[TRNSYS-users] Type 56 with AHU

[Marcus]

Hi Jean,

I never use the type 56 internal heating when coupling to AHU. I always
instead create i.e. a VENTILATION type in TRNBLD which is defined by INPUTS
for the temperature, flow rate, and humidity of incoming air. This provides
the input side. For the output side, I would read the temperature of the
zone, and feed that to the AHU controller. This defines the demand for that
zone, and it's closer to reality, a real controller would never directly
know the energy demand of a zone.

But it amounts to a lot of clicking and connecting if you have a lot of
zones, which I think you do. It's often a battle against the software
trying to get at the values we need...

In your case it sounds like you at a minimum need to externalize (create an
INPUT) the heating power of the heating type. This way you can turn it
off/on or regulate the power in the ideal type. Same goes for set
temperature, if you set the heating temp very low, this is the same as
turning it off. So generally, you need to lookup how to get values into/out
of TRNBLD? Maybe you already have, but click the play arrow icon in TRNBLD
for a field - change from constant to input - and then update the type 56
icon.

Hope that helps!
-- 
Marcus Jones,  M.Sc., LEED®AP BD+C
*Freelance energy consultant*
*Vienna, Austria


*
On Fri, Sep 14, 2012 at 2:33 PM, Jean Marais <jeannieboef at gmail.com> wrote:

> Dear Group,
>
> I'm stuck with a fundemental catch22. I report QSENS, the heating/cooling
> DEMAND from the building object Type 56. This, however does not report the
> demand, but instead the minimum of the demand and available "power". This
> means when, eg. "heating power" is set to 0, QSENS will report zero and
> when set to "unlimited" QSENS will report the actual demand to hit the
> defined setpoint.
>
> Going on to the zone...The cooling heating setpoints can only be assigned
> to the zone to do the previous calculation QSENS for the zone, when the
> heating/cooling is clicked "on".
>
> Thus, the actual demand for the zone QSENS can only be read out when the
> limit is set to "unlimited" and the heating/cooling is set as "on".
>
> HERE'S THE CATCH:
> I used QSENS to tell my AHU how much it should try and heat/cool. I send
> the resulting air into the zone which could be anything and does't matter,
> because even if the AHU can't meet the loads (or there is a power failure
> and the AHU is off for 2 hous), the resulting air temperature will never go
> outside of my heating/cooling setpoints (20/26), because unlimited cooling
> energy exists in the zone. This again is bad as the extracted air from
> zones is read from the building to be no higher than 26, which affects the
> heatexchanger, economizer, etc.
>
> At the moment I don't see a work around. The best I can do is report when
> the AHU Q does not meet the sum of zones Q at which point the simulation
> becomes "inaccurate".
>
> pls. advise,
>
> Kind regards,
>
> JEAN MARAIS
>
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>
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