[TRNSYS-users] multiplication factor and effective moisture capacitance estimation

[Avesani Stefano]

Dear all,

 

(Thanks David for your answer..)

I have furthermore investigated this issue and I have found the following example proposed in the TRNSYS mailing list some years ago.

 

I have now another question concerning how to get the "k = gradient of sorptive isothermal line". In the TRNSYS type56 manual there is a table of "material data for buffer storage humidity model", but there are no references concerning the sources and/or the calculation conditions. 

As "k" is not constant (at least over the 0%-100% RH range as it strongly varies with RH itself), which are the conditions at which the reported TRNSYS "k" refer?

 

Thanks for helping and supporting,

 

All the best 

Stefano

 

*	Date: Fri, 12 Jul 2002 01:17:49 -0500
*	From: "Matthias Rudolph" <rudolph at xxxxxxxxxxxxxx <mailto:rudolph at DOMAIN.HIDDEN> >
*	Subject: Re: AW: humidity calculation

________________________________

I think it is not that easy to define the absolutely correct value for the

humidity capacity ratio of

the Capacitance humidity model[...]

The default value for the humidity capacity ratio of the simple model should be

1

because this represents only the capacity of the air. The default values range

are 1-10 for a standard office because this depends on things like the quality

of the surface of walls. This could be the quality of a layer but also of a

color.

Maybe if you just take into account the surfaces of walls with a low diffusion

Resistance than

one rough way to estimate the humidity capacity ratio is e.g. for a room 5 m x

4 m x 3 m:

The mass of water in the air and the mass of water in walls, if all walls and

the ceiling have 0.005 m thickness of  gypsum. The Diffusion Resistance mü of

those walls is assumed to be low.

Material          roh [kg/m³]     kapa [kgH2O/kgmat/relhum]         mü

Gipsum                900               0.015                        8

m water air     = 60m³     * 1.2 kg_air/m³     * 0.016 kg_H20/kg_air = 1.15

kg_H2o

m water walls   = 0.37m³   * 900 kg_mat/m³     * 0.015 kg_H20/kg_mat = 5.0

kg_H2o

this would result in a Ratio =(mw_air+mw_wall)/mw_air= 5.3

kind regards,

Matthias Rudolph

 

 

From: David BRADLEY [mailto:d.bradley at tess-inc.com] 
Sent: venerdì 2 settembre 2011 16.37
To: Avesani Stefano 
Cc: trnsys-users at cae.wisc.edu
Subject: Re: [TRNSYS-users] multiplication factor and effective moisture capacitance estimation

 

Stefano,
 I have looked a bit in the literature and have seen that values between 5 and 15 are typical. Completely unscientifically, I usually use 10 for a "typical" room. I would use a higher value if I were dealing with a room that had a lot of furnishings or a lot of papers. I typically use a value of 5 for corridors and lobbies since they tend to be less heavily furnished.
Best,
 david


On 9/1/2011 10:58, Avesani Stefano wrote: 

Dear all,

 

I am wondering how to estimate the "humidity capacitance ratio" - = multiplication factor generally in the range of 1 to 10 - needed using the simplified (effective capacitance humidity model) type56 moisture model. 

Any suggestion, experience, literature references? 

 

I have looked in the manual but I could not find any clue!

 

Thanks a lot!

All the best

 

Stefano






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