How to charge sistem when you don't know right needed amount of refrigerant?

[nerijust]

Hi,

Need advice how to charge system when you don't know right needed amount of refrigerant?
Have old chiller for cooling water, need to change compressor and convert system from R22 to R407, but here is no information about amount of refrigerant.
Have some liquid in suction line so I suspect overcharging or maybe TEV failure.
Is obligatory change TEV when converting system from R22 to R407?

[mbc]

do have sight glass? if yes , you have to charge it untill is full, if not you have to use Evap. Temp. (suction press.) + Delta T = room temprature
Make sure you TEV Is working and use a right one R 407 nor R 22.
((if you can hear soud of TEV , in short liquid TEV nose (sound) comes down and goes up))

[frank]

do have sight glass? if yes , you have to charge it untill is full, if not you have to use Evap. Temp. (suction press.) + Delta T = room temprature

A new one on me.....does it work?

[lana]

Hi there,

There is a speculation that with Zeotropic blends (400 Series) the sight glass shouldn't be full otherwise the system is overcharged.

For correct system charge you have to observe many things at the same time. Of course if all the components are selected correctly.

1- Suction pressure according to design.
2- Discharge pressure according to ambient temp or water temp. If there is a head pressure control then you have to stabilize condensing pressure for a while so you can measure sub-cooling.
3- Super heat
4- Sub-cooling
5- Sight glass

This job needs experience and knowledge at the same time. It is not very complicated.
If you charge the system in winter then overcharging is a possibility but if you know what you are doing then it will be OK.

Cheers

[icecube51]

The TEV of R22 may stay, but the charge is far less whit R407C then whit R22.
The pressure for R407C is higher. it is difficult to charge on the sight glass, the system is to quicly overcharged.
best way is to calculate the needed amount of cooling, and the possible amount of the unit. also keep in mind that you have some capacity loss on R407C.

Ice

[Tesla]

In addition to lana's correct answer above check compressor current (rated) and aim for an evap split (out - in) of 5.5k at 90% - 100% of load. Roughly 6k superheat at comp inlet and 10k subcooling. Depending on compressor. If you need more detail provide us with details of chiller and compressor.

[martinw58]

if you have a reciever on the system check if it has a plate on it with volume in liters you can only fill to about 80% rull of thumb 1 lt = 1kg of refrigerant
if there is on head pressure control head pressure needs to be about ambiant temp + 15 oC converted to pressure

[nerijust]

It's very simply system without reciever. TEV was broken, chenged it and charge system according sight glass. It took some time.
After charging measured some data.
LP 4,6 Bar
HP 18,5 Bar
Temp after condenser 41 C
Temp after evaporator 14 C
Temp in condenser 29,2 C
Temp out condenser 41 C
Water temp 21
Data can be inaccurate due to "accuracy" of instruments.
Compresor copeland ZR81

[nerijust]

Air Temp in condenser 29,2 C
Air Temp out condenser 41 C

Temp in condenser 29,2 C
Temp out condenser 41 C

[hvacrmedic]

Check with the equipment manufacturer.

[nike123]

It's very simply system without reciever. TEV was broken, chenged it and charge system according sight glass. It took some time.
After charging measured some data.
LP 4,6 Bar
HP 18,5 Bar
Temp after condenser 41 C
Temp after evaporator 14 C
Temp in condenser 29,2 C
Temp out condenser 41 C
Water temp 21
Data can be inaccurate due to "accuracy" of instruments.
Compresor copeland ZR81

4,6 barg= 6,1°C (dew point)
18,5 barg= 44,7°C (bub point)

44,7-41 is 3,7 K Subcooling

14-6,1 is 7,9 K Superheat

Wait until water temperature is 2-3K near design temperature and check again subcooling and superheat.
If that is your design temperature than subcooling is low and you need to add more refrigerant until subcooling became about 8K.
Than check again superheat.

[Bashir01219]

If that is your design temperature than subcooling is low and you need to add more refrigerant until subcooling became about 8K.

Dear Sir,
I am not clear at all; I learned from this forum that sub cool temp should be between 2-5 K.>>
How u calculate all this?>>
(4,6 barg= 6,1°C (dew point)
18,5 barg= 44,7°C (bub point)

44,7-41 is 3,7 K Sub cooling, 14-6,1 is 7,9 K Superheat)
Plz. Explain and make simple for us.What is the best possible way to charge a undercharge system?

