Question 9.14: Calculate the cost savings in electric utility bills for an ......

Energy-Efficient Electrical Systems for Buildings [1086323]

Calculate the cost savings in electric utility bills for an industrial customer serviced by the RTP rate used in Example 9.13 if the excess electrical load experienced during the curtailment hours (between 3 p.m. and 8 p.m.) is shifted uniformly to the next 4 h (between 8 p.m. and midnight). With this load shifting measure, the demand during the curtailment hours would be 500 kW and the total daily energy use for typical days would remain the same, as shown in Table 9.12.

TABLE 9.12 Actual and CBL Hourly Energy Use Profiles for the Industrial Facility Assumed in Example 9.13
Hours	Typical Weekday Actual Energy Use (kWh)	Typical Weekend day Actual Energy Use (kWh)	Noncurtailment Typical Day CBL Energy Use (kWh)	Curtailment Typical Day CBL Energy Use (kWh)
0:00–1:00	345	250	220	220
1:00–2:00	455	270	230	230
2:00–3:00	676	305	325	325
3:00–4:00	785	320	360	360
4:00–5:00	980	360	455	455
5:00–6:00	1,200	405	645	645
6:00–7:00	1,800	460	1,715	1,715
7:00–8:00	2,905	510	2,450	2,450
8:00–9:00	2,825	525	2,545	2,545
9:00–10:00	2,800	520	2,480	2,480
10:00–11:00	2,845	535	2,560	2,560
11:00–12:00	3,015	550	2,765	2,765
12:00–13:00	2,500	565	2,745	2,745
13:00–14:00	2,765	560	2,730	2,730
14:00–15:00	2,890	535	2,650	2,650
15:00–16:00	2,815	525	2,590	500
16:00–17:00	2,825	530	2,520	500
17:00–18:00	2,780	510	2,370	500
18:00–19:00	1,755	495	2,175	500
19:00–20:00	1,100	480	2,080	500
20:00–21:00	845	395	1,945	1,945
21:00–22:00	635	345	1,680	1,680
22:00–23:00	535	290	1,230	1,230
23:00–24:00	385	270	575	575
Total	42,461	10,510	42,040	32,805

Step-by-Step

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(a) The excess load during the curtailment hours is first determined as follows:

Excess load $=2815 \ kWh+2825 \ kWh+1755 \ kWh+1100 \ kWh-4*500 \ kWh=6495 \ kWh$

(b) For each hour during the next 4 h (i.e., between 8 p.m. and midnight), the additional load will be $6495 \ kWh/4 = 1623.75 \ kWh$ . The additional energy cost during the noncurtailment hours associated to this shift is then

Energy cost increase= $1623.75 \ kWh*[(0.01523+0.01532+0.01723+0.01722)\$/kWh]=\$105.54$

(c) The shift of electrical load during the curtailment hours has the effect of eliminating any hourly energy cost during the curtailment hours from 3 p.m. to 7 p.m., as shown in Table 9.14.

That is, $\$2533.09+\$2049.15+\$811.67+\$292.50=\$5686.41$

(d) Since all the other charges remain unchanged, the reduction in cost savings is simply the energy charge avoided during the curtailment hours minus any energy cost increase during noncurtailment hours, or

Utility cost savings= $[\$5,686.41/day-105.54/day]*2 \ days=\$11,161.74$ for the month.

TABLE 9.14
RTP Hourly Energy Cost during a Typical Curtailment Day for the Industrial Facility of Example 9.13

Curtailment Typical Day Hourly Energy Cost ($)	Curtailment Typical Day Hourly Energy Price ($/kWh)	Curtailment Typical Day CBL Energy Use (kWh)	Typical Weekday Actual Energy Use (kWh)	Hours
2.09	0.01673	220	345	0:00–1:00
3.79	0.01683	230	455	1:00–2:00
6.07	0.0173	325	676	2:00–3:00
7.57	0.0178	360	785	3:00–4:00
9.98	0.019	455	980	4:00–5:00
11.82	0.0213	645	1,200	5:00–6:00
2.32	0.0273	1,715	1,800	6:00–7:00
13.15	0.0289	2,450	2,905	7:00–8:00
8.21	0.2932	2,545	2,825	8:00–9:00
10.28	0.03213	2,480	2,800	9:00–10:00
10.19	0.03575	2,560	2,845	10:00–11:00
8.56	0.03423	2,765	3,015	11:00–12:00
-8.47	0.03456	2,745	2,500	12:00–13:00
1.29	0.03677	2,730	2,765	13:00–14:00
9.54	0.03977	2,650	2,890	14:00–15:00
2,462.00	1.0635	500	2,815	15:00–16:00
2,533.09	1.0895	500	2,825	16:00–17:00
2,049.15	0.89875	500	2,780	17:00–18:00
811.67	0.64675	500	1,755	18:00–19:00
292.5	0.4875	500	1,100	19:00–20:00
-16.75	0.01523	1,945	845	20:00–21:00
-16.01	0.01532	1,680	635	21:00–22:00
-11.97	0.1723	1,230	535	22:00–23:00
-3.27	0.01722	575	385	23:00–24:00
8,197		32,805	42,641	Total