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Hello all,

I am using ecoinvent 3.7.1 in openLCA 1.10.3

I have this question regarding modelling heat recovery. 

My LCA is modelling a recycling process, I have two sub-processes for this full process- sub-process A and B. 

B is the following sub-processes of A. For each of them, I created a process in openLCA with inventories.

 A is a process that produces heat, B is a process that requires thermal energy. If the heat produced by A is not used in process B, it will be waste heat emitted to the environment, and process B will need an external energy input.

I want to model the following different scenarios, could anyone provide me some suggestions on how to model them accordingly? (using a. self-created product flow or b.waste flow or c. elementary flow in Input or Output table?; and the option of ticking as avoided product or avoided waste)

(1) The heat produced in process A is completely re-used in process B.

(2) The heat produced in process A is simply released to the environment. Process B requires other sources of energy input.

(3) The heat produced in process A is partially re-used in process B, and partially becomes direct emission.

Your guidance is highly appreciated!!

p.s. I already know that starting from ecoinvent 3.6., it had introduced the possibility to use material flow logic approach for end-of-life modelling.

in openLCA by (220 points)

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Hi, interesting questions. First, for the "sub-processes", you could create a product system with these two processes, and then integrate this product system in other product systems, making it really hierachical.

1) heat is just the product of A passed to B. You can inspect processes in ecoinvent to see how these are connected, for heat-using processes in ecoinvent

2) then heat is an elementary flow

3) then you need to split, it is a mix of 1 and 2, for A; since often, the share between the wasted and used heat is somewhat flexible, you can create a parameter that adresses this share (it is "used_heat" for the product, and 1-used_heat for the wasted heat, e.g.). Then, for B, you need to decide if A still provides all the heat needed (e.g., if used_heat is 0, this would not be possible); thus maybe you need to model for B the heat demand, and then again parameterise it (heat_required_from_A; 1-heat_required_from_A) with an additional process that provides the rest.

Best wishes,

Andreas

- material flow logic: you are here dealing with products and elementary flows, thus you do not need to go into waste modeling options
by (220 points)
Dear Andreas,

Thank you for your reply! It was very helpful, I followed your instructions and built the flows in my model.

I have a follow-up question would like to ask for help, it is about the results I got following your guidance.

I assume Process A produces a fixed amount of heat. (Let's say it's 1E+07 MJ) I created a product flow for this flow - 'Heat to be reused'.

case 1: 10% of the 1E+07 MJ is reused in Process B. So looking at the inventories:
Output table of Process A: product flow 'Heat to be reused' = 1E+07 MJ
Output table of Process A: elementary flow 'Heat, waste' = (1E+07 - 1E+06) MJ
*(I choose the elem. flow as 'Emission to air, unspecified population density)
Input table of Process B: product flow 'Heat to be reused' = 1E+06 MJ

I did a sensitivity test on the heat recovery
case 2: 100% of the 1E+07 MJ is reused in Process B.
Output table of Process A: product flow 'Heat to be reused' = 1E+07 MJ
Output table of Process A: elementary flow 'Heat, waste' = 0 MJ (all are used in Process B, so no direct emission in Process A)
Input table of Process B: product flow 'Heat to be reused' = 1E+07 MJ

The rest inventories have no difference. Therefore, the only difference is the elem. flow in Process A 'Heat, waste' and the amount of product flow 'Heat to be reused' in Process B.

Calculating the GWP 100a results of two cases, case 1 has 1500 kg CO2-eq larger than case 2.
Therefore, I am wondering if the elem. flow 'Heat, waste' has that big influence on GWP?
How can I find the LCIA of this single elem. flow? (since it's an elem. flow without a provider, I am not sure if this is available?)

How can I interpret the results better? Does it have something to do with my upstream activities?
(For Process A producing heat, there's also other inventories in Process A's input table)

Thank you in advance!
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