PDA

View Full Version : Propylene







Apoc
29-03-2004, 05:49 AM
Is there any reason why propylene is very rarely used in systems, other than it being highly flammable?

Bones
29-03-2004, 08:10 AM
government doesn't make as much money by selling it out of levies etc, as they currently would on *****... just my opinion, everything in this world is done to make someone else the almighty dollar.

iceman007
30-03-2004, 12:55 AM
Propylene is classed as a hydrocarbon, which makes it flammable in certain concentrations. Across the board hydrocarbons are flammable or explosive in concentrations of between 1.5% and 34%. The lower limit for butane is 1.5% and the upper limit for ethylene is 34%. For domestic applications hydrocarbons are becoming more common, but there's a limit on storage. For instance in the UK commercially 70kg is the storage limit, which is probably why retailers don't have stacks of refrigerators stored in their warehouse.
There have been other issues regarding the safety, in domestic rather than commercial applications, such as when Granny comes along with the knife to defrost the fridge, punctures the heat exchanger and gets very promptly propelled into orbit.

There are certain things for the use of hydrocarbons, and environmentalists will say how brilliant it is, due to the zero ODP etc etc, plus as well as that, a full system charge is typically 40-50% that of a R22 system (halocarbon).

So, there is less refrigerant in the system, it has zero ODP(but then again so does R410A which is being used more widely in air conditioning).

The thing that governs it all is this

Having only 50% of the weight of R22, most people would assume that it would also be a cheaper alternative, but how wrong they were. Propylene and other hydrocarbons cost approximately 3 times the amount of say R22, so the governing factor is quite simply put-COST. Propylene in the same capacity system as R22 costs approximately 50% more-half the weight three times the cost.

Regards
James

baker
30-03-2004, 04:10 AM
James makes some good points. In Australia, the pricing of refrigeration quality HCs is such that I don't see the point of using them. Then again, bottled water costs more than general purpose propane.

As someone who has a "bee in his bonnet" about the way that Joe Citizen perceives risk, I take exception to some of the more outlandish descriptions of the dangers of HCs in refrigeration. I fail to see how a kitchen with a gas stove can be made any more dangerous by the addition of a butane powered refrigerator.

I don't foresee any quick changes, but I would be surprised if natural refrigerants didn't have the bulk of the market in 20 years.

Apoc
30-03-2004, 08:21 AM
Thanks for your replies. You guys have some very good points.

The governing factor for me is the obtainability of a chosen refrigerant. This is one the main problems for hobbyists like myself. The fact that hydrocarbons lack the environmental concerns regarding them and therefore lack the same environmental protections that are in place, makes them a good choose for people like myself who do not have an EPA certificate.

Is refrigeration not a common hobby or something? :cool:

Bones
30-03-2004, 01:34 PM
There are a few on here who pursue refrig as a hobby.

HC's and natural refrigerant blends are going to be the market of the future. I think it is going to be fun retrofitting current R22 a/c systems with r410a, incompatible oils, pipes cant handle the pressure... there will end up being several drop in replacements like for R12. One of which is a part HC blend with R134a(SP34e).

And granny shouldn't be trying to defrost her fridge with a butterknife, thats just stupid... I hope her grand kids don't use a knife to get stuck toast out:rolleyes: maybe toasters should be banned?

Its a pitty commonsense and practacality are not involved in any aspect of design and manufacturing or implementation... It just gets pushed aside to the "what ifs".

A household fridge with say 80g of HC causes nightmares...? why? there are people living with gas lines for hot water and heating etc. which would have a far greater potential for an catastophe of an accident, we read about them in the papers everyday.

iceman007
30-03-2004, 09:40 PM
Guys

Alot of things are pushed out of proportion these days. Hydoocarbons are actually exteremely efficient refrigerants, weight for weight over twice as effective as hydrocarbons. I personally don't meet that many people who do refrigeration for a hobby. Most of them are fridgies like me, and it just becomes part of your life. I love my profession, and wouldn,t change it for anything. I have a refrigerant handling certificate and am registered with ACRIB as a licensed handler etc etc, because over here it's getting tighter on us poms, before long it's probable that you won't be able to even keep a bottle on your van, or pick one up from a supplier without a CFC/HFC licence.
Bones is quite right that these will be the things of the future. As far as retrofitting goes, ther are problems with this, but there are alot of misconceptions about gases like R410A. The main problem is the oil type with R22 is mineral based and most of all the pipework will be contaminated with chlorine, Mitsubishi make a model that cleans the pipework, by using one of 2 expansion devices to divert the flow of refrigerant through a small circuit, which uses a filter to neutralise the chlorine, alternatively they use an alkobenzene based oil on smaller systems to do the job, but R410A has alot going for it. It's efficient, zero ODP and has a small glide-about 0.7K compared to R407C which has about a 5K glide, the pressures are typically 15-20% higher and so existing pipework can be used, but make sure it's the correct size. The only drawback to using the existing pipe is that the runs have to be shorter than used to, to compensate for refrigerant velocity, to avoid oil migration and ensure oil is returned to the compressor, but some of the new generation kit has a built in oil separator to make sure this happens.

