ERV recommendations

Looking for ERV recommendations for a new two level ICF residence located at 6800 ft elevation with 6001 HDD base 65 and 0 CDD base 50. Radiant floor heating only. Conditioned living space is 20,000 cf per level plus small amount of conditioned attic due to foaming the roof deck. Lower level is walkout on one side and buried on three. Upper level has garage attached on one side only.

Using total volume * 0.35 ach / 60 min/hour = ~120 cfm flow per level. There are two baths and laundry per level and two bedrooms and great area on each level. Plan on drawing from baths and laundry and supply bedrooms and great area.

Looking for easy to install and maintain system with auto dehumidification boost capability for the bathrooms. Will install in storage room on lower level and conditioned attic space on upper. Prefer side pipes due to limited height in attic space. House as gas fireplaces on each level that vent to the exterior, though currently drawing from the house. Also, large range hood over island stove top with no makeup air. Considering making the house slightly positive pressure. 

What do you find that works in the dry southwest at altitude? Remote area with limited HVAC technicians to rely on! Any design considerations we should keep in mind?

Thank you in advance for sharing your knowledge.

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  • Thank you for all your comments. House is ICF and local code is 2018 IECC listing maximum 3 ACH50. Depending on zone and shielding selected ACH averages out about 108 CFMnatural. ASHRAE 62.2 calculation indicates 32 CFM continuous required (3 beds, 3670 sf). House has NO conditioned air ducting. Only radiant floor and ceiling fans. Concern is bathrooms are next to closets on both levels and both are where there is no natural air circulation or operable windows. Lower level is underground and farthest from the walk out side. I live relatively nearby and am dealing with humidity in my closets in a 5 ACH50 house with better air circulation.

    House will have enclosed gas fireplaces on each level, no wood, and highly encouraging them to connect to dedicated outside fresh air.

    Current design is to shoot for 60 cfm per level on low and 120 cfm on high. Each level is roughly 20,000 cf. Bathrooms to have 20/40/60 minute push timers for manual local condition control and humidistat installed and set high (~70%+) to handle shower/bath moisture loads automatically. All returns vent to the Great Room on each level.

    Considering Aldes ERV with CAR II inserts to maintain minimum air flow (20 cfm (2) bathrooms, 10 cfm closet and Great Room) and maximum air flow in closets & Great Room (10 CFM) and unlimited maximum in bathrooms on each level. Does anyone have experience with Aldes systems and using their constant air regulators?

    Alternate is Venmar system, using inline damper controls for defining flow rates at registers. General Contractor has previous experience with this brand.

    Location of equipment creates height limit of selected equipment and access issues to consider.

    Concern is limited skill of technicians in this rural area. House is 45 minutes from nearest small town with two old school HVAC contractors. Next contractor is 1.5 hours away.

    • I've used the CAR II regulators before. They work, but obviously it's more mechanical moving parts that might fail overtime. I've had good success using simple adjustable diffusers. Diffusers closest to the ERV will be more "closed" and ones farther from the ERV will be more open.

      If you give old school HVAC contractors a good ERV strategy outlining duct sizes and locations, they shouldn't have a problem. ERV/HRV systems can be as simple or as complicated as you want to make them. In your strategy (60-120 cfm per floor) I would use 6" trunks off the ERV and 4" branches to 2-3 locations.

      Example layout:

      ERV-1 operating at 60 cfm continuous and 120 cfm in boost.

      Supply: 6" trunk off ERV, 4" branch to bed1, 4" branch to bed2, 4" branch to great room.

      Exhaust 6" trunk off ERV, 4" branch to bath1, 4" branch to bath2. Boost timers wired from bathrooms to ERV for increased flow rate.

      Two 6" insulated trunks routed to the exterior 6" hoods -- hoods located minimum of 6 ft a part and preferably 4 ft above the exterior ground. 

      4" adjustable round diffusers (SEIHO) installed at the termination of each branch duct in ceiling. Adjustable to achieve the desired continuous flow rate in that location.

