Heat Pump Food Dryer - Page 4

MEMPHIS91 · 07-03-15, 06:43 AM

Ah OK. So your suggestion would be to have a intake right before the evap. Where would you suggest the discharge to go? Maybe at the top where most the heated moisture is? Or just use the intake at the evap as both intake and discharge?

jeff5may · 07-03-15, 08:24 PM

That is the biggest question. My best guess is wherever the air is the moistest. Not necessarily the warmest, but with a conventional dehumidification unit, the fan sucks air through both heat exchangers before exhausting the airstream in a generally cardioid direction. Some of this airflow hits the compressor below, helping to cool the shell.

Refrigerator units with compact condenser coils do the same thing. The hx is wound up like a clockspring or cinnamon roll on the intake side of the fan. In the exhaust side, the compressor is directly downstream of the fan. The condensate tray is either mounted on top of the compressor or directly downstream from the compressor. This setup guarantees all condensate will evaporate quickly.

With a dehydrator, the added heat of the compressor will enhance performance directly. It's like having all your refrigerator cycle energy for free. The only thing the power meter charges for is compressor energy, a lot of which is dissipated as heat. Any extra heat gleaned from the condenser is a bonus, as is the energy spent to remove moisture at the evaporator. It takes a lot of energy to condense water, so this water condensed is not as cheap to obtain as to exhaust. It should help more by drying the air as far as dehydration goes.How much more is up for grabs.

If the COP of the compressor cycle is high, the heating and cooling effects are higher than the compressor energy added. In this configuration, they cancel each other out as far as the power meter is concerned. For the dehydration operation, it makes sense to remove moisture from any incoming air. At the exit side, I'm beginning to believe the exit should be downstream from the point where the warm air has passed by the food, before it is recirculated. Leveraging the overall heating effect forces more moisture out of the food for the energy added.

The recirculated airflow is also unclear to me. Given the previous discussion of airflow, how much air would or should follow a path straight back through the condenser and past the compressor? How much air should go full circle through both heat exchangers, removing moisture from the recirculation flow at the expense of cooling the air?

MEMPHIS91 · 07-04-15, 03:10 PM

So here is some more progress, I decided it best to finish the build so I could get the air flow set before making final tune to the charge.
Here is the "inner" box. I simply built it out of foam board and aluminum tape.

The is the outer box made of 3/4 plywood. I'm going to paint the inside white and stain the outside to match the cabinets in the kitchen. This is the front there is a small slot in the very front for air and bunches of holes in the floor of it. (No top or door has been made yet).

This is the back, the hole is for a viewing window to see the evap coils are getting cold as they should. It will have a piece of plexiglass over it when I'm done.

Jeff, I think I'm starting to getting off track, my plan is to not vent any of the warm air back into the house. I want more than a unit to make hot air for less power I want to create I drying "box" that has no effect on the outside environment. Basically the air getting dryer and dryer every time it is cycled through. These are some pictures from the articles I posted.

As you can see its a closed loop. It may take longer to dry but that is ok I will not heat up my house as much, plus I can put it on a timer to shut off in a few hours and the food will stay dry because the box will be very well sealed. That is the idea anyway, sorry if I mislead you. Or maybe my idea isn't going to work at all. ??? We will know soon. =D

jeff5may · 07-05-15, 06:20 PM

I had planned on digging out the modded whirlpool dehumidifier today, but when I got to the barn, boy was I surprised! This monsoon weather we have been having the last couple of weeks wreaked havoc on the vegetable garden. I spent the whole day making bamboo stakes and tying up tomato and pepper plants. I guess my parents and their garden partners are too civilized to waller around in the mud. Good for me, bad for them.

I found the old nesco frisbee unit and brought it home to do small stuff like basil and oregano for now. I have to get something big set up so I can start drying peppers and tomatoes. The clock is ticking: bottom tomatoes are turning yellow and light orange. Green beans and cucumbers begun harvest last week. I don't know whether they planted squash or eggplants, but they are also turning colors.

MEMPHIS91 · 07-05-15, 07:40 PM

Its been crazy amounts of rain here too. Thankfully most my plants are in a greenhouse. I would love to see picture whenever you get the chance though. I had a couple more hours free today so I finished up the box for testing.
This is where the trays will go.

I cut slots in the door with the table saw and used some leftover door weather strip for the door.

Then I just mounted the door with 2 hinges.

And this is the finished project. I did find I needed more airflow so I made all my holes 2 times bigger.

Test ran for 3 minutes. Humidity went from 65% to 48% and the temp went from 81F to 88F. PROBLEM!! My evap froze up! I tested with much more airflow and miscalculated the size of the evap. Will be taking apart and making much much longer.

