Can one device to it all? Should it? Has its time finally come?
For a few years now, I have been seeing Alexandre De Gagné peddling his Minotair Pentacare Compact Air Treatment Unit at Passive House conferences, and not being a mechanical engineer, have spent some time trying to figure it out. It's what some have called a "magic box" that pulls together a number of air-handling functions, and it is different from what we are used to; after a 2016 conference I wrote that "I spent some time trying to figure out what it did, concluded it was a sort of heat pump that acted as the most complicated HRV ever, and ran away screaming."
In fact, it is really not so complex, and it's not magic. It has literally been years, but I believe that I finally can write about this, but first have to provide some background, explaining what it does and what it replaces.
What is heat recovery and why do we need it?
The official definition of Passive House or Passivhaus says, "Thermal comfort is achieved to a maximum extent through passive measures (insulation, heat recovery, passive use of solar energy and internal heat sources)." But that "heat recovery" element is not so simple, cheap, or passive.
"Heat Recovery" usually involves a Heat Recovery Ventilator (HRV) or an Energy or Enthalpy Recovery Ventilator (ERV) where outgoing air is pushed through a labyrinth of metal or plastic, which conducts heat from the outgoing stream of air to the incoming. The ERVs also transfer moisture by using a humidity permeable material (or an energy recovery wheel.) But it is not 100 percent efficient, and the fans have to do a lot of pushing to get the air through those little tubes. So the design of an HRV or ERV is a compromise of the area of the conducting surfaces, the size of the openings, and the power of the fans, and can never get to 100 percent efficient.
It is also often not enough. In cold climates, a bit of supplementary heat is required. In hot climates or places with hot summers (just about everywhere now), a little cooling or dehumidification might be needed for comfort. Many designers are now using air source heat pumps (ASHP) in addition to their HRVs, to provide both supplementary heating and cooling.
Heat pumps work by moving heat from coils inside the home to coils outside for cooling, and the reverse for heating, where they pull heat out of air that is often much colder than the air inside; efficiency drops with the outside temperature.
If you have a bigger building you probably have room for all this stuff, but in small houses or apartments, it takes a lot of space and money.
So what's in the Magic Box?
Which brings us back to the Minotair. It replaces the core of an HRV with a heat pump, which pulls the heat out of the air being exhausted and puts it into the incoming fresh air. Being a heat pump, there is a far greater difference in temperature than with just plate conduction, and far higher efficiency, to the point that it can provide supplementary heating. Running in reverse, it can actually cool and dehumidify the incoming air. It is a little magic box that does everything: Heat, cool, exchange and filter air. According to the company: "The PentaCare V12 produces Net Zero Positive+ Ventilation© performances in certain conditions having the best heat recovery performances of all HRVs and ERVs available in North America."
The Minotair has been around for a while; Martin Holladay wrote about it on Green Building Advisor in 2015. Since then, they have been working on certification, and finally now have HVI, an important standard. Martin worried then about whether a small Quebec company could provided enough support or whether local contractors could perform future repairs; I asked a number of architects at the NAPHN conference and they expressed the same reservations, worried about the unit's complexity; HRVs are relatively simple devices.
Allison Bailes raised a similar objection at an earlier conference, noting that "devices that try to do more than one thing usually can't do all of them well." I have often discussed this, what I called the Shimmer Syndrome after the old SNL skit: "It's a floor wax! It's a dessert topping!" But in fact, I no longer think that it is doing more than one thing; it's just moving heat with a heat pump instead of metal plates, and doing it much more efficiently.
Alexandre De Gagné is, if nothing else, persistent. He has been dragging his magic box around the world for a few years now, and designers are beginning to take notice. With the recent HVI certification, it may finally take off. De Gagné says the company now has trained contractors around most of North America, and that maintenance and service will not be a problem. He has answers to all these questions.
Architects and engineers are a conservative bunch; taking risks can be costly. Passivhaus designers are even more conservative; they have hard numbers to hit. I can see why it has taken a couple of years to build trust and get acceptance. As I noted in the first paragraph, I am not a mechanical engineer, and there may be other issues with respect to Passivhaus that I do not understand. I am hoping that there will be some comments from experts.
But I intuit that a heat pump is going to be more efficient at moving energy than a bunch of conductive plates, and that it can add or remove more heat at the same time; it just seems logical to combine the functions. Also, we need better solutions for small spaces. Perhaps the time has finally come for this Minotair Magic Box.
Specs for the data nerds: