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[EnergyPlus_Support] how do I verify zone heating loads?



In trying to resolve heating plant issues, I am first looking at what
appears to be a load error:

** Warning ** No valid range found for Loop Demand=726610.25 in Load
Range Based Operation Scheme=BLR STAGING.
   **   ~~~   ** All equipment will be turned off.  Other cases of
this condition will not be reported.

I assume that units for Loop Demand are watts, in which case this load
is far higher than expected. 

I chose a zone at random and selected report variable Zone/Sys
Sensible Load to Heating Setpoint, which I also found was about 200%
of design when run on a random winter day with a higher-than-design
outdoor drybulb. Question (1) does the value for this report variable
include ventilation loads?

With the intent to verify each component heat loss for that zone, I
first reported construction and surface details and checked u-values
in the .eio file. I was able to verify all u-values except the windows
which appeared to be center-of-glass u-values rather than overall
u-values. I was not able to find any frame u-values in this output
file, which leads to my second question: (2) is there any way to
verify the overall window u-value, including glass, edge effects, and
frame? 

Next, to verify heat loss through the envelope, I selected the
following report variables:
 -outdoor drybulb,
 -zone mean air temperature,
 -window heat loss (for each window in the zone),
 -window frame heat loss (for each window in the zone),
 -surface internal convection heat rate (for each surface in the
zone), and
 -zone infiltration sensible heat loss.

Using a simple Q = UA delta T for each window/surface, I could not
match my calculated loads to the ones in the report (reported window
heat loss more than double what I expected, wall heat loss less than
1/4 expected). This leads to the next two questions: (3) is UA delta T
valid in this case, or does night sky radiation significantly factor
into the heat losses? and, (4) Is my interpretation that the report
variable "surface internal convection heat rate" represents the
surface heat loss from the zone correct?

I also tried verifying the infiltration load with no success. My input
file uses 52 cfm with 1,0,0,0 factors allowing for a constant
infiltration rate. Using  52 cfm at 35 deg F OA and 43 deg F indoor
temp (low because the HW plant is not working), I should get a heat
loss of 1853 Btu/h or 534 Watts or 325,918 Joules over a ten minute
time step. The reported infiltration heat loss is 83,456 J. Question
(5) why the difference?

One final question: (6) there does not appear to be any report
variable that shows the actual zone heat loss rate (at the actual zone
node air temperature), whereby i could sum the losses through the heat
transfer surfaces, sub-surfaces, and by infiltration for comparison
purposes (assuming internal loads = 0).  am i missing this somewhere
in the reports?

Two departing comments: (a) I find it difficult in some cases to
interpret what was meant by a particular report-variable. is there a
dictionary of these somewhere? if not, this would be very helpful. and
(b) units for similar report variable headings are not consistent, e.g
"window heat loss" and "window frame heat loss" carry the unit Watts
while "zone infiltration sensible heat loss" carries the unit Joules. 

Many thanks in advance for your help!!!

Brian



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