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Stylized Text: Comparison of Previous and New Ratings.


Revised May 2005

Table 1.  Comparison of existing FSEC Energy Factor (EF) ratings and
          new FSEC EF ratings for representative generic systems
System Type
Collector Area (ft2)
/Tank
North
Central & South
Existing EF
New
EF
Existing EF
Central & South
New EF
Central
New EF
South
Drainback-Sidearm
HX
40/80
1.7
1.7
1.7
2.1
2.3
Drainback-Tank Wrap HX
40/80
1.5
2.0
1.6
2.4
2.5
Drainback-Tank Wrap HX
48/80
2.5
2.3
2.6
2.8
2.9
Drainback-Tank Wrap HX
64/80
2.2
2.6
2.3
3.3
3.5
Indirect Tank Wrap
HX Glycol
40/80
2.3
2.6
2.5
3.4
3.9
Direct - Diff
32/52*
2.1
2.3
2.2
2.9
3.4
Direct - Diff
40/80
2.7
2.9
2.8
4.2
4.7
Direct - Diff
40/80
2.7
3.2
2.9
4.9
6.4
Direct - PV
32/80
2.6
3.4
2.7
5.3
6.9
Direct - PV
40/80
4.1
4.4
4.5
8.4
13.2
Direct - PV
40/80
3.3
4.5
3.6
8.6
13.8
Single ICS
32/41
4.1
1.9
4.9
2.2
2.4
Single ICS
25/42
3.4
1.7
4.0
1.9
2.1
Double ICS
64/82
>15
2.9
>15
3.8
4.6
Double ICS
50/84
>15
2.4
>15
3.1
3.6

System Types:

Drainback - Sidearm HX: Indirect drainback forced circulation, flat plate collector, solar tank with upper element, side-arm heat exchanger with natural convection loop, AC pump, and differential controller.

Drainback - Tank Wrap HX: Indirect forced circulation, flat plate collector, solar tank with upper element and wrap around heat exchanger, AC pump, and differential controller.

Indirect - Tank Wrap HX: Indirect forced circulation, flat plate collector, solar tank with upper element and wrap around heat exchanger, AC pump, and differential controller.

Direct - Diff: Direct forced circulation, flat plate collector, solar tank with upper element, AC pump, and differential controller. (*Tank is 52 gal conventional electric retrofitted for solar.)

Direct - PV: Direct forced circulation, flat plate collector, solar tank with upper element, 24V DC pump, and 20-Watt photovoltaic module.

Single ICS: Integral collector storage, includes a 50-gallon electric auxiliary tank in system.

Double ICS: Integral collector storage, includes a 50-gallon electric auxiliary tank in system.

Notes:

  1. North Ratings: The old ratings were based on Apalachicola meteorological data. The new rating is based on Jacksonville TMY2 meteorological data.
  2. Central/South Ratings: The old ratings were based on an average of Orlando and Miami meteorological data. The new Central rating is based on Tampa TMY2 meteorological data. South is based on Miami TMY2 meteorological data.
  3. Collector Tilt: The old collector tilt was based on 12 orientations (azimuth from 0 to 45 degrees and tilt at 20, 30, and 40 degrees) and an average of the result. The new tilt for all three cities will be 24 degrees.
  4. Backup heater set point: The old set point was 122 F while the new set point is 120 F.
  5. Water mains temperature: The old water mains temperature constant was 72 F for all three locations. The new method is varied monthly using values for each city.
  6. Tempering valve: The effect of a tempering valve is included to meet plumbing code.
  7. In these comparisons we attempted to define the old and new systems as equivalently as possible. TRNSYS requires more detail to define the system, so in most cases additional information beyond that input to the previous F-Chart developed EFs was used.
  8. Note that Solar Fraction (SF) and Energy Factor (EF) are related to each other by the following relationship: SF = 1.0-(0.9/EF).