ERV choice
So looking at ERV for my build, and comparing models. Want something efficient, but not crazy $$$.
The house hopefully will be tight and well it is on the larger side.
Main floor is 2275sq’ walk-out basement is 1880sq’ of finished area. (including unfinished area it is 2275 also)
So 4155sq’ of living area, currently only 2 people and 2 large dogs.
Will have it’s own dedicated duct work (heating/ac hopefully will be mini-splits)
Zone 6 (20 miles SW of Peterborough,ON)
I’ve looked at the following models
Zehnder ComofoAir 550ERV -Nice but price is thousands more over others.( I was quoted this from Zehnder)
Broan ERV200TE
Vanee G2400E Ecm These seem to be all the same model different box colour. but rate well.
Venmar X24ERV ECM
Ultimate Air 200DX ERV RecoupAerator Seems like good unit but needs inline heater or water to air for defrost.
What are peoples experience with these units?
Any reasons not to look at these , are there any other choices recommended?
Do you think these units will work with my house?
感谢任何建议。
Dave
Replies
I'm going through the same right now, building in Ottawa. About 3200 sqft between the main and second floor, ~5000sqft if you include the full unfinished basement. Three people and a dog.
I'm looking at the Panasonic Intelli-Balance 100. It's super efficient and doesn't cost an arm and a leg. It's only 100 CFM, but based on building code requirements I can make up the difference with a single bath fan (which I will choose not to use).
ASHRAE 2010 requires only ~70 CFM for our finished area (4 beds and 3200 sqft finished area) and based on what I've read that should be plenty. If I can get my Engineer to sign off on those requirements instead of following the "room-by-room" requirement of the code, I won't even need the bath fan. TBD by the city officials.
The Renewaire EV90P also caught my eye. It's a small ERV with the core of a larger unit for high efficiency, and also doesn't cost a bunch.
From what I've seen, Zehnder gets their high efficiency ratings by having super low airflow at minimum speed. Once you adjust the speed up to where most people will use them I doubt their efficiency is that much higher than other efficient models. Just my opinion, but since they don't publish comparable data my opinion is all I have.
Dave,
The usual choice for anyone who can't afford a Zehnder ERV is the Renewaire ERV.
Thanks Martin and Lance
我用的是加拿大自然资源站点compare models, is there something I should be looking for when comparing models? I assume heat recovery and energy use, is there numbers I should be trying to get out of a unit as minimum. (similar to wanting a minimum R-value).
The Zehnder quote came back at over $10,000 US( 1 Million CDN) I would invest in this unit if I though my return on it was worth it, but even over a 20 year period would it's efficiency make up for the cost?
I don't think it filters any better than the others, is it quieter or have more features which makes it worth the extra?
As for the Renewaire ERV is there a reason for recommending this model?
They seem to be sold only by Mitsubishi Electric dealers in Canada.
It doesn't appear to be as efficient as the Venmar, but I possibly could be reading the numbers wrong.
Lance, the Panasonic seems like a good unit, not sure price, I need to look into that. I also need to find out what calculations my building inspector will be using to determine my needs.
We've been pleased with the Venmar ECM15, which we paired with the Venmar wall control that allows you to adjust the ventilation rates (20min, 30min, 40min, min and max) and switch from fresh air to recirculate. We run ours all the time and it is very efficient.
We are Zone 4A and 2100ft². We have a somewhat complicated separate duct system for the ERV and our installer was impressed that the unit was still able to easily hit target CFMs in all rooms.
Hope that helps.
Hey, a fellow local! Hello from Havelock! The Home Ventilating Institute has a directory here:https://www.hvi.org/proddirectory/CPD_Reports/section_3/index.cfm
You can list all the registered HRV/ERV's by efficiency and quickly find the best ones and have all their specs handy without looking them up on individual manufacturer's websites. In my hvac designs I usually spec a Vanee/Venmar (they are the same thing, as you have already noted) because they strike a good balance between cost and efficiency for most builders around here. The Renewaire doesn't seem to be rated @ -25° C like most Canadian units. If you are going with a dedicated duct system pay close attention to that rating, because that will affect your delivered air temperature when it's cold outside. The most important thing is to have your HRV ductwork properly designed to deliver the correct airflow. I've seen plenty that were just seat-o-the-pants and hardly move enough air to be worth running. And then when it's done, get someone in to commission the system.
