getting closer to helping my scrolls

[Magoo]

Hello Ek
I totally agree with Gary's comments, but any adjustments should be small then wait for TXV to stabalize. For a better understanding go back to my ealier post on setting TXVs

[Gary]

Hello Ek
I totally agree with Gary's comments, but any adjustments should be small then wait for TXV to stabalize. For a better understanding go back to my ealier post on setting TXVs

Exactly so. It takes at least 15 minutes for the TXV to stabilize between adjustments.

Make an adjustment... wait at least 15 minutes... then check the results... repeat as needed.

[ENERGY KNIGHT]

I adjusted the compressor superheat. it stays between 15 and 20 F. it does not stay exactly the same . still a little hunting. is that normal or ok. I have a clear sight glass and very steady fan control now. my water stays same but mabey I should check to see how much my water pump is changing?

[Gary]

Evap air/water in temp:
Evap air/water out temp:
Low side pressure:
Suction line temp at TXV bulb:

Cond air/water in temp:
Cond air/water out temp:
High side pressure:
Liquid line temp:

[Gary]

I adjusted the compressor superheat. it stays between 15 and 20 F. it does not stay exactly the same . still a little hunting. is that normal or ok. I have a clear sight glass and very steady fan control now. my water stays same but mabey I should check to see how much my water pump is changing?

A little hunting won't hurt anything as long as it is not flooding the compressor.

Why would your water pump change?

[ENERGY KNIGHT]

the water pump is variable speed. because when a chiller is off no water flows through it. there has been a lot of talk about how to control pump speed. clima cool wants 2.4 gal per min per ton. the pump was controlled by differential pressure. but that does not work because when the building demand changed so did the DP but it changed opposite than when the chiller demand changed. long story but I am now controlling pump speed by DT and that seems to be the best. I could play with the pid loop maby but I think its ok. now Im just waiting on my oil seperator to see if the oil will settle down some.
then I will post all of those readings to see if we made a healthy system. thanks everyone coments ?

[ENERGY KNIGHT]

Hi all and thanks for all the help I hope I will be able to help someone in the future.
I built a three foot tall wall on condenser but I think it should have been taller still getting some hot air recirculating. it was 100 deg f yesterday. if the wind gust blew just right I had 105 deg f air entering condenser. which gave me 320psi
so my condenser is working at 30 deg f above saturation witch is at design. good
my receiver is out by condenser and I get 10 deg subcooling at txv inside. good
witch means clear sight glass all the time. good
txv adjusted so I get 15 - 20 deg superheat. and compressor discharge stays bellow 200. good
Now I have two more concerns.
1. the oil sight glass on compressor Oil is very foamy Im worried about proper lubrication in there.

2. and could anyone help me with the low side pres. I would like to understand about the freeze up
of evaporator and low load or low temp.
what should the low pres be on r-22 with 52deg f entering and 42 degf leaving a bphe?

[Gary]

Think of pressure as a means to an end. You are looking at the pressure in order to determine the saturation temperature of the refrigerant. On the low side, we are looking for the saturated suction temperature (SST).

The difference between the leaving water temp and the SST is the "approach temperature".

Given normal heat load (normal dT) and full coil utilization (normal superheat), the approach tells us something about the heat transfer between the water and the refrigerant. The closer these temperatures are to each other (lower approach), the better the heat transfer between them... and vice versa.

The approach temp can vary considerably, depending on such things as relative evap size and type... so the question is what is the normal approach for your particular system? As a rule of thumb, anything over 20F approach for a chilled water evap indicates a heat transfer problem. However, on a high efficiency BPHE coil I would expect a much tighter (lower) approach.

From previous readings, I would say the normal evap approach for this system is about 8-10F... but the SH was low in those readings. New readings with normal SH may (or may not) tell a different story.

Given water leaving temp of 42F, with normal dT and SH, I would expect the SST to be roughly 8-10F lower... 32-34F SST... which for R22 translates to 57-60 psi. But then, there are a lot of ifs in there.

With all else normal, higher than normal approach indicates an insulative coating on the heat transfer surface slowing the heat transfer between water and refrigerant. This could be a mineral build-up on the water side or an oil coating on the refrigerant side (oil logging). Oil logging is generally intermittant, while mineral build-up is steady. Both are relatively rare in chilled water evaporators. Mineral build-up is far more common in water cooled condensers.

