Rooftop Units (RTU)

Rooftop Units (RTUs): A quick overview Rooftop units (RTUs) are self-contained heating and cooling systems installed on the roof of commercial and some multifamily buildings. They are designed to condition the indoor space without taking up interior space, making them a popular choice for small to mid-sized facilities such as retail shops, offices, schools, and small hospitals. What is an RTU and how does it work? - A packaged system: An RTU combines a compressor, condenser, evaporator, and fan in a single weatherproof cabinet. Some models also include a gas-fired burner for heating or an electric heating coil. - Ducted air delivery: Conditioned air is distributed through ductwork to supply and return air within the building. The RTU can also bring in a controlled amount of outdoor air for ventilation. - Controls and sequencing: RTUs typically use a thermostat or building automation system to control cooling/heating setpoints, fan speeds, and, in many cases, outdoor air dampers and economizers. - Economizers and ventilation: Many RTUs include economizers that use outside air for cooling when conditions are favorable, saving energy. Some units also offer staged or variable-speed components for better comfort and efficiency. Types and configurations - Single-zone vs multi-zone: Single-zone RTUs serve one HVAC zone, while multi-zone RTUs are designed to condition multiple spaces with appropriate dampers and controls. - Heating options: RTUs may use electric resistance heating, gas heating, or heat pumps (for heating and cooling in one unit). Some units provide hot water or steam coils as an alternative. - Air handling: RTUs can be configured for air-cooled or water-source cooling, depending on climate and building design. Most rooftop units are air-cooled and self-contained. - Size and capacity: RTUs come in a range of capacities, typically from about 3 to 25 tons or more. The right size depends on the building’s load, occupancy, insulation, and local climate. Advantages of RTUs - Rapid deployment: Factory-assembled and tested, RTUs can be installed relatively quickly with curb adapters and duct connections. - Space savings: By placing the system on the roof, interior floor space is preserved for occupancy and use. - Centralized equipment: A single piece of equipment can serve multiple zones, simplifying maintenance and management in some layouts. - Simpler retrofits: In existing buildings with limited mechanical rooms, RTUs can be a practical retrofit option. Considerations and potential drawbacks - Roof impact: Weight, vibration, and weathering require a proper structural assessment and durable mounting. Roof integrity and drainage must be addressed. - Energy efficiency: While modern RTUs can be energy-efficient, some older models may lag behind high-efficiency split systems or dedicated outdoor air systems. Proper sizing and controls are crucial. - Noise: Outdoor unit noise can be a concern for nearby tenants or building occupants. Proper placement and acoustic considerations help mitigate this. - Maintenance access: Regular service requires safe rooftop access and safety procedures for technicians. Choosing and installing an RTU - Proper sizing: A detailed load calculation (including climate, envelope, occupancy, equipment) is essential. Oversized or undersized units waste energy and reduce comfort. - Quality installation: A licensed HVAC contractor should install the unit, establish duct connections, curb sealing, electrical service, and refrigerant piping according to local codes. - Controls and integration: Align RTU controls with the building management system (if present) and ensure appropriate outdoor air ventilation, economizer operation, and staging. - Maintenance plan: Regular filter changes, coil cleaning, refrigerant checks, burner/service for gas heating, and seasonal startup/shutdown inspections extend life and efficiency. Bottom line Rooftop units offer a compact, relatively quick solution for heating and cooling in many small to mid-sized commercial buildings. When properly sized, installed, and maintained, RTUs can provide reliable comfort, simplified space management, and scalable performance for a range of applications. If you’d like, tell me the type of building, climate, and any ventilation requirements, and I can tailor a concise RTU overview or a checklist for selecting and evaluating units.