I am not throwing out the 1.65 dehumidifier with broken stat yet! For this family, the AC is pretty much a constant. Wanna take a stab at which is more efficient: the AC or the dehumidifier?

Some considerations:

-Standard oversized (double) AC in north New Jersey. soon to be downsized with GEO.
-The dehumidifier adds to the house AC sensible load.
-Were looking for most efficient at lowering RH, not pints per day.


On a similar note, this site seems to indicate lower the temp in the basement has positive implications on preserving what is down there. Not just mold growth.
http://www.dpcalc.org/

The central AC + 20watt continuous fan use may not be as energy efficient at drying out the basement as a standalone room dehumidifier (even a 1.65l/kwh version), but it would take multilple mesaurements through out the systems to determine where the breakpoint is. The amount of sensible cooling load it's adding is remarkably low unless you have VERY high ventilation rates (beyond all reason.)

It's not an energy disaster to go with the continuous fan, but it's not controlling to a dew point or RH setpoint. There is at least one GSHP manufacturer with units that can control to indendent RH & temperature setpoints in both heating & cooling modes, similar to the Daikin Quaternity mini-splits, but I don't remember which vendor/model that is off hand. Sometimes the tiny amount additional sensible heat is a good thing in a basement (but not this week, eh? :-) )

No, not this week. Come on dude, you are the multiple measurement king! You also use realistic assumptions. Great work!

I am leaning towards chilled water coil(s) for the geo. Here is why:
There are abundant cast Iron rads and radiant heat. The existing ductwork is in the unconditioned attic.


Maybe separate small coil in basement on humidistat? Or at least separate zone. The coil would be used for stage 2 heat on chilly mornings .

Thoughts? Gonna bury the ducts and put a "hat" on the handler.http://www.greenbuildingtalk.com/DesktopModules/ActiveForums/themes/gbt/save32.png

A blower coil in the basement set to it's lowest fan speed & operated under DE-humidistat control in summer could work, provided the chiller-temp is cold enough for efficient dehumidification. There will always be some amount of sensible cooling when operating in this mode, so minimizing blower cfm and chiller-water temp is key.

My $0.02
I had a similarly damp, humid, cooler basement. SImilar climate near the water in Southern Maryland. My GE Geospring water heater has addressed my basement humidity concerns 100%. Through the summer and shoulder months, the added cooling is beneficial or neutral. I have found through the first winter that it can get the basement a bit cool, but, it is an oft unused space. I have for periods of time in the winter when we needed to be in the basement for longer periods just switched the water heater to fully electric mode to eliminate the additional space cooling. Worst case, I have 3 months where I do not get the benefit of heat pump water heater and run straight electric.

Heat pump water heaters are good for drying out basements, but they come with significant sensible cooling where there's no (or low) sensible cooling load. This is a net heating load during the heating season, and depending on the efficiency of the heating system it could also come at net annual cost increase in energy use- it really just depends. In climate zone 4 NJ it might be a wash.

In a cooling dominated climate (particularly in the humid SE) heat pump water heaters are almost a no brainer.

A heat pump water heater is difficult to justify with efficient natural gas already in place. I think I would only be using it during the summer.

Off topic: Does anyone have an opinion on this technology: http://www.lbl.gov/tt/techs/lbnl2800.html

It mentions the efficiency of reheating the air - which doesn't apply in the case of a dehumidifier (where the hot and cool air are both retained).

An indoor heat pump water heater would ideally be used only during warmer weather. But I'm not sure people are ready for different water heaters for different seasons.

Posted By Dana1 on 06 Aug 2013 04:17 PM
Heat pump water heaters are good for drying out basements, but they come with significant sensible cooling where there's no (or low) sensible cooling load. This is a net heating load during the heating season, and depending on the efficiency of the heating system it could also come at net annual cost increase in energy use- it really just depends. In climate zone 4 NJ it might be a wash.

In a cooling dominated climate (particularly in the humid SE) heat pump water heaters are almost a no brainer.

I have done the math and determined that even with the added heating load in winter, using my goethermal to heat the space with its associated COP and then moving the space heat into the heat pump water heater with its associated COP, I still net out at a COP greater than 1.0. That being said, natural gas may garner better efficiency numbers. One number that would certainly need to be added to any efficiency calc is any additional electrical load if a dehumidifier is required.

Dana, do you have any opinions on this?: http://www.lbl.gov/tt/techs/lbnl2800.html or the smart fans I think are dew point activated?

Posted By jw on 07 Aug 2013 10:31 AM
Dana, do you have any opinions on this?: http://www.lbl.gov/tt/techs/lbnl2800.html or the smart fans I think are dew point activated?

Until there's a commercial product based on the compression ratio dehumidification it's hard to say how applicable it will be.  There have been many approaches taken to the problem (including decorative liquid dessicant waterfalls with solar heated recharge) that have never made it to market.

A dew point operated fan would be of interest, but I've not seen that sort of control outside of very custom situations.  Dehumidistat fan controls based on the relative humidity sensing are pretty common, now that there are cheap & reliable low drift capacitive RH sensors out there.  It doesn't take a supercomputer to map the psychrometric chart at a useful resolution, and there are plenty of dew point sensors out there used in larger scale commercial HVAC apps.  It's certainly possible to make a integrated dew-point fan control using existing technology, but I've not seen any do you know of an off the shelf product?

A quick search turned up this: http://www.smartvent.net/crawlspacevent.htm The website screams sketchy but who knows about the product.

I am guessing the benefit of something like this would be minimal in the northeast?

The net benefit would even be NEGATIVE in the NE for a ventilated crawlspace.

There are much higher efficiency blowers for moving the air around inside the house.