Equipment Sizing and % Hrs in Throttling Range

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All - I'm trying to resolve a gshp school system model, to reduce the
number of hours outside of throttling range for LEED purposes. I have
scowered multiple threads talking about sizing, throttling range, min
air flow ratios, reverse-action TSTATs, night-setback, gshp's, etc. and
have applied suggestions with minimal result. The only way I can take
considerable hours out of the % not in throttling range is if I increase
sizing ratios way beyond design capacities and strip out everything that
makes the model accurately reflect design conditions.

I've attached the before and after (.pd2) files for reference, however
results are still not seen. SS-R reports indicate hours in the 100+ load
range, but again this is going beyond manually specifying capacities and
using sizing ratios. Also to be noted, the ASHRAE baseline (Pkg Elec HP)
is also in the same range and is not responding to changes... which
would suggest something common to both within Appendix G criteria.

Experience and opinions would be greatly appreciated.

Matthew Higgins, LEED AP + ASHRAE-HBDP

Matthew Higgins's picture
Joined: 2011-09-30
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No Username provide's picture
Joined: 2011-09-30
Reputation: 200

Like Karen mentioned, without the inp files we can't really figure out
what's going on. I don't know how you specified it in the wizard files
(because the after file doesn't have the GSHP setup) but there is one
thing I would check. In the wizard, when specifying the GSHP, check if
you have a system per zone (not floor or shell) set up.

If not, it will set up the GSHP with a single zone controlling every
other zone, and just having the terminal reheat set up as "Heat Pump"
doesn't seem to fix the issue. So you'll find the control zone has very
few hours under heated/cooled, where as the rest of the zones under that
system will be at the control zone's mercy (if the loads are similar to
the control zone, you'll have fewer under heated/cooled hours than if
they are substantially different).


Eric O'Neill's picture
Joined: 2011-09-30
Reputation: 0

There was a post some time back on how to incorporate -999 in the
Min-Air-Sch. Any resolution on that? The schedule type fraction does not
allow for -999, and the min-air-sch seems to take only sch of type
fraction as input. Following is the info from the help file


Takes the U-name of a SCHEDULE that contains hourly values of the ratio
of minimum outside air flow to supply air flow. Values in the
MIN-AIR-SCH vary from 0.0 (no outside air flow; economizer inactive if
specified) to 1.0 (100% outside air flow). A value of 0.001 actives the
economizer. A value of -999 returns the hourly value to MIN-OUTSIDE-AIR
or to the program's calculated minimum outside air value (found on
report SV-A for the SYSTEM or for each zone for zonal systems). During a
warmup period, this schedule is normally set to zero and can then be set
to -999 during other hours to allow the specified or calculated
ventilation minimum damper position to be used. Note that schedules are
ignored in the design routines; therefore, the minimum ventilation air
desired for design must be specified either at the zone or system level.

Brahme, Rohini            UTRC's picture
Joined: 2011-09-30
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I believe you have to use the schedule type "Frac/Design"

Jay Keazer's picture
Joined: 2011-09-30
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Thanks. This worked. I had tried others - multiplier, on/off flag, which
don't work.

Brahme, Rohini            UTRC's picture
Joined: 2011-09-30
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Thanks Eric & Karen. I spaced on the (.inp)'s, now attached.

Matthew Higgins, LEED AP + ASHRAE-HBDP

Matthew Higgins's picture
Joined: 2011-09-30
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