Rooftop Package Selection Guide: Capacity, T1 vs T3, Heating and Ducting
A rooftop package unit combines compressor, coil, fan and controls in a single casing on the roof or ground. It is a common choice for cinemas, sports halls, workshops, large stores and any open space without an indoor plant room. This guide draws on a recognised manufacturer's technical catalogue (Midea, 2017) as a reference for comparison; it does not replace the data sheet of the model proposed.
Capacity: 3 to 30 tons of refrigeration
The reference catalogue covers roughly 36,000 to 360,000 BTU/h, which is 3 to 30 TR, in two series. For example, a 10 TR model delivers about 35 kW cooling and a 30 TR model about 98 kW under standard test conditions. Real capacity depends on outdoor and indoor temperature, so the nominal tonnage is only a reference; read capacity from the specification table.
T1 or T3? Ambient temperature decides
T1 units are designed for a normal climate and the catalogue reports cooling operation from 10 to 46 C ambient. T3 units are for hot and tropical climates and operate up to 52 C. For hot southern Iranian cities, or roofs that run hotter than the city air, check T3. At 46 C ambient a T3 unit delivers less than its nominal capacity at 35 C; a 10 TR model drops from about 35 kW to about 29 kW. Allow for this loss in your load calculation.
Heat pump or cooling-only with an electric heater
If the building needs winter heating, there are two usual routes: a heat pump model (the catalogue reports heating operation from -9 to 24 C outdoors) or a cooling-only model with an electric heater kit (EHK). A heat pump uses less energy but loses capacity in very cold regions. An electric heater is simple and independent of outdoor temperature but draws more electricity. For cold sites, include heating electricity cost in the decision.
Duct airflow and static pressure
Each model has a set airflow; in the reference catalogue it runs from about 2,800 CFM for 6.2 TR models to 11,200 CFM for the 30 TR model. External static pressure is adjustable up to a few hundred pascals. If your ductwork is long or has thick filters, give the pressure drop to the HVAC designer so the model and fan pulley are selected correctly. Poor ductwork is the most common cause of rooftop package complaints.
Structural and environmental points
- Weight: from about 230 kg in small models to nearly 950 kg for the 25 and 30 TR models; check the roof load capacity.
- Dimensions and service space: filter, fan and electrical doors must open; leave enough room around the unit.
- Frame and supports: mount on a level steel frame, with vibration isolators where needed.
- Salty or polluted areas: the catalogue offers anti-corrosion coil treatment as an option for coastal or acidic air.
Power and controls
The reference models run on 380 to 415 V three-phase, 50 Hz. A wired controller is standard and in large buildings up to 64 units can be linked to a central controller through a network module. If you have a BMS, state it in your quote request; the article on smart controls and BMS covers it.
What to prepare for a quote
Use and floor area, occupancy, ceiling height, city and climate, heating need, duct route and static pressure, roof load limit and available power. Then use the load calculator for a first estimate and send the details from the rooftop package page to a quote request. See an example of installation in the installation gallery.
