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Correct choice of Set point managers [closed]

asked 2016-03-17 04:48:32 -0600

FSilenzi gravatar image

Hello everybody, I am fairly new to the world of energy simulation but I was charged with a hard task. Basically I need to simulate an hospital building (15 floor total, 53.000 m^2 surface). I have created the 3d model with sketchup and assigned a very simple thermal zoning (1 floor= 1 zone). I have also begun to connect the HVAC systems, which are (for the moment) only 2 VAV with reheat. I modified the two system to have, on the hot water side loop, district heating as heat source. The chilled water loop is made by an absoption chiller linked to a simple condensing tower. The simulation runs smoothly except for some shading surface warnings (which I will adress later). The problem is that I have a lot of unmet hours during both cooling and heating. I think this could depend from the setpoint manager I have chosen. I selected a min max with deadband for both the VAV system, slightly modifying the standard schedules automatically created by openstudio. Can anybody help me adress the problem? I am sorry for my poor english.

Ps: what files shall I attach to the message to help adress the problem?

Thanks

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Closed for the following reason the question is answered, right answer was accepted by FSilenzi
close date 2016-03-22 02:35:48.656358

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answered 2016-03-17 10:08:30 -0600

The setpoint manager object SetpointManager:Scheduled:DualSetpoint is the wrong choice for an air loop. From the Input/Output reference for that object: "Currently the DualSetpoint Manager will be used with PlantLoop when the Plant Loop Demand Calculation Scheme is set to DualSetpointDeadband". When applied to an air loop, the DualSetpointManager will not control air temperature between the two setpoints, it will set the air temperature to the average of the scheduled high and low temperatures. This supply temperature likely does not match the zone, loop and terminal sizing parameters, causing the unmet hours.

VAV with reheat systems are usually controlled at the central air handling unit to a cool deck temperature (usually 55F), and the terminal units will re-heat the supply air to meet the zone thermostat temperature. You should make sure that the air loop and zone terminal units have sizing parameters that match their control operation, so the equipment will have enough capacity to meet the zone loads. See the answers to this post for more general tips on reducing unmet hours.

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Asked: 2016-03-17 04:46:48 -0600

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Last updated: Mar 17 '16