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Does anyone know if there is a manufacturer that makes an energy efficient, dual HVAC/ ventilation system that would satisfy both of my needs and eliminate the need for 2 duct systems?

minotto | Posted in Green Products and Materials on

I’m planning a moderate size home in SoCal in a semi-desert climate with adequate thermal mass. The home will have a tight envelope and my understanding is that some sort of ventilation system with separate duct work is required.

I was planning on an air-source heat pump to meet heating and cooling needs, but this will only be used in the summer and winter months mostly.

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  1. Expert Member
    Michael Maines | | #1

    Paul, HRV's and ERV's are available that have post heaters, meaning a small electric resistance heater for the supply air, which may (or may not) be enough for your heating needs. It would not help with your cooling needs, though.

    Do you definitely need a ducted heating/cooling system? Higher performing homes can often get by with 1-3 centrally located wall or ceiling mounted units, sometimes with a bit of electric resistance heating in bathrooms and bedrooms.

  2. minotto | | #2

    Thanks Michael. At this point i don't really know what i need. I'm looking at all options. I like the idea of 3 centrally located wall or ceiling mounted units. Are there any specific ones your might suggest?

    I just found out about this though: CERV -

    It seems to be a dual system with integrated HRV/ heat pump for heating, cooling and dehumidification using one system of duct work.

    I'll have to look into it further.

    It seems though as Building codes around the US require tighter envelopes in the future, and temperatures become more extreme everywhere, some sort of economically viable, integrated system will be necessary.

  3. Expert Member
    Dana Dorsett | | #3

    Setting up air source heat pumps to take in and distribute the ventilation air is almost always a mistake, since it over-ventilates when there is a significant load, and underventilates a tight house when there is little or no heating or cooling load. It's generally better to separate the functions.

    The air volumes required for ventilation are very small relative to those needed for heating & cooling, and using the same ducts for both is usually inefficient in ventilation-mode only.

    But it's also possible to go ductless with heat recovery ventilation using systems such as the Lunos e2 and it's variants. For larger houses or those with ventilation needs in multiple rooms so that it needs more than 2 pairs of fans it gets to be more than bit on the expensive side.

    For single-room balanced heat recovery ventilation the Panasonic FV-04VE1 WhisperComfort works fine in most SoCal locations (but has frost damage risk in colder climates, or higher elevation locations in SoCal.) At $350/room (sometimes less if you shop around) it may come in cheaper than a few pairs of Lunos, but probably not cheaper than a single pair of Lunos. The advantage is that it works in doored-off rooms, whereas the Lunos really needs reasonably open floor plans to get it down to 1-2 pairs.

  4. minotto | | #4

    Thank you Dana.

    Another option might be totally ductless. Without getting into specifics, just thinking in general terms:

    A 2500 sq.ft. home in SoCal on one level with a tight envelope

    - an open plan for the public spaces (kitchen, living room, dining area)
    - a separate Master Suite (bedroom and bathroom) on one side
    - a separate Guest Suite (2 bedrooms with shared bathroom) on the other side.

    Hypothetically, how many HRV's and minisplit sytems would be needed?

  5. user-2310254 | | #5

    Martin Holladay has an article on CERVs, which might help you to make a more informed decision.

  6. Reid Baldwin | | #6

    Another device that operates similar to the CERV is the Minotair ( Both have ventilation modes in which heat is actively transferred between the incoming airstream and the outgoing airstream via a heat pump (as opposed to passive heat transfer). In heating mode, that means the incoming air could be warmer than the outgoing air. They also offer non-ventilating modes in which heat is transferred between outdoor air and indoor air. The heating and cooling capacity is pretty low compared to traditional heating and cooling equipment. Few houses would have low enough heating and cooling loads for a CERV or Minotair to provide all space conditioning. Maybe in SoCal it would. Also, the COP of the heat pump is not very impressive relative to mini-splits. If your heating and cooling load is actually low enough for these devices to provide all space conditioning, then efficiency is not as important because space conditioning would be a small fraction of your electric usage.

