Electric dryer power reduction ???

[WindWizard]

I'm going to stick with the physics and thermo on this one. It is still going to take the same energy to effect the phase change of liquid water to water vapor. I would argue that dropping the power applied to the heating element by a factor of two will increase the drying time by a factor of two. That will cause the drum motor to run twice as long, and if it burns 500W, then the overall power consumption to dry the same clothes with the same water content will increase by 500W. The peak demand will drop by half the heating element wattage.

I will agree and disagree on this. My thought is that with a full load of wet clothes the heating element will not come up to temperature and so the temperature will be lower causing the drum to rotate longer thus increasing the total energy. When some of the moisture is removed from the clothes then the heat element will come up to temperature and cycle as normal and will not take any additional energy. The bottom line in my way of thinking, is that it will take more energy but the drum will not spin twice as long.

 

[Madco]

You are probably right! Other than the element input power reduction, everything else is just a SWAG. There are a lot of other variables involved that are hard to pin down!

 

[Quattrohead]

How many hours have you run it that way so far?

10 minutes LOL

 

[Madco]

I've done a lot of work with industrial thermal dryers (drying wastewater biosolids -that's the polite term for it anyway!) the basic algorithm is pretty cool.

You basically input heat to evaporate the water at a desired rate. Then the temperature of the material is monitored, knowing that it can't increase significantly above 212F until the water has been evaporated. When the material temperature does start to rise significantly above 212F, you know the material is dried.

I've noticed that my clothes dryer operates the same way, throttling the heat input as it detects the load's temperature increasing, probably by monitoring the exhaust air temperarure.

 

[efficientPV]

Many dryers will work if rewired to 120V. My heater element died. I had a universal replacement coil picked up at an auction and installed that. Never read the instructions that said to cut the length for higher power. Wife said she had to restart it twice to get clothes dry. Rather than pull the machine apart, just added a 50/50 timer in series with timer motor so the one hour timer became two. It had a moisture sensor, but she refuses to use that feature and set the timer instead. Replaced that dryer not much long after.

 

[SparkyJJO]

Heh, our moisture sensor is borked because half the time things are still damp at the end of the auto cycle.

 

[Madco]

Sounds like an energy star appliance - runs longer and uses more energy! Toilets too - just flush 6 times!!?

 

[Quattrohead]

Many dryers will work if rewired to 120V

But then you only get 1/4 of the heat, I think that will be too little.

 

[Quattrohead]

Sounds like an energy star appliance - runs longer and uses more energy! Toilets too - just flush 6 times!!?

No shit....down the bend !!!!!

 

[timselectric]

My thoughts are that it will definitely output half of the heat, continuously. And more than likely won't cycle on and off. So it probably won't take twice as long. But will still use more total energy. Because of the longer motor run time. But not twice as much.

 

[RCinFLA]

If running from an inverter it is not a good idea to put a half wave rectifier in a heavy resistive load. It highly imbalances inverter load current between positive and negative AC half cycles.

It can damage inverter.

A high power 240vac triac light dimmer on heating element would be better to use. It needs a fairly good heat sink capable of about 20 watts of heat dissipation as triacs have about 1.5-2v voltage drop.

 

[tinyt]

Some discussions here on loads with power reduced using half-wave rectifier.

 

[MajicDiver]

It highly imbalances inverter load current between positive and negative AC half cycles.

I’m going to hold off on trying it! In addition to tinyt’s link, the following gives some reason to proceed carefully- especially for someone like myself who definitely does not understand the potential implications. While not directly related, it’s illustrates the types of issues that can arise

Why You Should Not Mix Full-Wave and Half-Wave Powered Devices

 

[RCinFLA]

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Make sure you connect ground wire to the case for safety.

 

[Quattrohead]

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Make sure you connect ground wire to the case for safety.

I would not touch this POS with someone else's barge pole

 

[Checkthisout]

I bet reducing the heat increases efficiency even though the run time is longer.

 

[Jordi]

I think a heat pump based dryer will benefit from a lower wattage. When heat flow becomes lower due to lower power supply, the temperature gap from the heat pump becomes smaller and its COP increases (amount of heat transferred per unit of power). Longer drying time means also more time for heat loss through dryer door and surface as well as more motor rotation. I believe you may still save something here.

A dryer using electrical resistances to generate heat might see less benefits, its heating temperature could get lower leading to slightly less loss, but the longer drying time and motor rotation may cannibalize those savings.

When clothes are getting dry, so long these remain in the wet bulb drying phase, its temperature should remain constant. That does not change when power is halved, unless you go too low and then there is no enough heat to effectively dry clothes.

In general, requiring a lower power should be very beneficial for the grid and equipment costs, right?
Would inverters opperate more efficiently If the power demand is 2,5kW instead of 5kW?
I believe most home appliances aren't designed with a specific power because they need it but because people want things as fast as possible. Who wants to wait 8 minutes to boil water for tea? Most of us would like that in just 10 seconds or less.

 

[OzSolar]

Heh, our moisture sensor is borked because half the time things are still damp at the end of the auto cycle.

We know it's time to service the exhaust line and clean out the lint when that starts happening. Might not be your case.

 

[efficientPV]

I have a friend that wired up his dryer heating element up to his water heater that operates on a PV power point control. When he turns on the dryer, it switches from the water heater element to the dryer element. I have a dishwasher with the heating element wires going to a relay. When the relay closes, the heater element is powered by PV switched from my water heater. Dishwasher with the "sewing machine" pump draws less than 100W without the heater. Anyone can have a dishwasher even with a small system.

 

[SparkyJJO]

We know it's time to service the exhaust line and clean out the lint when that starts happening. Might not be your case.

I took apart and cleaned the dryer out (surprisingly not too bad inside), and I even ran a whole new (shorter) dryer duct because the original duct in the house was way too long and half full of lint. It made little difference. If we run the auto at "more dry" then run it again at "normal dry" it does fine, but takes forever. Plenty warm inside. I think it is just a bum dryer. But hey, it was free, new ones cost $$$ that I frankly don't have, and thanks to the solar on the roof it doesn't really cost me that much to run anymore, so it is more of a nuisance than anything at this point.