MEMPHIS91 · 07-06-15, 04:38 PM

I got the larger evap built and everything back together. I went for 5 loops of 15 inches long to 15 loops of 15 inch long. Charged to 190 psi discharge and 10 psi suction.

Everything is working amazing!

Here is the slight issue, I lost the frost on the evap at 102F. Which tells me I could use more charge. But my amps are steadily climbing. Do I need frost? I'm still making water on the evap.

.

I'm drying my wives shoes because after this last monsoon we got the campus was covered in 4 inches of water. So far the last numbers are 25% humidity at 112F pulling 1.95 amps (that is the fan included). I have no way to check psi because I was stupid and didn't plumb the service ports on the outside.

UPDATED 23% Humidity at 124F pulling 2.5 amps. Shoes are dry!

MEMPHIS91 · 07-06-15, 07:59 PM

First test run with some lemon mint drying.
Minutes Humidity Temp F Amps KW
0 55 86 1.65 0
5 40 90 1.73 .015
10 31 97 1.77 .027
15 27 100 1.79 .04
20 26 102 1.84 .056
25 25 106 1.87 .069
30 25 108 1.91 .084
35 23 111 1.98 .1
40 23 113 1.98 .116
45 22 115 2.03 .132
50 23 117 2.09 .15
55 22 118 2.12 .166
60 21 120 2.16 .184
65 22 122 2.2 .203
70 22 124 2.28 .226
75 21 126 2.33 .241
80 20 127 2.44 .262
85 21 129 2.58 .282

The mint is much much drier, sadly my sorry power company can not keep the power on for a solid 24 hour period and messed up the rest of the test.
With that data though I think a shorter cap tube might be needed. Also I'm thinking a thermostat that doesn't let the compress get over 120-125ish would be good. Once the air is dry and hot I can just keep the fan running until things cool back down and kick the compressor on again.

MEMPHIS91 · 07-08-15, 09:45 PM

I have been running tons of test and have found out loads of useful information. I found that running the compressor to higher temps used more power, so just by luck I tried turning the compressor off at 105F and letting the fan keep running til the temp dropped to 95F and turned it back on. My humidity went to 16% in less than a minute and my temp was only at 100F. I was going to keep running the machine but I discover my load was already dry.
So I added some science to it. I weighed 100 grams of water and soaked it into some rags, and turned on the machine. I cycled my compressor off at 105F and back on a 95F keeping the fan on the whole time. I collected the water when the rags where dry and it weighed in right at 107 grams. Only used .136 kw, total run time 1.5 hours. I am wiring the electric side of things now and will post pictures when I'm done.

jeff5may · 07-09-15, 10:33 PM

Awesome results! I have not had time to do anything but work and do damage control on the garden. Things are starting to get out of control. A gullywasher came yesterday and knocked down lots of plants. I stayed till dark tonight to stake up stuff. More rain tonight.

This is awesome knowing that the rig will indeed get up into the 130+ degree range with no problem. Making fruit and/or vegetable roll-ups requires temps in the 125 to 135 degree range for a decent length of time. The thicker the layer, the longer it takes. Same way as jerky. Tomato and banana and squash chips take a lot longer at 120 than 135 box temperature.

Running an evaporator with more surface area is much more efficient, even if it doesn't freeze up. The cold surface will just grab the moisture right out of the air stream. With a dryer or dehumidifier, the box temperature is more directly tied to drying time. Just 5 or 10 extra degrees will half the dry time if the moisture can be grabbed out that fast. With 3 times the evaporator as before, I don't believe your unit will have difficulty pulling out moisture.

MEMPHIS91 · 07-10-15, 06:43 PM

Jeff, I'm really sorry to hear about your garden. Its finally stopped raining here. But not before the moisture molded the boards I was just about to stain for the new pantry. Yes I am looking forward to trying some veggy chips on it soon. That will be the real test.

I got everything put back together. And the electric side roughed in.
Every surface was painted first with thin paint to soak into the wood, then normal thickness to seal the wood nicely.

Top side. Red is common, black is hot. Links to electronics used: Inkbird Digital Twin Timer Relay Time Delay Relay Switch 110-220V Black IDT-E2RH
Docooler® Digital Temperature Controller Thermocouple with Sensor (-58~194°F) 10A 110V

Here is a drawing I made to figure out where everything should go.

And here is the diagram.

Everything finished up. I now can really test some theories to see what dries things using as little power as possible.

