Too long of a pipe run?

[marc5180]

I got called over to a job that i had previously posted about, the water leak coming from the daikin wall unit.
Most people suggested it was due to shortage of refrigerant.
http://www.refrigeration-engineer.com/forums/showthread.php?p=158675#post158675

When i got there i connected my gauges and the SP was at 1bar (R407c) with a Sh of 28, liquid pressure was 13bar Itook the refrigerant out but got out enough for a pipe run of 32 meteres, standing charge 1.3kg for 15m + 20g pm

The unit should only do a maximum of 25m but this is at least 32m if the pipework runs diagonally from outdoor to indoor (which it probably doesn't) so it's probably more.

Whilst i had taken out the refrigerant i decided to completly remove the indoor from the wall to strip it down and check for any cracks in the tray or anything else that could be causing the leak, none were found.

I blew through both copper lines with OFN to be sure there was no obvious blockages anywhere which were causing the low suction pressure then put the indoor back on the wall braized it up and recommisioned it.

Straight away i ran it up and the suction pressure fell down to 1.5 bar, i began adding refrigerant to get the pressure up but by the time the pressure was at 3.5 bar i had addd an extra 800g..... I quickly took out the addional 800g and the SP dropped once again.

I'm thinking the piperun must be too long, has anyone ever had this?

[nike123]

Inverter or non inverter, TXV or capillary, outdoor unit above or below and how much, outdoor temperature, model #???

[Thermatech]

Two main problems with this one.

1/ The unit is in a room with a server which can make the heat load mainly sensible heat & the humidity can then be very low. If its lower than the 15 deg C wet bulb lower limit then the evaporating temp will be low & you will get the very low suction pressure as reported.
2/ The pipe length is long & with some bends makes large suction pressure drop which will also make low suction pressure as reported.

It would seem the system is over condensing with low discharge pressure which is typical of a comfort cooling split system working in high sensible cooling load application.

To offset these problems suggest try making the outdoor unit run at over 20 bar discharge pressure.

You will find that as you force the discharge pressure up the suction pressure will also increase.
If you can get the system to run at 4.5 to 5 bar suction then it will work much better & ice / coil frost prevention at the indoor coil will not be such a problem.

It will not be ideal but just making the best of what you have found.

[marc5180]

Nike1213: The model number is a R35GZV11, which is a non inverter.
Also it's a capillary which is in the condensor.
The outdoor is above by about 3m and outdoor temperature today was 12DegC.

Thermatech: The room is used as a post room but they do have 1 server in there as well as a photocopier.
I did think humidity could be an issue and so i used my sling to obtain the wetbulb temp and i got 18C.
In the manual i have it says this unit works down to 12C wetbulb.


Q.....When is the best time to take the WB readings, how long after the unit has been running? Should it be when the room is down to temp? If it can get down to temp?

When i first ran the unit up, the room was 25C but straight away the suction pressure dropped, which made me think the piperun could be an issue but this unit has been installed for 5 years and has worked fine.

[Thermatech]

At that suction pressure / evaporating temp the indoor unit will stop / start on coil frost prevention.
The longer the unit cools the room the lower the humidity will get & the lower suction will become.

What do you think about the discharge pressure ?

Much too low for R407c.
The system is over condensing with no HP control.
So what happened to the low ambient HP control ?
Suggest push discharge pressure up to over 20 bar the same as it would be during summer high ambient conditions.
Do this & see what happens to the suction pressure / temperature.
You will see what I mean.

When you get the sytem running at better discharge pressure & suction pressure / temp then you will make indoor coil temp above coil frost conditions & the indoor coil will not frost / ice up so then that will fix water leak problem.

[marc5180]

There is no HP control on this unit, at least not from what i can see.
When i go back i will block part of the coil and try what you said, if that works then maybe look at getting some sort of fan speed controller fitted

[Gary]

Straight away i ran it up and the suction pressure fell down to 1.5 bar, i began adding refrigerant to get the pressure up but by the time the pressure was at 3.5 bar i had addd an extra 800g..... I quickly took out the addional 800g and the SP dropped once again.


When you added the extra refrigerant, was the subcooling excessive? What was the superheat?

