Retrofitting an Existing Rooftop HVAC System with Economizer
Most packaged units RTUs have an optional economizer add-on package, which can be installed when the system is new or may be added to the system as a retrofit at a later date. Retrofitting old economizer control systems to make use of electronic controls is a simple, easy and straightforward operation that can also improve a building’s energy performance.
Caution: An economizer system needs to be designed with adequate relief air so that when outside air is drawn into the building, the excess air is relieved. Without an adequate relief system, the building can become overpressurized, causing exterior doors to stand open and air to whistle through exterior doors and elevator doors. There are three common types of relief systems that can be considered when retrofitting an RTU with an economizer: relief dampers, relief fans and return fans.
Features
CASING&STRUCTURE
The casing is made of zinc coated galvanised steel sheets. It is further treated with an electrostatic powder coat then over baked to provide a weather resistant finish to suit the harsh climate. The screws are also zinc plated to improved product durability.
COMPRESSOR
High efficiency scroll type compressor is hermetically sealed, quiet running and supported on rubber mounts to minimise vibration. All compressors are provided with an internal overload protection, and incorporate crankcase heater for smooth start-up under any conditions.
CONDENSER AND EVAPORATOR
The condenser and evaporator coils are manufactured from seamless copper tubes mechanically bonded to blue hydrophilic aluminium fins to ensure optimum heat transfer. The shoulder of each fin adjoins the shoulder of the adjacent fin, completely encasing the copper tubes for maximum heat transfer. The generously sized coils provide ample capacity under all normal operating conditions. All coils are pressure tested to 450Psi at the factory to avoid leakage. To improve corrosion resistance, a hydrophilic Gold Fin is provided as optional.
CONDENSER FAN AND MOTOR
Direct driven propeller axial fans are used for maximum condensing efficiency.
EVAPORATOR FAN AND MOTOR
Fans are of the centrifugal type that is designed for maximum efficiency for uniform air distribution. Traditional belt driven or EC plug-fan.
INSULATION
Ripple type acoustic insulation for compressor section, low noise. To prevent the likelihood of condensation occurring the unit is equipped with 10mm Polyethylene panel insulation for coil & fan section.
SAFETY
Electric panel consists of breakers and contactors for compressors and fan motors, phase sequence relay and other necessary protection devices for the main components. All electric parts are Schneider Electric brand.
*SIEMENS PLC controller is optional.*Main power supply breaker is optional.
EASY INSTALLATION AND MAINTENANCE
The base beams are fixed and provide a rigid foundation for the entire unit. The beam has forklift slots or rigging holes for easy handling. To keep installation as hassle-free as possible, Sendo Roof Top Units are fully factory assembled, tested and charged with R410A refrigerant. Only ductwork and external wiring connections are required to make the units completely operable ensuring rapid, low-cost installation. For ease of commissioning and maintenance, Sendo Rooftop Packaged Air Conditioners include easy access to the electrical cabinet and major refrigeration components. The unit provides external pressure gauge for convenient and fast checking system pressure without removing the panel. If the unit is in running with abnormal operation, the controller will show the error code for easy troubleshooting.
OPTIONAL ACCESSORIES
Tropical climate T3 application
Optional supply / return air configuration
Optional golden condenser & evaporator for some area need special anti-corrosion
Economizer/Free cooling
Additional water heating coil
Additional electric heater
Heat recovery
100% Full fresh air
Optional high level filter
Optional precision temperature & humidity control
Specification
| Model SRT-ST1HXXA(BD) | 12 | 15 | 20 | 25 | 30 | 35 | 45 | 50 | 60 | 70 | 90 | 100 | 120 | 140 | 150 | 180 | 200 | 300 | 400 |
| Cooling | Capacity | kW | 12 | 15.2 | 17.5 | 24 | 30.3 | 35.6 | 44.5 | 50 | 60 | 70 | 90 | 105 | 120 | 140 | 150 | 180 | 210 | 298 | 392 |
| Power Input | kW | 4.1 | 5.3 | 5.5 | 8.8 | 11.3 | 12.3 | 17.0 | 19.5 | 22.8 | 26.7 | 32.9 | 39.7 | 45.1 | 55.7 | 55.1 | 69.9 | 83 | 106.7 | 140.2 |
| Heating | Capacity | kW | 13.2 | 16.6 | 18.4 | 26.5 | 33.3 | 37.7 | 48.7 | 54.3 | 64 | 75.4 | 96.2 | 113.2 | 128.3 | 150 | 159.2 | 192.5 | 226 | 318 | 414 |
| Power Input | kW | 3.8 | 4.8 | 5.1 | 8.2 | 10.4 | 11.3 | 15.6 | 18 | 21 | 24.8 | 30.4 | 36.7 | 41.7 | 51.8 | 51.5 | 64.8 | 77 | 100 | 133.8 |
| Refrigerant | Type | R410A |
| Compressor | Type | Scroll |
| Condenser | Type | Copper Tubes Mechanically Expanded into Blue Hydrophilic Aluminum Fins |
| Condenser Fan | Type | Axial / Direct |
| Evaporator | Type | Copper Tubes Mechanically Expanded into Blue Hydrophilic Aluminum Fins |
| Evaporator Fan | Fan | Type | Belt-Driven Centrifugal Fans |
| Supply Airflow | m3/h | 2100 | 2600 | 3400 | 4100 | 5200 | 6300 | 7600 | 8500 | 10900 | 12500 | 16000 | 19500 | 21000 | 25000 | 26000 | 32000 | 38000 | 54000 | 67000 |
| ESP | Pa | 100 | 100 | 100 | 200 | 200 | 250 | 250 | 250 | 300 | 300 | 300 | 300 | 400 | 400 | 450 | 500 | 500 | 500 | 500 |
| Filter | Standard | Type | G3 Aluminium Filter / Washable |
| Sound Level | dB(A) | 67 | 67 | 68 | 71 | 72 | 72 | 73 | 73 | 73 | 74 | 74 | 75 | 76 | 79 | 79 | 80 | 80 | 82 | 86 |
* Performance values refer to the following conditions:
Cooling: room air temperature 27.0°C DB RH 50%, ambient air temperature 35°C;
Heating: room air temperature 21.0°C DB, ambient air temperature 7°C DB / 6°C WB.
** Noise level measured by adopting average value in the noise lab with background noise of 25 dB(A), at a distance of 1.5m high fan speed.
***Specifications are subject to change without prior notice for SENDO product improvement.
Workshop
Improved energy efficiency through new technology
Sendo contribution to combat rising energy costs and global warming is to design innovative, efficient and dependable HVAC products, while providing best comfort and air quality.
Benefits To Building Owners - One of the main reasons to use an economizer is to save money on electricity. The longer outside air can be used for cooling, the longer the compressor can remain off. Another benefit is the economizer actually can extend the life of the equipment - provided the Rooftop Cooling System is maintained properly. For questions or comments on Tech Basics, you may contact Sendo at sales(at)sendoac.com
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