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Dynamically Balancing (or not) House Ventilation – Bad Idea or Smarter Ventilation?

DennisWood | Posted in General Questions on

I’m working on an HRV setup that would potentially react to events in the home, to basically unbalance itself (add makeup air flow).

I realise that an unbalanced core is not as efficient.

I’ve taken a few measurements for example in my own home to find that with a kitchen exhaust running at 160 CFM (measured), the home is being pulled to negative .03 WG…the “recommended” threshold is .025 negative.

Given that I can control the two HRV EC fans independently via 0-10V and that the home is heavily automated, is there any reason not to do this?  The idea is to set a baseline for balanced normal (efficient) use, then ramp intake to bring the house more neutral when required only.

The same would apply say when the home is not occupied…the EC motors could be ramped down or turned off.  Based on my measurements/calculations we’re needing about 11K BTU per day to compensate for the HRV running at 89% efficiency @ 0 F (-17C)  @ 90 CFM.

So smarter ventilation or bad idea?

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Replies

  1. mr_reference_Hugh | | #1

    Hi Dennis, Martin H. Responded to a similar question a few years back. Check out this link.

    https://www.greenbuildingadvisor.com/question/rig-an-hrv-to-act-as-a-makeup-air-unit

    I was listening to a prior BS &Beer show yesterday and they mentioned that there are now HRVs that are designed and sold to double as makeup air units.

  2. mr_reference_Hugh | | #2

    There is a GBA article where Martin H replies to your question from a different person in the comments.
    https://www.greenbuildingadvisor.com/article/all-about-makeup-air

  3. DennisWood | | #3

    Mr Hugh, I do appreciate your replies. I read over those threads and the information got me thinking about an issue that I did not read about in those threads, but now seems obvious.

    We have an increasingly tight home so that just running the kitchen fan at 160 CFM brings the house over .03 WG negative. However, the fireplace uses outside air, water heater is direct vent, and the condensing furnace also uses outside air. Our clothes dryer is condensing so has no ducting. Some makeup air via the HRV (we don't need a lot) makes sense except for one big issue I see.

    We're in climate zone 7A. The HRV needs to be able to deal with temps below -35C. I've attached the defrost cycle table for this unit. There is just one sensor for temperature just inside the fresh air intake damper. The intake damper closes, and in doing this, opens the recirc damper...they are physically connected to the same damper motor. Air flow now goes through the core and returns to the home to warm it up. I'm pretty sure the defrost cycle is just on a simple timer...if the sensor sees -15 to -26 C intake air, it runs 6 minutes recirc, 32 ventilation time as per the chart.

    So if you ramp intake say 20%, at -15 C, the core will likely freeze up as you are cooling it excessively by unbalancing intake vs exhaust. The defrost cycle is likely set up during testing, based on balanced air flow over the core. And during defrost cycles, regardless, any makeup air would stop.

    So makeup air via HRV/ERV (even it is an alternating charge/discharge like the Tempeff units) for cold climate is likely not worth the problems it would cause just based on the thermal imbalance it would create at the unit's core. In warmer climates, I don't see why a unit could not adjust (at the expense of efficiency), say 100 CFM, to manage a very tight home.

    In cold climates and very tight homes, I figure the pressure switch managed makeup system with an inline heater still makes more sense to ensure a kitchen hood (even flowing less than 400CFM works as advertised. KISS rule prevails.

  4. mr_reference_Hugh | | #4

    Hi Dennis, after reading the articles myself I came to the same conclusion. Then I thought about the fact that this is just engineering. We need to deal with the laws of physics but there are many things that we need that have not been invented yet.

    I kinda wish I had a lab where I could work on this stuff, or maybe I need to learn to use modeling software. This makeup air issue is something that warrants a very simpler solution than what is currently available.

    The solution should be able to recapture the significant heat of the air leaving from the range hood and also be directed to create an air curtain around 3 sides of the stove.

    https://www.greenbuildingadvisor.com/question/residential-air-curtain-kitchen-ventilation-hoods

    Basically an HRV designed specifically to handle hot, humid, sometimes greasy air from the range. The core should be removable and something you can throw in the dishwasher.

    Wanna go in on it with me. We could make millions.

  5. DennisWood | | #5

    Ha, sure..count me in. If you're interested in what I think is the best ventilator out there...check this: https://www.tempeff.com/wp-content/uploads/2022/09/14094-Tempeff_RGSP-K_Sellsheet.pdf

    NRC has been testing in arctic conditions and they can't break it. It still doesn't solve the make-up air issue though.

  6. mr_reference_Hugh | | #6

    Of course it is not new apparently, just new to NA.

