Freq drives on new chiller but not old? Problems?

[Nuclrchiller]

First, I'm all about solid reliability above all else. The more simple, the more reliable. Yet, I would be OK with operating and maintaining a plant like what is being speculated about, if it's designed and installed from the ground up. However, I'm not a typical plant operator. I would be concerned for a typical plant operator that is going through the process of making such modifications on an operating(?) plant, while trying to maintain conditions. Can the OP's facility survive scheduled downtimes? How about unscheduled downtimes? How about after the modifications are completed and all contractors are off site, and the operator is all alone? It will happen. If the OP's higher ups decide to go this route, I hope he is up to the challenge.

[ZeroTolerance]

We are prepared to run everything at 60Hz, because even though we are only "operating engineers", we know what the effects of this new VFD Chiller and pumps is going to have on us. We are screaming at the higher ups and the actual Engineers designing the setup that it isn't going to work.

We know that the setup they are proposing isn't going to work and cause a hell of a situation for us. I brought forth my opinion to the engineers when they last came and you could tell a light bulb went off in their head that their proposed setup isnt going to work!!!!

[Nuclrchiller]

I hope things work out for the best for you. Good luck with trying to figure out what's going on in the head of an engineer.

[CraziFuzzy]

We are prepared to run everything at 60Hz, because even though we are only "operating engineers", we know what the effects of this new VFD Chiller and pumps is going to have on us. We are screaming at the higher ups and the actual Engineers designing the setup that it isn't going to work.

We know that the setup they are proposing isn't going to work and cause a hell of a situation for us. I brought forth my opinion to the engineers when they last came and you could tell a light bulb went off in their head that their proposed setup isnt going to work!!!!

Like I said earlier, it will still 'work' just fine, it just won't be able to provide the full efficiency advantage of the compressor VFD without being able to lower condenser temps. I'm betting the variable compressor will still have much better part-load efficiency than the non-vfd chillers, so as long as the controls sequence it to utilize the old chillers at near full load (where THEY are likely more efficient), and the new chiller at part load to control overall supply temp, you'll still likely be more efficient than a completely non-vfd system. Whether it will pay for the vfd upgrade, I'm not sure.

Another thing to consider is, how much life is left in the other chillers in the loop? Will they be replaced within the next 10 years or so? If so, if you DON'T go with VFD on the new one now, you'll be asking these same questions when the others are replaced down the road. Then, if you DID have 2 or more of your chillers variable, you can likely run through the shoulder seasons with the lower condenser temp just fine.

[Dallas Duster]

Like I said earlier, it will still 'work' just fine, it just won't be able to provide the full efficiency advantage of the compressor VFD without being able to lower condenser temps. I'm betting the variable compressor will still have much better part-load efficiency than the non-vfd chillers, so as long as the controls sequence it to utilize the old chillers at near full load (where THEY are likely more efficient), and the new chiller at part load to control overall supply temp, you'll still likely be more efficient than a completely non-vfd system. Whether it will pay for the vfd upgrade, I'm not sure.

Another thing to consider is, how much life is left in the other chillers in the loop? Will they be replaced within the next 10 years or so? If so, if you DON'T go with VFD on the new one now, you'll be asking these same questions when the others are replaced down the road. Then, if you DID have 2 or more of your chillers variable, you can likely run through the shoulder seasons with the lower condenser temp just fine.

I have a feeling it will not be running at part load with warm condenser water, it just might surge.

[ZeroTolerance]

Our other chillers were put in in August of 2007, so they are fairly new. They are both CVHE 600-tons running ucp4

[CraziFuzzy]

I have a feeling it will not be running at part load with warm condenser water, it just might surge.

Well, the way they control the compressor speed in most cases is to run just above the point of surging. Keep in mind, we're not talking about 'warm' condenser water, just not 'cold' condenser water. It shouldn't be any closer to surging than a constant speed compressor - and and part load, it should have no problem backing off speed a bit, improving part load efficiency.

Still, if the other chillers are that new, and not likely to be replaced, then the other part of my argument is invalid - unless of course they are new enough to receive VFD upgrades in the next few years.

