[TRNSYS-users] Type 940 : Tankless Water Heater

[Anas Majdouli]

Hi Jeff,

In this case, I should not have oscillations but only a lower outline temperature. 

Sincerely,
Anas MAJDOULI

From: thornton at tess-inc.com
Date: Wed, 8 Jul 2015 09:21:41 -0500
To: trnsys-users at lists.onebuilding.org
Subject: Re: [TRNSYS-users] Type 940 : Tankless Water Heater

Without seeing the project, I'm going to guess that the effective heating capacity is different between the two simulations.  The energy that can be added to the fluid is the rated capacity x thermal efficiency.  As you decrease the gas efficiency it means you have less capacity to heat water and the outlet temperature may sag from the setpoint.
Jeff ThorntonTESS

Sent from my iPhone
On Jul 8, 2015, at 4:23 AM, Anas Majdouli <majdouli_anas at hotmail.fr> wrote:




Hi TRNsys community,

I am comparing Gas & Electric tankless water heater using the same component (Type 940). According to the description of the type, Electric tankless water heater is simulated by setting the efficiency to 1. When I plot the outlet temperature for both gas & electric heaters, some oscillations occur at the beginning of the first water draw for each day (7 days simulation) only for gas heater (efficiency set to 0.8). I tried to change the deadband, it is not affecting the results. But when I reduce the efficiency of the device, the amplitude of the oscillations increase. Why isn't this happening for the electric heater, i.e. when the efficiency is set to 1 ? Is it just from how the type was designed ?

Please find attached the file of the simulation and the corresponding weather data. The concerned plots are "Tout" of the 1st and 2nd graphs.
Thank you in advance.

Yours Sincerely,
Anas MAJDOULI
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