Pumps Don’t Head: Valves Do (Part Two)

Comparing Total System Horsepower: VAV vs. Chilled Beam-LOFlo Systems 

By Greg Cunniff, Applications Engineering Manager, Taco, Inc.

This is the second part of our discussion series “Pumps Don’t Head: Valves Do”. In the first part, we examined how we calculate pump energy consumption.

Now lets graphically compare total system horsepower or electrical demand in the case of energy efficiency for an all-air VAV system, a conventional chilled beam system, and Taco’s LOFlo chilled beam system.

A comparison of peak power demand for a low-flow injection-pumping system.

A comparison of peak power demand for a low-flow injection-pumping system.

It’s interesting, and we’ll be the first to admit it, that the efficiency of a LoadMatch circulator used in the calculation is quite low. But focusing on the efficiency of the LoadMatch circulators misses the point, because the lower efficiency LoadMatch circulator does not see much head, so a LoadMatch system (or a LOFlo system which employs LoadMatch circulators) still has a lower overall pump horsepower.

The point is that pumps, regardless of how many are used, do not impose head on a system. Control and balancing valves do. Therefore hydronic systems like LoadMatch and LOFlo – using pumps instead of valves – will have lower overall pump horsepower.

Then there’s the use of variable speed drives to further reduce pump horsepower and energy consumption.  In a single pipe system, like LoadMatch, the VFDs are controlled from Delta T (differential temperature) and not Delta P (differential pressure). Pump mounted VFDs with an integral controller, which Taco now offers,  can sequence both Delta T and Delta P. In fact, Taco is the only pump manufacturer presently offering both control sequences in one on-board controller.

In conclusion, adding pumps doesn’t add head – they work to eliminate head. Single pipe systems (like LoadMatch-LOFlo) achieve savings in pump horsepower by splitting the horsepower between the primnary and terminal secondary pumps. Using a single pipe system eliminates the need for all control and most balancing valves, which in a conventional two-pipe system add head.

The takeaway: hydronic systems are more efficient than air systems and single pipe hydronic systems are the most efficient of all. We are interested in learning about your opinions and experiences.

2 Responses

  1. Interesting discovery. Now that I think about the different comparisons, it’s starting to make sense that the single pipe systems are more efficient. Cheers!

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