      Hard to make a full strategy without seeing the actual floor plans. But this is a pretty standard set up for an ERV in an ICF house. Balanced approach.

    • As a Rater and PH guy I have seen a number of units. You do get what you pay for. I also commission for Zehnder, about 180+ to date. Having the ability to dial  in every room to meet a design spec is really special. 2 ECM fans and there diffusers are very customizable. 

      I have seen a few with enthalpy wheels fall apart overtime. I am not a fan of the wheel. Baths should have a min of 20 cfm, But  a little room for filters reducing the flow is advisable 24cfm. A MERV 13 is pretty good too. Having a boost ability on top off that is also important as well when needed intermittently.

      I see many builders install a Zehnder systems themselves.They have some u-tube install advise too.

      Good luck! 

  •  I second Luke's recommendation for Panasonic, RenewAire, Zehnder, or Venmar (Broan). All good units with humidity recovery. Hook through bathrooms to encourage humidity retention. I personally would choose a Panasonic or Zehnder. The core material is what your humidity recovery is based on. 

    Also, how are you going to distribute the air in the house? Whole house distribution system? If its not being equally distributed through house it isn't much of a ventilation system.

    I would focus on controls instead of the basic Ashrae calcs. ASHRAE is based on radon and off gassing of new construction materials. Very little to do with occupant load. How many people live in the house, how much cooking, and bathing takes place. So having a low and high function is helpful to deal with occupant load. Also, you should base the settings on your air infiltration rate, blower door test. If you have a house at 1ACh you obviously need more ventilation. If you are at 4ACH you need far less. 

    Setting the balanced system for positive pressure will help with dust. But, setting to a slight depressurization will help keep wall caps shut and decrease loads on the house. 

    Do you have any gas combustion appliances? any, naturally drafitn? Be careful of back drafting. A tight house with fireplaces and combustion appliances do not mix.

    I would highly recommend efficient fireplaces with make up air from outside. Traditional fireplaces and new construction tight houses do not play nicely together. 

    Bottom line is you need to know how tight the house is. 

  • Hello David -- Do you have an expected air tightness? What type of blower door test results are you projecting?

    David is right; you should be using a low flow range hood of 300 cfm with good capture rate. Without an account for how that air will be replaced, you cannot use a large range hood. Even an ERV with slight positive continuous pressure is not going to assist when you are pulling 1000+ cfm from the kitchen.

    Shoot for 25 cfm continuous from the bathrooms and 40 cfm when boosted. Switch the dryers to heat pump options without an exhaust. Then pull 15 cfm from those laundry spaces continuously.

    My beginning recommendation would be to have 65 cfm per level continuously. 100-150 cfm during periods of showering. Duct size in this scenario would be 5" or 6" trunks with 4" branches to all the supply and exhaust diffuser locations. This should meet ASHREA 62.2 requirements for ventilation and give you a solid IAQ strategy.

    I would use push button boost options rather than humidity sensors. Sensors go bad over time, and might activate increased ventilation accidentally when you might not require it.

    You should have several options available. Choose an ERV with over 80% heat recovery, DC motors, and filtration over MERV10. Consider select high performance models from UltimateAir, Panasonic, RenewAire, Zehnder, or Venmar (Broan).

    FYI - I work for UltimateAir, but I believe that is a pretty unbiased recommendation :)

    • @Luke, since you work for a well-known ERV manufacturer, I'm curious if you have access to latent performance data (other than the single point @ summer conditions typically published). A graph would be ideal. I think most practitioners fail to consider what happens when an ERV is used as primary exhaust for high moisture events, especially showers.

      • Thanks, Luke. I agree it wouldn't make sense to design an ERV to accommodate high interior moisture loads. I think the simplest strategy for that is to not rely on an ERV to exhaust excess interior moisture, as they're not designed for that. Whether or not recycled (recovered) water vapor might push indoor humidity to risky levels depends on several factors, but at least designers need to be better educated on this point. Dismissing this as a non-issue is not helpful to that end.

