Comment by briHass | Hacker News Reader

Comment by briHass | Hacker News Reader

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Would've loved to see a different approach to the typical refrigerant-split units. I'm EPA certified, and do my own heat pump work, but something that could really blow up the heat pump space would be a closed-loop refrigerant system that uses water lines to the indoor coil/air handler. This would make the system a true DIY self-install, since you'd never be messing with refrigerant loops.

The indoor coil/AH could be made as lightweight and small as possible (or multiple configurations) so it could easily be installed by a DIYer or a handyman for extremely low cost using insulated PEX lines for the water with basic tools. The outdoor unit would be heavy and require an electrical circuit, but would otherwise be as easy as swapping a window-unit AC.

Just like with solar, the biggest problem with adoption of heat pumps is labor cost to install. The units themselves are shockingly cheap (and continuously getting cheaper), but labor adds 3-4X the cost of the unit itself. The certification, tools, and knowledge to handle the refrigerant is the 'secret sauce' used by HVAC companies to keep prices high. Imagine how few people would have window AC units or refrigerators if they needed to be installed by an HVAC company that wanted to make $300/hr to install.

> something that could really blow up the heat pump space would be a closed-loop refrigerant system that uses water lines to the indoor coil/air handler.

Add in hot water heating and storage, and that's basically what Harvest Thermal is doing:

https://www.harvest-thermal.com/product

They even use an off-the-shelf heat pump compressor (SanCO2) that as the name implies, uses CO2 as a refrigerant. It's a pricey compressor though.

Thanks for the link; I hadn't heard of them before. I can absolutely see a system similar to this being the future. With an additional water loop, when running in 'AC/cooling mode', the waste heat could be captured for the domestic hot water tank as well.

As with solar, energy/heat storage is likely to be an important component of the solution. Even without TOU rates, areas like mine (Mid-Atlantic) can hit temps at night that start to tax heat pumps (low teens F). However, the next day will often be above freezing and sunny. The HP could 'bank' available heat during the day to handle the late-night chill.

It's a different but valid approach. You still need a pump station and someone comfortable with hydronic loop install/fittings. Some areas also ban PEX. Northeast is definitely the place to do this, as there is way more hydronic knowledge than other parts of the US. System efficiency takes a hit because the secondary water loop adds more lift to the heat pump.

Absolutely this. 3-4x? Sibling of mine just had a minisplit installed where the unit was probably $4-$5k and the total was north of $24k.

A sealed water loop where any plumber and most DIYers could manage would be miles ahead in both reliability and accessibility.

Good point; I forgot to mention the reliability/environmental aspect as well. Most DIY, and even pro installs, of mini splits fail due to leaking flare connections, which must be made in the field. Modern refrigerants operate at very high (400+ PSI) pressures, and getting a perfect seal is critical. Having the entire refidgerant loop sealed and tested at the factory significantly decrease the common issues and prevents dumping climate-harmful gasses into the atmosphere.

Even with more reliable brazed connections, modern heat pumps are very sensitive to contamination of the refrigerant lines. Brazing must be done with utmost care not to overheat the copper, and nitrogen gas needs to flow through the pipe at specific volumes to prevent carbon deposits that can decrease the longevity of the system. Any damage caused by improper brazing is largely invisible (inside the pipe) and the process is time consuming and precise; in exact opposition to the incentives an HVAC installer to get it done quickly.

Though somewhat controversial, ZoomLock also seems promising. Agreed though, there are obvious benefits to having a fully factory sealed refrigerant loop.

I'll wait for more reliability data on ZoomLock, but it could easily prove to be the optimal solution. Unfortunately, it doesn't help the DIYer, because the crimping tools are outrageously expensive, and clearly aimed at a pro doing enough installs to make the time-savings worth it.

there are diy systems with threaded connectors, pre-vacuumed units and linesets filled with refrigerants.

True, but those linesets introduce other downsides. They can't be cut to length, so you often have to have unsightly loops of extra line set somewhere, and the loops can potentially trap the oils that mix with the refrigerant to lubricate the compressor. They're also much more expensive, and anecdotally, I've heard of leaks from over/under tightening the threaded connections.

Not to mention, installing them without an EPA 608 certification is technically illegal. MrCool and others that use them are relying on the EPA being understaffed and unlikely to pursue homeowners, but their stance on it is perfectly clear:

"Is technician certification required to install an R-410A mini-split?

Yes. Adding or removing refrigerant from a mini-split as part of installation, and/or connecting or disconnecting hoses or pre-charged lines requires a section 608 technician certification. Activities reasonably expected to violate the integrity of the refrigerant circuit include but are not limited to: Attaching or detaching hoses and gauges to and from the appliance; adding or removing refrigerant; adding or removing components; and cutting the refrigerant line."

https://www.epa.gov/section608/epas-refrigerant-management-p...

>True, but those linesets introduce other downsides. They can't be cut to length, so you often have to have unsightly loops of extra line set somewhere, and the loops can potentially trap the oils that mix with the refrigerant to lubricate the compressor.

well, i run my through crawlspace. had only a small extra loop. in crawlspace.

>They're also much more expensive,

per unit - yes. but... if you doing to diy mini-split not with precharged lineste, you need vacuum, refrigerant and probably license to buy it. it raises cost and make it viable if you plant to install multiple units (have coworkers that did it). if you want to get it professionally install, than in addition to ~$1.4k for 2ton unit you look into $6k-$8k for labor. Those were prices year ago for install in garage with 240v line connected to 40amp breaker available at install location.

>Not to mention, installing them without an EPA 608 certification is technically illegal.

technically, i guess much of the work done by home owners must be done by certified professionals and get approvals and inspections.

a closed-loop refrigerant system that uses water lines to the indoor coil/air handler

Sounds like an air to water monoblock heat pump. Common in Europe. But you can only get the water up to about 50C efficiently. Not as good as refrigerant. So you need a large radiator to get the heat out into the room. Using wet underfloor heating as a giant emmitter works well. But otherwise it makes them tricky.

Some people are trying for minisplits with propane in the lines which is not a greenhouse gas so they hope anyone will be able to install it without a licence.

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