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Rob S
07-02-2006, 05:41 AM
Does anyone know of a mounting kit to convert a system using Copeland Discuss Compressors to Copeland Scrolls?

guy in blue van
08-02-2006, 01:17 AM
why would you want to do that
your steping down using scrolls

guy in blue van
08-02-2006, 01:20 AM
is this a rack system and if so what make

Rob S
08-02-2006, 03:35 AM
Chambers. Some of the new environmental chambers coming out are using Scrolls. So yes the loss in capacity has got me thinking why? Plus scrolls do not like to run in a vaccum.
These thermoshock chambers will go though compressors.

guy in blue van
10-02-2006, 04:38 AM
just wondering what your trying to achieve by changing over to scrolls.

guy in blue van
10-02-2006, 04:42 AM
whats the make and model of the chamber in question.

Rob S
10-02-2006, 08:23 AM
Espec, Thermotron, etc. Mostly the 48ft^3 and larger. Few Walk-ins too. I'm not good with remembering M#
Most of them run two 7.5hp or 10hp... The larger shocks and walk-ins are 30hp. Like the new one being shipped in is three 30hp cascades for one thermo-shock. Monster.

Scrolls are cheeper and weight is less. (Ah pulled my back again :(

I'd like to get greater capacity control with out Hot Gas bypass. Countless hours of research is a hobby
Been thinking about VFD drives.. But I know copeland won't be any help on that subject. If its not in the data we won't help :) I hear carlyle's have been haveing success with VFDs

Andy
11-02-2006, 08:15 PM
RobS
copeland digital scrolls. The ordinary scroll will not run on VSD the scroll.
A good compressor for your application would be a Bitzer octagon on a VSD, this is a high effeciency compressor with no oil pump that lends it'self to speed control.

http://www.bitzer.de

Kind Regards. Andy:)

Rob S
12-02-2006, 12:33 AM
I have nothing against Blitzer. Think they make great compressors. We buy mostly from the same local supplier to get better rates. Atleast I do.

I wasn't refering to using a VFD on a scroll. More like you suggested but with a Copeland Discus. Only problem with this proposed usage is.... 50% min capacity. Around 35% with an unloader. We need 10% min. capacity.

Andy
12-02-2006, 12:05 PM
Only problem with this proposed usage is.... 50% min capacity. Around 35% with an unloader. We need 10% min. capacity.

Aparently you can select a smaller compressor and run it up to 70hz for peak loading, this should allow the turn down required.

Kind Regards. Andy:)

Peter_1
12-02-2006, 03:58 PM
We've Copeland scrolls running with VFD's till 30 Hz.
A digital scroll is cheaper.

You can go as low as 25 Hz, with an unloader at 25 Hz this will be the same as running at +/- 12,5 Hz.;)

We've ran a Bitzer several days on 15 Hz to test and monitored closely oil pressure.
Gave no problems but Bitzer Europe wont guarantee it.

Rob S
12-02-2006, 05:36 PM
How do you run startup? And are the VFDs providing a large enough saving?

Peter_1
12-02-2006, 09:40 PM
What do you mean 'How do you run startup'?

Large enough savings... I suppose you mean in money, not in electrical current or savings for the environment.

Well..this is my idea...in Belgium these VFD's are heavy subsidised by the Government (Kyoto agreement) (starting at 124 /kW and decreasing to 104 /kW for a 10 kW VFD and 84/kW for a 20 kw/VFD...) but otherwise..?????

I should say...no. It's in my opinion only usefull if you have different evaporators connected to one compressor (like a pack and even then...) of where you need a very precise evpaortaing temerpature or a precise capacity control.

My first apcks I made 15 years ago were made in a mathematical row: 1 Hp, 2 Hp , 4 hp, 7.5 Hp, 15 Hp,20 Hp...
The PLC chooses the needed steps in steps of 1HP by chosoing the right combination so that the combination matches the load.
I think this works as well as a VFD.
It's otherwise not worth the money.

US Iceman
13-02-2006, 12:25 AM
It's in my opinion only useful if you have different evaporators connected to one compressor (like a pack and even then...) of where you need a very precise evaporating temperature or a precise capacity control.

I agree.

VFD's used with compressors provide excellent part load capacity control. From an energy savings standpoint you may expect a small percentage of savings, but the use of VFD's on compressors is more about obtaining better capacity control.

I am working on a project using a VFD on a Discus compressor for a dairy farm. The VFD is being used for ramp-up speeds to reduce the high in-rush current and for part load control.

