Symptoms of two McQuay PEH066 (water cooled centrif chillers)

[kaon]

CH1:


After washing condenser tubes, condenser approach dropped from 4K to 0.5K.
However, condenser vessel still feels warm to the touch, (almost painfully warm) approx 50C. Condenser water is about in: 29C, out: 32C.
Evap approach is 7K!
Saturated evaporator temp is 1.5C, and is alarming and capacity limited to ~86% by "Evap Pres Lo-Freeze".


CH2:


Condenser tubes to be washed this coming weekend, last wash was 1 year ago.
Condenser approach is 2.6K.
Condenser vessel also feels about 50C.
Condenser water in/out is also roughly 29C/32C
Evap approach is 4.5K.
Saturated evap is 3.7C.
Running 100% RLA.


My thoughts:
Evaporator tubes have probably never ever been cleaned in these 18-year old chillers, they are thought not to require cleaning, because the chilled water circuit is a closed circuit. However, the high evap approaches might be due to dirty evap tubes.
Why is the condenser vessel so hot? I would've suspected non-condensable inside, but a high pressure 134A machine isn't expected to get air inside right?

What do you think?

TIA

EDIT:
Sorry, the model number is PEH063-GBAC

[centrifs]

dont know anything about mcquay centrifugals, but as a general rule of thumb the evap approach is high because you are low on refrigerant, it is limited at 86% and low evap press because it is way! low on refrigerant, and the top of the condenser shell is 50 *C because the tower water is on the limit of high at 29*C.
whats the flow rates evap and cond???
whats the rest of the chiller log pressures etc.???

how are you calculating approaches? from your numbers ch2 has 8.2*C LWT, ch1 8.5*C LWT.. what is EWT?

[kaon]

dont know anything about mcquay centrifugals, but as a general rule of thumb the evap approach is high because you are low on refrigerant, it is limited at 86% and low evap press because it is way! low on refrigerant, and the top of the condenser shell is 50 *C because the tower water is on the limit of high at 29*C.
whats the flow rates evap and cond???
whats the rest of the chiller log pressures etc.???

how are you calculating approaches? from your numbers ch2 has 8.2*C LWT, ch1 8.5*C LWT.. what is EWT?
Thanks, you were correct about the low-refrigerant-charge. There is a leak somewhere, oil level is low too.
Charging about 100kg of 134A, took the evap approach from 7 deg C back down to 0.5 deg C. Liquid line sight glass shows a higher level of liquid, still splashing around though. We plan to charge until it is completely filled with liquid.
Efficiency improved a lot too.
CH1 now has
ent chw temp: 11 C
lvg chw temp: 6 C
ent cw temp: 29 C
lvg cw temp: 34 C
which is pretty much smack on the design and commissioning figures.

CH2 is probably also low on charge, though not as serious, because there is no evap low pres alarm, and it is running at 100% rla.
It's evap approach is 4 deg C.
ent chw temp: 11 C
lvg chw temp: 7.5 C
ent cw temp: 29 C
lvg cw temp: 32 C

All evap approaches are read off the McQuay Microtech controller.

I've finally gotten down to measuring the temperature of the condenser barrel surface.
42 deg C for CH1 after charging gas
45 deg C for CH2, which is still low on charge.

[nike123]

This is from site http://www.air-conditioning-and-refrigeration-guide.com

Evaporator approach can be used to evaluate the refrigerant charge.
In a 1 pass evaporator, approach should be 10° to 14°.
In a 2 pass evaporator, approach should be 7° to 10°.
In a 3 pass evaporator, approach should be 3° to 6°.
Take all readings with the water cooled chiller at full load.
A higher than normal evaporator approach can indicate an undercharge.
A lower than normal evaporator approach can indicate an overcharge.

[kaon]

This is from site http://www.air-conditioning-and-refrigeration-guide.com

Evaporator approach can be used to evaluate the refrigerant charge.
In a 1 pass evaporator, approach should be 10° to 14°.
In a 2 pass evaporator, approach should be 7° to 10°.
In a 3 pass evaporator, approach should be 3° to 6°.
Take all readings with the water cooled chiller at full load.
A higher than normal evaporator approach can indicate an undercharge.
A lower than normal evaporator approach can indicate an overcharge.
(are those celsius-sized degrees or F-sized?)

My McQuay PEH063 has a 2-pass evaporator. I have 0.5K of approach, which according to the guidelines above might indicate overcharge... hmm.

What about the liquid line sight glass, should I charge till I see no splashing?

[Lowrider]

You're working on a centri and go by a book that states the superheat is too low, so you must be overcharged?

What type of evaporator does this machine use?

What's the discharge superheat, actual superheat and actual sub cooling, measured and not from the microtech!

[jason09]

superheat for flooded evap centrif is usually 0. if you have a low refrigerant charge you will also have a high discharge temp. when you check the operation of these types of ac always do a full log of operating conditions... taking pressures and temperatures at the display is like checking an electric motor at the contactor... if the system is having problems always check manually... nothing beats a good old fashion mercury thermometer!

[ptsac]

May be a bit late on this post, anyway here goes.
McQuay centrifs are traceable by a shop order number which i believe is on the nameplate of the microtech ( possibly listed as a style number). The shop order will list evap superheat, subcooling etc. etc. As a general rule of thumb Suction superheat should be 0-2f ( call it 0c ) discharge superheat should be 14-16f ( 7-8c ?). Subcooling should be 8 -10f (4-5c). At full load approach temperatures for evaporator and condenser may be 6f. If the subcooling is ok then charge should be ok. It is best to set superheat via the discharge superheat as trying to measure and adjust to 0 difficult. The correct superheat is vital for these machines to return oil. These figures are about right for 100% RLA and for r134a. Please ensure that the liquid injection valve is isolated ( if fitted) for measurement of discharge temperature. The Microtech sensors are inaccurate for pressures and I would only use manual readings taken with trusted instruments.
Best of luck

Phil

[hi-speed]

low oil level its probably sittin in the evap causing approach problems design water flow @ 100% 16 deg f dicsh superheat . you need the shop order to find water flow and design subcooling for that machine it will also give you approach temps.That is the old style evap so you should not have alot of trouble out of it make sure you disable liquid injection before taking readins:D