Single-phasing, Surge Arrestors, And HVAC

Beren

We're in the process of soliciting information and quotes from our electrical contractors. I value the expertise gathered here in this forum and also wanted to seek your input. (...and if you service the Pittsburgh area, send me a PM if you're interested in the following.)

The past weekend has been rough. Our power company had a line drop off a pole on Sunday (loose clamp resulted in arcing, and the line melted right off), and three-phase HVAC equipment doesn't work so well with only one leg. I arrived at our office in response to the power failure alarm and opened the breakers for our HVAC equipment.

The power company fixed the first problem and restored service. Well, now we have /two/ legs, but we need three! Turns out the first failure killed one of the transformers directly feeding our building.

Finally, after twelve hours, all repairs are made and we have three legs of power.

Our Liebert cooling system for the server room won't start. Four hours, a fuse and a relay switch later, and it's back running.

Yesterday, power went down and back up in a minute. The Liebert failed later that evening. The same fuse blown, and this time the control board is cooked.

We're looking at having improvements made to cut off power to the Liebert if single-phasing occurs, and to put surge arrestors in the main panel and all subpanels. (We currently only have a surge arrestor on the server room subpanel, with all ITE connected to a UPS.)

Questions:

1. Would single-phasing protection have been of help? What price range would you expect for this type of protection, either at the Liebert evaporator (which controls the consendor) or at our main panel? (400A, 3-phase.)

2. Would a surge arrestor on the main panel have been of help?

mdshunk

I'm very surprised that your Leibert unit doesn't have a phase monitor and an anti-short-cycle timer from the factory. It is certainly an option.

Your first Leibert unit failure was due to the phase loss, which could have been easily prevented with the installation of a 75 dollar phase monitor that would drop out the control power and shut the unit down.

Your second Leibert unit failure was probably due to the power "wink", and the unit fired right back up before the compressor pressures could equalize and it blew the fuse. The board probably fried because you were still getting counter EMF from the compressor slowing down when the utility power came back online. This probably made a wacky voltage spike when the unit tried to fire. This could have also been easily prevented with the insertion of a 20 dollar anti-short-cycle timer in the control circuit.

I'm not sure that a surge arrestor would have been of any benefit to you in this case, but while you're at it, it sure can't hurt. The money is probably pretty loose after such an incident, so go whole hog.

Three more controls that every commercial HVAC unit should have, unrelated to your present probelms, your unit may or may not have. High pressure switch, to dump the unit if the condenser gets dirty/blocked or if the condenser fan(s) stop. This will prevent frying the hermetic compressor or semi-hermetic compressor head. Low pressure switch, to dump the unit if the evaporator gets dirty/blocked or the evap fan stops. This will prevent icing of the evap coil which could flood the compressor with liquid and destroy the valves. Low ambient kit, to permit the unit to function at proper pressures (saving the compressor again) during colder months. Normally this is accomplished by cycling the condenser fans.

Beren

Believe me, you're not as surprised as I was.

The damage to the control board appeared to come from inside the unit (the board was visibly burned along traces next to a connector to another component, and not the power lead for the board itself).

Thanks for the info on the other three controls. I recall /references/ to those controls in the manual, but I will be darn sure to have their presence and proper operation verified.

Beren

Meant to ask: are there particular parts or manufacturer you'd recommend for the phase monitor and anti-short-cycle timer?

mdshunk

Everyone's phase monitor relays and anti short cycle timers are about the same, but I prefer the one's from SSAC purely on cost and my experience with them. They're darned good controls for the money. If your Leibert unit is fairly new, I'd recommend going with factory stuff, but if it's got some age on it, just do whatever.

Anti short cycle timer example: http://www.ssac.com/catalog/TL001A01.pdf

Phase monitor example: http://www.ssac.com/catalog/WVM02AL1.pdf

mdshunk

Just thought I should add that MARS and ICM Controls are two other companies who make nearly identical controls with a similar price point that provide equally effective service.

EDIT... the work you're asking about is on the borderline between what an electrician would do and what a HVAC man would do. I'd recommend that you hire a mechanical contractor rather than an electrician for this work. These matters you're discussing are more famaliar to an HVAC man than to an electrician, in my experience. I might have an unfair advantage, in that I also do a bit of HVAC controls work, which is unusual for the typical electrician.

mdshunk

Also, dont' expect very many contractors will be anxious to do this work for you. When I hear "data center" in the same sentence with "design build", I get scared off in a hurry. Contractors normally like an engineer involved with almost anything to do with a data center. You might have bumped into this in the past.