Dehumidifier seems to heat the garage

[600SL]

Hello, I have a question about dehumidifier quality. My garage is partitioned with 21 x 28.33 (~600sq=ft)area and a 16 x 28.33 (~450 sq-ft) areas. Both with 13' average ceilings. Both areas have dehumidifiers running at ~ 45% Rh. The larger room uses a ~ 10 year old Santa-Fe Advanced2 90 pint /day dehumidifier and everything works fine. The smaller room uses an ~15 year old Amana dehumidifier ~50 pints/day. It also works but it appears to heat up the room about 5°F higher than the larger room. So my question is. Is the significantly cheaper Amane heating up the room because its cheep or is it just possibly not working correctly. If I replace it with another $300 Amana am I going to get the same results. Or is a $1400 Santa-Fe really what I need.

 

[u3b3rg33k]

Hello, I have a question about dehumidifier quality. My garage is partitioned with 21 x 28.33 (~600sq=ft)area and a 16 x 28.33 (~450 sq-ft) areas. Both with 13' average ceilings. Both areas have dehumidifiers running at ~ 45% Rh. The larger room uses a ~ 10 year old Santa-Fe Advanced2 90 pint /day dehumidifier and everything works fine. The smaller room uses an ~15 year old Amana dehumidifier ~50 pints/day. It also works but it appears to heat up the room about 5°F higher than the larger room. So my question is. Is the significantly cheaper Amane heating up the room because its cheep or is it just possibly not working correctly. If I replace it with another $300 Amana am I going to get the same results. Or is a $1400 Santa-Fe really what I need.

you can check the label for the L/kWh. that'll tell you how much energy it'll consume (and heat it'll release) per liter pulled out of the air.

That does NOT include the latent heat released from the process! that's physics.

TLDR, running the machine consumes power (400W or so for a little unit) plus maybe another 1000W of heat from the latent heat side of the process.

 

[fitter30]

All dehumidifiers heat the air if they didn't they would be 100% efficient. Heat from compression, compressor motor and fan motor all is added.

 

[pcmeiners]

​

Agree with u3b3rg33k....

Perhaps you should consider a DIY install minisplit (s), an efficient unit(s) use little power, guessing as much as one of your humidifiers plus you get AC and heat. Install is easy if your mechanically inclined.

"All dehumidifiers heat the air if they didn't they would be 100% efficient."

Believe it would be a miracle and the laws of physics would need to be re-written.

 

[u3b3rg33k]

the real question is "do you care about the 5F". if no, then don't worry about it. problem with a minisplit is they can dehumidify but only if you have adequate heat load. This is why I have both a minisplit and a dehumidifier in my garage. I tried "dry" mode, and it works on really hot days.

without sufficient heat to maintain ambient, the temp will fall and the RELATIVE humidity will not. then you get a cold garage waiting to condense water on every tool the moment you open the door.

even a 100% efficient dehumidifier would heat the air, by transferring the latent heat of vaporization from the vaporized water in the air, to the discharge air, now lacking the water.

 

[mm08822]

Turn off the smaller one and see if the larger can cover both areas. May need a simple fan for circulation between the 2 areas.

Is each unit maxed out on the high humidity days? Do you have pans to empty or uses hose direct to drain?

 

[DaChev]

If you put a fan in an insulated box, it will heat up. The electricity that you put into the system will also be the heat that has to be removed.

 

[pcmeiners]

problem with a minisplit is they can dehumidify but only if you have adequate heat load.

Have no humidity problem with my (5) Fujitsu units, if they are on the areas are (wonderfully) dry.

 

[600SL]

I certainly do concur with everyone that a dehumidifier has to heat the room. But the question is to what extent. I miss reported the dehumidifier in the small room it is a 65pt/day LG. I got confused with the one in my basement. In any case the issue is still the same and the LG unit uses ~ 65% more energy per kWh as the Santa-fe so I would expect to see more heat output per kWh.

But to what extent. Any temp rise from the Santa-Fe is not noticeable. But temp from the the LG is very noticeable.

Performance of the Santa-Fe is 3.0 L/kWh verses 1.8 L/kWh for the LG. While that is a big difference does it account for 5° F

The Santa-Fe is certainly large enough for the entire building, in fact it came out of a larger 30' x 48' building in NC but ducting for a partitioned room would be a bit cumbersome and probably cost more than a low cost replacement.