Thanks Yupster, great link.
Are you installer or designer?
It's going to be a dedicated system, I'm still search of designers and will be getting it commissioned when done.
Any recommended people in the area for design or sales,of the Venmar/Vanee units?
The $10k quote from Zehnder will include their comfotube ducting, and other fancy accessories you may choose not to use. When comparing just the machines themselves, the price is not as much higher (though definitely still higher). I looked long and hard at the G2400E, but I will be going with Zehnder (if my building inspector allows it), for the fact that it has the bypass feature (important for my ground source cooling plans),swappable core, and technical support direct from the manufacturer. I don't really like the controls of the G2400, and its 2-speed fan limitation. The efficiency of the G2400E is hard to beat though.
兰斯,你跟进你的代码官方regarding the cfm requirements? When I brought up ASHRAE and some other standards to mine, he kind of gave me a talking to, pointed out that those are foreign standards that don't really have any standing in Ontario. I find it interesting, but more frustrating that there's such a wide range in the way code officials enforce different rules. I'm just waiting to see if he gives me the go ahead on both the Zehnder unit and the Jablotron 3" round duct. Otherwise I'm going to be having a really bad day.
Yupster, that -25C rating is a Canada only thing, and seems to be hit and miss whether it's enforced, so a lot of manufacturers don't bother with it. It doesn't mean that their HRV/ERV will not perform just as well as another that did the test. Honestly, it's a stupid test. No ERV can function with incoming air at -25C, all of them employ a strategy of either pre-heating or interior air recirculating to bring that air up to a higher temperature. So measuring the "efficiency" at -25C when it's stealing heat from the interior of the house, as is the case for the recirculating strategy, doesn't really seem like a test that's going to tell you anything meaningful.
I'm an hvac/architectural designer with a local structural engineering & design firm, Trevor Day & Associates. Feel free to give us a call when you're ready to select a designer. We also do construction plans and could guide you towards builders and installers in the area who have the right mindset for the kind of work that GBA encourages. Nice to see someone around here with an interest in going above and beyond!
Dave, I'm assuming the Zehnder quote was the all-in installed price, correct? Even still, that seems like a very large sum and my personal feeling is that the unit would never pay for itself with savings over a cheaper but still very high performing unit. Zehnder undoubtedly makes very high quality product that are among the highest performers, but from where I stand the value seems very low. Their lack of published performance data seems to bolster my gut feelings.
The Panasonic seems to sell for CDN$1300-$1500 as of right now, and sells online in the US for $800-$1000. I have not priced it through a local supplier yet. My only real concern with the Panasonic is the small size of the intake air filter, but other than that it offers nice features like independent controls for both supply and exhaust motors, allowing fully customized airflow and constant operation. It's also very efficient (81% SRE @ 53 CFM - 75% @ 86 CFM) and Panasonic has a well earned reputation amongst green builders for their ventilation fans.
The Renewaire EV90P stood out to me mainly for its efficiency. It sells for about US$1200. It has the core of a much larger unit with the lower flow fans of a smaller unit, giving it excellent sensible efficiency. It's about as efficient as the Panasonic but flows a little more (80% SRE @ 90 CFM) and has larger filters. The main drawback for me is that it's a single speed unit, so throttling the output will rely on a timer that only runs it for the desired period.
As far as efficiency goes, SRE (Sensible Recovery Efficiency) is the most important parameter. This reflects how much heat the unit will recover from the outgoing air, the main reason for using a recovery ventilator. Also consider the electrical power draw. Some ventilators use far more energy than others, and for an appliance that will spend the majority (or all) of its time running this can have a significant impact on operating costs.
