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ERV Linked to Carbon Dioxide Detector

linagee | Posted in General Questions on

I’ve been looking at what kind of ERV makes sense to get. I live in a 1,600 sqft 1940s house. (Probably not “tight” like a new build.) I want better ventilation during cold winters. I live in Zone 5/6 and it snows / gets down to -10F in the worst of it. Not the kind of weather where you’d open a window during.

I’ve been looking at ERV to improve my indoor air quality. Something I don’t understand is: Don’t they have one that links to a carbon dioxide detector to know how often to cycle? I’m a big believer in automation instead of “20/40 ought to be about right”. I would even go so far as to throw something together myself that regulates the carbon dioxide in the house, but I want to know if there’s anything off the shelf that would already do this.

Most of the HRV/ERVs that I’ve seen reviews for have a box on the wall with a button where you adjust how much fresh air you want. This just seems a bit silly to me. Make it automatic, or it’s going to take many minutes of my day or worse, I’ll just forget about it and never use it. I’m not trying to comply with ASHRAE or any building codes. I just want the cognitive benefits of more fresh air.

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Replies

  1. Jon_R | | #1

    You probably have a leaky (say over 5 ACH@50) house so the following may not matter much. But generally, while you should use high CO2 level to increase ventilation, you should not use acceptable CO2 levels to reduce ventilation below ASHRAE 62.1 rates. There are other pollutants that matter too.

    A nice summary of smart ventilation here.

  2. linagee | | #2

    "So this may not matter much. "

    Again, not going by ASHRAE standards. Going by carbon dioxide buildup. Even a "leaky" building with a bedroom door closed will have your carbon dioxide levels go above a safe level. (2,500ppm is not uncommon for a bedroom with the door closed.) Reading some studies and testing my own room, this became apparent to me.

    "But generally, while you should use CO2 level to increase ventilation, you should not use acceptable CO2 levels to reduce ventilation below ASHRAE 62.1 rates." <--- I said carbon dioxide, but I really meant all VOCs and such also. They have sensors like this. Have they just not made their way into common ventilation units yet? I want a PM2.5/CO2/TVOC/HCHO/temp/humidity sensor before the intake and after the filter and at least three other places in the house. (I am thinking kitchen, office, and bedroom.) I want the ventilation unit to know: "Is having the unit on pulling in extra pollutants past the filter? Let me shut it off for a few minutes and wait for some car exhaust that can make it's way past a HEPA filter." or even something like "pulling in air at top speed is increasing the humidity in the house too fast, I'll shut off the fan for a bit." It should be smart and not require my constant attention to tweak it.

    I am a developer and play with technology all day long, so it feels like a simple request, but somehow it seems like I am asking for the world when I can't find these things in an off the shelf unit. I'll probably have to cobble something together that fits these requirements. (Why? Because I care about the air I breath. Weird, right? I actually find it strange that people associate this with "being green" and not just "being smart".)

    1. Expert Member
      MALCOLM TAYLOR | | #6

      I wonder whether the relative absence of integrated monitoring in these units mightn't lead to some other device in the house taking on that task? Perhaps a home control system like Nest will include monitoring and adjustment - perhaps without the owner's input? More and more of this stuff seems to be moving to the Cloud.

  3. Trevor_Lambert | | #3

    Zehnder and UltimateAir have optional CO2 sensor integration. I would suggest using aftermarket sensors, as the ones they sell are very expensive. I have a Zehnder with two Dwyer CO2 sensors.

    With the Zehnder for sure, you can program it to respond to any kind of sensor you want, as long as it has a 0-10V output. I would guess the UltimateAir would be the same. I think monitoring the ambient air in specific locations makes more sense than monitoring the return air, which is just an average of the whole house air.

    1. linagee | | #4

      Trevor: Thanks for the info! It sounds like I just have to concentrate on getting a good HRV/ERV that has the ability to accept inputs like these. (Going through other posts on this forum with some reviews.)

