Water cooling coil design inputs

asked 2019-04-10 02:17:45 -0500

Hi! I am trying to define a specific fancoil in EnergyPlus v9.1. I am seting all the inputs to the fancoil and its cooling and heating coils (no autosized values). However, when I include in the same zone a Sizing:Zone object, the hourly results I get for the cooling rate and inlet/outlet temperatures of the cooling coil change.

This is, if I define the cooling coil design inputs and don't use a Sizing:Zone object, I get the results I expect. However, if I add a Zone:Sizing object, it seems that the UA values of the water cooling coil are calculated with the settings in the Sizing:Zone object. However there aren't any autosized fields in my fancoil components.

Particularly, I am trying to define a fancoil which is small for the cooling design load of the zone it is placed in. If I add a Zone:Sizing object, I have to input a "Zone Cooling Sizing Factor" value in order to get as "design air flow rate" my actual fancoil air flow rate. Then I get good hourly cooling rate results again.
Also, depending on the "Zone cooling design supply air temperature" in the Sizing:Zone object, I get a Severe error about bad starting values for UA calculation of the water cooling coil, despite the inputs to the water cooling coil model remain always the same.

Please, can anyone confirm whether this is OK? In my opinion, the water cooling coil should always use its defined input design values to calculate its model parameters, regardless of any other objects in the .idf.

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Comments

I have the same problem... I did not know that not using the Sizing:Zone could solve the issue. Maybe also this question could be useful, even if it is not a complete answer in my opinion. https://unmethours.com/question/13425...

How did you oversize the "Zone Cooling Sizing Factor" to get the right air flow rate?

Gio gravatar imageGio ( 2019-04-18 10:56:52 -0500 )edit

In the HTML outputs report, section HVAC Sizing Summary -> Coil Sizing Summary, there is the value of the "Reference Air Volume Flow Rate". This value matches the autosized supply air flow rate for the zone where the fan-coil is placed in. The "Zone Cooling Sizing Factor" can be calculated as the value of the actual air flow rate of the fan-coil divided by this reference air flow value. If you run the simulation then, you will see that the "Reference Air Volume Fow Rate" for the coil is the old reference value times the sizing factor.

Barbara Torregrosa gravatar imageBarbara Torregrosa ( 2019-04-24 07:33:12 -0500 )edit

The Sizing:Zone objects will size the fan coil fans as well, which may affect the calculation of the rating conditions for the coils. Try hard-sizing the fans also and see if the Sizing:Zone still changes things? Also, Sizing:Zone could cause the fan coils to take into account outdoor air which might not have been accounted for without it.

Matt Doiron gravatar imageMatt Doiron ( 2019-05-14 23:52:15 -0500 )edit

In the situation I described the fan coil fan is already hard-sized, with the same design air flow rate as the cooling coils. All the values of the zone equipment are hard-sized and there is no outdoor air inlet.

Barbara Torregrosa gravatar imageBarbara Torregrosa ( 2019-05-16 05:30:18 -0500 )edit