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Thread: HRV or ERV?

  1. #40
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    Oct 2003
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    Quote Originally Posted by teddy bear View Post
    Good post! One point you are illistrating is the lack of the need for mechanical venilation during cold dry weather. If no mechanical ventilation is required during the only time heat energy is saved, what is the benefit?
    I was re-reading this thread and just want to comment on this point for any future readers. The largest reason that our indoor RH was kept in check in February without running the ERV was because the builder ducted a fresh air/make up air supply duct to the return plenum. So every time the furnace fan operated, cold, dry air was being sucked into the return. This is the cheap way (upfront, energy costly in long-run) to provide air exchange and is completely unnecessary except for make up air after I installed the ERV. So, I will be installing a Belimo actuated damper tied into the Vision Pro IAQ to close off that hole in the wall unless there is demand for make up air. After doing this, mechanical ventilation will be required.

  2. #41
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    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by goldenear View Post
    I was re-reading this thread and just want to comment on this point for any future readers. The largest reason that our indoor RH was kept in check in February without running the ERV was because the builder ducted a fresh air/make up air supply duct to the return plenum. So every time the furnace fan operated, cold, dry air was being sucked into the return. This is the cheap way (upfront, energy costly in long-run) to provide air exchange and is completely unnecessary except for make up air after I installed the ERV. So, I will be installing a Belimo actuated damper tied into the Vision Pro IAQ to close off that hole in the wall unless there is demand for make up air. After doing this, mechanical ventilation will be required.
    Keep in mind that closing the make-up air inlet when the fan is not operating will save less than $10 for the year. Very little air moves through a small inlet with the fan off.
    Unless you have a furnace with a gravity chiminey, close the make-up air on the cold air return and operate you ERV a little more. Keeping the vent closed all the time will save $50 for the year and you do not need the Belimo. Keep us posted on the summer %RH during wet weather. Only tring to help. TB

  3. #42
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    Oct 2003
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    45
    yeah, key phrase in your statement being "when the fan is not operating!" However, everything connected to the system currently engages the fan. Also, everyone always says there's no infiltration through make up air duct unless house is in negative pressure. That's just plain wrong. When I was installing the Aprilaire 600, I stuck my hand in the drop and felt a lot of cold air pouring into the return plenum. The smell of cold, outside air was unmistakable. Everything was powered off, so no fan running. I think most of the infiltration is due to excessive wind in our area. 15+ mph is almost a daily average - kinda ridiculous. As soon as I installed the damper, no more cold, outside air. I also noticed the breaks between furnace cycles were significantly longer while running accessories such as ERV and humidifier that engage the furnace fan. That results in a direct energy savings.

    Summer RH is handled by AC. Excess humidity when no demand for cooling will be handled by a UA 100V.

  4. #43
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    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by goldenear View Post
    yeah, key phrase in your statement being "when the fan is not operating!" However, everything connected to the system currently engages the fan. Also, everyone always says there's no infiltration through make up air duct unless house is in negative pressure. That's just plain wrong. When I was installing the Aprilaire 600, I stuck my hand in the drop and felt a lot of cold air pouring into the return plenum. The smell of cold, outside air was unmistakable. Everything was powered off, so no fan running. I think most of the infiltration is due to excessive wind in our area. 15+ mph is almost a daily average - kinda ridiculous. As soon as I installed the damper, no more cold, outside air. I also noticed the breaks between furnace cycles were significantly longer while running accessories such as ERV and humidifier that engage the furnace fan. That results in a direct energy savings.

    Summer RH is handled by AC. Excess humidity when no demand for cooling will be handled by a UA 100V.
    I knew there was something I really liked about you. My point about a ducted fresh air inlet is about $10 worth of heat is required for the additional fresh air leaking into the home. Damper is ok. Saves $10/year. The average wind in WI is 7 knots/hour but location of the home and vent is everything. You have all the bases covered. Keep us posted on how your house works this spring/summer.
    Thanks again, TB

  5. #44
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    Oct 2003
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    TB - well spring and summer have passed us here in WI. I still have not got around to installing the Ultra Aire unit but will need to do so relatively soon since I am framing in the utility room and need to have things finalized prior to completing the rough carpentry work.

    The weather this year in SE WI has been all over the map as you know. No probs with indoor RH as monitored by the VisionPRO IAQ. Indoor temps were maintained @ 76-77F and RH was <50% with intermittent use of "basement" dehu in conditioned lower level. Yes, it's extremely energy inefficient and will be decommissioned soon.

