[TRNSYS-users] Trouble with type 676

[Lisa Hagg]

Hi,

I'm trying to model a system that contains a double-effect steam driven absorption chiller (type 676) but can't seem to make it work. It needs the steam pressure as an input, which I don't have. I've tried to add an evaporator (type 316), but it needs the output pressure (which is the one I'm interested in) as an input. To solve this I added a component that was supposed to calculate the pressure (type 58), but as soon as I connect the temperature from the cold side (i.e. the side with the absorption chiller) the program won't work. At first it takes extremely long time to execute the model (after several minutes only 50 hours have been simulated) and usually the entire program crashes. I have managed to get a message of errors in the model, and one time the list-file was too big to open (I can't remember what the messages said unfortunately). Another time the entire program crashed when I tried to see the messages and when it had started working again I couldn't open the list-file since it was too big (as in the previous case). All other times the program has crashed to the extent that I have had to restart it.

If I connect it to the hot side temperature (which is the wrong side, right?) the program works, but not as I want it to. I have a COP, but the temperatures are too high. And when analysing the different temperatures and flows I got the following result:


?
        ?Flow in
        Flow Out?
        Temperature In?
        Temperature Out?
?Chilled flow
        583 000    ?
        583 000?        Linear increase to 76 088 ?
        ?Linear increase to 76 098

?Cooling flow
        ?972 000
        972 000?
        92.95?
        98?
?Condensate/steam
        0?
        ~5000?  82?     82?

Obviously there is something very wrong with this (no inlet stream from the evaporator, but there is a pressure of 12-13 000 kPa (which seems way too high).

Also, by adding the evaporator there is a large decrease in temperature for the stream going in to the chiller, which I don't want. I simply want a heat transfer from the stream coming from my CSP system (with storage and heat exchangers in-between) that evaporates the fluid and creates steam for the chiller.

When I tried to change the evaporator to a heat exchanger and assuming steam with quality of 1 other issues occured.  The following values were taken with heat exchanger instead:


?
        ?Flow in
        Flow out?       T in?   T out?
?Chilled
        583 000
        ?583 000
        linear increase to 109 582?     linear increase to 109 572?
Cooling?        1000    ?97 200
        ~90.1?
        ~93.5?
?Condensate
        ?~160
        ~4700?
        ~114?   ~64?

Worth noting is that the capacity of the absorption chiller and the cooling tower (type 510) have not been properly sized yet, but when I've tried to change it the behaviour of the chilled flow and the cooling flow changed characteristics, i.e. suddenly the cooling flow increased extremely much in temperature.

If someone could help me I would appreciate it.

Best regards,

Lisa Hägg
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