[TRNSYS-users] increased capacity of air

[leen peeters]

Yep, but as wqe assume an overdimensioned value of the capacity of the
romm, indeed the inertia is wrong. I simulated on 3 minute base. The peaks
in required thermal power are thus wrong. That is what I mean ... Is there
a way to solve that? Maybe it is better if I use a mass flow rate instead
of ACH?


On Sun, Nov 18, 2012 at 10:00 AM, jeannieboef <jeannieboef at gmail.com> wrote:

> this can get complicated. If you had a CFD program you may be able to
> deturmine the "age of the air". in one hour all the air is seen not to have
> changed with 1 ACH. But thermodynamically, this is irrelevant. the exhaust
> air is not even considered. at each timestep air at enthalpy1 is injected
> into the zone (enthalpy or energy state is only a function of the mass
> temperature and fluid specific property the specific heat at constant
> pressure. It is assumed an equal mass flow of air leaves the zone control
> volume and although programs differ here, it is usually assumed the air
> leaving properties are equal to those. of the well mixed zone temp,
> humidity, etc, which again describe enthalpy2. So energy balance is
> massflow x (enthalpy1-enthalpy2).so really the question is how we come to
> the zone air temp. the zone air temp from the previous timestep is adjusted
> depending mainly on convection heat transfer from bounding surfaces, and
> here it's (air) capacity will also influence how fast it adjusts. the
> energy injection from the air is also considered (100% convective). exactly
> how and at which timesteps (with predictive correctors etc. ) is software
> dependant and numerical solving is different. The capacity of the zone air
> influences how fast the zone air temp changes. The stored energy in zone
> air may increase or decrease.
>
> Sent from my iPhone
>
>
> On 18.11.2012, at 01:43, leen peeters <l.f.r.peeters at gmail.com> wrote:
>
>  Hi all,
>>
>> I am simulating a low energy 18-zones building wioth mechanical
>> ventilation. I increased the capacity of the air in the zone by a factor 5,
>> as we generally do in TRNSYS simulations.
>>
>> Now I wondered, whether this is logical when considering the energy
>> losses through exhaust of the ventilation system: am I not taking 5 times
>> the energy content? Do I have to adapt my ventilation flow rates in order
>> to compensate?
>>
>> I use a flow rate expressed in ACH as input to type 56.
>>
>> Leen
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>>
>
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