I think the model remains the same, but the sizing routines have been updated. I've not tested 8.2 in this regard. This is a zone equipment so the massflow must be being sized with the temperatures already available from the plant side sizing. Hydronic tubing length and number of circuits has very minimal effect in the heat transfer rate and are only effecting the reaction time of the system together with a pressure loss (pressure loss is not modelled). The massflow rate is the total mass flowrate of the system...as far as I know the system does not keep track of individual mass flowrates in each pipe section and it's relation to the Nusslet number and heat transfer rates. (I say that provocatively, hoping that someone can shed more light on the matter).
At the end of the day this systems heat transfer rates are deturmined by the conduction coefficients of the radiative surface (which are surface temperature dependant), and the AMOUNT of transfer surface available. Users often complain that the system does not meet the loads. Mostly the problem is that they have too little active surface.
For cooling, condensation restricts the extremity of the surface temps you can use. And on that point it is imperitive to not simply select the entire ceiling or floor area as the surface, but to split the surface such as to only use the active area, otherwise the extreme surface temperatures will not become apparent and negate proper condensation analysis (and effect the proper convection coeff.s).
Mit freundliche Grü�en- Sent from my iPhone (excuse the brevity)
i. A.
Jean Marais
b.i.g. bechtold
Tel. +49 30 6706662-23
On 27.10.2014, at 11:24, "fpasserini.tn@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
In the version 8.2 there are new fields for the ZoneHVAC:LowTemperatureRadiant:VariableFlow object: "Heating Design Capacity" and "Heating Design Capacity Per Floor Area". At what temperatures (air temperature and water temperature) are these values evaluated?
If "Heating Design Capacity" is autosized, does the autosized capacity depend on the "Hydronic tubing length"? I mean, what is the role of the "Hydronic tubing length" in the new model?
Regards
Francesco
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