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HVAC consumption analyses

asked 2016-04-19 08:31:57 -0500

Wilson's avatar

updated 2016-04-23 19:05:36 -0500

Hi! My building model has a single zone with a Packaged rooftop heat pump. I'm using OpenStudio and I added 3 output measures in order to study HVAC energy consumption: Air System Total Heating Energy, Air System Total Cooling Energy and Air System Fan Electric Energy. I'm analyzing the results and I'm not understanding why the system starts to cooling the building in some periods of the day. We can see some little peaks of cooling consumption always at midnight and, in the 6th day of July we can see a cooling consumption when the interior temperature is between the choosen setpoints. image description In this summer week example I'm not understanting why there is cooling energy consumption if the interior temperature is so far to reach the cooling setpoint.

The same little peaks also occurs on a simulation for a winter week, always at 24 o'clock. image description

Can you give me your opinion about what can be happening?

Thank you

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answered 2016-04-23 14:18:31 -0500

updated 2016-04-23 19:59:42 -0500

This is interesting. The interior temperature is tracking the heating set point temperature. There should be no need for cooling, as your well aware. The time of cooling energy coincides with a change in thermostat set point temperature. Create a new plot to see what the program predicts as the zone load with:

OutputVariable,*,Zone Predicted Sensible Load to Heating Setpoint Heat Transfer Rate,detailed;
OutputVariable,*,Zone Predicted Sensible Load to Cooling Setpoint Heat Transfer Rate,detailed;

Does your HVAC system use node set point managers? If so, also plot the node temperatures and node set point temperatures.

From the results, it looks to me that the HVAC system is turning cooling on when the heating set point temperature drops from 21C to 15C. This "sort of" makes sense for a single temperature set point, but not for a dual temperature set point. Are you using a "4" (dual set point) for the Control Type in the Thermostat object?

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Thank you for your answer rraustad. I made the simulation and it was created results for 13 nodes. For better understanding I leave here the excel with the Simulation results. Thank you

Wilson's avatar Wilson  ( 2016-04-23 19:21:08 -0500 )edit

I'm using 1 cooling setpoint and one heating setpoint. Here are my Open Studio files. Is a single zone building(Sp Market Sales/Produce) and I put people, lights and electric equipment loads definitions to zero because I want to analize HVAC consumptions without the influence of these loads. Thank you

Wilson's avatar Wilson  ( 2016-04-24 14:07:26 -0500 )edit

You are controlling the cooling coil using the SetpointManager:SingleZone:Reheat object. Add another SPM to control the cooling coil using SetpointManager:SingleZone:Cooling.

rraustad's avatar rraustad  ( 2016-04-24 20:07:46 -0500 )edit

I don't have experience on HVAC design and this is a begginer question.I thought that adding Packaged Rooftop Heating Pump was enough to do the simulations that I need without doing changes on HVAC template.I'm trying to add another SPM using Open Studio but I don't find how.I thought that I could find SetpointManager:SingleZone:Cooling in my HVAC library and then I could drag and drop it into node 10(?),but I can´t find SetpointManager:SingleZone:Cooling in the library.How can I add SetpointManager into my model?Setpoint Manager Single Zone Reheat 1 also controls the heating coil? Thank you

Wilson's avatar Wilson  ( 2016-04-26 09:42:50 -0500 )edit

One of the OS experts will have to answer that question. I just use E+ directly.

rraustad's avatar rraustad  ( 2016-04-26 11:47:05 -0500 )edit

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Asked: 2016-04-19 08:31:57 -0500

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Last updated: Apr 23 '16