Winter Humidity

Intro

Well, I was wrong. Humidity became an issue, but during winter. Here’s what things looked like during a typical week in November of 2021. Relative humidity is in the high 60s to low 70s while the thermostat was mostly kept at 63F during the day and 55F at night. A brief web search indicates the upper bound for indoor RH is 50 or 60, but our pals at energy star state 40% is best for keeping condensation off the windows. And we had a lot of that. To the point we were getting mildew on the window frames.

Dehumidification options

Our HVAC system is a bit long in the tooth, so having an inline dehumidifier seemed expensive and might get replaced in the near future. Similarly, a HRV would be dandy since it would bring it bring it outside winter air, and disposing of the stale humid indoor air. If we keep a ducted system once this one gives up the ghost, I’ll be sure to ask for one but for now too expensive. That leaves us with standalone units. My wife didn’t want a loud machine running and I wasn’t particularly enthused about buying another potentially short-lived refrigerant-based device (looking at you crappy Samsung fridge). In a previous dwelling our windowless jack-and-jill bathroom had all sorts of condensation issues, which were mitigated by small thermoelectric dehumidifier with a humidistat. But it was noisy using a small computer fan to blow air across the heating and cooling fins, and didn’t seem to scale up to the 1200 square feet of the house. That kind of left me with one option: Rotary desiccant!

Rotary desiccant dehumidification to the rescue

source

It’s the neatest thing! While compressor dehumidifiers are more performant at warmer temps, as it gets colder the performance decreases and desiccant tech catches up. I wish they had this same chart with liters/kWh on the y-axis, but at my temperature range a dessicant dehumidifier is ~3x more performant (though I’m unsure of chart’s data quality, would love to find better research). The only moving parts in the desiccant dehumidifier are centrifugal fans and a rotating disc of desiccant material (more on that later), hence its fairly quiet. Another circumstantial boon is that it produces significant waste heat, which is doubly welcome in the winter thanks to solar power and a generous net metering agreement. So we’re dehumidifying and offsetting warmth which would otherwise be produced by our gas furnace. In the end I opted for this one, the Ivation 19 pint, aka IVADDH09.

IVADDH09 review

Straight to stats! measured @ 61F, 60% RH

I was surprised to see that efficiency remained the same between the two settings. Needless to say, low is much quieter so I’ve kept it at that setting. There have also been suggestions online that only running low will extend the lifetime of the device, since on high the desiccant is being blasted with a lot more heat and undergoes more extreme thermo-cycling. I also have it on the same breaker circuit as another space heater, but it hasn’t tripped yet on low. Emptying the bucket is easy, though there is an option for drainage hose. While the controls are simple enough, I’m still partial to analog controls since they seem more resilient to moisture and temperature swings. One quirk was that it would display Fn on the humidistat and just blow cold air for a while, then resume working. The manual mentioned nothing about such a reading, an online comment said its just indicating that its in fan mode cooling down the dessicant before idling.

Results

A better humidity profile, hovering around 50%. Anecdotally, there’s been less condensation on the windows. The thermostat taking the humidity measurements is quite far from the dehumidifier (a hallway and two rooms over). The dehumidifier lives by the central air conditioning’s return register, which is configured to recirculate air for at least 5 minutes per hour. This mighty machine, despite being rated for only 410 square feet is managing to tame the dampness. The dehumidifier humidistat was set to 45% RH, and during its runtime consumed about 3 kWh/day.

Final thoughts

Some confounding issues with the data is that we finally installed a vent in the master bath, decreasing the overall moisture load. The midnight spike of the dishwasher finishing it’s cycle often quite pronounced. When the dehumidifier starts after idling for a while, it has a distinct smell that I can only describe as kiln-y. Or like a clay roof-tile dying in the sun after a rain. It’s the Zeolite. I’m curious about whether the air is being purified as well by the dehumidifier. Oh California! The IVADDH09 falls afoul of CARB’s air cleaning standards, hence some retailers might not ship it here (but Home Depot didn’t seem to care). I believe the intent is to regulate ozone output, but no literature indicates that the desiccant would release ozone.