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Applications Handbook (ASHRAE 1999); these are based on the minimum capacity permitted by the Department of Housing and Urban Development (HUD) and the Federal Housing Administration (FHA) (HUD 1982). Energy factor is the National Appliance Energy Conservation Act minimum for the corresponding fuel type and storage capacity (DOE 2002a). An example set of DHW specifications based on a typical three-bedroom, two-bathroom Prototype is shown in Table 9. The BA Analysis Spreadsheet developed by NREL automates many of the equations discussed in the following paragraphs and can be downloaded from the BA Web site (http://www1.eere.energy.gov/buildings/building_america/perf_analysis.html). The BA Analysis spreadsheet also calculates the correct DHW inputs for the TRNSYS computer program, including standby heat loss coefficient (UA). The spreadsheet has a comprehensive set of inputs and outputs that can be used to help calculate DHW properties for the Prototype house (Burch and Erickson 2004).

Table 7. Characteristics of Benchmark Domestic Hot Water System Water Heater Fuel Type in Prototype

Storage Capacity (V) (Gallons) Energy Factor (EF) Recovery Efficiency (RE)

Burner Capacity Hot Water Set Point Fuel Type Tank Location

Electric

Gas

See Table 8

See Table 8

0.93 – (0.00132 × V)

0.62 – (0.0019 × V)

0.98

0.76

See Table 8

See Table 8

120°F Same as Prototype Same as Prototype *

*

If the Prototype does not have a DHW system, or the hot water system uses solar energy or a fuel other than gas or electricity, the Benchmark shall use the same fuel for water heating as that used for Benchmark space heating.

Storage (gal)

20

30

30

40

30

40

40

40

40

50

50

50

Burner (kBtu/h)

27

36

36

36

36

36

38

36

38

38

47

50

Storage (gal)

20

30

40

50

40

50

50

50

50

66

66

80

Burner (kW)

2.5

3.5

4.5

5.5

4.5

5.5

5.5

5.5

5.5

5.5

5.5

5.5

Table 9. Example Characteristics of Benchmark Domestic Hot Water System Based on a Prototype With Three Bedrooms and Two Bathrooms

6 All

Electric

Table 8. Benchmark Domestic Hot Water Storage and Burner Capacity (ASHRAE 1999)

  • #

    Bedrooms

    • #

      Bathrooms

Gas

5 All

≥3

1 All

≥3

≤1.5

4 2–2.5

≥3

≤1.5

3 2–2.5

≤1.5

2 2–2.5

Electric

Gas

Storage Capacity (V) (Gallons)

50

40

Energy Factor (EF)

0.86

0.54

Recovery Efficiency (RE)

0.98

0.76

Burner Capacity

5.5 kW

36,000 Btu/h

Water Heater Fuel Type in Prototype

Supply Temperature

120°F

Fuel Type

Same as Prototype

Tank Location

Same as Prototype

12

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