Electric hot water tank with a single temperature node: the temperature is assumed to be homogeneous (no stratification).
Hypothesis and equations
The tank is supposed cylindrical: diameter d and height H.
The insulator (conductivity lambda and thickness e) is uniformly distributed on the outer surface of the tank.
The mass of water is supposed to be at homogeneous temperature T_tank.
The heat storage in the tank results from the superposition of three heat flows:
- It is a hysteresis regulation with a half-band dT on both sides of the setpoint: Hyst = if T_sp+dT then 0 else pre(Hyst)
- The electric power injected into the water is equal to: Pelec = OnOff.P.Hyst
- The water heating power is equal to: debit.Cp.(T_tank - T_cold)
- An average coefficient of outside exchange is assumed: he = 10 W / (m².K)
- With a first approximation, the loss coefficient is equal to: KS = (1,1 +0,05/V).h.S avec 1/h = 1/he + e/lambda, S = pi.d.(H + d/2) et V = pi.d².H/4
Bibliography
[1] : E.C.S. : hot water in residential and tertiary buildings
Design and computation of facilities
Collection of AICVF guides, pyc edition, first edition 1991
Instructions for use
See example DHWResistiveWaterHeater.
Known limits / Use precautions
This model is very simple to implement in a study and enables a low computation time.
It is very sufficient and accurate to deal with consumption problems over a long period (1 year for example).
But for studies on power demands, it is advisable to use tank models taking into account the thermal stratification.
Validations
Validated model - Hassan Bouia 10/2012
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Licensed by EDF under a 3-clause BSD-license
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BuildSysPro version 3.6.0
Author : Hassan BOUIA, EDF (2012)
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