, and it can only reject heat into air that is cooler than its coil. Everything about siting follows from that sentence. It needs free air on the coil face, free air out of the fan, and it must not sit in a recess that lets hot air circulate back into its own intake. A unit installed in a closed balcony will run continuously, never reach set point, and draw more from the battery than the array can replace.

In hot climates, shade over the unit is worth more than any other single measure. A condenser in direct afternoon sun starts from a higher condensing temperature before it has done any work at all. A simple roof over the unit, open on three sides, is enough. Wall brackets are acceptable where floor space is unavailable, but the bracket must be rated for the weight of the unit and the wall must be able to take the pull out loads: a hollow block wall needs through bolts or a spreader plate, not plastic plugs.

A 48 V DC system is safe to touch but not safe to short. A battery bank will deliver its short circuit current without complaint until something melts, so the protection is not optional and it is not a single device. The installation guide asks for a 40 A DC breaker between the battery and the charge controller, and a second 40 A DC breaker between the charge controller and the solar panels. That gives three islands: array, controller, battery. Any one of them can be isolated without the others being live at the far end.

The cable between the controller and the battery cabinet is specified at 4 mm². That is the minimum for the currents this unit class draws over the short run inside a plant room; if the battery cabinet sits further away than the typical layout, the installer should calculate the drop rather than assume. The rule that matters is the one in the manual: the breaker goes close to the battery end of the cable, so the length of unprotected conductor is as short as possible.

The honest way to size an off grid air conditioner is to work from the nameplate and the load profile, not from the BTU figure and not from a table somebody published for a different climate. The nameplate gives the input power. The load profile is how many hours a day the compressor actually runs, which in a hot climate is longer than the hours the room is occupied, because the unit has to pull the room down first.

The arithmetic has four lines and they are all multiplication and division:

The 0.75 in line two is the part buyers forget. It covers dirt on the glass, cable loss, controller loss and the fact that a panel rated at 550 W does not produce 550 W at nine in the morning. It is not a safety margin for a bad design; it is the ordinary derating that makes a design honest. Use the worst month of the year, not the annual average, because the unit will be needed most in exactly the month the sun is weakest in the northern hemisphere winter and the heat is highest in the southern hemisphere summer.

If the arithmetic produces a number that looks large, that is the answer talking, not a fault in the method. A 24,000 BTU class unit running ten hours a day is a serious daily load, and the array that supports it should look serious. The alternative, undersizing and hoping the battery carries the shortfall, is how off grid cooling gets a reputation for not working.

Commissioning is a sequence, and the sequence is not negotiable. Each step exists to make the next one safe. The list below is the one we give to installation teams, and it follows the guide page by page.

Step seven is where a competent installer and a fast one separate. A unit that is short of charge will still blow cool air for a few minutes and then fade as the coil ices. A unit with air in the line will sound slightly different at the compressor and will not hold its set point. Both faults are invisible from the room side and obvious from the gauge. If the installer does not own a vacuum pump, that is the moment to stop: everything before that step is reversible, and everything after it is not.

An air conditioner in an off grid house is maintained by whoever owns the house, so the list has to be short enough to actually happen. Four habits cover most of it: keep the filters clear, keep the condenser clear, keep an eye on the drain, and look at the controller reading once a month.

Filters: lift the front panel, take out the mesh, rinse it under a tap, let it dry fully before refitting. In a dusty climate that is a fortnightly job during the dry season and a monthly job in the wet season. A clogged filter does not just reduce airflow, it drops the evaporating temperature and makes the coil sweat in the wrong place, which is how a machine that was fine in year one starts dripping on the wall in year three.

Condenser: brush or vacuum the coil face from the outside in, and check that nothing has grown into the fan guard. In coastal sites the coil fins benefit from a rinse and a light protective spray every year. Drain: pour a cup of water into the indoor tray and watch it leave. If it hesitates, clear the line before the wet season rather than during it. Controller: read the daily yield figure once a month and compare it with the month before. A sudden drop is either shade you did not have before, or a panel that needs cleaning.

This is a large room unit, not a bedroom unit. It belongs where cooling is part of the business rather than part of the evening routine, and where the grid is either absent or unreliable enough that the array is already there for other reasons.

We keep the dimensional and charge data on the order confirmation rather than in this page, because this unit is built in more than one configuration for different markets and a single figure printed here would be wrong for somebody. If you need the numbers before you quote a project, ask us for the build sheet for your destination and we will send the exact figures with the drawing.

Hangzhou Juka Solar Technology was founded in 2015 around one problem: putting solar energy, new energy and smart control to work inside a refrigeration circuit. The range has since grown from a single DC chest freezer to solar refrigerators, solar ice makers, mobile ice-cream carts, delivery tricycles and beverage retail carts - all of them exported, most of them to Belt and Road markets. The work does not stop at the container. Partners in Ghana, Gabon, Cameroon, Nigeria, Kazakhstan and India are supported in setting up their own local production for retail and delivery refrigeration, which is how a cold chain becomes permanent rather than a series of one-off shipments. For a solar system this matters more than for a mains-only freezer. Panel sizing, controller rating and battery capacity all depend on cabinet volume and site conditions, so the cabinet and the electronics are engineered together instead of being bought separately by the importer.

What is decided before the cabinet is built

Certification and test documentation

CE marking covers the electrical arrangement, and utility model patents cover the cabinet and the direct-drive control layout. Documents travel with the order so they can be presented at customs and to institutional or tender buyers.

CE - low voltage and EMC

CE - supplementary schedule

Utility model patent - cabinet structure

On the floor

Six control points behind every cabinet

Machines on the line

OEM, ODM and local assembly

Cabinet-only supply, private label, SKD and CKD shipments are all available, together with technical guidance for partners who would rather assemble locally than import finished units. Helping partners build their own refrigeration business is the part of the work that outlasts a single purchase order.

What can be changed on a standard order:

✓  Customer logo and cabinet colour

✓  Voltage options and plug type

✓  Packaging design

✓  Product configuration, baskets and fittings

✓  Panel, controller and battery included, or cabinet supplied on its own