Homemade Heat Pump Clothes Dryer - Page 3

AC_Hacker · 06-14-15, 08:49 AM

Quote:

Originally Posted by Xzeption

..This is the cheapest, ugliest, yet functional cabinet I could build. The corners are 2x4 boards 4 ft high. The sides, back and front are 2 ft x 4 ft OSB board. The sides and back are nailed to the 2x4s. The front (lying on the floor in the picture) is the same dimensions as the sides. I use some rope I had to hold the front to the box when in use. ...

This is excellent work!

I really like the way you are thinking about this. The old refrig/upright freezer is brilliant!

Weighing the clothes... terrific, just terriffic.

Keep it up, I'm cheering for you from the other side of the US!!!

Best,

-AC_Hacker

Xzeption · 06-16-15, 08:01 PM

Thanks for the words of encouragement! Now I need some experienced advice.

I ran the dehumidifier dryer for 60 minutes with a load of diaper liners. The liners had a mass of 1326 grams at the start and 978 grams at the end. This gives a total of 348 grams of water removed, or ~58% of the way to completely dry. Overall not too bad for a proof of concept prototype.

However, I measured the mass of water in the collection bin to be only 40 grams. This is perplexing me as it is no where near the 348 grams of water that was removed from the cloth. I can think of a few plausible explanations.

1) Moisture laden air is escaping the box. The solution would be to air seal it.

2) The dehumidifier is condensing more water from the air, but it is re-evaporating from the collection area. I have no idea how feasible this is. Hopefully another forum member can explain if this is possible or not.

3) Perhaps the temperature of the air in the box (over 100 degrees F) is above the design temperature of the dehumidifier and the evaporator coil is not getting below the dew point. I doubt this is the case but I am trying to think of all possible explanations.

Am I missing anything?

jeff5may · 06-16-15, 10:37 PM

My money is on door #1. This is exactly how food dehydrators operate.

Newer portable air conditioners also do this. The cooler coil is stacked above the heater coil inside the unit. Any condensate drains right down the face on its way to the sump. What moisture actually finds the bottom is either recirculated up top or sent to a mister nozzle. Either way, the moisture finds its way into the exhaust stream. Unless there is a lot of humidity in the airspace, the units never need to be emptied.

Daox · 06-17-15, 07:39 AM

I wonder how much moisture your box absorbs during that 1hr?

AC_Hacker · 06-17-15, 09:24 AM

Quote:

Originally Posted by Xzeption

...However, I measured the mass of water in the collection bin to be only 40 grams. This is perplexing me as it is no where near the 348 grams of water that was removed from the cloth.

Am I missing anything?

Your aim is to dry something, so why does this matter?

-AC

Xzeption · 06-21-15, 07:40 PM

I am going to try to use quotes for the first time on the forum. Let me know if anything goes wrong.

Quote:

Originally Posted by Daox

I wonder how much moisture your box absorbs during that 1hr?

I am hoping the moisture absorption of wood is insignificant, but I have no data backing that up. This is a relevant question that should be tested later.

Quote:

Originally Posted by AC_Hacker

Your aim is to dry something, so why does this matter?

-AC

I may be messing up the physics here, but I will describe what I am thinking. Evaporating a gram of water takes 2.11 btu/gram. Condensing the water releases the same amount of heat. If water is collecting in the bin, then it is condensing on the coils. The heat pump is transfering the latent heat to the air which can evaporate more water from the laundry.

If water is not collecting in the bin, then the dehumidifier is effectively acting as a resistance heater. Some drying cabinets are actually designed this way, but the theoretical efficiency does not have the same potential as a heat pump. Plus my central AC will have to remove the new latent heat.

Xzeption · 06-21-15, 08:32 PM

I have lots of data and will try to keep it chronological to avoid confusion.

On 6/16 I ran the dehumidifier dryer without the box fan. Unfortunately, I forgot to set a timer so it could have ran anywhere from 50 to 70 minutes instead of the precise 60 minutes. Mass in: 1295 grams; mass out: 1163 grams; water in bin: 14 g. So approximately 23% of water removed. I think this indicates having the box fan on is significant. But with the time inaccuracy, I can't accurately quantify the box fan effect. Two possible explanations are (1) the box fan provides air flow to evaporate air from the laundry and/or (2) the box fan keeps the air from being stratified with hot moist air above and cool dry air next to the dehumidifier.

At this point I noticed that the dehumidifier fan speed for air going through the coils was set on high. A certain "helpful" toddler had played with the controls and I did not notice the setting until now. The previous data points were run with this setting, but I will be changing the dehumidifier fan speed to low for future tests. I considered that this fan setting may have been why so little water is in the collection bin, so I tried the low speed with some dish towels I had washed. Again the towels dried but there was little water in the bin.

Time to try air sealing this. I cut a plywood top and nailed it on, leaving a gap for the box fan cord. Then I caulked the top and corners, pic attached. Last I added weatherstripping to the door. I did not air seal the bottom as the air in the box is warmer and will try to escape up the top. The door is not tightly sealed, but I hope this is sufficient. I still use a rope to hold the door tight, but am willing to take better suggestions.

Today 6/21 I am testing our the dehumidifier dryer with the box fan on and reasonable air sealing. Mass in: 1336 grams; mass out: 1064; mass in bin: 71; ~45% of water removed. This is a significant improvement in water mass in the bin but not much difference in drying capacity.

