To provide realistic measurement of solar potential, we estimate the rooftop mechanical systems on roofs that would block solar panel placement. The number of rooftop units needed is estimated based on the building's use type and characteristics. This is a simplified approach to estimate the number, dimensions, and locations of rooftop units, using the most common placement logic. It is not an exact representation of your roof.
Dimensions of a 5-ton unit
The methodology uses a typical 5-ton HVAC unit’s dimensions are rounded up to the nearest whole number using the Precedent® Rooftop Units (5-Ton Precedent™ - Standard Efficiency):
Width: 5 ft
Length: 8 ft
Height: 4 ft
Clearance on the sides of width and length: 3 ft
Clearance for height: 6 ft
Service floor area per unit
The floor area served by a typical 5-ton HVAC unit is 3,000 sqft building floor areas (How Much Can a 5-Ton AC Unit Cool?).
Two most common types of placement
Distributed placement is more common for buildings with large roofs and buildings with less investment in allocating rooftop mechanical systems closer together.
Centralized placement is more common for buildings with smaller roofs and buildings invested more on moving the rooftop mechanical systems closer together.
Methodology
For estimating number of 5-ton units needed:
Count of rooftop 5-ton units = Rounded up (Total floor area / 3,000 sqft)
Dimensions and size of an 5-ton unit in distributed placement: 5 ft x 8 ft
Dimensions of RTUs in a centralized placement: (5 ft + spacing) x (8 ft + spacing) x units count
This approach is an oversimplified estimation, which works best for buildings with less or equal to 3 floors. There are more factors to consider when sizing and locating rooftop units for buildings with more than 3 floors. The choice of distributed or centralized placement and adjustments are decided and applied based on the total floor area, number of floors and roof size.
Two exceptions:
Buildings with more than 7 floors and a footprint size smaller than 500 sqft, and any buildings with more than 20 floors): we assume that the majority of roof space is occupied by mechanical systems and elevator sheds, and there will be no solar panels placed on these buildings.
Buildings with a GFA less or equal to 2,000 sqft: we assume the entire roof area will be available for solar panel placement (with setbacks and access paths).
For example:
Building A has 3 floors, and its footprint/roof size is 5,000 sqft. The total floor area for the building will be 5,000 sqft x 3 floors = 15,000 sqft.
Count of rooftop 5-ton units = Rounded up (15,000 sqft / 3,000 sqft) = 5
The building falls under the category with distributed placement, so the area for each of the 5 rooftop units will be 5 ft x 8 ft and is placed at different locations on the roof.
Building B has 5 floors, and its footprint/roof size is 1,000 sqft. The total floor area for the building will be 1,000 sqft x 5 floors = 5,000 sqft.
Count of rooftop 5-ton units = Rounded up (5,000 sqft / 3,000 sqft) = 2
The building falls under the category with centralized placement, so the dimensions for the area representing rooftop units placed closer together will be roughly (5 ft + 3ft) x (8 ft + 3ft) x 2