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Duct Size vs. Airflow (2012)

russellking.me

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Re: Duct Size vs. Airflow (2012)

#11

Post by TEP_Kim_Il_Sung »

beastie29a wrote: post #2

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 dow…

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.

Re: Duct Size vs. Airflow (2012)

#12

Post by 2rsf »

londons_explore wrote: post #8

All this assumes airflow to every room all the time. But in real systems, you only want airflow to rooms with people in. And in a residential setting, you can be fairly sure that won't be all rooms at once. Which means ducts can be sized differently, as long as you have sensor vents on the end of each.

You shouldn't stop flow to unused rooms, maybe limit or reduce but not stop. You don't want too high/low humidity or temperatures in one room.

Re: Duct Size vs. Airflow (2012)

#13

Post by 2rsf »

alliao wrote: post #9
turtlebits wrote: post #6

Earlier quoted context omitted.

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..

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

Re: Duct Size vs. Airflow (2012)

#14

Post by londons_explore »

2rsf wrote: post #12
londons_explore wrote: post #8

All this assumes airflow to every room all the time. But in real systems, you only want airflow to rooms with people in. And in a residential setting, you can be fairly sure that won't be all rooms at once. Which means ducts can be sized differently, as long as you have sensor vents on the end of each.

You shouldn't stop flow to unused rooms, maybe limit or reduce but not stop. You don't want too high/low humidity or temperatures in one room.

Well that's what the sensors are for...

I like to have CO2+humidity+temperature sensors in each room, and then when any go out of an allowable range you open the vent.

I sometimes also install PM2.5 sensors hooked up to the vent because unattended cooking or toasters can make a lot of PM2.5 and not much of anything else.

Also obviously you want the vent to open proportionally to how in-range the measurements are, otherwise you end up with a vent opening and closing every 5 minutes all day long which is very annoying.

Re: Duct Size vs. Airflow (2012)

#16

Post by MengerSponge »

turtlebits wrote: post #6
beastie29a wrote: post #2

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 dow…

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.

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.

Re: Duct Size vs. Airflow (2012)

#17

Post by 2rsf »

londons_explore wrote: post #14
2rsf wrote: post #12

Earlier quoted context omitted.

You shouldn't stop flow to unused rooms, maybe limit or reduce but not stop. You don't want too high/low humidity or temperatures in one room.

Well that's what the sensors are for... I like to have CO2+humidity+temperature sensors in each room, and then when any go out of an allowable range you open the vent. I sometimes also install PM2.5 sensors hooked up to the vent because unattended cooking or toasters can make a lot of PM2.5 and not much of anything else. Also obviously you want the vent to open proportionally to how in-range the measurements are, oth…

I saw a Swedish "dream house" TV series where someone installed something like that, it cost a small fortune and I don't see the big benefit in it compared to "normal" mechanical ventilation, maybe with heat recovery.

Re: Duct Size vs. Airflow (2012)

#18

Post by arethuza »

TEP_Kim_Il_Sung wrote: post #11
beastie29a wrote: post #2

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 dow…

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?

Re: Duct Size vs. Airflow (2012)

#19

Post by londons_explore »

2rsf wrote: post #17
londons_explore wrote: post #14

Earlier quoted context omitted.

Well that's what the sensors are for... I like to have CO2+humidity+temperature sensors in each room, and then when any go out of an allowable range you open the vent. I sometimes also install PM2.5 sensors hooked up to the vent because unattended cooking or toasters can make a lot of PM2.5 and not much of anything else. Also obviously you want the vent to open proportionally to how in-range the measurements are, oth…

I saw a Swedish "dream house" TV series where someone installed something like that, it cost a small fortune and I don't see the big benefit in it compared to "normal" mechanical ventilation, maybe with heat recovery.

The big benefit is that heat recovery units only recover ~80% of the heat.

And if you want really good air quality in a room, you want 10 air changes per hour or so.

So, that means you are losing 20% of the heat in the air every 6 minutes. If you're doing this in the UK with gas heating and outdoor air of 0C, indoor air of 20C, a 2500 square foot average house and 9 foot ceilings, then it costs a whopping £14/day to heat just the heat lost in the heat recovery unit.

Considering that you can buy a CO2+temp+humidity sensor for £15, and then only use as much air as is actually needed for the occupants of the house, you can normally reduce this by 90% typically - saving £4000 per year - well worth it for £100 of sensors.

Math: https://www.google.com/search?q=700+J+%2F+kg+%2F+Kelvin+*1.2...

Re: Duct Size vs. Airflow (2012)

#20

Post by bombcar »

turtlebits wrote: post #6
beastie29a wrote: post #2

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 dow…

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.

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.

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