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Energy consumption for heating too low

asked 2017-04-18 10:11:49 -0500

PaoloMassaroni gravatar image

updated 2017-04-18 10:15:15 -0500

I modeled a office building in Rome-Italy, ashrae climate zone 4A. Window-wall ratio is 22% with a good performance envelope in terms of tramittance. HVAC is composed of a reversible Heatpump/chiller air-to-water (COP and EER around 3.0) and fancoils, with natural ventilation, which i assumed about 0.3 airchanges/hour. Annual consumption for cooling is 28000 kWH, while heating, accounted in water system - other (i used waterheater:mixed+waterheater:heatpump) is 1500 kWh. UnmetSetpoint hours are below 50 hours. Moreover in the PEAK ENERGY END-USE - ELECTRICITY table, values for heating and cooling are similar: with maximum respectively of 25.3 kW (which and 22.2 kW C:\fakepath\Cattura.JPG C:\fakepath\Cattura2.JPG The second screenshot is from resultviewer and shows how the heatpump coil and the chiller power are not so different.

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Some more information please - what is the size of the building? what are you assuming for thermostat temperatures? what specific HVAC objects did you use to model heating - what are their COPs in the model? What operational schedule does your HVAC follow? Do you have heat recovery?

mdahlhausen gravatar imagemdahlhausen ( 2017-04-18 11:14:45 -0500 )edit

Total building area is 810 m2 (8700 ft2); winter thermostat settings are 20°C (68°F), summer is 26°C (78.8°C), both considering 8 hour/day schedule. Heating system is composed by: waterheater:heatpump:pumpedcondenser with Coil:WaterHeating:AirToWaterHeatPump:Pumped which is 55,7kW-COP 3.3; i don't have any heat recovery.

PaoloMassaroni gravatar imagePaoloMassaroni ( 2017-04-18 12:11:45 -0500 )edit

I found out something interesting that may help resolving my issue:

1_Cooling coil total cooling energy of the coil:waterheating:airtowaterheatpumo:pumped doesn't work properly: it turns on just the first hour of the setpoint schedule, like a peak . Plant Supply Side Inlet and Outlet Temperature are identical (around 38°C) except at the time of the coil's peak, when inlet is 38°C and outet is 42°C.

2_Fancoils operation is normal in terms of schedule and rate

Any suggestion?

PaoloMassaroni gravatar imagePaoloMassaroni ( 2017-04-26 09:55:31 -0500 )edit

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answered 2017-04-28 11:02:31 -0500

PaoloMassaroni gravatar image

The problem was in the natural ventilation: the value assumed (0.3 airchanges/hour costantly as infiltration) was too low, so that cooling was overrated while heating was basically abstent, thanks to internal loads. A close envelope and the location climate confirmed this idea

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Asked: 2017-04-18 10:11:49 -0500

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Last updated: yesterday