How do you calculate heating savings with reduced CFM
How do you calculate heating savings with reduced CFM
(OP)
Problem: Bldg has toilet room exhaust fans operating 24 hrs per day year round. We will be time clocking the fans to run only 8 hours per day instead of 24 hours per day, and to have the fans run only 5 days per week instead of 7 days per week. What is the energy savings of not having to heat-up the exhausted air during the heating season?
Basic equation for the annual 24 x 7 operation heat loss would be BTU/Yr = CFM x DD (heating season only) x 24 x 1.08
How do you adjust the DD component for the reduced fan operation?
Basic equation for the annual 24 x 7 operation heat loss would be BTU/Yr = CFM x DD (heating season only) x 24 x 1.08
How do you adjust the DD component for the reduced fan operation?





RE: How do you calculate heating savings with reduced CFM
RE: How do you calculate heating savings with reduced CFM
RE: How do you calculate heating savings with reduced CFM
RE: How do you calculate heating savings with reduced CFM
Download the hourly bin data into spreadsheet. Delete all rows for hours of operation. Delete all rows where outside air is greater than or equal to design heating temperature. Subtract design temperaure (copy and paste) for all remaining rows. Muliply each row by 1.08. Multiply each row by CFM of exhuast avoided. Sum up the column and that will give you the yearly Btu savings.
I'd recommend first making sure that the exhaust isn't necessary for any air balance, and that supply is rolled back commensurate with exhaust. If you are not cutting back on supply you are not saving money by reducing exhaust.
As an alternative, you could close the bathrooms, turn off the fans and lights, and have everyone wear astronaut pants.
If you are going to include an occupancy sensor for lighting, I would recommend putting it on the outside of the stall. That way anyone staying too long has to wave their hand under the stall to get the lights back on, or use a "wide stance". After a bit of time, walking in and seeing the hands and feet waving and stomping might be enough to make people wait until they go home (or wear astronaut pants) and you can save on water and sewer, also.
RE: How do you calculate heating savings with reduced CFM
RE: How do you calculate heating savings with reduced CFM
RE: How do you calculate heating savings with reduced CFM
RE: How do you calculate heating savings with reduced CFM
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RE: How do you calculate heating savings with reduced CFM
RE: How do you calculate heating savings with reduced CFM
They only way to do it is with a weather file for your location.