Eqivelant Pipe Length - Refrigeration-Engineer.com forums

**frank** · #1 02-02-2002, 09:34 PM

I was looking through the latest manufacturers catalogue the other day and noticed that the maximum pipework length between indoor/outdoor unit had increased from 50m for an R22 unit to 70m for an R407c unit.
Can anyone explain why this is?

**Brian_UK** · #2 02-02-2002, 11:43 PM

Higher pressures, different compressors ?

No, now that I think more deeply, I do not know why...sorry.

BritCit_Juve · #3 05-03-2002, 11:34 PM

Can you give us some more info? Which manufacturer / unit?

Then we may be able to repond

herefishy · #4 06-03-2002, 09:26 PM

The manufacturer put more lubricant in the crankcase????maybe?

**frank** · #5 06-03-2002, 09:34 PM

sorry for the lack of information but it was Daikin a/c equipment, which we install quite a lot of, and, when doing a site survey, I was always thinking along the line of maximum indoor / outdoor limits, but suddenly I read the latest info sheets and was staggered to learn that the maximum length was increased to 70m for 407c.

No explanation has been forthcoming from Daikin and I can't really work out why this should be without technical backup.

**Andy** · #6 06-03-2002, 09:35 PM

Hi, i don't do much split work, but I was at the wholesalers one day and the Tech/sales guy was showing a new range he was selling. After looking through the leaflet I spotted the increaed pipe lengths before you have to add refrigerant, I asked why and he said simply that's what people want. The customer (us) have asked for something and they have responded.
He may have been spoofing, but it sounded good.
Regards. Andy.

Gibson · #7 16-03-2002, 07:06 AM

If you follow good piping practices you can just ignore what the manufacturers say about maximum lengths... Do your homework on the pipe sizing and consider the refrigerant and oil charges and you can cool Britain from Canada!

Jasper · #8 24-03-2002, 08:51 PM

Hi Gibson
Sorry i'm so late with this question BUT how can you say that it dos'nt matter about pipe length, when a compressor is only able to pump it's rated amount of refrigerant .

Gary · #9 24-03-2002, 09:31 PM

In a stabilized, closed loop, series system, the mass refrigerant flow is identical at all points.

In other words, if the compressor is pumping X pounds of refrigerant per minute, then the rate of flow at every point in the system is X pounds per minute.

The problem with cooling Britain from Canada would be friction. Friction anywhere slows the flow everywhere, resulting in the compressor reducing it's flow to match.

On the other hand, angled fittings are of much more concern than straight pipe length, each providing the friction equivalent of many feet of straight pipe. This is the equivalent length of the fittings.

Increasing the equivalent length by 20 meters isn't going to add a lot of friction. The effect on the system will be minimal, and can be compensated for by slightly reducing the friction at the choke point, i.e. metering device. In a TEV system, this would happen automatically.

As regards the rest of Gibson's post, I agree wholeheartedly.

Jasper · #10 24-03-2002, 09:44 PM

If that's true Gary why do manufacturers give a maximum pipe length

Gary · #11 24-03-2002, 10:17 PM

Quote:

If that's true Gary why do manufacturers give a maximum pipe length

Because they are selling a one size fits all product, containing refrigerant and oil charges, metering device, pipe sizes, etc. which must perform reasonably at both minimum and maximum pipe lengths. Compensatory changes can be made, but they aren't counting on your ability to make those changes.

A few meters of pipe length can be added to their maximum by simply redefining "perform reasonably", and/or maybe adding a few ounces of this or that.

There are a lot worse things that can happen to a system than a little extra friction. You might find it difficult to measure a difference in performance caused by 20 meters of extra piping, although you may need to add a little refrigerant to fill the extra liquid line.

Jasper · #12 24-03-2002, 10:39 PM

OK Gary i see your point
but does that mean that even with a pipe run that is longer than the manufacturers maximum they will still honour the warrenty on the equipment.