        As you point out, having multiple exhaust inlets reduces the incidence of recovered moisture, although I would argue it doesn't eliminate the risk. In any case, I doubt many designers (if any?) consider this when prescribing the number of exhaust inlets. Worst case is a single exhaust inlet - located in master bath. This scenario is certainly not unheard of and isn't addressed in ERV installation manuals, WhisperComfort being the exception (possibly because it's designed to be single-port, as you observed in a similar discussion here last year:

        Keep in mind, the problem I'm describing isn't really a summer issue. Highest risk is during swing seasons (when there's no cooling load), and in winter when moisture recovery is generally welcome. However, this can backfire in tight homes, which naturally have higher wintertime humidity than leaky homes (unless ventilated via HRV). I've seen been plenty of anecdotal reports of wintertime moisture issues in high performance homes.

        It's easy to understand why we need to maintain significantly lower RH levels in winter: (a) lower indoor ambients, (b) natural temperature variations across the house (especially in unventilated closets with exterior exposure), (c) aggressive nighttime setback and/or shutting off heat to unused rooms, and (d) potential for air leakage into exterior cavities. I generally advise clients that anything above about 40% RH is risky business in winter.

        As I mentioned in last year's discussion, I first became aware of this problem when my brother spent more than $20k to remediate mold, proven to be caused by his ERV that had a single exhaust port in master bath, along with a boost switch, and no stand-alone exhaust fan. Neither his mechanical contractor nor the builder understood why that's a problem. We need to do better.

        The obvious defensive strategy against excess interior moisture is to increase moisture removal at the source. Stand-alone bath fans are cheap, and very effective when installed properly.

      • When it comes to independently ducted ERV systems operating in humid climates during the summer; the high moisture event (shower), on a single exhaust branch combines with the other exhaust streams before reaching the ERV core, this lowers the total amount of moisture there is to "recover" back to the residence. Also, the event of showering is only taking place during a small part of the day. If you have three bathrooms, all with showers operating continuously, then you would probably want to dump all the moisture outside without recovering any for the interior. However, that is a very small period for most applications -- when you consider that the outside condition has the higher level of moisture content for the majority of the daily operation. You want to block the maximum amount of moisture from coming inside during 99% of the day.

        ERV systems are going to transfer a percentage of moisture from the higher air stream to the lower air stream. Generally during the summer, the higher moisture air stream is outside, and therefore you want moisture transfer to occur to prevent adding RH to the interior. During the winter, the higher moisture air stream is coming from the interior, and we are trying to not "dry" out the interior condition, so we again want moisture transfer to occur to keep some moisture inside.

        If an ERV system was able to actively measure the outside RH and interior RH and deactivate the moisture transfer ability when its not wanted....(turn itself into an HRV during periods of summer showering maybe)...that would be beneficial. For our system, you would need two separate wheels, one with heat exchange material, and one with moisture exchange material. Adjusting the speed of rotation given the interior/exterior condition. It would be very cool to do this, but very cost prohibitive.

  • Many ERVs, particularly those with enthalpic wheels, use only ONE motor to run two fans. The In/Out are balanced with dampers.

    The ASHRE standards are guidelines. The installed ventilation system should be capable of moving at least the amount of air recommended by ASHRE 62.2.Those standards are based on average conditions. They are not necessarily appropriate for say a 4,000 sf house with 2 occupants, or a 1,500 sf. house with 6 occupants, two dogs, three cats and 23 potted plants. Humidity can be used as a general guideline for indoor air quality, but as we make our houses tighter, other pollutants, such as CO2, PM 2.5s, and VOCs, will become more important guides to good ventilation.

    "Always look at the whole picture"; "The more you look, the more you see" and "if you don't look, you don't see".

  • Unfortunately I don't have anything to add here but wanted to give this post a bump as I'm a BPI Building Analyst and I'm trying to learn more about what ERV/HRV can accomplish as well as their installation. For what it's worth I'm also at a similar elevation.

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