staging package units

[Jwise]

I was wondering if there is a way to stage 2 15 ton and one 5ton package units. If each unit had several stages could they be connected in a way that they would only kick on in the order needed? Can three units operate off of one tstat? Really one tstat, not hiding others somewhere. I know two can be twinned together. A store owner I know wants something like this. He also wants it to operate all off of one tstat. I need to think about this for awhile but I thought I might get some input from all you hvac genuises. :anyone:

[btuhack]

Jwise, I don't have a clever scheme to share with you ( I could needlessly rattle off many obvious drawbacks/obsticles) but I have to ask...What advantage does (1) enormous CV system/zone offer that (3) seperate systems/zones can't. Is there an objective to be accomplished or is this a "stimulus" type of project/idea.

[Jwise]

Jwise, I don't have a clever scheme to share with you ( I could needlessly rattle off many obvious drawbacks/obsticles) but I have ask...What advantage does (1) enormous CV system/zone offer that (3) seperate systems/zones can't. Is there an objective to be accomplished or is this a "stimulus" type of project/idea.

I guess it is a man who wants to part with his money. I really don't understand why he would want 3 units in the first place. Seems to me he woull be better off with 1. Although I can see why with 2 he still has some air conditioning while getting one repaired. I have not bid on this job. I probably won't bid it. I was just wondering if what he was requesting was even possible.

[btuhack]

If you propose a normal design with multiple/independent systems, you will provide: a system that can respond to various loads, simplified duct design, low bid, and a satisfied customer. He's not the expert, you are. Make him believe, do it right, and get his money. or, let some other guy do it "his" way and offer to do the corrections in a year or two after the frustration sets in.

[Jwise]

If you propose a normal design with multiple/independent systems, you will provide: a system that can respond to various loads, simplified duct design, low bid, and a satisfied customer. He's not the expert, you are. Make him believe, do it right, and get his money. or, let some other guy do it "his" way and offer to do the corrections in a year or two after the frustration sets in.

I think this is very sound advice. Thanks for replying. I think I will look at a normal design, stick with what I know, and if he lets me do it, fine. If not that will be fine also. I may be somewhat of a hack (I get better everyday) but I am much less of a hack than most of my competitors.

[seascott]

Besides think of how interesting it will be to work out a proper solution to this system after someone cobbles together a scheme to operate 3 units from one thermostat. The time spent just thinking this through would easily pay for 3 separate thermostats.

[tipsrfine]

I was wondering if there is a way to stage 2 15 ton and one 5ton package units. If each unit had several stages could they be connected in a way that they would only kick on in the order needed? Can three units operate off of one tstat? Really one tstat, not hiding others somewhere. I know two can be twinned together. A store owner I know wants something like this. He also wants it to operate all off of one tstat. I need to think about this for awhile but I thought I might get some input from all you hvac genuises. :anyone:

There are controls for everything. On a 3 unit system in a walk-in cooler they had a controller (lion? I think) that was used to stage the units similar to what you mentioned. If you don't find it first or someone else with more knowledge before I do I will post back.

[tipsrfine]

Here it is:

http://www.redlion.net/

[seascott]

I was wondering if there is a way to stage 2 15 ton and one 5ton package units. If each unit had several stages could they be connected in a way that they would only kick on in the order needed? Can three units operate off of one tstat? Really one tstat, not hiding others somewhere. I know two can be twinned together. A store owner I know wants something like this. He also wants it to operate all off of one tstat. I need to think about this for awhile but I thought I might get some input from all you hvac genuises. :anyone:

How would you even twin 2 units together on one thermostat? Unless you have a fistful of isolation relays you will have tons of unanticipated voltage feedback problems. Every time that I have ever seen multiple units run off a single thermostat, the installer that put it together figured that all he had to do was disable one control transformer and run the signal through to both units after he blew up the first thermostat. Then I get to come unmelt the wiring and add a second thermostat. Of course you can gang the units together with DDC but how is that more sensible than spending $100 for two more thermostats?

[seascott]

I have a power supply room that has 4-12 ton units. They decided that although everything was working fine that the 4 thermostats weren't sexy enough so they "upgraded" to DDC. Now often I'm called out for service it's because someone has been fiddling with it and the mechanical cooling was operating with the economizers open and it's frozen up or the 2nd stage is operating before the first so there's no condenser fan and it locks out on high pressure. I'm not saying that you can't control the units this way and many do. I'm just saying that sometimes simpler is better.

[NYG-56]

How would you even twin 2 units together on one thermostat? Unless you have a fistful of isolation relays you will have tons of unanticipated voltage feedback problems. Every time that I have ever seen multiple units run off a single thermostat, the installer that put it together figured that all he had to do was disable one control transformer and run the signal through to both units after he blew up the first thermostat. Then I get to come unmelt the wiring and add a second thermostat. Of course you can gang the units together with DDC but how is that more sensible than spending $100 for two more thermostats?

I have to agree, with you on this one..:couch:

[Jwise]

Here it is:

http://www.redlion.net/

Thanks for the link tipsrfine. I told the guy I wanted to install one zoned system. He hired someone else who told him he could stage the units together so they kicked on one at a time as they were called for. I think this was entirely out of my capabilities. I hope I don't get called to repair it. (The store owner is getting all of this fancy work and getting Grandair units, if that tells you anything. I think I am glad not to mess with this one.

[tipsrfine]

Thanks for the link tipsrfine. I told the guy I wanted to install one zoned system. He hired someone else who told him he could stage the units together so they kicked on one at a time as they were called for. I think this was entirely out of my capabilities. I hope I don't get called to repair it. (The store owner is getting all of this fancy work and getting Grandair units, if that tells you anything. I think I am glad not to mess with this one.

I'm no expert, but the guy that got the job knows controls. You should look into it. The kind of control you would have needed for that job ain't that hard to figure out. I did it on site troubleshooting a similar system my first time running into it due to the manual being there. Big money cust's like that crap. Plus it's the future and beyond........

[Jwise]

I'm no expert, but the guy that got the job knows controls. You should look into it. The kind of control you would have needed for that job ain't that hard to figure out. I did it on site troubleshooting a similar system my first time running into it due to the manual being there. Big money cust's like that crap. Plus it's the future and beyond........

I know I am very weak in the area of controls. I just got my professional membership today. Controls is one of the first topics I am going to investigate. I look forward to learning from experts like you. Thanks again. That Lion site is really great, all kinds of controls there.

[tipsrfine]

I know I am very weak in the area of controls. I just got my professional membership today. Controls is one of the first topics I am going to investigate. I look forward to learning from experts like you. Thanks again. That Lion site is really great, all kinds of controls there.

If you think I'm an expert, wait 'til you get to some of the real one's on this site. By the way, when you have time, explore the education forum on this site. Great stuff.

[bmc]

Just for discussion purposes if you wanted a reliable, cost effective method of staging several units with a single controller check out honeywells line of T775 controllers I have used them in several applications and been very happy. Mount the controller out of the way somewhere and just install a remote space sensor. They make one model that will control up to 4 stages off of a single controller.

[Airmechanical]

a fistfull of relays, boy that is scary:rolleyes:

some tech's, are not working today

there are plenty of ways, with a few "or less" relays

but this would need to be discussed in the appropriate forum



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