Another North American Magic Box
Another North American Magic Box
Like the CERV, the new Minotair Boreal is a balanced ventilation system with a built-in air-source heat pump
Over the past few years, GBAGreenBuildingAdvisor.com has published several articles on “magic boxes” — a type of combination appliance that functions as a ventilation system, heating system, and cooling system. Most recently, I wrote about the CERV, a magic box manufactured in Illinois. Now a Canadian manufacturer has come out with a magic box that resembles the CERV.
The new device, the Boreal 12000, is manufactured by Minotair, a small company in Gatineau, Quebec. Like the CERV, the Minotair Boreal 12000 includes an air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps.. All of the heat pump’s components, including both the condenser coil and the evaporator coil, are located indoors. Like a heat-recovery ventilator (HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. ), the Minotair Boreal 12000 has four duct connections, including a fresh air duct that pulls outdoor air into the appliance and an exhaust duct that delivers stale air outdoors. During the winter, the exhaust air from the house passes over the heat pump’s evaporator coil, allowing the heat pump to scavenge some heat from the exhaust air. Since the condenser coil is located in the fresh-air duct, the Boreal 12000 delivers heat to the incoming ventilation air.
A motorized damper adjusts the airflow paths depending on whether the unit is in ventilation mode or recirculation mode. During the summer, the heat pump removes heat and moisture from the incoming outdoor air stream and delivers heat to the exhaust air stream, thereby lowering the temperature and humidity level of the incoming ventilation air.
MORE ON MAGIC BOXES
To read an overview article on magic boxes from 2010, see A ‘Magic Box’ For Your Passivhaus.
Three magic box manufacturers are now distributing these appliances in North America:
1. The Minotair Boreal 12000 is described in this article. For more information, contact the manufacturer: Minotair, 45 Rue de Villebois Unit 300, Gatineau, Quebec J8T 8J7, Canada; tel: 819-777-2454; e-mail: firstname.lastname@example.org.
2. The Conditioning Energy Recovery Ventilator, or CERV, provides fresh ventilation air while simultaneously exhausting stale air from the building. The CERV also provides a limited amount of space heating and cooling. For more information, see A Balanced Ventilation System With a Built-In Heat Pump.
3. When paired with the optional Cool Breeze unit, the Air Pohoda Ultima240E ERV provides fresh ventilation air while simultaneously exhausting stale air from the building. The Cool Breeze unit provides a limited amount of cooling. For more information, see New Green Building Products — May 2014.
The main purpose of the Minotair Boreal 12000 is to provide mechanical ventilation for a home in a way that pays close attention to the indoor humidity level. While the device appears capable of doing an excellent job of ventilation, it can also provide up to 9,400 BtuBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. /h of space heating and up to 8,700 Btu/h of cooling. While that’s not enough to heat or cool most homes, it might be enough for a very small Passivhaus.
It’s installed like an HRV
Ideally, the Minotair Boreal 12000 is installed like an HRV with dedicated ventilation ducts. In a pinch, though, it can be connected to the forced-air ductwork of a furnace.
According to the manufacturer, “The Minotair is an innovative device used to control the ventilation, temperature and humidity of your house. It filters, dehumidifies, heats, cools and renews the air to provide a healthy and comfortable environment all year round. … [It is equipped with an] innovative motorized damper permitting several operating modes such as air exchanger, heat pump, recirculation. … In addition to standard antimicrobial filters, there is also optional activated carbon filtration for odor removal as well as HEPA filtration for unsurpassed air quality.”
The maximum heat output is 9,400 Btu/h
I asked Karl Audet, the president of Minotair, about the heating output of the Boreal 12000. He responded, “It produces 9,400 Btu/h of heating when the outdoor temperature is at 47 degrees F. That’s the outdoor temperature at which it is rated.” Needless to say, the appliance’s heating output drops as the outdoor temperature drops.
“For colder outdoor conditions, you can attach a 3,000 watt electric coil,” Audet said. “We can set up the system so that the electric coil makes sure that the distribution air [during the winter] is always at 40 degrees C [104°F]. But the prime mission is not to be your central heating or cooling appliance. First and foremost, this is a heat exchanger” — in other words, a type of HRV.
