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Old 05-08-12, 10:27 AM   #11
Daox
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I'd say its definitely not enough pump for this application. 16 feet is 4.87 meters. The DDC3.2 is the newer pump design so thats what you'll probably get. It can't even pump up to 4.8 meters. You could use two of them in series though. That would give you double the flow rate at the same head, so at 4.8 meters you should have somewhere around 300 L/hour or 1.32 gpm. Then you have to add in the friction losses from the piping so it'll be lower than that.

According to some guesstimating on my part that doesn't sound like nearly enough. I think my 200sqft array will need between 5 and 10 gpm.


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Last edited by Daox; 05-08-12 at 10:31 AM..
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Old 05-08-12, 10:36 AM   #12
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Here found some good info on the subject. Gary at builditsolar did some testing and here we have it:

Determining Solar Water Heating Collector Flow Rate




So, lets say you go with .03. You'd need to be pumping 5 gpm.
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Old 05-09-12, 10:20 AM   #13
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I still need to measure where the top of the tank waterline will be (I believe that subtracts from the head height?), but I believe I will need two pumps as the system is in two panels and could possibly be shaded at different times. The last thing I need is to be unnecessarily pumping how water through a cool collector. Panel #1 is 86 sqft and panel #2 is 80 sqft, giving flowrates of 2.6 for #1 and 2.4 for #2. Panel #1 has maybe 14-15ft of head and #2 around 12 ft of head.

On the Pump selection Wizard on the Taco pump website, I get results well inside pump's PQ curve. I take it there must be some way to limit the flow rate then? Like valves or a control on the pump itself? Also, I'm wondering if the head pressure changes after the water starts flowing through the collector causing some sort of suction effect? Would that in turn increase the flow rate? I'll get some definite measurements of the heat heights.
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Old 05-09-12, 10:54 AM   #14
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The head height will be the top of the water line to the top of the collector outlet pipe.

You can limit the flow, but there really isn't a reason to. Find a pump that comes closest to meeting your flow requirements and just let it flow as much as it does. You could restrict the flow, but you'd still be using the same amount of power and with the reduced flow you'd just be loosing efficiency through the collector.

The head pressure won't change as things start flowing. Basically you're spending energy to get the water to the highest height, then gravity takes over and takes care of getting the water back down to the tank. Unfortunately there is no suction effect.

Also, I'm not sure how much distance is between your tank and collectors, but the pipe between them will add additional pressure to overcome due to friction. It probably won't be a ton, but its at least worth looking at. It will also determine what size pipe you go with.
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Last edited by Daox; 05-09-12 at 10:57 AM..
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Old 05-14-12, 08:44 PM   #15
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Thanks Daox, that simplifies things a lot. I just measured everything, and panel #1 has 13' 6" of head and panel #2 has 11' 6". As far as the distance goes, it's basically all vertical. The tank is on the basement side of the same wall the collectors are on. I'm thinking 3/4" pex to supply the collector right now...
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Old 05-14-12, 09:49 PM   #16
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The Taco 008 Circulating pump looks like a promising candidate for the first panel. Max head of 15ft, 2.5 gpm @ 14.5ft, 3.5 gpm @ 14ft and 4.5 gpm @ 13.5ft.
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Old 05-15-12, 09:04 AM   #17
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Yeah, the 008 sounds like a pretty good fit for the #1 panel. Looks like the 0010 might be a good choice for the 2nd panel, or another 008.

I threw this picture together real quick to show what we're looking at. Red is panel #1 and green is panel #2.

Some rough calculations show that you'll loose another .7 ft of head due to friction losses. Gary has a nice write up here on how to calculate this.

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Old 05-15-12, 09:24 AM   #18
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The Grundfos UP 15-18 B5 looks good for the second panel. Max head of 13.75ft. 2.25gpm @ 12.5ft, 3.25 gpm @ 11.5ft. Seems to be right in the sweet spot. $140 doesn't sound too bad either.

Both pumps pull under 1 amp so they could be relayed with a couple TinyDTC Temp Controllers. Anybody have any experience with them? Look like a bargain to me.
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Old 05-15-12, 09:53 AM   #19
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Never used them and haven't heard feedback on them. They seem like nice little packages and a good list of features for the price as long as you don't care about having it all packaged in a fancy plastic box.
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Old 05-15-12, 10:05 AM   #20
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Nice. Okay, so it looks like being conservative and allowing even a 1ft head increase from friction losses, the Taco and Grundfos are close to or above the .03gpm/sqft range. 2.25gpm for panel #2 -> .028gpm/sqft and 3.5gpm for panel #1 -> .041gpm/sqft. And I expect the flow rates will be a little bit higher if only .7ft of head is added.

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