Heat Pump Failure (who's fault?)

[derekk]

Hello.

I am both and electrical engineer and contractor. We were recently installing a generator in a large building and disconnected power to one of the server rooms (as part of a scheduled shutdown). My crew disconnected all the panels feeding this room and shut off the fan coil unit (FCU) serving this area. However, the exterior heat pump (which was paired with this FCU is located several floors below) was not turned off. Total power outage was approximately 6 hrs. The compressor in the heat pump failed as a result of this shutdown (to the interior FCU). The units were about 2-3 years old and the manufacturer agreed to replace the compressor itself under warranty, but the building wants us to cover the ~$10k of labor and misc. materials required to install it, flush the lines, etc.

We've installed hundreds of HVAC systems (and I've designed the electrical supply to several myself). I've never seen an electrical interlock between exterior and interior split system components (except in the larger or BMS controlled units) - not including those like the Mitsu's where one unit feeds the other. In this case, there are only thermostat wires run along with the lineset. My question is, should I be designing some type of interlock system so that the exterior unit will shut down in the event that the FCU fails? There are many reasons this could happen including a seized fan, belt tear, breaker failure, shunt trip, someone simply shutting down the unit, etc.

I had always assumed that the pressure switches integral to all modern heat pumps/AC units would shut down the system in the event that airflow was compromised in the FCU (probably the low pressure would trip first as the evaporator starts to ice up). Also, most modern compressors have heat sensors and other protective devices. With this particular manufacturer, the thermostat transformer is located in the exterior unit, but the wiring goes through the FCU before the thermostat, so it would be very easy to install a relay which would shut down the thermostat in the event the FCU lost power.

Any comments or siggestions? Thanks in advance.

 

[LarryFine]

My question is, should I be designing some type of interlock system so that the exterior unit will shut down in the event that the FCU fails?

If the compressor unit can be damaged by such an event, why doesn't the manufacturer include such an interlock, and/or make a warning known to the HVAC installer to include such?

That's what I'd pose to the manufacturer. I'd take the stance that the lack of a built-in interlock, or at least an obvious note to the installer, makes the damage the manufacturer's liability.

 

[ptonsparky]

Been a few years but high pressure cutouts would fail often enough. I would think that if I can set up 50 motors to interlock with each other you can certainly manage an a/c unit. My advantage is that I do not have to be low bid. Hi end residential units talk with each other via a two wire thermostat cable. Surely a large commercial unit can do the same.

 

[LarryFine]

Surely a large commercial unit can do the same.

Yes, they can, and don't call me . . . well, you know.

 

[__dan]

slogging liquid

slogging liquid

The compressor may have slogged liquid. Some liquid passed through the expansion coil with the fan off and returned through the gas suction line. The compressor tried to compress the liquid.

Just venturing a guess why the compressor failed. I certainly would not voluteer to pay for it or volunteer to guess as to what caused the failure. There are plenty of liable parties in line ahead of you. Where or what are the safety limits on the machine for this, where was the building engineer for the shutdown, what does the contract say, was the shutdown sequence of operations discussed and approved in advance, does your contract price include a contingency for unforseen damages arising from the shutdown. Lots of guys would play dumb and depend on their short memories.

Generally you as the contractor can be liable for conditions known in advance but are not liable for conditions discovered at a later date, conditions that cannot be forseen until discovered ... It's a grey area, not a black and white claim. The greyness can work in your favor as does diplomacy, schmoozing. Ultimately, the owner is first in line as the responsible party who provides the conditions you work under. Futher investigation is necessary, were the required safety limits installed and working.

 

[mtfallsmikey]

High pressure switch on the condensing unit should have caught this condition and tripped......my tenant's contracor just installed a 7 ton supplemental WSHP in an area, AHJ made them put an interlock on the unit to keep it from running when my base building unit was on...

 

[adelle]

Was this a computer room or technical space HVAC unit? Or was it residential junk being forced into commercial service?

A professional computer room grade HVAC unit would have built in protections like high head pressure cutoff. In fact I woould expect it to see the power loss to the FUA and shut down. As we know residential and light commercial stuff does not heave these features due to "build to cost".

So if they were using a non computer room rated HVAC unit, then what do they expect?

P.S. Just remembered that even residental units get the contactor voltage from the FAU. So kill power to that and the condensing unit should drop out automatically.

 

[Dennis Alwon]

I am very surprised that an outdoor unit would run without any protection. In almost all resi. units the transformer is in the inside air handling unit. You shut it down and the compressor cannot run.

