[TRNSYS-users] Type 940 : Tankless Water Heater

[Jeff Thornton]

Re: Type 940 

I took a look at your simulation and while I feel there are things you
could improve (no need for two identical weather readers and water draw
profiles and multiple integrators), the overlying cause of the strange
oscillations is a small bug in the Type 940 source code. The efficiency
of the device is not getting reset when two instances of the same model
are in the same project. I have fixed the source code and will get it
into the next release of the TESS Libraries. In the short term, if you
have a fortran compiler and are comfortable rebuilding DLL's then let me
know and I'll send you the updated code. I would also suggect that you
may want to lower the minimum input for the heating below 0.1 to improve
your outlet temperature control at low flow rates. 

Jeff 

---
Jeff Thornton
President - TESS LLC
22 N. Carroll Street, Madison WI USA 53703
Office: (608) 274-2577 Fax: (608) 278-1475
www.tess-inc.com
E-Mail: thornton at tess-inc.com

On 07/08/2015 8:47 pm, Anas Majdouli wrote: 

> Please find attached to this email the file of the simulation and the weather data, if it's possible that you see my plots. 
> 
> Thank you in advance.
> 
> Anas MAJDOULI
> 
> -------------------------
> From: majdouli_anas at hotmail.fr
> To: trnsys-users at lists.onebuilding.org
> Date: Thu, 9 Jul 2015 03:44:33 +0200
> Subject: Re: [TRNSYS-users] Type 940 : Tankless Water Heater
> 
> 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 Thornton 
> TESS
> 
> 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
>> < /div>
> 
>> <Case 1 - Instantaneous gaz heater UNITS ENERGY.tpf>
> 
>> <Type-99 -48hrs-6min.txt>
> 
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