Pros and cons of HRV vs Fresh Air Ventilation in a dry heating/cooling climate.

[garya505]

We specify a lot of foam and ERV is the answer. I personally use one in my renovated 1921 farm house and it is needed (wind blowing or no). We also specify and install ERVs as bathroom exhaust fans with master timer and individual 20 minutes push timers...RenewAire most of the time.

I lived in Albuquerque for three years and now reside in Minneapolis. However you are "conditioning" the air, you certainly don't want to waste what you paid to condition.

Seems like if you don't want to under-ventilate or over-ventilate, you either need to know your exact infiltration, or you would need to use some other parameter (like C02) to decide how much extra ventilation to provide. And wouldn't using a CO2 sensor work with a HRV, ERV, as well as a simple fresh air intake? Yes, I know the ERV would be the most efficient, I would think but over-ventilation would be very inefficient too.


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[BadgerBoiler MN]

Maybe if you live a space bubble. You are over-thinking this. In most cases for residential applications, simply using an ERV for bath and perhaps supplemental kitchen exhaust is sufficient. The rate of ventilation (after an ERV has been properly specified using long accepted standards) is a matter of user controlled personal preference. Why wife's nose is better than any CO2 sensor I have ever encountered.

[teddy bear]

Seems like if you don't want to under-ventilate or over-ventilate, you either need to know your exact infiltration, or you would need to use some other parameter (like C02) to decide how much extra ventilation to provide. And wouldn't using a CO2 sensor work with a HRV, ERV, as well as a simple fresh air intake? Yes, I know the ERV would be the most efficient, I would think but over-ventilation would be very inefficient too.


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Here some data on a WI foam insutlated home. The data was from a windy week in WI. This week the home was operated with 200 cfm of exhaust ventilation. The ventilation was operated 23% of the time. This is part of series of test with various ventilation types.
Homes like this get much more natural fresh air during the cold windy weather and very little during calm weather.
You are about right the ideal method of control of fresh air ventilation. Also you see what we are up against in trying to move the industry along to more effective methods of handling the mechanics of the home.
"You are over-thinking this. In most cases for residential applications, simply using an ERV for bath and perhaps supplemental kitchen exhaust is sufficient. The rate of ventilation (after an ERV has been properly specified using long accepted standards)"
Also exhaust devices need make-up air to function as designed. In many homes, a make-up fresh air ventilation is more practical. Controlling the operation any ventilation with CO2 controller is ideal to determine that the home is occupied and the natural ventilation needs to be supplemented.
Operating ventilation when it is not needed cost energy and is uncomfortable winter or summer. Most in the trades avoid ventilation during the moderate seasons because of the a/cs inability to maintain <50%RH during low/no cooling loads.
In green grass climates, a whole house dehumidifier is importat. In cold dry climates, a humidifier is also important for comfort.
Thanks for the interest in new concepts.
Regards TB

[BadgerBoiler MN]

You are about right the ideal method of control of fresh air ventilation. Also you see what we are up against in trying to move the industry along to more effective methods of handling the mechanics of the home.
"You are over-thinking this. In most cases for residential applications, simply using an ERV for bath and perhaps supplemental kitchen exhaust is sufficient. The rate of ventilation (after an ERV has been properly specified using long accepted standards)"
Also exhaust devices need make-up air to function as designed. In many homes, a make-up fresh air ventilation is more practical. Controlling the operation any ventilation with CO2 controller is ideal to determine that the home is occupied and the natural ventilation needs to be supplemented.
Operating ventilation when it is not needed cost energy and is uncomfortable winter or summer. Most in the trades avoid ventilation during the moderate seasons because of the a/cs inability to maintain <50%RH during low/no cooling loads.
In green grass climates, a whole house dehumidifier is importat. In cold dry climates, a humidifier is also important for comfort.
Thanks for the interest in new concepts.
Regards TB

We are "up against" the cost of relevant mechanical systems and their practical value. I live and work in a "green grass climate" and one in which severe cold is common. In my own home, here in Minneapolis, the humidity and fresh air are both balanced with the relatively new technology of the ERV. Getting the "trades off the relatively primitive HRV would be the first step in conserving energy while still maintaining IAQ. We might also consider the cost of operation of the typical ERV and weigh that against the theoretical ideal. But if a CO2 driven ventilation system is what they want and can afford, we are all about design/build.

[BadgerBoiler MN]

I forgot to thank you for the chart. What I see in it is a predictable daily spike, followed by a certain ventilator run time resulting in a 22% operating cycle. I suppose it is just coincidence that my own ERV is set to 20% operation and would wager the CO2 spikes apparent in your chart are not occurring in my own envelope. With the addition of push button terminals in the bathrooms (not often used while showering in winter) our rH is also nearly always between 40 & 50 with the use of a mini-split and basement dehumidifier in summer. CO2 control? Not a bad idea perhaps, but certainly not perfect and cost/benefit is still in question.

