Help - Modeling VRV-VRF System with eQuest

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Hi,

I am modeling VRV system based on a "Energy Trust of Oregon, Inc."
guidance document (attached) posted by Mathew Larson of Colorado dated
12/12/2011. The document recommends using a PVVT system to simulate a
VRV system. I used an air cooled PVVT system to model a VRV system.
However, the unmet hours on the heating is very high. The cooling part
is okay. Does anyone has experience on bringing down the unmet hours?

Thanks!

Loi Ng

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Hi Loi,

I have run across this as well with trying to model VRV in eQuest. PVVT is a difficult system to work with because it requires specifying 1 zone as the thermostat that drives the whole system. Therefore, 1 zone will drive what supply air temperature the central AHU delivers to each zone. This can make hours out of range on cooling difficult but, if heating is the issue you may have more flexibility with zone-level heating options (reheat or baseboards). However, that can start to look strange when in reality, these features do not exist. But, the hours out of range typically stem from this single-zone-thermostat issue with PVVT.

Another approach I have not perfected yet that I thought of was to try using the eQuest Water Heat Pump system. The Water Heat Pump ties to a WLHP water-loop (it appears yellow in the Water-Side tab). If you were to place a dry-cooling tower on this loop, effectively, the dry cooling tower would be (in my mind) the same as an air-source condenser, like we would see in reality with a VRV system (typically).

This may be good or bad on the airside in eQuest (I am hoping good) in that it provides another set of options and heat flow control at each system. Again, I have not dug into how this would go together best and I would imagine some post processing would be needed to understand the results.

Would love to hear any other creative ideas out there for VRV work-arounds.

Neil Bulger

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Neil:

I have modeled VRF systems as PTHP systems for high rise residential buildings
where the required baseline system is a PTHP.

The compressor on the PTHP can be specified as variable speed. so it seems to
work well. I just finished a 7 story building using a Daikin system. I built 4
custom curves per condensing unit and used the exceptional calculation method
outlined in the BSUG slide presentation to calculate the recovered energy. The
curves I created are the Cooling Capacity f(EWB,ODB), Cooling EIR f(EWB,ODB),
Heating Capacity f(EDB, ODB) and Heating EIR f(EDB, ODB).

I ended up with a 28% cost savings for the proposed HVAC system compared to the
baseline 90.1-2004 system which is in the range claimed by the manufacturer.

Paul Diglio, CEM, CBCP

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Gents -

Quick Q - why not just define one PVVT for each thermostat?

Aaron

Aaron Dahlstrom , PE, LEED(r) AP

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Last summer I did a VRF model for an office building. I used a 4 pipe fan coil served by a loop-to-loop heat pump. For the condenser loop I used a Lake loop, which in turn was connected to a ground heat exchanger. Then I specified the ground temps as equivalent to the outdoor air temps (8760 hour schedule). Although this sounds complicated, it worked fairly well and has some benefits. The loop-to-loop HP allows heat to be transferred between zones. While the condenser loop with outdoor air temps allows the heat pump to act like an air cooled heat pump when in that mode. The trickiest part was developing equipment curves, but that would be the case no matter which way you model it.

Michael Wilson, P.Eng.

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Hi,

Thanks to all your help. I have finished modeling the VRV/VRF system. Since VRV system is not an option in eQuest, packaged variable volume variable temperature (PVVT) system is used to resemble the VRV/VRF system as recommended. The baseline is an air-cooled split type single zone heat pump system and the proposed is the packaged PVVT system. The proposed PVVT system will not run on heating & cooling simultaneously. I expect I will get a reasonable energy saving. However, the saving is below 2%. I manipulated each and every one of the inputs to boost the saving. The saving is still below 2%. Any suggestions from you guys?

Thanks!

Loi Ng

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Loi,

Can you post your .pd2 and .inp files?

Steven

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Steven,

Attached is the baseline files. Proposed will be in a separate email.

Thanks!

Loi Ng

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Steven,

Here are the proposed.

Loi Ng

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Paul

It is amazing. How do you create all those custom curves? I have modeled DAIKIN VRF system as packaged variable volume variable temperature system (PVVT). There are so many performances need to be created. I have no idea how to create them. Can we obtain the performance curves from Daikin?

Thanks!

Loi Ng

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