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Foundation:Kiva warmups and initial thermostat setpoints

asked 2020-09-17 15:31:02 -0500

David Sun gravatar image

updated 2020-10-01 09:14:46 -0500

Hello,

I have a question about how the Kiva Foundation object is initialized in an EnergyPlus simulation using the accelerated initialization method.

I am running simulations of a model that includes a basement with a foundation:kiva object for ground heat transfer. For reasons specific to my project, the initial temperature setpoint of the baseboard heater in the basement is very high (30°C). Throughout my simulation, the setpoint is eventually reduced to 21°C but the zone temperature of the basement stays mostly constant at 25°C for the entire winter; there are no other sources of internal heat gains other than from occupants, lights, and some plug loads.

My questions are:

1) Could this odd behaviour be due to the initialization (warm-up) of the foundation:kiva object? I understand that it uses the initial temperature setpoint of any adjacent zones to initialize the ground temperature; over a warm-up period of months, could my basement temperature setpoint of 30°C be creating a huge thermal battery in an adiabatic system, preventing the basement from dropping in temperature?

2) If 1 is true, is there a recommended range of temperature setpoints that should be strictly followed when dealing with kiva foundations to avoid this behaviour?

I know that my situation is a bit odd with the initial temperature being set to 30°C (we need to observe thermal responses from many different conditions) but if anyone has any idea about what we're observing, it would help a lot!

Thanks to whoever took the time to read this, David Sun

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Can you share your basement setpoint schedule? By default, the zone setpoint temperature is used to initialize the model, though you can override this behavior by specifying the Initial Indoor Air Temperature in the Foundation:Kiva object.

Neal Kruis gravatar image Neal Kruis  ( 2020-09-17 16:09:05 -0500 )edit

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answered 2020-09-17 23:55:35 -0500

David Sun gravatar image

Hi Neal,

My basement setpoints are set by an external algorithm so it will always be different depending on the state of the building. Unfortunately, that means that I don't have a schedule to share. The scenario where zone temperature never drops below 25 happens with 0 auxiliary heating sources, though.

My model was actually in V8.9 and I transferred it to V9.2; without changing anything, the behaviour seems to have disappeared by itself!

Were there changes made to how the Foundation:Kiva object does its initialization since V8.9?

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Yes there were a number of fixes to the Kiva implementation since v8.9, including the feature I mentioned earlier. Glad to hear it was resolved!

Neal Kruis gravatar image Neal Kruis  ( 2020-09-18 10:16:26 -0500 )edit

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Asked: 2020-09-17 15:31:02 -0500

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Last updated: Sep 17 '20