07-03-15, 08:24 PM	#32
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	That is the biggest question. My best guess is wherever the air is the moistest. Not necessarily the warmest, but with a conventional dehumidification unit, the fan sucks air through both heat exchangers before exhausting the airstream in a generally cardioid direction. Some of this airflow hits the compressor below, helping to cool the shell. Refrigerator units with compact condenser coils do the same thing. The hx is wound up like a clockspring or cinnamon roll on the intake side of the fan. In the exhaust side, the compressor is directly downstream of the fan. The condensate tray is either mounted on top of the compressor or directly downstream from the compressor. This setup guarantees all condensate will evaporate quickly. With a dehydrator, the added heat of the compressor will enhance performance directly. It's like having all your refrigerator cycle energy for free. The only thing the power meter charges for is compressor energy, a lot of which is dissipated as heat. Any extra heat gleaned from the condenser is a bonus, as is the energy spent to remove moisture at the evaporator. It takes a lot of energy to condense water, so this water condensed is not as cheap to obtain as to exhaust. It should help more by drying the air as far as dehydration goes.How much more is up for grabs. If the COP of the compressor cycle is high, the heating and cooling effects are higher than the compressor energy added. In this configuration, they cancel each other out as far as the power meter is concerned. For the dehydration operation, it makes sense to remove moisture from any incoming air. At the exit side, I'm beginning to believe the exit should be downstream from the point where the warm air has passed by the food, before it is recirculated. Leveraging the overall heating effect forces more moisture out of the food for the energy added. The recirculated airflow is also unclear to me. Given the previous discussion of airflow, how much air would or should follow a path straight back through the condenser and past the compressor? How much air should go full circle through both heat exchangers, removing moisture from the recirculation flow at the expense of cooling the air? Last edited by jeff5may; 07-03-15 at 09:40 PM.. Reason: elaboration

07-04-15, 03:10 PM	#33
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	So here is some more progress, I decided it best to finish the build so I could get the air flow set before making final tune to the charge. Here is the "inner" box. I simply built it out of foam board and aluminum tape. The is the outer box made of 3/4 plywood. I'm going to paint the inside white and stain the outside to match the cabinets in the kitchen. This is the front there is a small slot in the very front for air and bunches of holes in the floor of it. (No top or door has been made yet). This is the back, the hole is for a viewing window to see the evap coils are getting cold as they should. It will have a piece of plexiglass over it when I'm done. Jeff, I think I'm starting to getting off track, my plan is to not vent any of the warm air back into the house. I want more than a unit to make hot air for less power I want to create I drying "box" that has no effect on the outside environment. Basically the air getting dryer and dryer every time it is cycled through. These are some pictures from the articles I posted. As you can see its a closed loop. It may take longer to dry but that is ok I will not heat up my house as much, plus I can put it on a timer to shut off in a few hours and the food will stay dry because the box will be very well sealed. That is the idea anyway, sorry if I mislead you. Or maybe my idea isn't going to work at all. ??? We will know soon. =D Attached Thumbnails

07-05-15, 06:20 PM	#34
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	I had planned on digging out the modded whirlpool dehumidifier today, but when I got to the barn, boy was I surprised! This monsoon weather we have been having the last couple of weeks wreaked havoc on the vegetable garden. I spent the whole day making bamboo stakes and tying up tomato and pepper plants. I guess my parents and their garden partners are too civilized to waller around in the mud. Good for me, bad for them. I found the old nesco frisbee unit and brought it home to do small stuff like basil and oregano for now. I have to get something big set up so I can start drying peppers and tomatoes. The clock is ticking: bottom tomatoes are turning yellow and light orange. Green beans and cucumbers begun harvest last week. I don't know whether they planted squash or eggplants, but they are also turning colors. Last edited by jeff5may; 07-05-15 at 06:57 PM..

07-05-15, 07:40 PM	#35
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	Its been crazy amounts of rain here too. Thankfully most my plants are in a greenhouse. I would love to see picture whenever you get the chance though. I had a couple more hours free today so I finished up the box for testing. This is where the trays will go. I cut slots in the door with the table saw and used some leftover door weather strip for the door. Then I just mounted the door with 2 hinges. And this is the finished project. I did find I needed more airflow so I made all my holes 2 times bigger. Test ran for 3 minutes. Humidity went from 65% to 48% and the temp went from 81F to 88F. PROBLEM!! My evap froze up! I tested with much more airflow and miscalculated the size of the evap. Will be taking apart and making much much longer. Attached Thumbnails Last edited by MEMPHIS91; 07-05-15 at 08:41 PM..

