Hi All,
Has anyone had experience modeling refrigeration cases? I posted a question
the other day but this one is different.
So under Air-Side HVAC Zone Parameters > Refrigeration Tab, Zone Load
(REFG-ZONE-LOAD) I entered the free cooling affect from the refrigeration
cases to the space (as described in the key word help). But looking at the
SIM file, this parameter is increasing my zone loads rather than decreasing
them, and in fact is causing my space to have more unmet load hours. Should
I apply a negative number to this parameter, or is this parameter not the
'free cooling' affect.
That along with the Walkin Box Load under the Air-Side HVAC System
Parameter. Not sure how the program is using this value.
Thanks!
Yoni G. Pollak, P.E.
There are a number of other REFG- keywords that depend on
REFG-ZONE-LOAD. For example:
REFG-AUK-KW - takes three entries (order corresponds to
REFG-ZONE-LOAD) of the fractional rated capacity of lights, fans,
anti-sweat heaters - the default is 40% of the REFG-ZONE-LOAD - I am
not entirely sure but I believe this heat ends up in the space.
Also, do you mean the unmet load hours are cooling load unmet or
heating load unmet?
>> Christopher Jones, P.Eng.
Chris,
You might be right about that heat ending up in the space, but that doesn't
sound right to me. I was getting an error when REFG-AUK-KW was 0, so I
reset it. I've actually played around with that number quite a bit since it
seems to have a large impact on the energy consumption. I'll revisit it
again this morning.
I'm talking aboiut umnet cooling load hours. The REFG-ZONE-LOAD keyword
seems to be directly related to my space loads but in the opposite way I
thought. The more REFG-ZONE-LOAD, the more system cooling the space
requires.
Yoni G. Pollak, PE
The manual states to enter the REFG-ZONE-LOAD as a negative. Are you
indicating that the larger the zone load, the more unmet cooling
hours? That seems counter intuitive doesn't it?
>> Christopher Jones, P.Eng.
I am rethinking my interpretation of the REFG-ZONE-LOAD - I know
believe the manual means "the load on the case work due to heat gain
from the adjacent space" - the larger ( larger in the negative
direction ) the zone load, the move compressor is used. The
reciprocal, heat loss in the space due to the coolness "spilling out
of the cases" is not taken into account by the program. Therefore
the larger the negative number, the more there is "heat" in the space
and the higher the unmet cooling hours. Just a guess but if you fix
the REFG-ZONE-LOAD and change the space temperature you achieve the
same effect - lower the space heating temperature set point, the
lower the unmet cooling hours. If that is the case, then I suspect
that the space somehow sees the zone load as increase in heat in the space?
This would indicate that there are other REFG keywords that might
influence the heat gain to the space due to the compressor working
harder when REFG-ZONE-LOAD is larger.
>> Christopher Jones, P.Eng.
The manual says to enter the value as a negative?! That makes sense, and
I'm glad you said that b/c that is what I did. Which manual are you
referencing? I've been using the help which does not say that at all.
Yoni G. Pollak, PE
Chris, thanks for the help!
I agree with what you are saying, the REFG-ZONE-LOAD is the load the space
imparts on the refrigeration case, but that is also the same load the case
imparts on the space, hence the 'free cooling'.
Thanks again for confirming the negative number in this keyword!
Yoni G. Pollak, PE
The equest help files are a subset of the DOE2.2 Manuals. The
Dictionary explains most keywords.
http://doe2.com/download/doe-22/
The DOE2Vol pdfs are the manuals I am referring to.