[Equest-users] Water Cooled VRF

[Neil Bulger]

Not many people have posted on alternate solutions. You are on the right
path, water cooled VRF is a different animal then air cooled in eQuest. I
would recommend looking into a few other ways to model this beyond the PVVT
system. You many not be able to capture the exact variable speed functions
but you may be able to better-approximate the flow of energy. For a faster
method, I would use a Water Source HP Air-System Types, attached to a
condenser-water loop with boiler and cooling tower. This will put 1
compressor in each zone on simulation and heat through the condenser water
loop. You would still have to post-process any heat recovery.

Another more detailed method is to create water-to-water heat pumps in the
water side of eQuest, attached to a Fan Coil system in each zone. This is a
bit more complex and takes a more detailed attention to creating part-load
curves but can be possible. The water-to-water heat pump has to be tied to
a lake-loop where more heat can be pulled from if needed. We ended up
taking the loads that resulted on this loop and calculating the energy
needed to maintain this temperature from a boiler/cooling tower outside of
the model. We also did post processing to account for any times the
compressor was in heating and cooling simultaneously  Quite a tedious
process but captures the bulk of how a VRF water cooled system will work.

Cheers,

-- 

*Neil Bulger*
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On Tue, Dec 11, 2012 at 8:12 AM, Tim Johnson <timj at ctagroup.com> wrote:

>  I am attempting to model a water cooled VRF system for a dormitory in
> northern Montana.  I have used Dana Troy's method for air source VRF
> systems several times with great success, but this is my first attempt at a
> water source system.  The model seems to work as expected with a single
> speed compressor, but when I change this to a variable speed compressor,
> the system doesn't function properly.  There is no flow in the water loop
> and the VRF heating energy disappears.  The model still shows no unmet load
> hours but is clearly not operating correctly.
>
> I have done some research in the help files and the forum archives and
> found little help.  Volume 3 of the DOE2 help file under Air-Side System
> Types - PVVT seems to hint at variable speed compressors being only for air
> cooled condenser types.  The eQUEST forums have a few posts of this same
> question with no conclusion.  What have you found?  What is the best way to
> simulate a variable speed compressor for a water source heat pump system?
> Am I missing something here?
>
> Thanks,
> Tim
>
>
>
> *Tim Johnson, PE, BEMP, LEED AP*
>
> *CTA : Mechanical Engineer*
>
> DIRECT: 208.577.5645
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