[desA]

The acceptable degree of sub-cooling will depend on the condenser design. This is important.

The balancing sub-cooling will also depend where in the operating cycle the system lies. Some condensers fill, others empty, during a moving rhvac cycle. It depends on the system.

Using overly simplistic rules of thumb will, in all likelihood, lead to system over-charging.

[nike123]

Dear Sir,
I am not clear at all; I learned from this forum that sub cool temp should be between 2-5 K.

http://www.refrigeration-engineer.co...2&postcount=13

http://www.refrigeration-engineer.co...ad.php?t=19701

How u calculate all this?
(4,6 barg= 6,1°C (dew point)
18,5 barg= 44,7°C (bub point)

http://www.centrogalileo.it/nuovaPA/...%20inglese.doc

44,7-41 is 3,7 K Sub cooling, 14-6,1 is 7,9 K Superheat)
Plz. Explain and make simple for us. What is the best possible way to charge a undercharge system?

http://www.mediafire.com/?wzgtwmyhzty

[nike123]

The balancing sub-cooling will also depend where in the operating cycle the system lies. Some condensers fill, others empty, during a moving rhvac cycle. It depends on the system.

Could you please elaborate on this little more.

[desA]

Originally Posted by desA
The balancing sub-cooling will also depend where in the operating cycle the system lies. Some condensers fill, others empty, during a moving rhvac cycle. It depends on the system.

Nike replied:
Could you please elaborate on this little more.

With pleasure.

What happens in the condenser, and the amount of sub-cooling it will manage, will depend on the type of condenser, and the high-side (HP) system pressure drop.

If the HP pressure drop is fairly low, then as pressure builds up in the condenser, it can be that the net liquid balance in the condenser reduces as HP rises. This can tend to lower the liquid level in the condenser, & so that amount of sub-cooling that the condenser will deliver.

In a heat-pump, for instance, it will not be unusual to see a high SC at start of heating cycle, but a much lower value towards the end of the heating cycle. The amount of SC can reduce to the point of 0K, if the system has insufficient charge. Here, one must be careful to charge enough for the hot operating condition, but not so much as to raise the cold operating condition too much. Practically, the heat-pump will run mostly at hot condition, so this is the more important SC to watch.

For a restrictive HP pipe system, the opposite effect can occur ie. the condenser backs up & SC rises over the cycle.

[nike123]

@desA

Thanks!

[desA]

^ It's a pleasure.

[nike123]

How u calculate all this?
(4,6 barg= 6,1°C (dew point)
18,5 barg= 44,7°C (bub point)

http://www2.dupont.com/Refrigerants/...mo_prop_si.pdf

[Bashir01219]

http://www2.dupont.com/Refrigerants/...mo_prop_si.pdf

Thanks Sir,
But i try but can't understand.......

[The Red Krawler]

Alot of water chillers are designed with plate heat exchangers which are too small - and means the unit is heavily reliant on the water pump providing a high enough flow rate of water to supply sufficient load to the evaporator.

If the pump becomes inefficient for any reason (blockages, wear, restriction on inlet) you will find the metering device (typically TX valve) cannot maintain the correct superheat due to low / no load and can result in liquid flooding back to the compressor. This is why suction line accumulators are so incredibly important on water chillers (sized to hold the entire liquid charge!).

If you are getting liquid flood back, and you have a plate heat exchanger, it may pay to check the flow rate of water through your evaporator.

Otherwise its just a matter of applying basic refrigeration principles as outlined above.

[nike123]

Thanks Sir,
But i try but can't understand.......

Dear Bashir, i think that you need some tutor to guide you thru your learning. It appears that you are thrown in field on which you are not up to requirement.
I am strong supporter of your will to learn on what you actually doing, but you cannot expect to deal with that project only with advice given here. Advice is advice, not solution.

[Bashir01219]

Dear Bashir, i think that you need some tutor to guide you thru your learning. It appears that you are thrown in field on which you are not up to requirement.
I am strong supporter of your will to learn on what you actually doing, but you cannot expect to deal with that project only with advice given here. Advice is advice, not solution.

Thanks a lot Sir, In Bangladesh there is no training center on HVAC system. Most of the company doing their maintenance through third party, even sometime we too, but I didn’t like it, today or tomorrow I will learn whatever I want to learn, and for this purpose I need your help, I believe you can help me.
basher.abdullah@radiant.com.bd