Comment by amluto

Comment by amluto 2 days ago

> On a global scale, that increases power and manufacturing on a huge scale. Why are we throwing power and more modern materials at a problem that was solved in Roman times?

Really?

A high quality modern balanced ventilator can ventilate an average sized house using 20-40W. That can supply over 100cfm and avoid around 90% of the conditioning that those 100cfm would otherwise require.

A good approximation is that 1 cfm at a 1 degree F temperature difference transfers 1.08 BTU/hr (sigh) or 0.317W of “sensible heat”. So, in a mild Mediterranean climate in the winter, heating by 30 degrees F, that 100cfm needs 0.317 times 3000 = 951W of sensible heat added.

So you can burn 951W of fuel. Or you can use 20-40W to get the same amount of fresh air but only need 95W to heat it. Or live in a climate with warm days and cool nights and require less thermal mass and therefore less material to moderate the temperature and avoid the need for active heating or cooling.

Without an HRV, either you don’t heat the building, or you ventilate less, or you use considerably more resources for temperature control.

Oh, and the device itself is two fans, a heat exchanger (fancy piece of plastic, generally), and some electronics and a box. Not exactly resource-intensive to build. And it can usually completely replace your bathroom fans if configured to do so, making it even less resource intensive.

In climates that require dehumidification or winter humidification, it’s more extreme because an ERV can exchange humidity (“recover latent heat”) too.

alt227 2 days ago

> Really?

Yes

> ventilate an average sized house using 20-40W

Lets take your conservative estimate of 20w

Quote from Googling: "As of July 1, 2023, there were 145,344,636 housing units in the United States"

145,344,636 x 20w = 2906892720W or 2906.89272MW.

Another quick google says that the average Nuclear power plant outputs 977 MW.

So thats 3 whole nuclear power plants required just to power the hrvs in American homes, using your conservative estimate.

That is without the power required to manufacture, transport, and install 145 million hrvs.

However you phrase it and whatever you say to justify it, thats a huge amount of power required to replace something which nature is quite capable of doing itself.

EDIT: I have just also considered the waste as well. The average HRV has a lifespan of 15 years, so that would be 145 million hrv pumps thrown out and new ones built every 15 years. Thats a massive amount of constant power being used, and mountains of unecessary waste, as well as the power to process that waste etc etc...

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amluto 2 days ago

You can multiply 20W by whatever you want, and if you multiply 1kW by the same number, you will get a number that is 50x as large.
Put another way, of course you can naturally ventilate a house to get the same air change rate that an HRV/ERV will get you. But (a) if you live somewhere with poor outdoor air quality, you have no opportunity to mitigate it with natural ventilation and (b) natural ventilation at high rates requires far more active heating and cooling in climates that need heating and cooling.
Even just the power needed to operate a large enough standalone air purifier in a naturally ventilated house will be far larger than the power needed to run a filtered ventilation system that will outperform that standalone filter (in a well sealed house or a positive pressure system).
As I write this, I’m running an ERV that is consuming 25W to supply HEPA filtered air at very slight positive pressure. The same ventilation rate, from unfiltered natural ventilation, would remove 500W of heat, and I’d probably need at least 100W of air purifiers running to get anywhere near the level of filtration that those 25W include at no additional cost.
You seem to be trying to tell me that the 25W would scale to a lot of power if everyone did this but that the 500W I would use otherwise would have no impact because the Romans didn’t worry about it. I’m unconvinced.
(This is a system where I replaced the mediocre and undersized filter from the manufacturer with a monstrous 24"x24"x12" nominal HEPA filter, a 24"x24" MERV 8 prefilter, and a carbon filter mat from McMaster-Carr. I expect the HEPA filter to last for several years, the extremely inexpensive prefilter to last for a year or so, and the carbon filter to need replacement more frequently if outdoor odors from wildfires become an issue. Why HEPA instead of a 99.9% filter with somewhat lower resistance? Because it’s much easier to buy a real HEPA filter and the added resistance is negligible. No additional power is consumed by any of this: it all has less resistance to airflow than even a brand new factory filter. The only real downside is that it’s physically large.)

Reply View | 2 replies
- alt227 2 days ago
  
  You seem very proud of your home ventilation system, and very keen to tell us all about it. Im not surprised you dont really care about the power usage to achieve that. Its quite telling that your alternative that you suggest is more power hungry air purifiers.
  I however will stick with my house which uses zero external grid power to heat or ventilate it, and I can be happy in the knowledge I am not putting any drain on the national power grid for my comfort.
  Also when we have power outages, which is quite often, it makes no difference to my home whatsoever.
  Its OK, we can agree to disagree. You are not alone in thinking electricity is an infinite resource. Lets just keep on building houses that require more and more power to run and see where that gets us!
  
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  amluto 2 days ago
  
  > Im not surprised you dont really care about the power usage to achieve that. Its quite telling that your alternative that you suggest is more power hungry air purifiers.
  Huh? I'm literally explaining, with actual measured numbers, how the ventilation system uses less power. I do care about it!
  
  Reply View | 0 replies