As far as mini splits, my problem is I need humidity control all the times. With a mini split I would only get de-humidification when I'm in the building and its hot out. I may be getting one anyway just to cool the place on hot days

 

[u3b3rg33k]

I think those are the old numbers for dehumidifiers,

Dehumidifier Testing and Capacity

www.energystar.gov

the new test is at 65F, to reflect a more realistic operating condition. power consumption will go down with lower temp/rh, but so will efficiency. but either way that santa fe unit is substantially more efficient than the LG. is it one with an internal energy core or heat pipe?

 

[pcmeiners]

"With a mini split I would only get de-humidification when I'm in the building and its hot out."

With a mini split you basically never turn it off. My 12k Fujitsu split heats and cools my 1080 sq ft garage, from-7° to 101°. Garage has average insulation, 10 ft ceiling. 2 large garage doors a couple windows, one wall is shared with my home. The air is dry at all times, it does not need to be "hot" to dry the air; if I lower the temperature to 50° it still remove humidity . Your garage is different than mine so this a rough idea, below is a link to the 12k unit I have, notice how much volt/current it uses . My electric only goes up $10-15 a month with it on 24/7, mind you I do not open the garage doors too often as I use it as a shop. If I do open a garage door, the mini split automatically goes on high, brings the shop back to the set temperature in minutes.

https://www.goodlifehvac.ca/images/Fujitsu_LZ_Series.pdf

 

[600SL]

I think those are the old numbers for dehumidifiers,

Dehumidifier Testing and Capacity

www.energystar.gov

the new test is at 65F, to reflect a more realistic operating condition. power consumption will go down with lower temp/rh, but so will efficiency. but either way that santa fe unit is substantially more efficient than the LG. is it one with an internal energy core or heat pipe?

They certainly are older numbers. Both were purchased before 2019. I have no idea if any of them have an internal energy core or heat pipe? Both are R410a systems. I found this in the Santa-Fe manual.

 

[600SL]

With a mini split you basically never turn it off. My 12k Fujitsu split heats and cools my 1080 sq ft garage, from-7° to 101°. Garage has average insulation, 10 ft ceiling. 2 large garage doors a couple windows, one wall is shared with my home. The air is dry at all times, it does not need to be "hot" to dry the air; if I lower the temperature to 50° it still remove humidity . Your garage is different than mine so this a rough idea, below is a link to the 12k unit I have, notice how much volt/current it uses . My electric only goes up $10-15 a month with it on 24/7, mind you I do not open the garage doors too often as I use it as a shop. If I do open a garage door, the mini split automatically goes on high, brings the shop back to the set temperature in minutes.

https://www.goodlifehvac.ca/images/Fujitsu_LZ_Series.pdf

Thanks good to know. I have been considering 2 12K units. 12K seems to be the best price point in fact Chinese 12K versions are available for $500. Those two are cheaper than 1 Santa-Fe compact 70.

 

[pcmeiners]

Thanks good to know. I have been considering 2 12K units.

I have a second 12k unit which is installed but never used as it is not needed. Basically it is just a backup, so if the working unit fails there is no rush to fix it (DIY) and I do not get rusty tools. Be careful in your split choice, the cheaper they go the less efficient they are and the heat/cooling output is less at all temperatures, especially at upper/lower temperatures.

 

[The Metric System]

Unless an appliance has a means to reject heat to another area, such as water cooling or an outdoor condenser, all of the power that comes down the cord will ultimately be rejected into the space around it as heat.

This is the case regardless of the type of appliance; even light, sound, or motion will ultimately be converted to heat. There is no difference in ultimate heat output between a 100W fan, a 100W lightbulb, or a 100W resistive heater operating continuously in a sealed room.

Therefore, for practical purposes the power consumption of an appliance is its heat load. For estimating this you can use the dataplate rating, if you need an application-specific value you can use a power data logger in situ.

 

[600SL]

Unless an appliance has a means to reject heat to another area, such as water cooling or an outdoor condenser, all of the power that comes down the cord will ultimately be rejected into the space around it as heat.

This is the case regardless of the type of appliance; even light, sound, or motion will ultimately be converted to heat. There is no difference in ultimate heat output between a 100W fan, a 100W lightbulb, or a 100W resistive heater operating continuously in a sealed room.

