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Sampling guidelines
When preparing the Final Application, a Project Sponsor is required to document each fixture or piece of equipment that is part of a project. Equipment with similar functional uses may be grouped together for M&V purposes. Once the equipment has been grouped, a sample of each grouping's equipment may be monitored and the results used to estimate the operating hours for all of the fixtures or equipment within that group. (For more information on specific equipment groupings, see the measure-specific M&V approaches for that equipment type.)
The table below shows how large the sample size must be to provide a reliable estimate for varying sizes of groups. The initial sample sizes represent 80% confidence/20% precision and have a coefficient of variation of 0.5; the suggested sample sizes have been increased by 10% to compensate for equipment failure or loss.
|
Group
population |
Initial
sample size (80/20) |
Suggested
sample size (80/20 plus 10%) |
|
4
|
3
|
4
|
|
5
|
4
|
5
|
|
12
|
6
|
7
|
|
16
|
7
|
8
|
|
20
|
7
|
8
|
|
25
|
8
|
9
|
|
30
|
8
|
9
|
|
35
|
8
|
9
|
|
40
|
9
|
10
|
|
45
|
9
|
10
|
|
60
|
9
|
10
|
|
65
|
9
|
10
|
|
70
|
9
|
10
|
|
80
|
10
|
11
|
|
90
|
10
|
11
|
|
100
|
10
|
11
|
|
125
|
10
|
11
|
|
150
|
10
|
11
|
|
175
|
10
|
11
|
|
200
|
10
|
11
|
|
300
|
10
|
11
|
|
400
|
11
|
13
|
|
500
|
11
|
13
|
The Project Sponsor may propose an alternative approach to determining sampling sizes, but it must be approved by CenterPoint Energy and be based on sound statistical principles.
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