Re: [EnergyPlus_Support] Extremely high user design load for heating for HVAC system 3

Qianmin

On Sat, Jul 9, 2011 at 7:31 PM, YuanLu Li <yli006@xxxxxxxxxxx> wrote:

For direct-expansion cooling, packaged and split system simulations: HVACTemplate:Thermostat
HVACTemplate:Zone:Unitary
HVACTemplate:System:Unitary

I think this grouping provide  both cooling and heating in the system:Unitary. The Zone Unitary can provide additional heating. Therefore the use of availability schedules must be very carefully considered.

In the IDF, the cooling is always ON.  Then what happens, when heat is required?
The expIDF did provide type 4 thermostat for you.
I am surprised that the use of Weekdays twice in the following schedule did not produce a warning.  The schedule should be split into Summer and Winter seasons.

Schedule:Compact,
Minimum Outside Air, !- Name
Fraction, !- Schedule Type Limits Name
Through: 12/31, !- Field 1
For: Weekdays SummerDesignDay, !- Field 2
Until: 24:00, 1, !- Field 4
For: Weekends WinterDesignDay Holidays AllOtherDays, !- Field 5
Until: 24:00, 0; !- Field 7

Because the expIDF used the template schedule, I think the above was not used. I think the expandIDF knows the preferred conditions and corrects them.================
HVACTemplate:System:Unitary,
UnitarySystem4, !- Name
School HVAC, !- System Availability Schedule Name
Zone 4, !- Control Zone or Thermostat Location Name
0.708, !- Supply Fan Maximum Flow Rate {m3/s}
continuous, !- Supply Fan Operating Mode Schedule Name
0.6, !- Supply Fan Total Efficiency
250, !- Supply Fan Delta Pressure {Pa}
0.9, !- Supply Fan Motor Efficiency
1, !- Supply Fan Motor in Air Stream Fraction
SingleSpeedDX, !- Cooling Coil Type
Always_On, !- Cooling Coil Availability Schedule Name
13130, !- Cooling Coil Capacity {W}
autosize, !- Cooling Coil Rated Sensible Heat Ratio
3.6635, !- Cooling Coil Rated COP {W/W}
Gas, !- Heating Coil Type
, !- Heating Coil Availability Schedule Name
16120, !- Heating Coil Capacity {W}
0.8, !- Gas Heating Coil Efficiency
, !- Gas Heating Coil Parasitic Electric Load {W}
autosize, !- Maximum Outdoor Air Flow Rate {m3/s}
0.22656, !- Minimum Outdoor Air Flow Rate {m3/s}
Minimum Outside Air, !- Minimum Outdoor Air Schedule Name
DifferentialDryBulb, !- Economizer Type
NoLockout, !- Economizer Lockout
25, !- Economizer Upper Temperature Limit {C}
, !- Economizer Lower Temperature Limit {C}
, !- Economizer Upper Enthalpy Limit {J/kg}
, !- Supply Plenum Name
, !- Return Plenum Name
BlowThrough, !- Supply Fan Placement
StayOff, !- Night Cycle Control
, !- Night Cycle Control Zone Name
None, !- Heat Recovery Type
0.7, !- Sensible Heat Recovery Effectiveness
0.65, !- Latent Heat Recovery Effectiveness
, !- Dehumidification Control Type
, !- Dehumidification Control Zone Name
, !- Dehumidification Setpoint {percent}
, !- Humidifier Type
, !- Humidifier Availability Schedule Name
, !- Humidifier Rated Capacity {m3/s}
, !- Humidifier Rated Electric Power {W}
, !- Humidifier Control Zone Name
; !- Humidifier Setpoint {percent}
============================

Some of the numbers are modified by the template expension. I have not look into the expanded version yet.
Because you are using multiple origines for the zones geometry, I have not b een able to associate the zone names with the room location yet. There are 6 zones, but the roof is divided into 8 parts.

The modified air flowrate by the template schedules may have changed your design values.

Dr. Li

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: zqianmin@xxxxxxxxx
Date: Fri, 8 Jul 2011 12:54:43 -0700
Subject: Re: [EnergyPlus_Support] Extremely high user design load for heating for HVAC system 3

yea, I found out the user design value are closed to my input.

Like what I said, it is a finished design project, so I will assume they selected the correct equipment based on their calculation. But from energyplus hvac summary report, the calculated design air flow is about 400cfm, which is too small compared to the equipment of 1800cfm for a 800ft^2 class room. Above is for zone cooling. For zone heating, the calculated design air flow are less than 70cfm for each classroom zone.

On Fri, Jul 8, 2011 at 12:14 PM, Jason Kirkpatrick <jason.alan.kirkpatrick@xxxxxxxxx> wrote:

The user design airflow is the calculated design airflow x the sizing factor

On Fri, Jul 8, 2011 at 2:15 PM, Qianmin Zhang <zqianmin@xxxxxxxxx> wrote:

Hello All,

First I want some help to better understand the result. Under HVAC Summary, for both heating, cooling, and airflow rate, there are two objects, one is calculated design, one is user design. I'm not that understand the difference between these two. Is there any relation between these two? Which document should I read to get know these things?

From the report summary, user design load for heating is much too high from my simulation. I used HVAC template, and I don't think I make any special change in my.idf file regarding the system. The weather data I used is Sacramento, CA. I found "zone/sys sensible heating rate" is really large. Could you take a look at my .idf and tell me the problem? It's a simply model. Thanks a lot.

Qianmin