    2. linagee | | #5

      Ah. Some deals to be had on eBay, just searching for "CO2 wall mount". Looks like some use 4-20mA sensing, and some do other relay or voltage output. I think this is the easiest way to get something that looks finished (in a nice box) without having to go down to the circuit level and build boxes myself. (Interestingly, the cost is around the same, $25 to $75 for a nice white box, around that same range for a good CO2 sensor. T8100 seems to be fairly standard.) This is much less than a $280 one that is towards HRV/ERV purchasing folks. (But might require more integration if it's not a NO/NC relay output.)

      I think sometimes people use these for safety reasons like in an industrial environment where large amounts of CO2 can be released causing lethal hazards.

    3. alan72 | | #9

      Sounds like Zehnder and UltimateAir are the only units with this capability (erv’s as opposed to the CERV).

      Trevor- was the price of the Zehnder “worth” it?

      It’s very difficult to tell which direction to go.

      1. Trevor_Lambert | | #10

        I don't have any regrets about the unit itself. It has useful features that no other competing product has, which goes a long way to explaining the price premium. A lot of the price difference is in the special ducting, which you can choose not to use.

  4. GBA Editor
    Martin Holladay | | #7

    Linagee,
    Another option is the CERV -- an ERV controlled by a CO2 detector. For more information on the CERV, see "A Balanced Ventilation System With a Built-In Heat Pump."

  5. jberks | | #8

    Since you're technologically inclined, I'm sure you could do a simple Raspberry Pi or Arduino monitoring and relay system.

    I have my ERV's running continuously (long story), so I don't get to be smart about it. but I do have unused 18g wire run to every room in the house I'm currently building , I would like to eventually set up an air quality monitoring system so I can see the data. Currently thinking I'll have to learn to code this with Raspberry Pi since there isn't an actual product for this application.

    1. Hawnes | | #11

      What is an 18g wire? How is this beneficial? Just asking out of curiosity

  6. johngfc | | #12

    It's just a small-gauge wire such as used for a thermostat. Having the wires run means he/she could easily hook it up to a CO2/VOC or other sensor without the hassle of figuring out how to get the wires from the sensor to HRV/ERV. MUCH more convenient to do this when building than drilling holes and routing later.

    1. Hawnes | | #13

      I see, makes sense! Thanks!

  7. BirchwoodBill | | #14

    Has anyone done this with a Resolv controller? In addition to CO2 monitoring, dew point control would also be useful for dehumidification.

  8. arossti | | #15

    I have an Airthings Wave+, Radon/PM2.5/CO2/Humidity/Temp sensor. It works with IFTTT, which works with google/nest. The furnace fan can be set to run when CO2 reaches a lower threshold, and the ERV can be interwired to run when the furnace fan does. In my home, circa 1955 build, the ERV is a VanEE90 ‘short circuit’ install to the furnace so that setup makes sense. Other models can use IFTTT to signal the dry wire of an EcoBee4 thermostat to run the ERV just like an on/off or hi/lo or crank timer switch would, but I have not tried that yet...

    1. T_Barker | | #16

      Now that's interesting! Did the connections take some hacking on your end, or just relatively simple wiring to ERV?

      1. arossti | | #18

        It's a work in progress. Currently the ERV tells the furnace fan when to run (based on it's own programmed controller, which is 'air-gapped' - not connected to wireless), and the Nest/CO2 sensor can tell the furnace fan to run, but I can't get the furnace Fan to tell the ERV when to run :/ - we are trying to find a way to get the HRV to respond directly to the CO2 sensor. VanEE's controls are not 'smart' - no bluetooth, etc. Just trying to figure out what wire to use to take an external signal that we can run a wireless switch to turn on the ERV based on an off-the-shelf 'smart plug' type device. If I had an EcoBee4 (and a fourth wire direct to the ERV) this would be easier. PS - wrote an entire article about HVAC upgrades to our older house. The entire HVAC industry is not positioned to transition us to net zero even if consumers are asking for it. My short answer is, promote hybrid systems with ASHP replacing cooling units when they die. https://www.thomsonarchitecture.ca/2021/02/09/future-heating/

  9. T_Barker | | #17

    This whole topic is a sore point for me. In general the HVAC industry is not very innovative, and there really aren't many choices (if any) for this type of control yet that I'm aware of.

