[Equest-users] 转发：The results of your email commands

[Nick Caton]

I was just looking into this recently.

 

For VRF systems, I¡¯ve seen direction to use PSZ, PVVT, and PTAC.  PVVT is
the approach endorsed/outlined by the Oregon energy trust in a powerpoint
PDF that has made the rounds here on the lists a few times, and as such is
probably ¡°most suggested.¡±  PVVT by distinction can model
variable/multispeed fan control at the terminal level, which may or may not
reflect your actual equipment (depends on make/model).  Fan control can also
be made ¡°constant¡± in that regard if need be, as such this may be the most
flexible solution.  PSZ stands out from this trio as a zonal system type ¨C
this fact may make it an easier system to consider in relation to a model or
baseline you¡¯ve already substantially developed with a zonal system type.

 

There is more than one right answer, and it¡¯s worth noting/acknowledging
VRF is fundamentally different in operation than any system type currently
within eQuest.

 

Review of LG and Mitsubishi¡¯s suggested practices / guidance shows some
slight contradictions.  Both notably prescribe system type PSZ, to start,
but Mitsubishi explicitly mentions PVVT and PTAC as viable alternatives as
well.  Somewhere along the way I recall reading that energy recovery
elements may be more easily accounted for with PSZ over PVVT¡­ can¡¯t recall
the specific source.  LG by has produced a library of (air-cooled) curves
specifically for use with modeling variable speed compressors.   Mitsubishi
in contrast (perhaps, in response¡­ also for air-cooled VRF) asserts it
isn¡¯t critical to explicitly model variable speed compressors to
approximate VRF within eQuest, rather that the PLR/EIR/Capacity curves
furnished by the manufacturer can, together, adequately address performance.


 

As I understand it, any chosen approach to VRF in eQuest involves
¡°post-processing¡± hourly reports to quantify and sum ¡°free¡±
heating/cooling energies.  There is some variance in guidance (between the
energy trust of OR and Mitsubishi) on how to sum those free heating/cooling
energies... both methods appear conservative to my understanding of how VRF
works (summing each hour¡¯s energies in isolation of the preceding hourly
results), but then I am certainly no expert. 

 

~Nick

 

 



NICK CATON, P.E.
Senior Engineer

 

360 Analytics
9750 3rd Ave NE, Suite 405

Seattle, WA 98115
office:  206.557.4732 ext. 205
 <http://www.360-analytics.com/> www.360-Analytics.com

 

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On
Behalf Of ????
Sent: Saturday, September 27, 2014 9:29 PM
To: Equest-users
Subject: [Equest-users] ת·¢£ºThe results of your email commands

 


Can someone explain why a PVVT is usually chosen to model VRV/VRF?
As we all know, Packaged Variable-volume Variable-Temperature (PVVT) systems
can be used to model VRV/VRF system in eQUEST software, but what I am
confused is why a PVVT system can be used.
Load adjustment in pvvt system is implemented by varying supply air flow and
supply temperature. But in VRv system£¬load adjustment is implemented by
varying refrigerant flow in each coil. There is a significant difference
between the vrv and pvvt system. And l always can not get reasonable result
using this way, the heating energy consumption is always too small.
Can someone explain why a PVVT is usually chosen to model VRV/VRF?





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