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Old 01-30-13, 06:05 PM   #11
Exeric
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Well, I just noticed that they got the colors of the arid southwest and the pacific zone mixed up. And for the pacific zone, after the correction, they say an ERV is optional. So maybe that's the way to go for your particular situation.

It still would depend on the humidity filtering being bidirectional, which I don't know about.


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Old 01-30-13, 07:28 PM   #12
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Well, that answers that. It seems to imply the humidity filtering only occurs in one direction - outside to inside. Too bad.
Well, the way it works is that as the higher temperature air, with it's load of water vapor, moves across a higher-to-lower temperature gradient, as the air temperature changes, if it crosses the dew point, will causes the vapor to condense and become water.

If you have a HRV, the water stays on the side of the barrier on which it condenses, and exits, usually through a tube to be disposed.

If you have an ERV, the barrier is permeable, and the water crosses through the barrier and evaporates into the air in the lower-to-higher temperature gradient.

I was very careful with my language to avoid words like "inside" and "outside" so that the description would be valid when read for heating as well as air conditioning.

* * *

So, if you wanted to ventilate AND save heat in a bathroom/shower, you would NOT use a ERV, as that would send the water vapor back into the loo. So in that case the proper choice would be a HRV.

-AC
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Old 01-31-13, 10:24 AM   #13
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AC and gang,

Good information on ERV vs HRV graphics.

First off, homes rarely have any CO2 buildup as the inherent ventilation of a home is far more than a school, office or other work space. This is because the ratio of surface area to living space is so large in a home.

Very, very tight homes still have an air turnover (with no HRV/ERV) of about 1 air change per day so CO2 is very rarely a problem in homes. With regard to "rest" recall that 6-8 hours is sleep (even less CO2 output than rest) and that few really do large workouts in the home. But we do have dishwashers, showers, and latent vapor coming off our lungs which all contributes to significant water vapor loads.

All that said, I also assume that a home has properly vented hot water heaters. furnaces, etc (if using propane/nat gas).

On the issue of ERVs moving water vapor. Yes, they are bidirectional if there is a large dew point difference between the inside and the ambient outside.

Air and water vapor permiance are important concepts. In very cold climates, the issue of water vapor permiance into walls can become very problematic. If sufficient water vapor goes into walls, there is the infamous critical freezing point in the middle of the insulation. If the insulation can become frozen and then water soaked (cellulose), then it turns to mush.

In northern climates, I far prefer to have a 6 ml poly sheet on every wall, just underneath the drywall, walls ceilings and lapped like you are building a boat. I also prefer to put a closed cell foam layer on the cold side of the wall and a water non-permiant insulation inbetween. Yes, foam is great (expensive), but fiberglass batting (R18-R20) is very acceptable if well done (properly fitted into cavity).

Obviously ANY air infiltration around electrical boxes must be sealed. The poly sheeting prevents water vapor going into walls and freezing there.

Older homes are a real pain as studs are not 16 OC and custom cutting fiberglass batts becomes very tough. Over stuffing in nooks/crannies is easy to do and almost destroys the insulation value.

In southern states, the opposite is true with the vapor barrier on the outside of the home as dew points are almost always higher there.

The use of ERV's can help a LOT with water movement as in the winter it will increase relative humidity in a home and then decrease it in summer (to a lesser extent).

HRV's don't move any water except that which may condense out on the cold side of the HRV.

But all that said, I still have a dehumidifier that kicks in here (central Oklahoma) on humid May days when there is not a large heat load, but showers, dishwasher, etc all add a lot of water vapor to the house.

I do encourage all to have a home humidity meter and to never allow it to go over 60%. I prefer to have it never go above 55%. In the winter, high humidity (in no wall vapor barrier) will accumulate in the ways "sogging" the insulation and in the summer it will contribute to mold build up in same.

AC, just get some "raw data" from the CO2 sensor ($10 is worth playing with!) and if you need help, feel free to call.

Great discussion!

