Clothes dryer: propane vs. electric

[Zach]

Hello Folks,

I've tried to do my homework for a guy who doesn't know much, but I still have an unresolved question I can't resolve on running a clothes dryer.

My family lives mostly without electricity. Wood heat, propane lights, enough juice for a computer and a Staber clothes washer.

We dry some of our clothes with the woodstove, and in the warmer season we use a clothesline and the stinky laundromat.

It's time to upgrade to a clothes dryer, and I assume propane makes sense. Nonetheless, propane is very expensive here, just over 4 bucks a gallon.

Gasoline is about the same price. So the question is: would a generator (and it would have to be a bigger generator) running an electric dryer make any sort of sense?

Our Staber washer gets clothes pretty dry, and we could get a clothes spinner to get the clothes even dryer.

Living in SE Alaska means we'll run a generator here and there, anyway.

I'm still assuming propane makes the most sense. Can anyone recommend a quality machine? I'm not opposed to spending more money on quality. Finally, the machine will go outside under cover.

Thanks and all the best,

Zach

[BB.]

Here is a quick calculator where you can compare the costs of wood, oil, natural gas, electricity, LP, etc...

In the end, it is all in how much it costs you to get heat to your clothes...

So, $4 per gallon LP is not cheap. But how much is the fuel to run your generator and how much power do you get from your's? I.e., what is your $/kWhr cost for generated power.

For example, a Honda eu2000i portable generator gets around 1,600 watts for 4 hours (or ~15 hours at 400 watts) on 1.1 gallons of gasoline (not bad for a portable--if you have fixed generator you may do better or you may do worst--especially if large generator and small loads)...

At max power:
1.1 gallons * $4pergallon of gas / (1.6kW * 4 hours) = $0.69 per kWhr

At minimum power:
1.1 gallons * $4 per gallon of gas / (0.4 kW * 15 hours) = $0.73 per kWhr

So, assuming $4 per gallon propane and gasoline, running generator at 25% of rated load (and no cost to buy/maintain generator), using the Fuel Cost calculator ($0.73 per kWhr):

Electricity will be ~$202 per million BTU (100% efficiency)
LP will be ~$57 per million BTU (assuming 78% efficiency)

Knowing exactly how much you use for power (kWhr or Watt*Hours) and how much fuel you used to generate it to get cost. Looking on the drier for a BTU requirement (mine is listed as 20,000 BTU / 5.9 kW--equivalent?). The burner does not run 100% of the time--but lets assume 1 hour of drying time:

($57/MBTU / 1,000,000 BTU/MBTU (LP) )* 1 Hour * 20,000 BTU per load = $1.14 per load ($4 per gallon LP)

Assuming 500 watts to run the drier for 1 hour...

0.5 kW * 1 Hour * $0.69 per kWhr = $0.35 worth of electricity.

$1.14 + $0.35 = $1.49 per drier load (big guesses here--but probably close enough to discuss).

Most cost effective... Getting the high speed water extractor for your laundry room.

Other things that may help... If you have to always use a generator--can it be used to heat up a drying shed or the hot air used to feed the drier (caution required here).

-Bill

[BB.]

I should do the same calculation for an electric drier... But I did not bother because the price of electric heat is about 4x that of propane.

Also, I did not have good numbers for a how much power an electric drier uses... But, I can guess... Say 20 amps at 240 VAC for heating element (4,800 watts or 4.8kW) and it takes 1.5 hours to dry the clothes...

(4.8kW + 0.5kW for motor) * 1.5 hours * $0.73 per kWhr = $3.87 per load

$3.87/$1.49 = 2.6x more expensive to go with an electric drier using your prices for fuel (assuming my SWAGs are anywhere near accurate) and ignoring any secondary costs (cost to purchase and maintain generator, etc.)

-Bill

[Zach]

Hello Bill,

Thank you for your insightful response. The calculator is helpful. It seems that everyone should be looking at the bottomline for electricity, on grid or off. Having lived most of my life with little to no electricity, I am astounded when friends quote their utility bills that fuel so many conveniences.

You confirmed my hunches on electric vs. gas, and that's enough to know that the generator route is crazy, especially considering wear and tear on a generator, compared to the ability to run the propane dryer with an inverter and off of gas. No starting the generator, no noise, just using the normal system and filling the occasional propane tank.

From what I can tell, propane dryers run longer with less maintenance time and money, despite a slightly higher initial investment.

The water extractor makes a lot of sense.

Thanks again for sharing your expertise.


Zach


--Can anyone recommend a good propane dryer?

[mike95490]

You confirmed my hunches on electric vs. gas, and that's enough to know that the generator route is crazy, especially considering wear and tear on a generator, compared to the ability to run the propane dryer with an inverter and off of gas. No starting the generator, no noise, just using the normal system and filling the occasional propane tank.

The water extractor makes a lot of sense.