So, let's suppose the air handler burned out during the evening hours and wasn't discovered for 6 hours or more. Does that mean the outdoor unit would have burned up. If so, that is one poorly designed system.

 

[Dennis Alwon]

Bump.--- I posted to this thread and the thread did not move to the top-- we'll see if this works.

 

[Electric-Light]

That's something you need to take it up with your insurance company and/or attorney.

Bath tubs have a drain. Suppose you went to a hotel, started filling the tub up, then you got a call from a friend to meet him at the bar. You forgot to turn off the water and caused a substantial water damage.

It flooded big time, because the over-flow drainage was not maintained to proper operation.

If the over-flow drain was not clogged, it wouldn't have overflowed.
If you didn't forget to turn off the water, it wouldn't have overflowed.

Was there a sufficient proximate cause? for a hotel, it's reasonably foreseeable that such forgetfulness occur and its also reasonably foreseen by guests that everything in the room will be maintained properly.

You'll need to have an attorney figure out the calculus of negligence.

 

[Electric-Light]

I personally think that there was deficiency in performing duty of care on your side.

If you were driving 55mph on a rural stretch of road with very clear view of what's ahead and you crashed into a UPS truck that was improperly parked and extending into the right of way, but you were not paying attention.

Sure, the truck shouldn't have been there, but given the view was clear and the reason you crashed is that you were inattentive, it doesn't absolve you from the duty to pay attention while driving.

 

[Electric-Light]

last post isn't showing up... test test

 

[derekk]

The units were commercial. A York EA series 10-ton heat pump and matching FA series fan coil unit. Turning over something like this to our attorney or insurance company is always a last resort.

This morning I was informed by the mechanical contractor that the compressor "went to ground" and that was the reason for the failure. We makes me angry is that the unit has:

1) Low and high pressure sensors that should trip the heat pump (either or both should go off if the FCU is shut down for an extended perioid of time)
2) A temp sensor on the liqud side (which also could trip as the temp will rise as the flow through the evaporator starts to constrict)
3) Internal protection at the compressor itself against excessive current and temperature

and yet none of these devices managed to shut down the unit before the compressor was damaged.

In hindsight we probably should have had the bulding mechanical contractor onsite during this shutdown (even if only for insurance), but I've got to believe it is not something that would occur to everyone.

For the poster who's AHJ required an interlock. What form did this take? Were the line voltage disconnects interlocked? Or did they use the control wiring?

 

[derekk]

To Electric Light, I'm not completely disagreeing with your "duty of care" argument.

However, losing a fan unit is something that can happen easily, for many different reasons - the most likely being a fan belt tear. That is essentially what we simulated by turning off power for 6 hours. I'm trying to determine if the liklihood of something like this repeating itself is high enough that I should include some type of interlock in my future electrical designs for split-systems. This particular system was existing and not my design. If we are going to accept some blame here, I want to make damn sure that the same thing doesn't happen again and if I need to interlock the equipment I will.

 

[__dan]

the compressor "went to ground" and that was the reason for the failure.

I don't buy it, saying it 'went to ground' sounds like something to say to a clueless person to make it sound like an electrical problem. What went to ground, the control circuit?, the line feed?, the motor winding? I'm sure an immediate challenge would look like an immediate insult. If I thought I was geting BS'd at that point I would keep repeating the key words "unforseeable", ''mechanical problem" and "supposed to have safety limit trip".

You cannot pay the claim, payment is acceptance of liability, your insurance agent will tell you this. You may have no choice but to send notice to your insurance company of possible damage claim along with your opinion "not at fault" and discuss with a good attorney. Then you can play middleman and ask politely for the damaged compressor for your third party testing. Chances are all parties will have a low appetite for fighting over it and the bill will get stuck with the weakest link, not the deserving party. The weak link will be the guy without a lawyer. It could be one of those things, if it drags on for a year or two they will forget about the claim but not forget about the invoice.

With the compressor floors lower than the expansion coil, any refrierant liquid passing through the DX coil falls down the gas suction line riser, liquid falls and gas in the line rises, and it's likely the compressor slogged the liquid causing immediate damage. If the reverse were true and the compressor was floors above the DX coil, liquid passing through the coil would have an impossible time filling the riser entirely with liquid sufficient to send liquid into the compressor gas suction side. There would be gas and liquid seperation in the riser with gas coming into the compressor (for a while).

