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> In the past HRVs were mostly used in colder climates Did you mean warmer climates? You went on to mention new membrane tech and pre-heaters that can handle c

> In the past HRVs were mostly used in colder climates Did you mean warmer climates? You went on to mention new membrane tech and pre-heaters that can handle colder temperatures.

shkkmo 4y ago
Those allow ERVs to operate at lower temperatures. HRVs don't need a membrane that passes moisture through, they just need a heat conductive surface.
- h0l0cube 4y ago
  Got it, thanks! If I understand correctly, HRVs have always been suitable for both warm and cold climates. Modern ERVs are becoming more suitable for cold climates with frost protection.
  - jaggederest 4y ago
    Not quite, HRVs are much less useful in a hot-humid climate, because most of the energy actually goes to condensing and removing the humidity, rather than the temperature difference. e.g. 25c -> 20c is only 5 kelvins different, but it might have to go from 95% relative humidity to 50% relative humidity at the same time. So the bottom line for a long time has been, don't bother with HRV in hot-humid climates because they only return ~20% of the embodied energy of the conditioned air, whereas in cold climates, 90%+ of the energy goes into the e.g. 25 kelvins differential in the temperature of the air, and the humidity is already low on incoming air (desirable, since people produce humidity through sweat, showers, cooking, and cleaning) Now that ERVs are coping with much colder temperatures, expect to see HRVs phase out except in extreme climates like Alaska, Alberta and the upper midwest US. I wouldn't expect to see either in very temperate climates like San Diego - there's just not enough energy payoff for the cost of installation. Better off just opening the windows when it's only 2 kelvins different inside and outside! PS the other major difference between ERVs and HRVs is that HRVs are more-or-less maintenance free for life, since they're basically just stacked aluminum plates. ERVs degrade in performance over time, being things like moisture-permeable membranes, so that's a concern for people interested in long term installation in remote areas, for example, but most commercial/residential usage isn't that worried about that.
    - throw0101c 4y ago
      > Better off just opening the windows when it's only 2 kelvins different inside and outside! Except for all the pollen, dust, and pollution that doing so would also bring in. ERVs can cost as little as US$ 1000 for the units themselves: * https://hvacdirect.com/residential-industrial-commercial-fans-ventilation-products/air-cleaning/erv-air-exchangers.html https://hvacdirect.com/residential-industrial-commercial-fan... If this is a retrofit, there can be challenges with installation, but plumbing into existing force air ducts is a common scenario.
      - jaggederest 4y ago
        Well, HRV/ERV have no built-in filtration in themselves, so they're exactly comparable to throwing open the window. If you run them before a filter, obviously they're better, but they have no inherent advantages to opening windows.
        throw0101c 4y ago
        > Well, HRV/ERV have no built-in filtration in themselves Open the linked PDFs for the Broan units and do a text search for "filter": you will find that they do. Further: even if they didn't, the RVs will have ducting for the intake, where you can put a box for a filter, which certainly take up space, but not a lot of money: * https://acinfinity.com/air-filter-boxes/ https://acinfinity.com/air-filter-boxes/ How do you install a MERV ≥8 filter into a window?
ericd 4y ago
He’s saying that you’d use an HRV instead of an ERV, because the moisture exchange of the ERV would start frosting up in a very cold climate. If that’s not a concern, the humidity conditioning the ERV does on the incoming air makes it preferable.
throw0101c 4y ago
>> In the past HRVs were mostly used in colder climates > Did you mean warmer climates? No: HRVs were in cold climates previously because HRV do not deal with moisture, and so there was less frosting / icing up of the membranes. ERVs were more focused in warmer climates, because warmer climates tend to have a lot of humidity, so if you had a dehumidifier in (e.g.) Texas or Florida, and you exhausted stale air, it would end up exhausting the conditioned drier air and intake the outside humid air, which you would then have to dehumidify again. Of course ERVs are also desirable in cold climates because cold air is dry(er), so you'd be drying out your house. So now that is technically more easy, ERVs are also being used in colder climates.
- h0l0cube 4y ago
  Thank you for clarifying.

