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[EnergyPlus_Support] Re: Heat Recovery Problems



Thank you and the team for the work Peter.

One more question, is the problem just on energy output numbers or is
it effecting the component actual performance? I mean, beside the
energy output values, are the other output of the model still good ?

Andrea.


   

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Ellis, Peter"
<peter_ellis@...> wrote:
>
>  
> Andrea,
> I have confirmed that there is indeed a bug with the water heater
object.  The thermal history of the tank is being incorrectly updated
several times per system time step (should be only once per sys time
step).  This is causing the problems in the energy balance that you
were seeing.  Originally the water heater did have the correct energy
balance.  This bug was most likely introduced one or two releases ago.
 Although we do extensive testing to try to make sure that we don't
"break" anything from release to release, this bug got by us somehow.  
>  
> The bug has now been fixed.  You should be able to successfully
confirm the energy balance in the upcoming release in October.  I have
also added a new report variable for the water heater that gives you
the final tank temperature at the end of the time step.  This should
allow you to show an exact energy balance between the tank starting
conditions and ending conditions and the various fluid flows.  
>  
> Thanks for your persistence and patience in dealing with this bug.
>  
> Peter Ellis
> National Renewable Energy Laboratory
>  
>  
> -----Original Message-----
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]On Behalf Of ingdallolio
> Sent: Tuesday, September 05, 2006 3:22 PM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: [EnergyPlus_Support] Re: Heat Recovery Problems
> 
> 
> 
> Peter,
> I understand source and use power do not match in a water heater but
> energy source and use should balance in a year period ( with stored
> heat and losses of course ), they do not match in any water heater I 
> tried like the example file collectorflatplate.idf.
> Mike Wite confirmed me the unbalance before summer but so far no info
> about the issue nor it's in the known issue list. The present version
> waterheater object can be considered reliable ?
> Grazie (Thanks).
> Andrea. 
> 
> I've also problem in balancing energy 
> 
> --- In EnergyPlus_Support@
<mailto:EnergyPlus_Support%40yahoogroups.com> yahoogroups.com, "Ellis,
Peter"
> <peter_ellis@> wrote:
> >
> > 
> > The "source rate" and the "use rate" refer to the heat gain rate (or
> loss rate) through the two sets of plant loop connections to the water
> heater. In your case, it sounds like you have the "source side"
> connected to the IC engine for heat recovery. I would guess that your
> "use side" is connected to some hot water load, like domestic hot
> water, or maybe space heating. The heat gain rate (or loss rate) for
> either side is calculated as the Q = mass flow rate * Cp * (Ttank -
> Tinlet). 
> > 
> > That said, it is not often the case that the source rate and the use
> rate will match each other. That is usually why the water heater has
> some volume to it for energy storage, and why there's a burner or
> electric heating element to provide auxiliary heat when necessary. If
> your water heater has an auxiliary heat source, you need to take that
> into account too. The report variable for that is "Water Heater
> Heating Rate". You may also have parasitics adding extra heat to your
> water heater also. 
> > 
> > Finally, keep in mind that the heat rates will only add up if the
> water heater is kept at a steady-state temperature. If, for example,
> you do not have a burner on your water heater and the use rate is
> greater than the source rate, the water in the tank will cool down
> until there's no more useable energy left. Or conversely, if you are
> adding more heat through the source side than you are using, the tank
> temperature will heat up until it hits the Maximum Temperature Limit
> at which point the heat is vented away and lost. 
> > 
> > As for the IC engine heat recovery, you should be able to verify the
> actual heat recovery rate delivered by the plant loop by looking at
> the mass flow rate through the IC engine, the inlet water temperature
> and the outlet water temperature. This calculation should match the
> water heater source rate. There may be some reason why the "total
> heat recovery rate" of the IC engine is defined differently, I don't
> know. Hopefully, they match. 
> > 
> > If this hasn't explained your problem yet, you can post the file.
> > 
> > 
> > -----Original Message-----
> > From: EnergyPlus_Support@
<mailto:EnergyPlus_Support%40yahoogroups.com> yahoogroups.com
> [mailto: EnergyPlus_Support@
<mailto:EnergyPlus_Support%40yahoogroups.com> yahoogroups.com]On
Behalf Of energypluser
> > Sent: Sunday, September 03, 2006 3:19 AM
> > To: EnergyPlus_Support@
<mailto:EnergyPlus_Support%40yahoogroups.com> yahoogroups.com
> > Subject: [EnergyPlus_Support] Heat Recovery Problems
> > 
> > 
> > 
> > Dear all
> > 
> > I connected a water heater to an IC engine for the purpose of
> recovering the exhausted heat.
> > When I was checking the results, I found something that I can not
> understand.
> > First, I found that the source rate of the water heater is much
> larger than the use rate. The 
> > difference is around 12kW in the winter design day and 7kW in the
> summer design day.
> > I checked that the heat loss rate is around 0.3kW in design days.
> > Why are some heat missing?
> > Second, I found that the total heat recovery rate of the IC engine
> was around 28kW in the 
> > design days. It is bigger than the source rate of the water heater!
> So the same problem 
> > appears again: there are some heat missing.
> > How can I explain this kind of things?
> > Thank you in advance!
> > 
> > mac.cz
> > 
> > 
> > 
> > 
> > 
> > 
> > [Non-text portions of this message have been removed]
> >
> 
> 
> 
>  
> 
> 
> [Non-text portions of this message have been removed]
>






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