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[EnergyPlus_Support] Small School - Unit Heater

Dear All,

I´ve been working on a small school simulation with heating only
requirements. I´m reposting the system description :

I´m simulating a small school, with 4 controlled zones. All the zones
are equipped with radiators. Two unit ventilators equipped with heating
coils, supply air, each one supplying air to a group of two zones. The
system is suppose to maintain the 4 controlled zones to a setpoint of
20ºC, so outside air is preheated to 20ºC by the ventilator's heating
coil, and injected at that temperature into the zones. The radiators
are responsible for the final heating requirement adjustments,
although they have priority. The building has no cooling requirements.

The system is only functioning during occupancy hours with a 20ºC
setpoint. It turns on when the temperature is below 20ºC and turns off
if the temperature is above that value. Uses 100% outside air and it
is not recirculated.


I´m studying the possibility to use the "UNIT HEATER" component as an
alternative to the "DIRECT AIR" solution. In I/O reference, this
component is described as a zone equipment forced air unit, being a
little bit different of the "DIRECT AIR" component, as this one is
described as an "AIR DISTRIBUTION" component. I my simulation, after
implementing this solution I´ve encountered several errors which
brought confusion in my understanding of this alternative. My
questions are as follow:

1. First of all, is this modelling solution possible, having in
account the system described above?

2. How can I guarantee 100% outside air? Do I have to model a exhaust
fan? It must always exist a return air path, even if the air flow is
100% outside air, right?

3. This is the description of the 2 first severe errors, from the
*.ERR:(I think the next 39 severe errors are consequence from the
first ones.)

** Severe  ** An outlet node in  Air Primary Loop AIR LOOP2 is not
connected to any zone
   **   ~~~   ** Could not match ZoneEquipGroup Inlet Node="ZONE
SPLITER2 AIR INLET NODE" to any Supply Air Path or controlled zone
   ** Severe  ** An outlet node in  Air Primary Loop AIR LOOP1 is not
connected to any zone
   **   ~~~   ** Could not match ZoneEquipGroup Inlet Node="ZONE
SPLITER1 AIR INLET NODE" to any Supply Air Path or controlled zone

Is this related to any impossibility to couple zone splitters with
this kind of component(UNIT HEATERS)? Can I use two zone splitters(one
for each air loop) and connect them directly to the zones, with a zone
air inlet node? I´m a bite confused...

I´m uploading my idf file so that you can have a look at it.

Thank you very much for the help
Nuno Brandao







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