Slogging liquid is a factor of not having the right safety devices or proving limit switches. I am not familiar if there is a specific safety limit trip for this. The factor of the compressor much lower than the DX coil and gas liquid seperation in the riser sending liquid to the compressor, that obviously sounds like a plumbing, mechanical design problem. "Unforseeable" from an electrical point of view.

I've seen compressors slog liquid twice and the damage was immediate. Both times there were two or three licensed refrigeration people right there doing doing startup - equipment swap - new install. First time I saw it we were starting up a Liebert chiller that made chilled glycol for the IBM 3090 mainframe processor board. The guys were bump running it and adding the initial refrigerant fill. I heard it chatter and they had to replace the compressor under warranty.

 

[SAC]

If you were at fault, why would the manufacturer replace the unit under warranty? Clearly they thought the unit malfunction was not a result of operating conditions beyond for which it was designed. But I guess it is also possible that they didn't have the full information?

 

[Mgraw]

I don't buy it, saying it 'went to ground' sounds like something to say to a clueless person to make it sound like an electrical problem. What went to ground, the control circuit?, the line feed?, the motor winding? I'm sure an immediate challenge would look like an immediate insult. If I thought I was geting BS'd at that point I would keep repeating the key words "unforseeable", ''mechanical problem" and "supposed to have safety limit trip".

You cannot pay the claim, payment is acceptance of liability, your insurance agent will tell you this. You may have no choice but to send notice to your insurance company of possible damage claim along with your opinion "not at fault" and discuss with a good attorney. Then you can play middleman and ask politely for the damaged compressor for your third party testing. Chances are all parties will have a low appetite for fighting over it and the bill will get stuck with the weakest link, not the deserving party. The weak link will be the guy without a lawyer. It could be one of those things, if it drags on for a year or two they will forget about the claim but not forget about the invoice.

With the compressor floors lower than the expansion coil, any refrierant liquid passing through the DX coil falls down the gas suction line riser, liquid falls and gas in the line rises, and it's likely the compressor slogged the liquid causing immediate damage. If the reverse were true and the compressor was floors above the DX coil, liquid passing through the coil would have an impossible time filling the riser entirely with liquid sufficient to send liquid into the compressor gas suction side. There would be gas and liquid seperation in the riser with gas coming into the compressor (for a while).

Slogging liquid is a factor of not having the right safety devices or proving limit switches. I am not familiar if there is a specific safety limit trip for this. The factor of the compressor much lower than the DX coil and gas liquid seperation in the riser sending liquid to the compressor, that obviously sounds like a plumbing, mechanical design problem. "Unforseeable" from an electrical point of view.

I've seen compressors slog liquid twice and the damage was immediate. Both times there were two or three licensed refrigeration people right there doing doing startup - equipment swap - new install. First time I saw it we were starting up a Liebert chiller that made chilled glycol for the IBM 3090 mainframe processor board. The guys were bump running it and adding the initial refrigerant fill. I heard it chatter and they had to replace the compressor under warranty.

HUH? "went to ground" is a common HVAC slag. It usually is caused by the stator touching the winding which is usually caused by one or both of the motor bearings failing. Bearings failing is usually caused by lack of oil in the compressor. Lack of oil in the compressor is usually caused by liquid refrigerant "flooding back" to the compressor. I have seen liquid "flooding back" hundreds of times, most of the time the compressors are OK.
The setup the OP stated is common. The best way I have found to prevent the compressor from running when the blower is not is to use a sail switch.

 

[Profish00]

Why is a system designed to burn up, what if the breaker tripped? They are taking you for a ride.

My house unit wont even work if the fain don't come on.

 

[Mgraw]

Why is a system designed to burn up, what if the breaker tripped? They are taking you for a ride.

My house unit wont even work if the fain don't come on.

Actually that depends on why the fan is not on. If the unit is calling for cool and the blower motor is bad the compressor will run, at least for a while.
As with most things you get what you pay for. If you want the cheapest price you will get the cheapest unit. If you want the top of the line unit then you need to pay for the top of the line.

 

[Profish00]

Actually that depends on why the fan is not on. If the unit is calling for cool and the blower motor is bad the compressor will run, at least for a while.
As with most things you get what you pay for. If you want the cheapest price you will get the cheapest unit. If you want the top of the line unit then you need to pay for the top of the line.

My cheap lennox 3 ton unit will/should turn off on high head pressure. or burn up and go to ground. case closed