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Big honking supplemental dehumidifiers

My buddy Blake Reid just posted this. Well worth a read. It's short.

terrawatthome.com/news/2017/03/13/you-need-bigly-dehumidifier-pt-1

For those of us in green grass climates, I'm becoming a bigger and bigger fan of these things. We recommend them for EVERY project. That doesn't mean they get installed. I particularly like ventilating dehumidifiers because they bring in outside air and pressurize a house a touch, which can tend to push contaminants outdoors. They also tackle dehumidification when there isn't cooling load, which is about 6 months/year here in Cleveland. They can allow much higher AC set points, pushing 80 degrees.

Blake has an XT155 in his basement. I just bought one too, I'll install it in the next few weeks. Four of my clients have them. Supplemental dehumidification was a subject at Summer Camp. (Ken Gehring of Thermastor spoke there this year, and was kind enough to donate a little dehu for the Habitat project we helped with.)

I'm coming out hard for these things. If you aren't recommending them for projects and moisture is an issue in your climate, you might consider it. That way, if there is a moisture problem later and the client doesn't do it, you're covered. Thoughts?

Comments

  • Nate AdamsNate Adams Posts: 569
    Also, while I will fight almost to the death to downsize HVAC systems, I see little downside to oversizing dehus. (They do add a substantial amount of sensible load, but there are split models that eject the heat.) In the case of the UltraAire line, once you step up to the XT line, the 105 and 155 models come in the same cabinet and only have a few hundred dollar price difference. Hence the big honking one Blake and I bought.

    Props to Blake, he's had it for a few years and does the same thing I plan to do: he uses window units for AC.
  • nperneynperney Posts: 7
    What the trade off in the load calc for not increasing the latent load via lower moisture in the in coming ventilation air stream. I never get to play with humid air, so I'm not sure. You might want to look at pushing that oversize factor of AC's down to just over 90% get some long run cycles with some sweet drying. It might feel a little warm on really hot days, but dry.
  • touchd77touchd77 Posts: 1
    Have you guys calculated the electric use to run these units? Are they energy efficient units?
  • These units are about 4 times more efficient than the little plug in ones from Wal-mart. did you know that even the Energy Star units have the same compressor efficiency? They only improve the fan efficiency. Small potatoes.
    They are great products, and are an excellent choice for many existing homes.
    I have been pretty happy with the Carrier Infinity/Bryant Evolution series of heat pumps and air conditioners; which can run very low to dehumidify without much cooling; at similar efficiencies to the Sante Fe and Ultra-Aire models.
  • Nate AdamsNate Adams Posts: 569
    Yep, Jake, I love the Carrier Infinity equipment too. The trouble is obviously when there is latent load, but no sensible, which is about 8-10 months/year here. For my northern climate, I actually like that they add a little sensible to the house. Just enough heat for those 55 degree days without firing the furnace or heat pump. =)

    I didn't know the Energy Star was just fan efficiency, great info!

    @touchd77 I don't need calculations, I measured. The 70H model uses 600 watts with fan. The XT155 uses just over 800 watts. The XT series seems to be worth spending the money on since dehus use so much energy. Since the XT155 is only a couple hundred more than the XT105, I lean towards getting the big one, which is what several of my clients and myself have done.
  • BryankingBryanking Posts: 1
    Working with crawlspace encapsulation, and firsthand witnessing the mold issues that can develop without insulation, we ALWAYS recommend a dehumidifier for crawlspaces or attics. The Sante Fe dehumidifiers are nicely compact and are offered in a number of different styles and sizes. Very informative post!
  • David ButlerDavid Butler Posts: 3,889

    We recommend them for EVERY project.

    I always push clients toward source control, if at all possible, to avoid the not insignificant energy costs associated with running a dehumidifier. By source control, I'm referring to tight envelop, ERV ventilation in humid climates, appropriate use of spot ventilation, blacklisting commercial range hoods, proper roof drainage, site design, etc.

    In closed crawlspaces, especially in new construction, despite what the code requires, you can avoid DH via source control. If you make the crawl virtually air tight so as to minimize the amount of water vapor that can enter. Ditto with encapsulated attics.

    In new construction, I consider dehumidification equipment to be an expensive band-aid -- expensive up front and even more expensive to operate over the life of the building.

    All of that being said, in retrofit situations, good source control is often cost prohibitive compared to supplemental DH. So I don't have a problem specifying DH systems in such cases, although retrofit rarely comes up in my work.
  • Danny GoughDanny Gough Posts: 185
    In re the Carrier Infinity system, did you know the heat pumps can be configured to do dedicated dehumidification with reheat? I can hear the objections now. Reheat is too expensive. But I'm not sure about that. The 9 kw auxiliary heater has 3 stages. So, depending on the size AC, reheat might only require 3 kw. Moreover, as Nate pointed out, the excess heat from a dehumidifier is substantial. And it has to be removed. So the cost to use an XT includes more than just what the 600-800 kwh the compressor and fan use.

    Years ago, I asked Don Gately how to compare energy use of a reheat set up using hot gas or electric and Ken's Thermastor units. Don sent me an entire Excel spreadsheet, which i could never figure out. So the answer is still up in the air.
  • Nate AdamsNate Adams Posts: 569
    edited July 12

    In re the Carrier Infinity system, did you know the heat pumps can be configured to do dedicated dehumidification with reheat?

    That is fascinating, Danny! I didn't know that, and I use those all the time. Have you set it up? I know the menus pretty well but haven't seen that one. I still lean towards a dehu, but when it isn't in the budget, that's not a bad option.

    As far as energy cost goes, my clients rarely care if something costs $50-100/year extra, as long as it delivers comfort. So I'd be ok with a little reheat. I can probably change a few light bulbs to buy that $50-100 back.