James

baker
31-03-2004, 02:10 AM
The laws in various countries are often at odds with common sense when it comes to refrigerants. Australia is moving from a state based regulatory system to a federal one. In my state, you have to be licensed to buy any refrigerant, including HCs. The proposed national legislation will ignore HCs and other natural refrigerants. In the US, the way the law stands at the moment, I believe, you have to recover all refrigerants, including CO2 and HCs (there are steps now to change this).

The computer overclocking movement will see more hobbiests enter this field, and it will be interesting to see how it is handled. Personally, I would like to see a system similar to that for radio amateurs where training and appropriate licensing is applied. Hobbiests cannot afford the equipment to properly handle fluorocarbon refrigerants, but HCs are practical. They just need to know the basics of refrigeration and the safety requirements.

frank
01-04-2004, 09:47 PM
but R410A has alot going for it. It's efficient, zero ODP and has a small glide-about 0.7K compared to R407C which has about a 5K glide, the pressures are typically 15-20% higher and so existing pipework can be used, but make sure it's the correct size.

Iceman

On an A/C application with R22 the suction pressure would be say 50 - 60 psig under normal running conditions. With R410a it is in the region of 150 psig - about 150% higher. :)

iceman007
02-04-2004, 12:11 PM
Iceman

On an A/C application with R22 the suction pressure would be say 50 - 60 psig under normal running conditions. With R410a it is in the region of 150 psig - about 150% higher. :)

Hello Frank,

I don't tend to work too much on pressures as much as temperatures, but for example take R22 at 55psi (gauge pressure), it equates to a saturation temperature in the evaporator of around -1 degree C. The same saturation temperature is achieved by R410A at about 97psi, an increase of around 76% in pressure. R22 typically saturates in the condenser at around say 45 degrees (depends on ambient temp), but usually at least 15 degrees higher than ambient. Take 45 degrees as an example. The pressure of R22 at a saturation temp of 45 in the condenser should have a pressure of around 235 psi. R410A at this temp should be at around 380 psi around 62% higher. Mitsubishi, for example state that the difference in pressure to be around 10-15 %, which is obviously incorrect. If you have a suction of 150psi on your gauges, it would mean a saturation point for 410A in the evaporator of 12 degrees. I happily concede that my original figure was low, but surely 150 % increase in pressure would be a bit too much ?

Best Wishes
James

frank
02-04-2004, 08:28 PM
Hi Iceman

When commissioning R410a systems it is not uncommon to see 10bar suction pressures. Obviously, as the system gets hold of the load then the suction does drop a little. A lot of the new kit operates with inverter compressors and it is difficult to judge just how the system is operating as the electronic controls have been designed to apply a set inverter speed, wait a while, then look around at the sensor readings and adjust as necessary. You really have to learn to have faith in these things until you get used to them.

I was commissioning a small 5kw split the other week and it took nearly 20 minutes before the compressor ramped up to apply maximum capacity - nearly lost the low side gauge as it was at the maximum pressure before I noticed :D . I hear what you are saying about saturation temperatures but these 410 systems seem to have a weird way of working until they settle down and start to do the job.

frank

iceman007
02-04-2004, 09:33 PM
Hi Frank

You're exactly right about what you say, they do have a mind of their own. I've started doing quite alot of the Mitsubishi R410A power inverters, and when we've commissioned them the needles have been all over the place, until they start to settle down a bit. But, we all make mistakes- I still do even now, but as my Grandfather used to say "only a fool makes the same one twice". I had one of these systems running at 9 bar suction the other week when we fired it up, then before you know it, the suction pressure is creeping up and up, all of a sudden it plunges down to less than 6 bar and eventually, once the inverter and system settles down it all stabilises. I suppose in theory you could look at it and think there was a problem, but theory and practice never seem to do the same thing.

It's funny how this thread started off about propylene though, and we seem to have gone off at a tangent !! Anyway enough said- have a nice weekend (unless you're working )

Best Wishes

James.