ASE (Apparent Sensible Effectiveness) is a parameter I still do not understand, even after deliberate effort to read up on it (it's not clearly defined, to me anyway). ASE is thrown around a lot by equipment manufacturers as the number always seems to be higher than the SRE, but SRE is how much heat the unit recovers which is what really matters.
Net moisture transfer is how much outgoing humidity is recovered by the incoming air. This can help with over-drying a house in the cold winter months and is a primary reason for choosing an ERV instead of an HRV (an HRV does not recover moisture). Running an ERV or HRV in the winter months will dry out the house, but an ERV will dry it out much less for a given amount of ventilation.
The smaller and tighter the house is built and the more people living in it, the less of a concern low humidity is in the winter. The larger and leakier the house and the less people living in it, the more of a problem low humidity is in the winter. Our 3200 sqft house with three people and a dog will likely benefit from an ERV, especially with my planned ventilation strategy aggressively targeting moisture removal at the source. This is, however, just a guess as no one knows exactly how tight the house will be, exactly how much moisture we will generate, or exactly how effective my ventilation plan will be.
Hi Trevor, I spoke with a different Ottawa code official on Friday and it seems you and your folks are correct, for the most part. It would seem that Section 9 of the OBC is gospel and any deviation from it requires the approval of an Engineer.
I'm going to ask if I can have an Engineer approve the ASHRAE 2010 guidelines based on Section 6 of the OBC, which would work out to requiring about 70 CFM for our build. This is very important to me after playing around with BEopt, which demonstrates that an impressive amount of energy can be wasted by over ventilating a house. Ultimately I would like to set my ventilation as low as possible while monitoring indoor air quality. I see absolutely no reason to waste money over ventilating when there's no benefit in IAQ.
This is my #1 driving factor in having an ERV with user selectable variable flow rates. Being able to tailor the flow to the requirement is worth paying a premium for up front if necessary, as I feel it will pay back quickly over time. Setting desired IAQ targets by monitoring CO2 levels etc. will ensure I'm only wasting as much energy as is absolutely required.
Yupster, I'm just up the road from you, building in Carp just west of Ottawa. If my Engineer balks at approving the ASHRAE requirements I may be getting in touch with you!
This is what I've surmised from the reading I've done on the SRE and ASE.
SRE is the efficiency that includes the electrical power consumption. This partially explains why the SRE tends to be lower at higher CFM, the fan is drawing more power. So if that SRE number is good, you don't really have to pay much attention to the electrical power consumption.
ASE is basically the SRE but with the power consumption taken out of the equation. So it is a good indication of how the user will perceive the efficiency (i.e. how the air feels) if he doesn't look at the electricity bill.
I notice that some manufacturers like to quote the ASE when bragging about their efficiency. This is dirty pool, IMO.
By the way, Zehnder has published data on all their units available on the HVI product directory.
One more thing regarding the Panasonic and cold temperatures, it does work at -25C, it just switches from ventilation to recirculation as you state. I still see the efficiency rating at -25C as being relevant as this is how efficient the unit is while exchanging air. In recirculation mode it's not putting heat energy outside the home.
Here's the cold weather operating chart from the Panasonic's manual:
Good info on ASE vs. SRE, I've never heard (or found it written) like that. Thanks!
My intention is to run the ventilation at the lowest rate with good air quality as well. But I do need to be able to temporarily boost it for bathroom and kitchen exhaust purposes (have no bathroom fan, and a recirculating range hood). So even if I end up with only 75cfm continuous, 100cfm max will not cut it. Code requires either 20cfm continuous in the bathroom, or boost to 50cfm, and this is a code requirement I fully agree with. So in the end, I was debating academically with the inspector, as I want a unit that more than meets the official cfm requirements. But I may be needing an engineer to say that the HRV of my choice is acceptable for my house, despite the lack of the -25C test data.