    Looking at it a slightly different way, the XT155 is nearly $4K installed, $4K buys a LOT of electricity. I don't feel that bad about using electricity, since we can produce it renewably. I fight like hell to get rid of the gas meter so there are no more fossil fuels involved.
  • Danny GoughDanny Gough Posts: 185
    edited July 12
    It is set up through installer options at the thermostat. You hold down the service hat until it turns green, then move through the setup options till it asks about reheat. Or you can do it through the HVAC Partners Admin portal.
  • David ButlerDavid Butler Posts: 3,889
    @Danny, why use electric reheat? If you're going to run the compressor to remove moisture, you might as well use hot gas for reheat. I don't see why you would need a spreadsheet to figure out that hot gas reheat is more efficient than electric strips! (hint: hot gas is going happen anyway!)

    As I'm sure you know, Lennox sells the Humiditrol reheat module that does exactly that. Hot gas reheat is how stand-alone dehumidifiers work, except stand-alone units are generally less efficient than even a min efficiency unitary split, and since stand alone units don't have an external condenser, they necessarily throw off a not insignificant amount of heat, as you noted, thus leading to higher cooling loads during warm weather. Not so with Humiditrol since the amount of reheat transferred to the airstream is controlled, the rest is sent outside, as would be the case in cooling mode. IIRC, dealer cost is in the high 3 figures, so very competitive with ducted stand-alone DH systems.

    @Nate, not sure what Humiditrol buys you in your situation since most contractors would probably be hesitant to install it on any system other than Lennox. I threw that out only to make a point to Danny re: his theoretical question about hot gas vs electric reheat. But when compared to installed cost of $4k for an XT, using strip heat for a limited amount of dehumidification seems like a no-brainer. I've done that on several projects, although some of those had gas-fired hydronic supplemental heat.
  • Nate AdamsNate Adams Posts: 569
    @"Danny Gough" , Wait there is an installer portal where you can change settings remotely? I am not the installer, I wonder if they would let me in or not.

    I know about the green hat thing, it AMAZES me how many menus and options there are in there. I just found out that low fan on the system I visited today uses 55 watts at .17" static while high uses 303 watts at .39 static.

    I wonder how many other manufacturers give you that info. 55 watts or about $7/mo to have continuous filtration. PM2.5 in that house is at the bottom that Foobots will detect. There's some pretty cool stuff out there...
  • Danny GoughDanny Gough Posts: 185
    edited July 12
    HGR depends on control. With geothermal units, they still tend to add heat. I think its excess compressor heat. My primary question was comparing the XT's with dehumidification via low speed fan and on board auxiliary heat. The XT's also have a heat exchanger that pre-cools the incoming air. Very efficient as dehumidifiers go.
  • David ButlerDavid Butler Posts: 3,889
    edited July 12
    Yes, added heat for a DH is the result of compressor heat. Unless you have an outdoor condenser, there's no way around that. But you're right, avoiding excess heat when you have an external condenser is a matter of control design, In my (not so humble) opinion, there's no excuse not to do that right, since it's very simple for the control designer to look at return and supply air temp!

    I don't think an XT can compare in efficiency to Humiditrol (or similar built-up system), even ignoring the huge difference in first cost. Stand-alone has too many handicaps to compete with integrated HGR. But if the DH load is low enough, I imagine there are situations where using existing supplemental heat for reheat may have a lower lifecycle cost, since there's essentially no additional first cost. In a situation like Nate's, I would definitely want to separately monitor reheat kWh (separately from AUX heat calls -- a bit tricky, but doable) in order to assess whether a ~$1,5k Humiditrol type solution might be warranted.
  • Danny GoughDanny Gough Posts: 185
    edited July 12
    Unfortunately, Humiditrol cannot be zoned. Or at least that used to be the case. It may have changed.
  • David ButlerDavid Butler Posts: 3,889
    Probably not. You could always advise your clients to move to Arizona (or send us their excess water vapor)
  • Nate AdamsNate Adams Posts: 569
    I have one client that has some humidity issues and we did an ERV instead of a dehumidifier. I'll try changing his settings. The thermostat tracks reheat, so I can see how much electricity it uses. Thanks for the tip, Danny!

    And David, we are on the same page that for retrofits source control can be prohibitive, particularly if it is the basement floor. My work is almost entirely retrofit.

    Danny, why is zoning important for dehumidification? I see differences in humidity, but they're typically not huge. I'm betting you have an example and am curious what that is.
  • Danny GoughDanny Gough Posts: 185
    edited July 13

    .....why is zoning important for dehumidification? I see differences in humidity, but they're typically not huge. I'm betting you have an example and am curious what that is.

    I was just saying the Humiditrol as an HVAC system choice is limited because it cannot be used for zoning. Here in NC, we are required to zone levels of a house as in basement-main level or main level-2nd level. If the load doesn't warrant a 2nd system and the logistics are favorable, we will opt for zoning the system. The Lennox Humiditrol cannot be zoned, at least the last time I investigated it. It has nothing to do with the humidity control. Just a limitation on the air side.

  • Nate AdamsNate Adams Posts: 569
    edited July 13
    Got it. That's wild that zoning is required in NC! We find with damper adjustments we can eliminate the need in most cases. Requiring multiple systems sounds onerous, expensive, and also likely to lead to poor humidity control from oversized equipment. We did a 4800 sf new house last year with a 3 ton heat pump on an 80K mod furnace. Two systems wouldn't have served that home well. (We did set it up to be capable of zoning, though.)
  • Danny GoughDanny Gough Posts: 185
    Its a strange place. Our state home builders association lobbied and were successful in removing the authority of code officials to ask for a Manual J load, which is by the way, still a code requirement.