ERV for crawlspace spplication

Brad White_9

I think the conditions will be chasing each other.

Using an ERV will exchange crawlspace air at a given, let's say acceptable humidity range. (System has been running we will assume it works or at least you need a starting point.)

Let's say the space is at 70 degrees and 50% OA.

In order for the ERV to work you have to exhaust that air. The incoming air would be higher in enthalpy (total heat both temperature and humidity).

So your leaving air (70/50%RH) knocks the incoming OA down to an intermediate level. What comes into the space is still higher in enthalpy than what you exhausted. Vicious cycle.

ERV's really are for use where you are throwing air away anyway and want to recover the heat from it. Not as a solution to an issue that needs other remedies. Unless of course you can leverage recovered air from other processes.

For that crawlspace, I would set up an enthalpy-based economizer to use OA when it is lower in enthalpy than the crawlspace. Can be as simple as RH but you lose the effect that a cooler crawlspace will increase in RH at the same humidity; this is why enthalpy control is so important.

When enthalpy control cannot do the work, close down OA and recirculate such as running a refrigerant-based dehumidifier or dessicant dryer.

If the house has AC, what do you think about placing the condensing unit (a horizontal one such as for ductless splits) down there? The increased temperature should not affect the house much and will depress the RH. Sort of the tail end of a dehumidifier, using the heat of rejection as reheat.

Not a tremendous number of options. Just some thoughts.

Wayco Wayne_2

I have a customer

who lives on top of a mountain. He has crawlspace under his entire house. He says in the Summer the air gets so high in humidity that he has to close off the crawspace vents or it will get so musty he can smell it on the main floor. He has been researching ERV's and would like to install one to control the humidity in his crawlspace in the summer. He also thinks it will give him a warmer crawlsapce in the Winter. What do youse guys think??? WW

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Constantin

You should send your client to BuildingScrience.com

.... so that he/she can educate themselves about crawlspaces. Based on the research I was able to read there, there is no point to having vented crawlspaces in the first place. Block them off, seal them from moisture, and benefit from lower energy bills, no humidity issues, etc. IIRC.

If, after applying Tu-tuff and other moisture-intrusion control measures there is still humidity down there, I would go a-hunting for holes in the foundation wall and between sill plates. Worst case, install a small automatic dehumidifier with a AC sump pump to dump the moisture outside. If the house sits on ledge, dig a trench around the perimeter, put in a perforated drain with a geotextile burrito around it + crushed gravel, then drain to daylight.

Water management is everything. We have clay conditions here, the worst you can deal with... the new basement is not only dry (thanks to 2" of XPS on the outside + Rub-R-Wall) but warm also. The previous foundation was destroyed by the lack of water management.