Necessity of air exchanger

dreambuilderFebruary 17, 2013

I spoke with our builder and he does not think an air exchanger is necessary. He says we are an active family in and out all the time so that brings in enough fresh air. He also says it makes no sense to make the home as tight as possible (insulation) and then bring in cold air to the house. Thoughts?

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You contractor obviously doesn't understand what a heat recovery air exchanger is or why it is needed so you should be talking to someone who does. I hope he didn't have anything to do with the design of your HVAC system.

    Bookmark   February 17, 2013 at 8:47PM
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Or anything to do with the framing, sealing and insulation of your house. Ask your contractor if he knows what a blower test is. If not, it may be time for a new contractor if you hope for an energy efficient house.

Good luck on your project.

    Bookmark   February 17, 2013 at 10:54PM
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Annie Deighnaugh

I agree....we have a heat recovery air exchange and it's necessary. Sounds to me like, if you want to go green, you're going to have to learn the stuff yourself and teach your builder, if you're going to stick with him.

We had to with ours. We put in a geothermal system and he wanted to know where the outdoor a/c compressor units were going!

    Bookmark   February 18, 2013 at 7:49AM
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In a cold climate fresh air (ventilation) in a house has traditionally entered through leaks in the building envelope especially at windows, doors and at the top and bottom of the exterior walls. Air leaks are assisted by negative pressure in the house from bath, kitchen and attic exhaust fans and the wind. The normal use of doors is unlikely to have a measurable effect on fresh air ventilation but if it did you would need entry vestibules to save the excessive energy lost.

As houses get tighter (don't assume yours is without some evidence) and more synthetic materials are used for interior furnishings and finishes, the traditional sources of fresh air are not enough to support good health. An architect or HVAC design consultant should know when an air exchanger is needed but it can't hurt to install one.

When your contractor warns you to not bring cold air into the house he apparently doesn't understand that the term "air exchanger" not only refers to the exchange of outside air for interior air (ventilation) but to the exchange of heat from those air streams. The generic term for the device "air-to-air heat exchanger" and the industry name for the installed system is "energy recovery ventilator" (ERV) or "heat recovery ventilator" (HRV) depending on how they function.

If the intent was to only exchange cold air for warm air all that would be needed would be a hinged intake panel that opened when an exhaust fan was running which must have been what your contractor was envisioning.

For an energy efficient house you need to talk to a professional HVAC designer.

    Bookmark   February 18, 2013 at 8:15AM
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A general rule of thumb (and I belive in some newer codes) is that if your kitchen has a range exhaust with a capacity of over 400 CFM, an ERV may be required.

Back in the day, a Fresh Air Intake (FAI), connecting the return air plenum to the outside with a damper was considered a good, optional energy saving device for use during temperate times of the year.

As has been said, you need to talk to a knowledgable HVAC person while still in the design stage of your house. If you are already building, you need that conversation ASAP.

Good luck on your project.

    Bookmark   February 18, 2013 at 9:13AM
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ashrae 62.2 ventilation strategy.

build tight, ventilate right.

depending on your climate
erv, hrv, or whole house dehumdifier.

best of luck.

    Bookmark   February 19, 2013 at 3:27PM
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ERV or HRV is a necessity. But what is the most cost effective way to ventilate while retaining the energy used for heating and cooling? According to specialists, central ventilation and filtration effectively eliminate airborne pollutants and excess humidity, thereby protecting your family’s health and the structure of your house. As your contractor is not well aware about ERV or HRV I suggest you to contact the Manufacturers or Service providers and fix a visit to your place. They will check your home and will give perfect solution. I am adding a list of manufacturers where my friends made their choice, check with them. Hope this will help you.

Here is a link that might be useful: List

    Bookmark   April 26, 2013 at 2:19AM
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This subject combined with mandatory blower door testing represents the biggest improvement in home quality since building codes first required insulation.

International Building Codes require mechanical ventilation that meets the ventilation standard ASHRAE 62.2. Most local codes have not yet adopted the requirement but local codes almost always catch up to International codes and if you are building a new home this is not something you want to ignore.

HRVs and ERVs are NOT required with ASHRAE 62.2 but they are a smart upgrade for most US building climates. ASHRAE 62.2 DOES require outdoor air introduction which is the best way to improve a home's Indoor Air Quality. The cheapest way to do this is with a continuously running, very-efficient bath vent fan.

The cheapest way usually isnt the best way and the biggest problem with that method is that there is little control of fresh air distribution. Ideally an HRV or ERV uses separate ducts to deliver fresh air exactly where its needed like bedrooms and living areas.

In very mild climates, upgrading to ERVs and HRVs is probably not cost-effective. The more extreme the climate, the more important to have an "air exchanger". Another big factor in this conversation is what is the ACH50 as measured by the blower door test?

When international building codes require ventilation per ASHRAE 62.2, it is based on the fact that the home has passed a minimum blower door test. Mandatory blower door testing is another important international code requirement that local codes have generally not adopted YET.

