Trotec 75S vs 100S dehumidifier at 20C 60% RH and desiccant comparison

About a year ago, my De’Longhi DES16E stopped working.  When it failed, it would run for 2 to 3 minutes, then cut out with the display completely blank for about 15 minutes and then cycle on like this.  It was just two years old, but out of warranty.  At this point, I debated on whether to go with a desiccant model or another compressor, but in the end decided to go with a larger compressor model after weighting the pros and cons:

Desiccant pros over Compressor:

  • Quieter running on low setting.
  • Sustained extraction even at low temperature.
  • Adds background heat.
  • Half weight of equivalent capacity compressor model.

Compressor pros over desiccant:

  • More energy efficient, particularly above 20C.
  • Usually larger water containers, some over 4 litres.
  • Cooler running, better for warm sticky days.

Desiccant dehumidifiers generally have excellent reviews for their water extraction capability and one thing I liked is that their water extraction rate is based on 20C 60% RH, which is very similar to the readings throughout our house for a good portion of the year.  Most compressor models are only rated at 30C 80% (or higher), which is generally several times the extraction rate of typical realworld conditions, at least in Ireland and the UK.

On the other hand, there were some negative reviews over their energy efficiency and about them adding too much heat to the room in the summer.  So in the end I decided to go for a powerful compressor model, as our house is generally 20C or higher all year around and figured that with a powerful compressor model, I could run it on a timer or while at work if too noisy.  I went with the Trotec 100S based on my experience with a Trotec 75S at the other end of the house.  They are mainly operated in alternation – the Trotec 75S while asleep and the Trotec 100S during the day.  So their noise is not an issue.

As there is very little information on how a domestic dehumidifier performs at 20C, I decided I’ll try my own experiment.  Due to the high extraction rate of the Trotec 100S, I ran into a problem as the humidity rate would drop too quickly to make any reasonably accurate measurement.  The humidity would drop over 5% in an hour no matter where it was positioned.  Just like how compressor dehumidifiers don’t extract much water at low temperatures, the water extraction rate also quickly drops off as the humidity level falls below 60%.  So although the humidity level may settle around 50% after a few hours of continuous operation, a test at 20C 50% would give a much lower extraction rate than a test at 20C 60% and thus not give a useful comparison against a desiccant model.

Performance testing

Due to a drainage problem behind our house, water ran into our garage a few times over the spring.   When I ran the larger 100S dehumidifier in the garage, I noticed something interesting – Over the course of the day, the temperature reached just over 20C and the humidity fell to 68%.  This gave me an idea – Put the 75S in alongside it.  After about an hour, the temperature reached 21C and the humidity level continued dropping about 2 percentage points an hour.

As the evening approached, the garage temperature fell slightly and gave nearly ideal conditions to run a test.  With the temperature just below 21C and humidity at 59%, I switched both dehumidifiers off for 10 minutes to allow any remaining water to drip into their buckets and emptied them.  Before I switched them on, I plugged each into a separate energy monitor and used a stopwatch to time 1 hour.  I used a Trotec hydrometer (one came with each dehumidifier), placed away from both machines so that it was not in any air flow.  When I previously tested two Trotec hydrometers side by side, they showed the same RH reading and a temperature 0.3C apart, so they seem to be accurate.  Normally they are sold for around €20 each, so they likely have better sensors than those cheap €5 models sold on eBay and Amazon.

In just the 10 minutes they were off the humidity level rose to 63%, but once I switched them on the humidity fell back to 61% within 5 minutes and to 59% after about 20 minutes.  After about 40 minutes, the humidity fell to 58%, so I switched on a high velocity fan at the other end of the garage to try to stop the level falling further.  The humidity level rose to 59% and stayed at that for the remainder of the test.  Throughout the test, the temperature ranged between 20.6C and 20.8C.  Once switched off, I waited 10 minutes to allow any remaining water to drip into their buckets.  To weigh their contents, I used a digital scale and weighed each container before and after emptying. 1g of water is 1ml.

Test results at roughly 59% 20.7C for 1 hour

Trotec 100S:

  • Water collected: 474g
  • Energy consumption: 0.45kWh
  • Energy efficiency: 1.05L/kWh
  • =>24 Hour rate: 11.38L

Trotec 75S (high fan):

  • Water collected: 321g
  • Energy consumption: 0.29kWh
  • Energy efficiency: 1.11L/kWh
  • =>24 Hour rate: 7.7L

What’s interesting about the 75S model is that its effective 24 hour rate is roughly that of a desiccant model for the same environment.  However, note the difference in wattage.  The 8 litre rating of most desiccant models is based on running them on high and most desiccant machines use 600 to 700 watts on high, roughly the equivalent of running these two machines simultaneously!

So for those planning on running a dehumidifier where the temperature is generally above 20C, it’s well worth considering a compressor model, even if it means running it on a timer.

Note that although the 75S seems more efficient, it does have a few drawbacks over the 100S model.  Its fan runs continuously (30 watts or 0.72kWh/day continuously), cycles several times an hour and doesn’t have hot gas defrost (to work effectively below 16C).  So what we do is run the 75S model in continuous mode on a timer to come on a few times a day.  For our house, 6 hours a day keeps the humidity within a 55% to 60% range for most of the year.  The 100S model turns its fan on only while dehumidifying and typically cycles every hour or two, similar to a fridge.

Although I went for Trotec machines, a few other compressor models worth looking at are the Meaco Platinum and the Olimpia Splendid 20+ litre ranges, which both claim to have high energy efficiency rates and one of the few brands to reveal their performance ratings at 26C 60%.  I have never used either, so can’t comment on their actual performance or reliability.

Update 15th February 2017 – Over the past two years the Trotec 75 S gradually got noisier to the point where it was clearly audible across the house when trying to sleep at night.  The vibration mainly came from its water tank, as the vibration would stop when pushing in at the water tank.  However, after having little luck trying to stop the vibration noise, I decided to sell it.  Then again, we had this dehumidifier for 4 and a half years and there was no noticeable deterioration in its performance despite being in nearly everyday use since purchase.  I have now purchased a Meaco Platinum 20, so may publish a review on it at a later stage.

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