    And this is a Winnipeg based company. Go Canada.

    https://www.tempeff.com/insights/researcher-says-theres-a-better-way-to-ventilate-homes-in-the-north/

    “The technology employed by Tempeff originated in Sweden more than 30 years ago, but company owner Garth Evans say it's still relatively new to North America”

    And apparently $5000 per unit. From what I read it is close to the cost of a Zehnder.

    https://www.greenbuildingadvisor.com/question/zehnder-erv-quote

    Has there been any GBA Q&A question on this unit?

    How did you find out about the unit and NRC research? Just curious to learn how others keep up with the ongoing innovations.

  7. DennisWood | | #7

    I found it researching cold weather options. I spoke with their sales manager.

    Unlike the Zhender though, there is no need for a ground loop or any kind of preheat strategy. I'ts basically a Lunos on steroids.

    https://nrc.canada.ca/en/certifications-evaluations-standards/codes-canada/construction-innovation/air-ventilation-systems-arctic-housing

    https://nrc.canada.ca/index.php/en/certifications-evaluations-standards/codes-canada/construction-innovation/canadian-centre-housing-technology-evaluation-dual-core-heatenergy-recovery-ventilation-systems

    This third link is the best summary of the KPSG-K

    https://www.canada.ca/content/dam/polar-polaire/documents/pdf/publications/aqhaliat/2019/energy-recovery-ventilation-system.pdf

    "Conclusions:

    This rigorous investigation has shown that, in
    comparison to a conventional single core ERV,
    the dual core ERV system had higher ASE and
    ATE, was more frost-tolerant, and was capable
    of withstanding an outdoor temperature below
    -30 °C. The dual core design showed no sign of
    frost problems, provided a continuous supply
    of outdoor air, and was capable of supplying
    air at temperatures up to 6 °C higher than the
    air temperature supplied by a single core ERV.
    Under extreme weather conditions, the supply
    POLAR KNOWLEDGE Aqhaliat
    AQHALIAT REPORT 2019 95
    air temperature dropped below an acceptable
    temperature. To correct this, a post-heating system
    before supplying air to the occupied space (indoor)
    would be required. However, the dual core ERV
    did not freeze and continued to operate without
    reduction in air exchange. Future work will focus
    on enhancing the dual core technology to make it
    a demand-controlled ventilation system, capable
    of adjusting the ventilation rate based on indoor
    needs (overcrowding, high activities, etc.)."

  8. mr_reference_Hugh | | #8

    Dennis, do you mind if I ask on the Q&A whether anyone has installed one or has seen a installation? I have never seen this unit being discussed as an option - of course I can't read every single thing on GBA.

  9. DennisWood | | #9

    Ask away. Aside from finding the NRC articles (they've been testing for quite some time) , I've seen zero mention of this system, anywhere. I had a great conversation with their sales manager and it sounds like they installed quite a few of the smaller KGSP-K units in schools to increase air exchange in response to Covid. The big attraction was that there was typically no need for any kind of auxiliary heat after installation, and the units would effectively isolate a few classrooms as well with respect to air transfer.

    The systems use aluminium heat exchange units made in-house. I'm still waiting to hear back from them with respect to reviewing a unit.

    He did mention that recovery of moisture is actually quite good in very cold temps (a concern in very cold climates) as condensation on the core is recovered during the flow reversals that happens via the central damper, every 60 seconds or so. It's basically the Lunos concept but with much larger/more effective exchangers, and the ability to scale to industrial CFM levels.

    1. Expert Member
      MALCOLM TAYLOR | | #10

      Dennis,

      If you come to any interesting conclusions, please come back and update this discussion.

      Thunder Bay brings back memories of piece-work tree planting in Geraldton for 4 cents each.

  10. DennisWood | | #11

    Malcolm, I spent a week with tree planters..lost a few litres of blood to the hoards of skitters. That is not an easy gig! On the NRC Tempeff exchanger, I have not heard back from them, other than an estimated cost likely in the $5-6K CAD cost.

    I've learned more than I was planning for in my current explorations with efficiency, air flow, temp differentials etc. I'm finding the data gathering with regard to air stream temps, CO2 levels in our home, ventilation rates very interesting.

    Draining the HRV turned out to be an unexpected challenge with regard to tubing, the need for an added vent (like house plumbing) so I had some unexpected freeze/flooding at the colder temps we're seeing. That's all resolved.

