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Pump energy too low with four pipe fan coil system

asked 2017-05-23 11:51:07 -0500

kmpiscopo's avatar

updated 2017-08-06 07:22:10 -0500

I am modeling a 50,000 sqft, 3 story office building in a hot and dry climate (Central valley, California). The building is currently set up with 3 thermal zones; one per floor. I am using a four pipe fan coil system with constant speed pumps for heating and cooling. The model runs well with no errors, and both heating and cooling setpoint temperatures are met throughout the year.

When I run the model, the HVAC energy is distributed as follows: cooling: 82%, heating: 12%, fans: 5%, pumps: 2%. Upon closer inspection of the hour-by-hour zone temperatures, setpoint temperatures, and chiller energy consumption, I can see that the chiller operates nearly continuously (even after the setpoint temperatures have been met). Additionally, the absolute value of fan and pumping energy is far below typical benchmark numbers for this building type and climate zone. Any thoughts here?

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Do you check fan pressure rise parameter ? Is that correct number ?

BL's avatar BL  ( 2017-05-26 11:05:41 -0500 )edit

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answered 2017-05-25 19:18:12 -0500

The model has 3 zones for 50,000 ft². That is not enough zones. Typically the largest zone in an office building will be 1,000 ft², maybe up to 2,000 ft² for a large open office. A core and perimeter zone split is common, as different perimeter zones will be in heating/cooling depending on orientation and time of day.

The core area in an office building will have internal loads and no heat loss so it will always be in cooling. EnergyPlus mixes all air in the zone for calculating loads. So what is likely happening in your model is that all facade heating loads are getting mixed in and nullified by being connected to the large core area that is always in cooling. Split your floors into core/perimeter areas to get a more accurate heating and cooling estimate.

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Thanks for the input @mdahlhausen. I changed the thermal zoning to represent a more realistic situation, and am still running into the same issues with very high cooling energy, and very low fan and pumping energy.

kmpiscopo's avatar kmpiscopo  ( 2017-06-07 11:42:21 -0500 )edit

can you post a link to the model?

mdahlhausen's avatar mdahlhausen  ( 2017-06-07 13:08:34 -0500 )edit

Link to a google drive folder below. There are 2 files in this folder - my question was originally targeted at the model 'OfficeBldg_FanCoil', which I've changed a bit since I originally posted the question. I am also running into similar issues with the 'BankofItaly' building. Thanks for taking a look - I really appreciate the assistance.

kmpiscopo's avatar kmpiscopo  ( 2017-06-07 20:21:15 -0500 )edit

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Asked: 2017-05-23 11:51:07 -0500

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Last updated: Jun 07 '17