Effective and efficient pump selection demands a thorough understanding of the system curve and how it reflects what happens in the actual system. This is especially true in today’s variable speed systems. It’s so important that even though we’ve touched on it many times before, we are going to “hit pause” in this series to focus specifically on ...
Variable speed drives do not compensate for an imperfect pump selection. In fact, they can make the situation worse. It is okay to be slightly conservative in your pump selection if you are not 100% sure how the pumps are going to be piped, but....
In our last blog we explained why in real life HVAC applications, variable speed pumps almost never operate at zero speed. Even at no flow, the impeller must be spinning enough to produce some amount of pressure at the 2-way valve in order to quickly establish full flow at the critical circuit IF demand suddenly occurs. Here's a silly way to think about it....
In variable speed pumping systems, does zero load ever result zero pump speed?
Practically speaking, the answer is no. In closed hydronic systems with 2-way valves there is almost always some amount of differential pressure created by continuous impeller rotation – even when....
It makes sense to select a pump based on a wide range of operating conditions, not just peak load. This will yield more savings than a pump selection based on the singular sweet spot of Best Efficiency Point (BEP). Instead of focusing on that point where the system curve intersects with the BEP, we need to look at a broader operating range, the boundaries of which form what is called an “Efficiency Island”. Efficiency Islands are....
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It should be clear by now that selecting a pump based on design conditions and best efficiency point (BEP) will not yield optimum system efficiency. We’ve also learned that virtually every HVAC pump system will have a minimum amount of pump head, even in the absence of demand. In between these minimum and maximum operating conditions lies the control range for our pump. Keeping all this in mind, how do we select the most efficient pump for a specific application?