The Ultimate Dehumidifier
 

Hey guys so in my area of the world we have this terrible things called humidity. It was what keeps us from using swamp coolers and cooling towers and really all the cheap ways of cooling your home. Thus the huge need for AC. WELL if you are brave (or stupid) enough to set your thermostat higher in order to "sweat it out" your in for quite the fight. Why, well because of the moisture in the air. Heat + moisture = death. So we (maybe just I???) run a dehumidifier to keep the moisture lower but as you may know these handy power hogs also produce heat. Even though it is still cheaper to run the dehumidifier more and AC less, it still really sucks to be heating up the air. This is where multistage compressors are REALLY nice but seeing as I don't have one of those and my AC uses a whooping 4,000 watts of power. SO here is why I am asking input on a design of a homemade heat pump dehumidifier.

Main goal: The create a dehumidifier that will use less or equal to the same power the current one uses (4.5A 120V) WHILE cooling the air instead of heating it WHILE still sucking out just as much if not more moisture from the air.

Budget: Low as normal

Bonuses: It would be awesome if it could heat in the summer time.

Design: So basically I'm building a mini split that is designed more around condensing than moving massive BTUs.
Thoughts: Maybe I could have an undersized condenser that freezes up and then a powerful fan kicks on and melt the ice, then turns off again to form more ice? Turning the compressor on and off a lot seems like a bad idea.

Condenser: Jeff said straight fin might be the best for dehumidification. Thoughts?

Refrigerate: I'm thinking R290 or R152A, but open to suggestions.

Evap: I can go either air or do another DX borehole, this time maybe do 2 boreholes?

I have a 6,500 btu rotary compressor, txv, and several air evaps ready to go.

I will get picture up as soon as the build starts.
Thanks guys, I look forward to sharing tons of data and pictures!

You do not want to form ice, requires heat of fusion to be withdrawn from evaporator.

For best efficiency, you only want the evap coils to be just below (about 3C) the dew point. Use a RelHumidity sensor from scrap dehumidifier.


re: Evap: I can go either air or do another DX borehole, this time maybe do 2 boreholes?
In dehumidifier usage, any borehole would be the CONDENSOR.
Evaporator is where you boil the refrigerant, which pulls heat from the air to boil the refrigerant and cools the coils to condense air moisture.

You have your heat exchangers mixed up. The evaporator is the cold one in the suction side, the condenser is the hot one on the discharge side, of the refrigerant loop.

What you have been doing with your DX water heater setup seems ideal for your purpose: big coil indoors with low airflow to grab lots of water vapor, condenser heating not indoor air, compressor located outdoors. With these smaller setups, the compressor is usually the weak link in the heat transfer equation. Due to the limited (nearly constant) displacement, it can only move so much gas.

With your half ton compressor, you can move around 6.3 megajoules of heat per hour. This translates to about 3 pints of condensed water per hour in a perfect process. i would shoot for a liter per hour tops. This is what you can hope for.

Mejunkhound, gotcha, I can fine tune the charge to set the EVAP to right at the dew point.
Thanks you and Jeff are totally right I did get the evap and condenser mixed up. I knew there was a good reason I was getting advise.

Jeff, OK so large Evap, should I go straight fins? And borehole for the CONDENSER.
So I should look for a 5,000 btu compressor instead.
Also I am thinking that I should be looking for a refrigerant with a dew point at as low a pressure as I can find. Less pressure should equal less power consumption. That is unless I want it the be able to heat as well.

I really wish I used more hot water and the heat pump water heater could do all the moisture removal. Then I would have yet another unit running. Or I guess I could put in more valves and route the borehole into the evap I already have. A dual purpose system.......

Also what if a slowed the fan down on my existing 4 ton central unit air handler? Would that cool slower therefore remove more moisture? The unit comes on like 40 times a day and only runs for 5 minutes or so. I have worked so hard on the house now my unit seems over sized. Lol

The two ton coil you rigged in to the hpwh is plenty large enough...but for a water grabber. You seem to have indicated it was doing a good job in that regard without overcooling the house. The thing you want to deal with is the high pressure side.

