9
OPErATING COSTS
According to AHRI guidelines (Appendix A), a 2000 ft
2
, two-person home with tight insulation requires 6.5 gallons of humidity per day to
satisfy home comfort. Both a large bypass humidifier and a TrueSTEAM HM509 can achieve this requirement, but they do so in different
ways, and with different associated costs.
Let’s first review how the large bypass evaporative humidifier operates to reach and maintain setpoint.
How large bypass humidifiers achieve the output requirement
A large bypass humidifier with a 17-GPD output rating will be able to deliver 4.25 gallons of humidity to the air during the six hours of furnace
run time.
With 4.25 gallons delivered against the daily requirement of 6.5, the large bypass humidifier must convert an additional 2.25 gallons using the
system fan without the benefit of heated air from the furnace. With fan-only operation, an evaporative humidifier’s output is typically only 50%
(0.35 gallons per hour) of what it is with the furnace running (0.71 gph). At 0.35 gph, it will take an additional 6.4 hours of fan-only operation
to make up the 2.25 gallon deficit.
As illustrated above, the air that passes through the pad will be cooled, and the furnace will use about 54,000 BTUs each day to reheat the
air. During the 12.4 hours of run time, the large bypass will consume 43.2 gallons of water, putting only 6.5 gallons into the home and 36.7
gallons go down the drain. That’s 1296 gallons of hot water used per month, with only 195 of those gallons going into the air as humidity.
When using heated water to supply the humidifier as recommended by some manufacturers, the energy used to heat all that wasted water
goes down the drain.
Using the national average utility rates, Chart 1 provides the daily operating costs for a large bypass humidifier to achieve 35% RH in a 2000
ft
2
tight home are provided. Notice the cost is significantly higher if using an electric furnace versus a gas furnace.
Natural gas heating and water heating
cost/day
Blower electrical $0.55
Water $0.26
Natural gas for humidifier $1.13
Natural gas for hot water $0.66
TOTAL $2.60
Electric heating and water heating
cost/day
Blower electrical $0.55
Water $0.26
Electric for humidifier $1.82
Electric for hot water $1.07
TOTAL $3.70
Chart 1: Large Bypass operating costs with furnace running 6 hours to convert water to vapor (cost calculation details in Appendix B)
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