Lance, just so you know, you don't actually need an engineer to use Part 6, just a competent designer who can design according to one of the standards in Part 6. It isn't limited to engineers. Ashrae 62.2 is good engineering practice and should be accepted by any building official. Of course "should" and "is" are different things.
ASE is calculated based on gains from the HRV's motor, through the casing, cross leakage, etc. It's useful for determining delivered air temperature but not for actual efficiency numbers of a unit. SRE is the key for that.
Hope your engineer works with you on this but if not, feel free to give us a ring!
Trevor, the -25°C test integrates a minimum number of defrost cycles and occurs over a 60h period. That's why the efficiency numbers are so much lower when it gets very cold. The defrost cycles detract from the efficiency. It's a very useful number to know. Like any laboratory test, it doesn't reflect real world conditions exactly but it still gives you a good idea of how it will perform.
In the time it takes me to get around to responding, I should really refresh the page. There are always more replies!
Yupster good to know, should I call or email?
Have plans done and builder picked, who is willing to work with me on the "special" parts willing to try new things and learn new things.
I see you do heat loss calculations also, still need them.
Aha, HVI holds the secrets. So looking at the Zehnder ComfoAir 200 ERV vs.Panasonic IB 100:
Panasonic @ 67 CFM:
SRE 77%
ASE 81%
NMT 0.76
Zehnder CA200 ERV @ 64 CFM:
SRE 77%
ASE 80%
NMT 0.77
Panasonic @ 86 CFM:
SRE 75%
ASE 79%
NMT 0.72
Zehnder CA200 ERV @ 85 CFM:
SRE 75%
ASE 79%
NMT 0.73
So there you have it. Zehnder advertises the CA200 as being 92% efficient by advertising only their PHI certification, when in reality their counter flow core is only 80% efficient per HVI testing, about the same as the Panasonic which costs roughly 1/3-1/4 the price (not sure what the Zehnder unit alone costs, I thought I read about US$3000). Granted, the Zehnder is a larger unit that has the capability of flowing more air if needed and also has a bypass mode for night time cooling.
I think Panasonic should submit their IB100 for PHI certification!
Glad to hear you found a flexible builder, they aren't always easy to find. We can help you out with heat loss calcs as well, 705-778-3291 will get you the office or you can email me directly at[email protected].
If you choose a large enough flow rate and put the stale air intakes in your bathrooms, you avoid the need for bathroom fans. IIRC, you need 50 cfm per bathroom with a shower and 30 cfm per bathroom without a shower. In a house with few actual occupants, you will run it part-time or at part-speed.
在寒冷的气候,是值得考虑的unit avoids frost. Frost occurs if the temperature of the outgoing air decreases below the dewpoint of the outgoing air and also below freezing. With an HRV, the dewpoint of the outgoing air is equal to the interior dewpoint. With an ERV, the dewpoint of the air drops as moisture gets transferred to the incoming air. Renewaire claims that their moisture transfer is effective enough that frost does not occur except in extreme situations. As mentioned in response #7, other manufacturers pre-heat the incoming air or go into a recirculation mode to heat up the core, thereby limiting the temperature drop of the outgoing air.
You will likely spend more getting the necessary ductwork installed than what you spend on the HRV/ERV unit itself.
I'm not so sure about the energy not being put outside the home. The way I see it is this. There's a couple of different ways recirculating can be employed, but it really comes down to this. Assuming a balanced system, the incoming air from the outside has to match the outgoing air. So you have say 75cfm incoming, 75cfm outgoing, and say 25cfm that is recirculating. The heat content in that 25cfm has come from the house. So what you have is 100cfm of air heat to bring in only 75cfm of outside air. I don't think that 25cfm comes out in the wash when you actually measure it, although it probably depends on exactly where the measurements are taken. If you measure the outside air coming in at -20C, and the air coming into the house at 15C, how would you account for the fact that more heat was taken out of the house due to the recirculation? Maybe there's a way, I but I don't see it.
