Subject: Re: Chiller charge problem

From: [email-masked] (TMETHOD)
Date: 5 Oct 1995 19:43:31 -0400

In article <[email-masked]>, John Cain
<[email-masked]> writes:

>
>To follow-up my original thread, please don't think I added vast amounts 
>of refrigerant, I added only about 1lb of R22 and after having noticed 
>no real change in system pressures I looked further into the heart of 
>the chiller and noticed the TEV (or as you would say TXV) problem.

250# head pressure (117F condensing temperature) at 60F ambient seems
excessive even if we assume refrigerant backed up from a restriction.
Backup from restriction is accompanied by reduced compressor load which
tends to lessen the effect. It has been my experience that high subcooling
associated with restriction is usually caused by someone overcharging the
system in an attempt to raise the suction pressure.

>I checked the obvious, like PD across drier and liquid line solenoid 
>valve, no temp drop so they were OK.  I also checked CHW flow rates 
>which were OK and the second stage was working fine hence I deduced it 
>was a fault on one stage only (evaporator fouling etc., eliminated).

If the second stage chiller cannot handle the load at 60F ambient (as
evidenced by 68F CWS), I wouldn't necessarily conclude that it is "working
fine". Nor would I deduce that the evaporator is not fouled. Insufficient
water flow tends to narrow the gap between evaporating temperature and CWS
temperature, while fouling (or high superheat) widens the gap. Without
knowing the evaporating temperature on the second stage, I would not
discount the possibility.

>I am certain from other threads (and direct e-mail, many thanks for this 
>but please in future post to the group as it may help others) that it's 
>the TXV. I also agree that there may be non-condensables in the system, 
>as I have only recently taken over the contract.  

Non-condensables would be another possible explanation for the high
subcooling.

>I like the thought of changing the filter-drier as a 'good practice' 
>measure and take this occasion to thank everyone for their responses.
>
>The group will hear in due course how the problem is solved, when I 
>return to site (this time with the proper equipment and new TXV) to take 
>accurate measurements. 

In addition to knowing how the problem is solved, I would love to see a
full set of measurements for both systems. Preferably before and after.

Gary

================================================
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     -Albert Einstein-

Gary R. Lloyd CMS
TECH Method Training
HVACR Trouble Shooting Books/Software
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