Rulemaking for Alternative Efficiency Determination Methods and Test Procedures for Walk

- In
Coolers and Walk

- In Freezers Data Supporting Evaporator Fan and Electric Defrost Energy Calculations April 24, 2014

In a Supplemental Notice of Proposed Rulemaking (SNOPR) covering alternative efficiency determination methods and test procedures for walk

- in coolers and walk

- in freezers (WICF s or walk

- ins), published February 20, 2014, the U.S. Department of Energy (DOE) proposed nominal values to be used when rating a condensing unit separately under DOE’s test procedure for WICFs, AHRI 1250

- 2009, “Standard for Performance Rating of Walk

- in Coolers and Freezers” (AHRI 1250

- 2009) . These nominal values
represent ed the evap orator fan and electric defrost energy contributions to a refrigeration system containing that condensing unit. See 79 FR 9818 at 9831. This memo discusses data DOE used to support the determination of nominal values for DOE’s forthcoming final rule cover ing test procedures
for WICFs

.

Unit Cooler On

- Cycle Fan Power Factor

DOE presented the data supporting its proposed nominal values for on

- cycle fan power in Table III.4 of
the SNOPR. 79 FR at 9830. However, these data did not cover the full range of capac ities that are used in WICFs, particularly larger enclosures. For the final rule, DOE surveyed data from manufacturer brochures covering capacities up to 250,000 Btu/h. Figure 1 and Figure 2 present the total fan power as a function of capacity for a range of systems available from several manufacturers

.

Figure 1 : Manufacturer Brochure Data for Fan Po wer of Medium Temperature Unit CoolersFigure 2 : Manufacturer Brochure Data for Fan Power of Low Temperature Unit Coolers

The results suggest that a nominal value of 0.013 watts per Btu/h of capacity is appropriate for medium temperature systems and 0.016 watts per Btu/h of capacity is appropriate for low temperature systems.

Unit Cooler Electric Defrost Energy Factor

DOE also presented the data supporting its proposed nominal values for electric defrost energy in Table
III.4 of the SNOPR. 79 FR at 9830. As with the fan power data, these data did not cover the full range of capacities used in WICFs. For the final rule, DOE surveyed data from manufacturer brochures covering capacities up to 250,000 Btu/h. The available data were in the form of electrical power in watts. Figure 3
presents electric defrost wattage data as a function of capacity for a range of systems available from
several manufacturers.Figure 3 : Manufacturer Brochure Data for Electric Defrost Power of Low Temperature Unit Coolers

The defrost energy per cycle can be found by multiplying the defrost wattage by the duration of the defrost cycle. DOE’s engineering model developed in support of its forthcoming final rule for energy conservation standards applied the capacity

- dependent d efrost durations shown in Table 3

.

Table 1 : Defrost Duration versus System Capacity Capacity (Btu/h) Defrost Cycle D uration (hours)

> 75,000 * 1
50,001

- 75,000 0.75

0

- 50,000 0.5 *DOE assumed that defrost durations over 1 hour in length would not be used because they would cause excessive heating within the WICF.

Using the manufacturer data for defrost wattage in Figure 3 and the defrost durations in Table 3 , DOE calculated the defrost energy per cycle for the same range of systems shown in Figure 3

. Figure 4 presents the total defrost energy per cycle as a function of capacity.Figure 4 : Electric Defrost Energy per Cycle for Low Temperature Unit Coolers

DOE observed that the relationship between capacity and defrost energy per cycle approximates a power series. Therefore, DOE is expressing the nominal value for electric defrost energy use as a power
function instead of a line ar equation.

Equation: Electric defrost energy per cycle (Wh/cycle) = 8.5 × 10 - 3 × (Gross capacity) 1.27