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Duct Size vs. Airflow (2012)

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Re: Duct Size vs. Airflow (2012)

#21

Post by walterbell »

londons_explore wrote: post #19
2rsf wrote: post #17

Earlier quoted context omitted.

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…

Is there a good ERV design that is suitable for one room, e.g. the ERV equivalent of a window air conditioner?

Re: Duct Size vs. Airflow (2012)

#22

Post by thedougd »

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..

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?

Re: Duct Size vs. Airflow (2012)

#23

Post by Retric »

londons_explore wrote: post #19
2rsf wrote: post #17

Earlier quoted context omitted.

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…

You also don’t gain anything by only exchanging outside air with one room.

Let’s assume people are willing to let indoor CO2 levels reach X PPM over outside air in a room with N people that takes say 1,000 cubic feet per minute to maintain. The same number of people in a room 50x times as large still takes the same 1,000 cubic feet per minute to maintain. In a larger room it takes longer to reach an equilibrium, but the amount of CO2 you’re removing is a function of the amount of CO2 in the air which reaches the same level. Thus you can setup your air exchanger to vent in response to a single CO2 reading above a fixed level in your HVAC system and automatically adjust for a packed multi hour thanksgiving dinner in your living room or an empty house.

Circulating Air within a house is beneficial independent of how much air your venting to the outside. For one thing you can better regulate temperature with increased airflow for another you can filter the air for dust etc. So you really should treat them as separate systems.

If it makes you feel better imagine that 10’x10’ room with ventilation to the outside is attached to a sealed 100’x100’ chamber by a ventilation system you can turn on and off. The larger room will only have the same or better air than the 10’x10’ room and thus can’t make the small room worse off.

PS: Detecting people in rooms or activity levels does let you adjust temperatures accordingly which may save some money. Also, you may want more ventilation for other reasons thus kitchen and bathroom exhaust fans.

Re: Duct Size vs. Airflow (2012)

#25

Post by MichaelZuo »

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..

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.

Re: Duct Size vs. Airflow (2012)

#26

Post by 2ICofafireteam »

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…

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...

Re: Duct Size vs. Airflow (2012)

#27

Post by dekhn »

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.

This is known as the "Die Hard Aliens Problem"

Re: Duct Size vs. Airflow (2012)

#28

Post by bob1029 »

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…

> 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.

Re: Duct Size vs. Airflow (2012)

#29

Post by owenfi »

walterbell wrote: post #21
londons_explore wrote: post #19

Earlier quoted context omitted.

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…

Is there a good ERV design that is suitable for one room, e.g. the ERV equivalent of a window air conditioner?

I put a Fantech SE704N in my WFH shed, which is 10x20 feet with 6-7 foot ceilings: Newer ERV: https://www.supplyhouse.com/Fantech-FIT70E-SE-Series-Energy-... In stock HRV: https://www.supplyhouse.com/Fantech-SH704-SH-Series-Heat-Rec... You can buy the core and swap HRV->ERV (not sure if FIT70E uses the same core).

I put it behind a Lutron Caseta Fan Speed controller, it struggles a bit to communicate due to range, but at the low settings I can barely hear it and it keeps CO2 PPM to ~1k if it's just me in here (usually), I turn it up to 3 if I want a gentle wind noise and rarely go to 4 (but would if I wanted to freshen it up). I used the Fantech 4" ducts and it was pretty easy to self-install.

Re: Duct Size vs. Airflow (2012)

#30

Post by turtlebits »

MichaelZuo wrote: post #25
alliao wrote: post #9

Earlier quoted context omitted.

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..

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.

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