Re: [EnergyPlus_Support] Steam Boiler GetSpecificHeatGlycol warning

For those of you who may be interested:

It appears that there is no practical way to avoid this warning. If the steam plant temperature is equal to or greater than 100C+SubcoolC on the radiator, the warning is apparent generated for every iteration of the radiator because the outlet condition is calculated to be greater than 100C. With the plant at 105C and the radiator sub cool at 5.1C, the warning still appears at low demand. Apparently the when the minimum steam gulp is taken and the demand load is very low, not enough energy is removed to lower discharge temperature from the radiator to the acceptable 100C. I have tried reducing both the steam temperature and the sub cooling, but odd things happen and outlet conditions went to negative temperatures for some reason.

I can only assume that conservation of energy applies in the model, and any excess energy at the radiator outlet means less energy needs to go in at the boiler.

This may be an Ideal Load radiator model, but it is far from an Ideal Steam Radiator model. An Ideal Steam Radiator model would always discharge condensate no matter what the inlet steam conditions are (no need to specify sub cooling), and it would have a minimum steam gulp when cycled on for a short duration that could overheat the zone.

Fortunately, this should not be a large error for most systems where steam loop temperature matches the radiator sub cool setting. If the demand is large enough or the radiator is scheduled off during periods of light demand, the error warning may not occur at all. Mismatching the steam temperature and generating the warning all the time probably affects the energy consumption of the boiler.

Ned Lyon, P.E. (MA, WV)
Staff Consultant

SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
781.907.9009 fax
www.sgh.com

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Edward G. Lyon
Sent: Friday, March 15, 2013 11:26 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] Steam Boiler GetSpecificHeatGlycol warning

Well as it turns out, this is an inherited problem. I ran the example file 5ZoneSteamBaseboard.idf and it throws the same warning?.

Ned Lyon, P.E. (MA, WV)
Staff Consultant

SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
781.907.9009 fax
www.sgh.com

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Richard Raustad
Sent: Friday, March 15, 2013 8:48 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Steam Boiler GetSpecificHeatGlycol warning

These 2 files did not look like they attached when I looked at the Yahoo group site, instead they were inline which was not my intention.

I upload them instead to the Files\Examples folder.

-------- Original Message --------

Subject:	Re: [EnergyPlus_Support] Steam Boiler GetSpecificHeatGlycol warning
Date:	Fri, 15 Mar 2013 08:01:17 -0400
From:	Richard Raustad <RRaustad@xxxxxxxxxxxx>
Organization:	Florida Solar Energy Center
To:	EnergyPlus_Support@xxxxxxxxxxxxxxx

Did you use the correct pump?

Pump:VariableSpeed:Condensate,
       \memo This pump model is described in the ASHRAE secondary HVAC toolkit.
       \memo Variable Speed Condensate pump for Steam Systems

It can be frustrating to manually create plant loops. But really, they are not that hard to understand. For example, I have used this " single cooling and heating plant" many times to connect to a single water based equipment model (usually VRF). Bottom line, since I already have this plant available it is very easy to add to any input file using macro language.

##fileprefix C:\MyProjects\EnergyPlus\EnergyPlus\Inputs\
##include VRFSinglePlantLoopBoilerTower.idf

The only connection between this stand alone plant input file and the main input file is here (this is in the main input file):

AirConditioner:VariableRefrigerantFlow,
    VRFCondInNode,           !- Condenser Inlet Node Name
    VRFCondOutNode,          !- Condenser Outlet Node Name

I'm including both files for review.

Main input file: VariableRefrigerantFlow_5Zone_HeatRecovery_WaterCooled.imf
Plant library: VRFSinglePlantLoopBoilerTower.idf

Using this method, basically from a library of plant configurations, it becomes easy to implement.

I developed the PTAC model in E+ and do not understand your comment on configuration.

On 3/14/2013 5:18 PM, Edward G. Lyon wrote:

I cobbled together a steam boiler system by robbing 5ZoneSteamBaseboard.idf so I could supply one steam baseboard in my model. I now fully understand how little I know about piecing together a functional mechanical system from EnergyPlus components without using templates (translation: what a pile of junk to add just to run a little radiator). I did not autosize anything because I know the radiator flow rate already. PlantPumps:CalcPumps is throwing a GetSpecificHeatGlycol warning because it has a 107C temperature fluid. I suspect that the plant is so oversized that it supplies steam to the pump, but I would appreciate any suggestions for resolving this without reverting to an autosized solution.

Also, any references that simply explain how to take a set of fans, pipes, and coils in a box and make the appropriate nodes, loops, branches and controls for EnergyPlus would be appreciated, Iâ??ve never seen a PTAC in the field that actually looks like the EnergyPlus PTAC most people use, so I should probably build my own?

Ned Lyon, P.E. (MA, WV)
Staff Consultant

SIMPSON GUMPERTZ & HEGER
| Engineering of Structures and Building Enclosures

41 Seyon Street, Bldg. 1, Suite 500
Waltham, MA 02453

781.907.9000 main
781.907.9350 direct
781.907.9009 fax
www.sgh.com

--

Richard A. Raustad

Senior Research Engineer

Florida Solar Energy Center

University of Central Florida

1679 Clearlake Road

Cocoa, FL  32922-5703

Phone:   (321) 638-1454

Fax:     (321) 638-1439 or 1010

Visit our web site at: http://www.fsec.ucf.edu

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