Dehumidifier energy usage, is it worth the extra upront cost?

wittynamegoeshere

Correction, here's the info from the Toolstation spec...

20L per day (30°C / 80%)

So if they're all measured in the same way then it is a measure of its capability, and efficiency is this divided by the power, e.g. 20L / 440W = 45ml per day per Watt.

As I say, unachievable in the real world but perhaps this is a way of comparing between them?

ChaunceyGardiner

dealyboy said:

I don't know that that's true. My humidifier (condenser Electriq CD12LE) alternates between warm and cold air outflow according to the ambient temperature. User manual states heating effect neutral. 

That machine uses up to 180W, all of which ends up as heat, mostly waste heat from the compressor. Plus, it recovers some latent heat from the room's humidity.

Astria

wittynamegoeshere said:

Astria said:

wittynamegoeshere said:

I've just bought a proper one from Toolstation, not some cheapo Amazon rubbish(!).  This...

https://www.toolstation.com/midea-20l-dehumidifier/p58437

I'd recommend it.  Its smart mode is excellent, it maintains 50-odd% humidity and switches completely off when not needed, even the fan goes off, not just the compressor.  So it actually consumes a lot less than its rated power over time.

Sounds exactly like my Amazon rubbish, but more expensive, less features and draws more power

Peltier dehumidifiers cost significantly more in energy because of how insufficient they are - I suppose if you want something running 24/7 it could be better to have one of those than a motor, pump and compressor turning on and off all the time though.

Now you're getting confused and confusing.  The toolstation one is a compressor dehumidifier.  It uses more (peak) power than the one from the american tax-dodging monopoliser because it's more powerful, i.e. it does a better job.

Yes, so really they are pretty much the same thing, the toolstation one is possibly more powerful, but also more 50% more expensive. What I do know is that if I do the washing and place it near it, the amount of water pulled out of the washing is impressive to the point that it's cheaper to run than the drier and although takes longer, does a better job as the clothes are not being tumbled so are less creased to the point that most don't even need ironing. It was the price that made me take a punt on it as I probably wouldn't have gambled £150 - £200 on one. It defaults to 50-odd% humidity but you can change that from the control panel and then completely shuts down, taking less than 1W when it's idle, starting back up when the humidity has risen by approx 5%.

wittynamegoeshere

The Costway one also quotes its specs at 30C, 80% so these numbers are supposedly comparable if the maufacturers are honest (big if).  So, the dehumidifiers discussed in this thread are...

Appliances Direct: 12L/day, 172W,  = 70ml/W/day

B&Q :  Website not working but appears to be 16L/day, 300W = 53ml/W/day

Amazon: 12L/day, 185W = 65ml/W/day

Toolstation: 20L/day, 440W = 44ml/W/day

So, according to my probably flawed science, the Appliances Direct one is the most efficient and mine is the worst. 

Astria

wittynamegoeshere said:

The Costway one also quotes its specs at 30C, 80% so these numbers are supposedly comparable if the maufacturers are honest (big if).  So, the dehumidifiers discussed in this thread are...

Appliances Direct: 12L/day, 172W,  = 70ml/W/day

B&Q :  Website not working but appears to be 16L/day, 300W = 53ml/W/day

Amazon: 12L/day, 185W = 65ml/W/day

Toolstation: 20L/day, 440W = 44ml/W/day

So, according to my probably flawed science, the Appliances Direct one is the most efficient and mine is the worst. 

Are all manufacturers reporting "typical" energy usage or maximum energy usage?

Mines a bit confusing as it says "maximum usage: 185W, rated input usage: 165W", but actual usage measured by myself using a dodgy kilowatt clone is 40W on startup, and then about 145W once the compressor kicks in about 15 seconds later. Never seems to go above that as after an hour of usage, the reported kWh is reported as 0.15kWh

As all dehumidifiers use compressors and motors I can assume there would be a certain amount of surge current when each part starts up (apart from crappy peltier ones which will use the same amount regardless as they are just a small hot and cold plate)

k_man

wittynamegoeshere said:

The Costway one also quotes its specs at 30C, 80% so these numbers are supposedly comparable if the maufacturers are honest (big if).  So, the dehumidifiers discussed in this thread are...

Appliances Direct: 12L/day, 172W,  = 70ml/W/day

B&Q :  Website not working but appears to be 16L/day, 300W = 53ml/W/day

Amazon: 12L/day, 185W = 65ml/W/day

Toolstation: 20L/day, 440W = 44ml/W/day

So, according to my probably flawed science, the Appliances Direct one is the most efficient and mine is the worst. 

Compressor based dehumidifiers all should quote the rate at 80% 30C, so should be comparable.

Interesting that the efficiency (using your maths, which is what I would have done too) goes down with power rating.
The cost for speed of drying?

They do all drop off in performance as the temperature (and humidity) drops, to extracting very little (compared to the stated) at around 15C.

Dessicant dehumidifiers don't vary much by temperature (as they include a heating component), so the stated values are valid across a much wider temperature range, but as such are also not directly comparable to compressor rates.
Dessicants also generally use a lot more power than compressor ones.
This doesn't however mean they are less efficient.
In a house using peak rate electric heating for at least some of the heating, desiccant dehumidiers are often a better choice.

Would be interesting to know if a compressor, in an electric heated room is comparable with a desiccant one (e.g. 150W compressor dehumidifier + 1kW heater (on 50% the time) Vs 650W desiccant dehumidifier)

Qyburn

A decent dehumidifier should include performance data for a range of temperature/humidity combinations. I don't thing 30 degrees and 80%RH is typical for inside a house, and a dehumidifier optimised for those conditions may be less effective at lower temperatures and lower humidities. For some example specs look under "Extraction Rate Data" here ..

https://www.meaco.com/products/meacodry-arete-one-25l-dehumidifier-and-air-purifier

Something not mentioned is that if using a dehumidifier you really want to reduce through ventilation, so really it's the complete opposite of the more normal heat+ventilation regime.

EssexHebridean

For those of us regularly needing the use of dehumidifiers, 80% may not be too far off a familiar number... 

Qyburn

EssexHebridean said:

For those of us regularly needing the use of dehumidifiers, 80% may not be too far off a familiar number... 

Indeed, but presumably not 30 deg C.

Consider that warmer air carries more water at a given RH. Also a compressor dehumidifier works by condensing water onto a cold surface, which is more effective the warmer the air is. Taken together it means that it's a hell of a lot easier getting xx litres of water out of air at 30 deg C than it is at more reasonable temperatures. It's likely to be limited by compressor power with no need for any clever heat exchanger or airflow design.

I have one in the unheated workshop part of our garage, it's aiming for 55% RH and I made sure I chose a model with documented performance at the expected conditions.

wittynamegoeshere

Wow, an interesting discussion in which people disagree, ideas are exchanged and nobody got irate or offended.  Perhaps this forum is improving!

I actually have two from Toolstation, the one I linked and another from about 3 years ago that's very similar in appearance and specs but has the "Xpelair" rent-a-brandname printed on it - I suspect they're probably from the same supplier.  But I've found that the similarly powerful newer one is quieter and performs better than the (perfectly adequate) older one.  Perhaps some improvements have been made, but I suspect that dust within all those heat exchanger fins, fan and airways probably plays a big part.  Despite me regularly cleaning the washable filter, it looks like some finer dust inevitably ends up in there.  It may be due an appointment with the hoover nozzle brush.

But... I've concluded it doesn't matter, as when we're using it the windows are closed and we probably want some heating on anyway, in which case that power is becoming heat in just the same way as it would if used by a room heater.