I still like the idea of the desiccant waterfall. A number of members have been interested in them but I haven't seen the results of anything yet from individuals. The basic idea is this: you pump a working fluid (salt water) between a water grabber indoors and a warmed evaporation unit outside. At lower temperature, the salt naturally wants to be a weak solution, at warmer temperature it naturally wants to be a stronger solution. I did a proof of concept experimental rig using calcium chloride ice melting salt, and found it works pretty darned well. I commented about it in another thread here. That method would use a whole lot less energy than a refrigeration cycle would to get the water vapor outdoors.

This liquid desiccant idea could work in tandem with your hpwh / dehumidifying rig you have going now. If the interior RH is too high and your water is hot enough, you could use the waste heat generated to heat your outdoor water shedder. This is known as "double effect" as you are reusing a waste product in the process to further the process. It is a proven way to gain another 30% or more efficiency from your system. Used all the time in industrial processes with waste heat products.

EDIT: Found the thread. Be my guest.
http://ecorenovator.org/forum/solar-...umidifier.html
The interesting begins about page 3 or 4. Leads to a discussion on the Coolerado and DEVAP units. Read that one too.

Jeff, yes the 2 ton coil is a great water grabber, but it doesn't like to let it go. For the 3 hours that that unit runs it does not produce much water out of the drain. It all gets caught in the spine fins and just evaporates back into the air. So that is why I was thinking of using the straight fin coils or make my own like I did with the food dehydrator with not fins only super sized set of copper tubes running vertical so that the water quickly falls off the coils and into the drain.
I also like the idea of it adding COLD air into the house. Yes the salt system has grabbed my attention several times in the past, but it will also add heat to the house and seems to be a lot of work + a lot to maintain. I will visit the idea again but for the time being I would like to finish running this phase changing system idea.

i hear you. Just throwing around ideas like usual. If you want to build another evap coil, save the bristle coil for further experiments. I would shut off the fan to see what if first though... As oversized as it is, you may not be able to freeze the thing completely before the water heater gets hot... The world may never know...

Otoh, a junk 2 ton a-coil wouldn't be hard to find, and would behave better for your purposes.

How leaky is your home? Just like with heating and air conditioning the cheapest way to reduce humidity levels is to prevent the humidity from entering in the first place. If your home is really leaky then the vapor pressure difference is going to drive moisture and air into your house. This is not really good for your structure, or health.

And for the LOW cost option, do what pappy did in the 1940's and 50's.

Take a couple pair of old nylons (old pantyhose would work great now), fill them with calcium chloride, and hang over a bucket or floor drain
- gallon or so per day per 2 foot of sock leg per day in central IL summers in the basement.

Mejunkhound, did you see this with your own eyes? That's a lot of water! And require no power. Can you give me more info?

The catch is that the calcium chloride gets "consumed", meaning you'll either have to keep replacing it or regenerating it by putting the container in sunlight on a hot day.

Gotcha, I guess I was thinking that somehow only the water went down the drain. But the salt is absorbing the moisture and becoming a solution and flowing out.

OK so I really don't mind the whole manual labor of taking the container out and letting the sun bake it. My question is how many lbs of salt would I need in order to suck about 5 gallons a day of water out of the air? I could do about 5 containers that way they were more spread out over the house. I could build 10 containers And just swap rack one out for a new one everyday.
Or build a waterfall closed loop system. Hhhhmmmm.....

EDIT: I found this on a web site for a 4lb tub. "DampRid's natural crystals effectively control musty odors caused by excess moisture for up to 60 days in areas up to 1000-square feet, and up to 6 months in a 250-square foot area, depending on temperature and conditions." So 4 lbs will do 1,000 square feet. I have 2,300 square feet so I should need 12 lbs just to be safe. Right? I don't see whats so hard in swapping this stuff out for a regenerated one? Seems too good to be true.

