Selecting a solar water pump - new circulating pump technologies for solar hot water?
 

I'm just wondering if anyone has heard of or knows of any new technologies that are applicable to a solar hot water setup, mine to be more specific. The pump will be on a closed loop with polypropolene coolant circulating water from the panels to a heat exchanger in my hot water tank.

I don't think that there is a ton to be gained by having a variable speed pump, but I'm not 100% sure on that. Other than that, I know there has been a lot of development in circulating pumps the past few years, and I'd like to take advantage of anything that is out there.

Are you talking about a vacuum tube array?

I'm not sure why that would matter. Hotter temperatures? But, no, these are flat plate collectors.

Not much new in the pumping field that is better than a standard Grundfos pump unless you want to go DC. A variable speed control like the RESOL can give about 8% better output over a single speed system and can be used with any of the can type pumps.

All the systems that are not drainback will need propylene glycol as an antifreeze. Type of panel doesn't matter.

I really like the ElSid pumps, they are an induction drive, so the impeller is 100% sealed off from the electronics and they impeller is the ONLY moving part, I think they make both A/C pumps and D/C variable speed pumps.

El sid pumps are good but the system has to be designed to have low head pressures so depending on how your system is designed (length of piping runs, 90s and height of panels) it might be a good pump. An alternate to the el sid is the Thermo-Dynamics pump which is bigger and more robust.

Thermo Dynamics Ltd. - Solar Pumps

This pump will run off a 20w panel and needs no controller at all. You usually don't get a digital output for DC pumps so monitoring is harder. That may not matter tho....

Unfortunately, the el sid is way too small for my application. My panels are ~100 feet from the tank. I'm planning on running 1" PEX to my 200 sq/ft of panels. Combine this with the antifreeze which thickens up the water and increases head loss and this gives me a target flow rate of ~10 gpm @ 23.5 feet of head. Only the larger inline taco or grundfos pumps even come close to this.

I also emailed Gary at builditsolar to see if he knew about any new stuff I should look out for. He said there really wasn't anything. So, I'm looking at a Taco 0011 or Grundfos UP26-120U.

remind me of how many m2 of panel you are putting in? You only need .25-.6L/m2/minute so if you have 10 x 2m2 panels x .6L= 12L/m or 3.2gpm-MAX. Try the T-D pump with a 30w panel.

The other issue is max temp on the panels. Most PEX systems won't last very long unless you are keeping it really low temp (less than 180F) and I don't know the specs for the panels. If you are going to bury it you want to be sure.

200 square feet is 18.6 square meters.

To size my pump I've been following the pump sizing guide on builditsolar. He recommends .025-.075 gpm per square foot (which Heliodyne, a solar panel mfg also recommends). His testing shows siginificant gains to staying a little above .025.

Your recommendation of .6l/m/m2 max puts me at .015 gpm per square foot (unless my math is wrong which is quite possible).

What else would you recommend for piping/tubing?

I always use either copper with armafex insulation or the insulated flexi stainless steel. If you drop the flow rate, you can drop the tubing size from 1" to 3/4" without any drop in performance. You will lose a lot of electrical energy trying to run a 26-120 or a 0011 verses a DC pump or a variable speed AC of the correct size.

The more efficient the panel, the faster you will need to move the glycol to get the heat out. Your panels are probably not as efficient as a new german panel or the Heliodyne which is the same absorber as many of the german ones so i wouldn't be as concerned about maxing out on the flow rate. My info comes from Viessmann and from a number of textbooks I have from Europe and while the numbers are not that different, many manufacturers have a different idea about pumping. Some like higher temps and lower flows, others do not. We have 2 manufacturers here that do "microflow" systems which use 3/8" tubing and a high head pump (T-D is one of those) and T-D has a very high output for their packaged system.

I would use at most a UPS26-99 but the wattage makes it hard for variable speed controls which are often limited to 1A. Try the numbers with a UPS15-58 or a Wilo Star21. These are used in a lot of European pump stations. Gotta get to work, i'm late