I've been online reading up a bit about air conditioning after seeing a nei ghbour having it fitted. I notice some installation manuals stress the need for the pipework to be nitrogen purged and pressure tested then a full(ish ) vacuum be drawn before introducing the refrigerant. Other sources don't s eem to mention this. Is a small proportion of nitrogen in the system a seri ous defect and what would it's effect be during operation?
I can't see anything too horrible happening. Nitrogen gas is very unreactive; in fact it's used in place of the noble gas argon in chemistry experiments where a *relatively* inert atmosphere is required at minimum cost.
If you buy one of the pre-charged split units then you can skip all that ;-)
Not a problem I don't think. How much is a little? Brian
Maybe they need to use it in the packaging of crumpets then, instead of global warming CO2!
Brian
If the ammonia plants don't start up again soon, we'll have nitrogenated Coca-Cola on the shelves!
There are two sorts of system. The small split units (ready filled and with self-seal connections) suitable for domestic and portacabin type just need to be connected up. Systems that don't come charged need the approach that you describe, same as car aircon.
Professionally installed AirCon usually comes at ambient air pressure and after installation is nitrogen flushed to remove water vapour and taken to vacuum. It is then filled with the correct weight of refrigerant. Doing it thus allows for pipes to be cut to size and neatly fitted.
Twin units meant for DIY install often come with both indoor and outdoor units pre-filled with refrigerant and sealed with push fit fittings. The pipes are positioned, any surplus coiled out of the way and the push fit joints made. The amount of refrigerant allows for a small loss when joining the fittings. Shortening the pipes is not an option.
There are now ones where the pipework and indoor unit are nitrogen filled to prevent oxygen and moisture getting in during storage, but you break the seals to fit the pipework, and then purge it by releasing some of the precharged refrigerant through the pipework after connecting up, and no vacuuming is required. These do not have self-sealing connectors and need to be properly plumbed. Note that if you braze copper refrigerant pipework, if must be nigrogen filled first, because copper oxide formed inside the pipe at brazing temperatures if there's any oxygen inside the pipe is a disaster for the system. Traditionally, aircon was always brazed rather than soldered, but some installers claim soldering is fine, and that avoids this problem because much less copper oxide is formed at soldering temperatures, and it doesn't flake off the inside of the pipe afterwards.
eighbour having it fitted. I notice some installation manuals stress the ne ed for the pipework to be nitrogen purged and pressure tested then a full(i sh) vacuum be drawn before introducing the refrigerant. Other sources don't seem to mention this. Is a small proportion of nitrogen in the system a se rious defect and what would it's effect be during operation?
They usually purge it with refrigerant gas. Frowned on now as it is not supposed to be released to the atmosphere.
You might do that, professionals that know what they are doing don't.
Like climate change believers don't install low carbon generation unless someone is paying them too.
Peter Parry hits right on my current problem : shortening the pipes.
I am installing a thru-wall split shortly. a small single pair, both at high level. I have conflicting advice from FGAS installers. Anybody really know about back-to-back thru-wall aircon installation? Even the manufacturers seem vague.
A salesman offering pre-charged units tell me there is a minimum pipe length of 3m each way and, as PP says below, I have to suffer a big loop of extra pipes in the room, which will be ugly, or outside the room, which will heat the garden nicely. They say there is no such thing as a back-to-back with the compressor on the wall brackets just behind the inside unit. But I see pictures of them in Aussie and US.
This pre-charge salesman says it's to ensure the decompressed vapour is fully turned to gas before it reaches the pump, as any liquid in the compressor would damage it. Also having less than the 3m/5/ minimum pipe lengths would invalidate warranty.
One manufacturer, Fujitsu, is saying the minimum pipe length of 3m is to reduce vibrated sound travelling into the room, no mention of warranty or damage to the compressor.
Some Aussie installers are saying a short half-metre back-to-back is OK, but not for a pre-charged system, as that would have too much volume for a shorter run. You have to fit an uncharged pair and then charge to the correct pressure for the shorter run. Purge, vacuum and fill, as PP says below.
Does anyone with FGAS experience have an opinion? Can I have a half-metre back-to-back split? Or do I have to have this ugly coil of pipe hanging on the wall?
Really? Not that it matters to me, but I remember this being done routinely by some fitters. Brian
Yet another salesman today insisting that less than 3m pipe runs would invalidate the manufacturer's warranty and the extra run is to ensure the flow has time to become fully gaseous before it reaches the compressor. He hung up on me before I could ask what units he was selling. Toshiba specification sheet gives a maximum pipe run of 15m, a maximum differential head of (8?)m but no mention of a minimum length. I've never seen a refridgerator with any length of gas run between the end of the rear radiator and the compressor. How does that work?
Having dug around some datasheets of A/C units in countries where it's standard fit, minimum length does appear to be a thing. This one it's 3m:
If you have pre-insulated pipe, how much does it matter to tuck it behind the external unit?
I'd guess that the rear condenser provides enough length of itself (given the diameter of the pipe is very small), while the external A/C condenser might have a much smaller length:width ratio? The A/C unit has a fan to help it fit in a small space, while the fridge condenser is passive and thus sized longer.
Theo
Thanks for that info Theo.
The install manual on my Toshiba RAS-13 gives no minimum pipe run, only a max of 15m, but that was fitted 3 years ago. I see the latest model does give a 2m minimum now, so must be a recent innovation.
I was hoping to do a bracket mounted back-to-back, but if I have to coil extra pipe behind the unit it will take most of the space because the light-weight brackets only give 100mm behind the outside unit. I don't want to drop it to ground level; bicycles and shrubs beneath,
Also the cost of installing has shot up a lot, FGas fitters on £650 a day now I hear! Maybe I'll go back to storage heaters instead.
Could you coil it underneath or above the unit? Ideally you don't want it in the airflow.
I'd probably try to select a unit with a 1.5m or 2m min if I could, as that's easier to lose than 3m.
Last time I checked (couple of years ago) the cost of an F-gas ticket was in that ballpark. Maybe worth getting one to DIY?
You do near the gear though, although much of the same kit is available fairly cheap for car aircon. The gauges and manifold are cheap Chinese (£20), a vacuum pump is about £100-200. And you do need to be able to make good gas-tight connections (flaring pipes etc) - the ticket is only confirming you can do it.
Theo
Unable to get much info about the how the old wall-split aircon was done, or why the minimum pipe length was introduced. Heard it may be to give the gas time to really evaporate completely before it hits the compressor, because any liquid can harm that. Does anybody really know? I tried a query to manufacturers but no response, as usual.
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