[Equest-users] Fan Night cycling and chiller operation

[Nicholas Caton]

I consider myself out of the loop in terms of 90.1 application nuances these days, but if there is no explicit direction concerning chiller operations then I think the correct fallback is “your baseline should match your proposed case” wherever possible for system operations.

That said… are you really saying your proposed design involves “locking off” space conditioning during unoccupied weekends/nights/holidays?  That’s to say… if the space temperature drops to below your setback temperatures in the winter, your engineers/architects don’t want the systems to provide heating until occupants arrive Monday morning?

Or is the case you’re making simply that the building is in a climate that’s mild enough to never need unoccupied conditioning?

My hunch is - the fact that you have setback temperatures at all suggests you really are going to be heating/cooling in the evenings, as needed (else what do those even mean?).  If that’s true, I think you simply need to determine the operating profile for your actual chillers (are they cycling as required or on standby, and what times of the day/year are they permitted to operate), then be consistent in making the chiller operate identically in the baseline case.

If it’s your true design intent to let the building get uncomfortably hot on a regular basis during weekends/nights/holidays, then I think the solution to “too many unmet hours” is simply one of recognizing you don’t have setback temperatures to maintain… Check 90.1 and any other rules regarding thermostat temps, but in that scenario I think you’d be justified in setting some extreme setback temps that would not trigger unmet hours.  Remember again however that those same schedules should be transposed to your baseline case.  This will mean there is no real advantage in terms of 90.1 performance rating, as your baseline case will also never have calls for heating/cooling during those times.

I conclude by reiterating – I’m really not a 90.1 guru the way I used to be… I just had many years reading between the lines to understand intent (some years ago).  I encourage anyone currently practicing to consider/agree/refute my suggestions here!

~Nick

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Nick Caton, P.E., BEMP
  Senior Energy Engineer
  Energy and Sustainability Services
  Energy Performance Contracting
D
M
E

913 . 564 . 6361
785 . 410 . 3317
nicholas.caton at se.com<mailto:nicholas.caton at se.com>
15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219

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From: Equest-users <equest-users-bounces at lists.onebuilding.org> On Behalf Of Rushi Quest via Equest-users
Sent: Thursday, April 23, 2020 2:45 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Fan Night cycling and chiller operation


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Dear E-questers,

I am working on a nine hours, five days a week office building operated by chillers to meet HVAC demand.
As per ASHRAE 90.1-2010 appendix G, fans must be cycled during unoccupied hours to meet the heating and cooling loads.
Now my query is that if night cycle fan control is kept on Cycle on Any then it is observed from the hourly reports that chillers are operated during night time and even on holidays, but this is not the actual case as chillers (or even the electric heating) won't be on during night hours or holidays.

I have checked the schedules and thermostat set points in zones and they seem to be fine. The temperatures are considered 75.2F and 70F respectively for cooling and heating in occupied hours and 82F and 64F in unoccupied hours.

So please let me know if it is correct that chillers are cycling on during unoccupied hours?  If no, then what should be done to operate them only in occupied hours.

Note: I tried to give on/off schedule to chilled water loop but it gives unreasonable amount of unmet hours.

Thanks in advance.


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