Go buy some at your favorite local big box store. This amazingly common product is called damprid. Super deliquescent anhydrous calcium chloride plus essence of smell. Pop the top and it starts grabbing water. Works well down to about 30 percent rh... By the pound, ice melter is cheaper. I believe someone broke this down before ad to the yield vs water-grabbing power.

Oops, it helps to update my browser before commenting...

Main idea is the solid salt dehydrates the air faster than a solution. A strong solution works faster than a weak one. More relative humidity is easier to remove than less.

I am interested in the waterfall idea, but I have a solar cooker, I'm thinking that if I put as much as I can in a super large black pot, let it soak up moisture and then throw it on the cooker, it will dry it out good for me.

SO many thoughts, I really want to get the humidity down to 40%ish and right now without the big ac coming on the lower my current dehumidifier will get it 47-50%.

I waterfall loop would be awesome, but I don't want to spend the time and money on a high maintenance system, and without some more examples of really well working systems it is hard to pull the trigger. IF I did build one, I'm thinking something that I can put in my window that way when winter comes I don't have to worry with freezing.

The calcium chloride solution is good down to like -40 degC before it freezes. Check out this chart:
http://www.phasediagram.dk/binary/CaCl2.PNG

In one of the previously cited threads, another similar chart was posted that showed the properties of the two forms of the intermediate-temperature crystals that form upon cooling. As long as there is some solid salt in the solution, it is saturated, and will closely follow the chart. On highways and roads, it is a better de-icer than rock salt.

Ok so I am far from an expert in HVAC and dehumidification so take what I say with a grain of salt (pun intended).

Your initial idea of running a GSHP with the goal of reducing the latent heat load on your A/C unit is basically a good one. You get a rise in Coefficient Of Performance (COP) by lowering the temperature of where you are pumping heat to. This is the same effect but in reverse as you saw with switching the heat source (where you are pumping heat from) of your heat pump water heater. You were also planning on increasing system efficiency by keeping the heat out of the house (by placing the compressor and condenser outside). This is also a very good idea as a stand alone dehumidifier is basically a 110% efficient (or higher) electric heater.

Now let us take a look at what happens with your system design if it is working in such a way that it removes all the water it possibly can from the air that enters it for a given evaporator temperature, let's say that temperature is 33°F. So what happens? The air enters the system at say 75°F and 60% Relative Humidity (RH). When it leaves the system it will be 33°F and 100% RH. This is because RH is relative, the percentage is the percentage of the amount of water the air can hold at that temperature.

This is not a very efficient way to operate a dehumidifier. Why? Because we are removing sensible heat also, not just latent heat. We we want to use a dehumidifier to dehumidify the air, not to cool it. We want to remove latent heat only... So how can we reduce the amount of sensible heat that is lost to the dehumidifier? Well if we remember that heat flows from high to low we see there is a temperature difference between the air flows. Ideally we want the temp of the air coming out of the dehumidifier at 75°F, not 33°F. Since the air entering is at 75°F already we can use that energy to warm up the air leaving right? There are multiple ways to do this, air-air heat exchanger, heat pump, heat pipes, etc...

An interesting thing happens when we do that. The Relative Humidity of the air going to the evaporator rises with the temperature drop. Ideally the temperature would drop to 33°F raising the RH to 100% before it gets to the evaporator now the heat pump in the dehumidifier is only moving Latent heat. Now this is impossible to achieve, but the closer we can get the air going into the evaporator to 100% humidity the more efficient it becomes at removing water from the air.

Now let us look at this from another angle. The refrigerant in the system has to be compressed in order to raise its temperature, it needs to be compressed enough that its temperature becomes higher than where the condenser is. The more we have to compress it to reach that temperature the more work the compressor has to do, thus using more energy. What we really want is the temperature difference between the evaporator and the condenser to be as low as possible. We can't affect the temperature of where we are pumping heat to and thus we can't control the ideal condenser temperature. We can control the temperature of the evaporator however, this is because we know that a dehumidifier is more efficient the closer to 100% RH the air entering the evaporator is. If we can raise the RH to 100% (no matter what the temperature is) then the evaporator can be at any temp.

