2009-02-11 16:12:38 UTC
For those of you that followed any of the discussions here about
whether using hot water versus cold water in a furnace humidifier
makes a difference in the amount of water that evaporates, I did the
actual test on my unit. Here's exactly how I did it and the results.
The unit is an Aprilaire 700A installed on a gas forced air furnace.
To do the test, I made sure to keep everything constant except the
incoming water temp. My unit is connected to hot water, so to change
the water temp, I turned off the water heater and used up the hot
water through normal household use. I got the hot water tank temp
down to 51F. The house humidity was 37% at the time of the test and
the temp was 67F. I routed the humdifier drain hose to a location
that I could put a gallon container under it and remove it without
disturbing the hose. I placed a temporary container under the running
hose to catch the water. I then started the furnace with the
humidifier set high enough to be running constantly. I let the
system stabilize for 5 mins to get to a steady-state. Then I quickly
replaced the temporary container with another empty gallon container
and started a stop watch. During the 5 min period, I also measured
the temp of the water exiting the drain hose. At precisely 5 mins, I
removed the container and used a measuring cup to determine the volume
of water. I also shut down the furnace.
Then, I fired the water heater back up and let it run to get the water
temp to a higher temp to see what happens with medium temp warm
water. I then turned the water heater off again. That temp turned
out to be 102F. I then repeated the process of starting the furnace,
letting it run for 5 mins to stabilize, then measuring the drain water
output for another 5 minutes. Next, I fired the water heater up
again and allowed it to come up to normal temperture. And again, I
turned on the furnace, let it stabilize for 5 mins, then measured the
water output for 5 mins.
Finally, I measured the amount of incoming water into the humidifier
by connecting the drain hose directly to the water tube where it would
normally drop onto the distribution tray at the top of the panel.
Here are the results:
Temp Water collected in 5 mins Temp of Water Exiting Drain Hose
51F 66.5 Oz 78.4F
102 61.5 78.0
135 58.0 79.2
Water collected during 5 mins direct from tube at top of humidifier,
ie incoming flow: 73.0 Oz
Now, doing the math, the amount of water evaporated during the 5 mins:
51F 73 - 66.5 = 6.5 Oz
102 73 - 61.5 = 11.5
135 73 - 58.0 = 15.0
Using hot water more than doubled the output. Or in percentage terms,
using 102F water resulted in 77% MORE water being evaporated compared
to 51F water. Using 135F water resulted in 131% MORE water being
evaporated compared to 51F water.
So, there you have it folks. This was IMO a very reasonable and
realistic mesurement and confirms why Aprilaire says you get higher
output with hot water.