@Harvey, great comment! Reminded me of the age-old problem of how often efficiency ratings are misused to extrapolate annual consumption for ROI or lifecycle cost analyses (mostly an issue with compression based products). Remember those “cooling hour” contour maps? Combine that with A/C capacity and SEER rating, and voila! Instant annual A/C energy consumption! HSPF (for heat pumps) is even worse due to very-difficult-to-model supplemental heat factor.

For the most part, federal efficiency ratings are useful for their intended purpose: product comparisons. But there’s far too much variation in operating conditions for a given home to use these ratings as the basis for energy modeling.

@Ty Newell wrote:
> Dehumidification efficiency and capacity both increase significantly (2 to 3 times) as humidity increases…. (these) efficiency and capacity performance increases can be achieved by dehumidifying outdoor air before it mixes with indoor air.

Great point. Whenever possible through design, you always want to maximize your deltas. Dedicated outside air systems (DOAS) in commercial buildings follow this approach. For the same reason, thermal storage is used strategically in heating (and cooling) hydronics to maximize the delta-T and thus increase both capacity and efficiency of the source equipment.

@Curt wrote:
> do the math to be sure that much capacity is really needed

How does one do that? Latent loads related to occupancy can be roughly estimated based on ASHRAE guidelines but it seems that latent loads from infiltration are too highly variable and depend more on partial vapor pressure differentials than the infiltration rate itself. And I’ve never even attempted to estimate latent loads from ground moisture, concrete curing, ineffective spot exhaust, etc…

Trial-and-error seems to be the only way to go at this, but if you’ve developed even a rough estimation method through your considerable experience with dehumidifiers, I’m all ears.

I have one in a 800 SF basement room in Massachusetts, another in a small barn in north Florida, and I’m planning another for a garden shed.

It is tempting to oversize dehumidifiers, but don’t succumb – before buying unis in the 40-70+ pint range, do the math to be sure that much capacity is really needed.

Looking forward to your book.
Good luck writing!

I would guess that the fan speed would be dependent on the size of the room. Say you wanted to move the dehumidifier around. So you get a dehumidifier that can cover the biggest area. And in that space, you have the fan on “high.” But you take the same dehumidifier and put it in a smaller room, and you might prevent (?) short-cycling by turning the fan down to medium or low, in order to get more run time with less interruptions, so that it can operate more efficiently. I don’t know. Not an expert.

I’m no expert, and I’m sure one of the helpful brainiacs here will correct me if I’m wrong. But I set mine on low for two reasons. First, it is quieter. Second, and more importantly, I believe it is more efficient for my specific circumstances. My room dehumidifier is placed in front of my home’s central return closet. This means that the air handler pulls air around the dehumidifier whenever the air handler is running, allowing fresh air to enter the dehumidifier. The fan on low expels the newly dehumidified air and mixes it into the room (and into the central return closet). The low fan speed is more efficient because it allows for more condensation to occur on the coils and drip into the bucket rather than being evaporated by higher air speed moving across the coils.

The disadvantage of using the low speed is that it results in less mixing of the dehumidified air. In my situation this is not a concern because the air handler is doing the mixing for me. If you need the expelled air to be mixed with the room air well, then it might be more efficient to run the fan on high.