Therefore, for practical purposes the power consumption of an appliance is its heat load. For estimating this you can use the dataplate rating, if you need an application-specific value you can use a power data logger in situ.

I certainly get all that and my LG is not as efficient as the Santa-Fe and therefore will contribute to more heating but is it normal in this case to go from a non perceptible temperature rise to a highly perceptible temperature rise based on the difference between the two efficiencies.

The same would happen if I put a 100W incandescent light bulb one one side and a 150W on the other. I wouldn't expect to see the 150W side raising the temp 5° over the 100W side in a building this size. But certainly it might in a telephone booth. In my case the LG unit runs at 1.3 amps (`150w) more than the Santa-Fe. So it would appear based on efficiency difference that it I were to run a 150W light bulb on the Santa-Fe side I would get an equivalent temperature rise. I'm not seeing a 150W bulb causing a 5° F temperature rise in this volume of building.

 

[Shiftless]

I'm not seeing a 150W bulb causing a 5° F temperature rise in this volume of building.

Right
150 watts is only 512 BTU’s

 

[DaChev]

The same would happen if I put a 100W incandescent light bulb one one side and a 150W on the other. I wouldn't expect to see the 150W side raising the temp 5° over the 100W side in a building this size. But certainly it might in a telephone booth. In my case the LG unit runs at 1.3 amps (`150w) more than the Santa-Fe. So it would appear based on efficiency difference that it I were to run a 150W light bulb on the Santa-Fe side I would get an equivalent temperature rise. I'm not seeing a 150W bulb causing a 5° F temperature rise in this volume of building.

It may be a matter of duration.

If the Sante-Fe humitity measurement is slightly different than the LG. It may be that the Sante-Fe pulls down to an actual 40% humidity while the LG pulls down to 45% humidity.

Then you would have to consider the amount of time your 150W light bulb is on in comparison to the 100W lightbulb.

As an experiment, try setting the Sante-Fe at 50% RH and leave the LG at 45%. See if the temp is more equal between the areas.

 

[600SL]

A simple AI search and I believe I found the answer. I did clean the filter before installing it but maybe it needs more extensive service or replacement.

 

[600SL]

It may be a matter of duration.

If the Sante-Fe humitity measurement is slightly different than the LG. It may be that the Sante-Fe pulls down to an actual 40% humidity while the LG pulls down to 45% humidity.

Then you would have to consider the amount of time your 150W light bulb is on in comparison to the 100W lightbulb.

As an experiment, try setting the Sante-Fe at 50% RH and leave the LG at 45%. See if the temp is more equal between the areas.

I think what I'm going to try is swapping the LG unit out for the new one I have in my basement. It's about the same quality price range as the LG but its only 2 years old.

 

[American Locomotive]

The AI overview really didn't provide a cohesive answer at all. It also misses the big point with dehumidifiers:

The actual process of condensing water produces heat. Think when you boil water: The entire pot of water doesn't magically turn into steam when it hits 212°F; you have to keep the stove on to continue boiling. This is because it requires heat energy to turn the water into vapor. The opposite is also true - if you want to turn water vapor back into liquid water, you have to remove that heat, and that heat has to go somewhere.

A dehumidifier removes heat from the water, and then puts that heat into the air. Your LG is rated at 65 pts, or 37L/day. To condense 37L of water will release 23.2 kWh or 79,158 BTU of heat. So over a 24 hour period, it's essentially the same as running a ~1kW or 3400 BTU/hr heater - just from the water being condensed (assuming you are producing that much water per day, which you're probably not?)

Then on top of that, the dehumidifier itself consumes power, which gets turned into heat - in your case the LG uses about 800 watts. So that's an additional 800 watts of heat or 2200 BTU/hr into the space. So in total you're putting about 1800 watts of heat into the space, basically a hair dryer on maximum. Now of course that assumes the dehumidifier is running 24/7, which probably isn't the case. A newer, more efficient dehumidifier will shave off some, but there is no getting around the heat released from condensing the water.

I don't know what's in your garage that's producing moisture, or why it's so critical to control the humidity, but you may be better served by switching to air conditioners if you spend a lot of time in there. At least that way you get cooling in addition to dehumidfication.