    If you think about it, as more houses head toward super insulated, super sealed, the HVAC loads drop to the point where the HVAC air flow requirements are in the same league as the ERV air flow requirements.

    So the obvious solution is that the HVAC equipment - whether it's a traditional furnace + A/C unit, or an air source heat pump type of system - should handle ALL of the space conditioning in one "unit", with one set of ducting for the entire house. So one "unit" from a single source should handle all of the following:
    1.) heating
    2.) cooling
    3.) humidification
    4.) de-humidification
    5.) ventilation (based on measured air quality)

    There's no valid argument against this, other than legacy excuses. Unfortunately, I think we are still many years away from this type of system in North America.

    1. Trevor_Lambert | | #19

      The validity of an argument is subjective. I have a couple of arguments against it.

      1. With all those features rolled into one device, a failure in that device means a failure of all of those functions at the same time. Whereas if your standalone dehumidifer or ERV conks out, you've still got heat (or cooling).
      2. Getting an ERV and heating/cooling system to share the same duct system is more complex than you're making it out to be. Just having approximately the same max air flow rates doesn't solve all the design issues. Rarely will the heating/cooling and ventilation demands be in sync. You still need to vary the amount of air that's coming from outside vs what's being recirculated by the heating/cooling system. While this is certainly not impossible, it's far from simple and it's not going to be cheap.

      1. Deleted | | #20

        Deleted

      2. T_Barker | | #21

        Fair points. But in my opinion I'd still rather deal with a single source, not to mention that all of the technology will usually work together better.

        Regarding your second point, I believe its all in the control logic. I agree not necessarily simple, but definitely achievable I believe. Someone in the business just needs to put their mind to it.

    2. AlexPoi | | #23

      I disagree. You want one unit to control all the equipments like it's done in the commercial world but you want different units so you can select the ones you need based on your load.

      Tekmar has some nice controls that can adress most of what you've listed but I don't think automatic ventilation is possible at the moment.

    3. Jemari | | #34

      Agree. Also annoying: 1) ASHRAE is a 'bare minimum' standard that doesn't ensure healthy air in any way. It is a very low bar. 2) I recently learned that the regulatory definition of, "VOCs" pertains to compounds that cause smog only... which means it is categorically NOT inclusive of many compounds that cause unhealthy indoor air quality. This means products like "Low VOC" paints can have actually have high VOCs, although they won't cause smog in your house. An independent non-profit called, "Green Seal" certifies paints low in indoor air quality pertaining compounds, but many familiar brands have not bothered to get listed as they are banking on our lack of education.

  10. arossti | | #22

    Switch options: Connect any crank timer to the OL/OC spots on the ERV control bus. Crank timer could be a smart switch (on/off) that has IFTTT enabled. Airthings Wave+ works with IFTTT, so a trigger for CO2 can be set to toggle b/t ON/OFF to bump the ERV into high speed when CO2 is over 1,000ppm, and off when under 1,000ppm. We find that for our install, 3 active adults + dog, the unit needs to be run at 125cfm to keep CO2 under 1,000ppm, but at night/sleeping, the unit can keep up at low speed. So the simple hi/low speed setting connected to a CO2 sensor works. We will try this next week and I'll report back. ps - unit as installed currently interwired to our furnace blower, so high speed call from ERV runs furnace fan also.

