Two researchers affiliated with the Virginia Tech College of Engineering have published a paper which reports that hot water recirculating systems touted as “green,” actually use both more energy and water than their standard counterparts. The research found that the “so-called green” hot water recirculation systems used more net water than the conventional systems after accounting for water needed to produce the extra energy.
I agree, my point is that recirculating systems are totally wasteful and the least desireable of all options (stored, point of use (POU) and recirculating). But POU systems, while unreliable at the moment, represent a technology that should receive an extended time to develop in the open market. Definitey at this point it isn’t ready for wide-scale domestic use where installed cost is a bigger factor, but they are widely used in large industrial and commercial application (often just to avoid having to run hot and cold pipes very long distances and large volumes of hot water aren’t the norm). But as an engineer I see the current issues as very solveable with some good sound basic design and manufacturing, not quantum leaps in physics and pure science. Part of the issue with the current POU is that improvements in stored systems keep pushing the break-even for domestic tankless POU further and further out just like improved MPG on conventional gas-only cars keeps raising the bar for hybrids.
Geoff has a good point, point of use is far too expensive at the moment. Conventional systems are better because you have a static mass of hot water rather than spread-out, building-wide radiator.
Howdy kenw
I dunno how widely point of use water heating may have replaced circulation. When our water heater went out a few years ago, I asked about the price of a Renai tankless system. $3K, roughly ten times the cost of a conventional water heater, and the payback was waaaay out. So I still use a tank system anyway.
Plus the point-of-use items will almost certainly never make a Mythbusters’ “gee, that went quite a way up” video.
Since when were recirculating systems ever green???? Any decent architect or facilities engineer would tell you they’re huge wastes of energy. You can insulate those pipes all you want but basically all you are doing is heating water, sending it out into cooler pipes in the hopes that someone will use it. If no one uses it, (most time no one does) the now-cooler water is returned to be reheated. I thought circulating systems were abandoned years ago for this very obvious reason. Point of use has largely replaced circulating HW systems to reducing wait time (wasted water while waiting for the hot to reach the user). File under “Well, duh”.
Gosh, where have I heard “green…failed to deliver”?