Matt Meier
New Member
I'm convinced. The simple simulation says that I can improve the efficiency up to about 11% by varying the system flow based on operating conditions. It's not a completely intelligent simulation. It doesn't try to optimize the flow, or balance the system over time. Those are things I wouldn't try to debug for this fall anyway. It's also only for one boiler/pump/zone/imaginary house combination. However, that's a sizable gain over time; enough to make me believe that it's probably worthwhile in most cases.
The downside is that I can't find suitable pumps. It seems the small residential ones are all boxed-up units, and you have to follow their prescribed operating curves. I can get pumps with speed-control inputs in the larger commercial units, but those are big, and also quite a bit more expensive. I'll work around that eventually, but I have a couple new questions.
First, I keep hearing that induction motor pumps are terribly inefficient, and that the ECM pumps are infinitely better. Why? It's just an induction motor, and we can get well into the 80% range even with older induction motors with proper control. Is this only because we assume that induction motors are full-on/full-off, and that the ECM pumps can modulate?
Second, I've read quite a few times that a large ECM pump with zone valves is much cheaper to operate than using zone pumping. Why? Flow is flow, and pressure is pressure, and they multiply to give the delivered power. For example, suppose we have one pump, pumping three circuits. Given an 8ft drop across the system, and the first circuit flows 2gpm, the second 3gpm, and the third flows 3.5gpm, that gives us a total of 29.4W. Assuming the pump is 85% efficient, that's 34.5W into the pump. Now, if we split the zones with three pumps, each operating at 85% efficiency, then we get the same total. Aside from the fact that the three pumps will be operating at slightly different efficiency points, where's the difference? Adjusting the operating points of the pumps slightly, assuming they're properly sized, won't create the discrepancy that's argued all over the web.
Thanks again. This is getting fun!
Matt
The downside is that I can't find suitable pumps. It seems the small residential ones are all boxed-up units, and you have to follow their prescribed operating curves. I can get pumps with speed-control inputs in the larger commercial units, but those are big, and also quite a bit more expensive. I'll work around that eventually, but I have a couple new questions.
First, I keep hearing that induction motor pumps are terribly inefficient, and that the ECM pumps are infinitely better. Why? It's just an induction motor, and we can get well into the 80% range even with older induction motors with proper control. Is this only because we assume that induction motors are full-on/full-off, and that the ECM pumps can modulate?
Second, I've read quite a few times that a large ECM pump with zone valves is much cheaper to operate than using zone pumping. Why? Flow is flow, and pressure is pressure, and they multiply to give the delivered power. For example, suppose we have one pump, pumping three circuits. Given an 8ft drop across the system, and the first circuit flows 2gpm, the second 3gpm, and the third flows 3.5gpm, that gives us a total of 29.4W. Assuming the pump is 85% efficient, that's 34.5W into the pump. Now, if we split the zones with three pumps, each operating at 85% efficiency, then we get the same total. Aside from the fact that the three pumps will be operating at slightly different efficiency points, where's the difference? Adjusting the operating points of the pumps slightly, assuming they're properly sized, won't create the discrepancy that's argued all over the web.
Thanks again. This is getting fun!
Matt