Steve
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Old 01-31-13, 11:50 AM   #14
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...Great discussion!...
No Steve, this in NOT a great discussion.

This is NOT a discussion thread.

My purpose in starting this thread is to build a CO2 (& ultimately humidity) sensing controller for an HRV.

The operative word is "build".

I tried to make that clear in my first post when I wrote:

Quote:
My project idea is that HRVs are used to provide fresh air and at the same time minimize home heat loss. The heat loss from the outgoing air can be reduced, but never reduced to zero.

A 'smart' HRV would sense the level of CO2 and when the level of CO2 reached a predetermined allowable level, it would run the fans. If the CO2 level was higher, it would run the fans at a higher speed, if the CO2 was lower, it would run the fans at a lower speed, and if the CO2 was acceptably low, the fans would not run at all.

This would increase the overall efficiency because the HRV heat loss would only be incurred when required.

So far, petty simple.

This project will use an Arduino to read a CO2 Sensor (Telair 6004) and then use the CO2 readings as input to control PWM fans in the HRV.
So far Steve, you have written 1117 words on the topic of why a CO2 sensing HRV controller should NOT be built.

And in response, I have written 480 words as to why I am going to proceed. Writing this has been a waste of my time, just as your writing of your 1117 words was a waste of your time... and worse yet it has discouraged interest in this project. There are quite a few Arduino-savvy members of EcoRenovator, and not a single one has posted to this thread.

I attribute this to your "Great discussion!"

I wish you would start another thread, a discussion thread, about why using CO2 monitors is futile, and leave this project thread alone. You can even request that your posts to this thread be moved to to your 'CO2 monitoring is futile' discussion thread. I'm pretty sure the administrators would do this for you.

Sincerely,

-AC
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Old 01-31-13, 02:45 PM   #15
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AC,

I apologize. Been down the road you are going (sensing CO2) many years ago and was trying to give you some factual information on sensing variables.

Again, sorry about the misunderstanding and I look forward to your HRV and CO2 build results.

Steve
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Old 01-31-13, 03:59 PM   #16
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Default Graph of Telaire 6004 in action...

On a site that uses sensors such as the Telaire 6004 in monitoring buildings, I came across this chart of the device in action...


I would presume that the room had a lower, continuous ventilation rate, and that the 'bump' is the result of a conference. It seems tantalizingly possible that from the rate of CO2 decline at the end of the meeting, that the continuous ventilation rate could be calculated. Either room size or number of people would likely be needed.

I also learned today that current Oregon code calls for CO2 monitors on each level of new construction. Hmmmmmmm..........

-AC
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Old 01-31-13, 05:38 PM   #17
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I see that, relatively speaking, the CEO in green is blowing a lot of gas. Yup.
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Old 01-31-13, 07:10 PM   #18
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I see that, relatively speaking, the CEO in green is blowing a lot of gas. Yup.
Yeah, and the 'cube farm' is very well ventilated, on average, much better than the CEO... lower CO2, clearer thinking.

This explains a lot!

-AC
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Old 02-02-13, 09:57 PM   #19
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Default Borrowed a Friends CO2 Tracker...

I borrowed a friend's CO2 tracker and got a nice readout of room parameters.


This is with one window opened about 3/4".

I think I'm on the right track.


Best

-AC
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Old 02-06-13, 03:00 AM   #20
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Default The Record Of The Day In CO2...

I did a rough log of today's CO2 data just to see what it looked like.


Y axis is CO2 in Parts Per Million (ppm)

X axis is time 24 hours per day (are you paying attention Piwoslaw?)

So, there's a steady increase from the time I wake up until about 10:00 when I went to do some errands. I returned at about 13:30 and logged CO2.

Around 17:00, another reading, then I took some soup to the neighbor, and stayed for a short visit and took a reading when I returned.

Shortly after that at around 19:30, a friend dropped by and we chatted for a few hours, at the end of which I took the final reading.

After he left, I opened two windows, to flush out the CO2... never did that before!

It's amazing... the record of the day in CO2.

Best,

-AC

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