Dryer Temperature Vs Dry Time

[Howard]

What is the impact of dryer temperature versus drying time? I currently have my dryers set at 180 Deg. What impact on drying time and energy use can I expect if I set them at either 170Deg or 190Deg.

[Gary_Crosby]

Howard
How long does it take to dry a load in your dryers? 18pd load.
Gary

[Gary_Crosby]

Howard

Sorry I hit the wrong key. I think it would depend on the type of dryer you have. There are some models that I don't think it would make much difference because of how the air flows. Like if the drum has holes front to back it's hard for the air to reach the front. versis a solid drum for 3/4 of the drum then vent holes. That type of dryer should show a larger impact with tempature change. It will be trial and error to find out. If you try I would like to hear how you made out.

Gary

[Marianne]

I have six 30# dryers in a row, half at 170 and half at 190. I'll time them for you. I had a bunch of stacks set at 190 and the distributors tech said that would damage the motors and possibly the clothes. He set them to 180 and thinks they may have to go down another 10.

[Gary_Crosby]

Marianne

Mine are set at 140 deg and I am happy with them and more importantly my customers are happy. Maytag 30# stack they will dry a full 18# load in 28 to 35 min. how does that compare?

Gary

[Howard]

Gary, my ADC236 dryers will dry an 18# load in 16-24 minutes when set at 180Deg. I've actually seen people do smaller loads in only 8 minutes.

As for the card system in your other post, there is a cost for the "system" and then a cost for each machine. I think with such a small operation you might find the upfront cost for the system hard to justify.

[petefritz]

Hi Howard.
We know dryers are rated BTU's an hour, so setting the temp will not change how much they burn an hour, only how much money it takes to dry, as 170 will take longer than 190. I guess 10% more money, as 170 is about 10% less than 190. I have all mine set at 180, and use a 1 min cool down. Even if the clothers are not dry, they are hot when the dryer stops becuase of the short cool down, so do not get many complaints on heat. With the 40% increase in gas, dryer that were 10 min should be 6 now. Sure, that will be easy!! I am looking at lowering temps from 7 1/2 to 6, and also raising tops to 1.50 from 1.25. I figure that will just about make up the increase, keep me making the same amount I did last year. As a note, lowering temps can cuase a back up in dryers if you do not have lots of them in the store.
Best,
Pete

[Howard]

Yes dryers are rated in BTU/Hr input, but note the word "Max". That means the most they will use is that number - not that they always use that amount. During cool down they are running but not burning. Also, the computer controls the burn rate to determine the temperature. Thus, it uses less gas (less BTU) to run at 170 than at 190. The question I have is how much less gas (I can calculate it in theory but I want to know in practice) and what impact does that have on the time it takes to dry the clothing. I know that a lower temperature will take longer - but how much longer? The bottom line is will it impact customers significantly, will it save me significant money?

Thanks

[Gary_Crosby]

I think there are to many variables to tell how huch less gas will be used. ie outside temp, spin out of the machine, weight of cloths (jeans v sheets) etc. So I would think theory is about the only way. I can tell you what I did. I dropped 5 degrees at a time untill I hit that threshhold that I thought customers would complain then went back up 5 deg. just to make sure. I am sure that the gas bill is much lower now. You could always try to drop the temp alot and get rid of the cool down time that way the cloths are hot when they come out of the dryer and the customers will think there is nothing different. It may be worth a try.
As long as the cloths are hot when they come out customers are usualy happy.

Gary

[petefritz]

Hi Howard
I gave some thought to your remarks,, there probably is less gas burned at 170 than 190 for sure. Probably like driving 55 mph vs at 70 mh, less mpg but get there faster! So burn the same amount/time driven?
The only way to answer your question is scientificaly <sp?) Do a load, dry at 170, see and time how much the burners are on, etc., do it at higer temp, same load, time burners on. I wonder if 10% less temp equals 10% less gas?? could it be that simple?

[Marianne]

Hi Howard, I haven't had time to time the dryers but will try again tomorrow.
The burner in the dryer is set with the size of orifice--a larger orifice allows more gas to be burnt at a time. However the gas always burns at the same temperature. So BTU/hr means how much gas would be burnt in an hour if it burned steady for that whole time. The temperature that you set the dryer just determines when the burner is shut off, if the temp is set at 170, the burner will normally shut off when the air going past the heat sensor is at or just above 170. The sensor is below the load so it is affected by the air that has been cooled from evaporating the water in the clothes. This is why the burners will stay on steady for the first half or so of the drying time. The water evaporating keeps the temp of the exhaust air low. Then as the clothes tumble, sometimes the exhaust air gets up to the 170 degrees and the burner turns off until the temp has dropped about 6-8 degrees. As the clothes get dryer the time the burner is off gets longer.