07-06-15, 04:38 PM	#36
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	I got the larger evap built and everything back together. I went for 5 loops of 15 inches long to 15 loops of 15 inch long. Charged to 190 psi discharge and 10 psi suction. Everything is working amazing! Here is the slight issue, I lost the frost on the evap at 102F. Which tells me I could use more charge. But my amps are steadily climbing. Do I need frost? I'm still making water on the evap. . I'm drying my wives shoes because after this last monsoon we got the campus was covered in 4 inches of water. So far the last numbers are 25% humidity at 112F pulling 1.95 amps (that is the fan included). I have no way to check psi because I was stupid and didn't plumb the service ports on the outside. UPDATED 23% Humidity at 124F pulling 2.5 amps. Shoes are dry! Attached Thumbnails Last edited by MEMPHIS91; 07-06-15 at 05:12 PM..

07-03-15, 06:43 AM	#31
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	Ah OK. So your suggestion would be to have a intake right before the evap. Where would you suggest the discharge to go? Maybe at the top where most the heated moisture is? Or just use the intake at the evap as both intake and discharge?

07-06-15, 07:59 PM	#37
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	First test run with some lemon mint drying. Minutes Humidity Temp F Amps KW 0 55 86 1.65 0 5 40 90 1.73 .015 10 31 97 1.77 .027 15 27 100 1.79 .04 20 26 102 1.84 .056 25 25 106 1.87 .069 30 25 108 1.91 .084 35 23 111 1.98 .1 40 23 113 1.98 .116 45 22 115 2.03 .132 50 23 117 2.09 .15 55 22 118 2.12 .166 60 21 120 2.16 .184 65 22 122 2.2 .203 70 22 124 2.28 .226 75 21 126 2.33 .241 80 20 127 2.44 .262 85 21 129 2.58 .282 The mint is much much drier, sadly my sorry power company can not keep the power on for a solid 24 hour period and messed up the rest of the test. With that data though I think a shorter cap tube might be needed. Also I'm thinking a thermostat that doesn't let the compress get over 120-125ish would be good. Once the air is dry and hot I can just keep the fan running until things cool back down and kick the compressor on again.

07-08-15, 09:45 PM	#38
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	I have been running tons of test and have found out loads of useful information. I found that running the compressor to higher temps used more power, so just by luck I tried turning the compressor off at 105F and letting the fan keep running til the temp dropped to 95F and turned it back on. My humidity went to 16% in less than a minute and my temp was only at 100F. I was going to keep running the machine but I discover my load was already dry. So I added some science to it. I weighed 100 grams of water and soaked it into some rags, and turned on the machine. I cycled my compressor off at 105F and back on a 95F keeping the fan on the whole time. I collected the water when the rags where dry and it weighed in right at 107 grams. Only used .136 kw, total run time 1.5 hours. I am wiring the electric side of things now and will post pictures when I'm done.

07-09-15, 10:33 PM	#39
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Awesome results! I have not had time to do anything but work and do damage control on the garden. Things are starting to get out of control. A gullywasher came yesterday and knocked down lots of plants. I stayed till dark tonight to stake up stuff. More rain tonight. This is awesome knowing that the rig will indeed get up into the 130+ degree range with no problem. Making fruit and/or vegetable roll-ups requires temps in the 125 to 135 degree range for a decent length of time. The thicker the layer, the longer it takes. Same way as jerky. Tomato and banana and squash chips take a lot longer at 120 than 135 box temperature. Running an evaporator with more surface area is much more efficient, even if it doesn't freeze up. The cold surface will just grab the moisture right out of the air stream. With a dryer or dehumidifier, the box temperature is more directly tied to drying time. Just 5 or 10 extra degrees will half the dry time if the moisture can be grabbed out that fast. With 3 times the evaporator as before, I don't believe your unit will have difficulty pulling out moisture.

07-10-15, 06:43 PM	#40
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	Jeff, I'm really sorry to hear about your garden. Its finally stopped raining here. But not before the moisture molded the boards I was just about to stain for the new pantry. Yes I am looking forward to trying some veggy chips on it soon. That will be the real test. I got everything put back together. And the electric side roughed in. Every surface was painted first with thin paint to soak into the wood, then normal thickness to seal the wood nicely. Top side. Red is common, black is hot. Links to electronics used: Inkbird Digital Twin Timer Relay Time Delay Relay Switch 110-220V Black IDT-E2RH Docooler® Digital Temperature Controller Thermocouple with Sensor (-58~194°F) 10A 110V Here is a drawing I made to figure out where everything should go. And here is the diagram. Everything finished up. I now can really test some theories to see what dries things using as little power as possible. Attached Thumbnails Last edited by Daox; 10-19-18 at 08:38 AM..