What Key Parameters Should Be Prioritized When Selecting Rooftop Units?

What Key Parameters Should Be Prioritized When Selecting Rooftop Units?

The core principle for selecting rooftop units is “precisely matching the load + adapting to the rooftop environment.” Six key parameters require close attention, and decisions must be made by comprehensively evaluating the building's purpose, area, and climate conditions to avoid oversizing that wastes energy or undersizing that leads to inadequate performance.

First is the cooling and heating load, which forms the foundation of selection. This must account for: - Building orientation (south-facing rooms receive stronger solar radiation, requiring a 10%-15% load increase) - Insulation performance (if exterior wall insulation thickness is below 50mm, load should be adjusted upward by 8%-12%) - Occupancy density (calculated at 100-150W per person for office buildings, shopping malls at 200-250W/person), equipment heat generation (e.g., data centers require additional server cooling at 50-100W/㎡), and other factors. Accurate values are derived using professional load calculation software (e.g., Hongye Load Calculation, Tianzhen HVAC). Then, select the rooftop unit's rated cooling/heating capacity based on “load × 1.1-1.2 safety factor.” heating capacity. For example, a 1000㎡ office building with a calculated load of 120kW should select a rooftop unit rated at 132-144kW.

Next is airflow volume and static pressure. The airflow volume of rooftop units directly impacts indoor air delivery effectiveness and must be determined based on “air changes per hour”: Office buildings typically require 4-6 air changes per hour, while shopping malls require 6-8 air changes per hour. For instance, a 800㎡ shopping mall with a ceiling height of 3m would require an airflow volume of 800 × 3 × (6-8) = 14,400 m³/h. hours, while shopping malls require 6-8 times/hour. For example, an 800m² mall with a 3m ceiling height requires an airflow of 800×3×(6-8) = 14,400-19,200m³/h. Static pressure must account for duct length and resistance. If total duct length exceeds 20m or contains multiple elbows (each 90° elbow adds ~50Pa resistance), select medium-to-high static pressure models (static pressure ≥300Pa) to prevent insufficient airflow at terminal outlets.

Additionally, energy efficiency ratios (EER/COP) directly impact long-term energy costs. Under China's energy efficiency standards, rooftop units require ≥3.0 EER (Class 1 efficiency) for cooling and ≥3.2 COP (Class 1 efficiency) for heating. In hot-summer/cold-winter regions (e.g., Yangtze River Basin), prioritize Class 1 efficiency models. Though initial investment is 5%-8% higher, annual electricity costs can be reduced by 15%-20%. In severely cold regions (e.g., Northeast China), if winter heating relies on electric auxiliary heating, pay close attention to the auxiliary heating power to avoid excessively high total energy consumption.

Additionally, installation dimensions and load-bearing capacity are critical considerations. Rooftop units must be placed on load-bearing beams or precast concrete foundations. During selection, verify that the unit's length, width, and height dimensions (e.g., a common 100kW rooftop unit measures approximately 3.5m × 1.8m × 2.2m) fit within the reserved rooftop space. simultaneously, the unit's weight (approximately 800-1200kg including the foundation) must match the roof's load-bearing capacity (residential building roofs typically have a live load capacity of 2.0kN/㎡, or 200kg/㎡; ensure the foundation area is ≥ (unit weight / 200kg/㎡) to prevent roof cracking.

Finally, climate adaptability: - In high-temperature regions, select “high-temperature” rooftop units to ensure normal cooling at ambient temperatures up to 45°C. - In cold regions, choose models with “low-temperature high-heat” capabilities (e.g., with jet injection technology) to guarantee heating capacity does not degrade by more than 20% at -15°C. Coastal areas require corrosion-resistant units (galvanized steel casing + fluorocarbon coating, 316L stainless steel heat exchanger) to withstand salt-laden sea air erosion.