MYCOM's manual

[NoNickName]

Proper industrial users have standby plant just for maintenance, they can't afford not to have

At least they should have one backup. Ordinary reality is much sadder than that.

try replacing a 8WB Mycom in the time it takes to do an overhaul, well you probably could but it would take a crane to do so, bit of a nonsense really

It all depends on proper chiller design. For our air cooled and water cooled, compressors are replaced and restarted in less than 6 hours.
Overhauling (on-site or off-site) is a matter of days.

You have hit the nail on the head, this short service interval is whay recips died out for a few years. The reason they are now popular is the screws have poor part load effeciencies

Well, you may be well right, BUT! ST microelectronics in Milan runs a plant with a total overall power consumption of over 100MW. Would you reckon what difference few dozens kWh per year makes?

When you take into account the seasonal EER the recip wins hands down.

Definitely.

[US Iceman]

this short service interval is why recips died out for a few years.

And I always thought the screw compressor salesmen did such a nice job.

I have heard some of these stories used to sell screws. 100,000 hour bearing life, no valves to replace, more efficient, can ingest liquid with no harm, cheaper to install, etc, etc.

When screw compressors were being sold some time ago, the salesman all said variable Vi was better than fixed Vi.

Recip compressors were less efficient than screws. All sorts of sales tactics were being used.

I think the simple fact is; both compressor types have some benefits that can be utilized... if done properly.

Screws can operate at high pressure ratios more efficiently. They require smaller areas for the equivalent capacity (on big systems).

But, I have never heard a salesman tell the owner the screw compressor is a lot more inefficient than a recip compressor at part load when trying to sell a screw.

And... I have never heard a screw salesman say recip's already have variable Vi. They don't even need control systems for variable Vi.

Although I would like to see someone add a manifold to a recip for economizers.

I'm in agreement with Andy. A lot of arguments are used to sell one compressor over another type. I think the arguments are based on what the salesman is trying to sell. Sometimes these are vary one-sided.

The reason they are now popular is the screws have poor part load efficiencies

I think people are starting to get smarter about how they select compressors.

There's a place for both. Now people are starting to use VFD's on screws. That's a big benefit for part load improvements.

...runs a plant with a total overall power consumption of over 100MW. Would you reckon what difference few dozens kWh per year makes?

2 dozen kWh is not much a savings. However, on the serious side, if the plant is using 100 MW, there has to be some room for improvement in energy use.

Many years ago I have been told (by people from Stal-Astra Sweden) you can build only two types of refrigeration plants:

1. Cheap plant without maintenance usually with short life - expensive

2. Expensive plant with maintenance to assure long life - cheap

I quite agree with this.

Number 1 is usually a system that is designed to be cheap on the first install price. Then the system is operated in a "run to failure" mode. No maintenance is done... just spend enough money to keep it running. This is not much different than HVAC systems.

Number 2 does cost more up for the initial install and continuing operation. These are usually systems where the people recognize the loss of cooling costs more in lost production time, than the cost of the maintenance.

Of course there are all sorts of arguments that can be made for this too. In general, I think Josip summed it up very nicely.

[Josip]

Hi,

Number 1 is usually a system that is designed to be cheap on the first install price. Then the system is operated in a "run to failure" mode. No maintenance is done... just spend enough money to keep it running. This is not much different than HVAC systems.

Number 2 does cost more up for the initial install and continuing operation. These are usually systems where the people recognize the loss of cooling costs more in lost production time, than the cost of the maintenance.

Of course there are all sorts of arguments that can be made for this too. In general, I think Josip summed it up very nicely.

I was thinking (couple of days before) to start a new thread with those opinions to ask you, what do you think : where are we today?

Best regards,

Josip