fresh air exchange, makeup air, dehumid: erv, ua150h or combo?

16 years ago

We need to make a decision on a fresh air exchange approach.

Here's our situation:

* Location: St Louis, MO

* Newly constructed tight home, 3,200 sq ft on each of two levels, walkout lower level 50% finished living space

* HVAC: WaterFurnace Envision 6 ton unit covering each level as a distinct zone

* Powered direct vent LP water heater, direct vent fireplace

* Individual exhaust fans for baths and cooktop

* Clothes dryer in fairly open laundry room

Obviously, we need fresh air exchange.

We may or may not need supplementary dehumidification.

It's unclear to me how makeup air is provided for the dryer and exhaust fans.

We don't have enough time in the house to understand whether the HVAC unit is going to remove enough humidity on its own.

It appears that our direction boils down to two options:

1) Just an ERV. Address dehmudification problems with a separate dehumidifier if and when a problem arises.

Open issue: What about makeup air for our exhaust vents?

2) Just a Whole House Ventilating Dehumidifier. Forgo energy savings of an ERV, but get the benefit of applying introducing fresh air, ensuring positive pressure to house and ensuring that dehumidification won't be an issue. Assumption is that air introduced from the outside will force equal amounts of air out the existing exhaust vents. I'm thinking of the Ultra-Aire 150H.

Open Issue: Would this approach really address any tangible makeup air concerns? For example, if the dryer is running, but the UA150H is not drawing air in from the outside, it doesn't seem as though we'd be addressing the makeup air concern.

If you tell me to not worry about the makeup air aspect, then I am inclined to go the ERV route and address dehumidification later on if and when it's necessary.

Comments?

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Comments (3)

energy_rater_la
16 years ago
We deal with dehumidification in tighly constructed homes in this manner..(note that my location is Louisiana)
We blower door test home to determine if fresh air is necessary. In many cases it is not, it takes an effort to build to the standard that requires fresh air intake.

La. mandates .35 air changes per hour (achN)Fla. mandates
.25 achN..as a rule of thumb I add fresh air @ .3 achN.

There have been a lot of misconceptions with erv's in my area, and cost and install are equal factors.
A few years ago we started using this approach.

12'x12' filter back grill installed (depending on house) under rear porch, soffit..easily acessable area as you will be changing a filter @ this location.
4" duct from filter back grill to return side of hvac system. Barometric damper installed in 4" duct.

In this install we are introducing fresh air, filtering it before it enters the return & controlling the air flow with the barometric damper. Once air enters the return it is clean, measured & dehumidified before entering the house.

I found a site..years ago..www.skuttle.com/216html..don't know if it still works, but this is were I first learned about barometric dampers.

The damper will adjust to the amount of air being drawn out of the house via bath fans, stove fan etc.
If all fans are running the barometric damper will be opened more, and as each fan is turned off the damper will close a bit more. The idea is to keep a slight positive pressure on the home rather than a negative pressure.

You don't have to add a great amount of fresh air..something like 10 cfm (cubic feet per minute) per person & combustable appliance (including fireplace inserts).

Oh cost for install is about $500. materials included.
Great performance in my area.

For additional dehumdidfication...stand alone dehumidifiers in the conditioned space. We try to catch this in the planning stages to have permanant drains rather than having to empty the dehumidifier on a regular basis.
One dehumidifier will cover about 2000 sq ft.cost is less than $200 @ HD & lowes.

I would first determine if the RH was high enough to need the additional dehumidification. Radio Shack sells a Relative Humidity device that measures RH in your home for about 30 bucks. In my area 50% RH is the goal.

Hope some of this helps you out in your situation.

(oh and ok guys....y'all's input???)
mica
Original Author
16 years ago
Thanks for the response energy_rater_la.

I've decided to perform a DIY install of the RenewAire EV300 EVR to address our fresh air exchange needs and to address dehumidification issues in our walkout lower level with a portable dehumidifier if and when necessary. I may still address makeup air through an approach similar to what you've described.

BTW, Duane at RenewAire has been extremely helpful with my questions about their products and ERVs in general. The folks at positive-energy.com have also been very responsive as a dealer for RenewAire products.
curt01hawk
16 years ago
mica

I am building a similar sized house in Kansas City and have been considering a WaterFurnace. What are your yearly energy bills? How much did your system cost to install? How long of a pay back period do you expect?

Thanks