Indoor air: too dry in the winter, too humid in the summer
Audet feels that most HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. systems do a poor job of controlling indoor humidity levels. “We need to get control of indoor humidity,” Audet told me. “HRVs dry out the indoor air too much in winter months, when you have cold air, very dry air, coming in the house — including infiltration through doors and windows.”
Audet noted, “The magic box concept originated in Europe. With the Nilan [a magic box manufactured in Denmark], at low outdoor temperatures your house becomes too dry. The unit didn’t provide a means to recirculate the air. In our [Canadian] climate, that is not acceptable. You need to be able to control it so it doesn’t always exchange the air.”
He continued, “Our unit will stop bringing in outdoor air until the indoor humidity comes up. And in summer we don’t let you go beyond 60% RH. It’s a convoluted machine, but humidity levels are looked at first and foremost.”
The Minotair Boreal 12000 has flexible control options. “The way it works, you set the humidity set-point to your liking,” said Audet. “By default, it is set at 45% for the winter. The ideal humidity level throughout the year is 45%, so that is the default. But you are free to play with that — to lower it or increase it. We just don’t let you go beyond 60% during the summer. The machine changes the algorithm in winter. As the outdoor temperature gets below the freezing point, the machine will lower that set-point automatically.”
Audet continued, “The controller allows several options for cold weather ventilation. It is user-settable. One option ensures that below a certain outside temperature, the unit will no longer do any air exchanging. At very cold temperatures, there is already plenty of natural ventilation occurring through your keyholes. And you have another setting that says that if the indoor air gets too dry, there will be no more air exchange until it gets a little more humid inside. Or, if you prefer, you can set it to intermittent mode, to always provide 10 or 20 minutes of air renewal per hour.”
Lowering indoor humidity during the summer
According to Audet, “This device has a special way of achieving cooling. We have an effect on indoor temperature, but our biggest effect during the summer is reducing the indoor humidity level.”
He continued, “Humidity is the battle that you have to win. Venmar makes air exchangers, but there is no way they can control the humidity in the summertime. For that, you have to use a compressor.”
- The appliance has two ECM blowers that can automatically increase fan speed to compensate for a rise in static pressure caused by clogged filters.
- Each fan motor draws a maximum of 136 watts, for a maximum fan wattage of 272 watts. According to Audet, unless the fans are facing high static pressure, they will usually draw much less than 272 watts.
- The airflow delivery rate is adjustable from 80 to 250 cfm.
- The compressor draws up to 725 watts. According to Audet, “The colder it gets outdoors, the easier it gets on the compressor. At -25 degrees Celsius, the compressor draws the least power, because the cold air makes it easier to condense the hot gas. The hotter it gets outdoors, the harder it has to work.”
Comparing the Minotair to the CERV
The specifications of the Minotair Boreal 12000 are similar to those of the CERV. Both appliances have a maximum airflow rate of 250 cfm. While the CERV claims to have a maximum heat output of 8,500 Btu/h, the comparable figure for the Minotair Boreal 12000 is 9,400 Btu/h.
One notable difference: the Minotair Boreal 12000 is much more compact than the CERV.
The cost of the Minotair Boreal 12000 is $4,200 (Canadian dollars), or about $3,213 at the current exchange rate. That’s less than the CERV, which costs $4,500.
Needless to say, it’s hard to estimate installation costs. “If you plug it into a furnace, the cost of installation might be $1,000 to $1,500,” said Audet. “But if you are going to be doing a full ducting job, the installation cost could be $2,000. Each house is different.”
Do you really need a magic box?
Emmanuel Cosgrove, the founder of a Canadian green building web site called Écohabitation, isn’t convinced that the Minotair Boreal 12000 is worth the cost. He wrote, “This type of machine is hard to recommend, especially since its cost often exceeds that of an excellent HRV and a better performing wall-mounted heat pump.”
It seems clear that the Minotair Boreal 12000 does a better job of controlling indoor humidity levels than a typical HRV or ERV. However, early adopters of this technology face a few risks:
- Will this small manufacturing company provide adequate technical support in the future?
- Will this appliance provides years of trouble-free operation, or will it require frequent maintenance?
- Will local HVAC contractors be able to perform future repairs?
As with any relatively new appliance, time will tell.
Martin Holladay’s previous blog: “A Backyard Test of Liquid-Applied Flashings.”
- Image #1 and #3: Karl Audet
- Image #2: Minotair
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