malibud
Registered Users
Posts:30
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| 07/22/2008 7:01 AM |
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My Hvac installer said that a cheaper verson of a ERV is to install a fresh air intake . It does not convert temperature but lets in the same amount of fresh air in is this true? This will be a very tight house.
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wes
Registered Users
Posts:376
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| 07/22/2008 7:30 AM |
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We have used the fresh air intake on a couple projects where clients simply would not spend the money for an ERV.
Essentially, its just a 4" duct from the outside tied into the return air of the HVAC. You can use a manual damper or an automatic system is now available that will open and close based on outside weather.
Overall, the system works fine for introducing fresh air into the house, and the temperature is tempered by mixing with the return air. However, you still have the loss of efficiency gained by the use of the ERV. Honestly, depending on your location, this loss of efficiency may only amount to a couple dollars a month on your utility bill. So the final decision has to be made on an individual basis. |
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Wes Shelby
Design Systems Group
Murray KY
wandr@ainweb.net |
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malibud
Registered Users
Posts:30
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| 07/22/2008 9:27 AM |
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So there still we be there air exchange like an ERV and I will not have any air quality issues just monetary . Correct?
thanks for the info
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Donaldson
Registered Users
Posts:92
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| 07/23/2008 8:51 AM |
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| The other advantage of just using the 4 inch duct and a damper is it will positive pressurize the house preventing any outside drafts which will possibly balance out the monetary loss if there really is any loss at all because you are not talking about large amounts of air. The damper should almost be closed, The biggest thing that you loose when not using the ERV is the exchange from the bathrooms. Most people vent the air from the bathrooms to the out side of the ERV to help take out moisture. But in a tight house with proper sizing of HVAC meaning it is small enough to run long enough to remove the humidity then you will be just fine. |
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wes
Registered Users
Posts:376
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| 07/23/2008 7:22 PM |
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Donaldson,
I would recommend the use of a 'traditional' bathroom vent even if an ERV were being used, and most certainly in this case I would use such a vent. I don't want all that moisture going through an ERV, and most HVAC systems don't pull enough air to remove the moisture quickly enough to eliminate the humid environment that could lead to the growth of mold and/or mildew in the bathrooms. You only have to remove moldy drywall from a bathroom one time to learn this lesson.
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Wes Shelby
Design Systems Group
Murray KY
wandr@ainweb.net |
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Mark Fleming
Registered Users
Posts:188
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| 07/24/2008 3:53 PM |
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I use my HRV all the time in the bathroom, but also have a regular bath vent right in the shower stall. The HRV control is next to the toilet, so I can turn it on while sitting. The HRV unit is set at 150cfm and there are 4 intake vents, so there's not a huge amount of air being taken out of the bathroom, but it works just fine. When the activate button is pushed, it runs for under 1/2 hour. The shower vent is 80cfm and I only use it when in the shower and turn it off when I leave the bathroom. It's the HRV that does the rest of the work pulling moisture out.
I've also started using a spray bottle of ammonia/water after finishing in the shower. There are commercial products for spraying down the shower that do the same thing (at 10 times the price). What the ammonia does is break the surface tension on the water droplets and they go down the drain. Instead of 4 ounces of water evaporating into the air from the shower stall, that water goes right down the drain. It cuts down on the drying time of the shower stall by hours, so it also reduces the chance of mildew. As a benefit, if I can still smell ammonia later, I know that the bath needs another run with the HRV.
Mark |
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dmaceld
Registered Users
Posts:494
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| 07/24/2008 11:46 PM |
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Dust in the fresh air is a consideration. If you have a lot of dust in your area you may have better results by filtering the fresh air through the HRV filter system rather than the furnace filter.
Be careful about the comment about fresh air only making a $2 or $3 difference in your utility bill. That will be case only if your heating & cooling load is low. Air exchange is a big factor in heating/cooling load calculations. For my ICF house, which I'm building now, heating the ventilation air is about 20% of the total heat load. That's why I'm installing an ERV.
An HRV or ERV will allow you to have a greater volume of fresh air exchange for the same cost as a direct fresh air intake. Also, if your house is really tight you need an exhaust system with essentially the same volume as the fresh air intake.
I'm not saying a direct fresh air system is not OK, it's just that there is more to consider than just a few dollars in energy cost.
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Building house - what a way to spend retirement! |
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wes
Registered Users
Posts:376
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| 07/25/2008 7:05 AM |
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The comment about the cost difference was an aside based on my experiences with actual projects. Two homes essentially the same size and construction. One with ERV, one with fresh air intake, the monthly utility costs are within a few dollars of each other. That seeming lack of operating cost difference certainly should not be the deciding factor and it certainly is not the only consideratin. Other circumstances may have different results. And I repeat, each project should be considered on an individual basis.
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Wes Shelby
Design Systems Group
Murray KY
wandr@ainweb.net |
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Brock
Registered Users
Posts:209
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| 07/25/2008 5:35 PM |
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Our HRV is exhausting air from our indoor pool room at 85F and incoming ranges from -20F to 95F. In winter with the pool open it will condense about a gallon in 5 minutes (condensate drains back to pool fill line) and raise the incoming air from -10F to 70F just a bit of heat recovery there. In our last house it was in place for 3 years without any issues from the humid air entering the unit. We did have to set the freeze protection down, it was fine when the pool was open, but as the room dried out and the air had less heat in it, the unit would often freeze up. We eventually found a good set point to keep it from freezing (shut off the intake 5 minutes every 25 minutes).