  11. arossti | | #24

    It turns out our NEST thermostat did not play nicely with our new modulating gas furnace, so we swapped it out for an EcoBee4, which had the added benefit of 2 dry wires for ERV/HRV/Ventilator controls. After first frying the ERV's board by energizing it with the wrong wire from the EcoBee (since replaced), we got it working with the R/G wires to the VanEE's OL/OC lugs. But the silly thing is, with EcoBee (which can be triggered by IFTTT and in turn IAQ sensors), it can only set a runtime of so many minutes per hour occupied and so many minutes per hour unoccupied. No setting of high speed, or low speed, or off. ALso EcoBee has split their controls into different functions, where an *HRV* can 'dehumidify' (so can an ERV!), and a *Ventilator* can be used for 'Free Cooling' (So can an ERV!!). Why they do not have an advanced ventilator control logic that can do all of these things without calling the equipment ERV/HRV/Ventilator - such as switch on/off, set hi/low, dehumidify/maintain humidity AND assist with free cooling - and basically over-ride or be used in place of a Ventilator's control box is beyond me. The workaround to get closer to the planned Airthings/IFTTT/EcoBee4/ERV implementation I was aiming for, is to simply raise the ventilation rate (ie from 20min/60min to 40min/60min) to remedy IAQ issues, and shut off the ERV's own controller so EcoBee can override. This negates any Humidity related controls tied to the ERV, but at least when the ERV runs, the furnace fan does too - both at low speed since that is how we wired the G wire (it could have also been high speed). Here is how EcoBee controls ventilation equipment: https://support.ecobee.com/hc/en-us/articles/360023859852-Troubleshooting-accessory-installations. Lastly, the 20min per 60 min is actually 5min every 15min - which EcoBee does not spell out in their manuals.

  12. johngfc | | #25

    This has got to be a very common issue -- any updates? Does anyone know if there's a way to use a CO2 monitor with IFTTT to trigger the boost mode on a Panasonic Intelli-Balance ERV?

    If not the Panasonic, are there other price-competitive ERVs that integrate with CO2 monitors in the 50-120 CFM range?

  13. jg_nj | | #26

    I think I have a solution to this issue. I have a Renewaire Premium L, which has a boost mode that's currently not being used.

    My plan is to find a CO2 and/or VOC sensor and integrate it with Home Assistant (https://www.home-assistant.io/), which is an amazing open-source home automation platform. Then I'm thinking of connecting a Shelly 1 (https://shelly.cloud/products/shelly-1-smart-home-automation-relay/), which is a wifi-connected relay, to my ERV. The Shelly 1 integrates very easily with Home Assistant. Within Home Assistant, it's simple to create automations, kind of like IFTTT. So my automation would monitor CO2/VOC levels, and when a certain threshold was reached, the Home Assistant automation would trigger the Shelly relay, turning on boost mode until the levels dropped to the desired level.

    For the sensor, I want to find one that supports wifi or Zigbee out of the box, and if not, one that can be easily connected to an ESP8266 (https://en.wikipedia.org/wiki/ESP8266). ESPHome (https://esphome.io/) would make it easy to integrate the sensor with Home Assistant.

    This probably sounds complicated, but these tools makes it really easy for any reasonably tech-savvy person to implement it. If/when I actually do it, maybe I'll write up a guide and post it here.

    1. paulneumann | | #27

      did you ever find any solutions? I have been exploring Shelly but unsure about being able to use the relay to boost rather than just on and off?

      1. tim_in_nc | | #28

        I've got this integration working on a Broan ERV140 -- at least on that device (and likely on others), the boost switch is not a simple on/off but instead communicates via a change in the resistance between two of the control wires.

        Automating boost mode required building a small custom arduino board with a digital potentiometer (e.g. https://www.robotshop.com/en/dual-digital-potentiometer-100k.html) and doing some testing to ID the right resistance range. Took a solid day or so of hacking but once set up it has been working very smoothly since. I'm using homeassistant + esphome to automate controlling the ERV, and using the CO2 readings from an AirVisual device I already owned.

        Not sure if the RenewAire uses the same control mechanism or not, but happy to share more details if it's helpful (and if I can remember!)

        1. jg_nj | | #30

          Does the Broan have a boost mode, or are you modulating the speed that would normally be dialed in during setup? The RenewAire does have a boost mode, but it's activated by closing the circuit on the high speed connectors. There are two sets of potentiometers for setting the high/low CFM. I guess I could theoretically use a controller for modulating the pots, but my current high/low setup is working pretty well.

