Mill Creek NetZero Home Heat Recovery Ventilator
I heard a story once about a man who built a house using insulated concrete forms (ICFs). While I don't advocate their use in general, ICFs have some distinct advantages (certainly over conventional construction). The primary of these advantages is supreme air tightness. ICF homes (those that are built with ICFs from top to bottom) can achieve hourly air change rates of 0.2. In contrast, the Mill Creek NetZero Home has an airtightness measurement of 0.36 ACH, which is really amazing for a wood-framed house.
So back to this guy who built the ICF house. He apparently wasn't aware of how air tight his house was, or at least the consequence of that air tightness. Six months after he moved in, he had to rip all of the drywall out because it had rotted. He had built a house as tight as a plastic bag, and forgotten a critical aspect: ventilation.
Since we don't have any furnace ducting (no furnace means no hot air to move around), we installed 6" piping throughout our house to bring fresh air in and out of the living spaces. The ventilation outlets and inlets have diffusers on them that can be adjusted to balance the air flow.
fresh air is delivered to the kitchen of the Mill Creek NetZero Home via a diffuser (the white circle in the upper right corner)
The outbound and inbound pipes meet in basement, where they enter (and exit) the Heat Recovery Ventilator (HRV).
The system exhausts stale air from the high moisture producing areas of the house: the kitchen bathrooms and laundry room. In the HRV, this stale air gives up most of its heat to the incoming fresh air which is delivered to the other rooms in the house. The ductwork is carefully size so the the air can be picked up and delivered in equal amounts and with the least possible fan power.
Heat Recovery Ventilator (HRV)
Lifebreath HRV, MCNZH
An HRV is a device that draws fresh, cold air from the outside while at the same time heating it up with warm, stale air from the inside. It does so by having the two streams of air pass by each other separated by a thin membrane (Lifebreath HRV's double core is made of conductive aluminium).
We chose the the Lifebreath ECM 195 (with an ECM motor) because it gave us the best combination of low electrical usage and high efficiency heat recovery. A fan powered by an ECM motor maintains its efficiency over a wide range of speeds, whereas that same fan with an AC motor draws the same amount of power no matter what speed it is at. VanEE and Venmar make some HRVs with even higher heat recovery efficiency than the Lifebreath, but these models are not available with ECM motors. The models they do make with ECM motors are less efficient at recovering heat from the outgoing stale so more reheating is needed.
As long as the ventilation system is keeping the house's humidity under about 40%, we are comfortable with ventilating at a rate lower than the recommended 1/3 Air Changes per Hour (ACH), thereby saving significantly on electrical energy for the fan. Our confidence comes from the fact that the house was built with materials that don't offgas (or barely do), making the air healthy by default. Note also that here in Edmonton, Alberta our air is very dry compared to other parts of Canada, so we need to exchange less air to keep our humidity levels down. Today I lowered the ventilation rate to its lowest setting, the 1st out of 5 speeds, and set it to run only 20 minutes out of every hour. The dry winter air should will keep the house humidity level under 40%.
At zero degrees Centigrade, the the Lifebreath runs at about 81% efficiency (recovers 81% of the heat that is in the indoor air). At minus 25 degrees, its efficiency is only 77%, because it needs to run in reverse every so often to rid itself of ice that occurs when the indoor air encounters the much colder outdoor air (numbers from page 3 of the manual). The low speed that we're running it at should increase the efficiency, because the outdoor air is in contact with the indoor air for longer since it is moving more slowly.
Ventilation is essential to an airtight home. If we didn't recover the heat from the outgoing air, we would be negating much of the benefit gained by building such an airtight house. We are hoping to push the envelope by finding a ventilation rate that is healthy, but that requires the least energy possible to achieve its benefits.
I chose the 195DCS because I thought the higher efficiency vs a single-core unit would save me enough money in energy costs to pay back the capital costs in less than 5yrs (and it gave me a slightly higher Energuide for new homes rating). The 195ECM wasn't available when I purchased mine.