I have experienced a similar finding of Peter's. The minimum speed I would recommend is about 25-30 Hz. I have also seen open-drive reciprocating compressors down to about 15Hz with no problem. I feel more comfortable with the minimum speed locked to 30 Hz to provide sufficient oil pressure during low speed operation.

Rob S, if you need 10% capacity for some reason then use a hot gas bypass valve for the low part load capacity. If the load is dropping lower than the capacity reduction system will accommodate, hot gas is the only way to go.

Rob S
13-02-2006, 01:47 AM
What i mean by start up is... Do you open a bypass valve from discharge to suction before ramp up on the VFD? Is the VFD programed to start at 60Hz (50Hz)?

Environmental Chambers will frequently run at around 12% capacity. But they want full capacity to keep the pull down time @ 20C per min.... The hotgas bypass and running the chamber at 50C for 2 weeks just burns the compressors up. Desuperheating doesn't work to well with such a low flow. When your bypassing most of the critical charge as it is. We want to keep the suction gas below 0F (-17C).
Just in case you don't know.. "Why would one run a cascade system at 50C? Because they want to keep exactly 50C. Not 49-51C. And thats the way all chambers are designed. Only one evaporator."

I guess I'm just going to have to wait for the refrigeration digital scrolls to come on the after market here.

The Saint
02-10-2006, 11:38 AM
Does anyone know of a mounting kit to convert a system using Copeland Discuss Compressors to Copeland Scrolls?

Too much comments without the specific answer mentioned here. Give me the scroll model and I will give you the mounting kit

Peter_1
02-10-2006, 02:07 PM
Wowww, God....sorry...The Saint has spoken.
Never heard from a conversion kit for a Discus to a scroll.

And that for me, who has visited already twice the Copeland Welkenraedt plant.

Shame on me!

I almost can't wait to read you answer and to see how this kit looks like.

US Iceman
03-10-2006, 02:01 AM
The hotgas bypass and running the chamber at 50C for 2 weeks just burns the compressors up. Desuperheating doesn't work to well with such a low flow. When your bypassing most of the critical charge as it is. We want to keep the suction gas below 0F (-17C).


I think you have several application problems to solve here.

One, if you use a VFD on the compressor you need to make sure you do not exceed the operating envelope. 20 to 30 Hz (on a 60 Hz power supply) should be OK as long as the compressor has pumped lubrication, not the splash type.

Secondly, desuperheating should not be that difficult to accomplish.

I would look into the hot gas bypass using the side port distributor made by Sporlan. This dumps all of the bypass gas into the evaporator, so the TXV should maintain the evaporator superheat reasonably well.

This method provides very good mixing in the evaporator and helps to stabilize the return gas temperature without too much fear of liquid slugging.

Most of the US semi-hermetic compressor manufacturers rate their compressors on a maximum return gas temperature of 65F (18.3C), so as long as the gas temperature stays below this value I would not expect any problems.

Why do you want to keep the suction gas temperature below 0F (-17C)?

If the minimum capacity were around 12.5%, then the compressor may only go down to 20% (just a guess right now for discussion purposes). If the evaporator load is 12.5%, the hot gas must supply the difference between the minimum evaporator load and the minimum compressor capacity. At this point your minimum mass flow would be established.

Agreed, prolonged part load operation can be painful to solve, but it's not impossible.

Copeland has external oil coolers and head cooling available. I would investigate those. I know they cost money, but... This is an environmental chamber. It's not cheap to start with.

What is an environmental chamber worth that works all of the time within the desired limits?

Note: the use of VFD's on postive displacement compressors does not per se offer energy savings. The VFD does however allow you to run the compressor to match the loads very precisely as long as you stay within the ocmpressor limits.

davej
03-10-2006, 07:35 AM
Hi Iceman have you had any dealings with ECR heat pumps in the state?
we are trying to adapt them to allow some capacity control for heating hot water via a plate heatx and underfloor heating in the uk and obviously they trip on hp when water temp is close to set point,
any suggestions how we can achieve either inverter control or suitable capacity control via valves?
have been suggested a parker charge compensator! what do you think

US Iceman
03-10-2006, 09:33 PM
Hi davej,

What is a parker charge compensator? That's the first time I have heard of that item.

I don't have any experience with ECR heat pumps, but it sounds like your system is not unlaoding when it reaches setpoint. Did I read that right?