[BLDG-SIM] What does ADJUST-LOADS adjust?

[Fred Porter]

All;

I should have known this already, but Jeff Hirsch clarified that DOE-2
users may need to adjust (carefully) the relative
COOLING/HEATING-DESIGN-Ts in buffer zones if auto-sizing airflows. I
USUALLY find the default minimum design airflows and safety factors
result in adequate airflows in the conditioned zones. However:

 

--- 
Jeff Hirsch responded:

Relative to the dT used for the interior wall heat transfer ... 

  

The hourly simulated heat transfer across an interior wall is based on
the hourly 

simulated temperatures on either side of the wall.  The design
calculation heat transfer 

across an interior wall is governed ONLY be the design temperatures of
the zones on 

either side of the wall. 

  

The "adjust loads" feature controls if the peak load arising from the
hourly fixed temperature

load calculation for each SPACE is "adjusted" during the HVAC sizing
calculation based

upon the specified heat/cool design temperatures for the ZONE that
represents that SPACE

for the HVAC simulation. 

  

The unconditioned and plenum design temperatures can start as a "guess"
and then be 

adjusted based upon simulation values.  There is no automated "capture"
of design day 

unconditioned/plenum zone temperatures at the time of each connected
conditioned 

zone peak load to feed into the calculation.  This is not unique to
DOE-2/eQUEST, but 

we are adding a better method to handle this and other sizing issues
automatically in 

the next version of DOE-2 (expected next year) 

  

From JJH's response above, if the design temperatures are the same for a
"plenum" and the space below, there will be no heat transfer during the
sizing calculation; that's why changing "plenum" roof characteristics
did not change design airflow in the conditioned space below the
ceiling.

--

Fred 

  _____  

From: Fred Porter 
Sent: Tuesday, July 17, 2007 9:29 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] What does ADJUST-LOADS adjust?

 

All;
When simulating (eQ v3-61, DOE-2.2 v44e4) a building with a "plenum"
(unconditioned or plenum), and changing the roof absorptance greatly,
the auto-sized design air flow does NOT seem to change in the zone
below, even though the ZONE SIZING-OPTION = ADJUST-LOADS. After
observing this in a big model, I tested this in a simple single zone
model (eQ Wiz). I made sure airflow sizing was driven by cooling loads,
and created a parametric run that changed the ABSORPTANCE of the roof
construction between 90% and 10%. Hourly cooling loads vary as expected,
but design airflow remains the same between both models. 

Raising the DESIGN-COOL-T (from the default 75F, same for all zones) in
the "plenum" increases the design airflow in the zone below (for both
absorptances), but I thought ADJUST-LOADS did more than just recognize
this input. The problem seems to persist whether I have a cooling design
day or not, and whatever I do with the LOADS SPACE "TEMPERATUREs" and
ZONE DESIGN-COOL-Ts. 

Any insights out there? Anyone else notice this behavior? Is this a bug,
or did I expect too much of the program? Unless the DESIGN-COOL-T is
raised (to a value one must estimate or find by inspection of hourly
reports), it appears the program under-sizes airflow to zones where a
significant fraction of the heat gain is through a ceiling
cavity/plenum/attic, or I suppose any "un-conditioned" buffer space.

Fred Porter 

 
 
>orterace.




 
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