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Renata
31-05-2017, 08:51 PM
Hello everybody,

I would like to know the best way, in your opinion, to control a closed economizer (subcooler). Follows data from the currently installed system that we would like to improve:

The existing liquid subcooling system has 2 shell and tube heat exchangers (closed economizer).
Each of the low-temperature circuit compressors has an intermediate suction port to meet each of the economizers.
These exchangers are supplied with liquid ammonia from the liquid container and have thermostatic expansion valves for reducing and controlling the evaporator pressure of the exchanger.
The sub-cooled liquid supplies one URL.
The construction project of the exchanger is not available.

tks

RANGER1
31-05-2017, 09:09 PM
Renata,
What would you like to know exactly?
Is this a single stage system, or 2 stage system, can you explain it more?
Normally you would turn liquid off to economiser heat exchanger when compressor in unloaded condition as it goes to suction at that point, say 70%.
Best to have modulating valve on liquid being subcooled for smooth constant operation of economiser.

Renata
01-06-2017, 06:01 PM
Hi Ranger1,

I am sending a figure with the configuration of the system.
I want to change the thermostatic valve by a eletronic expansion valve, mainly because I want to monitor the ECO remotely.

14826
tks, Renata

RANGER1
01-06-2017, 09:08 PM
Renata,
Usually use pulsing valve for this like Danfoss AKVA electronic valve.
Also not required to work until compressor close to full load.

Segei
02-06-2017, 12:23 AM
Liquid supply to the economizer should be turned of at capacity 70-80%. However, slide valve should be calibrated properly. For example. When slide valve is 100%, el. motor load is 100% as well. Start manually unload compressor. Motor load goes down but slide valve still 100%. When motor load is 80%, slide valve capacity start going down. Saw it many times. During manual unloading slide valve capacity and motor load should start moving simultaneously. However, rate of reduction will be different.

RANGER1
02-06-2017, 08:15 AM
Liquid supply to the economizer should be turned of at capacity 70-80%. However, slide valve should be calibrated properly. For example. When slide valve is 100%, el. motor load is 100% as well. Start manually unload compressor. Motor load goes down but slide valve still 100%. When motor load is 80%, slide valve capacity start going down. Saw it many times. During manual unloading slide valve capacity and motor load should start moving simultaneously. However, rate of reduction will be different.

Don't know if I understand this Segei.
Are you referring to a particular brand compressor?
Can you give example.

Thanks

Renata
02-06-2017, 06:04 PM
Ranger1,
The electronic valve will operate to maintain the superheat at the economizer, is it right?
Is there any optimum superheat set point?
tks, Renata

RANGER1
02-06-2017, 10:23 PM
Ranger1,
The electronic valve will operate to maintain the superheat at the economizer, is it right?
Is there any optimum superheat set point?
tks, Renata

Well normally suction line just out of heat exchanger is where to sense superheat to get best response.
Worst case you would get a bit of a flood back which always best to avoid if possible.
If superheat to high, poorer performance, if to low potential floodback.
I would have thought 6-8k of superheat, but if electronic it will work itself out to be able to control.
Like I mentioned earlier, a constant flow through heat exchanger will give best results so things can stabilize.
If on off, expect average results.

What type of valve exactly are you going to use on heat exchanger?

Segei
03-06-2017, 03:11 AM
Frick compressors have this issue.

Renata
06-06-2017, 05:32 PM
Propably I will use a Danfoss AKVA.