Mfg cut sheet or installer values for load calculations

[Fred B]

In sizing a service for new hvac heat pump, do you go by the mfg specifications for motor and heating loads or by an installer that claims it is a fraction of what the manufacturer's specifications state?

 

[David Castor]

You have to go by the nameplate data. and the NEC Just make sure it's clear what the minimum circuit amps are in the manufacturer's data. The installer will just point at you if there is any question on the feeder sizing.

 

[DrSparks]

In sizing a service for new hvac heat pump, do you go by the mfg specifications for motor and heating loads or by an installer that claims it is a fraction of what the manufacturer's specifications state?

I've run into this before. Heat pumps use refrigerant to heat under above zero temperatures. But they have supplemental resistive heating elements when it gets really cold. So what happens is, a tech will put an Amp clamp on the wires and see it's only drawing xx amps, but it's not running the heating elements.

Some heat pumps have multi stage supplemental heat too to further compound things.

Moral of the story: always go by nameplate FLA.

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[petersonra]

In sizing a service for new hvac heat pump, do you go by the mfg specifications for motor and heating loads or by an installer that claims it is a fraction of what the manufacturer's specifications state?

The manufacturer's specifications are supposed to be the worst case that you'll ever see. The installer is probably correct that you will never see worst case but you still have to account for it just in case it happens.

 

[Fred B]

You have to go by the nameplate data. and the NEC Just make sure it's clear what the minimum circuit amps are in the manufacturer's data. The installer will just point at you if there is any question on the feeder sizing.

That's what I thought. So here is why I ask.
This system that is being installed based on mfg specifications exceed the service by a lot. The 4 geo heat pumps and associated equipment based on cut sheet data is 214Amp, after reductions for non continuous and loads that will never operate at same time, and even after including these load into the residential calculation allowances only able to bring the added load to 176A. This is added to the existing 7600sqft house loads for which there is no historical data of peak demand. Everything added together indicates upping the 200amp service to a 400amp. (Technically I think is a 320Amp panel). The installer is claiming that it all can go on to the existing 200Amp service. Now the HO wants to forego the expense of upgrading due to the installers statement.
So I've already indicated I didn't believe that it was a good idea. Throughout the process as they originally was going to make the upgrade had been communicating with the POCO engineer who also reviewed the cut sheets to work out the service size and the new transformer they were going to install. Their opinion is this will not work on the existing service when I had to call to stop the process for new pole and xfer, he also stating that if this creates an issue on their system from this load that somebody will have to pay for damages.

The installer is trying to claim the entire system will only use 60-80A, now they only have one unit up because they wanted me to install another panel for their system and didn't. So I was there for some other work and metered the running system and had running load, not starting load, of 60Amps, not there are still 3 more pumps and another air source domestic hot water heater (1of 2) yet to go online. Cut sheets for just adding these is another 120A. Mfg specifications show the heat pumps each have a running load of 30.1A with a starting load with soft start of 40.8A the installer says that "no they only use 16A". With my test of 1 load opperating I tend to believe the mfg.

Is this as the POCO engineer alluded to a problem ready for making? If the system is overloaded by conservatively 100A how bad can it get on a 50yr old panel? It looks they are setting up to run the whole thing on a #4 Al SER cable.

 

[petersonra]

The panel is not going to care. The worst thing that might happen is a breaker will trip.

 

[David Castor]

The utility will do their own sizing calculations, but the service panel has to be sized per the NEC - Articles 220 and 230. It's common for the utility to size their service and transformers MUCH smaller than is required by the NEC, because based on experience they know the NEC load calculations are normally extremely conservative. But that doesn't change the NEC sizing requirements.

 

[Rock86]

What are the qualifications of the installer?? Are they an engineer who can give you a stamped and sealed document? Stand your ground... You're in the right.

 

[Fred B]

What are the qualifications of the installer?? Are they an engineer who can give you a stamped and sealed document? Stand your ground... You're in the right.

