Field Controls HHSC+, User Manual, Page: 9 / 20

page 9
EXAMPLE: MEETING ASHRAE 62.2 2010 with given conditions:
• 2000 square foot home (conditioned space) with 3 bedrooms
• 140 cfm of fresh air flow as measured in the fresh air duct while system is operating
SETTING THE VENTILATION % TO MEET VENTILATION CODES:
1. Determine the required constant ventilation flow rate from table: 50 cfm.
2. Measure the actual flow rate through the fresh air duct using a flow hood, anemometer, or Pitot tube
and manometer, with the HVAC fan running on lowest speed and the FAD damper open (temporarily
jumper AUX-IN to R terminal, or activate remote override device if connected): Example: 140 cfm
measured.
3. Calculate the Ventilation %: Divide the constant flow rate from the table by the actual fresh air flow rate
measured and multiply by 100%:
Ventilation % = 50 ÷ 140 x 100% = 36% (rounding up)
For this example, setting the Ventilation % at 36% will ensure ventilation meeting ASHRAE 62.2, regardless
of any other settings, as long as the HHSC+ system is set to on, and the inhibit feature is not active. Setting
Ventilation % to a higher value will raise the ventilation above the minimum as required by ASHRAE 62.2
To meet other ventilation codes, substitute the alternately required constant ventilation rate in cfm from step
1 into the calculation in step 3.
If the actual flow rate in the fresh air duct cannot be directly measured, the following table may be used to
estimate the Ventilate % setting required for adequate ventilation. Note: using these values will not ensure
ventilation meeting any particular code.