I did play with a 1000w heater on the fresh air intake to "defrost” the unit before I found out it had the freeze protection built in (remember to read more manuals). It took about 1000w to raise the incoming air from 20F to 70F. So if I didn't have an HRV, that’s a lot of BTU's being blown outside. I can't imagine it being as little as a couple of dollars, maybe in a mild climate? |
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Green Bay, WI. - geothermal heated indoor pool with a small solar setup |
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Donaldson
Registered Users
Posts:92
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| 07/29/2008 6:42 PM |
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Posted By wes on 07/23/2008 7:22 PM
most HVAC systems don't pull enough air to remove the moisture quickly enough to eliminate the humid environment that could lead to the growth of mold and/or mildew in the bathrooms. You only have to remove moldy drywall from a bathroom one time to learn this lesson.
Wes,
I live in central FL just north of orlando. It has poured rain here every day for the last five weeks. The outside humidity hasn't dipped below 80 in a long while. This is exactly why I chose steel sips to build with. My envelope is so tight that my HVAC a two ton unit for 1450 down stairs and a two ton unit for 1800 sq. ft. up stairs. I just checked my humidistate and the inside huidity is at 45%. If you have supply and return in your bathroom then you have the air circulation needed to remove the humidity. My shower is 5 X 5 with ten with a half wall and is completly open to the bath room so I am not trapping any moisture in the shower stall. And even in this heat I take hot showers that produce lots of steam and huimidity. The important thing is to not have any extra humidity filtering in from a convinetional roof, and having proper air circulation. If this is done then a dampner outside vent hooked into the HVAC return so that it does get treated will work without a build up of moisture causing mold. Mold needs 64% humidity as a minium to be able to form. The key is air circulation.
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malibud
Registered Users
Posts:30
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| 07/30/2008 5:05 PM |
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Ok going w/ an Erv april air 8100 where is the best placement in the return or seperatly into the house right now it is plan to be used in the return
thanks for all the reponces ! |
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kwalla101
Registered Users
Posts:12
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| 08/12/2008 5:14 PM |
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Any suggestions on best manufacturer/model? Malibud, what made you choose the Aprilaire?
THanks! |
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malibud
Registered Users
Posts:30
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| 08/12/2008 9:32 PM |
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| I am going w/ april air because my Hvac guy had one laying in his garage price was right |
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gregj
Registered Users
Posts:168
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| 08/13/2008 5:58 PM |
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Posted By malibud on 07/22/2008 7:01 AM
My Hvac installer said that a cheaper verson of a ERV is to install a fresh air intake . It does not convert temperature but lets in the same amount of fresh air in is this true? This will be a very tight house.
Even cheaper is to just open the window. And an open window is probably more effective than just a fresh air intake on a really tight house. I don't see how a fresh air intake will draw in much air at all in a tight house because there is nowhere for it to go. Try blowing up a glass bottle by mouth and see how much air you can get in there.
I think you made the right decision to go with an ERV. |
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hudelhaus
Registered Users
Posts:9
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| 08/25/2008 9:36 AM |
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I agree about the open window but I am not an expert in any means of the word.
For example, one of the benefits of SIPs + Radiant Floor heating is that there is less dust to move around so the air is "healthier" for people with serious allergies. Isn't that point made moot by having to have an external ventilation source that, essentially, moves all the dust around just like a forced air heating solution would?
Cheers,
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GWhittleAL
Registered Users
Posts:20
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| 10/16/2008 11:09 PM |
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I'm also considering an ERV with the intention to downsize my HVAC unit. Make sure you are properly sizing those HVAC units with consideration of the lower loads resulting from the ERV. If your HVAC is over-sized, they won't run long enough and they won't be able to pull enough humidity out of the house.
Being in a very humid climate, I'm considering including a humidistat in the design of my system to ensure that my system always runs sufficiently to prevent mold and mildew problems.
In a hot, humid environment, 50% of your AC loads can be dehumidifying air. This is one of the problems with a "leaking" envelope and why tight envelope's are more energy efficient. A leaking envelope lets moist outside air back into the envelope of the house to have to be conditioned AGAIN.
A well designed ERV system with humidity controls can also control the humidity of the intake "Fresh" air, thereby saving energy and improving indoor air quality [IAQ]. A simplistic fresh air intake can't do this. It only prevents negative pressure from causing exterior air from entering through nooks and crannies where dust, moisture, and mildew problems can generate IAQ problems. The "bad" outside air still comes in, but at least it enters a controlled, conditioning and filtering environment before it circulates through the house.
An ERV is far superior.
Google PassivHaus design and see how effectively ERVs have been used internationally to control energy consumption while maintaining IAQ.
Without an ERV half of the value of a "tight envelope" is wasted with the "fresh air intake." The goal with a tight envelope is once you have conditioned the air, you don't have to keep re-conditioning it (removing the same humidity, as well as the delta T) over and over again. Without an ERV, you just have a "cleaner and healthier" house that is only modestly more energy efficient. |
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