Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question
2

Energy consumption for heating too low

asked 2017-04-18 10:11:49 -0600

PaoloMassaroni gravatar image

updated 2017-05-08 12:14:43 -0600

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.

edit retag flag offensive close merge delete

Comments

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 -0600 )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 -0600 )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 -0600 )edit

1 Answer

Sort by » oldest newest most voted
2

answered 2017-04-28 11:02:31 -0600

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

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

 

Question Tools

2 followers

Stats

Asked: 2017-04-18 10:11:49 -0600

Seen: 87 times

Last updated: Apr 28