Does distance affect capacity?

[Dimitris]

A 6 ton AC split unit with proper piping size, has a distance,between in and out, of 35 meters. Does this distance cause a loss of capacity? I believe it does, even though the manual says that it can have a distance of 45 meters without affecting the units capacity. Some opinion please!

[US Iceman]

Hi Dimitris,

Welcome to the RE forum.

If the manual says the performance does not decrease up to 45 meters, my assumption would be the performance is rated on the pressure drop created by the pipe length of 45 meters.

If the manufacturer has based their ratings on the 45 meters you should be OK. You should ask someone from the manufacturer to confirm what they have based this statement on to be sure.

In general I would say the 45 meters is intended for a horizontal pipe installation only. A vertical rise upwards would create a totally different situation for the liquid line.

[Dimitris]

Hi Iceman, thanks for your reply. I have started up 2 identical units at this location, one has an 18 meter distance, and the other has the 35 meters I mentioned. The unit that has the 18 meter distance performs much better than the other. Both units have the proper amout of 407C refridgerant according to the piping. The pipes on both units are horizontal. On heat mode, there is no TXV to be adjusted, there are just accurators.

[Argus]

Dmitris,

The short answer is YES. Loss of capacity on AC systems is a very valid and important question. Bit of a question with many answers, too, but here goes.

All AC systems are rated to standard conditions that are laid down in technical standards. It depends where your machine originates as to which standard the manufacturer useless.
The relevant international Standard is ISO 5151, though US machines and some machines made by US manufacturers in third countries use ARI 240 / 210. It?s some years since I worked on American systems, so I?m a bit rusty on the latest amendments of this one. Japanese made machines rate to JIS B 8616.
However, and most importantly, as you are in the EU, there is an EU standard, EN 14511, that takes precedence and enforces EU law on energy labelling on system up to 12 kW cooling.

In short ?you pays your money and you takes your choice?.

Broadly speaking the heating and cooling capacities in all types of standard will follow the same actual ratings conditions. Generally there are 3 to select from in the cooling mode that allows you to select an output to use in which ever climate you are situated.
These are:

• Cool,
• Temperate
• Tropical.

In general most mass producers rate to the temperate condition and omit the remainder. In practice tolerances may vary between standards, so the results may vary between tests.

Rated line pipe lengths are stated in the standards and they are the lengths used to measure the capacity that you read in the specs pages. The rating lengths can vary. As I remember:

• The ARI standard was set at 25 feet and this translated to the ISO standard and became (as we use SI units) 7.5 metres.
• The Japanese standard rates at 5 metres.
• The EU standard is at 8 metres.

This means that when the units are rated by the manufacturer these are the benchmark conditions that appear in his data.

Knowing the length is important, because when the manufacturer sells the equipment with a predetermined running charge of refrigerant, (as most of them do), it is at this level that the base charge and capacity should be clearly stated in the installation manual, refrigerant additions at site are calculated based on the pipe size in grams per metre of extra pipe onwards.

The ultimate capacity of any AC system is dependant on a number of variants, including indoor and outdoor conditions, air-flow, and as you questioned, line losses.
Again with the data published on many small split systems you will see a number of graphs that allow you to de-rate the machine for extra line length and elevation differences between the two halves.
The pipe losses are generally shown twice:

• Firstly for a linear pipe length up to the manufacturer?s pipe limit, assuming only the friction losses of a pipe,
• Secondly, often with VRF units where it is very important, the total resistance losses for the entire system, taking pipe fitting losses into account.

In my experience, variation in unit performance using R 407C is not unusual. The relatively high glide, plus local ambient and room variations, plus service variations in the composition mix can be very significant. Thankfully, many AC manufacturers are now phasing it out in favour of R410A.

Assuming you?ve not dropped R407C into an R22 system, or there's something wrong that we don't know about - to be absolutely certain - I would recommend scrupulously working out the exact charge for the full pipe runs, reclaiming the xisting charges and then weighing in a charge of NEW refrigerant. You may be amazed at the results.

I hope this helps - it's complex subject.

.
________
volcano classic

[Dimitris]

Hi Argus, thanks a lot for your answer. It was very interesting. The machine was empty of ***** from the beginning. I pulled a very good vaccum and I put the exact amount of ***** according to the length and size of the pipes. The unit, in my opinion, is at its full possible capacity under the conditions it was installed in. I too beleive that the distance makes a difference.
I wanted to see if anyone else agreed.

[Argus]

I too beleive that the distance makes a difference.
I wanted to see if anyone else agreed.

Undoubtedly it does.

Manufacturers publish data on line capacity losses that suggest about 10% losses over 40 ? 50 m on a 10kW system. These losses in my opinion are extremely conservative and I would expect somewhere nearer 20% or more as a more practicable figure.

Your other problem may be that as the capacity falls, you lose the ability to return oil to the compressor and the oil logged in the evaporator and elsewhere will impair the heat transfer, thereby making a bad situation worse.

.
________
Honda CM125