          1. tim_in_nc | | #31

            Yeah it has a boost mode, just the control mechanism for the boost mode is more complicated than closing a relay -- I wish it were simpler, that'd be easier!

      2. jg_nj | | #29

        Hey, I actually gave up on trying to do anything based on AQ, since from what I've read most AQ monitors are not reliable. Here's a good recent writeup: https://halestrom.net/darksleep/blog/048_indoorairsensing/.

        What I did end up doing, though, was using a Shelly to attempt to manage humidity and temperature, by acting as a switch between high and low speed. In Home Assistant I have a trigger that controls the speed depending on a few things, like difference between indoor and outdoor dew point, outdoor temperature, etc. It's worked very well for the few months I've had it in place.

        One thing to note is that the Shelly 1 uses DC , so in order to have it powered by the ERV, which provides AC power, you need to install a rectifier, as discusses here: https://www.facebook.com/groups/ShellyIoTCommunitySupport/posts/1909883182444370/.

        I also have a Shelly 2 installed in the outlet the ERV is plugged into in case I want to turn off the ERV. Not sure how often I'll use this, but last winter a warehouse caught fire nearby and my house was in the direct path of the smoke. I had to bring the ladder upstairs and climb up into the attic at 1:00 AM to unplug the ERV so the smoke would stop being pumped into the house. And this was after downing three Heady Toppers!

    2. Jemari | | #35

      Did you work it out? Very cool by the way. I don't have the time to figure this out... I am doing too much DIY in other camps already.

      1. jg_nj | | #42

        Take a look at my reply here: https://www.greenbuildingadvisor.com/question/erv-with-carbon-dioxide-detector?oly_enc_id=9129B4625590G6D#comment-237104. Decided to just base the ERV automation on temperature and humidity.

  14. truesouth | | #32

    Some of the spot wall mounted ERVs that are available in the Asia market have built-in VOC/PM2.5 and CO2 sensors. Hopefully that's a sign this will become more standard.

    Recently I've seen a standalone ERV controller for sale with these sensors built in, although that's not necessarily where you'd prefer to have them. This controller supports wiring for an ERV with 3 fan speeds but interestingly also claims to be programmable via wifi app and has an RS485 interface.

  15. DennisWood | | #33

    I've been working on "smart" ventilation issues for a few years now but the easiest solution was just a 24 Volt C02 sensor (connected to air handler LV power) which by design closes a set of dry contacts at the high CO2 set point. Co2sensor.com wrote a blog entry about our simple setup with hardware details...it was not expensive or hard to do:

    https://www.co2meter.com/blogs/news/128721927-co2-meter-helps-lower-heating-costs-for-business

    If your ERV or HRV has a set of dry contacts (most do) for a boost function, you just connect that to the Co2 sensor dry contacts. I also helped out my brother with a Venmar EKO series HRV that has no furnace interlock. We just connected the HRV boost dry contacts to his Ecobee3 stat dry contact terminals (provided for optional ventilator use) so at least he can ensure the furnace fan/ERV minimum hourly run times and achieve the interlock via the Ecobee stat. So you can do a lot with the provided "boost" dry contacts on an HRV/ERV that may not actually be documented by the manufacturer.

    I took the additional step though using a VERA automation hub to shut the system off completely on high wind days as I had logged CO2 levels for a week or so and found out that on higher wind days (9000 square foot, furred air space assembly wall system, completely gutted and retrofitted, commercial building) there was actually no need for the large Venmar commercial 240V HRV to run. Keep in mind that this building was very tight in climate zone 7A, and cost less to heat than homes 1/5 the size.