So with our system instead of moving heat from the air going into the evaporator to the air coming out of the evaporator, what we really want to do is move moisture from the air coming out of the evaporator to air coming into the evaporator. Fortunately there are ways to do this, an energy recovery air to air exchanger is one way this is basically a material that can absorb water yet block air. Alternatively we can move a desiccant (a material that uses sorption to collect water from a substance, in this case air) between the air flows. When a desiccant becomes saturated it will give off a portion of its water to an air flow if the RH of that air flow is less than 100%. The common ways to do this are with a desiccant water fall or a desiccant wheel. Realistically the air going into the evaporator from the desiccant can never be at 100% RH, just like we can never move all the heat from in incoming air stream to the out going air stream.

Why not just use a desiccant and forget using any refrigeration equipment in the dehumidifying process? I mean we can move it outside and heat it up right? The issues with that are #1 controlling the dehumidification, and #2 we will need to dehumidify when there isn't solar energy to dry the desiccant.

Theoretically though you could use a large storage tank to hold a liquid desiccant and then do an indoor waterfall and an outdoor one in a solar oven. Given enough capacity of the tank you should be able to have a big enough buffer to cover the no solar times. The other issue is you would end up pumping heat into the house that way, likely more heat than you'd have with just using a dehumidifier.

An interesting side note here:

Joe Lstriburek once used cellulose insulation as a desiccant. If my memory serves this was in Florida and he pumped air through the attic insulation (blown in cellulose) during the night, then during the day the heat from the attic dried out the cellulose. He air sealed the attic, then used a vapor open membrane at the ridge to vent the moisture out of the attic. He still needed mechanical dehumidification, and he (understandably) wasn't comfortable blowing air through the cellulose.

BSI-088: Venting Vapor | Building Science Corporation

Jeff, yeah I saw the chart, I just don't trust liquids not freezing. Lol I'm not throwing any idea out the door yet. This dissucussion is awesome, and I'm trying to weigh all my options while sourcing parts for each build.

DEnd, nice write up, thanks for taking the time. I guess my thoughts are that I need both cold air and moisture removal and even though the dehumidifier is not removing as much water it is adding to my AC load by cause the 20+F heat gain. I probably could build a better designed dehumidifier with both the evap and condenser inside, I will add that to the list of things to look into. Right now my unit runs for about 10 hours and sucks about 2 gallons of water out keeping the house at 80-82F and 47-50% RH.

I do really like this salt idea, it is just way to cool to not put some serious time into testing. I have 50lbs coming in tomorrow and I'm going to source my large black pot today. (Yard sales).

I am going to build a small scale system just as soon as I source the parts. I can simply run it and the dehumidifier and see how much extra the salt absorbs.

All I really need is about 3 gallons of moisture removed without heating the house as much. I'm even giving thought to what jeff was saying about me using some of the HPWH water to recharge the salt. As cheap as my hot water is it would be a great idea, I'm just not sure how to build such a beast YET.

Thanks again, very very helpful post!

Since you are trying the desiccant idea, and regenerating it with solar energy what you really need is a way to cool it down after it is regenerated, that way you aren't increasing the heat load on your A/C. Since you don't want it adsorbing moisture the after it is regenerated it needs to be sealed from the air. My thought is find a high temp stable plastic bag, or maybe a metal pan with an air tight lid, then keep it outside at night. In essence you would have a three step system. The desiccant adsorbs moisture from the air inside, then you would move it to the solar oven which heats air (decreasing the RH) that is then moved over the desiccant to recharge it, then the desiccant is moved to an airtight container with a large surface area to cool down during the night, after it is cooled it is moved again to inside the house to start the process over.

60 or so years ago, but yes, saw with my own eyes.

Pop had the nylons hung over a coal bucket in the coal bin (still heated with gravity coal furnace in those days, $3/ton for lump coal, we hauled from the mine.

The chloride continually dripped water into the bucket, never needed to replace the chloride, just empty the bucket.

After pop finished the basement, got an electric dehumidifier as I slightly recall there was some residual odor from the chloride method. The water is also slightly corrosive and not friendly to cast iron plumbing.

