Comment

Comment by Jeff S on March 11, 2014 at 10:28pm

Cool chart. Now all I would have to do is determine how many BTUs the panel is producing to regulate properly.

Comment by John Malone on March 11, 2014 at 9:23pm

Heat Transfer In Solar Panels

Ref: Heat Transfer Vs. Water Flow

 

Ref : Determining Collector Flow Rate

Quote: "Basically, flow rates that are too low will not remove the heat efficiently from the collector, and the efficiency of the system will be low.  Flow rates that are too high will require larger pumps and plumbing that increase both initial and operating costs.  So, you want just the right flow rate."

Comment by Jeff S on March 11, 2014 at 9:09pm

@John, I'm not an expert at this but in all my years as an auto mechanic I found that if you run the water too quickly through the radiator (solar panel) then the water would not heat up enough to create enough heat to be usable i.e. heating the car (FT).

Comment by Dr. George B. Brooks, Jr. on March 11, 2014 at 3:55pm

Just an fyi, You are invited to my lecture on the "Power of Aquaponics" at ASU Tempe Az's, School of Sustainability Noon, Tuesday April 1st 12pm. Please RSVP at the link below. The room fills fast. We look forward to seeing you there.

http://bit.ly/1cO0ZgE

Comment by John Malone on March 11, 2014 at 10:15am

@Jim Troyer

The rate of heat transfer between two object is directly proportional to the temperature difference between those objects.   The greater the difference in heat, the faster the thermal energy will move to from the hot object to the cold one.   

When related to the solar panel, the faster you can get the water through the panel the better, otherwise it heats up and slows the transfer of solar energy to the water.

So, within reason, the faster you can move the water through the system the more efficient the solar water heater will be.

Comment by Jim Troyer on March 10, 2014 at 9:25pm

thanks for the update John. 

I'm not sure that increased water flow has anything to do with your solar collection device's efficiency.  I figure the same amount of sun is going to hit it either way.  The water should, in theory, absorb the same calories of heat energy at any reasonable velocity.

It is a slippery slope isn't it?

Comment by John Malone on March 10, 2014 at 10:42am

@ Jim Troyer

... and as for making changes to the system, I'll never stop changing, adding, improving, working, extending, and 'fixing' it.  

It's a constant shame when there's no room in the grow beds to plant anything.

Comment by John Malone on March 10, 2014 at 10:35am

@ Jim Troyer

The DWC bed is constant height.

Except... I use a small very cheap fountain pump to move water through the solar panel in the winter months.   It used to sit in the bottom of the in-ground fish tank, but then I had a brainwave.  Why not put the solar panel pump in the DWC bed.  It's higher, and closer to the solar panel, so I'll get better flow through the solar heater.   Brilliant idea.  It decreased the head height and shortened the lead pipes to the solar panel.   The result was a noticeably better flow rate which makes for a more efficient heater.

The very small amount of water that the solar panel pump moves is irrelevant in normal use, because of the volume of the DWC bed and the regular inflow of water from the system. But when I turned off the incoming water flow the little fountain pump just kept on chugging away, little by little.  The other plants in the bed didn't care about the situation, but the lettuce certainly did.  This surprised me, considering that the roots on the lettuce are a couple of feet long and would still be in the water.

As Michelangelo said:  "I am still learning."

Comment by Jim Troyer on March 10, 2014 at 10:24am

Hi John:  nice to hear you too are still making changes to your system. 

I was surprised to hear that your DWC bed is not constant height. 

How is the water level set in there and do you allow it to rise and fall regularly?

Thanks for sharing

all the best,

Jim

Comment by John Malone on March 10, 2014 at 10:16am

Radial Flow Filter Upgrade

I decided to raise the RFF so that it would be easier to empty the contents in to a 5 gallon bucket to be used in the garden.   After turning off the water I dismantled the filter and built a nice 20" frame for it to stand on.   Lovely.   I was worried that the extra height would be too much for the pump to overcome, and it is a slower flow-rate, but all seems well.  

What I didn't realise what that during the hour or so that I had the water off, the solar panel pump was slowly emptying out the DWC bed.   It's a really slow pump, so I didn't pay any mind to it.  The good lady came out while I was admiring my new RFF stand and said "What's wrong with the lettuce?"    Whaaaa?   It appears that lettuce takes a very dim view of not having their roots in water.

Turned the water on pronto and next day the lettuce was back to normal.  Whew!

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