 

[600SL]

The AI overview really didn't provide a cohesive answer at all. It also misses the big point with dehumidifiers:

The actual process of condensing water produces heat. Think when you boil water: The entire pot of water doesn't magically turn into steam when it hits 212°F; you have to keep the stove on to continue boiling. This is because it requires heat energy to turn the water into vapor. The opposite is also true - if you want to turn water vapor back into liquid water, you have to remove that heat, and that heat has to go somewhere.

A dehumidifier removes heat from the water, and then puts that heat into the air. Your LG is rated at 65 pts, or 37L/day. To condense 37L of water will release 23.2 kWh or 79,158 BTU of heat. So over a 24 hour period, it's essentially the same as running a ~1kW or 3400 BTU/hr heater - just from the water being condensed (assuming you are producing that much water per day, which you're probably not?)

Then on top of that, the dehumidifier itself consumes power, which gets turned into heat - in your case the LG uses about 800 watts. So that's an additional 800 watts of heat or 2200 BTU/hr into the space. So in total you're putting about 1800 watts of heat into the space, basically a hair dryer on maximum. Now of course that assumes the dehumidifier is running 24/7, which probably isn't the case. A newer, more efficient dehumidifier will shave off some, but there is no getting around the heat released from condensing the water.

I don't know what's in your garage that's producing moisture, or why it's so critical to control the humidity, but you may be better served by switching to air conditioners if you spend a lot of time in there. At least that way you get cooling in addition to dehumidfication.

I don't trust AI for anything but this part is what makes sense. My little test of swapping out dehumidifiers should give me the answer Im looking for.



This past week, we saw 100° F temperatures here in CT USA. That's when you notice the problem. But both dehumidifiers on ~50% of the time in those conditions.

The need to control humidity becomes obvious. When I had my garage in NC it would almost rain in there on certain days. I would come in and there would be dew on all metal surfaces. That was a slightly bigger shop but the Santa-Fe took care of it on its own without any difficulty. The possibility of a mini split is an option for the future but even with that my time in the garage is sporadic enough that keeping the AC on when not in use is very costly. Here in CT we have about the highest electric rates in the country.

 

[American Locomotive]

I don't trust AI for anything but this part is what makes sense. My little test of swapping out dehumidifiers should give me the answer Im looking for.

Think about that sentence - it's not saying anything at all. It's no different than your coworker at the water cooler shrugging their shoulders and saying "I dunno, maybe it's broken?"

As part of the natural process of a dehumidifier working, it HAS to add heat to the room - it has no choice. The more humid the air is, the more heat will be added to the room. On top of that, the dehumidifier itself consumes electricity which gets turned into heat, adding even more heat energy to the room.

Every dehumidifier will make the space warmer. How much warmer depends on how humid the space is, how big it is, how well insulated it is, the outdoor temperature and how powerful the dehumidifier is. The smaller the space, the warmer it gets. The more humid the space is, the warmer it will get. This past week, it was super hot and humid in New England. That means your dehumidifier would have stayed on for longer (putting more heat into the space), and the space will naturally lose less heat (because it's hotter).

A more efficient dehumidifier will shave off some heat, but there will always be heat added to the air because the laws of physics dictate it has to.

The need to control humidity becomes obvious. When I had my garage in NC it would almost rain in there on certain days. I would come in and there would be dew on all metal surfaces. That was a slightly bigger shop but the Santa-Fe took care of it on its own without any difficulty. The possibility of a mini split is an option for the future but even with that my time in the garage is sporadic enough that keeping the AC on when not in use is very costly. Here in CT we have about the highest electric rates in the country.

That's the point I'm trying to make. Dehumidifiers consume a lot of power. Running dehumidifiers instead of the AC in the summer is false economy for the most part.

Your LG dehumidifier uses as much power as a modern ~8,000 BTU window air conditioner. Your SantaFe unit uses about as much as a 6,000 BTU window unit. So if you're going to sit there plowing as much power as 14,000 BTU worth of window air conditioners would, you might as well get cool rooms out of the deal.

 

[600SL]

Think about that sentence - it's not saying anything at all. It's no different than your coworker at the water cooler shrugging their shoulders and saying "I dunno, maybe it's broken?"

As part of the natural process of a dehumidifier working, it HAS to add heat to the room - it has no choice. The more humid the air is, the more heat will be added to the room. On top of that, the dehumidifier itself consumes electricity which gets turned into heat, adding even more heat energy to the room.