    I think we have a lot of work to do in making our ventilation system smarter, so for me, finding a way to control 0-10V EC fan speeds with an inexpensive Leviton dimmer (that also connects to home automation via zigbee wireless) opens up a lot of possibilities. For example, the kitchen exhaust hood fan now triggers the HRV, however I found that the house was at most .04" negative, with all house fans running full tilt, so there is not a huge need to unbalance (nor should you at cold temps on intake).

    Ramping intake fan speeds when using the high efficiency fireplace (with outside air supply) worked wonders to eliminate back smoking when loading the unit. It's super easy to set this up via temperature, or just via a zwave/zigbee wall remote.

    It might be easier if you had questions to just post them as otherwise this post may go on for way too long. Here is the current control setup. I replaced the intake fan with a six inch EC version, which enables a balancing 100 CFM with the MERV13 filtration and full ducting connected. I've attached the latest dashboard...

  11. andyfrog | | #12

    Have you looked into the BuildEquinox CERV2 or Minotair units? I don't think they do exactly what you are looking for, but they might get close for an off the shelf solution.

  12. DCContrarian | | #13

    I'm trying to think what problem your aiming to solve.

    Replacement air is going to get into the house, it's just a question of whether it comes in through the HRV or infiltrates through openings in the house. If it comes through the HRV there's not going to be any more heat recovery, because there isn't a corresponding exhaust of interior air to provide the heat. So long as all of your combustion appliances have their own air supplies there's noting inherently bad about having slight negative pressure in your house.

    1. Expert Member
      MALCOLM TAYLOR | | #15

      DC,

      "So long as all of your combustion appliances have their own air supplies there's noting inherently bad about having slight negative pressure in your house."

      I was interested in whether the unbalancing could act as an alternative to having to make provisions for each appliance.

  13. DennisWood | | #14

    The primary goal was honestly to come up with an HRV solution (re purposing a unit that was heading for scrap) that could approach the efficiency of a "modern" unit. I'd say that job is done as we're seeing 80-85% efficiency, using only 23 watts of power.

    I wanted to have full control via automation (Hubitat) of the EC motors. I figured out how to do this using Leviton 0-10V dimmers that also use zigbee protocols. Finally, I needed live temp feeds of the four air streams. (Fibaro Smart Implant using DS18B20 temp sensors). The automation bits are less than $200 all in.

    A secondary goal (keeping in mind that I can measure and automate on the four air stream temps) was to see what is possible by controlling the HRV EC motors in response to events in the home. You could summarise what I've found so far as follows:

    1. Removing the inefficient (270 watt) internal motor and replacing with EC inline motors is 100% possible and effective. From 270 watts to about 23 watts in fact.

    2. Running a small positive pressure balance (which again can be easily automated) is very effective in reducing back draft smoke in our case from a high efficiency fireplace. Even with outside air, back puffing was always an issue..and even a small amount spreads throughout the house very quickly.

    3. With an kitchen exhaust fan automated and triggered by induction cook top use, synchronising the HRV to high speed along with a positive balance works well and keeps the house under .02" negative. It also solves the "they don't turn it on" issue 100%.

    4. HRV/ERV efficiency is very much affected by balance and can skew efficiency from about 70 to 92 % at the extremes in my tests with this core. The manufacturer (Venmar) 0f this unit indicates that a difference of 10 CFM is considered "balanced", so I've created four CFM options, each with a bias of 10 CFM to increase efficiency. Balancing via 0-10V control on the EC motors requires no dampers and is about as efficient as it gets.

    5. Draining an HRV with any kind of horizontal tubing run can be challenging. I was staring at icing and "flooding" from the HRV until I figured out that I had to use larger ID tubing, and actually add a vent...like a plumbing stack. Turns out that water movement, correct unit lean/tilt and drain performance needs to be correct as temps drop below freezing! Took me 3-4 days to figure all that out as icing was not due to the defrost logic, but rather drainage!

    6. Defrost on most ERVs is pretty "dumb". It's just based on a few temp set points and set times via a thermister. We can definitely do better (as in dynamically change the recirc time) by just comparing output temps vs stale air temps in recirc mode.

    7. Great care needs to be taken on air sealing, insulating and vapour sealing the duct work to the outside of the building. Even a small gap creates a ton of condensed water at low temps. In tight quarters, this can be a challenge to get right!

    8. You can likely use a smaller EC fan on exhaust vs fresh. But I'd 100% just use 6" EC fans (like the AC Infinity units i"m using) if doing this again.

    9. Adding a 14x14x4 MERV 13 inline filter box external to the HRV creates less resistance than the small internal HRV filters which are MERV 8 at best. I'm able to achieve a balanced rate of 100 CFM with all ducting and filters installed, although power use at this rate is closer to 45 watts.

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