I think this solves the mystery of where the water went. Hot moist air was escaping the box taking the water with it. Even currently some air was leaking from around the door. My next tests are going to be with better air sealing and toggling the dehumidifier fan speed.

AC_Hacker · 06-22-15, 12:50 AM

Quote:

Originally Posted by Xzeption

I have lots of data and will try to keep it chronological to avoid confusion...

I think that he way you are going about this is absolutely first class.

You are not only taking small steps, and measuring the results, but you are learning a lot about the principle of operation.

In addition, your carefully paced procedure is itself a model for us to follow.

Science lives!

-AC

jeff5may · 06-22-15, 08:00 AM

I agree. This could be good data to apply to a great many devices. As this thread is progressing, another user, Jake, is working on a heat pump powered food dehydrator.

AC_Hacker · 06-22-15, 09:30 AM

Quote:

Originally Posted by jeff5may

i agree. This could be good data to apply to a great many devices. As this thread is progressing, another user, jake, is working on a heat

link????

-AC

06-16-15, 08:01 PM	#22
Xzeption Lurking Renovator Join Date: May 2015 Location: Raleigh, NC Posts: 12 Thanks: 1 Thanked 2 Times in 2 Posts	Thanks for the words of encouragement! Now I need some experienced advice. I ran the dehumidifier dryer for 60 minutes with a load of diaper liners. The liners had a mass of 1326 grams at the start and 978 grams at the end. This gives a total of 348 grams of water removed, or ~58% of the way to completely dry. Overall not too bad for a proof of concept prototype. However, I measured the mass of water in the collection bin to be only 40 grams. This is perplexing me as it is no where near the 348 grams of water that was removed from the cloth. I can think of a few plausible explanations. 1) Moisture laden air is escaping the box. The solution would be to air seal it. 2) The dehumidifier is condensing more water from the air, but it is re-evaporating from the collection area. I have no idea how feasible this is. Hopefully another forum member can explain if this is possible or not. 3) Perhaps the temperature of the air in the box (over 100 degrees F) is above the design temperature of the dehumidifier and the evaporator coil is not getting below the dew point. I doubt this is the case but I am trying to think of all possible explanations. Am I missing anything? __________________ There is an exception to every rule. Including this one. I wish my country would switch to the metric system. My apologies to international readers who see me jump between metric and imperial units.

06-16-15, 10:37 PM	#23
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	My money is on door #1. This is exactly how food dehydrators operate. Newer portable air conditioners also do this. The cooler coil is stacked above the heater coil inside the unit. Any condensate drains right down the face on its way to the sump. What moisture actually finds the bottom is either recirculated up top or sent to a mister nozzle. Either way, the moisture finds its way into the exhaust stream. Unless there is a lot of humidity in the airspace, the units never need to be emptied. Last edited by jeff5may; 06-17-15 at 10:49 AM..

06-17-15, 07:39 AM	#24
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	I wonder how much moisture your box absorbs during that 1hr? __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

06-21-15, 08:32 PM	#27
Xzeption Lurking Renovator Join Date: May 2015 Location: Raleigh, NC Posts: 12 Thanks: 1 Thanked 2 Times in 2 Posts	I have lots of data and will try to keep it chronological to avoid confusion. On 6/16 I ran the dehumidifier dryer without the box fan. Unfortunately, I forgot to set a timer so it could have ran anywhere from 50 to 70 minutes instead of the precise 60 minutes. Mass in: 1295 grams; mass out: 1163 grams; water in bin: 14 g. So approximately 23% of water removed. I think this indicates having the box fan on is significant. But with the time inaccuracy, I can't accurately quantify the box fan effect. Two possible explanations are (1) the box fan provides air flow to evaporate air from the laundry and/or (2) the box fan keeps the air from being stratified with hot moist air above and cool dry air next to the dehumidifier. At this point I noticed that the dehumidifier fan speed for air going through the coils was set on high. A certain "helpful" toddler had played with the controls and I did not notice the setting until now. The previous data points were run with this setting, but I will be changing the dehumidifier fan speed to low for future tests. I considered that this fan setting may have been why so little water is in the collection bin, so I tried the low speed with some dish towels I had washed. Again the towels dried but there was little water in the bin. Time to try air sealing this. I cut a plywood top and nailed it on, leaving a gap for the box fan cord. Then I caulked the top and corners, pic attached. Last I added weatherstripping to the door. I did not air seal the bottom as the air in the box is warmer and will try to escape up the top. The door is not tightly sealed, but I hope this is sufficient. I still use a rope to hold the door tight, but am willing to take better suggestions. Today 6/21 I am testing our the dehumidifier dryer with the box fan on and reasonable air sealing. Mass in: 1336 grams; mass out: 1064; mass in bin: 71; ~45% of water removed. This is a significant improvement in water mass in the bin but not much difference in drying capacity. I think this solves the mystery of where the water went. Hot moist air was escaping the box taking the water with it. Even currently some air was leaking from around the door. My next tests are going to be with better air sealing and toggling the dehumidifier fan speed. Attached Thumbnails __________________ There is an exception to every rule. Including this one. I wish my country would switch to the metric system. My apologies to international readers who see me jump between metric and imperial units. Last edited by Daox; 06-22-15 at 10:07 AM..

06-22-15, 08:00 AM	#29
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	I agree. This could be good data to apply to a great many devices. As this thread is progressing, another user, Jake, is working on a heat pump powered food dehydrator. Last edited by jeff5may; 06-22-15 at 09:35 AM..