Your dryer will likely need a Pure Sine inverter to run it's motor properly, without burning it up. And with the large 500W load of the dryer, you may want to consider running the generator to charge the batteries, unless you have another chargeing source.

A gas appliance is easily converted from Natural Gas to Propane via just changing the Orifice Tip on the burner. Some regions, this is done at the shipping warehouse, some on site, all depends on your vendor. Propane company can also change the orifice too.

The dryer you can get the clothes before they go into the "tumbler" the better. I've also seen one installation, where a fellow ran ductwork from his hot attic, to the intake plenum of his dryer. Instant Preheater, and half the fuel use.

[BB.]

You can also look at Heat Recovery Ventilators... You may already use them in your area because they work well in climates with temperature extremes.

Connect one end to your drier's exhaust and vent outside. Take the other side of the exchanger and bring in cold, dry air from the outside and use the heat exchanger to remove the heat from the drier's warm, wet air and use it to preheat the air coming in from outside.

Work very well for keeping bringing fresh air into a home but preventing heat loss (works in both cold and hot climates). Problem with a drier is making sure the lint does not clog the heat exchanger. Also, there may be an issue if you install the heat exchanger outside in freezing weather--ice may form and block airflow.

I have a very nice Fisher Paykal top access gas drier. It is not cheap and I don't know if there is a propane version. Besides the top access (which I needed for our home) it has an automatic lint trap which seems to keep my ducts very clean. Other driers I have had/worked on tend to trap a lot of lint in the ducting... But that may also be because my ducting if very short on this home so it stays warm and does not condense and capture the lint.

I would just get a good brand with local service/parts available. Should last a long time.

One thing to remember is that many (all?) driers use an electric heating element to light the flame--so they use a bit more electricity (especially when lighting) than you would expect.

Get a kill-a-watt meter to measure the power requirements--and I too would suggest a true sine wave inverter if you are going to use batteries for powering the drier for best life and fewest "strange" problems with motors and electronic appliances.

-Bill

[Solar Guppy]

BB, Electric dryers are in the 6-8kWhr range, second to none in a electric load, more than even AC units!

Typical circuits are 40-50 amp @ 240vac

[BB.]

SG,

Sound good...

Given that I used a 1.5x fudge factor on the drier (in times past, I had found that electric driers tended to take longer to dry clothes--but that may have been a fluke/older driers/older homes with smaller main services than are available today--the reason why I added the 1.5 hours vs 1.0 hours for natural gas)--so the costs will remain about the same if the electric drier takes the same amount of time as a gas one--assuming 6-8kW and 1 hour dry cycle for both...

Zach, you can also look at the Yellow Energy Tags on the appliances and just plug in your own "calculated" values for energy costs. Example, instead of $0.10 per kWhr, use my estimate of $0.73 per kWhr:

$100 yellow tag electric number becomes $100 * ($0.73/$0.10) = $730 cost of power at $4 per gallon on generator power...

Using the fuel calculator. $1.50 per Therm (100,000 BTU or approximately per CC--hundred cubic feet):

$100 yellow tag for gas ($56.92perMBTU / $18.75perMBTU) = $303.57

The energy star tags are based on "average" usage--whatever that is (seems to be accurate for fridge/freezers for me in moderate climate).

At least the yellow tag comparisons are the same across brands--so you can look for the best for your situation.

By the way, has anyone found the Yellow Tag numbers online anywhere? For some reason, they do not seem to be available from the Energy Star site.

-Bill

[Gooserider]

I've been looking at appliances a lot lately, trying to decide if it is worth replacing any of our old, probably less efficient, but perfectly functional appliances with the newer energy star models.

According to the energy star people, they don't rate dryers because there isn't a significant energy savings potential there - a dryer heats air, and blows it through the tumbling clothes, so you essentially have a heater and a drive motor, neither of which has much potential for energy savings.

I've seen lots of suggestions that I should consider replacing my washer and / or refrigerator, NOBODY has suggested replacing the dryer - I had one of those "free energy audits" done by the utility co, and the guy explicitly said not to change the dryer.

Those same sites all said that gas driers were overall more efficient than electrics - the total production costs for the electricity to run the heating element in an electric meant much lower efficiency for that unit than the relatively efficient gas dryer burner.

I will admit I was looking mostly at Natural Gas units as opposed to propane, because that is what I have - cost aside, propane in general is less efficient than NG due to the basic chemistry involved, but still it's better than electric for this application.

Gooserider

[BB.]

Yep, there is not much that can be done for normal driers to make them much more efficient. Using them less with clothes lines and/or washers that spin-dry clothes faster or a real spin-extractor are going to be the most cost effective way to save money (other than fuel choice--gas vs electric).

The one draw-back to a gas drier is that they can turn your clothes "yellow" from the combustion gases that circulate through the clothes... Electric units don't do that... (not that you would notice with any of my clothes).

-Bill