Hello All,
I am working on a few projects which utilize Daikan VRV systems and I am
trying to model them using eQuest, without much luck. I have talked with a
couple of different people, including some at Daikan and eQuest, and have
heard that as of right now the only full building energy modeling program
that supports VRV systems is EnergyPro. I was also told that an update to
DOE2.2 and then eQuest which will address VRV systems is in the works, but
that these updates will most likely not be out for a couple of months yet
(maybe into next year). I also have heard that there have been some people
who have been able to approximate VRV systems within eQuest.
So my questions to all of you are:
1). What would be the best / most accurate approach to create a model of a
building with a VRV system? Unfortunately I don't think that we can wait a
few months for the updates, so would it make most sense to purchase
EnergyPro or try to use a workaround method within eQuest? Or is there some
third option that I am unaware of?
2). Does anyone know how to approximate a VRV system within eQuest and
could explain it to me? What kind of accuracy could I expect from this
method?
Any help would be much appreciated!
Thanks,
David P. Hostetter
David - I'm currently using Daikin's proprietary EnergyCalc program to
come up with performance curves for equipment and then interpolate those
points to HVAC performance data in eQuest. Modulating loads on
condensers and other parameters are necessary, but it appears to be a
worthy endeavor. The reps don't like this approach much, and feel as
though we should be seeing greater energy savings, but in our case we
don't have time to build two models for every project using VRV
equipment. The reason I say this is because I feel that eQuest is a much
more powerful design and evaluation tool.
If anyone can add/comment on this process please do so.
Regards
Matthew Higgins, LEED AP + ASHRAE-HBDP
Dave,
I have heard the rumors about a VRV system being added to DOE 2.2 in the
future as well. The last time I heard the rumor, the package was
supposed to be out this spring. As is true of the entire software
industry, that likely means it will appear sometime in the year 2012.
(Predicted release date + 3 years = Actual release date)
I hope there is someone on here who can better clarify the date and
progress of the package...
To your second point, our office has been modeling Daikin VRV systems in
eQuest for a few months now. Don't get too excited... we haven't
actually installed one yet so we have no real data with which to prove
that we are modeling the systems correctly. That said, we also have only
modeled their "Heat-Pump" line and not their "Energy Recovery" line,
which allows simultaneous heating and cooling between zones.
We created custom curves with which to model the compressor by taking
Daikin Engineering data out of Daikin tables and plugging it into
eQuest. Then we model the system using the "Packaged Single Zone" system
type. We set the Indoor fan to two-speed and gave it a very light static
pressure, due to the fact that the system has multiple indoor fans with
low static vs. one fan with lots of static. We hard-keyed the CFMs, the
rated capacities, the compressor RPMs, low and high, the minimum cycling
part load ratio, the cooling (and heating) EIR, and set the compressor
to variable speed type and gave it a minimum unload ratio, again, all
from Daikin literature. We used eQuest's default low-speed EIR curve.
The capacity curve and the EIR curves we custom-created using eQuest and
Daikin data.
The results seem logical. Again, it's hard to prove that things are
dead-on because we have no real building to compare our results to.
Hopefully, though, that will give you a place to start.
I am not confident that I am modeling defrost correctly, and winter
results in general seem more sketchy. I am using eQuest's default
defrost running time fraction, which I assume is more pertinent to
standard unitary equipment. Daikin's defrost seems more efficient. It
also doesn't help that Daikin doesn't use either resistive or reverse
cycle for their defrost strategy... it's actually hot-gas bypass.
One last thing, all of the engineering data that we obtained from Daikin
was published on their website, www.daikinac.com.
I hope this helps. Good luck!
Gary Schrader