Every dehumidifier will make the space warmer. How much warmer depends on how humid the space is, how big it is, how well insulated it is, the outdoor temperature and how powerful the dehumidifier is. The smaller the space, the warmer it gets. The more humid the space is, the warmer it will get. This past week, it was super hot and humid in New England. That means your dehumidifier would have stayed on for longer (putting more heat into the space), and the space will naturally lose less heat (because it's hotter).

A more efficient dehumidifier will shave off some heat, but there will always be heat added to the air because the laws of physics dictate it has to.

That's the point I'm trying to make. Dehumidifiers consume a lot of power. Running dehumidifiers instead of the AC in the summer is false economy for the most part.

Your LG dehumidifier uses as much power as a modern ~8,000 BTU window air conditioner. Your SantaFe unit uses about as much as a 6,000 BTU window unit. So if you're going to sit there plowing as much power as 14,000 BTU worth of window air conditioners would, you might as well get cool rooms out of the deal.

Yes that sentence is not saying any more than saying my lower efficiency LG unit is causing 5° temperature rise over my Santa-fe. They are all qualitative statements without realistic data. But the simple test of swapping out the LG for a newer one will answer 1000 expert opinions.

 

[HoosierBuddy]

This whole thread reminds me of Sunday before last, when my wife whispered to me "Why is it always so cold in this church?"

"Well honey, it's about the humidity."

Same reason they keep movie theaters so freaking cold. All those sweaty people who insist on breathing out water vapor with every breath.

I know when they built the new Walmart in town they did an energy study and went with a natural gas fired RTU (roof top unit) for humidity control. They did it in conjunction with AC, of course. RTU eliminates some of the issue of the dehumidifier heating up the room. Basically the energy study was to determine if it was cheaper to install more cooling tons and do all of the dehumidification that way or to "pretreat" return and makeup air to lower the humidity prior to cooling.

I believe the natural gas units don't cool the air to remove humidity. They place a desiccant wheel in the airstream to strip water vapor. The wheel slowly spins so dry desiccant is continuously moved into position and wet desiccant is moved out of the airstream and into the drying portion of the unit, where it's heated by natural gas combustion to drive off the absorbed water. If you did that INSIDE...it would be almost counter productive. RTU is how they make the $ numbers work out. The waste heat remains outside.

 

[u3b3rg33k]

This whole thread reminds me of Sunday before last, when my wife whispered to me "Why is it always so cold in this church?"

"Well honey, it's about the humidity."

Same reason they keep movie theaters so freaking cold. All those sweaty people who insist on breathing out water vapor with every breath.

I know when they built the new Walmart in town they did an energy study and went with a natural gas fired RTU (roof top unit) for humidity control. They did it in conjunction with AC, of course. RTU eliminates some of the issue of the dehumidifier heating up the room. Basically the energy study was to determine if it was cheaper to install more cooling tons and do all of the dehumidification that way or to "pretreat" return and makeup air to lower the humidity prior to cooling.

I believe the natural gas units don't cool the air to remove humidity. They place a desiccant wheel in the airstream to strip water vapor. The wheel slowly spins so dry desiccant is continuously moved into position and wet desiccant is moved out of the airstream and into the drying portion of the unit, where it's heated by natural gas combustion to drive off the absorbed water. If you did that INSIDE...it would be almost counter productive. RTU is how they make the $ numbers work out. The waste heat remains outside.

i wonder if they studied a full-flow ERV (wheel or plate), as a way to mitigate incoming humidity. brute force is expensive.

https://novelaire.com/images/pdfs/DDW_Brochure_20231.pdf

these things are basically running a (100-200k, depending on size) furnace outside, nonstop, to dry the desiccant.
and they definitely put out "hot" air if there isn't a cooling section (can't be cooled with OA or it'll pick the water right back up).



another common solution is a DOAS.

Dedicated Outdoor Air Systems | Applications | AAON

Discover AAON's dedicated outdoor air systems, providing energy-efficient HVAC solutions for commercial and industrial requirements.

www.aaon.com

 

[HoosierBuddy]

i wonder if they studied a full-flow ERV (wheel or plate), as a way to mitigate incoming humidity. brute force is expensive.

Not sure. The study was done in Benton by their corporate guys. All I did was supply them with the energy cost information.

This was 20 years ago. Not sure how much technology has changed. The gas bill for the RTU was running about $500/month in the summer. I know they watch every penny. If it didn't make sense, they wouldn't do it.