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Old 04-23-12, 02:21 AM   #11
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Think about this. If I open my window and put my furnace 800CFM (48000CFH) blower into it and open all the rest of my windows, I'll only be at 2.73ACH. That's a furnace blower maxxed out, plenty of wind there!

So, if 2.73 ACH will create a windy condition in your house, it seems like the levels of air change recommended by ASHRAE would condemn America to living in perpetual mechanical indoor hurricanes! How could ASHRAE have gotten it so very wrong?

-AC

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Old 04-23-12, 09:10 AM   #12
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My idea is to simply run a damped fresh air duct from outside to the furnace intake, and a dedicated one-way vent to allow air from the living space into the basement to supply make-up air for furnace and DHW combustion and the clothes dryer. That way, when the furnace is running, the combustion blower is pulling a set amount of air out of the basement, which pulls stale air from the house into the basement, and the difference in static pressure (between inside and outside the house) pulls fresh air into the furnace intake to be heated and sent to the living space.

This is obviously not a very efficient design, since there is no actual heat exchange going on, but it's better than opening windows on a cold day. Since the furnace is going to send a set amount of air out of the house anyway for combustion, better to have it come in from one spot and get heated directly than to have it seep in through cracks in windows and doors. I suppose a HE could be added eventually between the fresh outside air and the stale air entering the basement. That could make for a cold basement, but the difference would be less energy consumed to heat the supply air to the house.
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Old 04-23-12, 12:58 PM   #13
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My idea is...obviously not a very efficient design, since there is no actual heat exchange going on, but it's better than opening windows on a cold day... I suppose a HE could be added eventually between the fresh outside air and the stale air entering the basement. That could make for a cold basement, but the difference would be less energy consumed to heat the supply air to the house.
You live in a pretty chilly part of the country, come winter. The benefit to you would be greater than they would be for me, since the area I live in has milder winters. An HRV is definitely on my list.

There are commercial HRVs available for around $600 that can be integrated into your forced air system. The effort to integrate the HRV into your current system would be comparable to the above described project.

I would go that route myself, but I have decommissioned my forced air system and will need another approach.

In the DIY HRV thread, I posted plans for a simple homemade HRV that first appeared in a POP SCI magazine... pretty straight forward.

People I have talked to who have installed HRVs report an immediate positive personal benefit due to indoor fresh air in the winter time.

I'm in a position that is different from yours right now... I have tightened my house up to the point that sufficient fresh air is no longer being supplied by infiltration during the winter season.

I have decommissioned the forced air system and heat the living space with a small mini-split, so I don't have the furnace sucking in fresh combustion air through the prior infiltration points any more.

The $600 commercial HRVs that would work for your situation won't work for me.

So I'm looking at replacing the forced air ductwork with a fresh air delivery system like a Passive House style HRV system that will pipe in .35 ACH 100% fresh air (with recovered heat) to the living area, or perhaps some kind of direct-vent HRV which could be cheaper and easier.

If I go with the heat-recovered fresh air system, the size of the ducting would be significantly smaller than that of a whole heating system.

My results are not in yet.


-AC
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Old 04-23-12, 04:18 PM   #14
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MNRenovator, a ductwork retrofit is only an issue if you have a multi story house or a slab on grade house. I thought you had a ranch?
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Old 04-23-12, 07:31 PM   #15
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No, multi story. Quad split. I've sealed all ductwork to the level that is fully underground (except for about a foot to allow for external access to provide connections for the A/C, gas, laundry venting outside.) It stays a steady cool, but comfortable temperature anyway, no matter what the season. There is one level that is about 1/2 undergrade with only supply ducting, the level that is a foot above ground level(directly above the basement) is fully ducted but no supplies are easily accessible outside of the main supply trunks in the whole house except for the entry way and the kitchen. A few supplies are accessible for the ground level and two of the four returns(one ground and one upstairs on the same side of the house) are accessible from the basement but nothing on the opposite side. All of the return ductwork is run through the stud cavities on internal walls and the floor joist cavities. Wood and drywall make up most of the return ductwork outside of the metal that covers the floor joists to turn the 2x8 joists into ductwork.
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Old 04-23-12, 07:40 PM   #16
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But you have access to the plenum, right? Why not just plumb the HRV in there?
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Old 04-23-12, 08:53 PM   #17
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Yes, the return originally had an outdoor duct piped into it. I've blocked that off and my furnace heats the house much more effectively now and cut my heating bill tons along with not pulling the humidity to nothing. In the summer, not having a hole in the house directly to my ductwork kept the hundreds of spiders out of my house and the air conditioner ran much less.

Either way, ducting into a plenum is a bad idea. My furnace hasn't run for nearly two months now and likely won't start air conditioning for another month so it wouldn't matter anyway as there will be no fresh air in a system that doesn't need to run in the swing seasons.

