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What setpoint is used to determine unmet cooling hours?

asked 2016-10-05 17:43:37 -0500

Vern Smith gravatar image

I am using Design Builder ver 5.0 to model a small retail store with an entry vestibule that has a small electric cabinet heater, but no cooling unit. The vestibule floor area is 5-ft by 4-ft and has an exterior glass door, an interior glass door, large windows on two sides, and is exposed to ambient on three sides. In the summer it's basically a walk-through oven. Not a good design solution, but one that we've all experienced. For purposes of ASHRAE 90.1, I think it is classified as a conditioned heated space. The simulation location is in Climate Zone 6B. The zone heating setpoint is 50 F and cooling setpoint is 99 F. The maximum simulated dry bulb temperature is 105 F, but zone cooling set point not met time exceeds the number of hours when the temperature is above 99 F. From the attached chart, it appears that the simulation controls think the cooling set point is around 74 F, which is the cooling setpoint for other zones in the store. I have turned off mechanical cooling and the Design Builder inputs require a number between -58 F and 176 F. I need to reduce or eliminate the unmet hours. So, my question is, how does EnergyPlus (or Design Builder) determine the setpoint for calculating unmet hours for a zone? What have I overlooked? EntryVestibuleCoolingSetPointNotMet.png

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answered 2016-10-07 10:11:28 -0500

The EnergyPlus object to look for in DesignBuilder is OutputControl:ReportingTolerances. Also see this question for how these should be calculated per 90.1.


OutputControl:ReportingTolerances

This input object is created to allow more user control over some aspects of output reporting. Specifically, the reporting of “Time setpoint not met” hours See thermostat reporting (ZoneControl Thermostat Outputs).

Inputs

Field: Tolerance for Time Cooling Setpoint Not Met

This field allows the entry of a value for the tolerance away from the cooling setpoint reporting. If the zone temperature is above the cooling setpoint by more than this value, the following output variables will increment as appropriate

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Thanks, Matt. I had reviewed the Q&A's here as well as researched the EnergyPlus documentation that you referenced before posting. For this particular zone, which does not have a cooling system, I set the cooling setpoint to 99 F (even tried 150 F, same result). My thinking was that it should report hours above 99 F, but instead it's reporting all hours above 76 F. The Tolerance for Time Cooling Setpoint Not Met is 1.11 C (2 F) in DesignBuilder, and to the best of my understanding this variable affects all reported zones, not just my vestibule. I think there may be another issue.

Vern Smith gravatar image Vern Smith  ( 2016-10-07 11:32:00 -0500 )edit

Can you remove the cooling setpoint from that zone without causing an error? Also, what EP table does DB report the unmet hours from? I usually use the Time Setpoint Not Met table from the System Summary report and just look at the During Occupied Heating and During Occupied Cooling columns. From the EP tabular output (htm file): Table of Contents > System Summary > Time Setpoint Not Met

MatthewSteen gravatar image MatthewSteen  ( 2016-10-07 11:59:31 -0500 )edit

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Asked: 2016-10-05 17:43:37 -0500

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Last updated: Oct 07 '16