Variable speed demonstration trial

Result Demonstration Report

Variable speed pumps and fixed pumps

Collaborators: John Harvard, Darren Jost, Amy Bader

J. Enciso-Medina, Irrigation Specialist, Fort Stockton, TX

W.L. Multer, EA-IPM, Glasscock, Reagan, Upton, Garden City, Texas

Robert Scott, CEA-AG, Reagan County, Big Lake, Texas A&M University

Raymond Quigg, CEA-AG, Upton County, Rankin, Texas A&M University

Steve Sturtz, CEA-AG, Glasscock County, Texas, Garden City, Texas

Introduction

Cotton production is an important economic base in Far West Texas. However, the region has erratic and limited rainfall, usually ranging from two to seven inches during the growing season, causing producers to be dependent mainly on extremely limited groundwater supplies. The adoption of SDI systems from furrow irrigation started in 1983. Since then, about 30,000 acres of SDI systems have been installed. This rate continues in Far West at a rate of 5,000 acre per year. SDI has allowed users to achieve application efficiencies exceeding 90 percent, while making it possible to spread a small irrigation depth over a larger area in frequent, optimum watering, resulting in higher yields and better quality. The water use efficiency (yield per unit of water used) has increased from 35 lbs/ac-in for furrow irrigation to above 55 lbs/ac-in for SDI.

SDI systems have also increased profits due to reduced water, fertilizer, and cultural costs, and if properly maintained, have demonstrated a usable life span of up to 15 years. The systems require rather large up-front expenditures, but have proven to perform well in a variety of soil types, although they are best suited for areas where water is very limited (less than 3.5 gallons per minute per acre) or where water is expensive (more than $7 per acre-inch). The breakeven cost has been reduced with the adoption of SDI systems from $0.60 to $0.53 per pound.

Currently, we are trying to increase our water use efficiency and to reduce our breakeven cost through the use of fertigation, reduced tillage practices, and narrower spaced cotton. This study was planned to study the effect of variable speed pumps on the energy use, and if pumping costs can be further reduced.

Objectives

Compare 3 and 5 HP.
Compare variable speed pumps with fixed speed pumps for the 5 HP.

Study

The study consisted in 2 wells with 3 HP pumps, 3 wells with 5 HP pumps with drivers to control the speed of the pump, and 2 wells with 5 HP. The cost per kw-hr used in this study was $0.085.

Results

Energy cost for the 5 HP pumps with variable speed for a period of 5 months were $257 dollars lower than the constant speed pumps.

The cost per ac-in for the 5 HP variable speed pumps is $6.82, for the 5 HP constant speed pumps is $7.68, and for the 3 HP pumps is $6.33.

The 5 HP variable speed pumps pumped less water than the constant speed pumps.

Although the 3 HP pumps were more energy efficient, they pumped less water.

One of the possible advantages of the variable over the constant speed pumps: it is that variable speed pumps don’t need as much supervision for closing the valve to avoid air pumping. Additionally, if the valve is closed too much the pumping flow rate could be reduced considerably.

Variable speed demonstration trial - Darrel Jost's house
		Well
		1	2	3	4	5	6	7	Total
Date	Characteristic	5 HP	5 HP	5 HP	5 HP	5 HP	3 HP	3 HP
		with drive		with drive		with drive
06/11	Pressure	24	30	22	42	22	26	19
	Gallons	1072117	1157566	1084746	1293514	1246317	960403	221983	7036646
	GPM	29.31	25.48	23.85	28.85	27.57	21.12	21.87	178.05
	Energy (KW)	4633	5207	4270	5612	4859	2942	3202
	Cost	393.8	442.6	363.0	477.0	413.0	250.1	272.2
06/18	Pressure	21	28	21	48	20	27	21
	Gallons	1337027	1409484	1319131	1574452	1487431	1167001	435211	8729737
	Gallons accumulated	264910	251918	234385	280938	241114	206598	213228
	GPM	30.01	25.3	21.83	27.75	28.14	20.2	21.05	174.28
	Energy (KW)	5410	6031	4954	6524	5572	3512	3763
	Energy accumulated (KW)	777	824	684	912	713	570	561
06/25	Pressure	24	27	20	49	20	26	19
	Gallons	1605159	1650728	1540135	1840654	1737791	1363648	639703	10377818
	Gallons accumulated	533042	493162	455389	547140	491474	403245	417720
	GPM	30.3	24.28	21.23	27.11	30.97	19.62	20.73	174.24
	Energy (KW)	6204	6832	5607	7418	6313	4068	4317
	Energy accumulated (KW)	1571	1625	1337	1806	1454	1126	1115
07/2	Pressure	24	30	20	55	22	28	21
	Gallons	1873249	1895119	1762855	2109005	1992569	1562628	847562	12042987
	Gallons accumulated	801132	737553	678109	815491	746252	602225	625579
	GPM	31.62	34.38	21.83	26.4	24.24	19.95	20.66	179.08
	Energy (KW)	6994	7648	6264	8329	7063	4632	4884
	Energy accumulated (KW)	2361	2441	1994	2717	2204	1690	1682
07/9	Pressure	19	48	18	57	20	25	19
	Gallons	2136243	2135448	1980843	2374032	2240680	1758556	1053768	13679570
	Gallons accumulated	1064126	977882	896097	1080518	994363	798153	831785
	GPM	29.81	24.35	21.55	26.23	29.88	19.6	20.48	171.9
	Energy (KWatts)	7770	8470	6905	9239	7796	5187	5444
	Energy accumulated (KWatts)	3137	3263	2635	3627	2937	2245	2242
07/16	Pressure	21	49	19	60	18	25	19
	Gallons	2371031	2374128	2195484	2635789	2486560	1951896	1257936	15272824
	Gallons accumulated	1298914	1216562	1110738	1342275	1240243	991493	1035953
	GPM	20.2	24.42	22.22	26.33	24.99	19.46	20.58	158.2
	Energy (KW)	8531	9293	7538	10129	8522	5735	5996
	Energy accumulated (KW)	3898	4086	3268	4517	3663	2793	2794
07/23	Pressure	20	49	12	56	20	25	19
	Gallons	2605818	2605818	2401625	2891165	2726072	2140356	1456345	16827199
	Gallons accumulated	1533701	1448252	1316879	1597651	1479755	1179953	1234362
	GPM	27.08	23.64	15.95	26.44	30.37	19.56	20.59	163.63
	Energy (KW)	9269	10105	8155	11007	9230	6267	6536
	Energy accumulated (KW)	4636	4898	3885	5395	4371	3325	3334
	WHP	1.78	2.55	1.93	2.92	2.16	1.76	1.79
	Measured Watts	4636	4898	3885	5395	4371	3325	3334
	kw-hr from measurement	3.71	3.92	3.11	4.32	3.50	2.66	2.67
	WHP/kw-h	0.48	0.65	0.62	0.67	0.62	0.66	0.67
	Efficiency	54.07	73.35	70.04	76.22	69.54	74.55	75.59