ERV brings in and takes air from the return duct system.   It is piped in accordance with renewaire specification.

Zone dampers are full open.   Supply dampers are  not all full open.  HVAC contractor set a Balometer over each supply grille and set them all to some "number".   I don't have those numbers.

Plenty of returns, nothing high, nothing behind "closed doors".   Minimum size on any return grille is 16 x 20.  There are no filters in the return ducts.   Air filtration is done by a trane clean effects immediately in front of the waterfurnace in the return.

If you want to see pictures of the house before the brick went on, go to the fox blocks website (there is always a link up on my page when I am viewing this thread) go to the gallery, then go to willow creek home.  Front and rear views are available

Posted By BrianPK on 04 Jun 2012 08:16 AM
There are 5 people and two indoor cats. In the house.

No, A blower door test has never been run.  With the ICF and windows, and doors that were bought I would be very suprised if there were any big air leaks.

Thanks for your time.

While inherently tight wall systems plus better windows & doors make air-sealing easier, air tightness is by no means guaranteed.

Air-tightness starts with a defined primary air-barrier on all 6 sides of the cube at the design phase, and needs to be followed up on throughout construction. There are MANY ICF & SIP houses with higher than average air infiltration rates. Unless all trades & contractors involved with the project were both conscious of and dedicated to the notion of an air-tight house you can bet there are air leaks, and even big leaks would not come as a surprise.  The good news is that ICF houses are usually easier to retrofit air-seal than most timber-frame designs.  But the assumption that it's air tight requires a lot more than ICF walls and pretty good windows.

The air tightness of ceilings are always suspect since most come with multiple plumbing stacks & electrical penetrations or even utility chases that may be open at both top & bottom, duct penetrations, etc.  Air leaks at the top &  bottom of the structure are the most critical, since the volume of air driven by stack effect forces is usually higher than wind-driven infiltration.

If the ventilation rate high, whether active ventilation or parasitic infiltration, it adds to latent load when outdoor dew points are high. A dehumidifier converts latent load to sensible load, but it doesn't reduce the total cooling load. Instead it adds more sensible load on top- the power it takes to run that compressor & blower. Running the ventilation at the minimum ASHRAE rate (or even turning it off for a day) might give clues about what's really going on. It takes about 2x the compressor energy to reduce the dew point by 10F than it takes to lower the sensible temp 10F, so a high ventilation rate when outdoor dew points are into the 65F+ range can even add up to a serious cooling load even when not very hot outside.  And when it's 90F outside out the dew points can easily be in the 70s or even 80s. Healthy, comfortable indoor air has a dew point of ~55F or lower.

In a new ICF house the concrete itself can add quite a bit of latent load as the concrete cures.  If there isn't a capillary break at the footings and bulk water is hitting the exterior walls and seeping down to the footing or if the footing isn't wall drained, concrete can even wick up substantial amounts groundwater 24/365, which can find it's way into indoor air.

I have contacted the insulation company that did the work on the house.  They are going to come and do a blower door test.  The concrete is cured as it was poured over 1 year ago.  We have a moisture barrier installed under the carpeting in 4800 of the 5200 lower level sq. footage  (superseal carpet subfloor membrane).  The balance of the concrete has two coats of industrial grade flooring epoxy on it.

Dana's points are well taken

We recently commissioned a 4000 SF new construction ICF home. Single 3T air source heatpump, 4 zones. High pitched hip roof; some parts of attic 15+ feet high. Approx 3"closed cell spray foam on underside of roof sheathing.

The insulator swore he'd done a great job. First blower door test came in at 3800 CFM 50. We dragged the insulator back and smoked the house, then pressurized it. Successive rounds of improvements eventuall brought the blower door number down to 1300 CFM 50. No Dehu or ERV; owner happy.

My own 3400 SF ICF / foam house leaks 1600 CFM 50. A rule of thumb to determine ACH Nach puts leakage at 60-70 CFM, about what ASHRAE now calls for (0.01 CFM / SF + 7.5 CFM per person) no ERV or dehu. My Envision 038 is ticking along in low gear. Outdoors it is 74 and raining, inside it is 77 with 45 RH; owner happy.

Brian needs that blower door test, calculation of heat rejection, verification of unit staging and CFM per ton. That the ducts are all in conditioned space is good and good to know. The 150 pt / day dehu if installed properly woul likely trade 1/2 ton of latent load for sensible load and adding an additional 1/4 ton of sensible load.

If the dehu is misconfigured it is likely adding just sensible load. It would be a simple matter (and useful information) to measure condensate flow from both the dehu and the geo heat pump. The ERV may be malfunctioning and just providing "V" (100% outside air) if its enthalpy exchange media / wheel is inoperative.

A quick look at NWS Greenville 3 day history shows outdoor dewpoints have mostly been at or below 60 except a period in the mid 60s during daylight hours on 6/4. This is not particularly challenging weather for HVAC, but excessive air leakage coupled with low sensible loads may explain the humidity excursions, but not the system's inability to reach drybulb temperature setpoints.

The interplay between HVAC system issues and building science / psychrometric principals is interesting to watch