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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 clim

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?

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?