80/20 Pros & Cons

 

Direct Fired Recirculation 80/20 Heating Unit 

 

Pros of 80/20 units

  1. Less units – less gas/electric piping – lower day one equipment cost.
  2. Meets the .06 cfm p/sq ft code

Cons of 80/20 units

  1. With a direct fired burner, combustion products are directly inputted into the interior of a facility, i.e. on a 1,000,000 btu/hr burner this will amount to 5.7 gallons of water vapor p/hour.

With this quantity of water vapor, the danger of excessive condensation on the wall is possible which would probably cause mold.

  1. Due to the positive pressure in the units to meet the .06 cfm sq ft code during occupancy and unoccupied operations, this input cfm coming into the facility through these units can over inflate TPO roof systems in facilities, which could cause the roof to condensate between the roof and insulation panels, causing saturation of the roof insulation.   This condition would void the TPO roof warranty.
  2. Even though the 80/20 direct fired burner has a 92% combustion efficiency rating, the majority of units are shipped 60/40 (60% return air and 40% outside air) in order to reduce the size of the units. The unit fan runs continuously when outside air temperature is below outside air set point, which continually brings in 20% to 40% cold outside air. By continually operating such units, the season efficiency will drop to 52% combustion efficiency.  This is a key point that demonstrates the excessive operating cost of this system.
  3. If there are multiple tenants in a spec space and 80/20 units are installed, a design change is required to accommodate the needs of the various tenants.