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Re: [EnergyPlus_Support] Re: ProblemHeatPumpWaterHeater
You must have simulated 2 different water heaters based on the
description below and you did not provide enough information to
accurately describe what is happening. The source side nodes are usually
used to "recover" energy from some heat source (e.g. chiller with heat
recovery or solar hot water systems). The use side inlet nodes are
usually used to provide hot water to some sink (no pun intended), like a
hot water coil or potable hot water use. But the source and use side
nodes are interchangeable and can be used as you describe below. This
naming convention is really just an accounting issue with the tank nodes.
For the first question, it sounds like you have simulated a heat pump
water heater serving a hot water coil, but I am guessing. Were you also
drawing water from the use side inlet nodes? I would agree that the
water heater source rate (if used to supply a hot water coil) would be
nearly equal to the DX coil total water heating rate if there were no
additional draw on the tank. But you did not tell me if the DX coil
total water heating rate was 8% higher or lower than the water heater
source rate. And if there was a secondary heating element in the hot
water tank. Typically there is a backup heating element used in heat
pump water heaters. Is that what you simulated? If you simulated a
secondary heating element, did that element turn on? If so, then the DX
coil total water heating rate would be less than the water heater source
rate. And there are standby or skin losses for the tank itself that can
cause the DX coil total water heating rate to be larger than the water
heater source rate. So you see I can not give you a definite answer.
For the second question, it sounds as though you are using a gas water
heater with heat recovery on the source side of the tank. The only hot
water draw is on the use side of the tank. Is this correct? If the
heater thermal efficiency is set to 1, and the ON and OFF cycle loss
coefficient to ambient temperature is set to 0, and the source and use
side effectiveness values are set to 1, and the OFF cycle parasitic fuel
use is set to 0, then you should have been much closer on the energy
balance where Water Heater Use Rate = Water Heater Source Rate + Water
Heater Gas Consumption Rate. If your source and use side connections are
to a hot water "users", then your energy balance equation is incorrect,
it would be Water Heater Gas Consumption Rate = Water Heater Use Rate +
Water Heater Source Rate.
The expert on water heaters may also respond to this email if I have not
described it correctly.
Miguel Angel Pascual wrote:
> Dear Richard,
>
> Thank you very much for your answer.
>
> We followed your indications about the fan configuration and the exterior
> node for the water heater but we didn't notice any significant difference.
> We are worry about some variable results of the heatpump components.
> We were
> expecting to have similar annual results in the variables:
>
> * Water Heater Source Rate (source coil of the water tank)
> * DX Coil Total Water Heating Rate (hot water coil of the heat pump)
>
> The mean difference between these variables is about 8% (much more
> than the
> condenser pump power).
>
> We also can't understand the energy balance in the water heater tank. We
> have simulated an almost ideal tank with a gas heater (Heater Thermal
> Efficiency =1, with almost no heat loses), so we were expecting something
> like:
>
> * Water Heater Use Rate = Water Heater Source Rate + Water Heater Gas
> Consumption Rate
>
> But the power entering the water heater (Water Heater Source Rate + Water
> Heater Gas Consumption Rate) is about 55% bigger than the "Water
> Heater Use
> Rate"
>
> Can you help us with this question?
>
> Thanks again for your attention.
>
> Miguel Ángel Pascual
>
> Director Técnico
>
> MIYABI espacios urbanos bioclimáticos
>
> Leyre 11bis, 1ºC 31002 Pamplona
>
> Tel: 948 20 36 44 Fax: 948 20 78 60
>
> Email: mapascual@xxxxxxxxx <mailto:mapascual%40miyabi.es>
>
> Web: <http://www.miyabi.es/ <http://www.miyabi.es/>> www.miyabi.es
>
> _____
>
> De: EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>] En nombre de Richard
> Raustad
> Enviado el: viernes, 30 de marzo de 2007 18:00
> Para: EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> Asunto: [EnergyPlus_Support] Re: ProblemHeatPumpWaterHeater
>
> You will also need to change the input for Ambient Temperature Indicator
> in the Water Heater:Mixed object from Exterior to Outside Air Node.
>
> Richard Raustad wrote:
>
> > The heat pump water heater has an error when the HPWH is located
> > outdoors and a draw through fan is used. Change your fan configuration
> > to blow through. This problem will be corrected for the next release
> > of EnergyPlus V2.0 in April 2007. You will also need to add a node
> > name for the Ambient Temperature Outside Air Node in the Water
> > Heater:Mixed object.
> >
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> es> Description : Problems
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>
> --
> 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. <http://www.fsec.ucf.edu
> <http://www.fsec.ucf.edu>> ucf.edu
>
> UCF - From Promise to Prominence: Celebrating 40 Years
>
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>
--
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
UCF - From Promise to Prominence: Celebrating 40 Years
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