Don't really know his qualifications, he claimed to be mechanical engineer for heating/cooling system.
I was originally contacted to hook up power for the geothermal system for a customer I've worked for before. Contacted the installer and I told him for me to hook up electrical I need the specs on all that equipment going in, he never gave an issue and first he provided just a list of items and amperages. So called again for more info because what he gave totaled 214Amps, to find out if there were any loads that will not run concurrently, if motor loads were starting amp or running amp, was any soft starts being used, and if there was any auxiliary impedance heat added, because the loads he sent me was quite high. He seemed puzzled by the question. He said he wasn't sure on some of that so he was providing the cut sheets from the mfg.
After I got the cut sheets I asked if they did an electrical load calculation because my numbers were still too high for the 200Amp service, his response was "No we never do that, just size for heating and cooling requirements. He followed with "we've put in a lot of 2 pump systems in on 200 amp service and never had any issues". I asked if they ever did a 4 pump system in a 7600sq ft house. He said "no never that big, but a lot of 2 pump systems", he continued to say they've never had an issue before with electrical installation requirements. So I asked if there were any components that will not operate at the same time, the only thing mentioned was one of the well pumps, that they are stagered so that they will only one run at a time. Also the heat pumps will only one start at a time but all four may be running depending on heating cooling needs, after incorporating that I ran the numbers using that data it still was a lot over and was only to get the loads for the geo system down to 176Amps.
Add that into the 7600sqft existing dwelling load of 136Amps (calculated, actual demand load not available).
I just see all that fitting into a 200A service.

 

[Fred B]

The panel is not going to care. The worst thing that might happen is a breaker will trip.

This is an almost 50 yr old installation, and the main breaker like never replaced, have seen a lot of these old breakers not trip on overload as they are supposed to. Is there a reasonably easy method to "know" that the breaker will trip under the load that it is designed to trip at?

 

[DrSparks]

The panel is not going to care. The worst thing that might happen is a breaker will trip.

That's not the worst thing at at all. Yes the breaker will trip eventually, but the service wires will still suffer over time due heating, and the oxidized aluminum terminations may fail.

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[DrSparks]

The utility will do their own sizing calculations, but the service panel has to be sized per the NEC - Articles 220 and 230. It's common for the utility to size their service and transformers MUCH smaller than is required by the NEC, because based on experience they know the NEC load calculations are normally extremely conservative. But that doesn't change the NEC sizing requirements.

OH service drop also benefits from open air cooling.

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[DrSparks]

This is an almost 50 yr old installation, and the main breaker like never replaced, have seen a lot of these old breakers not trip on overload as they are supposed to. Is there a reasonably easy method to "know" that the breaker will trip under the load that it is designed to trip at?

You can use a breaker buster. But when I worked in industrial, we sent our frame breakers to a lab for testing, where it assume they use a fancy digitally controlled breaker buster. Mine was just a bunch of water heater elements in parallel that I could switch on one by one to increase the load. Even has a cooling fan to exhaust the heat. Not UL listed at all

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[kwired]

A heat pump that is operating in low temp extremes will draw less than in moderate temps.

Many will never draw what nameplate maximum says either.

That maximum on nameplate is the max the compressor is designed for, other installation factors may never allow it to reach that point, or at least without a malfunction factoring in there.

That said NEC still written that you sort of need to account for nameplate maximum load. One way around that is existing installs and use of demand history.

 

[electrofelon]

Seems that you did due diligence in asking for and computing things that would not run concurrently. One other thing to keep in mind, is if you have MCA figures off of equipment and you just add them up, you will be over counting for a feeder or service load because each MCA has an extra 25% on it where would you would only need 25% of the largest motor for feeder or service load. So that may buy you a little, but not all that much. I bet it will all be fine on a 200 amp service (HVAC usually draws 66% of MCA at full load in my experience, and most HVAC is oversized so wont run at full load ever or at least no very long). Sounds like it is probably is not code compliant however.