    The CERV and the Minotair differ in their control philosophies. The CERV controls focus on maintaining CO2 and VOC levels below a target. The Minotair controls focus on maintaining a target relative humidity, subject to minimum ventilation rates.

  7. charlie_sullivan | | #7

    The CERV and Minotair systems are clever, but they are rarely the most efficient option. If you don't want separate duct systems, I would recommend going ductless with one or the other, perhaps even both.

    If you are set on the idea of heating and cooling with the HRV/ERV ducts, you could add a hydronic coil on the supply side after the heat exchanger, and feed the hydronic coil with a Chiltrix air to water heat pump. Then if you need to supply a little more heating or cooling overall, you could add a fan coil unit or two. I think that would be a fantastic system. The only problem is that it would require finding a willing and capable system designer to figure out all the details. It can be a little hard to find qualified Chiltrix system installers even if you do it in a straightforward way. (You could also use the Chiltrix system without any integration with the ventilation system.)

  8. minotto | | #8

    If the CERV and Minotair systems don't have the capacity to heat/cool most homes, and some supplementary unit is required to make up the difference, it seems to defeat the purpose of creating an integrated, economical solution to a hybrid system using one set of ducts.

    Thanks for all the info and suggestions.

  9. GBA Editor
    Martin Holladay | | #9

    It sounds like you want information on a ventilation system, not a heating or cooling system. Here is a link to an article that discusses ventilation: Designing a Good Ventilation System.

  10. minotto | | #10

    Thanks Martin.

  11. Expert Member
    Dana Dorsett | | #11

    If the guest suites are normally not occupied, continuously ventilating & conditioning those spaces is just an unnecessary load.

    Without a floor plan and the room by room cooling/heating load numbers it's impossible to zoom in on the most optimal solution for ventilation, cooling, and heating.

    There simply isn't sufficient information here to make reasonable WAG at how many mini-splits it woujld take, but we can take a WAG at the HRVs.

    A Title 24 requires 60cfm continuous ventilation for a 2500' three-bedroom house:

    CA Title 24 requires total of at least 60cfm continuous ventilation to be installed for a 2500' three-bedroom house:

    A single pair of Lunos Nexxt (about $1600) is good for 53 cfm at max speed, a Panasonic FV-04VE1 can be set up for anywhere from 10-40 cfm. So with a Nexxt on the open space zone, and an FV-04VE1 per bedroom, you'd be looking at maybe ~$3K-3.5K (installed) for a ductless, zoned, ventilation system that meets current CA code.

  12. minotto | | #12

    Actually one of the guest bedrooms will double as an office and the other bedroom will be used about 3 times a week.

    And i assume the bathrooms would have a simple exhaust only unit or are these not necessary given that the rest of the house is ventilated?

  13. GBA Editor
    Martin Holladay | | #13

    Q. "I assume the bathrooms would have a simple exhaust only unit, or are these not necessary given that the rest of the house is ventilated?"

    A. As I wrote in my article on the topic (Bathroom Exhaust Fans): "According to the 2009 International Residential Code (sections R303.3 and M1507.3), a bathroom with an operable window does not need to have a bath exhaust fan." According to the code, any bathroom without an operable window must have an exhaust fan.

    I advised, however, that "In spite of the code’s archaic loophole, builders should install an exhaust fan in every bathroom or toilet room — even when the bathroom has a window."

    If you are considering the installation of a ducted HRV system, you should read this article: Does a Home with an HRV Also Need Bath Fans?

  14. minotto | | #14

    Thanks. Martin.

  15. Expert Member
    Dana Dorsett | | #15

    Though the IRC doesn't demand it, a fan for every FULL bath (with shower or tub) IS a requirement under California Title 24. It needs to deliver a minimum of 50 cfm minimum if intermittent, or 20 cfm continuous ventilation. Some inspectors will actually test it, since bathroom fans in-situ often underperform their rated cfm tested under laboratory conditions.

    A pretty-good Panasonic Whisper Green bath fan can efficiently meet Title 24 spec, at less than half the cost of their mini-HRV, which would have to run continuously to meet Title 24 spec.

    Half-baths (toilet + sink) are not required to have exhaust ventilation.

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