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[EnergyPlus_Support] Re: Small School - Modelling Simple Heating and Ventilation Equipment
The system you describe will not control to a 20C supply air
temperature. You should be using an air primary loop with a HW
heating coil controlled to 20C (Set Point Manager:Scheduled and
Controller:Simple). See example file 5ZoneWarmest. The zone radiators
will trim the zone temperatures. The unit ventilator is zone
equipment, it is not used in an air primary loop. The unit ventilator
is controlled by a thermostat and connects at the zone level (zone
exhaust and zone inlet nodes). I would be surprised if were able to
connect this to more than 1 zone without seeing node connection
errors.
Even though I recommend you change system type, I will try to answer
your questions.
1) The preheat temperature defines the temperature of air leaving a
preheat coil in the outside air system. This is the air temperature
that will be sent to the heating coil for sizing. If return air is
mixed, it will be mixed with this preheated air to calculate the air
temperature entering the heating coil. If there is no preheat coil in
the outside air system, this field will not be used. You will still
have to define a hot water coil for the unit ventilator. You will not
use this field for your input file.
2) The unit ventilator does not use a Controller:Outside Air object.
But you will need one if you switch to using an Air Primary Loop
object. You would then need Outside Air System and Outside Air Mixer
objects also.
3) Report the air node flow rates in each zone, Return, Supply and
Exhaust. Also report the outside air and relief node flow rates for
each unit ventilator. Make sure the unit ventilator's relief air flow
rate equals the total zone exhaust air flow rate (sum both zones).
Also make sure the unit ventilator's outside air flow rate equals the
zone supply air flow rate (sum both zones).
4) You do not have to actually simulate the exhaust fans. You can use
electric equipment and gas equipment objects to simulate the energy
use. I think you would set the Fraction Lost to 1 for these objects
to only simulate energy use.
5/6) You do not need a set point manager for the outside air system.
You would use a Set Point Manager:Scheduled (85C) for the hot water
loop temperature.
7) The unit ventilators and OA systems do not require controllers.
See the UnitVent5Zone exmample file for additional help.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "brandao_nuno"
<ncostab@...> wrote:
>
> I´m reposting my two previous posts hoping to get any help I can
get.
> I'm really desperate for some help here!
>
> Thanks in advance
> Nuno Brandão
>
> -------------------------------------------------------
> > Dear Group Supporters,
> >
> > I´m simulating a small school, with 4 controlled zones. All the
zones
> > are equipped with radiators. Two unit ventilators equiped 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've introduced the system in order to get the autosizing
results, but
> > I´m having hard time to figure out the excessive boiler autosized
> > capacity obtained from the "Report:Table".
> >
> > I´m expecting for an anual simulation:
> >
> > - Boiler capacity - 30 KW
> > - HVAC EnergyConsumption - 23626 KWh
> > - Miscellaneous Equipment Energy Consumption(including lights,
> > gas and electric equipment) - 51027 kWh
> >
> > However, I´m obtaining exaggerated high values. I suspect the
problem
> > is related to "System Control" and "Zone Sizing" issues, which I
still
> > don´t quite understand. My questions are as follow:
> >
> > 1. In the system sizing objects, what does the field "preheat
design
> > temperature" stands for? The I/O reference definition says that
it is
> > "The design air temperature exiting the preheat coil(if any)".
> > In my specific case, to obtain the heating coil capacity is it
enough
> > to specify an exit temperature in this field, or do I still have
to
> > define a COIl:WATER:SIMPLEHEATING object? If it refers to another
> > preheat coil, do I still have to specify a temperature even if the
> > coil does not exist?
> >
> > 2. As described above, the system uses 100% outside air with no
> > recirculation. Do I still have to specify a "CONTROLLER:OUTSIDE
AIR"?
> >
> > 3. How do I guarantee, that the system uses only 100% outside
air?
> >
> > 4. Air is exhausted from the building by exhaust fans located in 3
> > zones. I need to account for the fan´s and kitchen gas equipment
> > energy consumption, in the total building energy consumption
internal
> > gains from both equipments are ignored since I do not need to
estimate
> > zone loads or equipment size). Do I have to define a FAN object
for
> > each ventilator, or is it enough to use the "ELECTRIC EQUIPMENT"
and
> > "GAS EQUIPMENT" objects with an "ALWAYS OFF" schedule in order to
> > ignore heat gains?
> >
> > 5.If the inlet/outlet boiler temperatures are 85/70, and the
sizing is
> > done by using the design day "Maximum Dry-Bulb Temperature" which
> > temperatures do I need to specify at the "Set point at outside
> > low/high" and "Outside low/high" fields from the "SET POINT
> > MANGER:OUTSIDE AIR"? In I/O reference, the supply air set point
> > temperature at outside high(SATOH) for example, is described as an
> > outside air temperature, can it be a water supply loop
temperature?
> >
> > 6. If the inlet air at the "MIXED AIR BOX" is only outside air
with no
> > zone recirculated air, do I need a "SET POINT MANAGER:OUTSIDE
AIR"? I
> > use a "SET POINT MAANGER:OUTSIDE AIR" to control the hot water
loop
> > flow and a "SET POINT MANAGER:SCHEDULED" to control the both air
loops
> > air outlet temperatures, is this procedure correct? If not, how
do I
> > control the heating coil flow in order to meet the heat demand?
> >
> > 7. I´m using one controller for each AIR LOOP, and one for each
> > HEATING COIL, this assures the air control and the water control,
is
> > this right?
> >
> > I´m having hard time to understand how and what do I need to
specify,
> > to model system control procedures in EnergyPlus.
> > I would appreciate any help I can get. I´m uploading my idf file
so
> > that you can have a look at it if necessary.
> >
> > Thank you for your patience.
> > Nuno Brandão
> >
>
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