Comment by Animats | Hacker News Reader

Comment by Animats | Hacker News Reader

Everybody seems to agree that installation costs way too much.

There's a few parts to this. Everything has to be carefully sized - power, pipe sizes, unit locations. You need to put a house's thermal profile (how much heat loss, how much air leak, how much thermal mass) along with the regional thermal profile into an engineering calculation which computes what you need.

Thermographic inspections are a thing.[1] Usual price is around $400. They're not very standardized. You get IR images of a house, which is good for finding leaks but not quantitative enough to size a heating and cooling plant.

This would be a great drone application. Fly over and around the house. Build a 3D model of the house and paint heat loss on top of it. Crunch on data to get the engineering info needed to correctly size HVAC. Also discover big heat leak points. Turn this from experienced guessing into measurement.

Then submit that data sheet to multiple sites that offer heat pumps.

Startup opportunity here.

[1] https://www.energy.gov/energysaver/thermographic-inspections

I would argue that accurate sizing is not that important as labor constitutes the bulk of the cost. My total bill was about $20K and going for 30% less capacity would net about $19K so its easier just to go for the maximum. Calling in an IR imaging drone would certainly cost more than the potential savings from accurate sizing.

Unlike gas furnaces which basically can only do ON or OFF, heat pumps can regulate the heat with much higher granularity.

What certainly calls for innovation is managing the labor costs. In my case installation involved way too many people and way too many visits.

Reducing labor costs is hard.

For commercial applications, modular/off-site builds are a way to reduce labor costs. Yet, homes design are so fragmented that it's hard to build something plug-n-play.

Isn’t it important to right-size non-heat-pump installs anyway? Too large a system causes short cycling, humidity problems, temperature swings. I have read installers habitually guesstimate over size to over charge (rather than do the proper calculations).

The reality is that this is all solving a problem that people don’t have.

Forced air is a terrible way to heat a building yet thats how most homes are heated, and it is good enough for most people.

If you perfectly size a furnace for the coldest days of the year, it is now oversized for the other 90% of days.

The cheapest way is to install a multi stage heating/cooling system that works on first stage most of the time, and second when it needs to, like having 2 small furnaces. This passes the ‘good enough’ test for the vast majority of homeowners.

Are you just referring to a two-stage AC/furnace?

They oversize because customers who have an oversized system generally don’t complain but customers who have an undersized system definitely will complain when it can’t get to and hold their desired temperature.

This wouldn't work, unfortunately. A lot of insulation has a reflective layer yielding invalid readings from thermal imaging.

There are several other factors like air tightness which requires a blower door to measure and even the number of elbows in the duct system could have an effect. It's a surprisingly complex field. You wouldn't gain anything over a traditional home energy auditor.

The real opportunity is to scrap everything and rethink the system from scratch.

>There's a few parts to this. Everything has to be carefully sized - power, pipe sizes, unit locations.

No. Not even in the slightest. A two bit could make conservative guesses or work off a conservatively spec'd sizing table and then deal with the resulting excess capacity with controls/distribution.

Whether it's a sewer line or a hvac system or retaining wall it's the same stupid situation. The only reason that we do calculated minimum-ish sizing for all this stuff is because if you're being screwed by law into paying to make work for a credentialed professional you might as well make them save you money on the rest of it so that you're only getting screwed out of $0.95 on the dollar instead of $1 on the dollar instead.

or you could, you know, wing-it, like they do overseas, and I tell you, the world does not end.

You're better off guesstimating yourself than trusting contractors. The contractors are incentivized to severely oversize any AC units they install or else people leave bad reviews on their pages/listings when the installed unit can't keep up the one day every two years that the temperature gets abnormally hot.

I did this myself and insisted on a unit half the capacity that the contractors wanted. Several flat-out refused. But it works perfectly! Approximately one day ever two years it can't keep up. Which means that all the other time it doesn't short-cycle. Perfect.

I had to replace my home HVAC system this year and went with a variable speed system. It was eye-wateringly expensive, but it works much much much better than the system that was in here before, and completely obviated my concerns about sizing (the old system was an oversized single-stage unit, and the house always stayed cooled, but something or other was regularly breaking, probably due to the short-cycling).

With the new system, electricity consumption on a hot summer day is about a third of the prior system, it’s virtually silent and the comfort of the house (due to more granular temperature control and near-constant dehumidification) is substantially better.

That's fine for mini-split pairs. Whole house systems need more engineering.

Reply on news.ycombinator.com