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Hi,
I am relatively new to TRNSYS and I am not sure if my question makes sense or not.
I am trying to model a district heating system with two horizontal ground heat exchangers for exchanging heat separately during summer and winter. I want to use Type999. I have some problems that I would be grateful if anyone can give me hints on.
1- Am I also allowed to use Type997?
2- I want to have a 2 layers of pipelines with each pipeline comprise of 4 pipes. So in total it should have 8 pipes in the model. However, when I add these numbers, I receive 40 pipes and 40 pipe directions. I am not sure what is mistaken here.
3- I am not sure about the number of layers in the parameter section. Does it mean that the soil has two different layers with distinct properties? What I am in need is using two different soil types; one a type with high conductivity and specific heat (Probably sand) which encompasses the pipeline with 20 cm thickness over the pipe and the other is another soil type (Not sure, it might be clay or other ground soil types). Should I have two layers of soil for this issue or not?
4- When should I use the parameter "R-value for surface insulation" and what is the value of "Approximate depth of perimeter insulation"? Since the pipelines I am going to use are delivering low temperature fluids, I do not need any insulation for the pipeline. So should I keep them as zero? I also could not differentiate between "R-value for surface insulation" and "R-value for perimeter insulation". That are their differences?
5- For the length of surface extension, there wouldn't be any conditioned elements over the soil that the pipelines are buried beneath. What number should I insert for these parameters?
6- What is the depth and perimeter of groundwater? Since I want to implement pipelines in shallow depth, does it have much influence on my analysis?
I know that these are a lot of questions. I appreciate if you can guide me through these questions although they might seem quite simple and fundamantal.
With regards
Shams
Hello @shamsoddinghiami,
1) You can use either Type 997 or Type 999. Type 999 will run slower, but allows you to have multiple instances of Type 999 in a project. You might want multiple instances of Type 999 if you're running side-by-side comparisons of the heat exchanger under different scenarios, or if you're simulating multiple geo-sites within a single simulation. If you're only using one instance, I would use Type 997, as it'll simulate about twice as fast as Type 999. The two components are mathematically identical.
2) I am not sure how you got 40 pipes and 40 pipe directions out of two layers of four pipes each. When I specify '4' for Parameter 1 (Number of pipes in each layer) and '2' for Parameter 2 (Number of pipe layers) in either Type 997 or Type 999, I see 8 pipes and 8 pipe directions appear at the end of the parameter list. They are numbered by layer, then by pipe within the layer, as in 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, and 2-4. Is it possible the proforma was modified, and the parameter cycling got corrupted?
3) Yes, it sounds like you will want to enter '2' (at least) for the number of soil layers to model. The thermal conductivity, density, specific heat, and thickness of each soil layer are specified about halfway down the parameter list, following the thermal properties of the pipe fluid. If your layers are sandwiched (such as clay, then sand, then clay) you'll want to specify '3' for the number of soil layers to model, specifying the thermal properties of clay for layers 1 and 3 and sand for layer 2. The thickness of layer 1 will be the thickness above the sand layer (between the sand layer and the surface), the thickness of layer 2 will be the thickness of the sand layer, and the thickness of layer 3 will be however much clay you want to model beneath the sand layer.
4) These parameters are explained if you click the "More" button next to each parameter. The insulation specified here is not for the pipes themselves, but rather for the top and sides of the soil surrounding the pipes. Imagine the insulation as a bottomless box over the buried pipes, with its top at the soil surface; 'R-value for surface insulation' is the R-value of the insulation at the soil surface directly over the pipes, and 'R-value for perimeter insulation' is the R-value of the left, right, front, and back sides of the box. If you are not modeling any insulation, you can set both values to 0.
5) If there's no insulation or conditioned space over the buried pipes, you can leave the surface extension values at 0.
6) Depth and thickness of groundwater are used when modeling influence of aquifers, wells, or other buried fluid streams on the buried pipes. If you don't want to model any groundwater, you can set the depth of the groundwater well below the deep-earth distance and/or set the thickness of the groundwater layer to 0.
Thanks for your response.
I managed to figure out the process to model the ground heat exchanger and put all the parameters in place; however, the system would run as I receive an error that the number of pipes are exceeding the maximum amount. As far as I went through the "MORE" button in the component, the number of pipes can be infinite; however, the error shows that 195 pipes exceeds the maximum value.
The same happens about the number of nodes long the pipe axis and I can not put a large number in it although it is written that the maximum value is infinite.
Can I make some modifications to the code to remove the limitation?
The parameters for the GHX is attached
Thanks
Shams
I increased the maximum number of the pipes in each layer to 300 in the code; however, I receive the same error mentioning that the maximum number is exceeded
@shamsoddinghiami My apologies if this is obvious but once you modify the source code of a component you have to recompile it and recreate the dll in which it lives. Trnsys does not compile the source code on the fly when you launch a simulation. Type997 and 999 live in the TESS GHP library dll (TESS_GH_v18_0_64.dll) along with a number of other components. You would have to recreate the dll for the whole library.
It might be simpler for you to contact your distributor and ask them to create a version of the library that has an expanded limit on the number of pipes. If you aren't sure who to contact, you can send a direct message to techsupport@tess-inc.com.
kind regards,
David
@shamsoddinghiami Regarding the second question from the original post, about the number of pipes and pipe directions ...
I still can't say exactly what happened when you tried to model 2 layers of pipes with 4 pipes in each layer and got 40 pipe inlets and 40 pipe directions. However, it IS a known issue that the cycling of the pipe inlets and directions doesn't always sync perfectly with the number of pipes and layers specified. For example, if you change the number of pipe layers from 1 to 2, then change the number of pipes in each layer from 5 to 15, you'll still only see 5 pipe inlets and 5 pipe directions in each layer. If you instead change the number of pipes in each layer first, *then* the number of pipe layers, the number of pipe inlets and directions will be correct. The issue is related to how nested cycling is carried out on the parameters, which unfortunately is a deeper programming issue that hasn't been resolved yet. Should you need a workaround in the meantime, we have found the following order of operations works:
- Set the "Number of pipe layers" to 1.
- Change the "Number of pipes in each layer" to the value you want. If you've already entered the value you want, you may have to change it first to a different value, then re-enter the value you want.
- Change the "Number of pipe layers" to the value you want.
It is also a known issue that if you edit the Type 997 or Type 999 proforma (say to change the upper limits on the number of pipes in each layer or the number of pipe layers), then use the right-click -> Replace method to update the proforma in your project, the pipe inlets and directions may be dropped from the replaced proforma. You may have to replace the proforma by dragging and dropping the new proforma into your project and re-drawing the connections.