In retrospect, the added cost wasn't worth it (vs a 155ECM for example). The reason is the natural air infiltration rate of the house in winter is sufficient to provide good indoor air quality. Indoor C02 levels are kept below 1000ppm with 10cfm/person. A house with 27,000cf of volume and a natural air infiltration rate of 0.04ACH in Jan/Feb gets 18cfm of natural air infiltration. If the average occupancy is 3 people, and the high speed volume of the unit is 160cfm, then 108 minutes/day of high speed use (from kitchen/bath timers) will make up the difference.
Lifebreath's dual-core units seem to use the same defrost cycle as the single-core units, and the high-speed dehumidistat is not used as an input to the defrost cycle.
With a bit more intelligence in the control board, defrost cycles could be initiated only when frosting conditions exists (when the temperature of the 2nd heat exchanger is below 0C & the dew point of the exhaust air is >0C).
It also has a 15C outdoor air temperature over-ride for the dehumidistat; i.e. it won't run at high speed to try to dehumidify. This is non-adjustable, so on mild winter day with a 10C dewpoint and the dehumidistat set to 40% (indoor dewpoint of 4C@20C) the unit will increase the indoor humidity instead of decrease it!
35%RH is getting down to unhealthy levels, though it can be hard to keep it above 40%RH without forming condensation on double-glazed windows (another good reason to go with triple-glazed IMHO).
With all the media hype about H1N1, I'm surprised I didn't see any news coverage discussing the benefit of maintaining indoor humidity.
http://www.cdc.gov/ncidod/EID/vol12no11/06-0426.htm
I've measured indoor RH of <20% in office buildings in Ottawa, and read an engineering paper about a university residence in Vermont where the winter indoor RH was modeled as low as 12%.
Where did you manage to find an HRV in Edmonton? There seems to be multiple manufacturers in Canada but no-one supplying them to the public in Alberta!
some naive questions, bear with me:
what about opening the windows just for a moment or two in winter- rather than relying on the HRV?
do you ever find the house/room stuffy?
Shafraaz,
We've never found it stuffy. We shouldn't, because after all it's being ventilated all day with fresh air.
Opening the windows would be akin to just leaving a hole in one of the walls (or several small holes to spread out the cold air). The reason not to is that the warm air that leaves the house by those holes contains valuable heat. With the HRV, 75%+ of that heat is recovered.
Conrad
Hi,
How much did the 195ECM cost? I've been considering one too, and wanted to know how far to bend over.
Thanks
I suspect it would have cost $2.5-$3K including installation & ductwork. I paid $3K for my 195DCS, but I probably have double the amount of duct work given the size of my house.
Wolseley HVAC sells the Lifebreath line but I haven't checked with they sell the unit itself for; I suspect somewhere around $1000.
The 195 lifebreath line have one big flaw for passive solar use; no recirculation mode. On sunny winter days I'd like to run my HRV to distribute the warm air evenly throughout the house.
I have a Venmar AVS Eko 1.5 on order from Emco Heating. It's costing me $1580. Retrofit install will be in the order of around $600, so $2180 total. Emco has told me that I'm the first person to order this unit. It seems like people in the Edmonton area aren't too interested in high efficiency stuff.
As a comparison, I was quoted $1800 installed for a Lifebreath 155ecm and $1200 installed for a Fantech shr-1504.
The venmar has a really nice control unit that can close the dampers for internal recirculation and a low-speed mode that takes only 17w of power.
A search on the net shows the 155ecm having some humming noise issues. Any such issues on the 195ecm?
I have a 195 ECM and it definately hums especially at the higher speeds. The sound is different but only a little louder than a better quality bathroom exhaust fan. The unit has a recirculation mode as well as a defrost mode.
I stand corrected (already). After my previous post I realized that I had not actually tried the unit in recirculation mode. Upon careful inspection I discovered that despite instructions on the control panel describing recirculation mode the 195ECM does in fact not have a recirculation mode. The "not necessarily available on all units" fine print got me!
Regards
has but depressurize the house
u must buy Part # 99-LS-01
The optional Lifestyle MAX Programmable Control is fully
digital and allows you to program when and how much fresh air
will be entering your home.
I am thinking of the EKO Altitude 15 HRV or the Venmar HE 1.3....tight space. As I do not have a basement, there is a furnace room. Does anyone know how noisy any of these models might be and whether the noise from them would be distracting....for ecample, is it as loud as a gas fired high efficience water heater when it goes into heat cycle
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