[Marianne]

First trial:
washed a load of clothes and spun them in the extractor.
load weighed 17.5 # from the extractor, reduced to 11.8# after 20 minutes in dryer set at 190 degrees.

clothes soaked and spun in extractor. load weighed 16.2# so I did it again and it weighed 16.2 # after the extractor again.
20 minutes in dryer set to 170 degrees lowered the weight to 11.6 #.

Faulty trial because I was not the one who weighed the clothes after the first spin in the extractor. Bummer!

Still it looks as though the higher cut off temperature did nothing to improve results.

[Gary_Crosby]

Marianne, I find that very interesting. I will try to do the same test. It has long been a question of mine. Can the air carry more moisture at a higher temp? From your test it sounds like it does not, however I am sure there is a low point where it starts to reduce evaporation. I had mine set at 160 when they were delivered to me then dropped to 140 and there seems to be little or no difference but I did not weigh them at the time. Thanks for your input here.

Gary

[Howard]

Marianne and Gary: Those are very interesting data points. I look forward to seeing the next test you run. The question that we now need to get answers to is what impact does this have on gas consumption. If it is only minimal, then maybe it is better to keep it hot so when the customer touches the door it feels really hot.

Howard

[Gary_Crosby]

Howard
I really don't think there is an absolute answer to that question. Here are my reasons.
make up air temp ie. outside air is 20 degrees ver outside air 75 degrees 300% differance in temp should make it a much larger or smaller % increase for that jump from 170 to 190 so your persentages of gas usage will change daily. Then add enough make up air +/- and the type of stack you have. All together or seperate vent. I hope I made sense. what do you think?

Gary

[Howard]

While what you say about make-up air and other factors is true if we compare your dryers to mine, they have no impact for you or for me. What I mean by that is there will be a constant savings for my dryers in heating to 170 versus 190, and a constant for yours. That constant may be different. The outside air has no impact, as you can think of it this way: I expend whatever gas to heat to 170, if I only heat to 170 then there is no extra cost, if I heat to 190 I incurr the cost of raising the temperature from 170 to 190 - the starting point is always 170. Hope that makes some sense.

[Gary_Crosby]

Howard
I see what you mean. I guss I just don't know if a 20 degree increase in temp will consitantaly cost the same. I will do some more thinking about it. Someting just nags at me that it can't be consistant. There must be some conection to the old bell curve thery. The other thought I had is a stack dryer may differ a little from a single because of back pressure when both tumblers are going it might change air flow a little as with a trunk system. Less cfm would require less gas to bring it up to temp. I guess in the end I really have no answer. I will continue to try to figure it out it gives me something to work on. Not that I am bored! :)

Gary

[Marianne]

Did my second test today. Made two loads of towels that weighed 10 # after the extractor. Put them in dryers for 16 minutes. Both dryers heated the loads to 170 degrees in the same amount of time--eight minutes. The dryer "A" that had its top temperature set at 170 then began to cycle off briefly until the temp dropped 10 degrees and then fired again until the temp hit 170. It cycled 8 times in 7 minutes, then went into a one minute cool down. Cooled to 128 degrees. The load was still damp and weighte 6.8 #. It took another 8 minutes to dry that load fully, but it had cooled and had to be brought up to temp again. Dryer "B" was set to 190 degrees. It took an additional 4 minutes to hit 190. It had fired steady for 12 minutes. Then it cycled on and off 2 times and went into the one minute cool down. The load was bone dry after 15 minutes of drying and one minute of cool down. It cooled to 146 degrees and weighed 6.4 # when dry. Since each nonfiring cycle took about 10-12 seconds to drop the temp about 10 degrees and initiate firing again, there really wasn't much off time. So I would say it takes less gas to dry clothes at a higher temperature.
These were 30 # single pocket dryers, 90,000 BTU/hr. That would mean it cost about 22,000 BTU to dry the load at 190 degrees. Cost about 30,000 BTU to dry the load at 170 degrees.

[Howard]

Wow, that seems very strange that higher heat would consume less gas. If this holds, you would save money on gas, but would that make-up for what you loose in revenue for each extra cycle that the customer would not need? Hummm, where do we go from here?

[petefritz]

Marianne I thank you for you time. Your test makes us think of time vs temp. My installer once told me, when I was putting in new dryers and wanted to cut temp, not to, as people will pay more for hot dryers.
Now your research seems to show hot dryers are cheaper to operate. I wonder if it is like my boat, if it is not on plane, going faster, it costs more to run it, gals per hour. Dryers evaporate moisture, so the lower temps may mean they have to work harder.

[Marianne]

Results surprised me too. I was told that the flash point for evaporation of water was 135 degrees. Maybe someone could try to replicate the test. I just flipped the program switch after the dryers started so the LED screen would report temperatures instead of time left. It was around 10 degrees fahrenheit that day.

[Marianne]

Has anyone replicated my test or tried a test of his/her own?

[Howard]

No, have not tried it yet - just have not had enough time.