Carrier 19FA Betriebsanleitung PDF herunterladen (Seite 15)

HVAC Training

Page : 15 of 42

Title:

Chiller Maintenance

Lesson Plan

NMH30C000105

Due to the reactor being shutdown for maintenance the “B” essential chiller had been operated at a

low load condition for several days. Oil had been added to the oil sump several times during this

time. When the chiller was secured following reactor startup, it was not noticed that the oil level

was below the bottom of the lower site glass. Operating the chiller at low loads for extended

periods will cause oil to be entrained in the refrigerant and accumulate in different parts of the

chiller. The low indicated level does not represent a loss of oil in the chiller. When the chiller is run

with sufficient load the oil will be recovered.

Previous evaluations established a low oil level limit of "visible in the sight glass" although the

chiller will operate as long as the oil pump can supply above 13 pounds of pressure. There is no

way to visually identify the actual level in the sump below the lower site glass. The bottom of the

lower sight glass equals 6.5 gallons of oil in the sump. The bottom of the sump is 12 inches below

the sight glass. At 0.625 gallons per inch, the as left level was 12.75 inches and the as found level

was 10.35 inches. The suction of the oil pump is located approximately 1 inch above the bottom.

With 9.35 inches of oil above the suction the oil pump would have easily provided the necessary

13 pounds of pressure. The chiller would have performed its safety function.

Oil temperature gauge 2JECBTI0512 was reading 106 degrees F. The ¼ inch diameter stem of the

temperature gauge is mounted in the oil sump through a wet well that is even with the bottom of

the lower site glass on the chiller sump. It is likely that the temperature gauge sensing element was

not immersed in oil because the oil level was below the sensing element. The oil temperature

indicator was measuring the temperature of the free space above the oil and not the oil

temperature because the sensing element was not in the oil.

The oil sump temperature controller 2JECBTC0518 is mounted through a drywell in the oil sump.

The bottom of the oil sump temperature controller is about one inch below the bottom of the lower

oil sump site glass. The oil temperature controller was still immersed in oil based on the volume of

oil added to the sump to bring the visible oil level to 75 % of the lower site glass. The temperature

controller was controlling the oil sump between 140 and 150 degrees F. A review of the weekly

chiller logs for the essential chillers in all three units was conducted. The present oil levels and the

total oil volume inventory in each essential chiller are acceptable.

Conclusion:

Operating the essential chillers at low load and low condenser cooling water temperatures for an

extended period of time is vary hard on the chillers. Problems such as refrigerant stacking and loss

of oil level in the sump to other area in the chiller have been addressed in the past at Palo Verde.

Installation of the refrigerant head pressure control valve (RHPCV) has greatly reduced the

number of times that the essential chiller were in a condition of low oil levels by throttling the

condenser water flow during low loads and low cooling water temperatures. The operating

procedures provide guidance to Operations personnel to place a load on the chiller if it must be run

for extended times under low loads. However, w e know there w ill be times that w e will have to

operate at low loads to support normal plant operations. The key is to recognize these times and

manage the situation.

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