line size

[stvsxm]

good morning,
I am a moderately experienced amateur and have done maybe a hundred installations of small split systems in my own properties and have good equipment. what I don't have is any professional training so lack any fundamental theoretical knowledge and my question is in that area. I have a 9000 btu system that works fine in the room that it is in. the use of the room has changed so now the system needs to be a bit larger and also relocated. the 9000 uses 1/4 and 3/8 lines and those lines are " impossible" to change due to the way they were installed. the new 12000 btu system will use lines a size larger I believe ( maybe not and I haven't seen it yet but I think so ). the new inside unit will be roughly 10 feet away from the original location. the outdoor unit will be in the same position. both systems are 410a . so... the question is... can I reuse the original lines and mix the line sizes ? i.e 10 feet of the larger size to the smaller sizes and the a couple feet of the larger sizes at the other end to connect to the new outdoor unit ? my formal training is that of a mechanical engineer and theoretically all I would expect to see is an increase in flow velocity and pressure in the smaller pipes but what I don't know are any of the practical " side effects" in the refrigeration aspect of things. I really don't want to tear the wall up to do new lines if I don't have to....if you know what I mean but in the end, the thing has to work properly. thanks for your time

steve

[The Viking]

Hi Steve and welcome to the forum.

Short answer to your question is; Yes, you could re-use the original pipes.

However, if you think of the pipes as water hoses. Your garden hose might allow you to fill a bucket of water in 2 minutes but when the fire brigade turn up they will be able to fill the same bucket in a matter of seconds. The difference? Their hoses are bigger bore than your garden hose.
The same applies to refrigerant pipes.

Pipework sized for 9000 Btu will deliver 9000 Btu even when connected to a 12000 Btu unit.

You might be lucky and your pipes will be big enough but always make sure that you got the pipe sizing as per the manufacturer's manual.

:cool:

[nike123]

The line size for 12000 btu will be the same as for 9000 btu. Therefore you could use same pipes if your old AC was on HFC refrigerants and pipe wall thickness is 0,8mm (for 3/8 line) and above for new R410A unit!
If pipe wall thickness is OK and old unit is using mineral oil (Refrigerant was R12 or R22) than you should flush pipes with some pipe cleaning solution recommended for HVAC systems!

And, of course, Viking was faster than me!;)

[chemi-cool]

It is hot and humid in the caribbeans, A 1\2 suction tube will be better.

[stvsxm]

Hi Steve and welcome to the forum.

Short answer to your question is; Yes, you could re-use the original pipes.

However, if you think of the pipes as water hoses. Your garden hose might allow you to fill a bucket of water in 2 minutes but when the fire brigade turn up they will be able to fill the same bucket in a matter of seconds. The difference? Their hoses are bigger bore than your garden hose.
The same applies to refrigerant pipes.

Pipework sized for 9000 Btu will deliver 9000 Btu even when connected to a 12000 Btu unit.

You might be lucky and your pipes will be big enough but always make sure that you got the pipe sizing as per the manufacturer's manual.

:cool:

well... yes and no. as I said, my backround is mechanical engineering and flow thru a pipe size has everything to do with how the medium is delivered.... in your example if the fire brigade is using a positive displacement pump and 2 " dia hose then the pressure inside that hose will be x at a given pump speed and have a flow rate of y gal per min. if I hook my garden hose up to their pump the pressure in the hose will probably be 50 x , and the velocity of the water will be correspondingly increased at the the same pump rpm because the pump is going to move a fixed volume per revolution... the flow rate will be the same but the velocity out of the end of the pipe will be astronomical as will the pressure inside the hose... now... these compressors pumps in an airco are vane type pumps I think but im not sure if they are positive displacement or not. I know they have some limitations because the manufacturers are picky about the max pipe lengths per installation so that's where the variables start to stack up and I run out of data. intuitively I don't think its a garden hose situation and intuitively I think I should be ok... but then again, I don't know what I'm doing... in a hydraulic situation like the garden hose , if asked the same question I could answer " yes... it will work just fine as long as the hose can take the pressure and the added velocity isn't an issue and you have the extra power available to push the fluid thru the hose because the pump will have to work a bit harder to maintain the same revs " but this is refrigeration and I don't really know what goes on underneath that housing. per the other replies, the systems will be same manufacturer and same specification so I am assuming the oils etc will all be the same.

I REALLY don't want to tear up the wall.

[nike123]

Don't worry, we have been there! "10 feet away" is negligible for pipe size in your case!

[cduque]

Assuming a total lenght of 16 ft (5 mt), if you pass an external unit of 9000 BTU to one of 12000 BTU without changing the pipes, in the liquid line you pass from 0,76 m/s to 1 m/s and a drop charge equivalent from 0,2 ºC to 0,3ºC, this is insignificant. In the suction line you pass from 14 to 19 m/s and a drop charge equivalent to 2ºC from an original 1,2ºC. I believe you can move on without any major problems.

[stvsxm]

sold. and thanks to all.

[el_donks]

well... yes and no. as I said, my backround is mechanical engineering and flow thru a pipe size has everything to do with how the medium is delivered.... in your example if the fire brigade is using a positive displacement pump and 2 " dia hose then the pressure inside that hose will be x at a given pump speed and have a flow rate of y gal per min. if I hook my garden hose up to their pump the pressure in the hose will probably be 50 x , and the velocity of the water will be correspondingly increased at the the same pump rpm because the pump is going to move a fixed volume per revolution... the flow rate will be the same but the velocity out of the end of the pipe will be astronomical as will the pressure inside the hose... now... these compressors pumps in an airco are vane type pumps I think but im not sure if they are positive displacement or not. I know they have some limitations because the manufacturers are picky about the max pipe lengths per installation so that's where the variables start to stack up and I run out of data. intuitively I don't think its a garden hose situation and intuitively I think I should be ok... but then again, I don't know what I'm doing... in a hydraulic situation like the garden hose , if asked the same question I could answer " yes... it will work just fine as long as the hose can take the pressure and the added velocity isn't an issue and you have the extra power available to push the fluid thru the hose because the pump will have to work a bit harder to maintain the same revs " but this is refrigeration and I don't really know what goes on underneath that housing. per the other replies, the systems will be same manufacturer and same specification so I am assuming the oils etc will all be the same.

I REALLY don't want to tear up the wall.

As they've already told you, you might not need to change the piping, but you were wrong in your assumption.

If you hook your garden hose to the fire brigade's, you will have greater pressure, thus velocity, but also losses on the "piping". The pump will have to deal with these greater losses, then it won't be able to hold the same flow. If your assumption were true, why would anyone use bigger/expensive pipes? Flow velocity? Probably you'd rather give people ear protectors... :D