DEnd, good ideas, yes I was thinking of having a pot just sit on the solar cooker with a one way valve letting air/water vapor out, and let it sit through the night cooling it down to use the next day. I don't run any dehumidifiers at night, so night time running isn't needed.
I will start experimenting as soon as the salt arrives tomorrow.

Though I am still planning on the heat pump build as well. Just to see which is the easiest/cheapest/best.
I only used 17 kwh of power yesterday. Finally getting into a good green range, though I did have to paint the roof white...... :eek: :D

more soon,
Shalom

Regeneration of the strong solution by using waste heat sounds like a great idea. Whatever you do, use something nonmetallic for a heat exchanger. The calcium chloride solution corrodes metal for breakfast.

Well it's not really waste heat, but it is very cheap heat, Lol so PVC to PVC exchanger?

The rig (a solar still) I built looked like this design:
https://ecorenovator.org/forum/attac...1&d=1591543008
EDIT: different picture with more elaborate feed path. Mine fed directly inside the unit. Drain was the submersible fountain pump.

If you heated the drain water from the indoor water collector, it would only help. At night, the glass would fog up even more and might offset no solar gain.

I think there are some things missing from your last post Jeff.

I was just thinking that the bottom of my borehole is 59F right now. What if I drilled another well even lower and just ran a air-water exchanger? I should be able to make condensate down to about 40% RH with 60F water right? I could do a closed loop system with a very slow flow pump. Insulate the crap out of the pipes and make water!
Just another crazy idea.
https://en.wikipedia.org/wiki/Dew_point

As long as the indoor water-grabbing part doesn't contain a whole lot of fluid mass or a high flow rate, heat gain shouldn't be a problem. My indoor collector had maybe an 8 by 12 inch footprint, and was a rock stairstep waterfall. The pump fed a few gallons per hour of strong solution into the top, and the solution descended the stairwell and drained through a toilet-style overflow tube. The thing worked a lot better than I thought it would.

If you really want to cool the strong solution on its way inside, I would definitely do it somehow so the pipe doesnt clog up with salt crystals. It wouldn't be impossible for the saturated liquid to try to change phase in the heat exchange zone. It would suck to have a borehole clog up with no easy way to unclog it.

What's you indoor air temp?

at 75°F (at sea level) to pull water out of the air at 45%RH you need to get the heat exchanger down to about 51°F. Which means you need the borehole water to be below that. Because to affect just a RH change if the water coming out of the heat exchanger is above that then we are not removing as much water as we could. If we can get the RH in the dehumidifier up to 70% at 75°F then we can use 60°F borehole water, with a temperature rise to 65°F (at least at sea level).

My indoor air temp is 80F, and humidity tops at 57%. 1-2 gallons of water will drop that to 47ish%.

I think I have decided to build what I KNOW how to do and ponder of salt magic fountains at a later date.

SO new parts and fun stuff have arrived. I got a outside mini split condenser (unknown size, will know tomorrow). And a nice 70 pint dehumidifier. Both free.
My idea/s. Outside condenser with a 12v fan from the greenhouse. Maybe adding another coil (or 2) if it will fit. I want HIGH efficiency, with LOW fan speed if possible. Even if a have 3-4 tons of coils in the condenser... the more the better right?
The compressor will be from a window unit (r22 6,000 btu) and mounted outside in the mini split condenser.
The dehumidifier will be inside where I will tie both coils together in series, and add as much coil as will fit.
CONCERNS!!! I had NO idea the coils on dehumidifiers where SO small...... I don't want this things freezing up on me. I can wire in some controls so at a certain temp the indoor fan kicks into high gear but I'm still not sure if that will keep it from frosting up.

Ideas? Are there other more WAY over the top complicated designs that I can waste DAYS deciding that are WAY to much trouble or have I gone over board enough on this one?

Again the main goal is DE HUMIDIFICATION, cooling is just a plus.

Thanks guys. I'm ready to build so pics coming soon!

