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Comment by beastie29a | Hacker News Reader

Ever since buying a house I've been engrossed in this topic along with indoor air-quality and mechanical HVAC systems. There's so much to know about these topics and I feel it helps when dealing with HVAC companies to make sure I'm getting what I want and not be price-gouged. One expert I follow on these topics is Allison Bailes, he has a blog entry on a similar topic of duct design[0]. I find his way of breaking down certain topics simple to follow and enjoy seeing how he's implemented his teachings in his own home.

[0] https://www.energyvanguard.com/blog/basic-principles-duct-de...

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The important part of good air shaft design is making them large enough to fit a squad of marines, and yet small enough not to fit biomechanoid xenomorphic invaders.

Isn't there also an important material selection choice to be made - your ducts (getting a bit Brazil about it) have got to be impervious to angry biomechanoid xenomorphs who can smash through thick steel doors but also easy enough to cut and weld with small handheld tools?

This is known as the "Die Hard Aliens Problem"

Bonus topic near and dear to my heart: Ducting design is a biggie, but a neglected issue, and the biggest sin I see in residential HVAC, is ignoring a design's peak heating or cooling energy demands and installing oversized heat pumps.

The bigger is better mentality in that area results in (sometimes dramatically) shorter run cycles with an unnecessarily large compressor. It's not good for your electric bill or the equipment, and you get a monster motor dimming your lights every 10 minutes.

If I had a dollar for every time an HVAC contractor offered me a quote including an upgrade option for a heat pump three times larger than is needed...

> I feel it helps when dealing with HVAC companies to make sure I'm getting what I want and not be price-gouged.

Indeed. I've got a crew replacing my coils & dehumidifier as I type this.

If I didn't know what I know about HVAC, the sales rep I worked with yesterday would have absolutely taken me for a ride.

Many of the initial questions they ask you when they get to your home are intended to gauge your ability to call out their bullshit.

Why not get some indoor sensors and DIY? I’m planning to install an ERV and a whole home dehumidifier to see if I can get that ideal indoor air quality.

I can't help but think HVAC is the perfect industry for the limited AI we have right now... it just need to hit a sweet spot of relative humidity and temperature, with constraints given by the assets you have and its' performance envelope given input from mixture of indoor/outdoor air..

but right now HVAC industry is treating relative humidity like some ultimate luxury tier item..

Terra Bloom has 4/6/8" EC duct fans that can be controlled by wired/wireless remotes and DIY MCU/RPi via PWM, including a tachometer readout of actual fan speed, https://terra-bloom.com/blogs/news/how-to-choose-a-fan-speed... & https://github.com/albahmed23/terrabloom_ec_fans.

PID and other basics of control theory have been around for ages, they're just not used in residential HVAC. Perhaps the limiting factor has been the traditional split system with only on and off states. As we move towards variable speed compressors and fans, we may see more intelligent controls. Maybe an AI can help tune the control constants?

Maybe because relative humidity is more expensive to control? in an ideal case it's just moving and mixing different levels of air temperature and humidity, but in reality you need to de-humidify or add humidity

I found it inordinately difficult to get humidity to a stable point in Canadian winters, because practically no homes are designed with relative humidity in mind.

Houses are designed to control/shed moisture, not control humidity.

It's fairly inexpensive get a standalone dehumidifier and just set a humidity target.

A house usually has several rooms. And in Canada humidification demands are much higher in wintertime then dehumidification in summertime.

So your looking at literally dozens of humidifiers and dehumidifiers to maintain the optimal 40% to 60% range at all times in the average sized house.

A lot of it is managing the air barriers (not vapor barriers!) and sealing the house to prevent air leaks.

But if you're concerned about air quality there are some major things you can attack first - water heater being electric or forced-vent, furnace being forced vent, etc.

The less "burning" inside the house the better off you'll be to start.

Instrument things and DIY to tune, but start from Passivhaus standards. There's a ton of great developments on ERVs and insulation that could use more attention in the US.

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