In any case, the fact that there is data for one unit at -25C and not for another is not evidence that the one we have the data for is actually better at -25C. We can speculate that they didn't do the test because they knew it would fail, but it's more likely they saw no reason to do the test since the vast majority of the market doesn't care, and it's expensive. If, as in my case, you have a way of pre-heating the incoming air for almost no cost (a 10W circulation pump), then the efficiency at -25C is quite literally irrelevant. The ERV is never going to see that condition. This is a better solution than recirculating, but the rigid application of the code actively discourages it.
Trevor, absolutely! If you need the CFM you're stuck with a larger unit. I'm sure the Zehnder will not disappoint and should prove an excellent and reliable solution.
Interesting regarding your recirculating range hood. I considered the same but wasn't aware the ventilation system was allowed to make up for it. Another thing I need to look into! I will be very curious about how your install works out, please share once you're done. My wife is from India and does lots of "spicy" cooking, so I'm not sure if a recirculating hood would be up to the task for us?
Trevor, the Panasonic is either recirculating or ventilating, I don't believe it mixes incoming air with house air.
Is your Zehnder equipped with a fresh air preheater? You'll need to rely on constant ventilation if using to ventilate your kitchen while cooking. No time for defrosting.
Took me so long to write my reply, I missed replies too. So I will retract my statement of position that the efficiency rating at -25C is in any way not reflective of actual efficiency. But I will say that, assuming a similar strategy, the efficiency at 0C is going to be predictive of the efficiency at -25C. Nothing magic is going on there, it's basically just a matter of duty cycling.
Oh, and Dave, you'll need to check out SB-12 and make sure whatever ERV/HRV you choose meets the requirements of your chosen compliance package:
http://www.mah.gov.on.ca/AssetFactory.aspx?did=15947
Lance, whatever unit I end up with is going to be pre-heated with a geothermal loop that is already installed. It should provide somewhere in the order of 1kW or more pre-heating.
I think Zehnder's efficiency claims come from their HRV verisions, which are genuinely >90% efficient. The PHI certification has different criteria, but I don't think it's actually easier to achieve. It is the only one that actually specifies a minimum incoming air temperature at a specific incoming air temperature, for comfort reasons.
There's nothing in the code that specs out a range hood. If you have a lot of strong smelling cooking, recirculating might not be the way to go. However, I've lived in multiple houses that had recirculating range hoods, and it wasn't that big of a deal. In theory, the smells should not linger any longer than it takes to do a complete air exchange in the house, and if they are actually bad smells, I wouldn't want to be eating that food. The recirculating hoods do have carbon filters, which should reduce odors as well.
Re: the vanEE G2400, Venmar X24, Broan 200 series are all the same unit. Venmar owns vanEE, and Broan re-badges ERVs made by others (and when you add this fact to the pictures and specs, it becomes pretty obvious). If you go with any of these, make sure you get an installer who is going to fully commission the system (unless you want to do it yourself). The official instructions from vanEE are just to balance the unit itself (i.e. the main exhaust and supply), not the flow at individual registers. In my opinion, this is a pretty bush league type of install.
I planned on doing the install, but would have it commissioned to get it perfect. I'm sure they run fine with out but not as efficient.
Lance thanks for the link I have looked at that before, I think I should be good.
I forgot about your geo loop Trevor, smart move!
Yes, Zehnder advertises the numbers from their HRVs which are more efficient:
Zehnder CA200 ERV @ 64 CFM:
SRE 77%
ASE 80%
NMT 0.77
Zehnder CA200 HRV @ 65 CFM:
SRE 86%
ASE 90%
NMT N/A
Zehnder's marketing frustrates me since there's no reason for them to not advertise the HVI tested performance other than to hide behind their PHI certification. To be completely fair, the numbers Panasonic advertises are incorrect compared to the ones on HVI's website (I used HVI's numbers for comparison, lower ASE). I'm assuming the HVI numbers are correct and the Panasonic numbers were their best pre-launch guess at how the unit would perform in HVI testing? Who knows, but they should be corrected in the specs and they have not been.