This conversation DOES make me glad our plant has 2 separate towers. We've got 2 1985 vintage CVHE-750's on one tower, and 3 1990 vintage CVHE-1250's on the other. We are in the planning stages of replacing the 750's with some newer 750's, but since they are on a separate tower and can run colder, the VFD's are a no-brainer.

One recommendation I have is, if they DO end up putting in the VFD chiller, perhaps it might be worth it to see what it would take to add a 3-way, or a pump return bypass, on one or two of the constant speed chillers. You might be surprised how little it would cost, and the gains would be huge.

[CraziFuzzy]

Since you already have dedicated pumps for each chiller (I think you said that), getting variable temp condenser water to each chiller may only require cutting in a simple modulating valve across each pump take-off like so:

This way, the pump is just concerned with the right GPM through the chiller, and the bypass valve will vary to regulate the temperature of the water into the chiller.

[Dallas Duster]

Well, the way they control the compressor speed in most cases is to run just above the point of surging. Keep in mind, we're not talking about 'warm' condenser water, just not 'cold' condenser water. It shouldn't be any closer to surging than a constant speed compressor - and and part load, it should have no problem backing off speed a bit, improving part load efficiency.

Still, if the other chillers are that new, and not likely to be replaced, then the other part of my argument is invalid - unless of course they are new enough to receive VFD upgrades in the next few years.

This conversation DOES make me glad our plant has 2 separate towers. We've got 2 1985 vintage CVHE-750's on one tower, and 3 1990 vintage CVHE-1250's on the other. We are in the planning stages of replacing the 750's with some newer 750's, but since they are on a separate tower and can run colder, the VFD's are a no-brainer.

One recommendation I have is, if they DO end up putting in the VFD chiller, perhaps it might be worth it to see what it would take to add a 3-way, or a pump return bypass, on one or two of the constant speed chillers. You might be surprised how little it would cost, and the gains would be huge.

So most likely it will be running balls to the wall all the time.

[CraziFuzzy]

So most likely it will be running balls to the wall all the time.

That would depend on the other chillers setpoints.

[CCSPIERCE]

My opinion ( for what it is worth) is that all of these mechanical design engineers need to start paying for their mistakes and experiments. They have become just like doctors, they cover for each other and admit no mistakes. Seems like every start up i go into has the same old stupid mistakes. You would think that by now they should now what to do with head pressure controls. Maybe it's my impatience, but i get tired of the same old arguments. I have however seen a few good enginnered projects, but they are getting less frequent.

My statement does not ascertain that service engineers and building engineers are smarter than desigb, but sometimes i think they need to listen to the voice of experience.

In your case it would seem that a serious discussion needs to occur. Reading these posts indicates the answers are available, it simply is a matter of everybody getting on the same page and planning well ahead of time, especially the controls.

[R123]

Our other chillers were put in in August of 2007, so they are fairly new. They are both CVHE 600-tons running ucp4

Then they have the refrigerant pumps and can take the lower condenser temps.

[jayguy]

...This conversation DOES make me glad our plant has 2 separate towers. We've got 2 1985 vintage CVHE-750's on one tower, and 3 1990 vintage CVHE-1250's on the other. We are in the planning stages of replacing the 750's with some newer 750's, but since they are on a separate tower and can run colder, the VFD's are a no-brainer.....

i would agree with you here. earlier, i was thinking of 3 way valves on the towers instead of on the individual condenser pumps...working in the heat had gotten to me. that i also like and it may work if the controls are set up properly and left alone. it does add for individuallity of the condenser water temperatures per chiller. i have had trane chillers that lost all of their oil with entering condenser water temperatures below 84F and i have had trane chillers that never lost a drop at 65F. individual control allows for age differences and mechanical issues. i would be concerned about being able to write a proper sequence and maintaining it. i don't have that kind of faith in the industry.

it used to be that the experienced mechanical techs moved into the BAS field...now it is mostly young punks who grew up playing video games and don't know what dirt under a fingernail feels like.