Gary · #13 24-03-2002, 11:55 PM

I suspect so, and I don't see why not, but you would have to ask them to know for sure. Personally, I wouldn't tell them. What are they going to do...come out and measure?

puddleboy3 · #14 23-03-2006, 11:30 AM

Bored at work and trawling through old threads found this one and thought i would bring it up to date! Had a problem with a split type system i wont mention any brands. Unit installed was new model with new pipe limits *problems* *problems* Lets just say i didnt work so the message here is always stick within the Equivelant or actual piping limits to cover yourself and yes they will come out and measure the pipe work

NoNickName · #15 23-03-2006, 04:06 PM

As a manufacturer of big DX close control with generously sized liquid receivers, I can only recommended a maximum of 15 meters of equivalent pipe length. Beyond that, a pipe layout design is required with appropriate refrigerant piping accessories.
Too long discharge pipe will result in unexpectedly high HP, while a too long liquid pipe will not do too much harm, but starvation.
The point is that oil must be added, and god knows how much, not too little or not too much, and excessive liquid migration in the condenser coil in winter time at standstill, which will result in condenser drowning and low pressure alarms while standby (in countries of harsh winters and all year long operation, like computing centres).
So beware of generous manufacturers. No one gives away anything for free.

Renato RR · #16 23-03-2006, 04:26 PM

Try to calculate pressure drop.Danfoss have good program for calculation.If pressure drop cose ading 3 C to condesation or 3 C to suction temperature should be ok.

Best regards,
Renato

mccoolair@yahoo · #17 25-03-2006, 12:26 AM

Hello, I am working on a similar problem, as well. I need to calculate the amount of R-22 required to recharge several systems where someone walked-off with the line sets overnight at a supermarket. #1 system- a produce cooler (24 ft.) has a 125' line length, lineset - 1/2" liquid and 1 1/8" suction with a Heatcraft condenser (HD10502M6C) and an antique Tyler case (Y12TVBH 1041B) Mfg. pressure setings Cut in: 36 and Cut out: 14-19. I must calculate the amount of refrig. required for the bid price, and I'm not sure how to go about it. Can anybody give me a clue where to start?

**US Iceman** · #18 25-03-2006, 04:03 AM

Measure the total lineal feet of each pipe. Then find the volume of each pipe. (lineal feet times pipe cross sectional area in square feet = cubic feet)

For the suction line charge multiply the suction line volume (cubic feet) times the vapor density at the suction pressure.

Cubic feet of volume times pounds per cubic foot. That will give the total refrigerant charge for the suction line. Similar process for the other piping.

For the liquid line charge multiply the liquid line volume (cubic feet) times the liquid density at condensing the pressure.

For the discharge line charge multiply the discharge line volume (cubic feet) times the vapor density at the condensing pressure.

You will need to add some charge for the receiver, since the diptube in the receiver must have a liquid seal on it before liquid can flow out.

Heatcraft should have the condenser charge in a catalog somewhere. If you are using head pressure controls to flood the condenser, you also need to find out how much this will be.

In Texas this is probably not too bad. If the system were installed in Montana, it would be a different story.

Add all of the different amounts of refrigerant and you have your total. To be safe add 20% to this amount so you have enough money allowed for minor changes.

**Peter_1** · #19 25-03-2006, 07:14 PM

NoNnickName, visted last Thursday X-Change (Flumignano) and Intherm (Gregorio di Veronella, nearby Verona)
They will start a production with oval pipes in their drycoolers.
Both factories were very clean, well organised and I was impressed of what I saw at X-Change.
Are you also a customer of Intherm?

NoNickName · #20 25-03-2006, 08:17 PM

No, I'm not, but will take a look

**Peter_1** · #21 25-03-2006, 10:56 PM

Daniele Stolfo is the present boss, previous founder or co-founder of Thermokey.
The oval tube is in my opinion a nice 'invention'

wambat · #22 26-03-2006, 01:20 AM

Quote:

Originally Posted by frank

I was looking through the latest manufacturers catalogue the other day and noticed that the maximum pipework length between indoor/outdoor unit had increased from 50m for an R22 unit to 70m for an R407c unit.
Can anyone explain why this is?

The molecular weight of R-22 and 407c are nearly the same , However say at 40*F SST the cuft/lb of 407c is less then that for R-22 therefor less pressure drop so a longer suction line is possible.