    ERV has been on continuous probably 65% of the time, 35% intermittent. Have used makeup air vent as needed based upon exhaust use. Have opened windows less than 5x this year. Our indoor air is cleaner than outside air.

  6. #45

    sizing an erv

    I stumbled across this forum 3 days ago. It has exactly the info I've been wondering about.

    I also live in SE Wisconsin and am planning on installing a renewaire erv. My question is sizing the erv. I have a house with a vaulted ceiling and walkout finished basement.

    The upper level of the house 2400 ft2. The basement heating and cooling is not optimal as there are only two heat vents, no returns. Assuming I will not change anything in the basement regarding forced air heat, do I size the erv for the 2400 ft2 upstairs or do I include the basement too?

    the units I am looking at are the ev130 (handles 2700 ft2) or the ev200 which handles an area >2700ft2.

    side note: the ev200 seems a bit more energy efficient, but I don't really understand the numbers... http://www.renewaire.com/for_your_ho...t_fits_you.php

    thanks in advance.

  7. #46
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    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by wetwindows View Post
    I stumbled across this forum 3 days ago. It has exactly the info I've been wondering about.

    I also live in SE Wisconsin and am planning on installing a renewaire erv. My question is sizing the erv. I have a house with a vaulted ceiling and walkout finished basement.

    The upper level of the house 2400 ft2. The basement heating and cooling is not optimal as there are only two heat vents, no returns. Assuming I will not change anything in the basement regarding forced air heat, do I size the erv for the 2400 ft2 upstairs or do I include the basement too?

    the units I am looking at are the ev130 (handles 2700 ft2) or the ev200 which handles an area >2700ft2.
    .
    Sounds like you are living the home currently. I would size the ERV on the need for fresh air. All homes have a natural leakage rate. Most homes leak enough air during cold weather to not require supplemental fresh air. The sign of inadequate winter fresh air is dripping moisture on windows during cold weather. <.5 " of moisture on the bottom of a window during the 1st cold snap is ok. Also avoid deep t-stat set-back, keeping the window warm during cold evenings. Any of these excess moisture signs indicates moisture sources inside the home or a need for year around additional fresh air ventilation.
    Severe window condensation suggest 100 cfm of fresh dry air ventilation. Using an ERV which returns about half of the exhaust air humidity, requires double the volume of fresh air for the same amount of moisture removal.
    Moderate condensation suggest 50-75 cfm of additional make-up fresh air ventilation. This could achieved by operating a bath fan on a daily routine.

    After getting enough fresh air to keep the window from dripping, maintain the same ventilation when the windows are closed through the summer. In green grass climates, maintain <50%RH (summer) to avoid mold/dust mites and provide comfort.
    Regards, TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  8. #47
    Join Date
    Aug 2005
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    18
    Quote Originally Posted by wetwindows View Post
    I stumbled across this forum 3 days ago. It has exactly the info I've been wondering about.

    I also live in SE Wisconsin and am planning on installing a renewaire erv. My question is sizing the erv. I have a house with a vaulted ceiling and walkout finished basement.

    The upper level of the house 2400 ft2. The basement heating and cooling is not optimal as there are only two heat vents, no returns. Assuming I will not change anything in the basement regarding forced air heat, do I size the erv for the 2400 ft2 upstairs or do I include the basement too?

    the units I am looking at are the ev130 (handles 2700 ft2) or the ev200 which handles an area >2700ft2.

    side note: the ev200 seems a bit more energy efficient, but I don't really understand the numbers... http://www.renewaire.com/for_your_ho...t_fits_you.php

    thanks in advance.

    I think the recommendation for sizing are based on about a total air volume change every 3 hours. I have 4000 sq ft and I got a EV200. The limit of 2700 sq ft for the EV130 is for 100% run time. If you get the EV200 (which is more efficient), you can get the same result as a EV130 by running 65% of the time. You can do this by using a ERV controller (RenewAire has one, I used AirCycler instead).

  9. #48
    Join Date
    Oct 2006
    Location
    Emerald Coast, FL 30.1N 85.8W
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    681

    Maryland -- ERV

    For your conditions, the ERV is better suited since it provides better moisture control and enthalpy(energy) transfer.

    Both ERV & HRV utilize bypass dampers and wheel speed control, but the ERV spanks the HRV's butt when it comes to latent energy effectiveness (ERV & HRV have similar sensible energy effectiveness).