[Quality]

Inverter or non inverter, TXV or capillary, outdoor unit above or below and how much, outdoor temperature, model #???

are you marcs dad ?

[nike123]

If system has worked OK 5 years in simmilar outdoor and indoor conditions, than I would first look for proper indoor air flow (measuring actual air flow) and then search for problems in blocked refrigerant circuit or lack of refrigerant.

High superheat as you described and low suction pressure point to obstruction in low side or low air flow or lack of latent heat load.

13 bar (31°C SCT BP) for outdoor ambient 12°C looks OK or slightly high and you could probably raise suction pressure for some amount if you block condenser partially but high superheat will stay high if that is not only problem.

I would order and change capillary/strainer and see what happens.

[nike123]

are you marcs dad ?

No!:D

What makes you think that?:confused:

[Gary]

There is no HP control on this unit, at least not from what i can see.
When i go back i will block part of the coil and try what you said, if that works then maybe look at getting some sort of fan speed controller fitted

Whether it works or not, if you are going to run this in cold ambient it should have a fan controller.

[Quality]

He is a young chap clever as it seems-but when I read your post it looked a bit demanding to me. no offence intended;)

[marc5180]

When you added the extra refrigerant, was the subcooling excessive? What was the superheat? the liquid temp was 12C but i didn't try and work out the subcooling since it's uses a capillary.

The superheat from memory was 20+ degrees, which made me think either a restriction in the suction line or even in the capillary but i had blown through with OFN and there didn't seem to be any sort of restriction.


Whether it works or not, if you are going to run this in cold ambient it should have a fan controller.

I agree, it's something i will have to look into when i go back on site next week.

[marc5180]

are you marcs dad ?

:rolleyes:
If he was he wouldn't be able to spend so much time on here because instead he would be teaching me:D

[marc5180]

If system has worked OK 5 years in simmilar outdoor and indoor conditions, than I would first look for proper indoor air flow (measuring actual air flow) and then search for problems in blocked refrigerant circuit or lack of refrigerant.

High superheat as you described and low suction pressure point to obstruction in low side or low air flow or lack of latent heat load.

13 bar (31°C SCT BP) for outdoor ambient 12°C looks OK or slightly high and you could probably raise suction pressure for some amount if you block condenser partially but high superheat will stay high if that is not only problem.

I would order and change capillary/strainer and see what happens.
When i removed the indoor, i took it away and stripped it down fully, making sure the coil was clean and the fan was ok.
I also blew down each of the suction and liquid lines ( both ways) to check for any signs of blockage and there didn't seem to be any.

I will partially block the condensor to increase discharge/suction pressure then take a note of the superheat if that is still high then i will ordera new capillary for it also.

[Thermatech]

When you force up the discharge pressure then if there is any restriction problem it should become more apparent as the suction pressure will stay low.

If no restriction then the system will work much better with normal suction pressure & installing some type of low ambient HP control will resolve this problem.

[Gary]

the liquid temp was 12C but i didn't try and work out the subcooling since it's uses a capillary.


Capillary or not, if the subcooling is high (too much refrigerant in the high side) and the superheat is high (not enough refrigerant in the low side) then there is a restriction in between.

[nike123]

He is a young chap clever as it seems-but when I read your post it looked a bit demanding to me. no offence intended;)

I just like as much information as possible to make better picture of situation.;)

[nike123]

The superheat from memory was 20+ degrees, which made me think either a restriction in the suction line or even in the capillary but i had blown through with OFN and there didn't seem to be any sort of restriction.



You cannot know that from blowing OFN. Only what you can be sure from that test is that capilary is not totaly or severly blocked.

If SCT pressure is higher than normal and subcooling is high you could be sure that you have blockage, and by measurements you gave us earlier I think that SCT is high for that low ambient temperature if outdoor unit fan is blowing at full speed.

As I recollect, you have Digicool and that diagnostic is piece of cake with it.

[marc5180]

OK ......i can be sure that the capillary isn't totally blocked at least.

When i return next week i will update myfindings........and yes you are correct i do have Digicools but they can only tell me so much my brain has to remember the rest.:rolleyes: