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Abstract
A virtual flow measuring is integrated with the best efficiency staging and the loop differential pressure (DP) reset method to unleash pump power saving potentials from a variable flow primary pump system. Based on the measured pump head, speed, and power, the virtual measuring determines the pump operation condition in an accurate and fast way. The pump operation parameters are then used to realize the best efficiency staging and the loop DP reset control, which calculate the optimal number of operating pumps and each pump's speed respectively. Simulation shows that this control strategy is most energy efficient, and it saves on pump energy consumption by 74.8% compared with a constant flow pumping system. The experiment from a retrofitted two-pump system also shows that the control strategy provided 64.5% pump energy saving over the original constant flow system. In addition, this control strategy requires a lower initial cost, simplifies the implementation process, makes system operation more reliable and stable, and reduces maintenance demands.
Nomenclature
| α | = | the ratio of independent loop head to the total system design head |
| a0, a1, a2 | = | coefficients of pump head-flow second order polynomial equation under design speed |
| A, B, C, D | = | the pump powers at the system loads of 100%, 75%, 50%, and 25%, respectively |
| b0, b1, b2 | = | coefficients of pump power-flow second order polynomial equation under design speed |
| = | cooling degree days | |
| = | pump differential pressure | |
| Effic | = | pump efficiency |
| H | = | system head |
| η | = | pump efficiency |
| n | = | current pump speed |
| = | number of running pumps | |
| P | = | current pump shaft power |
| = | rated pump power ( | |
| Q | = | current pump load (water flow rate) |
| Qt | = | system load, total system water flow rate |
| = | rated pump load (Q/Qdes) | |
| = | system power (VFD input) | |
| ω | = | the ratio of current pump speed to the design pump speed |
| Subscripts and superscripts | = | |
| des | = | the design condition |
| ext | = | existing |
| IPL | = | integrated part load method |
| low | = | low limit |
| lp | = | loop |
| min | = | minimum condition |
| month | = | monthly |
| n = 1, n = 2 | = | single-pump and two-pump running conditions, respectively |
| opt | = | optimal |
| pred | = | predicted |
| set | = | set |
| trend | = | trended data, trending time |
Appendix A
The plot profiles for the trended data on June 16, 2012 (sampling every 5 minutes).
