Harvest - Lettuce Temperature Problem [Under Investigation]

[belugaleuca]

Update for Day 1 - Unplugged overnight, and Day 2 - Plugged in with no pump and no lights.



Day 2 - Plugged in but no pump or lights. I did not change the water.



Note 1 - Now that the air temperature is measuring correctly, it is clearly wiggling up and down. I suspect this is because the sensor and gardens are on the counter next to the refrigerator, which might heat the surrounding air periodically like that.

Note 2 - The overnight measurement with gardens unplugged confirms that the water stabilizes at a temperature cooler than air.

Note 3 - It looks like having the gardens plugged in (but no pump or lights) makes no difference in temperature.

I've plugged in the pumps at 10 pm tonight, we'll see if the pumps make a difference tomorrow!

[airscapes]

Just curious, do these units have multiple wall warts or is it just a single plug with the power supplies inside?  Normally the submergible pumps use an AC motor and the rest needs DC.    So if a  single external PS then there would be the need to rectify and regulate inside.    I assume they are wall warts as the PS with a 40w LED panel produces a lot of heat.  Having that PS inside would really heat things up.

[lynnee]

Such interesting research, belugaleuca!

[belugaleuca]

Mar 27, 2022 11:35:55 GMT -5 airscapes said:

Just curious, do these units have multiple wall warts or is it just a single plug with the power supplies inside?  Normally the submergible pumps use an AC motor and the rest needs DC.    So if a  single external PS then there would be the need to rectify and regulate inside.    I assume they are wall warts as the PS with a 40w LED panel produces a lot of heat.  Having that PS inside would really heat things up.

There is only one wall plug (edit: wall Wart) for the Harvest. The plug goes into the base. There is a detachable cable from the reservoir pump that goes into the base. And the light fixture connects to the base with the extendible post, I assume it has a wire running up the post and all of the electronics for power management is in the base.

Maybe that explains why the base was feeling warm while the light is on. I do believe that the Harvest is 20W if I remember correctly.

[belugaleuca]

I just checked and the Wall Wart says 12V 2.5A

[belugaleuca]

Day 3 - Pumps on, Lights off



The pumps were turned on at 10:00 pm yesterday night and ran all day on the built-in schedule of 5 minutes on, 25 minutes off.

There is a temperature spike at 6am this morning when we had the heater on briefly, but I don't know what else to make of it. 

On the one hand, the temperature did not drop alongside air temperature last night like it did the day before. The local weather station says that this morning was 10% more humid than yesterday (70-80% relative humidity vs. 60-70% between midnight and 6am) but I'm not sure if that's why.

On the other hand, it looks like the temperature still stabilized below room temperature during the day today when the pumps were still on.

[airscapes]

I think you will need to leave the pumps on for a few days to get a true reading.. after all it takes a while to heat a swimming pool. The pump is small compared to the volume of water.    Also, in this schedule the water temp probably will only climb about 2 degrees from what I have seen in my own DIY Bounty with small jebco pump and 2 gallon water capacity.

I have had my pump running 24x7 now for  a week or so in that same DIY Bounty. I will post the temps from before to current if I remembered to mark it on the spread sheet.


 Not a week.. only been 2 days.. not enough data.. 

[belugaleuca]

Yes airscapes you're right this is short and I should run this longer! It is only on for the default 5mins on 25 mins off so I didn't expect there to be a huge difference though. Is your 2 degree difference 24 hours on or on a shorter schedule?

Unfortunately I need to get some basic answers before the Aerogarden return slip runs out, so I am truncating the study to confirm primarily whether the Old Harvest is defective or not. Maybe after figuring it out I'll run it again and see what happens if just the pumps are on for longer.

[belugaleuca]

Day 4 -
Night: OldHarvest pump ON, NewHarvest pump OFF (I turned its pump on at 11:20 am), and
Day: Lights on at 6:00 am. 


Note 1: The NewHarvest had its pump off at night. This did reduce its temperature compared to the OldHarvest which had its pump on.

Note 2: At 6am, the lights turned on. An immediate jump in air temperature happened, with a gradual increase in water temperature.

Note 3: It maybe possible to see a bump in water temperature when I plugged the NewHarvest's pump in again at 11:20am.

