Ideal IAQ for a 4-yr-old home, 2100 sqft in Fresno's central valley?

[tuan]

At first, all I looked at was HEPA filtration to achieve ISO7 (class 10,000) or better. After reading many posts here, I also need to look at fresh air, humidity, UV (for molds and VOCs).

At work, I have a Pure Air 600 CFM HEPA filtration system that can output ISO6 air for two - 100sqft positive pressure (0.05" WC) clean rooms. I can purchase another unit for my house, but it looks like I should use something else that can draw in fresh air, hu/dehu, and UV. I'd like to draw some fresh air for positive pressure, which can also get rid of some VOCs as well as achieve ISO7 or better.

The temps in Fresno can be as low as 25's in the winter and 120F in the summer; RH around 30-50%.

[drk]

I'd skip the UV. Over rated with high maintain cost.

[teddy bear]

Foremost is the fresh air change rate. Most suggest a fresh air change in hours at a minimum when occupied. A merv +11 filter is also recommended. The fresh air should be blended with the house air, filtered and circulated throughout the home.
Fresno is a moderate to dry climate but has occasional +65^F outdoor dew points. The key to eliminating any indoor biological growth is to maintain <50%RH which is a 50-55^F indoor dew point. With normal occupancy of +2 people, you need a couple lbs. per hour of dehumidification during high outdoor dew points and low cooling loads. A small whole house ventilating dehumidifier may be the ideal device for blending fresh air with the house air, filtering with the optional merv 14 air filters, and circulating throughout the home. Also the units dehumidistat will dehumidify when the indoor humidity rises above 50%RH. The Ultra-Aire whole house ventilaing dehumidifier has time schedule ventilation with optional high eff. filtering.
Keep us posted.
Regards TB

[tuan]

drk,
I agree regarding UV. It's great if you or someone in your household have sensitive lungs. Other than that I think it's a waste.

teddy bear,
Thanks for your input. It sounds like you recommend an ERV. What do you think about installing an ERV along with HEPA filtration. I know you recommended MERV 11, but IMHO MERV 11 is not enough to filter out ALL pathogens.

Where would be the best place is my question. HEPA filter the fresh air before or after the ERV?

[teddy bear]

drk,
I agree regarding UV. It's great if you or someone in your household have sensitive lungs. Other than that I think it's a waste.

teddy bear,
Thanks for your input. It sounds like you recommend an ERV. What do you think about installing an ERV along with HEPA filtration. I know you recommended MERV 11, but IMHO MERV 11 is not enough to filter out ALL pathogens.

Where would be the best place is my question. HEPA filter the fresh air before or after the ERV?

A HRV may not be ideal for you. The pay back is is minimal in your climate. Pressurizing your home with 100 cfm of fresh make-up air blended with the house air and circulated throughout would be ideal. Pressurizing the home with out exhausting slows infiltration of outside air. I would get an air filter of your liking. Filter the fresh air/house air blend with the filter.
The finest filtering made will not eliminate the dust in a home. Most dust enters homes on clothes and during wind.
Regards TB

[pmeunier]

Maybe not eliminate, but I measure particle counts @0.5 microns more than 50x lower with positive pressure and HEPA filtration of fresh air, even when it's windy. There's not a chance of achieving this with a MERV 11 filter.

It makes no difference in particle counts if you filter the fresh air before or after an ERV. However, your ERV will be cleaner and therefore more efficient if you filter the air before it enters it. If I had an ERV, I'd install the HEPA filter first, before the fresh air reaches the ERV. But, even with an ERV you need a humidity sink (dehumidifier). The ERV simply lowers the needed capacity.

[tuan]

Broan GSEH3K HEPA filtration +ERV sounds like it would fit my needs.

http://www.iaqsource.com/product.php?product=111247

I'm thinking of exhausting the kitchen air (tons of voc from cooking and garbage can) through the Broan HEPA+ ERV and venting fresh air into the existing HVAC right at the return air where I can T it off.

Similar to the diagram "Better" here:
http://www.iaqsource.com/hrvs_ervs.php

Let me know what you guys think.

[pmeunier]

I dislike the oval connectors on the Broan filters because flex duct can slip off of those, and doesn't naturally fit. This can be frustrating, as tightening a zip-tie too much can hasten the slip by bending the plastic of the oval connector. I also dislike the fact that air can bypass the prefilter for the HEPA and significantly shorten the HEPA's life, and the fact that the pre-filter is non-standard and expensive.
Make sure that the noise will be attenuated by long lengths of duct. It's loud -- all HEPA filters are loud, unless they are run at a low speed just enough to bring in the desired amount of fresh air. I've given up on running HEPA filters at their "normal" speed inside conditioned space.

[Joseph Milton]

I have installed one of those Broan units for a customer of mine. I was not impressed with the amount of styrofoam inside this unit. For the price, it just seemed very cheaply made.

[tuan]

Thanks for your input. I will stay away from the Broan. Do you have a unit you can recommend?

For our cleanroom at work, we installed the 600HS plus from pureairesystems
http://www.pureairsystems.com/Pure-A...-350_e01d.html

Joseph,
Are you in Fresno? I thought I saw a "Milton Air" installation van driving around town. Maybe I can hire you to install my unit once I figure out which one I want.

[pmeunier]

Thanks for your input. I will stay away from the Broan. Do you have a unit you can recommend?

Sorry, I don't know enough about ERV models to make a recommendation, or even if they are a worthwhile investment for you. I just had some irritation to "vent" with "Groan"...

[pmeunier]

Here's something to think about: dehumidifying with an ERV and a small high efficiency dehumidifier costs about the same in energy as dehumidifying with a large high efficiency dehu ("Using EnergyPlus to Perform Dehumidification Analysis on Building America Homes" Xia Fang, Jon Winkler, and Dane Christensen http://www.nrel.gov/docs/fy11osti/49899.pdf). They both are the most energy efficient options. Compare the purchase cost of the ERV + small high efficiency (4.2 pints/kWh) dehu to that of a large high efficiency (7.8 pints/kWh) dehu -- about the same. However, an important difference is that the ERV doesn't support significant positive pressure, whereas the large high efficiency dehu does. Positive pressure provided by air filtered through a HEPA filter greatly diminishes infiltration and particle counts.

In conclusion, a HEPA filter run on the fresh air, used with a large high efficiency dehu, can provide the best combined IAQ and energy efficiency.

[pmeunier]

P.S.: I think that a dedicated outdoor air system (DOAS) should be even more energy-efficient, and also supports positive pressure; however this is not a well-known and easily available residential option. It wasn't tested for that publication.