If someone is using a ventilation system in Minnesota in the season where the dew point is below 50f, exhaust ventilation via a super efficient bathroom fan designed for continuous ventilation is ideal, of course combined with an appropriately placed passive air inlet with a correct trap. In the summer that's a bad idea as it just introduces tons of humidity, last summer we had higher dew points than what my basement regularly sees, no way I'm pulling that in except through the return plenum. So to me, the scheme would be based on the season if I saw a need to pump unconditioned air into my house but I'm not convinced my air is stale and it seems that there is enough infiltration or I'd still smell the bacon I cooked up this morning after I got home tonight after being gone, but I don't.
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Old 04-24-12, 12:27 AM   #18
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This issue of frosting in HRV's in cold climate area seems to me be working in direct opposition to when you need it the most so after inefficient operation from frost, defrosting cycles or addition costs of pretempering intake air to prevent frosting is enough really saved to pay for it? Especially for a small home with clean lifestyle and few VOC's. Oxygen/CO2 are a concern but what level of ACH will cover just that? Does ACH have to be constant or can it be higher during daytime activity and less at night? Simpler/cheaper solar air collectors can supply a lot of heated fresh air during the day, would it be enough to make it through the night? Could some fresh air be preheated thru a graywater HX during non solar periods? I just know that an aggressive insulation/air sealing retrofit on our 50's doll house cut the heating bill by 2/3 and we have no HRV. We do get condensation inside DP windows on coldest days that needs to be wiped up some mornings. I counted an average of 20 times a day of opening/closing exterior doors(even in winter) how many ACH does that add to that would happen even with an HRV? I'm just not yet sure of an HRV real savings as its theory. A DIY one would certainly help if it lowered cost but they still have frost issue to overcome. Seen many energy projects installed that are now removed or in disuse from not being realistic. Yet some are good but it is buyer beware not to get sold a bad one.

My next home being designed and built has an advantage of better construction methods and energy conservation practices than retrofitting old ones. But there are not less "great ideas" to sort thru.
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Old 04-24-12, 02:25 PM   #19
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Default Fresh Air Is A Waste

From an energy-conservation point of view, introducing fresh air into a house is a waste. You will have to get rid of existing heated air, in order to introduce fresh air, so introducing fresh air will be an energy loss, and therefore, a financial loss.

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I'm just not yet sure of an HRV real savings as its theory.
The energy saved by an HRV, even an extremely efficient one will be very small. The direct pay-back will be long... you might not live long enough to see an HRV that you install, ever break even.

Whether or not you bother to put one in depends on whether the entire house has reduced infiltration to extremely low levels... If you live in an air-tight house, it will feel uncomfortable from the beginning, and eventually it will affect your health.

Even if you choose eco materials in your house, you still bring in toxic materials. For instance, new clothes are treated with toxic substances which out-gas, new furniture with synthetic fabrics and foam cushions contain toxic materials which out-gas, any plastic that flexes contains toxic materials which out-gas, cleaning products contain toxic materials, carpet and carpet padding is loaded with toxic materials which out-gas, as are many beds and bedding which out-gas, sheetrock is covered on both sides with pre-processed cellulose (AKA: paper) which easily supports mold growth which enters indoor air... I personally know people whose immune systems have essentially collapsed under the sustained load of environmental toxins, and they now have to live in extreme conditions to avoid further exposure.

This is why we want adequate ventilation, to avoid the buildup of toxins (and oxygen depletion/CO2 buildup) in our air... It is a compromise we make in order to continue a healthy life.

If you live in a house that has enough leaks to flush out the mold (which is everywhere) and CO2 and toxins from your air, you would be a fool to spend $2000 on an extremely high efficiency HRV to recover a few dollars worth of heat every month. In fact, the power to run an HRV might cost you more than the recovery value of the energy saved.

Fortunately for you, this is something that you can measure... you don't need to take the advice of strangers who may not actually know what they are talking about. Hire a certified blower-door operator to come in and do a blower door test to actually determine what your infiltration rate truly is. The companies that do this are already quite familiar with what constitutes the level of critical tightness, and they can advise you if you need mechanical ventilation... they probably already know which brands of HRVs actually work the best, I am hearing the same brand names from several independent groups and agencies... you don't have to guess on this.

But if your house is critically tight, it would be false economy not to mechanically ventilate. Health is more precious than a few paltry dollars.

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Oxygen/CO2 are a concern but what level of ACH will cover just that?
The German Passive House Initiative tested this very thing, because they had achieved air-tight house construction, and people were uncomfortable and people were getting sick. The minimum level they came up with is 0.35 ACH. They also determined that at the critical levels of tightness, natural infiltration alone was not adequate to supply continuous fresh air... on windy days it was fine, but over several consecutive days of relatively still air, natural infiltration was insufficient.

* * *

It all depends on the level of natural infiltration in your house, which you should measure.

You don't need to risk getting bad advice and you don't need to guess about this one.

-AC
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Old 04-24-12, 03:17 PM   #20
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Healthier indoor air is critical especially for those who are susceptible to respiratory ailments, colds, viruses and bacteria. Studies by the Environmental Protection Agency indicate that billions of dollars are spent every year on medication to help Americans breathe better or cure their respiratory illnesses, including such ailments as asthma, hay fever and other allergies. Many times its the imbalance between negative and positive ions found in most indoor environments, particularly where homes or buildings are insulated to save energy or winter cold. A natural way to improve indoor quality and the balance between the negative and positive ions, Air-ReNu a paint additive it only has to be applied once works 24/7.
I've seen this paint additive ad posted around on the net, have you actually used it?
If you did, how well did it work? Did it balance your + & - Ions?
I've only seen one review on-line..

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