> In the past HRVs were mostly used in colder climates Did you mean warmer climates? You went on to mention new membrane tech and pre-heaters that can handle colder temperatures.

shkkmo 4y ago

Those allow ERVs to operate at lower temperatures. HRVs don't need a membrane that passes moisture through, they just need a heat conductive surface.

h0l0cube 4y ago
Got it, thanks! If I understand correctly, HRVs have always been suitable for both warm and cold climates. Modern ERVs are becoming more suitable for cold climates with frost protection.
- jaggederest 4y ago
  Not quite, HRVs are much less useful in a hot-humid climate, because most of the energy actually goes to condensing and removing the humidity, rather than the temperature difference. e.g. 25c -> 20c is only 5 kelvins different, but it might have to go from 95% relative humidity to 50% relative humidity at the same time. So the bottom line for a long time has been, don't bother with HRV in hot-humid climates because they only return ~20% of the embodied energy of the conditioned air, whereas in cold climates, 90%+ of the energy goes into the e.g. 25 kelvins differential in the temperature of the air, and the humidity is already low on incoming air (desirable, since people produce humidity through sweat, showers, cooking, and cleaning) Now that ERVs are coping with much colder temperatures, expect to see HRVs phase out except in extreme climates like Alaska, Alberta and the upper midwest US. I wouldn't expect to see either in very temperate climates like San Diego - there's just not enough energy payoff for the cost of installation. Better off just opening the windows when it's only 2 kelvins different inside and outside! PS the other major difference between ERVs and HRVs is that HRVs are more-or-less maintenance free for life, since they're basically just stacked aluminum plates. ERVs degrade in performance over time, being things like moisture-permeable membranes, so that's a concern for people interested in long term installation in remote areas, for example, but most commercial/residential usage isn't that worried about that.
  - throw0101c 4y ago
    > Better off just opening the windows when it's only 2 kelvins different inside and outside! Except for all the pollen, dust, and pollution that doing so would also bring in. ERVs can cost as little as US$ 1000 for the units themselves: * https://hvacdirect.com/residential-industrial-commercial-fans-ventilation-products/air-cleaning/erv-air-exchangers.html https://hvacdirect.com/residential-industrial-commercial-fan... If this is a retrofit, there can be challenges with installation, but plumbing into existing force air ducts is a common scenario.
    - jaggederest 4y ago
      Well, HRV/ERV have no built-in filtration in themselves, so they're exactly comparable to throwing open the window. If you run them before a filter, obviously they're better, but they have no inherent advantages to opening windows.
      - throw0101c 4y ago
        > Well, HRV/ERV have no built-in filtration in themselves Open the linked PDFs for the Broan units and do a text search for "filter": you will find that they do. Further: even if they didn't, the RVs will have ducting for the intake, where you can put a box for a filter, which certainly take up space, but not a lot of money: * https://acinfinity.com/air-filter-boxes/ https://acinfinity.com/air-filter-boxes/ How do you install a MERV ≥8 filter into a window?

ericd 4y ago

He’s saying that you’d use an HRV instead of an ERV, because the moisture exchange of the ERV would start frosting up in a very cold climate. If that’s not a concern, the humidity conditioning the ERV does on the incoming air makes it preferable.

throw0101c 4y ago

>> In the past HRVs were mostly used in colder climates > Did you mean warmer climates? No: HRVs were in cold climates previously because HRV do not deal with moisture, and so there was less frosting / icing up of the membranes. ERVs were more focused in warmer climates, because warmer climates tend to have a lot of humidity, so if you had a dehumidifier in (e.g.) Texas or Florida, and you exhausted stale air, it would end up exhausting the conditioned drier air and intake the outside humid air, which you would then have to dehumidify again. Of course ERVs are also desirable in cold climates because cold air is dry(er), so you'd be drying out your house. So now that is technically more easy, ERVs are also being used in colder climates.

h0l0cube 4y ago
Thank you for clarifying.