Replies

1. GBA Editor
   Martin Holladay | Sep 19, 2018 08:31am | #1

   Charles,
   When engineers design a dehumidifer, I'm sure that each they consider the fan speed during the design phase, and attempt to optimize the fan speed for the most efficient dehumidification.

   If we can trust the appliance design team -- and with an Energy Star dehumidifier, I don't see any reason why we shouldn't -- the fan speed should be in the Goldilocks sweet spot -- not too high and not too low.

2. 
   walta100 | Sep 19, 2018 12:03pm | #2

   Martin I think you have misunderstood the question.

   Let me rephrase it.

   My dehumidifier has 2 setting for the fan speed. Will my dehumidifier remove more gallons of water per watt hour of electricity used when set to high or low?
   Second question
   Will my dehumidifier remove more gallons of water per day with the fan set on high or low?

   Walta

   
3. Expert Member
   Peter Engle | Sep 19, 2018 12:27pm | #3

   Walta,

   I've never seen any data on this. I suspect the answer is that you get more dehumidification per watt hour on the lower fan speed, but there are some factors that could make that not the case. The manufacturer might have more specific data somewhere in their information.

   Most dehumidifiers will remove more gallons per day on the high fan setting than the low setting, but I think this is more related to better circulation of the air in the space. If the space is small and open, it might remove the same amount of water on either speed.

   I haven't seen any dehumidifiers where the refrigeration coils and compressor modulate in response to humidity and/or fan speed, and it is the capacity of the coils that determines the majority of the power use and water removal capacity.

   This seems like a good opportunity for an experiment. if you've got a kill-a-watt meter, hook it up and try it. Measure the power used for a couple of days in both modes and the water drained from it, and you will have your answer. Let us know how it comes out.....

4. 
   charles3 | Sep 19, 2018 04:03pm | #4

   Walter understands my question. In my case 3 fan speeds are possible.

5. 
   AlanB4 | Sep 19, 2018 05:50pm | #5

   I have also wondered which speed is more efficient but i don't know.
   Also mine is not an ECM motor, using the lower speed saves something like 4W on my energy star unit while the airflow may be half or less. So i just use the highest speed assuming the highest throughput over the cold coils will get the most moisture.

6. Expert Member
   BILL WICHERS | Sep 19, 2018 06:07pm | #6

   Hmm. Interesting question. I would guess (I’ve never really thought about this before even during the design of large cooling plants) that dew point may effect the optimal fan speed, but the design of the unit may negate that at least partially. All a dehumidifier is is a small air conditioner that uses the evaporator coil to make a temperature drop to condense out water from the air stream passing over it. I’m going to guess that the small units put the condenser ahead of the evaporator to maximize that temperature drop, but I’ve never looked. Large units do sometimes preheat the air ahead of the cold surface to allow dehumidification to occur under conditions that otherwise wouldn’t allow it.

   I think you’re best bet is to setup a simple experiment: get a kill-a-watt meter, run your dehumidifier for 24 hours for each of the three fan speeds (making this a 72 house expieriment), keep track of the volume of water produced, the kWh consumed, and the ambient temperature and humidity level for each run. Ideally you want to conduct the experiment with constant temperature and humidity levels so that you’re only measuring power consumed per unit of water removed from the air at each fan speed.

   If you do the experiment, please share your results!

   Bill

1. 
   AlanB4 | Sep 19, 2018 06:59pm | #7

   I thought about experimenting but the humidity level tracks with changes in outdoor temperature and outdoor humidity so i can't do it.
   Garbage in, garbage out.

1. Expert Member
   BILL WICHERS | Sep 19, 2018 08:58pm | #8

   If you have a few consistent days, a 24 hour cycle will average out the variance within each individual 24 hour period so you’ll still get good results. If your swings are really severe between days, you could shorten the test cycle but then you'll get less averaging and thus a bit less accuracy in your results.

   My guess is that there probably isn’t a huge difference except for maybe at the extremes of its operating range (really humid or really hot or cold). The effect of the fan circulating air better in the space may be enough to swamp any change in efficiency of the actual dehumidification process too. The short answer is any cost savings to operate at one fan speed over another is probably pretty minimal.

   Bill