With solar heating systems characterised by their relative low flow and high head, I was wondering what the state of the art is with regard to solar application specific circulation pumps? It seems that many systems employ circulation pumps that run at extremely low inefficiencies.
As my experience with circulation pumps is limited, I would greatly appreciate any comments related to this query.
www.sciencedirect.com/science/article/pii/S1877705815028775/pdf?md5...
www.asse-plumbing.org/chapters/NOH%20SolarWtrHtg%20Pres.pdf
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0ahUKEwie3aCJ3dTUAhXIKo8KHfF3CzYQFggyMAI&url=http%3A%2F%2Fwww.mdpi.com%2F1996-1073%2F8%2F12%2F12365%2Fpdf&usg=AFQjCNHvhRCeZUlbbCmmxdRSW-NtVKrl9g&cad=rja
http://ac.els-cdn.com/S1877705815028775/1-s2.0-S1877705815028775-main.pdf?_tid=41c8b8e6-584c-11e7-be84-00000aacb361&acdnat=1498247200_f85c2711e7d64ce2d9b532960e42016c
According to my experience with solar systems, the best way is to find a variable speed pump, because with variable speed pumps run by a suitable PID or similar alogirthm, you can make your solar collectors work with constant and sufficiently high temperatures all day long, and thus with high efficiency.
I suggest you the following papers:
http://www.sciencedirect.com/science/article/pii/S0196890413006043
http://www.sciencedirect.com/science/article/pii/S221067071730238X
Do you really mean "... that run at extremely low inefficiencies." ?
If you meant "at low efficiencies": this is true for some older installation. Current installations should include variable speed, electronically controlled pumps (as Valeria Palomba stated), delivering reasonable efficiencies.
The main reason for this are the costs for electricity per kWh. Thus, in countries with low electricity costs low efficiency pumps may still dominate due to lower initial invest. But it is reasonable to go for high efficiency pumps: not only to lower energy consumption (which may or may not pay off), but also to increase pump lifetime (lower power, (eventually) lower average rpms -> lower operating temperatures -> longer life).
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