District heating based on BuildingSystems library

[ricard...@ucdconnect.ie]

Hello all;

My name is Ricardo as part of my master's thesis I am trying to model my college district heating network. My main input is the heat load per hour during a year, which I have from measured data. my supply temperature is from 70C to 85C and the network is set to have an increase in temperature between 10C and 15C. I have 9 substations and a central which supplies the heat load.

I am modelling my network like this:

the main components of my model are:

My central is configured like this:

my pipes:

my substation:

Right, this is a little description of my network so far, my problem is no matter the parameters I put on my central and pipe, the mass flow within the whole system does not change. When I change the supply temperature and the efficiency of my central, the temperature of the fluid entering the substation does change however the mass flow is always the same. Also in relation to my pipes, it seems that my system does not react to any changes I make to the pipes parameters as well.

In summary, my issue is, my network seems to be working as separate systems, one component does not react to the changes I make to another component.

Can you try to help me with this. Thanks very much

[Carles Ribas Tugores]

Hi Ricardo,

 

 When I change the supply temperature and the efficiency of my central, the temperature of the fluid entering the substation does change however the mass flow is always the same.

It seems you are using a constant temperature drop in your substation (dTHex ?). The mass flow will be slightly difference because of the increase/decrease of heat losses but it wont change drastically.

Try to change your parameter dTHex and check mass flow rate again. 

Not related to your question, but ... I am not sure if your parameter lambdaIns is correct. Is the pipe thermally insulated?  0.18 W/mK seems too be a high value for insulation material.  

Regards,

Carles

[Carles Ribas Tugores]

The mass flow will be slightly difference because of the increase/decrease of heat losses but it wont change drastically.

Actually it wont change at all! my bad.

Regards,

Carles

[ricard...@ucdconnect.ie]

When I change dThex the mass flow changes a little, but in your opinion does this model is representing reasonable a DH network? you mentioned my 0.18 ... if I change to 18 for example my model does not react to any changes apart from the dThex

regards

ricardo

[Carles Ribas Tugores]

• The mass flow rate is function of your load and temperature difference.These are the main variables/parameters that will determine the mass flow rate.
• Reasonable? I do not know your system... are you modeling an existing District Heating System? I would remark that,
  
• A central pump is a more common approach, you could use a central pump (add a pump in the central model) and substitute the pumps of your consumer per a valve. Then close/open the valve according to your load and temperatures.
  
• A temperature drop of 10 K is quite low. Are you assuming heat is being used in a radiant floor heating system?
  
• the thermal conductivity 0.18 W/mK is just to high, values between 0.02 and 0.03 W/mK are more realistic. It has nothing to do with the mass flow rate, it was just a comment... . You can check some manufacturer documentation, e.g. Logstor.
  

 

[ricard...@ucdconnect.ie]

I see, makes sense.

And yes I am modelling a real DH. It is from my college. The only data I have is the hourly heat loads, and this is my main input so it is difficult to validate my model. I have other 2 models one of them has a pump on the central heating system but I does not run, keeps giving an error I cannot fix.

My substations are the same 

I got from the buildings library from the idealsystem3cluster and I cannot edit them, I used this one because it is simple and my model runs with them, I don’t have another substation. I will use .018 instead of .18 the person who gave me this value must got it wrong.

And if I increase dThex too much my model crashes as well... I don’t know what to do, I am really lost

[Carles Ribas Tugores]

Hi!

And yes I am modelling a real DH. It is from my college. The only data I have is the hourly heat loads, and this is my main input so it is difficult to validate my model.

Ask them if they have more information or can help you with your assumptions, such as dT = 10 K.
 

And if I increase dThex too much my model crashes as well... I don’t know what to do, I am really lost

It might because of too low temperatures (<0 °C).


 

[ricard...@ucdconnect.ie]

I am trying to get more data, but the system is new, apparently, the only data they can provide now is the heat load. 

[laban...@gmail.com]

Hi have you check on the attributes part? I m Laban and following up this conversation. Thanks.

[ricard...@ucdconnect.ie]

Hello Dr Laban

So, i am aware of this section:

[ricard...@ucdconnect.ie]

What should i be checking for here? Thanks once again

[laban...@gmail.com]

Put them under parameter specific option and see if there's a difference.