Hacker News Reader

Comment by jonhohle | Hacker News Reader

Others have made the comment about lower current requirements at high voltage, but from a maintenance perspective, that $20 capacitor is a common failure part. Calling an HVAC repair company to diagnosis, parts, and labor it costs around $200 for anyone not electrically minded. Over the life of an AC unit, starter/run caps might have to replaced twice.

Even if an extra conductor in the line was a few hundred dollars, I’d rather have one less common failure point. In AZ AC is effectively required in the summer. AC outages are similar to winter furnace outages in northern areas. I have extra caps ready to deploy (we lose a cap about every 3 years across multiple units) but have never needed to unexpectedly replace copper.

View on HN

Don't more modern AC units use VFDs that can run the compressor at arbitrary speeds, which is an improvement over both fixed 3 phase power and a starter capacitor? Maybe this tech hasn't made it into the house-sized units yet, though.

It was only present on the high end when we were replacing our system in 2021.

I just replaced one of my two HVAC units with a variable speed compressor. It cost a lot more than the single or 2 stage units but it is more comfortable, uses less electricity, and runs at "low" to dehumidify longer.

Unfortunately these more modern units are still stupid expensive (in the US) compared to the older style. Unclear why; probably some sort of shenanigans with the HVAC manufacturing companies.

Little variable-speed units sold as ductless minisplits are fairly inexpensive in the US. They’re especially reasonable if you actually use them in a ductless configuration, because you don’t have to install ducts.

The fact that they might have a higher list price than a conventional single-speed outdoor unit and indoor evaporator coil is a red herring, as the conventional units can’t do anything on their own, and they need a furnace and a fan added to be useful.

VFDs / "inverters" are happier on 3 phase as well, because the input rectifier caps can be much smaller. Whereas with single phase they have to be large enough to store energy for riding out the zero crossings of low power delivery.

My point isn't that the single individual wire to your HVAC is $100 vs. a $20 cap, though. There is likely hundreds or thousands of dollars of additional infrastructure needed to handle 3-phase input to a house. You have breakers, busbars, the transformer into the house is different, and on and on.

I agree that less failure points is nice, however you have to consider the tradeoff. Is it worth $100? Probably. What about $1000? $2000? If it's $2000, why not just get a more efficient inverter based one, which doesn't have a starter cap in the first place?

> There is likely hundreds or thousands of dollars of additional infrastructure needed to handle 3-phase input to a house. You have breakers, busbars, the transformer into the house is different, and on and on.

Split-phase system and 110V are currently more expensive in term of infrastructure.

The distribution itself is done in 3-phases power, even in the US. The conversion to 110V and split phase is done in the last mile as close as possible to the termination point to limit losses. You have to have tiny power transformers everywhere and this has a significant cost.

At the opposite, end-to-end 400V three phases system requires to have only one large transformer by Area. Generally directly connected to High Voltage (20KV in Europe).

This isn't any different in the US vs. in Europe. Split phase is done at the last mile, just as it ought to be done in Europe for 3 phase power. I highly doubt entire neighborhoods or districts are serviced with a single extremely large 400V 3-phase transformer in Europe.

Standalone houses usually have multiple houses connected to one single transformer. How much depends on density of the houses. For apartment buildings and other dense power needs, there's high voltage directly into the complex, then it's stepped down within the complex to meet the needs.

US distribution transformers are around 50 kVA, in the EU they are more like 300-1000 kVA, so they can power 10-20x more homes per transformer.

Instead of those little pole-mounted transformers that are common in the US, we have one of these buildings with a large transformer for each neighborhood https://dms-cf-08.dimu.org/image/032ykUus1ixX?dimension=1200...

https://electrical-engineering-portal.com/north-american-ver...

Very interesting. Seems like that works much better as the power demand per house in the EU is lower, and the higher voltage gives you a bit more leeway. Frankly, I would be concerned about voltage drop for the far houses... even 400V is going to have some pretty beefy voltage drop under load unless the conductors are enormous.

> I highly doubt entire neighborhoods or districts are serviced with a single extremely large 400V 3-phase transformer in Europe.

They do currently.

I can at talk for the French and Swiss system.

- Entire neighbourhood are served by a single 400V 3-phase transformer.

- For critical infrastructure, you do have sometimes two transformers in redundancy on the same local loop in case of failure on one.

There is no need for the pole type of transformer everywhere in the street with double layers of cable like in Japan or in the US.

One note regarding the pole transformers: in many parts of the US they've migrated to underground cabling and larger transformers. My neighborhood has that, and we have about 1 transformer every 4 houses or so. No idea how big the transformer is from a kVA rating, but pretty much every house has 240V/200A service, so they must be pretty large. The transformers themselves are approximately 3' x 3' x 3' and enclosed in a box at the front of certain yards.

> My neighborhood has that, and we have about 1 transformer every 4 houses or so.

You might find that interesting:

https://data.enedis.fr/pages/cartographie-des-reseaux-conten...

This map references all transformers and distribution lines for the french network nationwide for terminal loops. These are open data: Enedis is a the public operator.

"Poste" is the French Jargon for transformer. BT is for low voltage. HT is for anything >1000V.

Like you will see yourself, the density of transformer is of the order of 10x less than in the US/Japanese model.

Just had to have my apartment's AC capacitor replaced last week.

Reply on news.ycombinator.com