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Heating/Cooling Coil of PTAC or PRooftopAC Electricity Consumption?

asked 2015-07-13 13:41:15 -0500

nadish21 gravatar image

updated 2015-07-13 19:40:05 -0500


I am trying to simulate the HVAC System of a small house with a PTAC or Packaged Rooftop Air Conditioner. Generally when the HVAC system works in a real life scenario (i.e. for a small house) the Heating or Cooling Coil or the Fan consumes a constant electric power whether they are working on Part load or Full load conditions. But in the system I am trying to simulate ,Although regulated by a sophisticated Energy Management System Control (With the help of @Ivan Korolija), The Output of the Electric Equipment has a varying Power Consumption. How can I get rid of this problem?

Background of the question: For the Same problem there were experiments conducted a few years back on a small House' s HVAC system. The power consumption was almost constant. Hence for my research I am trying to simulate the exact same conditions.

I am sharing the links of IDF File and the Excel Results File here. Anyone can excess them on google drive (no sign in would be required.

Link for Excel Results File:

Excel Results File

Link for The IDF File

IDF File

I would be extremely grateful for any help that can be rendered to tackle this issue. Thank you in Advance.


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answered 2015-07-17 13:45:35 -0500

Your question, and the EMS programming, is in regards to HVAC system operation. I assume by "Electric Equipment" you mean the HVAC system and not the zone electric equipment. Your EMS program simply enables the system to operate via the availability schedules. These schedules control the availability of the components, not their performance. In this case your expectation is that the components will run at full capacity when they are available, this is not actually the case. In your input file, the performance of these components is controlled based on the set point managers. The coils are still trying to meet a load and that load is varying since SetpointManager:SingleZone:Reheat is being used. This SPM calculates a temperature required to meet a zone load. If you want the coils to turn on at full capacity when available, use scheduled SPM's to place a very low/high temp at the outlet of the cooling/heating coil (use 2 SPM's). Then when the coils are "available" they will try to meet a very high load (via the temps at the outlet nodes which is what controls the performance).

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Hello Sir,

Thank you very much for your comments on the IDF file, I was suspecting something else like a Time constant in the Electric Heating/Cooling Coils was preventing them to operate on full load in the time of operations. So if I understand correctly, I would need different setpoint managers to fool the HVAC system in believing that the Load is too huge to meet and hence It should operate on Full load conditions, and at the same time the Availability managers in the EMS will control the availability of the coils with respect to the Temperature sensed in the Apartment Temp Sensor?

nadish21 gravatar image nadish21  ( 2015-07-19 15:11:35 -0500 )edit

Yes, correct. Place 2 scheduled SPM's at the outlet node of the coils. One with low temp for cooling, the other a high temp for heating. Then run your simulation and see if the coils are operating at full capacity. You can test to see if this is working by reporting the node temperature and node setpoint temperature. The coil outlet temp should never reach the setpoint temp. If it does, the setpoint should be adjusted.

rraustad gravatar image rraustad  ( 2015-07-20 07:12:42 -0500 )edit

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Asked: 2015-07-13 13:41:15 -0500

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Last updated: Jul 13 '15