5 ms·

These is more generally known as "heat recovery ventilation", HRV (the term is first used about half-way down the article): * https://en.wikipedia.org/wiki/Hea

These is more generally known as "heat recovery ventilation", HRV (the term is first used about half-way down the article): * https://en.wikipedia.org/wiki/Heat_recovery_ventilation https://en.wikipedia.org/wiki/Heat_recovery_ventilation There are also energy recovery ventilators, ERV, which in addition to tempering the temperature of incoming air, also temper the humidity: * https://en.wikipedia.org/wiki/Energy_recovery_ventilation https://en.wikipedia.org/wiki/Energy_recovery_ventilation In the past HRVs were mostly used in colder climates, as the humidity exchange would cause frosting of the exchange core, but modern core membrane materials have improved in recent years, and some units can operate frost-free down to -10C / 14F: colder than that and you may need a have pre-heater running on the intake, or the unit may have a defroster. * https://www.broan-nutone.com/getmedia/d7230185-8067-4256-a1a2-32127fe9328a/Owners-Manual-ERV100S-ERV100SP.pdf?ext=.pdf https://www.broan-nutone.com/getmedia/d7230185-8067-4256-a1a... Some units have defrost modes so that they can run even in -27C (though it will probably be defrosting a lot): * https://www.broan-nutone.com/getmedia/3ec22979-19c4-4f1e-94fd-1388d9e66583/Spec-Sheet-B160H65.pdf?ext=.pdf https://www.broan-nutone.com/getmedia/3ec22979-19c4-4f1e-94f...

h0l0cube 4y ago
> 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.
- 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.
stuaxo 4y ago
Is this the same thing as MVHR ?
oaiey 4y ago
That defrosting feature is very expensive. Move triggered early December for like 5 days. It runs at 1000W permanently. In our lovely energy process this translate to 15€ a day or 450€ if run for a full month. Switched it off air exchange for dinner days until it got the one degree weather where the dentist is not needed
- Volundr 4y ago
  That's odd. I've got a heat pump, and it defrosts a couple times an hour, but the defrost cycle only lasts a couple minutes. Are you sure it's not malfunctioning?
  - oaiey 4y ago
    Good question. Will have a look.
- Johnny555 4y ago
  The defrost on the linked Broane units apparently works by recirculating the inside air through the unit, not by a 1000W heating element. It sounds like you have a pre-heater?
  - oaiey 4y ago
    Yes, you are right. It is the pre heater. Maybe i understood defrosting the wrong way.
- oaiey 4y ago
  My apologies for this mess of a comment. Auto completion is a disaster for me

h0l0cube 4y ago

> 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.
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.

stuaxo 4y ago

Is this the same thing as MVHR ?

oaiey 4y ago

That defrosting feature is very expensive. Move triggered early December for like 5 days. It runs at 1000W permanently. In our lovely energy process this translate to 15€ a day or 450€ if run for a full month. Switched it off air exchange for dinner days until it got the one degree weather where the dentist is not needed

Volundr 4y ago
That's odd. I've got a heat pump, and it defrosts a couple times an hour, but the defrost cycle only lasts a couple minutes. Are you sure it's not malfunctioning?
- oaiey 4y ago
  Good question. Will have a look.
Johnny555 4y ago
The defrost on the linked Broane units apparently works by recirculating the inside air through the unit, not by a 1000W heating element. It sounds like you have a pre-heater?
- oaiey 4y ago
  Yes, you are right. It is the pre heater. Maybe i understood defrosting the wrong way.
oaiey 4y ago
My apologies for this mess of a comment. Auto completion is a disaster for me