So what are the opinions on the defrost choices between units,
1. electrical heater
2. Geo loop with pump
3. Recirculated air
Do any have advantage over the others? costs/efficiency/maintenance
电加热器是最简单、最可靠的。Least energy efficient, but whether that matters much depends on your specific circumstances. Recirculated air is the cheapest up front, as it's built in. There's a limit to how cold or how long you can run it that way, since at a certain point it's not going to be providing sufficient clean air anymore. I remember specifically for vanEE that there is a temperature at which it just goes into standby mode. If that lasts for a while, and your whole ventilation system relies on that unit, you then have to open a window (and it's like -40 outside). Geo loop is by far the most expensive. I'm excited about it, but if I had to start all over again and knew all the costs, I'm not sure I would have gone for it. It can give you virtually free cooling in the summer, though this requires either careful design consideration or careful selection of HRV/ERV (needs to have a bypass mode, and ideally one that you can program). Basically, you can't cool the air before it goes through the heat exchanger, otherwise it's fighting the ERV/HRV.
Correction to an earlier post, Zehnder only has one HRV rated at >90%, the Novus 300.
我想知道关于循环的空气和如何this would effect air quality in the house. Say having a New Years dinner with numerous people and lots of cooking and it's very cold outside. Is the unit going to be able to keep up or will there be a problem. This of course will not happen often, but nice to know.
I know someone who installed the ground loop with an Ultimate Air unit and they seem to like it.
Dave,
我的下一篇博客中,将于周五公布March 16, is titled "Preventing Frost Buildup in HRVs and ERVs." The article weighs the pluses and minuses of all the available defrost strategies.
No spoilers here. You have to wait until Friday for my opinion.
UGH Friday..... I can't wait that long!!!!
Great Thanks Martin
I think you guys need a podcast maybe live, the Fine home building one is great!
Dave, in that scenario you're correct. If the ERV limits its duty cycle due to cold weather right when you need it most, it may under-ventilate. In the case of the Panasonic, the chart I posted above indicates between -20 and -27 it operates 27 min then recirculates for 9 min and repeats. Between -27 and -30 that operation cycle drops to 20 min and 9 recirc. Below -30 it only ventilates 4 min an hour.
Thankfully for much of Southern Ontario temperatures below -30C are very seldom seen. I was looking over my Ecobee data on the weekend and it seems we only had a handful of hours below -30 here in Ottawa this winter (-22F for those in the US following along), and it would have been a few degrees warmer closer to Toronto (I grew up in Port Perry, north of Oshawa).
The New Year's dinner scenario was a real one this year! The morning of Jan 1st was one of those times when the mercury dipped below -30C here, though during the night of Dec. 31st I think it only got down to -28 by midnight or so. In that case the Panasonic would have kept ventilating in the 20 min out of 29 (69%) cycle. More than OK, especially if I planned ahead and cranked it up to 100% to somewhat compensate.
I am personally planning an EAHX (Earth Air Heat Exchanger), basically an intake air duct that runs underground to preheat my incoming air. I'm working through the details of this with city code officials right now, making sure it's not in violation of Part 6. This will hopefully keep the incoming air well above ambient temp, hopefully warmer than -10C even during the coldest weather.
Even at -20, I would be concerned about that duty cycle. If you're already operating at near the limit of the ventilator, and you drop down to 75% duty cycle for an extended period (days), that's a problem.
If you have a big gathering, your ventilation needs go up, not down, so any reduction in that scenario is undesirable. I think you'd have to crack some windows in remote parts of the house.
Four minutes an hour is basically zero, and I suspect the main purpose of those four minutes is to periodically sample the outside air to check if it should change modes.
Lance, have you looked at any data for how much heat you'll be able to recover via the underground air? Air doesn't have a great heat capacity. I'd make sure it's going to be significant before you commit a lot of time and effort towards it.