    I have done some calculations on a new system for our home (uses two EC fans, external to the HRV) and figured at current efficiency (90%, measured) that our heating system will need to add about 11K BTU per day to offset the temp difference. That's about 10-15 minutes of extra run time on the 60K BTU furnace. I would suggest then that there are far more gains to be made by updating to an EC fan ERV/HRV with high efficiency (a large core) than complicating the control by adding bits. I'm taking a 250 watt draw down to 20 watts by using the EC fans, and dropping heat load (over 1 day) from 30K BTU to 11K BTU by using a more efficient unit. We are in CS 7A, so efficiency on very cold days is a challenge.

    That said, you're going to hear a lot more about this as hydro and gas prices nearly double this winter.

    1. Jemari | | #36

      What we need is something like a thermostat - that is both a sensor and has some light duty programable logic. You could mount it on the wall, connect it to the boost circuit on your ERV, and dial in your settings on the device using a couple buttons. No complicated software downloads, subscriptions, bluetooth, or wifi needed! I prefer solid state tech that is low maintenance. Fiddling with sensors and software during my precious free time is not my idea of a good life. We actually had something exactly like this at my office when I worked there before COVID. It did heat and CO2. I don't remember if it did VOCs that were not CO2, or particulates/humidity.

      1. Expert Member
        MALCOLM TAYLOR | | #37

        Jemari,

        I agree. That's the direction I hope things go.

        We have code mandated full time mechanical ventilation here, and a lot of people turn it off because they don't see any benefit, or know what it is doing. The average homeowner doesn't want to monkey with a something complex, but I think what you suggest would be both simple, and give an incentive to care about the system.

        1. Expert Member
          Akos | | #39

          There are a number of commercial sensors that do just that such as Honeywell C7233. This is a simple 24v sensor with dry contact output. You can connect this to the boost input on an ERV.

          The problem is they are pretty spendy.

  16. user-7833485 | | #38

    An option that is coming to market in May is the Fresh-R. It looks like a good retrofit option and has some interesting room to room fans. It does detect CO2 and that is what determines the functioning. It will be available from Small Planet Supply.

    https://www.smallplanetsupply.com/freshr-hrvs

  17. entropic | | #40

    Just echoing Martin in post #7 on mentioning the CERV2. It’s not a mainstream product, but I’d be curious to hear what some of the expert members think of it as a solution to the original question.

    https://buildequinox.com/

    1. rondeaunotrondo | | #43

      The CERV2 essentially does everything that everyone is asking for in this post (monitoring, on demand, energy saving, etc). I’ve been retrofitting one into my 1920s bungalow for the last year. It’s made an unbelievable difference in my monitored IAQ. I ducted an in-line aprilaire e080 dehu with it. I’ve been working on airsealing and insulating on and off for 3 years as well.

  18. DennisWood | | #41

    There has been (a few?) ERVs with 0-10 volt fan control (the UltimateAir Recoupaerator 200DX had a 0-10v control option, but they are out of business). Their manual advertised this capability so would allow you to control the fan speeds outside of the unit. Page 33 of this manual ( https://d3pcsg2wjq9izr.cloudfront.net/files/41746/download/712491/50.pdf ) shows the option to choose levels from 36 to 195 CFM based on on 0-10 V control. So it was doable quite some time ago :-) 0-10 volt controllers that tie into home automation systems are now available from Zooz (Zen54) and Leviton ZS057-D0Z. Both are under $75.

    Any unit today with a set of extra dry contacts for a remote switch can use an off the shelf CO2 sensor relay as I linked to a few post back for simple on/off control.

    The next level (which I'm using today) is to not just turn the unit on/off via a CO2 set point, but ramp the unit's ventilation rate based on occupancy. This way it can idle back to something like 15-20 watts (which many ECM units will do at 50-60 CFM) if occupancy is low or zero. If I'm doing this today with an off the shelf CO2 sensor and 0-10V control, then there is no reason there will not be a commercial offering sooner than later. My setup ramps to four discrete balanced air flow profiles (OFF, 50, 60, 75, 90 CFM) which target 700 PPM CO2 but it would not be a stretch to continuously vary the fan speeds. I'm using an Ecowitt CO2 sensor which also does PM2.5 and PM10 which again would allow one to adjust on PM2.5 as well as CO2.

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