PS. Since we use superior space heating provided by radiant floor panels, humidity is easier to manage and set-back unnecessary as infiltration is reduced and ambient temperature lowered with greater comfort and lower fuel consumption than forced air systems. We setback the design water temperature at night and use weather responsive reset to control the water temperature delivered to the radiant floors.

I tend to over-think ways to get people to invest in any reasonable mechanical system instead of "investing" in fancy roof lines, landscaping and floor coverings.

[garya505]

TB, nice chart! I have a question though. In my reading it looks like outside air is normally about 400PPM CO2, and some commercial DCV CO2 controllers bring in outside air when indoor CO2 gets to 800PPM. However, on your chart it looks like your controller is opening the OA vent at about 575PPM, and you never get over 650PPM inside.

ETA: Ah I see, now that I've looked at the DEH 3000R specs. This is a dehumidifer/ventilator controller that does not use a CO2 sensor. So, the lowering of the CO2 is just due to dehumidification using some outside air ventilation? So can inside home in a home ever get to 800PPM, even without ventilation?

[teddy bear]

TB, nice chart! I have a question though. In my reading it looks like outside air is normally about 400PPM CO2, and some commercial DCV CO2 controllers bring in outside air when indoor CO2 gets to 800PPM. However, on your chart it looks like your controller is opening the OA vent at about 575PPM, and you never get over 650PPM inside.

ETA: Ah I see, now that I've looked at the DEH 3000R specs. This is a dehumidifer/ventilator controller that does not use a CO2 sensor. So, the lowering of the CO2 is just due to dehumidification using some outside air ventilation? So can inside home in a home ever get to 800PPM, even without ventilation?

this is a custom designed Ultra-Aire CO2 controller. In this case we are looking for an air change in the home in 5 hours when the home is occpuied. That is why the controller activates the ventilation much soooner. The outside CO2 is approx 475 ppm. This allows agressive ventilation when needed and no ventilation when the home unoccupied and/or is windy. It appears to be very effective at minimizing the running hours of properly sized ventilator. Most are using on/off timers which cycle when not needed. The summer cycle is much different with more ventilation required.
Regards TB

[garya505]

this is a custom designed Ultra-Aire CO2 controller. In this case we are looking for an air change in the home in 5 hours when the home is occpuied. That is why the controller activates the ventilation much soooner. The outside CO2 is approx 475 ppm. This allows agressive ventilation when needed and no ventilation when the home unoccupied and/or is windy. It appears to be very effective at minimizing the running hours of properly sized ventilator. Most are using on/off timers which cycle when not needed. The summer cycle is much different with more ventilation required.
Regards TB

So I'm curious what "typical" residential indoor CO2 levels are. I know, it will vary a lot due to construction and age, but someone must have studied this.

[chuckcrj]

this is a custom designed Ultra-Aire CO2 controller. In this case we are looking for an air change in the home in 5 hours when the home is occpuied. That is why the controller activates the ventilation much soooner. The outside CO2 is approx 475 ppm. This allows agressive ventilation when needed and no ventilation when the home unoccupied and/or is windy. It appears to be very effective at minimizing the running hours of properly sized ventilator. Most are using on/off timers which cycle when not needed. The summer cycle is much different with more ventilation required.
Regards TB

Is the Ultra Air CO2 sensor proprietary to their dehumidifier? Or is a simple set of contacts? Does it have a display so you can see how many ppm it is sensing?

[garya505]

FWIW, I saw two of the Honeywell C7232A CO2 sensors on the walls in a local Starbucks today. My guess is that they have an economizer in the unit on the roof.

[teddy bear]

Is the Ultra Air CO2 sensor proprietary to their dehumidifier? Or is a simple set of contacts? Does it have a display so you can see how many ppm it is sensing?

This is a custom Ultra-Aire DEH 3000R controller. It displays the CO2 PPm setting and levels. There have be questions about the typical CO2 levels in homes. I am attaching data from a FL home with 2 occupants. The home is typical of FL construction and only needs mechanical ventilation during calm weather.
Regards TB


11 14 12 FL house data fin.pdf

[garya505]

Thanks for the data. Looks like CO2 never gets above 800.

Do the occupants have the doors open sometimes?
Does the Ultra-Aire 90 bring in outside air when dehumidifying?

[teddy bear]

Thanks for the data. Looks like CO2 never gets above 800.

Do the occupants have the doors open sometimes?
Does the Ultra-Aire 90 bring in outside air when dehumidifying?

Yes doors open sometimes. Ultra-Aire bring in fresh air when controller calls for fresh air. Dehumidification and recirculation are independent. This home needs 80 cfm of fresh air to get the air change in 4 hours. Two occupants will not get the CO2 above 800 ppm.
Regards TB