    You alluded to the Carrier unit sounding like both an HRV & ERV. Some units use a Precooling Air Reheater that utilizes humid outside air, which is precooled through the exchanger and subsequently passes through the cooling coil. Then, the cooled dehumidified air is reheated by passing through the other side of the exchanger, reheating the supply air -- I suspect the Carrier unit does this.

  10. #49
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    Apr 2002
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    In the winter, the ERV has the advantage over the HRV in that it will not over dry the house if the steady constant supply of fresh air is desired.

    In the summer the ERV CAN be installed to greatly reduce the latent load of the fresh air you are supplying to the home.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  11. #50
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    Jun 2003
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    Quote Originally Posted by montr View Post
    I think the recommendation for sizing are based on about a total air volume change every 3 hours. I have 4000 sq ft and I got a EV200. The limit of 2700 sq ft for the EV130 is for 100% run time. If you get the EV200 (which is more efficient), you can get the same result as a EV130 by running 65% of the time. You can do this by using a ERV controller (RenewAire has one, I used AirCycler instead).
    All homes have a natural leakage rate from wind and stack effect. The amount of leakage is varible and depends on outside/inside tempature differential and the volcity of the wind. Most homes leak enough fresh air during the winter weather to approach the 200 cfm of fresh air. This makes the home very dry and may require humidification. The tightest of home are 50-75 cfm of natural. Add in the effect of clothes drier, kitchen hood, bath fans, and gas water heater for the total the air change effect. Operating balanced flow ERV/HRV adds to the natural ventilation of the home. Sizing ventilation should consider natural leakage of the home and the number of occupants more the total sqft. of the home. Adding 100 cfm of balanced fresh air ventilation to home to the best of homes means +150 cfm. The time of year that natural ventilation is the lowest is spring/summer/fall during low wind. Under this condition, 50-100 cfm fresh air is adequate to purge pollutants and renew oxygen. A sign of inadequate fresh air is sweaty windows during cold weather. During winter, adding ventilation to home with dry windows may not be necesary. Most homes would benefit from fresh during the rest of the year. In green grass climates, warm weather ventilation has a moisture load. Maintaining <50%RH is critical to avoid mold and dust mites. 100 cfm of 70^F dew point outside fresh air in through a 50% effecient ERV is 2 lbs. of moisture per hour added to the home. When the clothes drier is operating, 150 cfm or 6 lbs. moisture per hour. Each adult is .25 Lbs. per hour. A 2,500 sqft. basement maybe 1-2 lbs. per hour. An a/c operating at full cooling load will remove all this moisture and maintain <50%RH. With rainy weather and no a/c cooling load, 70-100 pints/day of dehumidifcation is required to maintain <50%RH. If 200 cfm is the amount of fresh air ventilation, up the dehu capacity to 150 lbs. per day.
    ASHRAE recommends 7.5 cfm per adult + .01 cfm per sqft. + natural ventilation as a starter. Regards Dehu TB.
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #51
    Join Date
    Apr 2002
    Posts
    11,808
    Tight home is in the eye of the beholder teddy.

    Many are significantly lower than the natural rate of 50 to 75 CFM.

    And when you run a one sided ventilation scheme, by pressurizing and exhausting, you already know that the natural infiltration goes out of the equation.

    In a cold climate, after the water of new construction was gone, such as the second winter an HRV even on low speed like 75 CFM, combined with the natural infiltration will overdry a house and people will be tempted to install humidifiers. The ERV has an advantage here.

    An HRV, capable of moving a higher volume of air at about 0.3 airchanges an hour can function intermittenrtly on a rise in humidity and keep those windows clear. As indoor humidity rises so does CO2, so indirectly the CO2 is being controlled in the winter time.

    The ASHRAE ventialtion rates also assume so much infiltration occuring in the space, perhaps 2 CFm for every 100 square feet. This was in the back of their minds when they came up with some many CFM per person and so much ventilation CFM per square foot.

    With one sided ventilation this is gone in the tighter homes.It may very well take a steady 50 to 75 or more CFM on the one sided systems to provide the IAQ because the infiltration has been eliminated.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  13. #52
    Join Date
    Oct 2007
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    34
    Quote Originally Posted by Carnak View Post
    In the winter, the ERV has the advantage over the HRV in that it will not over dry the house if the steady constant supply of fresh air is desired.

    In the summer the ERV CAN be installed to greatly reduce the latent load of the fresh air you are supplying to the home.
    yes.I have the same opinion

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