On air cooled condensers the approach would be the difference between leaving air temp and saturated condensing temp (SCT) and high approach usually indicates carbon build-up from car exhaust in heavy traffic areas... requiring chemical cleaning.

[MikeHolm]

I have watched this thread with a lot of interest and must admit, I have learned a lot. EK, you have a great teacher in Gary.

gary, you should put your 8 measurements on your tag line. It is repeated far too often.

[ENERGY KNIGHT]

now remeber I have only changed the piping and moved reciever on one out of eight.
so seven of the compressors still have reciever inside and about a 40 psi pressure drop in the condenser line and no clear sight glass.

all eight seem to run good at high outside temps or high discharge pres. above 270psi or so.
but last night the outside air temp droped to arround 60 deg. f and three compressors kicked out on low pres. (about 50 psi setpoint)

I guess Im asking you guys what I should do.
re-pipe condenser to rid the pres. drop and move recievers on the rest of the units or just set my controls to raise my water setpoint when oat. drops or do I do both.

also why do they trip on low pres when high side is under 260psi. is it the huge pres. drop and no clear sight glass
I just need to be clear because my boss will want to know why I need to re- pipe everything when the all worked by just adding the wall on top of condenser.
It looks like moving the reciever and re-piping is more for lower oat than higher oat?

[install monkey]

lower ur lp cut out to prevent nusance tripping- in lower ambients u should have condenser fan speed controllers or pressure switch to cycle the fans.
the lp could be lowered to 1 bar -15psi

[Gary]

Since the condensers have subcooling circuits, I would try removing/bypassing a receiver on one of the units. If the sight glass can be cleared without driving up the high side pressure, possibly the receiver can be eliminated.

Receiver or condenser subcooling circuit. One or the other, but not both.

[Magoo]

With eight systems and the problems you have, there has got be some re-course back onto supplier installer to supply stable operational systems, with what ever local ambient conditions.

[ENERGY KNIGHT]

yes I have condenser fan speed control. when the factory guys were
here trying to figure this thing out they wanted me to set the fans to maintain 275 psi on the high side.
I think that is too high and is just a bandaid.
I think we are very close to getting this .
I originaly had two problems (but didnt know it)
1. high head pressure.....finally came down to hot discharge air recuirculating back through condenser.
that part is pretty much fixed although I could use a little taller wall like 6 feet instead of 3 feet.
2. low suction pressure.....I think there is two ways to fix this. simply remove reciever and charge to a clear sight glass.
or re-pipe condenser to get rid of subcooler and pres drop and move reciever out to condenser.
I would like to see everyones opinions on which way would make a better system thanks everyone!

[ENERGY KNIGHT]

Gary I removed reciever and cleared sight glass, but like you said the high side might climb too high . it did. the high side is 40 deg above saturation and it should be 30 deg f.

my next step is re-piping condenser and using the subcooling circuit at bottom of condenser as a surge reciever.

does that make sense to anyone?

and you guys help has been better than any school.(and cheaper too) I do need to go back for spelling though

[Gary]

Gary I removed reciever and cleared sight glass, but like you said the high side might climb too high . it did. the high side is 40 deg above saturation and it should be 30 deg f.

That pretty much answers your previous question, then.

I would still like to see a full set of measurements for the modified system. Once perfected, this system sets the pattern for the other seven systems.

[ENERGY KNIGHT]

evap water in temp: 54 f
evap water out temp: 45 f
low side pressure: 60 psi
suction line temp at compressor: 50 f

cond air in temp: 90 f
cond air out temp: 110 f
high side pressure at compressor: 235 psi
high side temp at compressor: 170 f
high side pressure at txv: 225 psi
liquid line temp at txv:100 f

[install monkey]

looks good!

[Gary]

Those numbers are near perfect. You have made your compressor very happy.

[engineerhvacr]

In my opinion the air cooled condenser seems to be of problem, for a 25 ton air cooled unit the heat rejection capacity will be around 32 TR and the coil should have cfm around 25000 to 30000 and coil face area with 4 rows around 64 sft. your condenser size 50 x 70 = 24.5 sft seems to be on undersize.

[engineerhvacr]

25 Tr x 2 nos compressors, can u post all the major component details such as
compressor model / make / quantity
phe model / make / quantity :
air cooled condenser data - no of fans, total face area,no of rows, total cfm, ambient temp
expansion valve data..: model / make / quantity
will help to evaluate from design point of view...