[EnergyPlus_Support] Re: Heat Recovery Problems

["ingdallolio" <ing.dallolio@xxxxxxxxx>]

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@xxxxxxxxxxxxxxx, "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@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]On Behalf Of energypluser
> Sent: Sunday, September 03, 2006 3:19 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> 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]
>







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