Demonstration rigs teach the cycle, fault rigs teach diagnosis, and a practice bay teaches the hands that employers hire. How to balance the three, plus refrigerant handling, cylinder storage and the heat every rig rejects into the room.
There are two ways to leave a refrigeration and air conditioning course in Bangladesh. One graduate can plot a pressure and enthalpy diagram and calculate a coefficient of performance. The other can braze a joint, pull a vacuum, read a manifold gauge set and find out why a split unit is icing up. The servicing trade hires the second one. A laboratory that only produces the first has bought the wrong half of the equipment list.
Refrigeration and air conditioning is one of the few engineering trades in Bangladesh where a diploma holder can walk into paid work within weeks. The employers are split unit installation and service companies, cold storage operators, transport refrigeration workshops, hotel and hospital maintenance departments, and the growing domestic appliance manufacturing sector. What they test at interview is practical: can this person recover refrigerant properly, evacuate a system to a proper vacuum, charge by weight and by superheat, and diagnose a fault from pressures and temperatures.
That does not make the theory optional. A technician who cannot read superheat and subcooling is guessing. But it does change the shape of the purchase: for every computer-controlled demonstration rig, the laboratory needs practice hardware that students are allowed to break, join, evacuate and refill.
Think of the equipment in three layers, and fund all three rather than buying deeply into one.
The cycle layer. One clear demonstration of the vapour compression cycle with visible components and instrumented state points. A refrigeration cycle demonstration unit such as the TCRB or a simple compression circuit such as the TSCR does this at low cost, and a computer-controlled vapour compression unit such as the TRCVC does it with logged data for a report. One good unit here is enough. Beyond that, the variants earn their place only when the syllabus asks the specific question: two-stage compression (TSCC), absorption refrigeration (TRAB), different expansion valves (TCREV), different capillary tubes (TCRCT), an open compressor (TRCC), a refrigeration and freezing chamber (TRRC) or heat exchangers in a refrigeration circuit (THER).
The diagnosis layer. A capacity control and faults unit such as the TCFRC is the closest a catalogue gets to what employers want, because it lets an instructor introduce a fault and a student find it. A variable load circuit such as the TRCAC teaches why a system behaves differently in April than in December. If the budget allows only one computer-controlled purchase, make it the fault rig rather than another cycle demonstration.
The trade layer. A split air conditioner unit such as the TACS, a domestic refrigeration unit such as the TRD2PC, an automobile air conditioning unit such as the TAAU where the institute also feeds the automotive trade, plus a practice bay: lengths of copper tube, flaring and swaging tools, a brazing set, a vacuum pump with a micron gauge, manifold gauge sets, an electronic leak detector, a recovery machine, recovery cylinders and nitrogen with a regulator for pressure testing.
Air conditioning proper sits alongside: a laboratory air conditioning unit such as the TAAB or a recirculating unit such as the TARB for psychrometric work, and a unit with a climatic chamber such as the TSAC or TACC where the department wants to set a room condition and measure what it takes to hold it.
Bangladesh is a party to the Montreal Protocol and is working through the phase-out of HCFCs under its national management plan, with the servicing sector as one of the main consumers. A laboratory that teaches students to vent refrigerant to atmosphere when they finish an exercise is training a practice the trade is being moved away from. Recovery equipment is therefore not an optional extra; it is part of the curriculum.
This is the commissioning problem that catches nearly every new refrigeration laboratory in Bangladesh, and it is entirely predictable. Almost every teaching rig rejects its condenser heat straight into the room. Run six or eight rigs simultaneously in a closed room in April and the room temperature climbs until the condensing pressure rises, the high pressure switches trip, and the class ends early. Departments then report an equipment fault. It is not an equipment fault.
Two things have to be settled before the room is finished. Size the room cooling against the total heat rejected by all rigs running together, not against occupancy. And provide condensate drainage: every rig with an evaporator below the dew point makes water, and in Dhaka humidity it makes a lot of it. That means a floor fall to a trapped gully, or at minimum a drip tray per rig with a routed drain rather than a bucket someone forgets to empty.
There is a third consideration for the practice bay. Brazing needs local extraction and a fire-resistant surface, and it should not be in the same corner as the refrigerant cylinders. Separate them by layout, not by a rule.
A refrigeration laboratory consumes copper tube, flare nuts, brazing rod and flux, filter driers, compressor oil, nitrogen, refrigerant and gaskets. None of it is expensive individually and all of it stops the class when it runs out. Write the annual consumable list at handover, with the commissioning engineer present, and get a recurring budget code for it. A laboratory with no consumables budget becomes a demonstration room within two years.
Size the hand tools to the assessment, not to the class. If the practical examination requires a student individually to evacuate and charge a system, then the count of vacuum pumps and manifold sets sets how many students can be examined per day. Four students sharing one gauge set during teaching is tolerable. Four students sharing one gauge set during an examination is not, and the timetable will not absorb it.
One last piece of advice that costs nothing. Insist that the supplier's commissioning includes a supervised first run of each rig with the department technician and at least two faculty members present, and that the technician performs the operations rather than watching them. A demonstration that ends with the supplier's engineer packing up is not training, and the difference shows in the second semester.