I am adding couple of loops, fins and a trip tray to my cold water lines where they enter the house. Fan blowing across the fins will condense, drip into tray and run into the sewer lines.

simenad, what temp is your water entering your house?

UPDATE!!!
So I decided the dehumidifier coils were to small. http://ecorenovator.org/forum/attach...1&d=1469131461
AND my guy with the free mini split backed out, so I remembered replacing my grandparents 3 ton r22 split system and decided to use that instead. Yep, 3 tons for a 5,000 btu compressor. :thumbup:

So I hacked the old compressor and parts out and added my tiny compressor.
http://ecorenovator.org/forum/attach...1&d=1469131558
http://ecorenovator.org/forum/attach...1&d=1469131558

Next was the indoor coils, I cut a hole in some scarp plastic and mounted my 12V fan. Then added the TXV.
http://ecorenovator.org/forum/attach...1&d=1469131558

I got all the electric side done, I simply just wire in all together. No switched, no sensors, just go go go. Its like a mosquito trying to suck the blood out of an elephant, IT JUST AIN'T GONNA HAPPEN. So I will have it on a timer to run when I think it best.
http://ecorenovator.org/forum/attach...1&d=1469131558

I added a 5 watt 120V fan to the outside coils and again used scarp plastic to fill in the gaps.
http://ecorenovator.org/forum/attach...1&d=1469131558

Here are the coils in the house. They are tuck away nicely. Kind of a steampunk style. I will build a wooden table to go over them one day.
http://ecorenovator.org/forum/attach...1&d=1469131558

And lastly I charged her up.
http://ecorenovator.org/forum/attach...1&d=1469131558

DATA: Charge (R290) was huge! Not sure how much but that is A LOT of copper tubing.
75 psi suction
225 psi discharge
10-13 superheat
3-6 subcooling
Its 104F outside
Pulling 3.3 amps total. This is including both fans.
Results, Drip, drip, drip, drip, SUCCESS!
Only real way to know is to see just how much water it can pull out of the air.
I might need a larger indoor fan, or figure out how to control the speed on this one. I got 3 wires. Red and Black make it go, and White I think is speed control. But I think I need a PWM thingi. Anyone know?

If it doesn't suck out enough moisture, I can always add a slightly larger compressor. But I not wasting this propane, I'll BBQ for a couple weeks as it slowly drains out. lol

Enjoy, as always please reply with ideas, concerns. Thanks guys!

ground temp, well water is about 50 degrees

Simenad, I only wish I could get water that cold. How deep is your well? 60F is the temp for me at 30 feet deep.

Thats outrageous! A 6x too big set of heat exchangers ought to max out your COP. Just remember that all the compressor cares about is pressure and compression ratio. With 100 degree outside temp, the pot will have to pump against this high pressure.

what brand/model is your fan? Is it electronic commutated or a brush drive motor?

Same fan, just without the LEDs https://www.amazon.com/Cooler-Master.../dp/B00FBMRT6K

75-80 feet.

those case fans are ecm. you can feed them less voltage to make them slow Down.

simenad, wow, really nice temps for that deep. If I had that I would total have a solar powered well pump going though a radiator or two and feeding back into another well.

Jeff, yes I was hoping to be able to speed it up, not slow it down. I did a lot of digging and came to the same conclusion. SO I stole a fan from the disappointing dehumidifier and wired it on low. Then I had to add more charge because my super heat went crazy.
New data
Suction 91 psi
Discharge 241 psi
Superheat 9-12
Subcooling 10-12
Amp draw 4.06 @ 117 volts.

This morning I had it run for 4.5 hours (with the old fan and charge) and it sucked out slightly over a gallon. But now I can FEEL the cold air, plus it is going drip.drip.drip.drip, instead of drip..drip...drip..drip, and sometimes it even goes dripdripdripdrip.drip. LOVE it. It is 95F outside, and i've only used 24.8 kwh today. AND today is wash day. :thumbup::thumbup::thumbup: Compared to 72 kwh a year ago!! And I haven't even put in the geothermal unit yet. :D

Love your drip.drip.drip.drip descriptions! Keep it up!

Steve