I believe that the simplest and cheapest approach to the frost problem is the one that Renewaire uses. Avoid frost by transferring enough moisture.
The big gathering argument is not really much of a concern for most people. Unless this is happening every week, it's not something you should design your ventilation system around. If you have enough people over to exceed the limits of your ventilation system, you also have enough people to be generating excess heat that will make up for a cracked window somewhere.
I've looked through Renewaire's literature, and I'm not buying that their ERV is not going to frost up. The only mention I can find about it is this nebulous statement:
"The very simple answer to both of these questions is that no condensate (liquid water) forms. Without water in the liquid phase, there is no need for a drain, and no solid ice forms in the RenewAire ERV energy exchange core, which also keeps functioning without interruption in typical winter conditions."
That all but tells you that it IS going to frost up at some point. Typical winter conditions? Typical for where? And even if I am in that region, what happens when the temperature is atypically cold? Their lack of any detail or specs as to minimum operating temperature speaks volumes. Their specs on latent moisture transfer of 0.62 at 0C don't look impressive enough to convince me that it's an all encompassing solution.The vanEE G2400E has the same spec at -25C, and yet it needs to recirculate and even shut down at some point to protect from frost.
edit: If you look at Renewaire's control features, they have a frost control feature. Most likely that is a recirculation strategy similar to their competitors.
Trevor, in my case (3200 sqft 4 bed) ASHRAE 2010 recommends about 70 CFM. No doubt I'm approaching the upper limit of what that ERV is capable of providing. However, the number of days where we don't get above -20 are very few and far between, and we are rarely if ever in a position where everyone is home all day every day for days on end.
Worst case scenario, super cold night, big gathering, party until the wee hours... maybe we crack a window here and there. I'm starting to get why the experienced people on this board work comfortably with 99% design numbers; on the 100th day it doesn't all fall apart, but there may be a slight workaround or temporary inconvenience to deal with. The other 99 days the equipment is right sized and working efficiently.
你在一个完全不同的球场如果need ventilation overhead for a boost mode to vent your kitchen. As curious as I am about recirculating range hoods I'm pretty sure I'd get shot for even daring to mention it!
Agreed, 4 min an hour is pretty much just checking when it's safe to start ventilation again. So far this year that would be the case for about 10-15 hours in Ottawa, if there was no pre-conditioning of the air.
Regarding air/ground heat exchange, it's all about temperature difference and surface area. How much surface area will your water/air heat exchanger have? Will it be more than the interior surface area of a 75 foot long 8 inch pipe? The temperature difference will be the same. ;-)
What system did you end up going with for your HRV/ ERV? I'm currently going through the same process, although in a retrofit scenario in a similar sized home just across the river.
Yupster, post 39, agreed!
Trevor, post 40, agreed!
Hmm, I really think it's more than just the surface area. If you ran water down a pipe, and ran air down the same sized pipe, they're not going to exchange the same amount of heat. If they did, people would probably run hot air through in floor heating pipes, rather than deal with water and glycol. Having said that, I have no idea whether the 75' 8" diameter pipe will transfer adequate heat, maybe it will be more than my system. Yours is a simpler, just one heat exchange. Mine is two, once from the ground to the glycol loop, then from the glycol loop to the incoming air. You obviously need to make sure you don't have mold or other things growing in the pipe.
Trevor , how do you like the glycol loop, originally I planned to use Ultimate Air System with there Air/water pre-heat, as I know someone that use this system, they seemed happy.
It's new build so easy to drop the loop in around the footing.
Lance, I agree with Trevor are you not worried about possible mold growth and similar problems that earth tubes have.
I haven't got it installed yet. Still waiting for the inspector to give me the go ahead on my HRV purchase. I would suggest that the only way it makes financial sense is to build it yourself. I recall UltimateAir's system ran about $1100, and Zehnder's almost $2000.