Saturday, September 08, 2018

dehumidifier 2

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My new small dehumidifier has been working hard in the basement using almost 94 kWhr in August!

Working hard and getting results but with high electric usage I hadn't anticipated yet less than I calculate.

Results: The freezer has no condensation. The puddle that once lived under the old freezer is long gone and the floor is desert dry. The basement seems slightly warmer and smells fresher.

The energy graph for the dehumidifier's plug looks like this, from the Itead EWeLink app. 93 kWhr for the month of August! Or 2-3 kWhr per day. I haven't loaded the tiered prices by time of day so there is no dollar amount.

This is a huge chunk (about a quarter) of my monthly usage of 355 kWh for August. Hydro One nags me about it on my August bill! Your usage has increased by 38% compared to the same period last year! They are right! It is because of this dehumidifier.

Another effect is an increase in both On-Peak and Mid-Peak usage since I am not controlling the dehumidifier for time of day. It runs when it wants to. I'd like to see how it behaves without that added complexity for now.

I am visiting the basement several times a day because of this dehumidifier. Good stair climbing exercise. It will have to be made more automatic but I am enjoying seeing the result of it's work.

I am surprised at the amount of water produced even at the the relatively "low" humidity setting of 70%RH. I have to carry a bucket a day out of the basement or it stops running. I can empty the machine into the bucket three times but then I have to carry it out.

The dehumidifier uses 400 watts when it is running and it runs a lot, even at 70%RH.

This data [click to enlarge] shows the outlet temperature of the Danby dehumidifier over one week Aug 4 to Aug 12 from an Elitech RC-4 temperature data recorder. The black areas show when the dehumidifier is running. When it runs, the instantaneous usage shown by the Itead is 400 watts.

When not running, usage is 0.58 watts. The longer gaps of not running are when the internal reservoir fills and it shuts off because I have not emptied it.

Towards the right end of the chart is when things are working more of less properly, the bucket is getting emptied and the machine is catching up with it's 70%RH set point. If I try to set lower, say 60%, it runs more or less continuously until full. I cannot separately measure RH% of the basement air. I should have a way to do that.

Heating season is starting so I expect that the furnace will soon keep the basement dry. The dehumidifier should work less and I expect I will retire it for the winter.

The new furnace (which I have yet to tell you about) has a condensate pump so I might connect the dehumidifier into that pump. The furnace and the dehumidifier should run in alternate seasons. I have a spare of the same pump.

Thanks for your interest

George Plhak
Lions Head, Ontario, Canada

An update on the energy required to operate my dehumidifier:

The energy used by the dehumidifier is 93kWhr for August as taken from the Itead S31.
93kWhr is equivalent to 334800 KJ (using the Google unit converter)
I was not so careful about measuring the water but I'll use an average of one bucket per day. For the weight of this average bucket I'll use 8.4 kg H2O per bucket as before although the last bucket was destroyed and the new one is very slightly smaller. August has 31 days so 31x8.4= 260.4 kg H2O was produced in August by the dehumidifier at a "cost" of 93kWhrs.
Recall: The Latent Heat of Vaporization - the input energy required to change the state from liquid/vapor at a constant temperature - for water 2260 KJ/kg.
The energy to condense 260.4kg of H2O as required by physics would be 260.4x2260= 588504 KJ
I used only about half that amount so something is not right.
Your comments/suggestions are appreciated - what am I doing wrong?

A homework type help reference

INDEX to the series


George Plhak said...

Sarcastic but useful video about dehumidifiers as sources of drinking water, solar/wind powered or otherwise, to do with a $1.5M X-Prize:

George Plhak said...
"More than 400,000 dehumidifiers recalled in Canada for fire risk"
Fortunately my Danby is not on the list.