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Strange result after applying VRFwithDOAS measure

asked 2018-06-14 04:26:56 -0500

JoJo's avatar

updated 2018-06-14 07:22:05 -0500

I use the 'create DOE prototype building' measure to establish the model and change the u-value of the window in the simple glazeing system window material while keep the rest as default. The EUI shows a reasonable increase when I largen the u-value. However, after I change the HVAC system by applying 'VRFwithDOAES' measure. The EUI incresed a lot while the U value keep decreasing. Is there anyone meet the same problem ?

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It's likely that the default VRF+DOAS system you pulled off of BCL has some incorrect curves and/or cops. Also check that the terminal units have a reasonable fan pressure and are cycling, not constant fans.

You may want to use an explicit manufacturer's system components on the BCL component library instead of the default ones built by the measure.

mdahlhausen's avatar mdahlhausen  ( 2018-06-14 18:14:45 -0500 )edit

Please share your model or show the properties of the initial and alternative HVAC systems. As others have pointed out, there are multiple inputs in defining an HVAC system, which can affect the outputs. You cannot compare two systems if all of these inputs are changing. I can give more feedback after looking at the HVAC properties in your models.

Ehsank's avatar Ehsank  ( 2018-12-26 13:53:24 -0500 )edit

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answered 2018-12-24 13:25:32 -0500

Matt Koch's avatar

updated 2018-12-27 06:52:07 -0500

I have tried - so far in vain - for many months to compare a "VRF with DOAS" system to a "RTU with integrated OA" system and see the roughly 25% energy advantage of the former over the latter that is predicted in other software, such as Trace-700. However, I mostly see a 0% to at most 5% advantage. I used the "VRF with DOAS" measure and even rolled my own Daikin copy from Trace-700. The latter seems to improve energy performance, but fails utterly on unmet hours - so I have put that on ice for now.

Anyway, I did notice that the measure puts in something like 1.3" for fan pressure rise, while, for example, the Daikin systems suggest something more like 0.4". Also, how can I ensure that the terminal (or system?) fans are cycling and not running constantly? Which parameter do I need to adjust for that?

Finally, I noticed in the DOAS part of the "VRF with DOAS" measure, the operation of the air loop shows up as "On/Off", rather than "VAV" - shouldn't it be VAV? Plus, the diffusers on the various thermal zones have "Control for Outdoor Air" set to No rather than Yes, while the thermal zones themselves have "Account for Outdoor Air" set to Yes rather than No. Shouldn't both be set to Yes?

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Asked: 2018-06-14 04:26:56 -0500

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Last updated: Dec 27 '18