I recently wrote much more about these important issues in some blog entries but GW does not allow me to provide links to them. A search of my name and the keywords should bring them up if anyone wants to learn more.

    Bookmark   April 27, 2013 at 11:48AM
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The cheapest way to do this is with a continuously running, very-efficient bath vent fan.

and how long will this continously running
very efficient bath vent fan last??
seems cost prohibitive to me.
a very efficient bath vent fan will cost
upwards of $300 plus operation & replacement/
installation costs. plus safery issues.

we have been adding make up/fresh air
for years with a very simple system.
that uses no electricity.

12x12" filter back grill to exterior (with filter)
located in porch ceiling or similar location
to exterior. 12"x12" supply box or similar
sized small duct board plenum.
6" flex duct to return air plenum
of hvac system. Barometric damper at return
air plenum.
set barometric damper to cfm required..
air is filtered before entering return plenum
and conditioned (& dehumidified in my area)
before it enters the living space.

using this method...the only duct is from filter
grill to return, and air is distributed through out
the house via ductwork for hvac system.

barometric dampers like the skuttle 216 work
well in this application.
for minimal investemet this is a system that
cost nothing to operate, and has no mechanical
parts to fail other than the lever of the damper.
I've yet to have to replace any barometric dampers
in the 15 years I've installed these fresh air intakes.

ASHRAE 62.2 will finally force builders & hvac to
deal with adding fresh air. finally.

but without knowing how tight the house is...
by means of testing with a blower door to actually
measure infiltration..people who have no need
of mechanical ventilation...(.aka leaky houses)
are spending a lot of money on erv/hrv that isn't
needed. lots of new homes are NOT as tight
as homeowners imagine them to be.

building a tight house is more than just building
a house. special details for air sealing have to
be incorperated before the first wall is built.
and in every step thereafter.

I'll check out your blog Brian. I enjoy your posts.
this post is not to correct you, but to share with you
what I've learned. these types of fourms are great
for exchange of ideas IMO.
when I first posted I thought about including the
barometric damper application I use...but was
pressed for time & really wanted to introduce
ASHRAE 62.2 into the thread.

best of luck.

    Bookmark   April 27, 2013 at 1:24PM
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Thanks energyrater, love your posts as always and agree that GW is an invaluable source of information.

The "how" in meeting ASHRAE 62.2 is very interesting (to some) and this should be a good warm up for a future blog post on the subject. For those concerned with Indoor Air Quality IAQ, understanding and implementing even some of this information will have a MUCH bigger impact than any other IAQ measure.

ASHRAE 62.2 only provides rates; "how much" in (Cubic Feet per Minute CFM) of ventilation minimums. It does not tell us "how" to do it which is nice because of its simplicity. Its likely that future updates will prescribe some "how" which will change this conversation completely. I think most feel that some "how" is needed due to excessive energy use by ventilation equipment and inadequate fresh air distribution.

There are 3 basic strategies for whole house ventilation in regards to ASHRAE 62.2:

Exhaust Only
Supply Only

The "bathroom vent fan" method I mentioned is considered "Exhaust only" and is probably the most common way of doing it for most of the country. The method energyrater describes is a "supply only" and is probably better known by those in the industry as a "central-fan integrated supply". This is probably the most common method in the Southeast US.

I think between the two more affordable options (supply or exhaust only) which one is cheaper depends on the situation. Same with the operating costs. Each situation and climate can use a different approach and there are many ways to the same goal. Each method has benefits and drawbacks.

For those highly concerned with IAQ and want the most possible control, the balanced approach with separate ducts and a wall control cant be beat. This set up gives the occupants the most possible control over their IAQ. Whether the occupants use it well is another story. I highly recommend this approach for almost all new homes.

"Separate ducts" is worthy of its own thread but I feel small and open floor plans can share the heating and cooling ducts. I think three levels with a bedrooom on each level needs separate ducting.

I think energyraters method should work great for most homes MAINLY because of their attention to detail given to design, layout and installation (and hopefully needed adjustments/commissioning) . Drawbacks with systems like that is that you are using a big fan (big energy costs) to circulate what essentially should be a relatively small amount of CFM needed for fresh air. This assumes that there is an extra level of control; the unit should be configured to run when there is no heating or cooling demand. Also the fresh air duct should be closed when the air handler is running constantly during peak seasons to avoid overventilating and having to condition all that outdoor air.

Barometric dampers can be problematic as they are effected by wind, other exhaust sources in the home, temperature and neutral pressure planes. Curious in your experience how the filter effects the measured performance and whether the CFM setting on the damper is effected by other exhaust vents in the home (dryer, woodstove, vent hood, bath vent fans)?

This post was edited by Brian_Knight on Tue, Apr 30, 13 at 15:18

    Bookmark   April 30, 2013 at 3:14PM
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