Note4: The OldHarvest seems to have been hotter than the NewHarvest, and I don't think it's because of the pump. Is this because it is defective? Another theory is because the OldHarvest is in the corner it could get hotter. To solve this once and for all they will both be run again tomorrow with lights and pumps on and I will swap their locations.

[Shawn]

As I was reading I was thinking location and as I read on ...  you stated you were going to swap them

[belugaleuca]

Day 5 - Pumps on, lights on, but this time NewHarvest in the corner.


Alright! Today, the New Harvest was in the corner, and it was a little hotter than the Old Harvest.

I think this probably means the Old Harvest is not defective, but that heat contributions of the Harvest by design and location makes it hot during the day, and also raises the local air temperature. I think I have enough to send to Aerogarden now to let them know my Harvest wasn't defective after all.

The next question is what kind of things can we do to reduce the heat? Hopefully the next thing to try will be to get a piece of styrofoam or insulator on top of the deck like airscapes suggested.

[belugaleuca]

Eureka! There's been a new development in the Aerogarden heat theory  

The last 4 days I switched the locations back to the original position (Old Harvest in the corner) and measured with lights & pumps on without disturbing the system. The temperatures read the same!  


This means, on day 4 when the gardens were in the same positions, the ~1 C difference between the gardens was due to the pump being on and not due to location as we previously suspected.

Thumbnail of Day 4:

However, such a large difference in pump-on vs. pump-off temperatures is only apparent during the lights-on period. Previously when the pumps were on, and the lights were off, the water was still below air temperature (Day 3):


I think this means that when the pump is on, and the lights are on, the water is collecting heat from the deck, which is warmed by the light like this:

So what I think is - even though the pump itself contributes a small amount of heat using the 5 mins on, 25 mins off schedule, having the pump on can contribute a fair amount to heating during the lights-on period by pushing the water through the warmed deck.

If this is true, then having a piece of insulation on top of the deck might be able to solve both problems at once!?

[Sher]

That is brilliant, belugaleuca. 

[lynnee]

Apr 3, 2022 19:17:22 GMT -5 Sher said:

That is brilliant, belugaleuca. 

x2!

[Shawn]

x3

[lynnee]

belugaleuca, earlier I meant to say that I really like your colorful diagram of the heat transfers in the Bounty! It makes your point very clear.

[belugaleuca]

Apr 4, 2022 19:21:19 GMT -5 lynnee said:

belugaleuca , earlier I meant to say that I really like your colorful diagram of the heat transfers in the Bounty! It makes your point very clear.

I'm glad you like it! That all said my ideas along the way could be wrong though so please take it all with a grain of salt!

[Sher]

Apr 6, 2022 17:20:03 GMT -5 belugaleuca said:

Apr 4, 2022 19:21:19 GMT -5 lynnee said:

belugaleuca , earlier I meant to say that I really like your colorful diagram of the heat transfers in the Bounty! It makes your point very clear.

I'm glad you like it! That all said my ideas along the way could be wrong though so please take it all with a grain of salt!

It seems to me that your conclusions were sound.

Some people put Reflectix on top of their Kratky containers to keep the water from being warmed by the lights or the sun.

[belugaleuca]

Here's a new chart with the New Harvest's pump ON (5 min on/25 min off) and the Old Harvest's pump OFF, with lights ON (at 6am), for three days:



This is with the deck bare and open, and no fan; it seems like the pump running on its schedule results in ~0.5 - 0.9 C extra heat from 12pm onwards (lights on at 6 am). 

It would be interesting to see if this pattern holds or not with a fan, with plants or with the deck covered.

[belugaleuca]

Alright, four more tests!

1. Lights off, OldHarvest pump ON, NewHarvest pump OFF, but this time for 3 days. This confirms that the pump dose not add much heat when the light is off.



2. Added cardboard with holes to try to insulate the top. Nothing happened compared to having the lights on with no cardboard!



3. I thought maybe heat was radiating through the cardboard so I added tinfoil. It didn't have much if any effect, though.



4. Raised the aerogardens off the base using half of a plastic egg carton for each Harvest. This did something!! This time the aerogardens are not exceeding air temperature. However, the OldHarvest with the pump ON is still hotter compared to pump OFF, so that means there's something about the lights being on that's still causing the pumped water to get warm. Checking back to the first graph in this post (lights off), the I don't think the pump is adding this extra heat on its own.

Maybe it is the holes in the top? Next I'll try to cover the holes and see if that makes a difference.