Hello All,

I'm wondering about fan autosizing in eQuest. When we select "variable speed" fan control, the fan energy plummets by 80-90%. Report SS-L (attached below) shows the first fan only running about 60% for 4 hours per year, and never running above 70%. This is typical across all 10 systems in the building - with the exception of 1 zone that runs above 60% for 36 hours per year and above 90% for 4 hours per year.

The result of this is that when "variable speed" is chosen, ~90% of the fan energy goes away. Any idea why the 'autosized' fan is so much bigger than is needed? We're finding this situation on a lot of models that we review, and it's making savings from VFDs seem much bigger than what is measured in the field. How should we be modeling this?

Thanks in advance,

Christopher Cox 

I've attached the .inp and .pd2 files for your reference, but want to point out these 2 inputs:
Sizing ratio: = 1.00
Sizing option: = Coincident (but irrelevant because only one zone on this system).

FAN ELEC FAN ELEC FAN ELEC FAN ELEC -------- Number of hours within each PART LOAD range --------- TOTAL

DURING DURING DURING DURING 00 10 20 30 40 50 60 70 80 90 100 RUN

HEATING COOLING HEAT & COOL FLOATING 10 20 30 40 50 60 70 80 90 100 + HOURS

MONTH (KWH) (KWH) (KWH) (KWH)

----- ----------- ----------- ----------- ----------- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----

JAN 1.344 0.109 0.000 0.184 466 2 1 0 0 0 0 0 0 0 0 469

FEB 0.741 1.575 0.000 0.302 326 13 9 7 1 0 0 0 0 0 0 356

MAR 0.355 6.352 0.000 0.478 273 52 18 11 14 5 0 0 0 0 0 373

APR 0.158 8.066 0.000 0.376 203 48 27 20 20 2 0 0 0 0 0 320

MAY 0.042 12.987 0.000 0.267 131 99 63 49 19 0 0 0 0 0 0 361

JUN 0.003 15.799 0.000 0.062 64 115 123 58 11 0 0 0 0 0 0 371

JUL 0.000 22.947 0.000 0.000 17 108 108 68 47 8 0 0 0 0 0 356

AUG 0.000 32.307 0.000 0.007 18 98 112 95 48 35 0 0 0 0 0 406

SEP 0.000 25.667 0.000 0.057 51 133 72 39 34 39 4 0 0 0 0 372

OCT 0.113 17.743 0.000 0.343 170 51 31 24 25 28 8 0 0 0 0 337

NOV 0.445 2.875 0.000 0.493 294 12 9 12 5 1 0 0 0 0 0 333

DEC 1.179 0.010 0.000 0.287 448 0 0 0 0 0 0 0 0 0 0 448

----------- ----------- ----------- ----------- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----

ANNUAL 4.381 146.437 0.000 2.857 2461 731 573 383 224 118 12 0 0 0 0 4502