why vrf system by autosizing in equest generate many unmet hours

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Nick, by & large I agree. One thing maybe you can shed some light on/confirm is my second comment above, on if eQuest, when autosizing, it uses design day data, which can be different from the weather file. This can results in issues especially since the 'sizing' is done separately/before the actual 'simulation'. Can you comment/confirm on this?

Confirmed! Sorta... =)

You can easily "trip up" auto-sizing by eQUEST if you do not pay mind to your DESIGN-DAY inputs. To ensure overlap between the design day calculations and with the building's peak in simulation, I'd advise reading up on the optional NUMBER-OF-DAYS input for both cooling and heating design days. I believe it defaults to 1 when you (or the wizards) don't say otherwise.

Also, it's often appropriate when you are trying to match external load calcs/sizing to your model's auto-sizing to specify more stringent design day conditions (i.e. 99.6% for heating).

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... I also want to mention DESIGN-DAY inputs are by-and-large most easily editable directly in the INP. In wizard-borne models, they'll be located near the top of the file in the section following Global Parameters. EDIT: you can adjust CDD and HDD NUMBER-OF-DAYS within the interface by double clicking your CDD/HDD in the component tree for the Project & Site tab.

Seen & reviewed the EnergyTrust of Oregon presentation, It lays out both the Water Source HP and Air Cooled HP approaches, great. It does say 1 system/zone for both, but doesn't give a 'why'; it may have been verbally stated at presentation, but not noted on slides. The issue with this is that 1 system/zone may not reflect the design. One would need to make sure that the 'control' zone is the zone where the t-stat is indicated on plans [or adjust the design, as needed.] In eQuest there is not a different between a zone & space, as there is in EnergyPlus. Combining rooms must be done carefully.

Comment above isn't abrasive, but a note that zoning & sensibly combining multiple rooms into zone must be done carefully, especially with sensitive zone equipment types such as VRF. Chris; Can you comment on/have any experience with the adjusting the Design Day data to address these issues?

@dradair, I have not experimented with adjusting the design day data in eQuest. Note that eQuest does not do a design day calculation for sizing unless specifically instructed to do so. The design day data has to be entered into the eQuest model when specifying a design day calculation. Note that eQuest (doe2.2) has significantly less fields for the design day data than did doe2.1e. I did ask why at one point but I didn't receive an answer. I haven't a feel for how the less design day data fields in doe2.2 affects the sizing calculation.

Hum, I haven't had a chance to play with this either, but good info. I didn't realize the 'downgrade' DOE2.1 to DOE 2.2. With DOE running LOADS simulation, then a SYSTEM simulation, I'd also be curios to know if adjusting the T-sat scheduels are used in both the LOADS and SYSTEM simulations OR if the setpoints in the 'Zones' input would change the sizing/unmet hours. It is known that the Thermostat schedules are used in the SYSTEM simulation, but I don't know if the T-Stat schedules are used in both...hum...